EP4603191A1

EP4603191A1 - Nozzle body for a liquid spray gun

Info

Publication number: EP4603191A1
Application number: EP24158348.3A
Authority: EP
Inventors: Ryan D. Erickson; Stephen C. Joseph; Bryan J. HAYWARD
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2024-02-19
Filing date: 2024-02-19
Publication date: 2025-08-20
Also published as: WO2025177130A1

Abstract

Nozzle body (1) for a liquid spray gun, the nozzle body including a nozzle tube (66) comprising
a) an elongated nozzle tube passage (58) extending between a nozzle tube inlet and a nozzle tube outlet (52),
b) a nozzle tube wall (71) having
- a front end (80) surrounding the nozzle tube outlet (52),
- a radially-inner surface (76), in contact with the liquid,
- a radially-outer gas-guiding surface (75) for guiding a flow of pressurized atomizing gas (110) towards the front end (80).

The gas-guiding surface (75) comprises a lowland portion (90) and a plurality of circumferentially-spaced elevations (100), each protruding radially outward from the lowland portion, for generating vortices in the flow of atomizing gas (110).

Each elevation (100) comprises two side surfaces (102) oriented relative to each other such as to converge towards the front end (80).

Description

This disclosure relates to liquid spray guns in which a liquid to be sprayed is atomized by a pressurized gas. It relates more specifically to nozzle bodies for use in such spray guns, and to nozzle assemblies and spray guns comprising such nozzle bodies.
Spray guns according to the present disclosure are used, for example, in automotive repair shops to apply liquid paint to surfaces of a vehicle using pressurized air or another pressurized gas. Most of these spray guns have a spray gun body or a spray gun platform with a trigger and a handle for manual spraying operation, while others are used with robots and are equipped with mechanical or electrical interfaces to allow computer-controlled spraying operation by the robot.
Spray technology and environmental regulations are trending towards spray guns which utilize lower gas pressures or can be laboratory certified to produce certain levels of paint "transfer efficiency". A challenge with using lower gas pressures is that the amount of energy available to both draw-out and atomize the liquid paint is reduced. This situation can negatively impact the application speed and paint finish quality. The challenge is compounded by the fact that paint manufacturers are moving to liquid paint formulations which are water-based and have an increased solids content. These liquid paints tend to have higher viscosities which, at identical atomizing gas pressure and gas flow rates, can result in reduced paint flow rates and in the liquid paint being more difficult to atomize. A stronger flow of atomizing gas can provide for a finer atomization that generates a finer paint spray. However, increasing the pressure of the atomizing gas also increases the volume of undesirable high-frequency noises, generally results in lower transfer efficiency, increases consumption of pressurized atomizing gas, and causes higher operating costs.
Nozzle bodies are known from traditional liquid paint spray guns. A nozzle body generally comprises a nozzle having a nozzle opening through which the liquid to be sprayed exits the nozzle body into outside air. Specific traditional nozzle bodies are described in PCT patent applications WO 2012/109298 A1 or WO 2013/016474 A1 , for example. The United States patent application published as US 2017/0348710 A1 is directed to a spray gun capable of setting a spray gas pressure at a relatively low pressure and performing good atomization without making auxiliary gas holes in a gas cap. Similarly, United States patent US 7,431,223 B2 refers to a housing of the spray gun provided with an air guidance duct through which the compressed air responsible for atomization flows to an atomizer nozzle, wherein surfaces of the air guidance duct and/or atomizer nozzle, and/or an air cap, which come into contact with the stream of compressed air, or are wetted, are provided wholly or in part with a structured surface in the form of indentations and/or protrusions worked into the surfaces whereby the air resistance is decreased with the effect that transport quantities can be increased significantly without additional energy having to be consumed.
It is desirable to further improve atomization of the liquid without having to increase the flow rate or the pressure of the atomizing gas. Alternatively, it may be desirable to achieve acceptable atomization using a reduced gas flow rate which will improve transfer efficiency. It is also desirable to enhance the mixing between atomizing gas and liquid, i.e. to obtain a more homogeneous mixing ratio between the liquid and the atomizing gas.
In an attempt to address these needs, the present disclosure provides a nozzle body for a liquid spray gun for spraying a liquid, the nozzle body including a nozzle tube comprising

a) an elongated nozzle tube passage, extending lengthwise between a nozzle tube inlet through which, in use, liquid enters the nozzle tube, and a nozzle tube outlet, through which, in use, the liquid exits the nozzle tube passage into outside air in a spray direction, wherein the spray direction through a centroid of the cross section of the nozzle tube outlet defines a spray axis, wherein the spray axis defines axial directions and radial directions orthogonal to the axial directions,
b) a nozzle tube wall having
- a front end surrounding, and concentric with, the nozzle tube outlet,
- a radially-inner surface delimiting the nozzle tube passage and being, in use, in contact with the liquid,
- an opposed radially-outer gas-guiding surface for guiding a flow of pressurized atomizing gas, in contact with the gas-guiding surface, towards the front end such that the flow of atomizing gas, downstream of the front end, can atomize the liquid after the liquid has exited the nozzle tube outlet,

wherein the gas-guiding surface comprises a lowland portion and a plurality of circumferentially-spaced elevations, each protruding radially outward from the lowland portion, for generating vortices in the flow of atomizing gas,
characterized in that each elevation comprises two side surfaces, each side surface extending radially-outwardly from the lowland portion and extending towards the front end, the side surfaces being oriented relative to each other such as to converge towards the front end.

The elevations on the gas-guiding surface of the nozzle tube wall generate vortices in the flow of atomizing gas. The converging side surfaces are particularly effective in creating vortices as the pressurized atomizing gas flows along and over the converging side surfaces. Due to the converging orientation of the side surfaces the pressurized atomizing gas portion flowing along the first side surface and the pressurized atomizing gas portion flowing along the second side surface are being directed towards each other and eventually meet and mix at the front end of the nozzle tube wall. In addition, the converging side surfaces are oriented at an angle with respect to the axial flow direction of the atomizing gas flowing from the rear along the gas-guiding surface towards the front end. This angular orientation of the side surfaces creates zones of lower pressure and zones of higher pressure in the atomizing gas flow which results in laminar flow of atomizing gas being broken up into a more turbulent flow. Hence the atomizing gas exits the atomizing gas outlet not in a purely laminar flow, but at least a portion of its flow is a turbulent flow. The turbulent flow and the vortices in it provide for improved atomization and an improved mixing, compared to mixing by a laminar flow, of atomizing gas and atomized liquid downstream from the nozzle tube outlet. The result is generally a more homogeneous distribution of smaller liquid droplets in the spray when the spray impinges on the target surface, and hence a more evenly coated surface.
The noun "liquid" as used herein refers, inter alia, to liquid paints such as those comprising pigments or other suspended particles or dyes, to liquid primers, and to liquid clearcoats, liquid lacquers, liquid base coats, or liquid varnishes. A liquid may be coloured or colourless. Liquid paints are, for example, those liquid paints used in auto repair shops to coat surfaces of vehicle parts. Generally, as used herein, "liquid" refers to liquid coating materials that can be applied to a surface using a spray gun system, including (without limitation) paints, primers, base coats, lacquers, varnishes and similar paint-like materials as well as other materials such as adhesives, sealers, fillers, putties, abrasive slurries, mold release agents and foundry dressings which may be applied in atomized form depending on the properties and/or the intended application of the material. A liquid according to the present disclosure may comprise a carrier liquid and solid particles (pigments, powders, granules, etc.) suspended in the carrier liquid.
As used herein, a (non-gaseous) substance is considered liquid if its dynamic viscosity at 20 °C and atmospheric pressure is lower than about 20000 mPa.s, particularly if its dynamic viscosity at 20 °C and atmospheric pressure is lower than about 2000 mPa.s.
Many traditional spray guns use pressurized air for atomization of the liquid and shaping of the spray jet. However, other gases and gas mixtures are sometimes used for these purposes. The term "gas" as used herein refers to a gas, such as, for example, nitrogen, oxygen, argon, carbon dioxide, or helium, as well as to a mixture of gases, such as air. The use of "air" in conventional technical terms like "air cap" for a component of a spray gun is not meant to preclude the useability of this component with another gas mixture or with another gas.
Like in traditional nozzle bodies, when in use, a nozzle body according to the present disclosure is generally connected to a barrel (such as to a barrel holding a paint cup) or to the body of a spray gun. Liquid is supplied into the nozzle body through the barrel or through the spray gun body. A nozzle port on the barrel or on the spray gun body can be engaged with a corresponding matching barrel port on the nozzle body, so that the liquid to be sprayed can flow from the barrel or the spray gun body through the nozzle port and the barrel port into the nozzle body and - within the nozzle body - to the nozzle tube outlet where it exits the nozzle body and the spray gun.
A nozzle body according to the present disclosure comprises a nozzle tube having a wall, an inlet, an outlet, and a passage through which the liquid flows from the inlet to the outlet. At the nozzle tube outlet, the liquid exits the nozzle body in a spray direction. The liquid is then atomized close to the nozzle tube outlet by a flow of pressurized gas ("atomizing gas") to form a spray of minute liquid droplets which propagates through surrounding air to eventually hit the surface that is to be coated with the liquid.
The nozzle bodies according to the present disclosure are for use in spray guns which spray a liquid and atomize the liquid using pressurized gas. Nozzle bodies and nozzle body assemblies for other types of spraying devices, such as airless spray guns are outside the scope of this disclosure.
Nozzle bodies according to the present disclosure comprise a tubular nozzle tube having a wall ("nozzle tube wall"), an inlet ("nozzle tube inlet"), an outlet ("nozzle tube outlet") and a passage ("nozzle tube passage"). A nozzle tube may be a tubular element of any length. It may be, for example, a tubular element of a length of 2 millimeters (mm) or more, or of 5 mm or more, or of 10 mm or more.
The nozzle tube extends in a length direction. The length direction of the nozzle tube may define axial directions of the nozzle tube and of the nozzle body. Radial directions of the nozzle tube are directions orthogonal to the axial directions of the nozzle tube.
The nozzle tube comprises a nozzle tube passage which extends lengthwise between the nozzle tube inlet and the nozzle tube outlet for conducting the liquid from the nozzle tube inlet to the nozzle tube outlet. In a certain position along its length, rearward/upstream from the nozzle tube outlet, the nozzle tube passage may have a cross section. The shape of the cross section is not particularly limited. At a certain longitudinal position, rearward from the nozzle tube outlet, the nozzle tube passage may have, for example, a circular cross section or an elliptical cross section. It may have an irregular (e.g. non-symmetric) cross section in at least a longitudinal section of the elongated nozzle tube passage. The nozzle tube passage may have, for example, a cross section which varies in size or shape along its length direction, such as from a circular to an elliptic cross section or from a larger circular cross section to a smaller circular cross section.
In certain embodiments the nozzle tube passage is straight. In certain embodiments the nozzle tube passage is a straight passage of identical circular cross section along its length. In other embodiments the nozzle tube passage is bent or curved. In certain embodiments the nozzle tube passage comprises a straight axial section. In some of these embodiments the straight axial section comprises the nozzle tube outlet.
The nozzle tube may be connectable or connected, e.g. at the nozzle tube inlet, to a liquid-conducting element, such as a liquid-conducting element of a barrel or of a spray gun body, for conducting the liquid into the nozzle tube.
The nozzle tube inlet is a first end of the nozzle tube passage. In use, liquid enters the nozzle tube through the nozzle tube inlet. The nozzle body may comprise a barrel connector for connecting the nozzle body to a barrel. The nozzle tube inlet may be comprised in the barrel connector.
The nozzle tube inlet may be shaped such as to be connectable, directly or indirectly, to a liquid nozzle port on a barrel of a nozzle assembly or on a spray gun body. "Direct connection" and "directly connectable" refer to a connection in which the nozzle tube inlet is in surface contact with the liquid nozzle port, whereas an "indirect connection" and "indirectly connectable" refers to a connection in which one or more intermediate elements connect the nozzle tube inlet with the liquid nozzle port. A connection of the nozzle tube inlet to a liquid nozzle port on a barrel may allow liquid to flow from the barrel or from the spray gun body, as the case may be, into the nozzle body and through the nozzle tube passage to the nozzle tube outlet where it exits the nozzle body into outside air and is atomized by atomizing gas.
A nozzle body according to the present disclosure may be connected to a barrel directly or indirectly. Where the nozzle body is indirectly connected to the barrel, the nozzle body may be indirectly connected to a barrel via a face plate. The face plate may be comprised in the nozzle body. It may, for example, be integrally formed with the nozzle body. Alternatively, the face plate may be comprised in the barrel. It may, for example, be integrally formed with the barrel, or it may be a separate component of the barrel.
A nozzle body according to the present disclosure may be connected to a spray gun body directly or indirectly. Where the nozzle body is indirectly connected to the spray gun body, the nozzle body may be indirectly connected to the spray gun body via a face plate. The face plate may be comprised in the nozzle body. It may, for example, be integrally formed with the nozzle body. Alternatively, the face plate may be comprised in the spray gun body. It may, for example, be integrally formed with the spray gun body, or it may be a separate component of the spray gun body.
The nozzle tube outlet is the second end of the nozzle tube passage, arranged opposite to the first end. In use, the liquid exits the nozzle tube passage through the nozzle tube outlet into outside air. The nozzle tube outlet may have a cross section which is axially symmetric with respect to the spray axis. In certain embodiments the nozzle tube outlet has a circular cross section and is arranged coaxially with the spray axis. In some of these embodiments the nozzle tube outlet comprises the spray axis. In certain other embodiments the nozzle tube outlet has an annular cross section and is arranged coaxially with the spray axis.
In certain embodiments the nozzle tube outlet is arranged in a plane ("nozzle tube outlet plane") orthogonal to the spray axis. In some of these embodiments the front end of the nozzle tube wall is arranged in the nozzle tube outlet plane.
The nozzle tube outlet is an aperture in the nozzle tube at an end of the nozzle tube passage through which the liquid exits the nozzle tube passage and the nozzle body and enters the surrounding air. The nozzle tube outlet is one end of the nozzle tube passage and is delimited, in radial directions, by the front end of the nozzle tube wall which extends axially up to the nozzle tube outlet.
Viewed in the outlet cross section, the shape of the nozzle tube outlet determines the cross section of the flow of liquid as it exits the nozzle tube and enters the surrounding air, before the liquid is atomized. Viewed in the outlet cross section, the nozzle tube outlet may have, for example, a circular shape, an elliptic shape, a square shape, a rectangular shape, a polygonal shape, or a star shape.
In certain embodiments the nozzle tube outlet comprises the spray axis, i.e. liquid exits the nozzle tube outlet in the position of the centroid of the cross section of the nozzle tube outlet. In other embodiments, the nozzle tube outlet does not comprise the spray axis. In some of these other embodiments the nozzle tube outlet has an annular shape (e.g. a ring shape extending for a full 360° circle around the spray axis) and does not comprise the spray axis. In such scenarios the spray axis is a symmetry axis of the nozzle tube outlet.
Viewed in the outlet cross section, the shape of the nozzle tube outlet may be symmetric about a center point or about a center of the nozzle tube outlet. The cross section of the nozzle tube outlet may be rotationally symmetric or axially symmetric about a center point or a center of the nozzle tube outlet. Viewed in the outlet cross section, the shape of the nozzle tube outlet may be rotationally symmetric or axially symmetric about the spray axis. Viewed in the outlet cross section, the nozzle tube outlet may alternatively be of an irregular shape, e.g. a shape exhibiting no symmetry.
In order to define in a most general manner a center point or a center of the nozzle tube outlet as viewed in the outlet cross section, the commonly known notion of a "centroid" is applied. A centroid of a planar shape, such as of the nozzle tube outlet as viewed in the outlet cross section, is commonly known to be the arithmetic mean position of all the points in the surface of the shape. To illustrate the concept of a centroid: Assuming a uniform mass density, the center of mass of the planar shape coincides with the centroid. Informally, the centroid can be understood as the point at which a cutout of the planar shape (with uniformly distributed mass) would be perfectly balanced on the tip of a pin.
In certain embodiments the nozzle tube passage is straight between the nozzle tube inlet and the nozzle tube outlet. In certain embodiments the nozzle tube passage is a straight cylindrical space of identical circular cross section along its length. In certain embodiments the nozzle tube passage comprises a straight axial section. In some of these embodiments the straight axial section comprises the nozzle tube outlet. In certain other embodiments the nozzle tube passage is a straight tubular space of varying circular cross section along its length. In some of these embodiments the nozzle tube passage comprises converging portions (in which the diameter of the open cross section of the nozzle tube passage decreases along its length in a downstream direction) and diverging portions (in which the diameter of the open cross section of the nozzle tube passage increases along its length in a downstream direction).
In other embodiments the nozzle tube passage is curved. In some of these embodiments the nozzle tube passage comprises a curved section and a straight section. The straight section may comprise the nozzle tube outlet.
The nozzle tube passage may have a cross section. The shape of the cross section may not be particularly limited. The nozzle tube passage may have, for example, a circular cross section or an elliptical cross section or an irregularly shaped cross section.
The axial position at which the liquid exits the nozzle tube passage into outside air is the axial position "at the nozzle tube outlet", as used herein. As the nozzle tube wall delimits the nozzle tube passage which ends at the nozzle tube outlet, this axial position is the axial position at which the nozzle tube wall (and the nozzle tube) ends. In other words, the nozzle tube wall extends axially up to the nozzle tube outlet. Also, the outer surface of the nozzle tube wall ends at the nozzle tube outlet. The terminal end portion of the nozzle tube wall at the nozzle tube outlet is referred to as the front end of the nozzle tube wall. In a nozzle body according to the present disclosure the front end of the nozzle tube wall surrounds the nozzle tube outlet, such as by a full 360° circumference around the spray axis. The front end is concentric with the nozzle tube outlet. The front end and the nozzle tube outlet may be concentric with the spray axis. The front end may be arranged in the plane of the nozzle tube outlet.
The cross section of the nozzle tube passage at the nozzle tube outlet determines the cross section of the liquid flow in the specific axial position in which the liquid exits the nozzle body, i.e. at the nozzle tube outlet. This particular cross section is to be taken in a plane through the nozzle tube outlet orthogonal to the spray axis. This particular cross section is also termed "outlet cross section" herein.
The nozzle tube wall may extend generally lengthwise in axial directions. It may extend from the nozzle tube inlet to the nozzle tube outlet. The nozzle tube wall may separate the nozzle tube passage from a space outside the nozzle tube or outside the nozzle body, such as from an atomizing gas passage.
The nozzle tube wall may have a thickness. The thickness may be defined by the extension of the nozzle tube wall in radial directions. The thickness of the nozzle tube wall may vary along the length of the nozzle tube. Alternatively, the thickness of the nozzle tube wall may be constant along the length of the nozzle tube.
The choice of material or materials of the nozzle tube wall is not particularly limited. In certain embodiments of the nozzle body according to the present disclosure the nozzle tube wall is made of, or comprises, a polymeric material or a metal. In certain embodiments of the nozzle body according to the present disclosure the nozzle body is made of, or comprises, a polymeric material or a metal. Polymeric material can generally be molded or cast or 3D-printed or otherwise formed to a high degree of precision at reasonable cost to form the nozzle tube and the nozzle tube wall. Metals are versatile materials which can be machined, metal injection molded, cast or otherwise formed to a high degree of precision at reasonable cost to form the nozzle tube and the nozzle tube wall as well as the gas-guiding surface with its elevations. Within the group of polymeric material and the group of metallic materials, a number of suitable materials are known that don't significantly react chemically with typical liquids and thereby can be used over extended periods of time, making polymeric and metal materials versatile substances for manufacturing nozzle bodies and nozzle tube walls according to the present disclosure.
The nozzle tube wall comprises a radially inner surface and an opposed radially outer surface, namely the gas-guiding surface. Relative to the spray axis, the gas-guiding surface is thus arranged radially outward from the inner surface of the nozzle tube wall. The inner surface and the gas-guiding surface are separated by a thickness of the nozzle tube wall. The inner surface is oriented radially inward and faces the nozzle tube passage. It delimits the nozzle tube passage. In use, the liquid, conducted by the nozzle tube passage, is in contact with the inner surface of the nozzle tube wall.
The gas-guiding surface of the nozzle tube wall is generally arranged opposite to the radially inner surface and radially outward from the inner surface. The gas-guiding surface is oriented radially outward and faces away from the nozzle tube passage. In certain embodiments the gas-guiding surface is rotationally symmetric with respect to the spray axis or to a straight center line of the nozzle tube passage. In certain embodiments the gas-guiding surface is concentric with the inner surface.
In use, the gas-guiding surface is in contact with the atomizing gas as the atomizing gas flows forward and downstream towards an atomizing gas outlet for atomizing the liquid after the liquid has exited the nozzle tube outlet. The gas-guiding surface is suitable (such as arranged suitably and/or shaped suitably) for guiding a flow of pressurized atomizing gas, in contact with the gas-guiding surface, towards the front end of the nozzle tube wall such that the flow of atomizing gas, downstream of the front end, can atomize the liquid after the liquid has exited the nozzle tube outlet. The gas-guiding surface may be operable to guide pressurized atomizing gas, e.g. towards an atomizing gas outlet in the vicinity of the nozzle tube outlet. The gas-guiding surface may thus not only delimit the nozzle tube wall and the nozzle tube, but in certain embodiments also delimits, in conjunction with another element, e.g. with an element of an air cap as explained below, an atomizing gas passage in a nozzle assembly. In some of such embodiments, the gas-guiding surface is in contact with atomizing gas conducted through the atomizing gas passage towards an atomizing gas outlet, arranged circumferentially around the nozzle tube wall at the nozzle tube outlet.
The term "downstream", as used herein, refers to directions generally from the rear, e.g. from the nozzle tube inlet or from a barrel or from the spray gun body, towards the front of the nozzle body, e.g. towards the nozzle tube outlet or towards the front end of the nozzle tube wall, or even further outward beyond the nozzle tube outlet or beyond the front end. A downstream direction is a general flow direction of the atomizing gas. The term "upstream" refers generally to directions opposite to downstream directions, i.e. it refers to directions generally from the front towards the rear of the nozzle body towards the barrel or towards the spray gun body, against the general flow direction of the atomizing gas.
In certain embodiments the gas-guiding surface of the nozzle tube wall is shaped to direct atomizing gas emanating from the atomizing gas outlet angularly away from the spray axis. Within this angularly-outward directed flow of atomizing gas the pressure in front of the nozzle tube outlet is lower than it is in traditional geometries in which atomizing gas flows in directions along the spray axis or towards the spray axis. The lower pressure before the nozzle tube outlet generally draws more liquid from the nozzle passage and increases the liquid (e.g. paint) flow rate, although the consumption of pressurized gas may be unchanged with respect to traditional nozzle bodies. To obtain a liquid flow rate similar to those obtained with traditional nozzle bodies, the pressure and/or volume of the pressurized atomizing gas can be reduced in spray guns featuring such a nozzle body. This may result in energy and cost savings. A lower pressure of the atomizing gas may also result in less generation of high-frequency noise or in lower volume of high-frequency noise during spraying operations, which reduces occupational noise exposure and associated health risks for human operators. Directing at least some of the atomizing gas away from the spray axis is believed to create a larger zone of low pressure in front of the nozzle tube outlet, which may help extracting liquid more effectively and increasing liquid flow rates without having to increase the pressure of the atomizing gas.
According to the present disclosure, the gas-guiding surface of the nozzle tube wall is a structured surface in that it comprises a lowland portion and a plurality of elevations. The lowland portion is generally the radially innermost portion of the gas-guiding surface, i.e. the portion closest to the spray axis. In certain embodiments the lowland portion is shaped like a portion of a cylindrical surface or like a portion of a conical surface. This cylindrical surface or this conical surface may be coaxial with the spray axis. This cylindrical surface or this conical surface may be coaxial with the nozzle tube passage. In a longitudinal sectional view taken in a plane through the spray axis the lowland portion may appear as a straight line or as a curved line.
The lowland portion may be a smooth surface, e.g. free of protrusions (other than the elevations) or recesses. The lowland portion may be interrupted by the elevations. An elevation may subdivide the lowland portion into subportions. In one axial position the lowland portion may extend for a full 360° circumference around the spray axis. The lowland portion of the gas-guiding surface may be axially symmetric about the spray axis. When the nozzle body described herein is in use, the lowland portion is in contact with the flow of pressurized atomizing gas. Being a portion of the gas-guiding surface the lowland portion helps guide the flow of pressurized atomizing gas towards the front end of the nozzle tube wall.
The lowland portion may be shaped and oriented such as to guide atomizing gas in a direction parallel to the spray axis downstream from the front end of the nozzle tube wall. It may be shaped and oriented such as to guide atomizing gas in a direction towards the spray axis downstream from the front end of the nozzle tube wall.
In certain preferred embodiments, however, the lowland portion is shaped and oriented to guide atomizing gas away from the spray axis at the front end of the nozzle tube wall. In a longitudinal sectional view, the lowland portion may, for example, appear as an inclined profile, or as a "ramp" in which a first axial section of the lowland portion, located at the front end of the nozzle tube wall, has a greater radial distance from the spray axis than a second axial section of the lowland portion rearward/upstream from the first axial section. Generally, a flow of atomizing gas away from the spray axis is believed to obtain a more effective atomization in certain scenarios and/or facilitate an increase in liquid flow rate without having to increase the pressure of the pressurized atomizing air.
In certain embodiments an outwardly ramped lowland portion is shaped like a portion of a conical surface diverging with decreasing axial distance from the front end of the nozzle tube wall, coaxial with the spray axis. The lowland portion may be considered shaped and arranged as if it were part of the lateral surface of an imaginary cone centered on the spray axis. Where the apex of the imaginary cone is located upstream from the front end of the nozzle tube wall, the lowland portion is thereby shaped to guide atomizing gas away from the spray axis. This is an example of an outwardly ramped lowland portion.
The lowland portion of the gas-guiding surface forms a surface portion from which elevations protrude, similar to how a hill or a house rises from a plain, for example. An elevation (and any elevation of the gas-guiding surface, for that matter) protrudes generally radially outward from the lowland portion. The radially-outward direction is a height direction of the elevation. A height of the elevation may be determined using the radial "level" of the surrounding lowland portion as a zero-height reference level. A height of an elevation may thus be the maximum extension of any portion of the elevation in radial direction over the surrounding lowland portion.
In certain embodiments the number of the plurality of elevations is between three and thirty. Preferably the number of the plurality of elevations is six or eight or twelve. More elevations will generally create more vortices in the flow of atomizing gas and may thus result in improved atomization of the liquid. However, in most embodiments the space around the circumference of the front end of the nozzle tube wall is limited. To accommodate more elevations, these elevations must be smaller and therefore create smaller vortices. Where the number of elevations is three or greater, and up to thirty, the balance between number and size of the resulting vortices is believed to be useful to obtain good atomization. Nozzle bodies having six, eight or twelve elevations appear to provide particularly satisfactory atomization and mixing of the liquid.
In certain embodiments of the nozzle bodies according to the present disclosure the elevations are spaced evenly about a circumference of the gas-guiding surface. Even circumferential spacing refers to the angular interval, measured circumferentially about the spray axis, at which the elevations are arranged on the lowland portion of the gas-guiding surface. An even spacing helps maintain the flow of atomizing gas, comprising the vortices, even and symmetric, which in turn helps obtain a more even spray pattern of the spray gun and a more even atomization and mixing of the liquid.
The elevations, and any elevation of the gas-guiding surface, generate vortices in the flow of atomizing gas as the gas-guiding surface guides the flow of pressurized atomizing gas towards the front end. The elevations can be considered vortex generators. Such vortex generators are known from other technical fields, such as on rotor blades of wind turbines. For the purpose of creating vortices, each elevation comprises the two converging side surfaces. In other respects, the shape of the elevation is not particularly limited. An elevation creates vortices by forming an obstacle in the flow of atomizing gas along the gas-guiding surface. An elevation forces the flow to change direction, whereby zones of higher pressure and zones of lower pressure are created in the flow of atomizing gas. In following these pressure gradients, the velocity field of the flow becomes more irregular, creating streamwise vortices and turbulence on various scales. These vortices can energize the flow near the gas-guiding surface by mixing a higher momentum flow with a low-momentum flow near the gas-guiding surface. As a result, the flow of atomizing gas downstream from an elevation forms a pair of vortices, is generally less laminar and more turbulent than upstream from the elevation.
The elevations in the nozzle bodies according to the present disclosure are shaped to create vortices in the flow of atomizing gas. The term "vortex", as used herein, refers to a region in the flow of atomizing gas in which the flow revolves around an axis line in a well-defined pattern. Measured a short distance downstream from the elevation, the diameter of the region and thus the diameter of the vortex is in the order of magnitude of the height of the elevation over the surrounding lowland portion.
In contrast to "vortex", "turbulence" is considered herein to refer to smaller scale, irregular structures in the flow of atomizing gas. In turbulence the pattern of velocity vectors is chaotic and irregular. A vortex is deemed to decay into turbulence.
In a nozzle body according to the present disclosure each side surface creates a major vortex which extends downstream from the elevation in the flow of atomizing gas. Due to the constant flow of pressurized atomizing gas this major vortex is a stationary vortex. The diameter of the major vortex close to the elevation is about the "height" of the elevation by which it rises above the surrounding lowland portion. The major vortex rotates about an axis generally parallel to the flow direction of the atomizing gas. Its direction of rotation depends on the geometry: looking downstream along the spray axis, the vortex created by the right-hand side surface of an elevation rotates generally in a clockwise direction, while the vortex created by the left-hand side surface of the elevation rotates in a counterclockwise direction. With increasing axial distance downstream from the elevation, the major vortex smears out and decays into smaller eddies and dissipates its rotational energy into small-scale turbulence.
Hence in certain embodiments, when the nozzle body is in use, each elevation is arranged and shaped to create a pair of counter-rotating vortices in the flow of atomizing gas. The counter rotation generally results in a more effective atomization of the liquid. "Counter-rotating" refers to the two vortices having opposite rotation directions, e.g. one rotates around its axis in a clockwise direction, the other rotates around its axis in a counterclockwise direction. In certain of those embodiments each vortex of the pair of counter-rotating vortices has a diameter roughly equal to the height of the elevation. The height of the elevation is the radial distance of that portion of the elevation from the surrounding lowland portion which is located radially further away from the spray axis than any other portion of the elevation.
Besides its two side surfaces described above, an elevation may comprise other surfaces defining its shape. Generally, the shape of an elevation is not particularly limited. Its shape may be defined by many different curved surface portions and flat surface portions. In certain embodiments the shape of an elevation may be defined by only flat surface portions. In some of these embodiments the geometric shape of at least one elevation, or of all elevations, of the plurality of elevations is a convex polyhedron. The edges between adjacent flat surfaces delimiting a polyhedron may help introduce a specific desirable vortex pattern into the flow of atomizing gas.
In a nozzle body according to the present disclosure each of the two side surfaces of the elevation (and of any elevation) extends radially-outwardly from the lowland portion, i.e. "upwards", in a height direction of the elevation. Each of the side surfaces also extends generally from the rear of the nozzle body towards the front end. At least one of them may extend generally from the rear towards the front end in a skew manner, not parallel to a plane through the spray axis. Such a skew arrangement may help create vortices more effectively. Just as the remainder of the gas-guiding surface, the side surfaces are in contact with the atomizing gas when the nozzle body is in use.
In certain embodiments at least one elevation, or each elevation, of the plurality of elevations is shaped symmetrically relative to a plane through the spray axis and through the elevation. Symmetric elevations will generally create symmetric pairs of vortices and thereby reduce skew velocity components in the flow of atomizing gas. This may result in a more even velocity distribution in the flow of atomizing gas as it exits the spray gun and hence a more even spray pattern of the spray gun.
Where two elevations, several elevations, or preferably all elevations, of the plurality of elevations have an identical shape and size, the resulting flow of atomizing gas with the vortices introduced by the elevations will generally have a more even velocity vector distribution. This may translate into a more even spray pattern of the spray gun. Therefore, in certain embodiments, at least two, or all, elevations of the plurality of elevations have an identical geometric shape and an identical geometric size.
The side surfaces of an elevation are oriented relative to each other such as to converge towards the front end. "Converging towards the front end" refers to respective axially rearward, upstream portions of the side surfaces being spaced further apart - in circumferential directions - from each other than their respective axially forward, downstream portions.
One or both of the side surfaces of an elevation may be flat. One or both of the side surfaces of an elevation may be curved. Flat side surfaces of an elevation are generally simple to manufacture. Hence in certain embodiments the side surfaces of at least one elevation, or of all elevations, of the plurality of elevations are flat.
The side surfaces of an elevation converge towards the front end of the nozzle tube wall. Where the side surfaces of an elevation are flat surfaces, they may form a convergence angle between them. The existence of a convergence angle is generally independent from the side surfaces meeting or not meeting. The convergence angle may be, for example, between 45° and 90°. Correspondingly, where the side surfaces are flat surfaces, their respective surface normals may form an angle of between 135° and 90° between them. An elevation with side surfaces forming a convergence angle of between 45° and 90° generates vortices most effectively, and hence helps facilitate improved atomization of the liquid without having to increase the flow rate or the pressure of the atomizing gas, enhances the mixing between atomizing gas and liquid, and helps obtain a more homogeneous mixing ratio between the liquid and the atomizing gas. Where each elevation has two respective side surfaces with this orientation, the beneficial effect is even more pronounced.
The convergence angle between flat side surfaces of an elevation can be determined by determining for each side surface the straight line ("foot line") where the side surface meets the lowland portion. The convergence angle is the angle between the respective foot lines of the side surfaces.
Therefore, in certain embodiments of the nozzle body according to the present disclosure, the side surfaces of at least one elevation, or of each elevation, of the plurality of elevations are flat and oriented relative to each other such as to form a convergence angle of between 45° and 90° between the side surfaces.
The side surfaces of an elevation converge towards the front end. In other words, they converge in a generally front-rear direction, i.e. in a general axial direction. Independent of this axial convergence, the side surfaces of an elevation may converge in a top-bottom direction, i.e. in a radial outward-inward direction. Convergence in a top-bottom direction can be visualized by taking a cross section of the nozzle body in a plane orthogonal to the spray axis, wherein the plane intersects both side surfaces of the elevation. In this cross sectional view the side surfaces appear as separate lines ("section lines"). Where the side surfaces are flat, the section lines are straight. The section lines may meet or may not meet.
Where in that cross sectional view the section lines converge towards the "top" of the elevation, i.e. the section lines, if extended, would meet at a point radially outward from the elevation, the side surfaces are further apart at the radial level of the lowland portion, and they are closer to each other at radial levels that are "higher" (i.e. further radially outward). Correspondingly, where in that cross sectional view the section lines converge towards the "bottom" of the elevation, i.e. towards the lowland portion, the side surfaces are closer to each other at the radial level of the lowland portion, and they are further apart at radial levels that are "higher" (i.e. further radially outward with respect to the lowland portion). In the intermediate scenario in which the section lines are parallel to each other in the cross sectional view, the side surfaces are parallel to each other. All three scenarios may occur in a nozzle body according to the present disclosure and have their respective advantages.
Where the nozzle body is manufactured by molding, the nozzle body is generally easier to remove from the mold if the side surfaces of an elevation, and of each elevation, converge towards the top of the elevation. Similarly, where the nozzle body is manufactured by machining, the nozzle body is generally easier to form if the side surfaces of an elevation, and of each elevation, converge towards the top of the elevation. Therefore, in certain embodiments, the side surfaces of one elevation, or of each elevation, of the plurality of elevations converge towards the top of the elevation. In some of these embodiments the side surfaces are flat and meet at a straight line ("fold line") radially outward from the remainder of the elevation, in others of these embodiments the side surfaces don't meet radially outward from the remainder of the elevation.
In a cross section of the nozzle body in a plane orthogonal to the spray axis, wherein the plane intersects both side surfaces of the elevation, the side surfaces appear as section lines, as described above. These section lines may meet or may not meet. Where the side surfaces are flat, in that cross section, the section lines of the side surfaces of an elevation are straight and may form an angle between them, referred to as a "draft angle" of the elevation herein. The draft angle of an elevation, or the respective draft angles of all elevations, may be between 1 ° and 90°.
Generally, the side surfaces of an elevation converge in a front-rear direction towards the front end of the nozzle tube wall, and they may or may not converge in a top-bottom direction as explained above. Where the side surfaces of an elevation are flat, the orientation of each side surface is defined by a surface normal on the side surface. The respective surface normals on the side surfaces point away from the elevation. The surface normals of the side surfaces may form an angle of between 45° and 90° between them.
One or both of the side surfaces of an elevation may extend in a downstream direction up to the front end of the nozzle tube wall. Alternatively, one or both of the side surfaces of an elevation may extend in a downstream direction up to an axial position upstream from the front end of the nozzle tube wall.
The two side surfaces of an elevation converging towards the front end may meet. Where the side surfaces of an elevation converge such as to meet, they may form a kind of apex at the meeting location, similar to how the arms of the letter "V" meet at the bottom to form an apex. Since the side surfaces of an elevation extend radially-outwardly from the lowland portion, the apex is a line that is referred to as a "joint line" herein. The joint line may extend radially outward from the lowland portion. Elevations that have converging side surfaces which meet at a joint line are particularly effective in creating vortices, because they use the maximum possible length of the upper edge of each side surface to create a vortex.
Nozzle bodies in which the joint line is straight are generally easier to manufacture, e.g. to mold or to machine, than those with other joint line geometries. A straight joint line may also provide a more consistent, less variable geometry of the vortices in the vortex pair. In contrast, a curved joint line may facilitate generation of vortex pairs having advantageous velocity distributions for a more effective atomization.
Therefore, in certain embodiments, the converging side surfaces of at least one elevation, or of each elevation, of the plurality of elevations meet at a joint line, wherein the joint line is straight or curved.
The radially innermost end of a joint line of the side surfaces of an elevation, i.e. a "bottom end" of the joint line, is also referred to as the "foot" of the joint line. The foot of a joint line is located at the radial level of the lowland portion from which the side surfaces extend radially-outwardly.
Independent of their respective axial positions, the angular positions of the joint line feet of the plurality of elevations may be spaced evenly about a circumference of the gas-guiding surface. Such an arrangement may help obtain a more evenly distributed pattern of vortices and a more even spray pattern.
The foot of a joint line of an elevation may be located in different axial (i.e., forward-rearward) positions. In certain embodiments the foot (i.e., the radially innermost end) of the joint line is arranged at the axial position of the front end of the nozzle tube wall. Such an arrangement results in the vortices generated by the elevation to exit the spray gun right after they are generated, so that they can expand and decay in the surrounding air outside the spray gun, thereby atomizing the liquid effectively. Also, the foot of the joint line is more easily accessible from outside the spray gun, e.g. for cleaning.
In other embodiments the radially innermost end ("foot") of the joint line is arranged at an axial position upstream (rearward) of the front end of the nozzle tube wall. Such an arrangement can result in the vortices being generated, and propagating for a certain distance, inside the spray gun in a gas passage delimited by the gas-guiding surface and an inner surface of an air cap. When these vortices exit the spray gun, they may have a different shape, be weaker and less pronounced, which may be desirable in certain scenarios.
A straight joint line of an elevation may have various different orientations. It may, for example, be tilted "sideways" (i.e. tilted in a circumferential direction), which would promote the creation of a non-symmetric pair of vortices by that elevation. Since it is generally desired that the pair of vortices be symmetric for the spray pattern to be more even, a tilt in circumferential direction is often avoided and the straight joint line is preferably arranged such that it lies in a plane through the spray axis. In certain embodiments, thus, the joint line lies in a plane through the spray axis.
Independent of a tilt in circumferential direction, a straight joint line may be tilted in a forward/rearward direction. In this case the joint line forms an angle with a radial direction lying in a plane through the spray axis and through the foot of the joint line. This angle may be 0°, in which case the joint line is not forward/rearward tilted, but is a purely radial direction. Where the angle is not 0°, it may be negative, which - by convention herein - refers to a scenario where the radially outermost end of the joint line is located axially downstream from the foot. Correspondingly, a positive forward/rearward tilt angle refers to a scenario where the radially outermost end of the joint line is located axially upstream from the foot of the joint line.
A forward/rearward tilt angle may be beneficial in order to accommodate the nozzle tube wall with the elevations in a limited space close to the front end of the nozzle tube wall. It may also help in tailoring the shape and path of the vortices generated by the elevation. Forward/rearward tilt angles of between -70° and +70° currently appear to be advantageous in these respects. Hence, in certain embodiments of the nozzle body according to the present disclosure, the joint line is oriented at an angle of between -70° and +70° with respect to a radial direction in that plane. In certain of these embodiments the joint line is oriented at an angle of 0° with respect to a radial direction in that plan, in other words, the joint line is oriented parallel to a (purely) radial direction and thereby orthogonal to the spray axis. Such elevations with a joint line having no forward/rearward tilt may be more rugged and easier to manufacture than those with a forward/rearward tilted joint line.
Certain advantageous embodiments combine the absence of a circumferential tilt with a certain range of forward/rearward tilt of a joint line. Hence in these embodiments the joint line lies in a plane through the spray axis, and the joint line is oriented at an angle of between -70° and +70° with respect to a radial direction in that plane.
Alternatively, the forward-rearwardly converging side surfaces of an elevation may not meet. Where the converging side surfaces of an elevation do not meet, their downstream-most ends may be located at the same axial position. Where the converging side surfaces of an elevation do not meet, their downstream-most ends may be connected with each other by a front wall extending radially-outwardly from the lowland portion.
The side surfaces of an elevation may delimit the elevation laterally, i.e. in generally circumferential directions around the spray axis. The side surfaces may be outer surfaces of the elevation. They may, for example, be generally opposed outer surfaces of the elevation. The elevation may comprise two side walls, wherein each side wall comprises one of the side surfaces. Between the side walls, the elevation may be hollow. Alternatively, between the side walls, the elevation may be solid, filled or partially filled.
A side surface, whether curved or flat, may be delimited in a radially outward direction by an edge. Where the lowland portion is considered a "bottom", the radially outermost edge of a side wall may be considered an "upper edge" of the side wall. The upper edge, and any edge of an elevation, may comprise a chamfer or be rounded in order to be able to manufacture the nozzle body in a molding process. The radially outermost edge of a side surface may be straight or curved.
In a nozzle body according to the present disclosure, an elevation of a gas-guiding surface may comprise a roof connecting the respective radially outermost edges of the side surfaces of the elevation with each other. In use, the roof may be in contact with the flow of atomizing gas. The roof may be a flat surface, a one-dimensionally curved surface (such as a cylindrical surface or a conical surface) or a two dimensionally curved surface (such as a surface of a sphere or of a trumpet funnel).
Where an elevation comprises a roof, the atomizing gas flows along the gas-guiding surface of the nozzle tube wall towards the front end of the nozzle tube wall over the roof. Where the gas-guiding surface is smooth, the flow is generally laminar. Where a roof is rearwardly inclined, the atomizing gas flows over the elevation and a portion of the flow is directed away from the spray axis by the rearwardly inclined roof. When that portion of the flow, as it flows towards the front end, reaches the end of the roof at the upper (i.e. the radially outermost) edge of one side surface, it will "see" a low-pressure zone and follow the pressure gradient in a direction towards the spray axis. Due to the convergence of the side surfaces, the pressure gradient has an oblique component, giving the portion of the flow a circumferential velocity component. Various portions of the flow reaching the end of the roof at the upper edge of one side surface at different axial positions and following the respective pressure gradient results in these portions of the atomizing gas forming a vortex which rotates about an axis roughly parallel to the spray axis and which propagates forward towards and beyond the front end to exit the spray gun and to atomize liquid exiting the nozzle tube outlet.
Portions of the flow of atomizing gas reaching the end of the roof at the upper edge of the other side surface of the same elevation will follow a corresponding similar pressure gradient and form a second vortex rotating in an opposite rotation direction. In the flow of atomizing gas comprising the two vortices formed by the side surfaces of the same elevation, the vortices rotate in opposite directions. As they propagate forward to exit the spray gun, they will atomize the liquid more effectively than a similar flow that has no vortex.
Hence in certain embodiments at least one elevation, or each elevation, of the plurality of elevations comprises a roof connecting the respective radially outermost edges of the side surfaces of the elevation with each other, wherein in use, the roof is in contact with the flow of atomizing gas.
In certain embodiments the roof is shaped like a portion of a cylindrical surface or like a portion of a conical surface. This cylindrical surface or this conical surface may be coaxial with the spray axis. This cylindrical surface or this conical surface may be coaxial with the nozzle tube passage. In a longitudinal sectional view taken in a plane through the spray axis the roof may appear as a straight line or as a curved line.
In certain embodiments the roof is shaped like a portion of a conical surface diverging with decreasing axial distance from the front end of the nozzle tube wall, coaxial with the spray axis. The roof may be considered shaped and arranged as if it were part of the lateral surface of an imaginary cone centered on the spray axis. Where the apex of the imaginary cone is located upstream from the elevation, the roof surface is thereby shaped to guide atomizing gas away from the spray axis. This shape and orientation of the roof surface tends to generate larger and stronger vortices in the flow of atomizing gas. Generally, a flow of atomizing gas away from the spray axis is believed to generally obtain a more effective atomization in certain scenarios.
Therefore, in certain embodiments of the nozzle body according to the present disclosure, the roof is shaped and arranged such as to be comprised in the lateral surface of an imaginary right circular cone centered about the spray axis, wherein the apex of the imaginary cone is located upstream from the elevation and wherein the cone angle (half angle) of the imaginary cone is between 0° and 45°.
In contrast, where the apex of the imaginary cone is located downstream from the elevation, the roof surface is shaped to guide atomizing gas towards the spray axis.
In certain embodiments, however, at least one elevation, or each elevation, of the plurality of elevations has no roof and the side surfaces of the elevation do not meet.
The liquid exits the nozzle tube at the nozzle tube outlet into outside air in a spray direction. The spray direction is thus the flow direction of the liquid flow at the position where the liquid exits the nozzle tube passage. This position is a position at the nozzle tube outlet, i.e. in the most forward portion of the nozzle tube wall in the vicinity of the nozzle tube outlet. Depending on the circumstances, further downstream the liquid flow may not have a well-defined "flight" direction anymore. The definition of the "spray direction" herein is therefore based on the direction of the liquid flow at the position where the liquid exits the nozzle tube passage into outside air.
The spray direction is generally determined by the orientation of a terminal portion of the nozzle tube passage, i.e. the portion of the nozzle tube passage closest to the nozzle tube outlet. The spray direction through the centroid of the cross section of the nozzle tube outlet, viewed in the outlet cross section, defines a spray axis. The spray axis thus always passes through the centroid and is collinear with the spray direction at the position of the centroid. In embodiments in which the direction(s) at which the liquid exits the nozzle tube outlet into outside air is/are symmetric with respect to a symmetry axis, the spray axis may be the symmetry axis of the spray direction(s) at which the liquid exits the nozzle tube outlet into outside air.
The spray axis defines axial directions. Axial directions are directions parallel to the spray axis. Radial directions are directions orthogonal to the axial directions, such as directions orthogonally towards the spray axis or orthogonally away from the spray axis. Circumferential directions are directions angularly around the spray axis.
The nozzle tube outlet may be arranged around the spray axis, e.g. a full 360° around the spray axis. In certain embodiments the nozzle tube outlet has an annular shape as viewed in the outlet cross section. In certain embodiments the nozzle tube outlet comprises the spray axis. Liquid thus exits the nozzle tube passage at the position of the spray axis. In such nozzle tube outlets liquid exits the nozzle tube passage through the nozzle tube outlet at the position of the spray axis. This geometry may help in obtaining a contiguous jet of liquid which may be altered or shaped further downstream by the atomizing gas into a consistent and balanced spray pattern.
The flow direction of the atomizing gas may be determined by the orientation and/or shape of the gas-guiding (outer) surface of the nozzle tube wall alone, or by the orientation and/or shape of the gas-guiding surface of the nozzle tube wall in conjunction with another surface of the nozzle body. In many known spray gun designs, however, such as in certain ones shown in the international patent application published as WO 2012/109298 A1 , the flow direction of the atomizing gas is determined by the orientation and/or shape of the gas-guiding surface of the nozzle tube wall and an orientation and/or shape of a surface of an air cap. Air caps are generally known from many existing spray guns: an air cap is an element directly or indirectly attached to the barrel of a nozzle assembly or to the body of the spray gun and helps direct pressurized gas in suitable directions for atomizing the liquid jet and for shaping the jet of minute droplets of atomized liquid. Certain air caps are provided with air horns having shaping air apertures. Shaping air apertures direct so-called shaping gas from opposite directions towards a jet of atomized liquid in order to shape the spray jet into a desired pattern.
When an air cap is connected directly or indirectly with a nozzle body according to the present disclosure, the gas-guiding surface of the nozzle tube wall may be arranged to form, in conjunction with a surface of the air cap, an atomizing gas outlet arranged around the nozzle tube outlet in a generally circumferential direction. The gas-guiding surface of the nozzle tube wall, with its elevations, may, for example, be arranged opposite to that air cap surface, and/or parallel to that surface. The atomizing gas outlet may be formed between a surface of the air cap and the gas-guiding surface of the nozzle tube wall at the nozzle tube outlet, i.e. between a surface of the air cap and a portion of the gas-guiding surface of a terminal end of the nozzle tube wall. Where the gas-guiding surface of the nozzle tube wall can form a portion of the atomizing gas outlet, this avoids the necessity to provide an additional element of a spray gun which would direct the atomizing gas into a desired direction in a desired pattern.
In certain embodiments of the nozzle body according to the present disclosure the gas-guiding surface of the nozzle tube wall is therefore arranged to form, in conjunction with a surface of an air cap when the air cap is connected directly or indirectly with the nozzle body, an atomizing gas outlet arranged circumferentially around the nozzle tube outlet, such that the pressurized atomizing gas exits into outside air through the atomizing gas outlet and atomizes the liquid after the liquid has exited the nozzle tube outlet. The atomizing gas outlet may be arranged in the plane of the nozzle tube outlet orthogonal to the spray axis. The atomizing gas outlet may be arranged in the plane through the nozzle tube outlet orthogonal to the spray axis.
A generally circumferential arrangement of the atomizing gas outlet around the nozzle tube outlet is not limited to a circular circumferential arrangement, but includes, for example, elliptic circumferential arrangements, square or rectangular or other polygonal circumferential arrangements, star-shaped circumferential arrangements and circumferential arrangements of irregular shape. The atomizing gas outlet may have a generally annular shape, a generally circular shape, a generally elliptic shape, a generally square or a generally rectangular or another polygonal shape, a star shape or an irregular shape.
The delimiting surface of the air cap may be referred to herein as nozzle aperture edge. The nozzle aperture edge forms an aperture for accommodating the nozzle body in a front wall of the air cap in which aperture the front end of the nozzle tube wall is arranged. The nozzle aperture edge may be a circular edge or an elliptical edge, for example.
The "shape of the atomizing gas outlet" is a shape perceived as the atomizing gas outlet is viewed from the front, looking rearward along the spray axis at the atomizing gas outlet. The shape of the atomizing gas outlet may be the shape of the atomizing gas outlet in the plane of the nozzle tube outlet or the shape of the atomizing gas outlet viewed in the outlet cross section.
Although the shape of the atomizing gas outlet is not particularly limited, it is preferred that the atomizing gas outlet forms essentially a full 360° circumference (for example of circular shape or elliptical shape or another suitable shape) around the nozzle tube outlet. This helps ensure proper atomization of the liquid. In alternative scenarios, however, the atomizing gas outlet may form an incomplete circumference (of any shape) around the nozzle tube outlet.
The width of the atomizing gas outlet is not particularly limited. "Width of the atomizing gas outlet", as used herein, is the extension of the atomizing gas outlet in radial directions in the plane of the atomizing gas outlet. In certain configurations, the width is the radial distance between the gas-guiding surface of the nozzle tube wall at the front end and the nozzle aperture edge of the air cap. The atomizing gas outlet may have a width of between 0.01 millimetre (mm) and 5.00 mm, for example. Preferably, the atomizing gas outlet has a width of between 0.10 millimetre (mm) and 1.00 mm. At a given atomizing gas pressure a wider atomizing gas outlet will result in lower gas speed and hence a reduced shear stress/velocity gradient between the gas and the liquid to be atomized. In contrast, a narrower atomizing gas outlet lets less gas pass through but the gas may flow at a higher velocity and thereby increase the shear stress between the gas and the liquid. The preferred widths are chosen amongst a large set of design parameters (desired air consumption, desired liquid flow rate, atomization quality, etc.) to help obtain an acceptable balance between these effects.
The atomizing gas outlet may be concentrically circumferentially arranged around the nozzle tube outlet at a certain radial distance from the nozzle tube outlet. This radial distance may be the thickness of the nozzle tube wall at the front end, i.e. at the nozzle tube outlet. The radial distance, at the nozzle tube outlet, between the nozzle tube outlet and the atomizing gas outlet may be between 0.01 mm and 5 mm, preferably it is between 0.1 mm and 1 mm. Since the atomizing gas exit velocity is often highest at the atomizing gas outlet and decreases moving downstream, there can be benefits to placing the nozzle tube outlet as close as practically possible to the gas outlet. One way to do so is by minimizing the radial distance between the nozzle tube outlet and the atomizing gas outlet. Generally, a greater radial distance may allow for a thicker and hence more stable nozzle tube wall. Conversely, a smaller radial distance may result in more efficient extraction and atomization of the liquid.
The nozzle tube outlet may be arranged in a geometrical plane, such as a plane orthogonal to the spray axis. The atomizing gas outlet may be arranged in the same geometric plane as the nozzle tube outlet, or it may be recessed or protruding from the plane of the nozzle tube outlet, e.g. by up to 5 mm.
The gas-guiding surface of the nozzle tube wall may also be arranged to form, in conjunction with a surface of an air cap when the air cap is connected directly or indirectly with the nozzle body, an atomizing gas passage for conducting a pressurized atomizing gas toward the atomizing gas outlet. The pressurized atomizing gas can thus exit the atomizing gas passage into outside air at the atomizing gas outlet and can atomize the liquid after the liquid has exited the nozzle tube outlet.
A first portion of the atomizing gas passage may thus be formed by a surface of the air cap, while a second portion of the atomizing gas passage may be formed by the gas-guiding surface of the nozzle tube wall. Before the air cap is connected with the nozzle body, the atomizing gas passage may thus not exist, or may be incomplete because it is not properly delimited so that pressurized atomizing gas is not conducted toward the atomizing gas outlet. However, in the absence of an air cap the outer surface of the nozzle tube wall is suitable (e.g. suitably shaped, and/or suitably arranged, and/or with a suitable surface structure) to form a portion of the atomizing gas passage, once a suitable air cap is connected.
A suitable air cap may be connected with the nozzle body according to the present disclosure directly or indirectly. Where two elements are connected without intermediate elements and in surface contact with each other, they are considered to be "directly connected" herein. Where two elements are connected with each other via one or more intermediate elements they are considered to be "indirectly connected" herein.
A nozzle body as described herein, in conjunction with an air cap and a barrel, can form a nozzle assembly. In a nozzle assembly or otherwise, the air cap may be connected with the nozzle body in a fixed spatial relation. The fixed spatial relation can help keep the shape of an atomizing gas outlet formed between a portion of the air cap and the nozzle tube wall constant under external forces. The nozzle assembly may be attachable to a platform of a spray gun, such as by attachment of the nozzle body to the spray gun platform or by attachment of the air cap to the spray gun platform or both.
In certain of these nozzle assemblies the air cap is connected with the nozzle body in a fixed spatial relation, wherein the air cap includes a front wall facing generally in the spray direction and comprising a nozzle aperture delimited by a nozzle aperture edge. The nozzle tube outlet is arranged in, or protrudes outwardly through, the nozzle aperture, such that the atomizing gas outlet is formed between the nozzle aperture edge and the nozzle tube wall.
Such a nozzle assembly may be advantageous in that the radially inner delimitation of the atomizing gas outlet is formed by the nozzle tube wall and the radially outer delimitation of the atomizing gas outlet is formed by the nozzle aperture edge. A nozzle body as described herein can thereby be used with air caps of different geometries. This, in turn, allows for geometric variations of the atomizing gas outlet, e.g. of its shape, width or its orientation, just by utilizing different air caps, and without having to change the nozzle body.
In certain embodiments of such a nozzle assembly the nozzle tube is arranged in the nozzle aperture such that the front end is flush, or almost flush, with the front surface of the front wall of the air cap. The front surface of the front wall of an air cap faces generally in the spray direction. In other embodiments the nozzle tube wall protrudes outwardly through the nozzle aperture such that the nozzle tube outlet is located in a plane forward from a plane in which the nozzle aperture is located.
ooking closer at the air cap in such a nozzle assembly, the front wall of the air cap is an outer wall of the air cap. The front wall comprises a front surface facing generally forward, i.e. facing generally in the spray direction. The front surface of the front wall is generally in contact with the outside air. The front wall may be a wall of the air cap, of which a portion may be arranged between opposite air horns, comprised in the air cap, if such air horns are present. Air horns are known in the industry to be axially protruding elements of an air cap, arranged opposite to each other with respect to the spray axis, which have respective openings through which pressurized "shaping air" is ejected towards the jet of atomized liquid in order to provide the jet with a desired geometric shape.
The front wall may form a nozzle aperture in which the forward end of the nozzle tube may be arranged or through which the forward end of the nozzle tube protrudes outwardly. When in use, the air cap including its front wall is arranged centered about the spray axis. The nozzle aperture may be arranged centered about the spray axis, and concentric with the nozzle tube outlet. In the plane of the nozzle tube outlet, a gap between the nozzle tube and the nozzle aperture edge may exist. The gap may extend circumferentially around, and concentric with, the nozzle tube. A width of the gap extends in radial directions. The gap may form the atomizing gas outlet described herein. The atomizing gas outlet may be arranged circumferentially around the nozzle tube outlet, such that the pressurized atomizing gas exits into outside air through the atomizing gas outlet and atomizes the liquid after the liquid has exited the nozzle tube outlet.
For an evenly covered target surface it is sometimes desired to obtain a jet of liquid spray which is perfectly rotationally symmetric with respect to the spray axis. In order to get close to a symmetric jet of liquid spray, in certain embodiments of the nozzle bodies described herein the nozzle tube outlet and/or the nozzle tube wall are of rotationally symmetric shape and are arranged concentrically with each other, such as centered on the spray axis. Similarly, the entire air cap and/or the nozzle aperture edge may be of rotationally symmetric shape and may be arranged concentrically with each other, such as centered on a symmetry axis of the air cap.
In order to get closer to a symmetric jet of liquid spray, in certain embodiments of the nozzle assemblies described herein the nozzle tube outlet, the nozzle tube wall, the nozzle aperture edge, and the atomizing gas outlet are each of rotationally symmetric shape and are each arranged concentrically with respect to the spray axis.
Certain liquid spray guns include a barrel attached to the spray gun platform through which the to-be-sprayed liquid flows from an external container into the spray gun. After a spraying operation only the barrel and the nozzle body need to be cleaned from liquid, not the spray gun platform. A rear portion of the barrel is usually attached to the spray gun platform, while a front portion often serves to attach an air cap and a nozzle body. A further function of a barrel is to conduct pressurized gas from the spray gun platform to the atomizing gas outlet and potentially towards a shaping gas outlet (e.g. in air horns) at the front portion of the spray gun. A barrel may comprise separate ducts for conducting liquid, atomizing gas and shaping gas. In some embodiments, the barrel and the nozzle body are integrally formed as a single component.
Nozzle assemblies comprising an air cap and a nozzle body according to the present disclosure have been described above. Nozzle bodies according to the present disclosure can be, in use, directly connected to a spray gun body, but alternatively they can be attached to a barrel which is attached to the spray gun body. Also, an air cap can be directly connected to the spray gun body, but it can alternatively be connected to a barrel which is attached to the spray gun body. Where the air cap and the nozzle body are each connected to the same barrel, these connections to the barrel may help establish and maintain a fixed spatial relation between the nozzle body and the air cap. This fixed spatial relation generally helps maintain a constant shape and orientation of the atomizing gas outlet, which is formed between a portion of the air cap (e.g. its nozzle aperture edge) and a portion of the nozzle body (its nozzle tube wall). Maintaining the shape and orientation of the atomizing gas outlet helps keep the jet of atomized liquid in a consistent, fixed geometry and contributes to an atomization which is more constant over time and under external forces.
Therefore, the present disclosure also provides a nozzle assembly comprising i) a nozzle body as described herein, ii) an air cap, connected with the nozzle body in a fixed spatial relation, and comprising a front wall facing generally in the spray direction and comprising a nozzle aperture delimited by a nozzle aperture edge, and iii) a barrel having a liquid port connector for directly or indirectly connecting a liquid reservoir to the barrel, wherein the air cap is connected with the barrel, and the nozzle body is connected with the barrel, such that the air cap is connected with the nozzle body in a fixed spatial relation, and wherein the nozzle tube outlet is arranged in, or protrudes outwardly through, the nozzle aperture, such that an atomizing gas outlet is formed between the nozzle aperture edge and the nozzle tube wall such that atomizing gas can exit the nozzle assembly through the atomizing gas outlet.
Nozzle bodies according to the present disclosure can be connected to a spray gun platform, directly or indirectly via their connection to a barrel connected to the spray gun platform, to form a liquid spray gun in which the gas-guiding surface of the nozzle tube wall comprises elevations for generating vortices in the flow of atomizing gas, and wherein each elevation has converging side surfaces, extending radially-outwardly from the lowland portion and extending towards the front end. The elevations generate vortices in the atomizing gas and thereby help improve the mixing of liquid and atomizing gas and help improve atomization of the liquid. This in turn helps consume less of the pressurized atomization gas while obtaining a comparable degree of atomization and mixing.
The present disclosure also provides a liquid spray gun for spraying a liquid, comprising a nozzle body as described herein, or a nozzle assembly as described herein. The spray gun and the nozzle assembly include a nozzle body in which the gas-guiding surface comprises elevations having converging side surfaces as described herein. The elevations help create vortices in the flow of pressurized atomizing gas which help provide a more effective atomization of the liquid and a better mixture of atomizing gas and liquid.
Nozzle bodies according to the present disclosure can be manufactured in traditional manufacturing processes like, for example, machining or molding. They may also be created via additive manufacturing processes using a 3D printer. Digital data describing the nozzle body may be stored on a machine-readable medium and may be sent to the 3D printer by digital processors such that the 3D printer "prints" the nozzle body.
The present disclosure thus also provides a non-transitory machine-readable medium having data stored thereon representing a three-dimensional model of a nozzle body as described herein or of a nozzle assembly as described herein, the data being formatted to be accessed by one or more digital processors interfacing with a 3D printer, wherein the one or more digital processor(s) is/are operable to cause the 3D printer to manufacture the nozzle body or the nozzle assembly, respectively.
Nozzle bodies, nozzle assemblies and spray guns according to the present disclosure will now be described in more detail with reference to the following Figures exemplifying particular embodiments:

Fig. 1: Exploded perspective view of a spray gun comprising a first nozzle body according to the present disclosure;
Fig. 2: Perspective view of the first nozzle body, attached to a barrel;
Fig. 3: Perspective view of a spray head assembly comprising the first nozzle body and the barrel of Figure 2;
Fig. 4: Longitudinal sectional view of the spray head assembly of Figure 3;
Fig. 5: Perspective view of the first nozzle body of Figures 1-4;
Fig. 6: Perspective front view of a forward portion of a second nozzle body according to the present disclosure;
Fig. 7: Perspective front view of a forward portion of a third nozzle body according to the present disclosure;
Fig. 8: Perspective front view of a forward portion of a fourth nozzle body according to the present disclosure; and
Fig. 9: Perspective front view of a forward portion of a fifth nozzle body according to the present disclosure.

Figure 1 is an exploded perspective view of one illustrative embodiment of a liquid spray gun comprising a first nozzle body 1 according to the present disclosure. The liquid spray gun has a variety of components including a liquid spray gun platform 10 and a spray head assembly 20 that is - preferably releasably - attached to the liquid spray gun platform 10 at a barrel interface 11. The spray head assembly 20 provides features that control movement of both the liquid to be sprayed (a liquid paint, for example) and the atomizing gas (air, for example) used to atomize the liquid as described herein. In some embodiments, the spray head assembly 20 is disposable and can be thrown away after use, although in some instances it may be reused. If disposed after use, cleaning of the spray head assembly 20 in some embodiments can be avoided and the spray gun can be conveniently changed over by, e.g., attaching a different spray head assembly 20 connected to the same or a different liquid container. Connection of the spray head assembly 20 to the barrel interface 11 of the spray gun platform 10 may be achieved by any suitable technique. For example, connection structures on the spray head assembly 20 may cooperate (e.g., mechanically interlock) with openings 11a and 11b at the barrel interface 11 to retain the spray head assembly 20 on the spray gun platform 10.
The spray gun platform 10 depicted in Figure 1 defines a variety of cavities that, taken together, form the passages that deliver pressurized gas to the spray head assembly 20. Among other features, the spray gun platform 10 includes a fitting 12 such that the gas supply passages in the spray gun platform 10 can be connected to a gas source (not shown) that supplies gas to the spray gun platform 10 at greater than atmospheric pressure. A needle passage is also provided in the spray gun platform 10 to allow a needle 14 to pass into the spray head assembly 20 attached to the barrel interface 11. Control over both gas flow and liquid flow through the liquid spray gun is, in the depicted embodiment, provided by a trigger 15 that is pivotally engaged to the spray gun platform 10 by a retaining pin 16a and clip 16b. The needle 14 extends into the spray head assembly 20. The trigger 15 is preferably biased to the inoperative position in which needle 14 closes the liquid nozzle opening in the spray head assembly 20 and also closes a gas supply valve 17. When the trigger 15 is depressed, needle 14 is retracted to a position in which its tapered front end 14a allows liquid to flow through liquid nozzle tube outlet in the spray head assembly 20. At the same time, gas supply valve 17 also opens to deliver gas to the spray head assembly 20 from the passages in the spray gun platform 10. Gas and liquid flow may be further controlled by a fan gas control assembly 18a which controls gas delivered to a fan gas passage outlet 19a and to atomizing gas outlet 19b from the gas supply manifold in the platform 10, and atomizing gas control assembly 18b which restricts how far the trigger 15 may be depressed and thereby limits the total flow of gas and paint. In particular, the control assembly 18b controls the atomizing gas/liquid stream emanating from the spray head assembly 20, and control assembly 18a controls gas flow to the air horns (if provided) of the spray head assembly 20 to adjust the spray pattern geometry.
The spray head assembly 20 includes a barrel 30, an air cap 40 attached to the barrel 30, and a first nozzle body 1, shown generally in Figure 1, according to the present disclosure, attached to a nozzle port on the barrel 30. The nozzle body 1 may be a separate element as shown in Figure 1, or may form, in conjunction with the air cap 40, an integrated air cap/nozzle body.
Figure 2 illustrates, in a perspective view, the first nozzle body 1 of Figure 1 as it is attached to the barrel 30, which in turn is to be attached at its rear portion 38 to the liquid spray gun platform 10 at the barrel interface 11. The barrel 30 has a liquid inlet 73 through which the liquid is conducted into the barrel 30 and toward the nozzle body 1. A liquid port connector 74 at the end of the liquid inlet 73 is formed as a connector structure via which a liquid container (not shown), such as a liquid paint cup, can be connected to the barrel 30. The liquid can flow from the liquid container through the liquid inlet 73 and a liquid passage in the barrel 30 into a nozzle tube passage of the nozzle body 1. The liquid is sprayed through a nozzle tube outlet 52 in the front of the nozzle body 1 and exits the nozzle tube passage into outside air in a spray direction 300 along a spray axis 200 which passes through the center of the nozzle tube outlet 52. The outer surface 75 of the nozzle body 1 is a gas-guiding surface 75 as explained below. The shape of the nozzle body 1 is rotationally symmetric about the spray axis 200.
The barrel 30 and the nozzle body 1 are shown before the air cap 40 is arranged over the front portion 36 of the barrel 30, so that an atomizing gas passage 33 in the barrel 30 is visible through which, in use, pressurized atomizing gas flows through the barrel 30 generally toward the nozzle tube outlet 52.
Once a suitable air cap 40 is mounted over the front portion 36 and the nozzle body 1, an inner surface of the air cap 40 and the gas-guiding surface 75 of the nozzle body 1 cooperate to form the atomizing gas passage 33 for conducting pressurized atomizing gas towards an atomizing gas outlet 54 (see Figure 3) arranged circumferentially around the nozzle tube outlet 52.
Figure 3 illustrates, in a perspective view, the barrel 30 and the first nozzle body 1 of Figures 1 and 2 with an air cap 40 mounted over them, together forming a spray head assembly 20. Only the front end 80 of the nozzle tube wall 71 (see Figure 5) of the nozzle body 1 is visible in Figure 3. The gas-guiding surface 75 of the nozzle body 1 at the nozzle tube outlet 52 forms a first portion of a delimiting surface of the atomizing gas passage 33, shown in Figure 2, for guiding a flow of pressurized atomizing gas towards a generally annular atomizing gas outlet 54 arranged circumferentially around the nozzle tube outlet 52, such that the flow of atomizing gas exits the atomizing gas passage 33 into outside air at the atomizing gas outlet 54 and, downstream from the front end of the nozzle tube wall, atomizes the liquid after the liquid has exited the nozzle tube outlet 52.
The air cap 40 comprises two air horns 43a, 43b, arranged opposite to each other. So-called shaping gas exits the air horns 43a, 43b through two shaping gas apertures 46 on each of the air horns 43a, 43b. The shaping gas apertures 46 on the air horns 43a, 43b are located on opposite sides of the spray axis 200, diametrically opposed to each other, such that shaping gas flowing through the barrel 30 under greater than atmospheric pressure is directed against opposite sides of a jet of atomized liquid, formed from liquid exiting the nozzle tube outlet 52 into outside air in the spray direction 300. The forces exerted on this jet by the shaping gas can be used to change the shape of the jet of atomized liquid to form a desired spray pattern (e.g., circular, elliptical, etc.).
Figure 4 is a longitudinal sectional view of the spray head assembly 20 of Figure 3, which comprises the first nozzle body 1 of Figures 1-3 and the air cap 40. The nozzle body 1 comprises a nozzle tube 66 having a nozzle tube wall 71 which, in this embodiment, has the shape of a funnel narrowing towards the nozzle tube outlet 52. The liquid to be sprayed flows through the liquid inlet 73, through the barrel 30 and passes, from a nozzle tube inlet 57, through an elongated nozzle tube passage 58 to the nozzle tube outlet 52 through which, in use, the liquid exits the nozzle tube passage 58 into outside air in the spray direction 300 along the spray axis 200. The spray axis 200 defines axial directions 220 parallel to the spray axis 200, and radial directions 210 orthogonal to the axial directions 220. The spray direction 300 is an axial direction 220.
The rear portion 38 of the barrel 30 can be attached to the liquid spray gun platform 10 at the barrel interface 11, as shown in Figure 1, so that the spray gun platform 10 and the spray head assembly 20 form a complete liquid spray gun.
The air cap 40 is connected with the nozzle body 1 such that it is arranged rotationally symmetric about the spray axis 200. It has a front wall 60 which forms a circular nozzle aperture delimited by a nozzle aperture edge 65. In this embodiment the nozzle tube outlet 52 at the forward end of the nozzle tube 66 is arranged in the nozzle aperture delimited by the nozzle aperture edge 65 of the front wall 60 such that the nozzle tube outlet 52 is almost flush with the front surface 62 of the front wall 60 of the air cap 40 which faces generally in the spray direction 300.
The atomizing gas outlet 54 is formed between the nozzle aperture edge 65 of the front wall 60 of the air cap 40 and the radially outer, gas-guiding surface 75 of the nozzle tube wall 71. The atomizing gas outlet 54 therefore has a generally annular shape and is arranged circumferentially around the nozzle tube outlet 52. For clarity, smaller-scale structures on the gas-guiding surface 75 are not shown in Figures 1-4, they will be explained below.
Figure 5 is a perspective front view of the first nozzle body 1 of Figures 1-4. having at its forward end the nozzle tube outlet 52, through which, in use, the liquid exits the nozzle tube passage 58 into outside air 93 in the spray direction 300. In the embodiment of Figure 5, the nozzle tube 66 is rotationally symmetric about the spray axis 200, so that the length direction of the nozzle tube passage 58 and the spray direction 300 are both parallel to the spray axis 200 and collinear with it.
The nozzle tube 66 comprises the nozzle tube wall 71 which in turn comprises the radially-outer, gas-guiding surface 75 and the opposed radially inner surface 76 of the nozzle tube wall 71. The inner surface 76 delimits the nozzle tube passage 58 and is in contact with the liquid when the nozzle body 1 and the spray gun to which it is mounted are in use. The gas-guiding surface 75 extends in axial directions 220 from the rear of the nozzle tube wall 71 to the front end 80 of the nozzle tube wall 71. The front end 80 of the nozzle tube wall 71 is circular and lies in a plane orthogonal to the spray axis 200.
The spray direction 300 through a centroid 310 of the cross section of the nozzle tube outlet 52 defines the spray axis 200. The nozzle tube outlet 52 is arranged around, and comprises, the spray axis 200. The liquid exits the nozzle tube outlet 52 as a generally laminar flow in a well-defined direction (the spray direction 300), since turbulence is introduced into the liquid only downstream from the nozzle tube outlet 52. Turbulence introduces irregular velocities into the liquid after the liquid has exited the nozzle tube outlet 52 and thereby disturbs its laminar flow.
The gas-guiding surface 75 of the nozzle tube wall 71 is operable to form, in conjunction with a surface of a suitable air cap 40 (not shown), when the air cap 40 is connected directly or indirectly with the nozzle body 1, an atomizing gas outlet 54 (see Figure 4) arranged circumferentially around the nozzle tube outlet 52, such that a flow of pressurized atomizing gas, indicated by arrows 110, exits into outside air 93 through the atomizing gas outlet 54 and atomizes the liquid after the liquid has exited the nozzle tube outlet 52. The gas-guiding surface 75 guides the flow of atomizing gas 110 towards the front end 80 of the nozzle tube wall 71.
The flow of atomizing gas 110 flows along, and is in contact with, the gas-guiding surface 75 of the nozzle tube wall 71.
The gas-guiding surface 75 comprises a lowland portion 90 and a plurality of circumferentially-spaced elevations 100 for generating vortices in the flow of atomizing gas 110. Each elevation 100 protrudes radially outward, i.e. in a direction radially away from the spray axis 200, from the lowland portion 90 and comprises two side surfaces 102 each of which extends radially-outwardly from the lowland portion 90. In axial direction 220 the side surfaces 102 extend towards the front end 80 of the nozzle tube wall 71. The side surfaces 102 of each elevation 100 are oriented relative to each other such as to converge towards the front end 80. The side surfaces 102 of each elevation 100 form a convergence angle of about 70° between them.

(Joint line)

In the embodiment shown in Figure 5 the side surfaces 102 form a right angle (90°) with the surface portion of the lowland portion 90 from which they rise. Generally, it is contemplated that the side surfaces 102 of an elevation 100 can converge towards the front end 80 without meeting each other. In contrast thereto, in the embodiment of Figure 5 the two side surfaces 102 of each elevation 100 meet at a joint line 104. The joint line 104 is orthogonal to the spray axis 200 and its axial position is the axial position of the front end 80 of the nozzle tube wall 71. The convergence angle between the side surfaces 102 of an elevation 100 can be determined at the joint line 104.
The radially innermost end of a joint line 104 is considered a "foot" 106 of the joint line 104. The foot 106 of a joint line 104 is located at the radial level of the lowland portion 90.
The length of the joint line 104 corresponds to the "height" of the elevation 100, i.e. the maximum distance of any portion of the elevation 100 from the surrounding lowland portion 90 from which the elevation 100 rises. The height of the elevation 100 determines the diameter of the vortices generated by the elevation 100 just downstream from the elevation 100. The diameter of each vortex in the pair of vortices created by the elevation 100 is roughly (order of magnitude) the height of the elevation 100 over the surrounding lowland portion 90, measured a short distance downstream from the elevation 100.
In certain embodiments, not shown in Figure 5, a joint line 104 does not extend strictly orthogonally to the spray axis 200. A joint line 104 may, for example, be oriented at an angle of between about 1° and about 70° with respect to a radial direction 210, where a 0° angle would be the orthogonal extension. A joint line 104 may lie in a plane through the spray axis 200, i.e. a plane containing the spray axis 200. A joint line 104 may lie in a plane through the spray axis 200 and be oriented at an angle of between about 0° and about 70° with respect to a radial direction 210 in that plane. Alternatively, a joint line 104 may lie in a plane not comprising the spray axis 200 and/or not intersecting the spray axis 200.
In certain embodiments, the axial position of the foot 106 of a joint line 104 may be upstream (or rearward, if the spray direction 300 is considered a downstream or a forward direction) from the front end 80 of the nozzle tube wall 71, as shown in Figure 6.
In the embodiment shown in Figure 5, the gas-guiding surface 75 comprises six circumferentially-spaced elevations 100 of equal shape, of which four are visible. The six elevations 100 are circumferentially evenly spaced. Each of their joint lines 104 is thus arranged at an angular distance of 60° from an adjacent joint line 104, when going circumferentially along the gas-guiding surface 75 about the spray axis 200 at the front end 80.
In the embodiment shown in Figure 5, each of the circumferentially-spaced elevations 100 is delimited, in a radially-outward direction, by a top surface 108, also referred to as a roof 108. A roof 108 of an elevation 100 connects the radially outermost edge 122 of the first side surface 102 of the elevation 100 with the radially outermost edge 122 of the second side surface 102 of the same elevation 100.
A roof 108 may be a flat surface. In the embodiment of Figure 5, however, the roof 108 is a one-dimensionally curved surface that has, in a circumferential direction 212, a circular curvature corresponding to the radial distance of the roof 108 from the spray axis 200. The roof 108 is flat in axial direction 220.
In the embodiment of Figure 5 the respective roof 108 of each elevation 100 is axially inclined. As the Figure indicates, the radial distance of the roof 108 from the spray axis 200 is smaller at the rear (upstream) end of the roof 108 than at its forward (downstream) end. This inclination of the roof 108 is also referred to as the roof 108 being "rearwardly inclined". In alternative embodiments, not shown in Figure 5, a roof 108 may be "forwardly inclined", in which case the radial distance of the roof 108 from the spray axis 200 is greater at its rear end than at its forward end.
With the rearward inclination of the roof 108 shown in Figure 5, the flow of atomizing gas 110 passing over the roof 108 is directed away from the spray axis 200 by the roof 108. The roof 108 is shaped and arranged such that it can be considered a portion of the lateral surface of an imaginary right circular cone centered about the spray axis 200. Due to the rearward inclination of the roof 108 the cone's apex is located on the spray axis 200 upstream from the elevation 100. The cone angle (half angle) is about 30°. The roofs 108 of the remaining, identically shaped elevations 100 are shaped and arranged such that each of these roofs 108 can be considered a portion of the lateral surface of the same imaginary cone.
Where a one-dimensionally curved roof 108 is forwardly inclined (not shown), the apex is located on the spray axis 200 downstream from the elevation 100. Where a roof 108 is not axially inclined at all (not shown), the imaginary cone has a cone angle of 0° and turns into an imaginary cylinder.
In the nozzle body 1 of Figure 5 the atomizing gas 110 flows along the gas-guiding surface 75 of the nozzle tube wall 71 towards the front end 80 of the nozzle tube wall 71. In regions where the gas-guiding surface 75 is smooth, the flow is generally laminar. Where the atomizing gas flows over an elevation 100, a portion of the flow 110 is directed away from the spray axis 200 by the rearwardly inclined roof 108. When that portion of the flow 110, as it flows towards the front end 80, reaches the end of the roof 108 above one side surface 102, it will "see" a low-pressure zone and follow the pressure gradient in a direction towards the spray axis 200. Due to the convergence of the side surfaces 102, the pressure gradient has an oblique component, giving the portion of the flow 110 a circumferential velocity component. Various portions of the flow 110 reaching the end of the roof 108 above one side surface 102 at different axial positions and following the respective pressure gradient results in these portions of the atomizing gas 110 form a vortex which rotates about an axis roughly parallel to the spray axis 200 and which propagates downstream and forward beyond the front end 80 to exit the spray gun and to atomize liquid exiting the nozzle tube outlet 52.
Portions of the flow of atomizing gas 110 reaching the end of the roof 108 above the other side surface 102 of the same elevation 100 will follow a similar pressure gradient and form a second vortex. The two vortices in the flow of atomizing gas 110 formed by the side surfaces 102 of the same elevation 100 rotate in opposite directions. As the flow of atomizing gas 110 with its vortices propagates downstream to exit the spray gun, it will atomize the liquid more effectively than a similar flow that has no vortex.
Figure 6 is a perspective front view of a front portion of a second nozzle body 2 according to the present disclosure, identical in most aspects with the first nozzle body 1 of Figures 1-5. For convenience, like reference numerals are used to indicate parts corresponding to like elements in the first nozzle body 1, and identical features are not described again here.
In the embodiment of Figure 6 the axial position of the feet 106 of respective joint lines 104 is upstream from the axial position of the front end 80 of the nozzle tube wall 71. The axial distance between the axial position of the front end 80 and the axial position of the respective feet 106 of the joint lines 104 is about one third of the axial extension of the elevation 100, indicated by dashed line segment 109 for one of the elevations 100.
Figure 7 is a perspective front view of a front portion of a third nozzle body 3 according to the present disclosure, identical in most aspects with the first nozzle body 1 of Figures 1-5. For convenience, like reference numerals are used to indicate parts corresponding to like elements in the first nozzle body 1, and identical features are not described again here.
In the embodiment of Figure 7 the six identical elevations 100, distributed evenly about the circumference of the circular gas-guiding surface 75 in the vicinity of the front end 80 of the nozzle tube wall 71, have two-dimensionally curved roofs 108. Their curvature in circumferential directions 212 is similar to the curvature of the roofs 108 of the first nozzle body 1 of Figure 5. In addition, the roofs 108 of the third nozzle body 3 in Figure 7 have a second curvature in axial direction 220. This second curvature results in a pronounced tip 111 at the top of the joint line 104 of each roof 108. The second curvature of the roof 108 modifies the pressure gradient, compared to the pressure gradient caused by the one-dimensionally curved roofs 108 of Figures 5 and 6, and can therefore result in the generation of stronger vortices in the flow of atomizing gas 110 and eventually in a more effective atomization of the liquid.
Figure 8 is a perspective front view of a front portion of a fourth nozzle body 4 according to the present disclosure, identical in most aspects with the first nozzle body 1 of Figures 1-5. For convenience, like reference numerals are used to indicate parts corresponding to like elements in the first nozzle body 1, and identical features are not described again here.
In the embodiment of Figure 8 the six identical elevations 100 (of which four are visible in Figure 8), are again distributed evenly about the circumference of the circular gas-guiding surface 75 in the vicinity of the front end 80 of the nozzle tube wall 71. Each elevation 100 has converging side surfaces 102 which don't meet. Instead, each side surface 102 of each respective elevation 100 has a front edge 112 at the downstream end of the side surface 102. In the embodiment of Figure 8 these front edges 112 are straight edges which extend in radial directions 210 (in other embodiments, not shown here, the front edges 112 may be curved edges and/or extend in other directions). A flat front surface 114, extending in circumferential directions 212 and in radial directions 210, connects the front edges 112 of an elevation 100 with each other. In the embodiment of Figure 8, the front surfaces 114 of all elevations 100 are arranged in one single plane which is orthogonal to the spray axis 200. In other words, as shown in the embodiment of Figure 8, each flat front surface 114 is oriented such that a normal of the front surface 114 points parallel to the spray axis 200. In other embodiments, not shown here, one or some or all of the flat front surfaces 114 may be oriented such that a normal of the front surface(s) 114 forms an angle of between -45° and +45° with the spray axis 200.
The front surfaces 114 are arranged axially rearward, or upstream, from the front end 80 of the nozzle tube wall 71. This upstream arrangement allows a vortex in the flow of atomizing gas 110 to develop and grow before it exits the atomizing gas outlet 54 formed between the fourth nozzle body 4 and a suitable air cap 40, as explained in the context of Figure 4 above. This, in turn, may result in a more desirable atomization pattern of the liquid in certain scenarios. In other scenarios, not shown here, it may, however, be found advantageous to arrange a front surface 114, or all front surfaces 114, at the axial position of the front end 80 of the nozzle tube wall 71.
Figure 9 is a perspective front view of a front portion of a fifth nozzle body 5 according to the present disclosure, identical in most aspects with the first nozzle body 1 of Figures 1-5. For convenience, like reference numerals are used to indicate parts corresponding to like elements in the first nozzle body 1, and identical features are not described again here.
In the embodiment of Figure 9 the six identical elevations 100 (of which four are visible in Figure 9), are again distributed evenly about the circumference of the circular gas-guiding surface 75 in the vicinity of the front end 80 of the nozzle tube wall 71. Each elevation 100 has converging side surfaces 102 which meet at a joint line 104. Different from the nozzle bodies 1, 2, 3, 4 described previously, the elevations 100 of the fifth nozzle body 5 have no roof 108. Rather, each of the elevations 100 is V-shaped and comprises two side walls 116 that are oriented relative to each other such as to converge towards the front end 80 of the nozzle tube wall 71. Each side wall 116 has an inner surface 118 and an outer surface 102. The outer surfaces 102 are the side surfaces 102 of the elevation 100. While the normals of the side surfaces 102 of an elevation 100 point away from the elevation 100, the normals of the inner surfaces 116 of an elevation 100 point generally towards the inner space 120 between the side walls 116 of the elevation 100. This inner space 120 is comprised in the respective elevation 100. The inner space 120 may be a one-dimensionally curved surface on the radial level of the lowland portion 90 outside the elevation 100, as is the case in the embodiment illustrated in Figure 9. Alternatively, the inner space 120 may rise - in radial directions 210 - above the radial level of the lowland portion 90. It may comprise a structured surface, for example, that is suitable to guide a flow of atomizing gas 110 towards a top edge of the side walls 116.
In the fifth nozzle body 5 of Figure 9 the atomizing gas 110 flows along the gas-guiding surface 75 of the nozzle tube wall 71 towards the front end 80 of the nozzle tube wall 71. Where the gas-guiding surface 75 is smooth, the flow is generally laminar. It is currently believed that where the atomizing gas flows over an elevation 100 having V-shaped side walls 116, a portion of the flow 110 is forced "upwards", i.e. away from the spray axis 200, by the inner surfaces 118 of the side walls 116. When the atomizing gas 110 hits the oblique inner surface 118, its velocity will receive a component in circumferential direction 212 and a component directed radially outward. When that portion of the flow 110, as it flows towards the front end 80, reaches the outer side surface 102, it will "see" a low-pressure zone and follow the pressure gradient in a "downward" direction towards the spray axis 200. Due to the convergence of the side surfaces 102, the pressure gradient has an oblique component, giving the portion of the flow 110 a circumferential velocity component. Due to various portions of the flow 110 reaching the end of the side surface 102 at different axial positions and following the respective pressure gradient, these portions of the atomizing gas flow are not laminar any longer and form a vortex which rotates about an axis roughly parallel to the spray axis 200 and which propagates forward beyond the joint line 104 and the front end 80 to exit the spray gun and to atomize the liquid after the liquid exits the nozzle tube outlet 52. Portions of the flow of atomizing gas 110 reaching the upper (radially outermost) edge 122 of the opposed side surface 102 of the same elevation 100 will follow a similar pressure gradient and form a second vortex. The orientation of the inner walls 118 is expected to provide the atomizing gas flow 110 with vortices which are different from the types of vortices created by elevations 100 comprising a roof 108. Vortices created by the fifth nozzle body 5 may, for example, comprise a more turbulent flow and may provide for a more even distribution of the minute liquid droplets in the atomized mist of liquid at a greater distance from the spray gun.

Claims

Nozzle body (1, 2, 3, 4, 5) for a liquid spray gun for spraying a liquid, the nozzle body including a nozzle tube (66) comprising
a) an elongated nozzle tube passage (58), extending lengthwise between a nozzle tube inlet (57) through which, in use, liquid enters the nozzle tube (66), and a nozzle tube outlet (52), through which, in use, the liquid exits the nozzle tube passage (58) into outside air (93) in a spray direction (300), wherein the spray direction (300) through a centroid (310) of the cross section of the nozzle tube outlet (52) defines a spray axis (200), wherein the spray axis defines axial directions (220) and radial directions (210) orthogonal to the axial directions,

b) a nozzle tube wall (71) having
- a front end (80) surrounding, and concentric with, the nozzle tube outlet (52),

- a radially-inner surface (76) delimiting the nozzle tube passage (58) and being, in use, in contact with the liquid,

- an opposed radially-outer gas-guiding surface (75) for guiding a flow of pressurized atomizing gas (110), in contact with the gas-guiding surface (75), towards the front end (80) such that the flow of atomizing gas (110), downstream of the front end (80), can atomize the liquid after the liquid has exited the nozzle tube outlet (52),

wherein the gas-guiding surface (75) comprises a lowland portion (90) and a plurality of circumferentially-spaced elevations (100), each protruding radially outward from the lowland portion (90), for generating vortices in the flow of atomizing gas (110),

characterized in that each elevation (100) comprises two side surfaces (102), each side surface (102) extending radially-outwardly from the lowland portion (90) and extending towards the front end (80), the side surfaces (102) being oriented relative to each other such as to converge towards the front end (80).
Nozzle body (1, 2, 3, 4, 5) according to claim 1, wherein the number of the plurality of elevations (100) is between three and thirty, preferably six or eight or twelve.
Nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims, wherein the elevations (100) are spaced evenly about a circumference of the gas-guiding surface (75).
Nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims, wherein the side surfaces (102) of at least one elevation (100), or of each elevation (100), of the plurality of elevations (100) are flat and oriented relative to each other such as to form a convergence angle of between 45° and 90° between the side surfaces (102).
Nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims, wherein at least one elevation (100), or each elevation (100), of the plurality of elevations (100) is shaped symmetrically relative to a plane through the spray axis (200) and through the elevation (100).
Nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims, wherein at least two, or all, elevations (100) of the plurality of elevations (100) have an identical geometric shape and an identical geometric size.
Nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims, wherein the side surfaces (102) of at least one elevation (100), or of all elevations (100), of the plurality of elevations (100) are flat.
Nozzle body (1, 2, 3, 5) according to any one of the preceding claims, wherein the converging side surfaces (102) of at least one elevation (100), or of each elevation (100), of the plurality of elevations (100) meet at a joint line (104), wherein the joint line is straight or curved.
Nozzle body (1, 2, 3, 5) according to the preceding claim, wherein the joint line (104) lies in a plane through the spray axis (200), and wherein the joint line (104) is oriented at an angle of between -70° and +70° with respect to a radial direction (210) in that plane.
Nozzle body (1, 2, 3, 5) according to any one of the preceding claims, wherein the lowland portion (90) is shaped and oriented to guide atomizing gas (110) away from the spray axis (200) at the front end (80) of the nozzle tube wall (71).
Nozzle body (1, 3, 5) according to any one of the preceding claims, wherein, when the nozzle body is in use, each elevation (100) is arranged and shaped to create a pair of counter-rotating vortices in the flow of atomizing gas (110).
Nozzle body (1, 2, 3, 4) according to any one of the preceding claims, wherein at least one elevation (100), or each elevation (100), of the plurality of elevations (100) comprises a roof (108) connecting the respective radially outermost edges (122) of the side surfaces (102) of the elevation (100) with each other, wherein in use, the roof (108) is in contact with the flow of atomizing gas (110).
Nozzle body (1, 2, 3, 4) according to the preceding claim, wherein the roof (108) is shaped and arranged such as to be comprised in the lateral surface of an imaginary right circular cone centered about the spray axis (200), wherein the apex of the imaginary cone is located upstream from the elevation (100) and wherein the cone angle (half angle) of the imaginary cone is between 0° and 45°.
Nozzle assembly (20) comprising
i) a nozzle body (1, 2, 3, 4, 5) according to any one of the preceding claims,

ii) an air cap (40), connected with the nozzle body in a fixed spatial relation, and comprising a front wall (60) facing generally in the spray direction (300) and comprising a nozzle aperture delimited by a nozzle aperture edge (65), and

iii) a barrel (30) having a liquid port connector (74) for directly or indirectly connecting a liquid reservoir to the barrel (30),
wherein the air cap (40) is connected with the barrel (30), and the nozzle body (1, 2, 3, 4, 5) is connected with the barrel (30), such that the air cap (40) is connected with the nozzle body in a fixed spatial relation,

and wherein the nozzle tube outlet (52) is arranged in, or protrudes outwardly through, the nozzle aperture, such that an atomizing gas outlet (54) is formed between the nozzle aperture edge (65) and the nozzle tube wall (71) such that atomizing gas can exit the nozzle assembly (20) through the atomizing gas outlet (54).
Liquid spray gun for spraying a liquid, comprising a nozzle body (1, 2, 3, 4, 5) according to any one of claims 1-13, or a nozzle assembly (20) according to the preceding claim.