Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
  • B05B7/02—Spray pistols; Apparatus for discharge
  • B05B7/10—Spray pistols; Apparatus for discharge producing a swirling discharge
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N1/00—Pretreatment of moulding material
  • B27N1/02—Mixing the material with binding agent
  • B27N1/0263—Mixing the material with binding agent by spraying the agent on the falling material, e.g. with the material sliding along an inclined surface, using rotating elements or nozzles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B1/00—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means
  • B05B1/34—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl
  • B05B1/3405—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl
  • B05B1/341—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl before discharging the liquid or other fluent material, e.g. in a swirl chamber upstream the spray outlet
  • B05B1/3421—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl before discharging the liquid or other fluent material, e.g. in a swirl chamber upstream the spray outlet with channels emerging substantially tangentially in the swirl chamber
  • B05B1/3431—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl before discharging the liquid or other fluent material, e.g. in a swirl chamber upstream the spray outlet with channels emerging substantially tangentially in the swirl chamber the channels being formed at the interface of cooperating elements, e.g. by means of grooves
  • B05B1/3442—Nozzles, spray heads or other outlets, with or without auxiliary devices such as valves, heating means designed to influence the nature of flow of the liquid or other fluent material, e.g. to produce swirl to produce swirl before discharging the liquid or other fluent material, e.g. in a swirl chamber upstream the spray outlet with channels emerging substantially tangentially in the swirl chamber the channels being formed at the interface of cooperating elements, e.g. by means of grooves the interface being a cone having the same axis as the outlet
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
  • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
  • B05B7/02—Spray pistols; Apparatus for discharge
  • B05B7/12—Spray pistols; Apparatus for discharge designed to control volume of flow, e.g. with adjustable passages

Definitions

• the present invention relates to an improved nozzle for creating small droplets from a flow of liquid, a process known as atomisation.
• the nozzle of the present invention has been designed especially to operate in conditions whether the liquid droplets are required in an environment where the pressure is above atmospheric; this places design constraints on the nozzle, to ensure it will operate reliably, since the nozzle cannot easily be cleaned or serviced while in the above atmospheric environment.
• the nozzle of the present invention has been designed especially for injecting resin into a blowline carrying a high speed stream of fibre particles for manufacturing fibreboard, and will be described with particular reference to this application.
• the nozzle of the present invention could be used in any application where it is necessary to break up a stream of liquid into small droplets.
• the nozzle of the present invention is most suited to applications in which there is a large volume of liquid to be atomised and where the number of nozzles which can be used is limited by practical considerations.
• Fibreboard in particular medium density fibreboard (MDF) and high-density fibreboard (HDF), originally was made by mixing resin with dry fibres obtained from wood or other cellulosic based materials and then forming the resulting mixture to shape in a heated press. This gave a usable product, but unfortunately blending the resin with the dry fibres tended to produce resin spots in the panel where the resin had aggregated to produce local areas of high resin content. These resin spots were much harder than the adjacent panel, and this caused cutting and machining difficulties, and also could affect surface finishes.
• MDF medium density fibreboard
• HDF high-density fibreboard
• the blowline is a pipe which carries a high velocity stream of fibres, mixed with steam, from the refiner, (where the fibres are prepared) to the drier.
• droplets of resin became attached to the fibres in the blowline, and the fibres and resin together were dried, and then processed in the usual way by being moulded and pressed at a high temperature and pressure to form the end product.
• the flow in the blowline is highly turbulent (typical Reynolds numbers are between 700,000 and 3,000,000) and the fibre stream velocity generally is in the range of a minimum of 50 metres per second calculated at 8 bar pressure to a maximum of 474 metres per second at atmospheric pressure (0 bar gauge).
• Resin is introduced into the blowline through a series of nozzles set in the wall of the blowline at a location where the pressure in the blowline is above 3.5 bar, preferably at a pressure above 6.5 bar.
• the turbulence of the fibre flow breaks up the jet of resin to a certain extent, and if relatively small nozzles are used to introduce the resin, reasonably satisfactory results can be achieved.
• the smaller the nozzle the more prone it is to blockage.
• the smaller the nozzle the greater the number of nozzles needed to introduce the required amount of resin, and the less easy it is to detect a nozzle blockage. Because of the operating conditions, it is difficult or impossible to monitor the operation of each nozzle individually, so the nozzle blockages can be detected only by the dropoff in the flow of resin, and if a large number of nozzles are used, this drop-off can be very difficult to detect, so that blockages can continue undetected.
• Nozzles used to inject the resin into the blowline have generally been of the pressure atomised type where the droplets are generated by the pressure drop across the nozzle.
• the pressure drop that can be used across such a nozzle is limited by the diameter of the blowline at the point where the nozzle is situated; if any part of the resin jet reaches the far wall of the blowline then the resin forms a mass on the wall that can only be removed by impacts with the fibres following in the blowline.
• This is a limitation of the pressure atomised nozzle.
• each nozzle uses gas jets (generally steam or air) to provide the energy to atomise the resin close to the point where it enters the blowline.
• the nozzle of the present invention is the type which uses jets of steam or air to interact with the resin jet as it leaves the nozzle. This provides greater control of the interaction between the gas and liquid streams, while achieving the break up of the liquid resin stream into droplets much closer to the nozzle.
• Another known design provides six equidistantly spaced jets of steam all inclined at the same small acute angle to the resin jet.
• nozzles have improved resin performance over the alternative pressure atomised nozzle by generating smaller resin droplets within the space available in the blowline.
• the mean droplet size generated in a gas atomised nozzle is largely determined by the gas: liquid mass flow ratio.
• the mean droplet size increases as the gas: liquid mass flow ratio decreases.
• the geometry of a gas atomised nozzle is such that this ratio tends to fall as the liquid capacity is increased. For the reasons discussed above it is not desirable to increase the number of nozzles to achieve the required gas: liquid mass flow ratio, but within this limitation it is important to achieve the best possible interaction between the gas jets and the liquid stream.
• the present invention provides more effective control of the interaction between the gas and the stream of liquid resin, within the limits imposed by the conditions in the blowline.
• the present invention provides an atomising injection nozzle which includes:-
• said atomising gas inlets also are configured to introduce atomising gas to impinge on said jet of liquid at at least two different points along the liquid jet.
• the present invention further provides an atomising injection nozzle which includes:- a) a central aperture for providing a jet of liquid; b) a plurality of atomising gas inlets spaced around said central aperture; c) wherein said atomising gas inlets are configured to introduce atomising gas to impinge on said jet of liquid at at least two different points along the liquid jet.
• said atomising gas inlets also are configured to introduce atomising gas to impinge on said jet of liquid at at least two different angles.
• each gas inlet is formed with a restriction at which the cross-sectional area of the inlet is reduced to provide a choke point.
• any number of atomising gas inlets from two upwards may be used; the inlets may be equidistantly spaced around the central aperture, but need not be.
• the term "equidistantly spaced" means that each inlet is the same distance from each adjacent inlet.
• the preferred embodiments describe the use of even numbers of gas inlets arranged as opposed pairs, this is not essential:- the number of inlets may be even or odd and the inlets, may be arranged symmetrically or asymmetrically.
• the only consideration in selecting the number, spacing and grouping of the inlets is that the arrangement should minimise interference between the gas jets because, as explained above, interference reduces the atomising effect of the gas jets on the resin jet.
• the nozzle provides six atomising gas inlets substantially equidistantly spaced around said central aperture:
• a first pair of opposed atomising gas inlets are configured to introduce atomising gas at a first angle
• a second pair of opposed atomising gas inlets are configured to introduce atomising gas at a second angle different to said first angle; - and a third pair of opposed atomising gas inlets are configured to introduce atomising gas so as to impinge on said liquid jet further from the nozzle than the atomising gas streams supplied by the first and second pairs of inlets.
• the nozzle provides four atomising gas inlets substantially equidistantly spaced around said central aperture; one pair of opposed inlets are configured to introduce atomising gas at said first angle; the other pair of opposed inlets are configured to introduce atomising gas in the same manner either as the second pair or as the third pair above.
• Arranging the atomising gas inlets in these ways helps to minimise interaction between the gas jets themselves, and thus maximises interaction between the gas jets and the resin stream.
• said first angle is approximately 60° and said second angle is approximately 45°; both angles are measured as the included angle between the liquid jet and the atomising gas jet.
• the atomising gas inlets may be all of the same cross-sectional shape, but need not be.
• the cross-sectional shape is not restricted to any particular shape, and could be any of a wide range of cross-sectional shapes (regular or irregular).
• the cross- sectional area of an individual gas inlet is selected in conjunction with the angle of the atomising gas inlet with respect to the centreline of the liquid jet and its displacement along the centreline of the resin jet to minimise the interference between the gas jets.
• the cross-section of the atomising gas inlets is a polygon, generally with three or four sides, of which one or more sides could be a curve of simple (circular or parabolic) or more complex form.
• FIG. 1 is a simplified view of a steam atomising resin injection nozzle assembly and associated components, in accordance with the present invention
• Figure 2 is an isometric view of the forward end of the nozzle of Figure 1 , with the nozzle cap missing;
• Figure 3 is a view similar to figure 2, but showing the steam and resin jets
• Figure 4 is a diagrammatic side view of the nozzle of figure 2, with the nozzle cap shown in broken lines;
• Figure 5 is a diagrammatic plan view of the nozzle of Figure 2;
• Figure 5a is a diagrammatic plan view of a variant of the nozzle of Figure 2;
• Figure 6 is a section on line A - A of Figure 5;
• Figure 7 is a section on line B - B of Figure 5;
• Figure 8 is a section on line C - C of Figure 5;
• Figure 9 is a section similar to Figure 7 but on a larger scale; and Figure 10 is a section partly similar to Figure 7, partly a section taken at 90° to that of
• a steam atomising resin injection nozzle assembly 1 for use in combination with a fibre blowline is shown in Figure 1.
• the nozzle assembly 1 is secured to the blowline 2 by welding the nozzle housing 5 to the blowline in such a way that the point where the resin leaves the nozzle is close to the inner wall of the blowline.
• the steam jets interact with the resin jet to create the small resin droplets that have been shown to improve resin performance in the product.
• the resin enters the nozzle assembly through a port 3a and travels down a central pipe 3 to the nozzle tip 4.
• the steam enters through a port 5a and passes into the nozzle housing 5, which forms a manifold that distributes the steam to the channels 6.
• Each channel 6 includes a flow restriction at the entry to the channel (as hereinafter described) that ensures that any expansion due to the choke flow condition occurs before the steam jet leaves the channel, ensuring that the steam jet is directed precisely at the selected point of the liquid jet.
• the choke flow condition is reached when the velocity of a compressible fluid flowing through an orifice or other path, calculated at the pressure at the exit of the path, exceeds the speed of sound for the fluid, taken as 474 m/s for steam. If this occurs, the pressure upstream of the exit of the path will rise to the point where the fluid compresses to the point where the Mach 1 limit is not exceeded in the closed path.
• the pressure wave "blocks" the flow path so that the fluid leaves the path with an internal pressure known as the choke pressure. When the fluid stream is free of the path this internal pressure causes the jet to expand laterally. If this expansion occurs as the gas jet leaves the channel, it changes the relationship between adjacent gas jets.
• the nozzle assembly incorporates a plunger 7, that can be raised or lowered by an air powered actuator 8. This can be used to clear the resin path if this is blocked; it can also be left in the "down" position to prevent fibre from the blowline entering the nozzle if resin is not flowing.
• the resin or adhesive used in the blowline is selected from a range that includes formaldehyde based systems such as urea formaldehyde, melamine formaldehyde, or phenol formaldehyde, or isocyanate based systems or any other suitable system.
• the resins may added to the blowline individually, or in various combinations that may be prepared during the manufacture of the resin, or mixed prior to being added to the blowline, or added separately through different nozzles in the blowline.
• the resins are usually water based with the resin component being present in solution, or as colloidal or emulsified particles, but other solvent systems can be used. Catalysts, hardeners or other materials that modify the adhesive performance may be added to the resin prior to the mixture being added to the blowline, or may be added separately through nozzles independent of those used to add the resin.
• a combination of computer modelling and experimental work by the inventor has shown that for a satisfactory final product with the minimum quantity of resin it is important that the resin is dispersed into small droplets. - typically an average droplet size of 20 microns is desirable. A droplet of this size provides approximately one resin droplet for each fibre the size of a typical P Radiata or similar softwood fibre. Larger droplets can mean that some fibres are not able to be bound into the fibre network that constitutes the fibre board product unless they are broken up into smaller particles before the final material is formed from the fibre with the added adhesive. The larger the resin droplets are when they are injected into the blowline the less likely they will be broken up by the fibre - resin interactions that occur in the highly turbulent blowline flow.
• Figures 2 - 6 show the detail of the forward end 10 of the nozzle 11 , i.e. the end of the nozzle through which the jet of liquid resin enters the blowline.
• the nozzle 11 includes a forward end 10, (i.e. the end of the nozzle through which the jet of liquid resin enters the blowline) which is partially closed off by a cap 10a, and a rearward end which provides a mounting 12, one end 13 of which is externally screw threaded (not shown) to mount the nozzle in its support, and the other end 15 of which is formed as a hexagonal collar which can be engaged by a wrench for fitting the nozzle.
• the outer surface of the cap 10a is received in a mounting aperture 2a in the wall of the blowline 2.
• the forward end 10 of the nozzle is formed with a central aperture 16 through which the stream of liquid resin passes in use.
• a central aperture 16 Surrounding the central aperture 16 are three pairs of equidistantly spaced atomising gas inlets.
• the atomising gas most commonly used is steam, and the inlets will be referred to as steam inlets, but it should be appreciated that other atomising gases may be used.
• Each of the six inlets A1/A2/B1/B2/C1/C2 is formed as inclined slots cut in the outer surface 23 of the forward end 10 of the nozzle and in the nozzle cap 10a. Steam passes down these slots to enter the blowline, and each set of slots in combination forms an inlet, so that the angle of each set of inlet slots controls the angle at which each jet of steam leaves the nozzle.
• the nozzle cap 10a is formed with a central aperture corresponding to the aperture 16 in the forward end of the nozzle 10, to allow the stream of liquid resin to pass through the nozzle cap in use.
• the inner surface of the nozzle cap 10a is formed with slots corresponding in angle and position to each of the slots in the forward end 10 of the nozzle, to form inlets A1-C2 inclusive.
• the nozzle cap 10a is omitted from the Figures 2, 3 and 5.
• the nozzle cap 10 a may be formed as a separate component from the forward end 10 of the nozzle, as shown in Figure 9; the nozzle cap may be secured to the remainder of the nozzle in any suitable manner.
• the nozzle cap 10a is formed integrally with the forward end 10 of the nozzle, as shown in Figure 10.
• the steam inlets formed by the combination of the slots in the forward end 10 of the nozzle and the slots in the cap 10a are the same in shape and angle whether these components are formed separately or in one piece.
• FIG 3 and Figures 6-8 show the steam jets A1-C2 inclusive and the resin jet 17 as solid shapes.
• the resin jet 17 is indicated by a large arrow, the steam jets by small arrows.
• the six inlets A1/A 2/B1/B2/C1/C2 are formed as three pairs; the inlets of each pair are opposed to each other across the central aperture 16.
• opposed means that each pair of opposed jets is placed one on one side of a diameter line, the other on the other side of that diameter line, so that in use the jets impact on different parts of the resin jet.
• the first pair of inlets A1/A 2 provide an angled inlet surface 24 which is at an angle of 30° to the plane of the central aperture 16; this means that steam passing through inlets A1/A2 impinges on the resin jet passing through the aperture 16 at an angle of 60° (angle X in Figure 6, measured between the longitudinal axes of the steam and resin jets).
• the second pair of inlets B1/B2 provide an angled inlet surface 25 which is at an angle of 45° to the plane of the central aperture 16; this means that steam passing through inlets B1/B2 impinges on the resin jet passing through the aperture 16 at an angle of 45° (angle Y in Figure 7, measured between the longitudinal axes of the steam and resin jets).
• Figures 9 and 10 are partly based upon Figure 7, but show the actual gas inlets rather than showing the steam jets as solid shapes, as in Figure 7.
• Figure 9 shows the section of Figure 7 on a larger scale and illustrates the variant of the present invention where the nozzle cap 10a is formed as a separate component from the forward end 10 of the nozzle; the dividing line between the portion of each inlet provided by the nozzle cap and the portion of each inlet provided by the forward end of the nozzle is indicated by line 50.
• the resin jet 17 is indicated by the large arrows; the path of the steam jets by the smaller arrows.
• Figure 10 illustrates the preferred form of the invention, in which the nozzle cap 10a is formed integrally with the forward end 10 of the nozzle.
• Figure 10 shows two different cross-sections:- on the side marked B of the dividing line D-D, there is shown the same section as in Figure 7; on the side marked A, there shown a section at 90° to that of side B, through a portion of the nozzle where no inlet is formed, showing the connecting web 51 between the forward end of the nozzle and nozzle cap.
• the third pair of inlets C1/C2 provide an angled inlet surface 26 which is at an angle of 45° to the plane of the central aperture 16.
• surface 26 is offset by a distance d so that steam entering through these inlets impinges on the resin jet passing through the central aperture 16 approximately 1 mm further away from the nozzle than steam entering through the other inlets, at an angle of 45° (angle Y in Figure 8).
• the angle of the third pair of inlets C1/C2 is the same as the second pair of inlets B1/B2, but does not need to be:- the third pair of inlets may be set at a different angle to either the first or second pair, or to the same angle as either the first or the second pair.
• the angle selected for the inlets depends upon the geometry of the system and on the velocity of the gas jets and the resin jet, and on the blowline velocity.
• the angles 60° and 45° have been found to work well in practice, but may be varied, depending upon the criteria discussed below.
• the maximum angle which can be used is that which allows the gas jet to interact with the resin jet while clearing the opposite side of the nozzle. This angle is determined by the depth of the slots in the forward end of the nozzle/nozzle cap, and by the diameter of the resin jet.
• the minimum angle which can be used is determined by the influence of the blowline steam flow. As the inlet angle decreases, the gas jet from the nozzle travels further through the blowline steam flow before it encounters the resin jet; the greater this distance, the more the gas jet from the nozzle loses energy and its direction is influenced by the blowline stream flow.
• the above described nozzle is used in known manner; i.e. liquid resin passes through the central aperture 16 and jets of atomising steam pass through each of the inlets A1 - C2 inclusive, impinging on the jet of resin just as the resin enters the blowline.
• the variation in the angles of the inlets A1 - C2 inclusive, as described above, ensures that the available steam is used as effectively as possible, by minimising interaction between the steam jets:- each jet of steam impinges on the jet of resin at a different angle and/or a different position to each adjacent steam jet; this ensures that as much of the kinetic energy of each steam jet as possible is transferred to the resin jet, rather than being wasted by impinging on adjacent steam jets.
• each of the inlets A1 - C2 inclusive is formed with a restriction 27, 28, 29 where the cross-sectional area of the inlets is reduced to about 80% compared to the portion of the inlet immediately adjacent the end of the nozzle.
• the restrictions 27, 28, 29 effectively provide a "choke point" in each inlet to limit the flow through the inlet.
• the purpose of this restriction is to ensure that the choke flow condition does not occur in steam passing through the inlets as the steam leaves the inlet:- this means that the direction of each steam jet can be accurately controlled in service.
• Figures 6 - 8 show one set of possible positions for the restrictions 27 - 29 inclusive, but the preferred positions for the restrictions are further away from the nozzle end of the inlets, as shown by reference numeral 28 in Figures 9 and 10.
• FIG. 5a A further variant of the above described nozzle is shown in Figure 5a.
• this embodiment instead of six equidistantly spaced inlets, there are only four. These four inlets are equidistantly spaced around the central aperture 16 and are constructed, and function in the same manner as described with reference to the six inlet version.
• the first pair of inlets A1/A2 are the same as the inlets A1/A2 described with reference to the six inlet version.
• the second pair of inlets, labelled B1/B2 may be the same as inlets B1/B2 of the six inlet version, or may be the same as the inlets C1/C2 of the six inlet version.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Nozzles (AREA)

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• 2008
  • 2008-03-18 NZ NZ56675108A patent/NZ566751A/en unknown
• 2009
  • 2009-02-16 EP EP09722604A patent/EP2268411A1/de not_active Withdrawn
  • 2009-02-16 WO PCT/NZ2009/000016 patent/WO2009116877A1/en active Application Filing
  • 2009-02-16 CN CN2009801077281A patent/CN101959607A/zh active Pending

Non-Patent Citations (1)

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