GB2099332A - Detonation coating apparatus - Google Patents

Abstract

A mixing device 4 has two chambers to provide a homogeneous three- component mixture of gases by mixing the components of an explosive mixture and an inert gas in two subsequent stages. A first chamber 27 is connected via valves 9 and 10 with a source 5 of one of the components and with a source 7 of an inert gas. A second chamber 38 communicates with the first chamber 27 and is connected via a valve 11 with a source 6 of another component. The mixing device 4 is connected via a check valve 49 and a safeguard device 3 with an elongate ignition chamber 1 of a detonation coating apparatus outlet port 48 of the second chamber 38. <IMAGE>

Description

SPECIFICATION Detonation coating apparatus The present invention relates to apparatus for applying a coating to the surfaces of articles by spraying a coating material, utilizing detonation. The present invention can be used to the greatest advantage for applying coatings to elements subjected to significant corrosion, erosion, and heat destruction when in use. The main fields of application are aircraft and shipbuilding industries, space technology, machine building industry, gas turbine technology, textile and paper industries, production of gauges, and chemical apparatus building industry.

In such apparatus it is desirable to maximise the homogeneity of the gas mixture fed into the ignition chamber, in order to ensure high quality of the coating. The apparatus should also be explosion proof.

The invention apparatus for applying a coating utilizing detonation which comprises a tubularshaped ignition chamber closed at one end, a proportioner connected with the ignition chamber and adapted for batchwise feeding a powdered material, and a two-chamber mixing device whose inlet ports are connected via valves with sources of gaseous components of the explosive mixture and an inactive gas, the first chamber having inlet ports to feed one of the components of the explosive mixture and an inactive gas, and the second chamber being connected with the first one by the ports for the mixture of gases produced in the first chamber to pass into the second chamber, the latter having an inlet port adapted to introduce the second component of the explosive mixture, and an outlet port which is connected via a check valve and a safeguard device with the ignition chamber to feed thereinto the mixtures of all said gases.

Presence of two chambers in the mixing device allows one to mix in the first chamber an inactive gas with one of the components of the explosive mixture, for example, with an oxidizer, and then in the second chamber to mix the mixture produced in the first chamber, with another component of the explosive mixture, for example, with a fuel. Experiments have proved that this facilitates the production of a more homogenous three-component mixture than that produced when three components are mixed in a single closed container. This provides more uniform heating of the coating powder at the instant of detonation, which results in an improved quality of a coating, demonstrated by the uniform strength of adherence of the coating particles to the sprayed surface of an article.

In addition, the construction of the mixing device provides better explosion-proof characterstics when mixing a fuel and an oxidizerthanthose performed by the existing apparatuses, because one of the said components is preliminary diluted by an inactive gas.

The first chamber of the two-chamber mixing device can be divided into two half-chambers by a repel disc having through ports, the ports of the disc being preferably inclined in the tangential direction, and their inlet orifices preferably being shifted along the circumference relative to the opposing outlet orifices of the inlet ports of the first chamber so that they are not aligned. This tends to impart turbulence to the streams of gas, thus contributing to their intensive mixing.

A body of the two-chamber mixing device can, in particular, be made of three detachable parts: a mixer which has two cavities divided by a diaphragm having ports designed for a passage of gases, a distribution plate adjacent the mixer at the side of one of the cavities to form a closed first chamber of the mixing device, and a cover, butted at the mixer at the side of another cavity to form a second chamber of the mixer, the inlet port of either chamber, passing via the distribution plate, being connected with the valves mounted on said distribution plate. The inlet port of the second chamber can, in particular, be made partially in the central portion of the mixer. The outlet port can be made in the cover and connected with a check valve mounted thereon.

The body with this construction is more compact and less metal-intensive that that of the known apparatuses and provides a minimum length of gas travel.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic representation of the general view of an apparatus for applying a coating by detonation (the ignition chamber and the safeguard device are shown in section); Figure 2 is an enlarged sectional view of the mixing device of the apparatus shown in Figure 1; Figure 3 is a section on line Ill-Ill in Figure 2; Figure 4 is a section on line IV-IV in Figure 3; Figure 5 is a view taken along the arrow A in Figure 2; and Figure 6 is a section on line VI-VI in Figure 5 (the view is turned).

The detonation coating apparatus illustrated comprises an ignition chamber 1 (Figure 1) made in the form of a pipe closed at one end and open at the other. The length and the width of the chamber 1 are selected in such a way as to make it possible to form and to propagate in the chamber a detonation wave such that optimum energy characteristics will be imparted to particles of powdery coating material carried by the said wave.

The ignition chamber 1 is connected at or near its closed end with a proportioner 2 for batchwise feeding of the powdery material and via a safeguard device 3 the chamber 1 is connected with a mixing device 4 designed to prepare an explosive gaseous mixture. Sources 5 and 6 of the gaseous components of the mixture, as well as sources 7 and 8 of an inert gas, are connected via electromagnetic valves 9 - 12 with the mixing device 4, as is further described in detail below.

In the cavity of a detachable hollow body 13 of the safeguard device 3, there are mounted in series: a lattice 14 designed to break up a flame (in the case of a blowbackthrough a coil 15 into the cavity of the body 13) and a diaphgram 16 of porous refractory material, for example a cermet. The safeguard device 3 communicates with the mixing device 4 through an inlet cavity 17.

In addition, the apparatus comprises a pulse generator 18 designed to supply a high voltage to a spark plug 19 set in the ignition chamber 1 to ignite a gas mixture fed thereinto, and a control unit 20 for energizing the electromagnetic valves 9-12 of the mixing device 4 and a valve 21 which controls the feed of the transporting medium into the proportioner 2 from a source 22.

The mixing device 4 has two chambers 27,38 and comprises a detachable body 23 (Figure 2) which consists of the interfixed detachable parts represented by a distribution plate 24, a mixer 25, and a cover 26.

The cavity of the first chamber 27 (considered along the gas supply path) of the mixing device 4 is defined by the walls of a cavity 28 of the mixer 25, having an annular form, and by the adjacent plane D of the distribution plate 24 fixed against shifting in the radial direction by a centering projection 29 of the mixer 25.

The chamber 27 is divided into half-chambers 30 and 31 by a repel disc 32, which makes it possible to intensively mix gases fed into the chamber 27 by means of repeated repulsion of the jets thereof. The disc 32 is set on a cylindrical surface 33 of the projection 29.

The half-chambers 30 and 31 communicate by means of through ports 34 (Figures 3 and 4) made in the disc 32. The ports 34 are inclined, as shown in Figures 3 and 4, in the tangential direction in order to produce an eddy which contributes to intensive mixing of gases in the chamber 31, the inlet orifices of the ports 34 (in the plane E) being shifted along a circumference relative to the outlet orifices (in the plane D) of inlet ports 36 and 37 (Figures 2 and 3) made in the distribution plate 24, in order to achieve a repulsion effect.

The cavity of the second chamber 38 (Figure 2) of the mixing device 4 is defined by the surface of an annular cavity 39 of a centering projection 40 of the cover 26 and by the plane of a diaphragm or partition 41 which separates an annular cavity 42 of the mixer 25, enveloping the projection 40, from the first chamber 27.

An orifice 43 is made in the centering projection 29 of the mixer 25, from the tapered bottom of which orifice diverge a plurality of orifices 44 which form a circumferental row. The orifices 44 in combination with the orifices 43 of the mixer 25 and a coaxial orifice 45 of the distribution plate 24 form an inlet port 46 to feed into the second chamber 38 one of the gaseous components of the explosive mixture.

The inlet ports 36, 37 and 46 of the mixing device 4 communicate with the outlet orifices of the respective electromagnetic valves 9, 10, and 11 mounted on the distribution plate 24.

The chambers 27 and 38 of the mixing device 4 intercommunicate by means of through ports 47 made in the diaphragm 41, to let into the second chamber 38 a mixture produced in the first chamber 27, which mixture comprises one of the components of the explosive mixture and an inert gas.

An outlet port 48 of the mixing device 4 has the form of an orifice made in the cover 26 communicating with a check valve 49 mounted thereon. The entrance into the orifice 48 is restricted by a hub 50 of the mixer 25 enveloping a cylindrical projection 51 of the cover 26 with a clearance, which creates additional potentials for intercrossing and repelling the jets thus contributing to the intensive mixing of gases.

The valve 9 is connected with the source 5 (Figure 1) of an oxidizer (in particular, oxygen), the valve 10 is connected with the source 7 of an inert gas, and the valve 11 is connected with the source 6 of a fuel (for example, acetylene). In addition, mounted on the distribution plate 24 (Figures 2, 5, 6) is the electromagnetic valve 12, which is connected with the source 8 of an inert gas (Figure 1). The valve 12 is connected through a port 52 (Figure 6) with the cavity 17 (Figure 1) of the safeguard device 3. The system formed by the source 8, the port 52, and the valve 12 is designed to fill the cavity of the safeguard device 3 with an inert gas after a gaseous mixture is fed into the ignition chamber 1, and to purge the safeguard device 3 and the ignition chamber 1 after the coating material is projected therefrom.

The apparatus operates as follows.

The electromagnetic valves 9, 10, and 11 open on a command sent from the control unit 20 (Figure 1).

Oxygen is fed from the source 5 into the first chamber 27 of the mixing device 4 via the valve 9 and the inlet port 36 (Figure 2), and an inert gas (for example nitrogen) is fed from the source 7 into the chamber 27 via the valve 10 and the inlet port 37. The jets of both gases strike against the surface of the disc 32. This is accompanied by their repeated repulsions from the surface of the disc 32 and the plate D of the distribution plate 24 resulting in intensive mixing of gases fed into the half-chamber 30. Jets of the mixture produced are fed into the half-chamber 31, via the tangentialiy inclined ports 34 (Figures 3, 4) of the disc 32, where a still more active mixing of gases takes place due to the eddy produced by the ports 34.

Acetylene divided into small jets by the orifices 44 is fed from the source 6 (Figure 1) into the cavity of the second chamber 38 of the mixing device 4 via the valve 11 and the inlet port 46 (Figure 2). In the chamber 38, the acetylene is intensively mixed with the mixture of nitrogen with oxygen fed thereinto via the orifices 47. Such a two-stage formation of a mixture reduces the hazard of occurrence of explosion in the mixing zone, because not pure highly active oxygen meets with acetylene, but a less active mixture of oxygen with nitrogen. Besides, the mixture of three gases, forming in this case, is significantly more heterogeneous than the same kind of mixture produced in a one-chamber mixing device.

The mixture enters into the inlet cavity 17 (Figure 1) of the safeguard device via the narrow annular gap between the hub 50 and the projection 51, then via the outlet port 48 and the check valve 49; from the cavity 17 the mixture penetrates through the pores of the diaphragm 16 and the slits of the lattice 14 into the coil 15, and thence into the ignition chamber 1. On a command from the control unit 20 the valves 9-11 close and the valve 12 opens to fill the device 3 with inert gas and to force out the remainder of the explosive mixture into the ignition chamber 1. Following this operation all valves close and the pulse generator 18 sends a signal to the spark plug 19 which ignites the explosive mixture in the chamber 1. The formed detonation wave projects the powder of the coating material against a treated workpiece C placed in front of the open end of the ignition chamber 1. The control unit 20 then sends a command to open the valve 12 to completely purge the safeguard device 3 and the ignition chamber 1 with an inert gas. Nitrogen is fed from the source 8 through the port 52 (Figure 6) into the cavity 17 of the safeguard device 3 and further via the diaphragm 16 (Figure 1), The lattice 14, and the coil 15 into the ignition chamber 1, purging from the latter all combustion products.

Then the above-described cycle repeats.

The construction of the mixing device makes it possible to feed a more homogenous mixture into the ignition chamber and those produced on the existing apparatuses. This stabilizes ignition and propagation of the detonation wave and, consequently, provides uniform heating of the powder partices of the sprayed material, and produces, as a result, a high-quality coating having constant properties.

Claims (6)

1. Apparatus for applying a coating by detonation, comprising an elongate ignition chamber closed at only one end, a proportioner communicating with the ignition chamber and adapted for batchwise feeding of a powdered material, and a two-chamber mixing device whose first chamber is connected via respective valves with a source of one of the gaseous components of an explosive mixture and with a source of an inert gas, respectively, and whose second chamber is connected via a valve with a source of another of the gaseous components of the explosive mixture and communicates with the first chamber, the second chamber communicating with the ignition chamber via a check valve and a safeguard device.

2. Apparatus as claimed in claim 1, in which first chamber is divided into two half-chambers by a disc having ports, one of the half-chambers communicating with the two first-mentioned sources, and the other half chamber communicating with the second chamber.

3. Apparatus as claimed in claim 2, in which ports of the disc are inclined in the tangential direction.

4. Apparatus as claimed in claim 2 or 3, in which the two first-mentioned sources are connected to inlet ports of the first chamber, which inlet ports are not aligned with the inlet orifices of the ports of the said disc.

5. Apparatus as claimed in any of claims 1 to 4, in which the mixing device comprises three detachable parts, viz: a mixer which has two cavities separated by a partition having ports; a distribution plate adjacent the mixer at the side of one of the said cavities to form the first chamber; and a cover adjacent the mixer at the side of the other cavity to form the second chamber; inlet ports of both chambers passing through the distribution plate and being in communication with the respective valves, which are mounted thereon, an inlet port of the second chamber being made in the central portion of the mixer, and an outlet port of the second chamber being made in the cover and communicating with the check valve, which is mounted thereon.

6. Apparatus for applying a coating by detonation, substantially as described with reference to, and as shown in, the accompanying drawings.