US3915381A - Method and apparatus for applying particulate coating material to a work piece - Google Patents

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 [191 Melton, Jr. et al.

[4 1 Oct. 28, 1975 [54] METHOD AND APPARATUS FOR APPLYING PARTICULATE COATING MATERIAL TO A WORK PIECE [75] Inventors: Rosser Melton, Jr., Helotes; John M. Clark, Jr., Seguin; Ronald J. Mathis, San Antonio; William D. Weatherford, Jr., San Antonio; Charles D. Wood, III, San Antonio, all of Tex.

[73] Assignee: Southwest Research Institute, San

Antonio, Tex.

[22] Filed: Oct. 26, 1973 [21] Appl. No.: 409,962

Related US. Application Data [62] Division of Ser. No. 198,806, Nov. 15, 1971, Pat. No.

[52] US. Cl. 239/81; 239/85; 239/101; 117/22; 117/105 [51] Int. Cl. B0515 l/24; C23C 7/00 [58] Field of Search 239/79-81, 239/85, 70, 99, 101; 117/22, 105, 105.1, 105.2, 46 ES [56] References Cited UNITED STATES PATENTS 2,714,563 8/1955 Poorman et al. 117/22 X 2,774,625 12/1956 l-lawley et al. 239/81 X 2,861,900 ll/1958 Smith et al 117/105 2,950,867 8/1960 Hawley et al. 239/79 X Primary ExaminerR0bert S. Ward, Jr. Attorney, Agent, or F irml-1ubbard, Thurman, Turner & Tucker [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.

7 Claims, 10 Drawing Figures US. Patent Oct. 28,1975 Sheet1of4 3,915,381

Ava 60 966 Fssem/o/ U.S. Patent Oct. 28, 1975 Sheet 2 of4 3,915,381

ISQQQQQ ls fins, M144 lascm'os Cow/1Y6 P679100 US. Patent Oct. 28, 1975 Sheet 3 of4 3,915,381

METHOD AND APPARATUS FOR APPLYING PARTICULATE COATING MATERIAL TO A WORK PIECE RELATED APPLICATION This is a divisional application of copending applica tion Ser. No. l98,806,"fild Nov. 15, l97l, now US Pat. No. 3,801,346. This invention relates to a" method and apparatus for applyingiparticulate coating'ma'terial to a work piece, and in particular to a system in which the coating material is directed in termit tentl y' against the work piece in a heated condition in a highvelocity gas stream.

applying coating materials, it is advantageous with certain materials in view of their high melting points, non-galvanic properties or forother 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 fl attened and weld melting during continuous operation may render the apparatus unduly heavy and cumbersome.

It may sometimes be desirable, therefore, to utilize an intermittant or pulsed coating system. ln 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 sustain a supersonic detonation wave may make the device unnecessarily lengthy for installation at locations where space is at a premium. Additionally; by injecting the to each otherandto the workpiece to producea hard,

non-porous coating. 7

[n.performinga coating process of this general nature, it has, beenfound 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 at impact of the particles which is a function both of the temperature to which they areraised 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 providea suitable degree of' control over these coating process variables.

For-example, oneprior-"coating system utilizes a tubular housing fed with continuous streams of acetylene, oxygemand 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 purpose for which itis intended, certain problems may arise under particularcondit-ions. For example, a continuously operating system subjects the workpiece to a large uninterrupted stream of very hot burnt gases which could easily overpowder at a location downstream of the combustion zone, the opportunity to heat the powder directly in the combustion zone is los'tJAlso, by the time the detonation wave reaches the powder injection zone downstream of the combustion zone, some of the peak pres-' zone has necessarily sure-attained in the combustion already been dissipated.

SUMMARY OF THE INVENTION The present invention provides a method and appara- .tus for applying particulate coating material to awork eous combustible mixture into a combustion chamber heat the work.-piece-an"d subject it to severe thermal erosion or distortioiizfln addition, such a system operatin'gcontinuously at velocities in'the order of 2,000 feet per second would'tend to deposit-coating material at a very high rate and on certain types of small work pieces this rate of coating build-up might 'not allow heat to escape from the work piece sufficient 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 usuallyrequires that the proportion of powder in the combustion gases be about 5-10% ofgas mass as high concentrations would supply material so rapidly as to "even further compoundthe heat dissipation problems just described To avoid these potential hazards, it wo uld be preferable to emply a pulsed systemallowing tiine between applications of coating material in which sufficient heat dissipation from the work piece could occur to avoid distortion; Additionally, the need fora water cooled barrel to prevent the barrel from 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 tively, approximately at the time the pressure in the combustion chamber reaches its peak value andterminating 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 for a coating on the work piece. I

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 effecient 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 sub? stantial proportion of the peak pressure, it is insured that almost all the particulate material 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 mately 400 psi, and a velocity of outflow of the com-.

busted gases of about 3,000 feet per second with the entrained particulate material traveling at about L500 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. I 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, r

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. I,

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

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

FIG. 7 is a cross-sectional top view of thefuel inlet unit shown in FIG. 6 taken along the lines 77 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 isa schematic graph of current and voltage versus time for the electrical circuit shown in FIG. 9A.

Referring now to the drawings, and particularly to FIG. lot the drawings, an apparatus for applying particulate coating material, constructed in accordance with the preferred embodiment of the invention, is

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 particulatematerial. 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 2, which is formed of steel or similar material, is configured generally as an inverted bulb witha 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 from the inlet unit 8. Other locations may be chosen for the spark plug. The spark ignition plug 10 is a conventtional 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 75 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 ,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 regionto the internal diameter of the nozzle 4 (d in FIG. 3) should be at least 5 to I 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% inches providing a ratio of D/d of 7 /2. 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 throughv 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 about5 milli-seconds, the period of gas outflow"(sometimes called the blow down) during which gas escapes from ,the' nozzle, should be several times longer. For example, a $4; inch internal diameter nozzle requires a chamber volume of at least 8 cubic inchesgiving a blow down period of about 10 milli-seconds and in practice a chamber capacity of 12-14 cubic inches isprovided. With these dimensions, powder can be injected and substantially eliminated from the combustion chamber 2 before the pressure in it has dropped to a valuegwhich 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 proportional to particle size and inversely proportional to firing pressure. Therequired 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 additionalheating 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 approximately 1,200, with adhesion in excess of 1 1,000 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 milli-seconds. 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 10 milli-seconds 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 travelled 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 alreadybeen 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 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 th'readedly 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 rim, 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.

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 psi and it passes through a variable restrictor 92, interposed in the conduit 88, which controls the supply of propane into the mixting 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 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 ofthe injector housing includes a conventional pressure type seal (not shown) permitting vertical sliding 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 anupper, storage container 144 containing a supply of the coating material anda 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 l48into the hopper 146. In addition, the threads 152 at the lower end of the shaft 150 help to 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 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. v

As the particulate material must be fed into the combustion 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 areconnected .to the upper chamber 136, the interior of the-storage unit 144, and the interior of the hopper 146, respectively.

To inject the material in the lower chamber 138, the stem 132 is raised vertically, lifting the valve head :128 off its seat. The high pressure within the lower chamber 138 injects the particles into the combustion chamber in a direction toward the nozzle 4-. By injecting the particles at the side of the combustionchamber 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 beforethey enter the high velocity combusted gas stream through the nozzle 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, 10 are mounted on the inlet valve mechanisms 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 milli-seconds 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.

What is claimed is:

1. An apparatus for applying particulate coating material to a work piece comprising:

a combustion chamber having a gas inlet and a restrictive gas outlet, valve means in the gas inlet for blockingflow of gas fromthe chamber out through the gas inlet during combustion in the combustion chamber,

the combustion chamber having a cross sectional area substantially larger than that of the gas outlet such that a major portion of the gases will be retained in the combustion chamber by the restrictive gas outlet while the combustible gaseousmixture is deflagrated whereby the pressure within the combustion chamber will rise sharply as a result of such .deflagration, fuel feed means for forming a combustible gaseous mixture in the chamber by forcing gases through the gas inlet into the combustion chamber, ignition means for igniting a combustible gaseous mixture in the combustion chamber, particle feed means for injecting a predetermined quantity of particulate coating material into gases of combustion in the combustion chamber, and

control means for thevalve means, fuel feed means,

ignition means and particle feed, means for respectively forming acombustible gaseous mixture in the combustion chamber, igniting the combustible gaseous mixture to produce a sharp increase in pressure in the combustion chamber, and injecting a predetermined quantity of particulate material into the chamber while a substantial .portion of the gases of combustion are still in the combustion chamber, whereby the particulate material will be heated by the gases of combustion and accelerated by the gases of combustion issuing from the gas outlet for impact against a work piece.

2. The apparatus of claim 1 wherein the fuel feed means comprises:

fuel-air carburetor means for producing a combustible mixture of fuel and air,

a source of air at a super atmospheric pressure, and

means connecting the source of air at super atmospheric pressure to the carburetor and the output of the carburetor to the gas inlet of the combustion chamber, and wherein the valve means controls the admission of a fuel-air mixture from the carburetion means to the combustion chamber.

3. The apparatus of claim 2 wherein the fuel feed meanshas sufficient pressure capacity to force gas into the combustion chamber at a rate greater than the rate at which the gas escapes through the gas outlet to achieve a pressure substantially greater than atmospheric in the combustion chamber prior to combustion of the gases. 1

4. The apparatus of claim 2 wherein the fuel-air carburetion means comprises:

a source of liquified natural gas,

a mixing tank in fluid communication with said internal passage in said inlet valve housing, an air surge tank in fluid communication with a source of air under pressure and with said mixing tank for delivering air under pressure thereto,

conduit means connecting said source of liquified propane gas and said mixing tank; and

flow control means connected with said conduit means and with said air surge tank for regulating the proportions of air and propane gas fed to said mixing tank.

5. The apparatus of claim 1 wherein the particle feed means comprises:

an injector housing having a closed injector chamber therein,

an outlet port in said injector housing placing one end of said injector chamber in fluid communication with the interior of said injector chamber in fluid communication with the interior of said combustion chamber,

an injector valve having,

an injector valve head which in a closed position thereof closes said outlet port,

I actuating means connected with said injector valve head extending outwardly of said injector housing for selective movement of said injector valve head to an open position exposing said outlet ports;

dispenser means connected with said injector housing for delivering a charge of the particulate material to said injector chamber in the region of said valve head; and pressure means in fluid communication with said injector chamber for supplying gas thereto at a pressure in excess of the peak pressure developed in said combustion chamber, whereby when said valve head is raised off said outlet port the pressure within said injector chamber is sufficient to inject the particulate material within said injector cham' her into said combustion chamber.

' 6. The apparatus'of claim 1 wherein the gas outlet is formed by an elongated nozzle of substantially constant diameter for accelerating the particulate material.

' 7. The apparatus of claim 6 wherein said combustion chamber and said nozzle are of generally circular cross section with the ratio of the internal diameter of said combustion chamber to--theinternal diameter of said nozzle being at least 5 to l.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,915,381

DATED October 28, 1975 NVENTOMQ I Rosser B. Melton, In; John M. Clark, Jr.; Ronald J. Mathis;

William D. Weatherford, 3r.; Charles D. Wood, Ill.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 12, line 42, "ports" should be --port--.

Signed and Scaled this Second D3) Of November 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummisrimrer uj'Parenrs and Trademarks

Claims (7)

1. An apparatus for applying particulate coating material to a work piece comprising: a combustion chamber having a gas inlet and a restrictive gas outlet, valve means in the gas inlet for blocking flow of gas from the chamber out through the gas inlet during combustion in the combustion chamber, the combustion chamber having a cross sectional area substantially larger than that of the gas outlet such that a major portion of the gases will be retained in the combustion chamber by the restrictive gas outlet while the combustible gaseous mixture is deflagrated whereby the pressure within the combustion chamber will rise sharply as a result of such deflagration, fuel feed means for forming a combustible gaseous mixture in the chamber by forcing gases through the gas inlet into the combustion chamber, ignition means for igniting a combustible gaseous mixture in the combustion chamber, particle feed means for injecting a predetermined quantity of particulate coating material into gases of combustion in the combustion chamber, and control means for the valve means, fuel feed means, ignition means and particle feed means for respectively forming a combustible gaseous mixture in the combustion chamber, igniting the combustible gaseous mixture to produce a sharp increase in pressure in the combustion chamber, and injecting a predetermined quantity of particulate material into the chamber while a substantial portion of the gases of combustion are still in the combustion chamber, whereby the particulate material will be heated by the gases of combustion and accelerated by the gases of combustion issuing from the gas outlet for impact against a work piece.

2. The apparatus of claim 1 wherein the fuel feed means comprises: fuel-air carburetor means for producing a combustible mixture of fuel and air, a source of air at a super atmospheric pressure, and means connecting the source of air at super atmospheric pressure to the carburetor and the output of the carburetor to the gas Inlet of the combustion chamber, and wherein the valve means controls the admission of a fuel-air mixture from the carburetion means to the combustion chamber.

3. The apparatus of claim 2 wherein the fuel feed means has sufficient pressure capacity to force gas into the combustion chamber at a rate greater than the rate at which the gas escapes through the gas outlet to achieve a pressure substantially greater than atmospheric in the combustion chamber prior to combustion of the gases.

4. The apparatus of claim 2 wherein the fuel-air carburetion means comprises: a source of liquified natural gas, a mixing tank in fluid communication with said internal passage in said inlet valve housing, an air surge tank in fluid communication with a source of air under pressure and with said mixing tank for delivering air under pressure thereto, conduit means connecting said source of liquified propane gas and said mixing tank; and flow control means connected with said conduit means and with said air surge tank for regulating the proportions of air and propane gas fed to said mixing tank.

5. The apparatus of claim 1 wherein the particle feed means comprises: an injector housing having a closed injector chamber therein, an outlet port in said injector housing placing one end of said injector chamber in fluid communication with the interior of said injector chamber in fluid communication with the interior of said combustion chamber, an injector valve having, an injector valve head which in a closed position thereof closes said outlet port, actuating means connected with said injector valve head extending outwardly of said injector housing for selective movement of said injector valve head to an open position exposing said outlet ports; dispenser means connected with said injector housing for delivering a charge of the particulate material to said injector chamber in the region of said valve head; and pressure means in fluid communication with said injector chamber for supplying gas thereto at a pressure in excess of the peak pressure developed in said combustion chamber, whereby when said valve head is raised off said outlet port the pressure within said injector chamber is sufficient to inject the particulate material within said injector chamber into said combustion chamber.

6. The apparatus of claim 1 wherein the gas outlet is formed by an elongated nozzle of substantially constant diameter for accelerating the particulate material.

7. The apparatus of claim 6 wherein said combustion chamber and said nozzle are of generally circular cross section with the ratio of the internal diameter of said combustion chamber to the internal diameter of said nozzle being at least 5 to 1.

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