US3801346A

US3801346A - Method for applying particulate coating material to a work piece

Info

Publication number: US3801346A
Application number: US00198806A
Authority: US
Inventors: R Melton; W Weatherford; C Wood; J Clark; R Mathis
Original assignee: ZACHREY H CO
Current assignee: ZACHREY H CO; ZACHREY H CO US
Priority date: 1971-11-15
Filing date: 1971-11-15
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: HU174657B; NO139912C; BR7207932D0; DE2250750C2; AU467770B2; CS170455B2; ZA727456B; FR2160390B1; SE398979B; BE790902A; PL79703B1; AU4853072A; IL40695A; NL7215183A; NO139912B; AR195981A1; JPS5547944B2; CA984233A; JPS4859138A; NO773683L

Abstract

A system for applying particulate coating material to a work piece, in which the particulate material is directed against the work piece in a series of pulses. Each pulse includes an initial step of feeding a charge of combustible gaseous mixture into a combustion chamber provided with an outlet nozzle. The combustible mixture is ignited and the outflow of gaseous mixture through the nozzle is constricted sufficiently to cause a rapid pressure rise during combustion to a peak value, followed by a period of falling pressure during continued outflow of the combusted mixture through the nozzle. A charge of the particulate coating material is injected into the combustion chamber for a brief period which terminates while the pressure in the chamber is at least a substantial proportion of the peak pressure. The outflow of combustion mixture and entrained particulate material is directed through the nozzle at high velocity against the work piece to cause the particulate material to form a coating on the work piece.

Description

United States Patent Melton, Jr. et a1. Apr. 2, 1974 METHOD FOR APPLYING PARTICULATE 3,552,653 1/1971 lnoue 239/81 2,972,550 2/1961 P611011 117/22 COATING MATERIAL TO A WORK PIECE [73] Assignee: H. B. Zachrey Company, San

Antonio, Tex.

[22] Filed: Nov. 15, 1971 [21] Appl. No.: 198,806

[52] U.S. Cl 117/16, 117/22, 117/104, 117/105.l, 239/79, 239/81, 239/85 [51] Int. Cl. B44c l/08, B44d 1/08 [58] Field of Search 117/16, 105.1, 22, 105, 1l7/105.2, 46 ES, 18; 239/79, 80, 81, 85

[56] References Cited UNITED STATES PATENTS 2,861,900 11/1958 Smith etal 117/105 3,084,064 4/1963 Cowden et al... 117/105 X 2,714,563 8/1955 Poorman et al. 117/22 2,950,867 8/1960 l-lawley et a1. 239/79 X 2,774,625 12/1956 Hawley et al.... 239/81 3,150,938 9/1964 Pelton et al 117/22 12/1936 Garesche 117/105.1 X

Primary Examiner-William D. Martin Assistant ExaminerShrive P. Beck 57'] ABSTRACT A system for applying particulate coating material to a work piece, in which the particulate material is directed against the work piece 'in a series of pulses. Each pulse includes an initial step of feeding a charge of combustible gaseous mixture into a combustion chamber provided with an outlet nozzle. The combustible mixture is ignited and the outflow of gaseous mixture through the nozzle is constricted sufficiently to cause a rapid pressure rise during combustion to a peak value, followed by a period of falling pressure during continued outflow of the combusted mixture through the nozzle. A charge of the particulate coating material is injected into the combustion chamber for a brief period which terminates while the pressure in the chamber is at least a substantial proportion of the peak pressure. The outflow of combustion mixture and entrained particulate material is directed through the nozzle at high velocity against the work piece to cause the particulate material to form a coating on the work piece.

13 Claims, 10 Drawing Figures METHOD FOR APPLYING PARTICULATE COATING MATERIAL TO A WORK PIECE BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for applying particulate coating material to a work piece, and in particular to a system in which the coating material is directed intermittently against the work piece in a heated condition in a high velocity gas stream.

In applying coating materials, it is advantageous with certain materials in view of their high melting points, non-galvanic properties or for other reasons, to direct the coating material in particulate form against a work piece in a high velocity gas stream at an elevated temperature. If the conditions are carefully chosen, the particles of coating material become flattened and weld to each other and to the work piece to produce a hard, non-porous coating.

In performing a coating process of this general nature, it has been found that at least three variables are of critical importance, the rate at which material is deposited, the velocity at which the particles hit the surface and the temperature of impact of the particles which is a function both of the temperature to which they are raised in the gas stream and their kinetic energy on impact which is converted into an additional temperature rise. Various prior coating systems have therefore been devised intended to provide a suitable degree of control over these coating process variables.

For example, one prior coating system utilizes a tubular housing fed with continuous streams of acetylene, oxygen and a carrying gas (which may also be oxygen) containing powdered coating material. The gases are ignited continuously within the tubular housing and directed down a water-cooled barrel to impinge upon the work piece in a continuous stream at a velocity of at least 2,000 feet per second. Although such a system may be generally satisfactory for the purposefor which it is intended, certain problems may arise under particular conditions. For example, a continuouslyvoperating system subjects the work piece to a large uninterrupted stream of very hot burnt gases which could easily overheat the work piece and subject it to severe thermal erosion or distortion. In addition such a system operating continuously at velocities in the order of 2,000 feet per second would tend to depositcoating material at a very high rate and on certain types of small work piece this rate of coating build-up might not allow heat to escape from the work piece sufficiently rapidly, thereby further contributing to thermal distortion of the work piece. Another problem with such a system may be inefficient utilization of fuel as a continuous gas flow system usually requires that the proportion of powder in the combustion gases be about 5-10 percent of gas mass as high concentrations would supply material so rapidly as to even further compound the heat dissipation problems just described. To avoid these potential hazards it would be preferable to employ a pulsed system allowing time between applications of coating material in which sufficient heat dissipation from the work piece could occur to avoid distortion. Additionally the need for a water cooled barrel to prevent the barrel from melting during continuous operation, may render the apparatus unduly heavy and cumbersome.

It may sometimes be desirable, therefore, to utilize an intermittent or pulsed coating system. In one such prior system a combustible gaseous mixture is ignited in a combustion chamber at the upstream end of a gun barrel which is sufficiently long to permit a supersonic detonation wave to be established in and travel down the barrel. Downstream of the combustion chamber particulate coating material is fed into the gun barrel so that the particles are carried down the barrel at high velocity and directed against a suitable work piece. Again, although generally satisfactory for its intended use, a prior device of this second type may also be unsatisfactory under certain conditions. For example, the need to have a sufficiently long barrel on the device to sus tain a supersonic detonation wave, may make the device unnecessarily lengthy for installation at locations where space is at a premium. Additionally, by injecting the powder at a location downstream of the combustion zone, the opportunity to heat the powder directly in the combustion zone is lost. Also, by the time the detonation wave reaches the powder injection zone downstream of the combustion zone, some of the peak pressure attained in the combustion zone has necessarily already been dissipated.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for applying particulate coating material to a work piece, which is intended to obviate or minimize problems of the type previously described.

In more detail, the method of the present invention directs particulate coating material, e.g., tungsten carbide, against a work piece in a series of pulses. Each pulse includes an initial step of feeding a charge of gaseous combustible mixture into a combustion chamber provided with an outlet nozzle. The combustible mixture is ignited and the outflow of gaseous mixture through the nozzle is constricted sufficiently to cause a rapid pressure rise during combustion of the mixture to a peak value followed by a period of falling pressure during continued outflow of the combusted mixture through the nozzle. A charge of the particulate coating material is injected into the combustion chamber for a period commencing just prior to ignition or altematively, approximately at the time the pressure in the combustion chamber reaches its peak value and terminating while the pressure in the chamber is still a substantial proportion of the peak pressure. The outflow of combusted mixture and entrained particulate material is directed through the nozzle against the work piece at high velocity to cause the particulate material to form a coating on the work piece.

It will be appreciated that by using a pulsed system, the rate of application of material to the work piece is reduced sufficiently to permit the work piece to dissipate some of the heat between successive applications of coating material thereby minimizing the possibility of distortion. Pulse operation also provides more efficient use of fuel as the wastage of combusted gases occurring during a continuous flow against the work piece is avoided. By terminating the entry of particulate material into the chamber while the pressure is still a substantial proportion of the peak pressure, it is insured that almost all the particulatematerial is applied'to the work piece while the velocity of the outgoing stream is still sufficiently high to form a satisfactory coating. Thus, by the time the velocity of the stream has dropped below an adequate level substantially all the coating material in the charge has already been applied.

It may be noted that the conditions of pressure and velocity contemplated by the present invention are a peak pressure attained in the chamber of approximately 400 psi and a velocity of outflow of the combusted gases of about 3,000 feet per second with the entrained particulate material traveling at about 1,500

feet per second.

BRIEF'DESCRIPTION OF THE DRAWINGS An apparatus for applying particulate coating material to a work piece, constructed in accordance with one preferred embodiment of the invention, is illustrated in the accompanying drawings in which:

FIG. 1 is a side view of an apparatus for applying particulate coating material, constructed in accordance with the preferred embodiment of the invention, showing certain principal elements of the apparatus including a combustion chamber, a fuel inlet unit, and a powder injector,

FIG. 2 is a schematic view of a source of combustible gaseous mixture for supplying the apparatus shown in FIG. 1,

FIG. 3 is a cross-sectional side view of the combustion chamber shown in FIG. 1,

FIG. 4 is a schematic circuit diagram of an ignition circuit for a spark plug connected with the combustion chamber shown in FIG. 1,

FIG. 5 is a timing diagram showing the relative periods of operation of various of the principal elements shown in FIG. 1,

FIG. 6 is a cross-sectional side view of the fuel inlet unit shown in FIG. 1,

FIG. 7 is a cross-sectional top view of the fuel inlet unit shown in FIG. 6 taken along the lines 7-7 therein,

FIG. 8 is a cross-sectional side view of the powder injector shown in FIG. 1,

FIG. 9A is a schematic electrical circuit diagram showing the electrical connections to an electrical solenoid forming a part of the fuel inlet unit shown in FIG. 6; and

FIG. 9B is a schematic graph of current and voltage versus time for the electrical circuit shown in FIG. 9A.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawings, an apparatus for applying particulate coating material, constructed in accordance with the preferred embodiment of the invention, is there shown.

The components of the unit include a combustion chamber 2 shaped generally like an inverted bulb and a downwardly directed nozzle 4 through which particulate coating material entrained in a high velocity gas stream is directed in intermittent pulses at an underlying work piece 6. Associated with the combustion chamber 2 are, a fuel inlet unit 8 for periodically feeding a charge of combustible gaseous mixture into the combustion chamber 2, a spark plug 10 mounted on the combustion chamber projecting into its interior to ignite the charge of combustible mixture and a powder injector unit 12 for feeding in a charge of the particulate material. Many particulate materials may be used including higher melting point coating materials such as tungsten carbide, as well as flaked metal coatings and other coatings. A separate description of these components follows.

THE COMBUSTION CHAMBER The combustion chamber 2, which is formed of steel or similar material, is configured generally as an inverted bulb with a flattened, enlarged upper end region of mean diameter D (FIG. 3) tapering down to a reduced neck portion. Welded to the free lower extremity of the neck of the combustion chamber 2 is a block 20 which is threaded to receive the correspondingly threaded upper end of the previously mentioned nozzle 4 which is a short pipe aligned concentrically with the vertical axis of the combustion chamber 2.

A horizontal bushing 22 extends through the wall of the combustion chamber 2 into its interior in the upper, enlarged region of the combustion chamber. The bushing 22 is threaded internally and mounts correspondingly threaded portions of the previously mentioned fuel inlet unit 8. Periodically (as will be described hereinafter) the fuel inlet unit 8 injects a charge of combustible gaseous mixture, which in the preferred embodiment is a mixture of propane gas and air, into the interior of the combustion chamber 2.

The mixture is then ignited by the previously mentioned spark plug 10 (FIG. 1) which is tapped through the wall of the combustion chamber 2 projecting into its interior. The spark plug is positioned centrally of the enlarged upper portion of the combustion chamber displaced ninety degrees from the inlet unit 8. Other locations may be chosen for the spark plug. The spark ignition plug 10 is a conventional automobile spark plug which, when it is energized, initiates a flame front that extends through the charge of combustible mixture.

In an important aspect of the invention, combustion within the chamber is by deflagration as opposed to detonation, by which it will be understood that the flame front proceeds through the mixture in the combustion chamber at a subsonic velocity, which is about feet per second. In the preferred embodiment it is contemplated that the combustion of the mixture occurs entirely by deflagration.

In an alternative embodiment of the process, however, the chamber 2 may be so dimensioned that the pressure rise during deflagration is so rapid that, for a final unbumt portion of the combustible mixture in the chamber, which may be referred to as the end gas, the last part of combustion is by auto-ignition in which spontaneous ignition of the end gas at substantially all the points in it occurs simultaneously.

An important characteristic of the chamber in attaining a sufficient pressure rise during combustion to provide a satisfactory coating is the ratio between the diameter of the upper, enlarged portion of the combustion chamber 2 and the diameter of the outlet nozzle 4. In the preferred example the combustible propane air mixture is admitted to the chamber 2 at about psi and it is necessary to achieve a pressure rise to a peak value during combustion of about 400 psi. If the outlet nozzle 4 has too large an internal diameter, too much gaseous mixture may escape through the nozzle before the pressure has built up sufficiently. To achieve such a pressure it has been found that the ratio of the mean internal diameter D of the combustion chamber of the enlarged upper region to the internal diameter of the nozzle 4 (d in FIG. 3) should be at least 5 to l and preferably somewhat greater. For example in the preferred embodiment where the internal diameter d of the nozzle 4 is one-third inch, the chamber diameter D in its enlarged region is about 2 /2 inches providing a ratio of D/d of 7%. Stated in another way, the ratio V/d should exceed about 50 where V is the volume of the chamber in cubic inches and d is the diameter of the opening. Of course if a length of the chamber becomes significantly greater than the diameter of the chamber, the time required for the flame to propagate through the chamber may become so great as to materially reduce the pressures reached in the chamber because of the escape of gas through the open nozzle during the period of deflagration. The combustion chamber pressures and dimensions described result in a gas velocity through the nozzle of about 3,000 feet per second with the velocity of the entrained powder being about 1,500 feet per second.

Another important characteristic of the combustion chamber 2 is its overall cubic capacity in relation to the cross-sectional area of the nozzle 4. The cubic capacity of the chamber 2 should be sufficiently large to provide for a period of outflow of gas through the nozzle which lasts sufficiently long to enable the period of injection of the charge of particulate material (which will be described hereinafter) into the combustion chamber to be completed while the pressure in the combustion chamber still remains at a high level. Thus, in the preferred embodiment, wherein the injection period of the powder can be accomplished in about 5 milli-seconds, the period of gas outflow (sometimes called the blow down) during which the gas escapes from the nozzle, should be several times longer. For example a A inch internal diameter nozzle requires a chamber volume of at least eight cubic inches giving a blow down period of about 10 milli-seconds and in practice a chamber capacity of 12-14 cubic inches is provided. With these dimensions, powder can be injected and substantially eliminated from the combustion chamber 2 before the pressure in it has dropped to a value which is too low to project the coating material against the work piece with a sufficient velocity for satisfactory coating.

Various considerations affect the nozzle length. Nozzle length is determined by required powder impact velocity, powder particulate size, and firing pressure, for a given velocity being proportionalto particle size and inversely proportional to firing pressure. The required velocity is that which will hammer particles into a dense, well-bonded coating; too much velocity will break up in-place coating or even remove substrate material while insufficient velocity leaves the coating porous. Temperature plays a subordinate role by softening particles to facilitate impact deformation but temperature is primarily gained from exposure of the powder to hot gas by injecting across the combustion space, with relatively little additional heating occurring in the nozzle. Relatively high firing pressure (related to available fuel and air supply pressure) permits high velocity from a short nozzle; the nozzle could be made much shorter than described here by proportionately increasing firing pressure, or vice-versa, by manipulating powder size and/or fuel-air supply pressure. For example applying a coating of tungsten carbide in the 325 mesh 15 micron size range, a satisfactory coating was obtained, using a nozzle of 4 inches length, having an amorphous structure with a Knoop hardness of ap- 7 pounds per square inch using standard tests.

Important advantages obtained by using a relatively short nozzle are that the relative significance of wall friction and wall heat losses are substantially reduced. By contrast, a soda straw nozzle, e.g., one having a length to diameter ratio in excess of 30, has a large amount of wall surface area in relation to its crosssectional area with the result that wall friction appreciably slows down gas flow during passage through the nozzle and there is an additional relatively high, heat loss. Additionally, the ability to function with a short nozzle facilitates installation of the apparatus in locations where space is at a premium. By conducting combustion through a process of deflagration in the present invention rather than by detonation causing a supersonic shock wave, it is possible to avoid the need for a nozzle length sufficiently long to sustain a detonation wave.

The process occurring in the combustion chamber with reference to the pressures and dimensions of the preferred embodiment described are depicted graphically in FIG. 5. Starting a pulse or a flow at zero time, combustible mixture at psi commences admission to the chamber through the inlet unit 8 (as will be described in more detail hereinafter) for about 8 milliseconds. At about 5 milli-seconds, a charge of the particulate coating material is injected into the chamber and injection of the coating continues until it terminates at about 10 milliseconds. About midway through the powder injection, after 7.5 milli-seconds have elapsed, the spark plug 10 ignites the mixture causing a rapid rise in pressure within the combustion chamber to a peak value of about 400 psi attained at about T0 milliseconds after commencement of the cycle.

This injection of the powder ceases at approximately the time the pressure in the chamber is at its peak value. At about that time the first particles injected have traveled out of the combustion chamber 2 and through the nozzle 4 to impact the work piece, thus starting a coating period which continues for about 2 milli-seconds. The coating period is shorter than the injection period because the later particles injected catch up with the earlier particles in the nozzle due to the pressure build-up in the chamber. By the end of the coating period substantially all the particulate material has been blown out of the combustion chamber 2 with the result that by the time the pressure in the combustion chamber eventually falls below that necessary to sustain an adequate velocity for coating, all the particulate charge has already been applied.

It will be appreciated that the pressures, times and dimensions described for the preferred embodiment can be selectively varied, if so desired, to facilitate the 'use of larger or smaller coating apparatuses following this invention. In addition the timing of the coating material injection period can be selected to commence after, rather than before ignition, for applications in which it is desirable to introduce the powder into an atmosphere in which all the oxygen has already been combusted, to reduce particle oxidation.

THE FUEL INLET UNIT The previously mentioned fuel inlet unit 8 (FIGS. 6 and 7) includes a cylindrical inlet housing 30 having a reduced, threaded boss 32 at its forward end which threadedly engages the previously described bushing 22 in the side of the combustion chamber 2. Extending rearwardly into the inlet housing 30 from its forward end is an inlet passage 34 which terminates at about the midpoint of the inlet housing. Extending rearwardly from the inlet passage 34 through the remainder of the inlet housing is a second passage 36, of relatively smaller diameter, which slidably receives a valve stem 38 carrying a valve head 40. The valve head 40, which is beveled along its n'm, seats on a correspondingly beveled valve seat 42 on the inlet housing body 30 and closes off fluid communication between the inlet passage 34 and the combustion chamber 2 in a closed position of the valve head.

To hold the valve head in its closed, seated position, the rearward end of the valve stem 38, which projects rearwardly beyond the inlet housing 30, is provided with an undercut, annular groove 42 providing a forwardly facing shoulder 43 which is engaged by a circular collar or spring retainer 44. A circular compression spring 46 spaced concentrically around the valve stem 38 extending between the inlet housing 30 and the collar 44 is just sufficiently strong to hold the valve head 40 closed against the pressure exerted by the incoming supply of combustible gas which is delivered continuously to the interior of the inlet passage 34 through a conduit 48 (FIG. 7).

To move the valve head 40 forwardly off its seat, thus placing the inlet passage 34 in fluid communication with the interior of the combustion chamber, two electrical solenoids 50 are fixedly mounted on the exterior of the inlet housing 30 on opposite sides thereof. The solenoids 50 are of conventional construction, each having an electromagnetic coil 51 (FIG. 9A) with a plunger 52 mounted for axial reciprocation forwardly into the coil when the coil is energized. Connected to and carried by the plungers 52 is a transverse yoke 54 (FIG. 6) in continuous abutting contact with the free rearward end of the valve stem 38.

In a de-energized condition of the solenoids 50, the biasing spring 46 urges the valve stem 38 to move the yoke 54 rearwardly so that the plungers 52 are in an extended rearward position when the valve head 40 is seated. Energizing the solenoids 50, which causes the plungers 52 to move into the solenoids, carries the yoke 54 forwardly (to the dotted line position shown in FIG. 6) carrying the valve stem 38 forwardly and raising the valve head 40 off its seat. At this time the combustible mixture, which is at a pressure of 100 psi in the preferred embodiment, starts to feed into the combustion chamber 2. The solenoids 50 are de-energized at approximately the time the spark plug is fired. The rapid pressure build-up that then occurs in the combustion chamber 2 during charging allows the spring 46 to return the valve head 40 to its seat rapidly closing off the combustion chamber 2 from the inlet passage 34 before the advancing flame front can reach the mixture in the inlet passage.

To prevent leakage of the combustion mixture outwardly of the inlet housing along the stem 38, which could create a fire hazard, an annular recess 56 in the inlet housing 30 surrounds the valve stem at approximately the midpoint of the second passage 36 (FIG. 7 Air is delivered to the passage 56 through a conduit 58, at a higher pressure than the pressure at which the combustible mixture is supplied to the inlet passage 34. As a result, any leakage of gas between the stem 38 and the second passage 36 is in a direction from the recess 56 towards the inlet passage 34, preventing escape of combustible mixture rearwardly into the atmosphere. Additionally, in an alternative embodiment of the invention in which the particulate material is introduced into the chamber 2 through the fuel inlet valve by entraining it in the fuel gas supply, the flow of gas introduced through the recess 56 is very important for preventing powder from filling the passage around the valve stem and jamming its swift movement between the open and closed positions.

To energize and de-energize the solenoids 50 for pulsed or cyclical feeding of mixture into the combustion chamber the electrical circuit shown in FIG. 9A is employed. The preferred rate of operation is at a pulse rate in the region of 5-25 pulses per second although this may be varied. The coil 51 of the solenoid 50 is connected in series with a capacitor 62 which is charged by a high voltage (300 volts) power supply indicated by battery 64 when switch contacts 66a and 66b are closed. When switch contacts 66a and 66c are closed the capacitor 62 discharges through the coil 51 of the solenoid moving the associated plunger 52 forwardly. When the switch contacts 66a and 66b are remade the capacitor 62 is recharged through coil 66 from power supply 64. A rectifying diode 70 is included in the circuit to the solenoid coil 51 to prevent reverse current flow when the capacitor charge swings in its opposite polarity (FIG. 9B), insuring that the solenoid experiences only a single current pulse. This circuit minimizes the electrical energy drain on the system.

Similarly to energize the spark plug 10 (FIG. 4) a capacitor 70 and a primary coil 72 of a standard ignition transformer, having its secondary coil 73 connected to the spark plug 10, are connected in series with a battery 74. A pair of switch contacts 76 are connected across in parallel with the capacitor 70. The switch contacts 76 are opened and closed by movement of the valve stem 38. When the valve stem moves to open the valve head 40 the points 76 close, starting current build-up in the primary coil 72. As the valve stem closes the valve head 40, the points 76 reopen, initiating a voltage change across the coils of the transformer which causes the ignition spark. Although a system utilizing only one spark plug has been disclosed, it will be appreciated that the ignition system may be readily modified to energize two of the spark plugs 10 located on opposite sides of the combustion chamber 2.

THE FUEL/AIR SOURCE As previously mentioned, a supply of combustible mixture is supplied through the conduit 48 to the inlet passage 34 in the inlet unit 8. The supply of combustible mixture is from a source system shown in FIG. 2 which includes a fuel air mixing tank 80 connected to the conduit 48, in which air and propane gas are mixed at a pressure of approximately psi to provide the combustible mixture. When the inlet valve head 40 opens, the mixture flows through the conduit 48 and the inlet passage 34 into the combustion chamber 2 which, after completion of the preceding pulse, is at a pressure substantially lower than 100 psi.

Air is supplied to the mixing tank 80 from an air surge tank 82 connected to a high pressure source of air, such as an air line, operating at 100 psi. The air surge tank 82 is connected through an intervening conduit 84 to the mixing tank 80.

Propane gas is. supplied to the mixing tank 80 from a bottle 86 containing liquified propane, through connecting conduits 88. Positioned outside the propane bottle 86 are electrical heating lamps 90 which raise the temperature of the liquid propane so that it boils off. The heating of the liquid propane creates a supply of propane gas at about 120 psi and it passes through a variable restrictor 92, interposed in the conduit 88, which controls the supply of propane into the mixing tank 80. Connected in the conduit 88 with a branch connection to the air conduit 84, is a slave regulator 94 which automatically regulates the supply pressure of the propane gas to that of the air pressure.

Two safety features are included. A pressure sensor 98 in fluid communication with the propane gas in the conduit 88 is connected with the electrical supply to the heating lamps 90 for the propane bottle, so that if an excessive pressure rise is detected by the unit 98 it automatically turns off the heating lamps. It is also necessary to turn off the heating lamps 90 when the liquid propane in. the bottle 86- has been exhausted and for this purpose a weight-sensor indicated schematically as 100, is also connected with the propane bottle. The weight-sensor 100 cuts off the electrical supply to the lamps 90 whenever the weight of the bottle 86 and its contents drops below a predetermined level.

The mixing tank 80 and the air surge reservoir 82 are of very much larger volumetric capacity than the combustion chamber 2 to minimize variations in supply pressure of the combustible mixture during flow of the gas into the combustion chamber.

Although a source utilizing liquified propane gas has been disclosed, it will be understood that, by appropriate modification, a liquid fuel or mist can be mixed with air and supplied to the combustion chamber to provide the combustion mixture.

THE POWDER INJECTOR UNIT The previously mentioned powder injector unit 12 (FIG. 8) includes a vertical, closed hollow cylindrical injector housing 120. The housing 120 has a threaded boss 122 at its lower end which engages a threaded bushing 124 welded to and extending through the wall of the combustion chamber 2 at its upper end. A vertical passage 126, extending through the boss 122, places the interior of the injector housing 120 in fluid communication with the interior of the combustion chamber 2. The passage 126 is normally closed, however, by an injector valve head 128 which seats on an annular neoprene sealing ring 130 mounted in the lower end of the injector housing. The injector valve head 128 may be lifted vertically off its seat 130 by an injector valve stem 132 extending upwardly and outwardly through the upper end of the injector housing 120. The upper end of the injector housing includes a conventional pressure type seal (not shown) permitting verticalsliding motion of the stem 132 without loss of pressure within the housing.

Fixedly secured to the stem 132, adjacent the midpoint of the housing, is a piston 134 which divides the interior of the housing into an upper chamber 136 and a lower chamber 138. The piston 134 guides the valve stem for vertical sliding motion to insure that the valve head moves vertically off and onto its seat 130.

Particulate material is periodically fed into the lower chamber 138 through a horizontal conduit 140 connected to and extending through the sidewall of the housing 120. At its opposite end the conduit 140 communicates with the lower end of a dispenser unit 142 comprising an upper, storage container 144 containing a supply of the coating material and a lower, hopper 146. The storage container 144 is a closed, vertical hollow cylinder having a cone-shaped bottom wall leading into a narrow throat 148. Passing centrally through the storage unit 144 is a vertical shaft 150 having a threaded region 152 at its lower end positioned in the throat 148, spaced from the walls thereof. A valve head 154 is threadedly secured to the bottom of the shaft 152 and has an upwardly directed conical portion which seats on a correspondingly shaped seat at the lower end of the throat 148.

Normally, flow through the throat into the underlying hopper 146, which is connected to the storage unit 144 by an intervening neck 160, is prevented by the valve head 154. However, the shaft 150 may be selectively moved downwardly so that particles can pass through the throat 148 into the hopper 146. In addition, the

threads 152 at the lower end of the shaft 150 help to I carry particulate material downwardly into the lower hopper. From the hopper 146 the particles pass through the intervening conduit 140 into the lower chamber 138.

By the use of both a storage unit and a hopper, the quantity of material fed into the powder injector housing 120 on each charge, can be controlled. Moreover,

by providing the hopper 146, it is insured that a volume of particulate material mixed with a relatively larger volume of air is fed through the conduit 140, thus avoiding clogging of the conduit as might occur if it were attempted to feed directly from the mass of material in the storage unit into the conduit without an intervening hopper.

As the particulate material must be fed into the com bustion chamber during a period in which the pressure in the chamber rises to a peak of about 400 psi, it is necessary to insure that the pressure in the interior of each of the injector housing 120, the storage unit 144 and the hopper 146 are all at a still higher pressure. For this purpose, a supply of air from a conventional higher pressure source at about 1,000 psi (not shown) is connected through a supply conduit 162 feeding

branch conduits

164, 166 and 168 which are connected to the upper chamber 136, the interior of the storage unit 144, and the interior of the hopper 146, respectively.

138 injects the particles into the combustion chamber 4 in a direction toward the nozzle 4. By injecting the particles at the side of the combustion chamber remote from the nozzle 4, the particles are given a sufficient residence time in the combustion chamber 2 to provide a necessary degree of preheating before they enter the high velocity combusted gas stream through the nozzle 4.

Return of the valve to its closed position thereafter is assisted by the high pressure on the upper side of the valve head 128 which gives a particularly rapid and effective valve closing action.

The valve stem 132 may be raised and lowered by the use of a solenoid and associated switching circuit, similar to one of the solenoids 50 and associated circuits, previously described in connection with the fuel inlet unit. Thus, it will be appreciated that the fuel inlet solenoids, the powder injector solenoid and the spark plug are each energized in response to operation of the switches in their respective associated electrical circuits. As previously discussed the make and break points for the spark plug are mounted on the inlet valve mechanism so that timing of the spark at the desired interval after opening of the inlet valve is achieved automatically. Similarly the opening of the powder injector valve in the timed relation previously described is achieved by arranging the switch contacts to the powder injector solenoid to close approximately 3 milliseconds after the fuel inlet valve head 40 commences to open. This can be achieved by mounting cams on a common rotating shaft controlling the operation of the switches controlling the inlet valve and the powder injector plunger in the desired timing relation. Other conventional timing circuits could alternatively be used.

In an alternative embodiment of the invention, the coating material instead of being introduced into the chamber separately from the combustible mixture, may be introduced into the chamber already mixed with the combustible mixture. This may advantageously be done by introducing the coating material into the line 48 between the fuel/air source and the fuel inlet valve or, alternatively, by introducing the coating material into the chamber 34 within the fuel inlet valve 8 via a suitable conduit. In either event the coating material enters the combustion chamber with the combustible mixture.

We claim: 1. The method of impacting particulate material against a work piece which comprises repeatedly:

filling a chamber having a gas outlet with combustible gaseous mixture at a first pressure, then deflagrating the combustible gaseous mixture in the chamber, the chamber having a sufficiently large volume relative to the size of the outlet that the gaseous mixture is substantially deflagrated before a sufficient volume of the gaseous mixture can pass through the outlet to materially limit the increase in the pressure produced by the deflagration of the mixture to thereby produce a second pressure substantially higher than the first pressure,

mixing the particulate material with the gases of combustion, and

using the second pressure to drive the gases of combustion and the particulate material through a nozzle to accelerate the particulate material against the work piece.

2. The method of claim 1 wherein the combustible gaseous mixture is introduced to the chamber at a sufficiently high rate to raise the pressure of the mixture substantially above atmospheric pressure and the deflagration of the gaseous mixture is initiated while the gaseous mixture is substantially above atmospheric pressure.

3. The method of claim 1 wherein the gaseous mixture is fuel and air.

4. The method of claim 1 wherein the particulate material is introduced to the gaseous mixture before a major portion of the gaseous mixture has been directed through the nozzle. 5. The method of claim 1 wherein a portion of the gaseous mixture is combusted by auto ignition after the pressure of the gaseous mix- 5 ture has been increased by deflagration ti. The method of claim 1 wherein the particulate his injecting particulate coating material into the combustion chamber so that the particulate material will be preheated before leaving the combustion chamber, and

directing the gases of combustion and heated particulate coating material issuing from the outlet through an elongated nozzle to accelerate the particles and impact the particles against the work piece.

8. The method of claim 7 wherein the combustible mixture is substantially fuel and air.

9. The method of claim 7 wherein the pressure in the combusion chamber prior to ignition is at least about three atmospheres.

10. The method for applying. the particulate coating material to a work piece using a combustion chamber having a restrictive gas outlet which comprises:

introducing a combustible gaseous mixture to the combustion chamber at a sufficiently high rate to increase the pressure of the gaseous mixture in the chamber substantially above atmospheric pressure,

combusting the gaseous mixture in the chamber by deflagration to cause an additional rapid rise of the pressure in the chamber,

injecting particulate material into the gaseous mixture while a major portion of the gaseous mixture is still in the combustion chamber, and

directing the gases and particulate material issuing at high velocities from the gas outlet through an elongated nozzle to accelerate the particulate material against the work piece.

11. The method of claim 10 wherein the combustible gaseous mixture is confined such as to substantially minimize the maximum deflagration flame propagation period and thus increase the peak pressure obtained as a result of the combustion.

12. The method of claim 10 wherein the combustible gaseous mixture is a carbonaceous fuel and air.

13. The method of claim 12 wherein the particulate material is a material having a high melting point.

PatentNo. 3,801,346 Dated April 1974 .M Inventor(s) osser B elton Jr et 81 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Inventors:

"Johm M. Clark, Jr." should read John M. Clark, Jr

Assignee: I

"Zachrey" should read Zac hry Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

- McCOY GIBSON JR. C. MARSHALL DANN Attestlng Officer Commissioner of Patents FORM PO'wSO uscoMM-Dc 60376-P69 U 5 GOVERNMENT PRINTING OT'ICE: o

Claims

2. The method of claim 1 wherein the combustible gaseous mixture is introduced to the chamber at a sufficiently high rate to raise the pressure of the mixture substantially above atmospheric pressure and the deflagration of the gaseous mixture is initiated while the gaseous mixture is substantially above atmospheric pressure.
3. The method of claim 1 wherein the gaseous mixture is fuel and air.
4. The method of claim 1 wherein the particulate material is introduced to the gaseous mixture before a major portion of the gaseous mixture has been directed through the nozzle.
5. The method of claim 1 wherein a portion of the gaseous mixture is combusted by autoignition after the pressure of the gaseous mixture has been increased by deflagration.
6. The method of claim 1 wherein the particulate material coats the work piece.
7. The method for applying particulate coating material to a work piece comprising feeding a gaseous combustible mixture into a combustion chamber having an open gas outlet the diameter of which is substantially smaller than that of the combustion chamber at a sufficiently high rate to increase the pressure in the chamber substantially above atmospheric pressure and then igniting the mixture to cause an additional rapid pressure rise within the chamber to a peak value as the mixture is burned substantially within the chamber, injecting particulate coating material into the combustion chamber so that the particulate material will be preheated before leaving the combustion chamber, and directing the gases of combustion and heated particulate coating material issuing from the outlet through an elongated nozzle to accelerate the particles and impact the particles against the work piece.
8. The method of claim 7 wherein the combustible mixture is substantially fuel and air.
9. The method of claim 7 wherein the pressure in the combusion chamber prior to ignition is at least about three atmospheres.
10. The method for applying the particulate coating material to a work piece using a combustion chamber having a restrictive gas outlet which comprises: introducing a combustible gaseous mixture to the combustion chamber at a sufficiently high rate to increase the pressure of the gaseous mixture in the chamber substantially above atmospheric pressure, combusting the gaseous mixture in the chamber by deflagration to cause an additional rapid rise of the pressure in the chamber, injecting particulate material into the gaseous mixture while a major portion of the gaseous mixture is still in the combustion chamber, and directing the gases and particulate material issuing at high velocities from the gas outlet through an elongated nozzle to accelerate the particulate material against the work piece.
11. The method of claim 10 wherein the combustible gaseous mixture is confined such as to substantially minimize the maximum deflagration flame propagation period and thus increase the peak pressure obtained as a result of the combustion.
12. The method of claim 10 wherein the combustible gaseous mixture is a carbonaceous fuel and air.
13. The method of claim 12 wherein the particulate material is a material having a high melting point.