US3266727A - Apparatus for applying heat fusible coating on solid objects - Google Patents

Description

ug- M, W66 A. P. SHEPARD ETAI. 3,266,727

APPARATUS FOR APPLYING HEAT FUSIBLE COATING ON SOLID OBJECTS 4 SheeS-Sheet l Original Filed April 18, 1957 ARTHUR F. SHEPARD FEED/NAND J D/TTR/CH :e Po wn ATTORNEYS ug A6, A966l A. P. SHEPARD ETA. 3,266,727

APPARATUS FOR APPLYING HEAT FUSIBLE COATING ON SOLID OBJECTS Original Filed April 18, 1957 4 Sheets-Sheet 2 FEED/NAND o/TT/a/CH MMM l www M? Aug., 16, 1966 A. P. SHEPARD ETAL 3,256,727

APPARATUS FOR APPLYING HEAT FUSIBLE COATING ON SOLID OBJECTS Original Filed April 18, 1957 4 Sheets-Sheet 5 P RIOR ART 7 INVENTOR A/eTHu/a n sHEPA/z m2o/NAND l wrm/CH ATTORNEYS ug. E6, 1966 A. P. SHEPARD ETAL 3,266,727

APPARATUS FOR APFLYING HEAT FUSIBLE COATING ON SOLID OBJECTS Original Filed April 18, 1957 4 Sheets-Sheet 4 INVENTOR ARTHUR F. SHE/ARD FEED/NAND J D/TT/E/CH BY @a 7/ ATTORNEYS United States Patent Office ,amd uguaziz' `7 ,2`66,727 APPARATUS EUR APPLYING HEAT FUSiBLE COATENG N SOLID OBJECTS Arthur P. Shepard, Flushing, and Ferdinand it'. Dittrich, Beihnore, NSY., assignors to Metallizing Engineering Co., line., a corporation oi New Jersey @riginal appiication Apr. 18, 1957, Ser. No. 653,602, now Patent No. 3,111,267, dated Nov. 19, 1963. Divided and this application Jian. 8, 1963, Ser. No. 258,092 11 Claims. (Cl. 239-85) This application is `a division of application Serial No. 653,602, now Patent 3,111,267.

This invention relates to an apparatu-s for `applying heatfusible coatings on solid objects from heat-'fusible materials in divided, such as powdered, form. 'Ihe invention more particularly relates to a Igun construction for spraying heat-fusible mate-rial, using a fuel 'gas and a combustion supporting gas where said material is fed int-o the gun in finely divided, solid form.

Heat-fusible material spray guns of the powder type -are devices in which powdered material is lfed to a heating zone wherein it reaches `a molten or at least heatplastic condition, and from which it is propelled, at a relatively high velocity, onto the object to be coated. Heat-fusible material spray guns of this type provide means for conveying the powdered material to be sprayed from Va hopper to the heating zone by `a stream of gas, in which the iinely divided powdered material is entrained.

Such guns are most commonly used for spraying metal powders `and hence are frequently referred to las powdertype metal spray guns.

All of the previously known powder spray guns and the methods of spraying the powder used thereby have been subject to certain 4fundamental limitations. Some guns of this type have been satisfactory only for spraying very low melting point materials. New guns have been developed, however, which are satisfactory for spraying higher melting point materials, such as nickel base 4alloy metals and refractory ceramic materia-ls, including alumina and zirconia.

Y[these guns, which are satisfactory for higher melting point materials, differ 'from previous powder spray guns in that `they supply the powdered material to the cen-ter of the iiame at a relatively low velocity and do so by using a relatively small amount `of carrier gas in proportion rto the solid material carried.

All previously known heat-fusible material spray guns and spraying methods Ihave been subject to certain fundamental limitations, however. All such previously known guns, for instance, are very critical to operate with high melting point materials. The carrier -gas pressure and volume must be adjusted very accurately, and the ow of solid powdered material lto be sprayed -must be adjusted and control-led very accurately to produce satisfactory coatings. This lrequires a well trained, highly skilled operator, since it is extremely difficult to tell when these adjustments are properly made. For instance, when spraying refractory ceramics, if the velocity of the carrier gas as it enters the flame is slightly too high, then soft coatings result, and lif it is slightly too low, coatings with large spattered lumps of material result. Since this adjustment is very critical, the operators must frequently produce spoiled and `defective coatings in order to get the ygun adjusted properly. Some operators have been unable to consistently produce satisfactory coatings.

Another limitation of even the most efficient previously known guns is that they require very accurate grading in a narrow range of the particle 4size of the material to be sprayed. For instance, with such guns alu-mina must be graded to a particle size range of from l0 to 45 microns, and zirconia must be graded from to 40 microus. Even when accurately so graded, materials of this type give the diiiiculties described above when sprayed. Grading these materials `accurately is very expensivenot only because of the cost and time required for the grading operation, but also because Ionly a very small amount of the original commercial material can be used for spraying and the balance must be discarded.

The construction and method in accordance with this invention overcomes the aforesaid limitations and difficulties.

The construction and method in accordance with this invention makes it possible for the first time t-o spray refractory powdered materials (including refractory metals and refractory ceramics) so that consistent hard coatings can be produced without spatter by unskilled operators.

'Ihe construction and `method in accordance with this invention makes it possible for the yrst time to spray refractory powdered materials comprising Ia relatively wide range of particle sizes and particularly finer m-aterials than previously have been sprayable. For instance, when sprayed in accordance with this invention, alumina of a particle size of from 2 Ato 60 microns, and zirconia of a particle 'size `of from 2 to 50 micron-s, may be successfully sprayed commercial-1y.

In accordance with this invention carrier gas containing lnely divided solid heat-fusible material is introduced into the central zone of a heating flame, such that the velocity of every part of the cross-section of the stream of said gas is essentially `the same and whereby said gas and the entrained particles of said material are diffused throughout t-he cross-section of said flame.

The spray gun nozzle for eifec-ting the method in -accordance with this invention has means Ifor passing a combustible rliuid and a combustion supporting fluid, such as gases, with a substantial forward linear velocity for llame combustion from the tip of said nozzle, a carrier gas conduit terminating substantially adjacent said tip of said nozzle, said conduit being positioned 4and adapted for introduction of carrier gas into the central zone of said flame, and diffuser means in said conduit cooperatively positioned with respect rto said conduit .to diffuse said carrier gas throughout said flame and thereby distribute said material evenly into said flame.

For purposes of illustration and not of limit-ation, the invention will be described in further detail with reference to several preferred constructional embodiments, as shown in the drawings in which:

FIG. l Iis a side elevation of one embodiment of a heat-fusible material spray gun in accordance with this invention;

yFIG. 2 is ya vertical longitudinal section of the embodiment of FIG. 1;

FIG. 3 is a partial cross-section of FIG. 2;

FIG. 4 is a front elevation of the showing in FIG. l;

FIG. 5 is a plan view, partially in section, of the underside of FIG. 2;

FIG. 6 is a vertical cross-section of the nozzle of the embodiment shown in FIG. 2;

FIG. 7 is an end view taken in the direction 7-7 of the showing of FIG. 6;

FIG. 8 is a cross-section of the nozzle -of a heat-fusible material spray gun showing an alternative embodiment of the invention;

FIG. 9 is an end view taken in the direction 9-9 of the showing of FIG. 8;

FIG. l0 is a cross-section of the nozzle of a heatfusible material spray gun showing a preferred embodiment -of the invention;

IFIG. 1.1 is an end view taken in the direction i11 11 of the showing of FIG. l0;

FIG. 12 is 'a cross-section of the nozzle of a heatfusible material gun showing an alternative embodiment of the invention;

FIG. 13 is an end view taken in the direction i13-413 of lthe showing of FIG. 12;

FIG. 14 is a schematic diagram illustrating the flame of a previously known heat-fusible material spray gun; and

fFIG. 15 is a schematic diagram illustrating the flame of a spray gun in accordance with this invention.

Referring to the drawings, 'l1 shows the body of the spray gun, on which is mounted the inclined7 tubular material hopper `2. Material hopper 2 is held by a saddle 3 (fFIG. 1) fastened to body I1 by a through-pin 4, which is threaded into saddle 3 at one end to hold it securely in place. The entire hopper 2 with its saddle 3 can be removed for convenience by removing threaded pin 4. A hole 5 (FIG. 2) is provided in the hopper 2 in communication with the duct 6 in saddle 3. A valve block 7 is securely mounted on top of body 1 and provided with duet 8, which is in line with duct 6. A nipple 9 is mounted between block 7 and saddle 3, so as to connect ducts 6 and 8. The nipple 9 `is held in place by a plate '110 and screws 11. A packing washer `12 is provided around nipple 9.

A small piece of rubber tube 13 tits over the lower projecting end of nipple 9 and is held in place by a rubber ring l14. A valve chamber -15 is provided in block 7 and is fitted with a piston 16, having the packing rings 17 and '18.

The piston :16 is operated by a valve-operating mechanism which will be more fully described hereafter.

The body 1 is provided with a powder feed chamber 19, a longitudinal bore 20 extending centrally through the front end of the body, back to and communicating with a central duct 21 and a hole 22 communicating the powder chamber with the bore 20.

A seat plug 23 in .the form of a cylindrical, hanged plug is fitted into the bore 20 with a sliding fit and has a flange extending over the en-d of body i1. The body 1 is provided with a threaded section 24, onto which is threaded a nut 25. A nozzle 26 is mounted on the flange of seat plug 23 and held in place by nut 25, which simultaneously holds seat plug 23 in place.

The nozzle .26 has a central bore 27 which communicates with the central conical bore 28 of seat plug 23 in such a manner that the two form a continuous extended bore. A groove 29 is provided in seat plug 23 on the upper half only and communicates bore 28 with hole 22. A jet screw 30 is centrally located in seat plug 23 and is screwed into a central threaded hole in seat plug 23. The jet screw 30 is provided with a small central jet hole 31 which is concentric with the bore 28 of seat plug 23. Packing rings 32 and 33 are provided to seal seat plug 23 in the bore 20 at both sides of groove 29.

A dowel pin 34 `is provided between body r1 and seat plug 23 to hold it in a predetermined position.

A bleeder hole 35 is provided from powder chamber 19 to the front end of body I1. The nozzle 26 (FIG. 6) is provided with an annular groove at its base 36 and a multiple number of parallel nozzle jet holes 37, arranged in a circle. Nozzle 26 is also provided with air holes 38, which are located alternately between holes 37 and terminate inwardly of holes 37, nearer to bore 27, and extend at a relatively steep angle to the outer surface of nozzle 26.

The seat plug 23 is provided with a hole 39 through its flange, which communicates wi-th annular groove 36. Body 1 is provided with duct 40 which communicates with hole 39. Body 1 is provided with duct 41 for combustion supporting gas and duct 42 for combustible gas. These ducts can be seen by referring to FIG. 5 which also shows more clearly the connecting ducts between ducts 411 and 42 with duct 40.

The connecting duct between 40 and 41 is the connecting duct 43, and the connecting duct between 40 and 42 is the connecting duct 44. These ducts are provided by cross-drilling through body 1 and plugging the outer ends of these ducts with small steel screws at 45 and 46. Valves 47 and 48 are provided and mounted on the rear of body 1 by means of mounting plate 49 and screws 50. These valves are arranged to communicate with ducts 41 and 42 respectively, and these connections are sealed by packings 5&1 and 52 respectively.

A valve 53 is provided and mounted on body 1 by means of screws 54. The details of this valve construction can best be seen in FIG. 3. A cylindrical bore 55 is provided in body 11 for mounting of this valve. The valve consists of a valve body 56, into which is threaded a needle valve needle 57, on which is secured valve handle '58. Packing ring 59 seals between the inner bore of valve handle 58 and the body 56. Body 56 is provided with a conical seat `60 into which the needle of the needle Valve 57 tits. Body 56 is provided with packing rings 61 and 62, which are spaced on each side of a groove 63 on the outer cylindrical surface of body 56. A hole 64 is provided from the bottom of the bore 55 into duct 42 or a similar hole may be provided into duct 41.

`Refer-ring -to FIG. 2, la small duct 65 is provided in body 1 connecting bore 55 with central duct 21 and terminating in bore 55 in direct communication with annular groove 63 in valve body 56. Hole 90 connects annular groove 63 with the bore in valve body 56.

A handle 66 is mounted on body 1 by means of screws 67. Screws 67 also hold mounting bracket 68, which extends to one side of the gun and has stud 69 secured at its terminus. Mounting bracket 68 and stud 69 provide convenient means for mounting the gun when it is not being used by hand.

A trigger 70 is connected through a mechanism, hereinafter to be described, to valve piston 16. Pin 71 in body 1 pivotally supports the trigger 70. Spring 72 holds trigger 70 in a forward position away from handle 66. Trigger 70 (FIG. 1) extends upward on both sides of the body 1 and at its upper end is mounted a cross pin 73. Cross pin 73 engages a slot in hollow square piston 74. A housing 75 is mounted on body 1 by screw 76 and denes a square piston chamber between itself and the top area of body 1. A cam 92 is mounted on pivot pin 77 in housing 75 and is held in a neutral position, as shown in drawing, by spring 78.

A secondary piston 79 slides in a bore provided in piston cylinder 74, and is held in a forward position by spring 80, which presses against snap ring washer 81, which is fastened to. piston 79. A screw 82, which is screwed into the bottom of piston cylinder 74, acts as a limit stop in both directions for secondary piston 79. Valve piston 16 has spring 83 engaging housing 75 at one end and snap ring washer 84 at the other end, so as to hold valve piston 16 in a rearward position.

The top of square piston 74 has a forward cutout section 85 and a rear cutout section 86 on its upper portion. These cutout sections, and the forward and rearward termini thereof, act to engage the cam projections of cam 92, as will be hereinafter more fully described.

Valve handle 58 is provided with milled grooves 87 which engage the pointed end of detent piston 88. Detent piston 88 slides in the space provided for it at the rear of housing 75 and is pressed rearwardly by spring 89.

Trigger 70 operates to open and close a powder feed valve which comprises rubber tube 13 and the piston 16. In the closed position, with the piston 16 in its rearward position, the piston squeezes the end of rubber tube 13 closed. This position is shown in FIG. 2. When piston 16 is moved to a forward position it releases the squeezing pressure on the end of rubber tube 13, opening it and permitting powder to ow through the rubber tube.

In the open position of rubber tube 13, powder is permitted to ow by gravity from hopper 2 through hole 5, duct 6, the passage in nipple 9, through rubber tube 13, through valve chamber 15 and into powder chamber 19.

When trigger 70 is pulled rearwardly towards the handle 66, pin '73 is moved in a forward direction, causing cylinder piston 74 to move in a forward direction, carrying with it secondary piston 79, which also therefore moves forward. Piston 79 engages and also pushes forward valve piston 16 and hence opens the valve. When valve piston 16 is all the way forward, at the limit of its stroke, piston cylinder '74 continues to move forward. This iadditional movement is permitted since after secondary piston 79 stops moving forward, spring 80 is compressed. During the forward movement of cylinder piston 74 the rearward terminus of cutout section 85 engages the lower projection of cam 92 and rotates it clockwise until the rearward projection yof cam 92 engages the rear ter-minus of cutout section 86 of piston cylinder 74. This stops the forward motion of the piston cylinder 74, and at this point the lower projection of the cam 92 is positioned just `above the groove 85a in the partition separating the cutouts 85 and S6. As the trigger 70 is released, the piston cylinder 74 is urged rearwardly by the spring 80. It, however, can only move a very short distance rearwardly before it is stopped by the engagement of the lower projection of the cam 92 in the groove 35a, preventing further rearward movement. The Valve therefore remains in a locked, open position even after the trigger '70 is released.

To release the valve the operator simply again squeezes the trigger 70 toward the handle 66 a second time. This causes forward motion of the piston cylinder 74, which is permitted, since the cam 92 can rotate slightly in a clockwise direction and since the lower projection of the cam can slide out of the open, rearward end of the groove 85 into the cutout section 86. The lower projection of the cam 92 is already past the highest point on the partition separating the cutouts 85 and 86 so that the rearward terminus of the cutout section 85 will not rotate the cam to a position Where its rear projection will stop the forward motion of the piston cylinder 74 by contacting the rearward terminus of the cutout section 86. The operator then releases the trigger and the cylinder piston 74 and the trigger 70 will return all the Way to the original position as shown in FIG. 2. The rearward motion of the piston cylinder 74 will merely cause the cam 92 to rotate in a counter-clockwise direction when the lower projection strikes the partition separating the cutouts 85 and 86, and after riding over this projection the spring 7 8 will cause the cam to snap back, with its lower projection in the cutout 05. The spring 00 will act to push the cylinder piston 74 rearwardly only until the secondary piston 79 disengages the piston valve 16. Thereafter the rearward motion is caused by the action of the spring 72, which urges the trigger 70 forward and thus the pin 73 rearwardly.

The trigger and powder valve mechanism thereby permits the operator to open the valve by pulling a trigger a first time, and the valve will remain open even after the trigger is released. The valve is closed by pulling the trigger a second time and then releasing it.

In operation, the powdered material to be sprayed is placed in hopper 2, and fuel gas and combustion supporting gas hoses are connected in the conventional manner to valves 43 and 47 respectively. Sources of fuel gas and their hoses and fittings are not shown, since these are conventional and well known for use with such equipment. With the powder valve just described closed, and the powder feed valve 53 closed, the gun is rst lighted by slightly opening valves 48 and 47 and lighting the gases as they emerge from nozzle jets 37.

The fuel gas flows through valve 48 into and through conduit 42, through connecting conduit 44 and into conduit 40. The combustion supporting gas flows through valve 47 and into and through conduit 41, through connecting conduit 43 and also into conduit 40, where it mixes with the fuel gas. The mixed gases flow from conduit 40 through hole 39 and into annular groove 36, and from thence through multiple nozzle jets 37 where they are ignited upon emergence.

The discharge of the gases from nozzle jets 37 causes reduced pressure at the face of nozzle 26, which causes objectionable turbulence at the face of the nozzle, which in turn tends to cause deposit of fusible material on the face of the nozzle. When the nozzle is lighted, however, the reduced pressure at the face of the nozzle is substantially relieved by the induced flow of a small amount of atmospheric air through holes 38, which terminate at the face of the nozzle in alternate positions between nozzle jet holes 37. While the flow of air through holes 38 is very small, it is sufficient to completely eliminate the tendency for material to collect and build up on the face of nozzle 26.

To start the powder flow, valve 53 is first adjusted. The detent piston S8 engaging the grooves 87 in valve handle 58, provides a convenient means for determining the setting of the valve by counting the number of clicks from a fully closed position. The detent also securely holds the valve in a predetermined position. When valve 53 is open, a small amount of fuel gas Hows from conduit 42 through hole 64, through the valve 53, and past needles 60, into the bore of valve body 56, through hole 90, into annular chamber 63, and from thence through conduit 65 into central duct 21. From central duct 21 a very small amount of gas is permitted to ow through jet hole 31 in jet screw 30. This jet of fuel gas extends across groove 29 and exhausts out through powder conduits 28 and 27 to the center of the flame.

To start the powder feeding, the operator pulls back on trigger 70, which opens the powder feed valve as hereinabove described. The powder then flows from powder chamber 19 into groove 29, where it is picked up by the jet of fuel gas emerging from jet hole 31. The powder is then carried forward through conduits 28 and 27 and emerges at the nozzle face in the center of the flame.

Hole 35 is provided into powder chamber 19 to maintain atmospheric pressure in said chamber. This is of importance since otherwise a partial vacuum is created by the action of jet 31, which varies with the flow of powder and hence causes an excessive variation in the powder feed. Most metal powders feed satisfactorily by gravity from hopper 2 down through the various passages to powder chamber 19 and groove 29. The hopper 2 has been mounted at an angle so that the material feeds satisfactorily for all positions of the gun through from horizontal to practically vertically down.

The end or tip of nozzle 26 (FIGS. 6 and 7) has a counter-bored section 601 which comprises a continu-ation of an enlargement of conduit 27. At the tip of the nozzle and at the terminus of conduit 601 is wire screen 602. Screen 602 is fitted into the end of nozzle 26 by providing a slight additional -counter sink to receive it. It may be fastened in place in any conventional manner, such as by friction tit or brazing. Screen 602 may be of a mesh size of from 20 to 80 but is preferably of a mesh size of from 30 to 50, and is most preferably a 40 mesh screen made from .009 diameter wire.

An alternative embodiment of this invention may be seen by reference to FIGS. 8 and 9. In this embodiment nozzle 826 is similar to nozzle 26, in that it has nozzle jets 887, In this embodiment, however, the internal construction of the nozzle differs from that shown in FIGS. 6 and 7. In this embodiment the nozzle 826 is counter-bored at 801. Into bore 801 is press-fitted cylindrical diffuser plug 802. The forward cylindrical section of plug 802 is somewhat smaller than counterbore 801, so that annular passage 003 is provided between plug S502 and bore 801. Annular groove 804 is provided on the outer periphery of plug 802 and is positioned to communicate with radial holes 805 in nozzle 026.

Nozzle 026 has conduit 827, which connects with an extension of this conduit 806 in plug 802. The outer end of conduit 806 is taper-bored to a conical shape. A small cone 807 is centrally fixed in the conical bore of 806 so as to provide an annular conical groove or passage 808. Cone 807 is supported by legs 809 which may be brazed to plug 802 and cone 807 to hold it in position.

In operation the holes 805, groove 804, and annular passage 803 provide a passage for atmospheric air which is drawn by the flame through this passage. The function performed by this air is the same as that provided by air passages 38 shown in the embodiment of this invention described in connection with FIGS. 2 and 6. However, in this construction the air is more evenly `distributed, and it is possible to avoid the collection of material on the tip, provide a more even flame, and use less air for diluting and cooling the flame.

The construction in accordance with another embodiment of this invention will be seen by reference to FIGS. 10 and 11. In this embodiment of the invention, the nozzle 1026 is externally similar to nozzle 26 and has jet holes 1037 similar to jet holes 37 and conduit extension 1027 similar to conduit extension 27. In this embodiment nozzle 1026 is counter-bored to provide bore 1001. Into bore 1001 is press-fitted cylindrical plug 1002. Cylindrical plug 1002 is provided with a groove 1004 and a smaller cylindrical section at its end to provide annular space 1003. Communicating with annular groove 1004 are radial holes 1005. The external plug construction and holes perform the same function as the embodiment previously described in connection with FIGS. 8 and 9.

Plug 1002 is provided with bore 1006, which forms an extension of conduit 1027. From conduit 1006 extending forward to the face of the nozzle are holes 1007. Holes 1007 are provided at an angle to the nozzle axis so that they diverge toward their outer ends.

A still further alternative embodiment of this invention can be seen with reference to FIGS. 12 and 13. The nozzle 1226 is similar in external construction to nozzle 26 and is provided with jets 1237 similar to jets 37. Central conduit 1227 is similar to central conduit 27 except that this conduit terminates before it reaches the flame tip of the nozzle. Extending from the terminus of conduit 1227 are holes 1201. These holes 1201 have their axes on an angle so that they diverge toward the tip. So as to provide holes, the ends of which are at right angles to their axes, the face of nozzle 1226 is turned slightly conical at 1202.

Some powders, however, due to their configuration, size and other properties, do not feed as readily as other powdered materials. In cases where the powders tend to pack or feed unevenly, it is advisable to shake or vibrate the gun slightly. An extremely small amount of vibration or shaking is required to cause smooth flowing of even those powders with the worst flowing characteristics. For this purpose, and when needed, a small vibrator, for instance an electric vibrator, such as an electric buzzer, is attached to the bottom of the gun body, such as by screws 91. Such vibrators are well known in the art and hence this construction has not been shown in the drawings, nor is the vibrator described in detail.

While the hopper 2 may be made of any suitable structure and material, it is an advantage to make it of clear plastic material so that the operator can see the amount of powder remaining in the hopper.

In place of the hopper 2, a separate, as for example, a larger capacity hopper may Ibe supported above the gun and connected to the duct 6 by means of a flexible hose, as for example, a flexible rubber hose. The powdered heat-fusible material in the hopper, which is for example suspended from the ceiling, will feed through the flexible hose by gravity into the duct 6. This construction relieves the operator of the strain of holding the weight of the heat-fusible material and allows the use of a much larger capacity container. With such an arrangement the gun may be operated between a position pointing almost vertically down to a position pointing almost vertically up.

Powder ducts 27 and 28 cooperate to form a continuous section toward the outlet and, together withthe arrangement of jet hole 31 and groove 29, comprise carrier means which carry and introduce a large amount of powder into the center of the flame at a very low velocity. This velocity is so low as to be negligible in comparison with the velocity of gases of the flame. The result is that the acceleration of the particles takes place in the flame and through its hottest area. This results in thermal etiiciency of a much higher order, as previously described. Materials of melting points as high as those of molybdenum, among the metals, and alumina and zirconia, amongthe ceramics, can be satisfactorily sprayed. Another result is substantially increased deposit efhciency.

When in operation, using the apparatus and method in accordance with this invention, the carrier gas carrying entrained finely divided solid material passes through its conduit and upon emergence from the nozzle diffuses outwardly into the flame at a rapid rate, so that finely divided solid material is fairly evenly distributed throughout the flame cross-section. With previous metal spray guns, this result was not achieved. With previous constructions the finely divided solid material was delivered to the center of the flame by the carrier gas in a sharply defined cone of carrier gas densely populated with material particles. Such a cone is illustrated schematically as 1401 in FIG. 14, the nozzle being indicated at 1426 and the flame at 1402. In this case there is a sharp line of demarcation between the carrier gas cone 1401 and the flame 1402, indicated at 1403.

With any of the constructions in accordance with this invention, diffusion of the carrier gas into the flame takes place, so that there is no sharp line of demarcation between the carrier gas cone and the flame, but on the contrary the carrier gas rapidly diffuses into the flame, carrying the finely divided material with it. The flame produced with the apparatus and method in accordance with this invention is represented schematically in FIG. 15, in which 1502 represents the flame and 1526 the nozzle. Carrier gas and entrained solid material particles are distributed through the flame, as illustrated in FIG. 15 by lines in the flame 1502.

In their previous constructions, material particles from the cone 1401 from FIG. 14 received very little heat until they left the tip of the cone. However, after reaching the cone tip, such particles are accelerated so rapidly by the flame that they have very little time in which to be heated thereafter. In the embodiment in accordance with this invention, such particles are introduced into the llame so that each particle is heated by the flame for a longer period of time.

The function of the diffuser nozzle is not only to distribute the particles throughout the flame by diffusion of the carrier gas into the flame, but to accomplish this result without using more carrier gas and preferably by using less carrier gas. Additionally, the function of the diffuser nozzle is to accomplish these results and at the same time to reduce the velocity of the particles as they enter the flame.

When the carrier gas emerges from an open conduit, the velocity of the various elements of the stream of the carrier gas is not constant across the stream cross-section. Due to skin friction, the velocity at the edges of the conduit will be materially less than the velocity in the center. This uneven carrier gas velocity has many disadvantages. The velocity in the center may be too great, causing the particles to pass through the flame too rapidly, whereas the velocity at the edge of the flame, particularly at the bottom edge, may be too low to prevent particles from actually dropping out of the flame. It is this latter dropping out of the flame which frequently causes material `to collect temporarily on the nozzle tip and thereafter be blown as spatter on to the work. The construction in accordance with this invention corrects the difliculties that result from uneven carrier gas velocities by providing a substantially even velocity across the crosssection of the carrier gas stream a short distance beyond the nozzle tip.

Improvements in accordance with this invention result in high operating efficiency of the process, so that not only may finer, less accurately graded materials be used, but there is in addition a material improvement in the deposit efhciency. Deposit efficiency is the ratio of weight of solid material fed into the gun to weight of material deposited on the base to be coated. Not only is the deposit efficiency improved by the construction in accordance with this invention, but the rate of spraying, as measured by pounds of material per hour, is increased with the same flame adjustments.

EXAMPLE 1 Zirconia in vfinely divided powdered form is provided with a particle size of from i2 to 50 microns. A gun in accordance with the preferred embodiment, as described above, and with a nozzle illustrated in FIGS. l and 1l, is attached to a source of acetylene, at a pressure ott 15 p.s.i. gauge and a source of oxygen gas at 20 p.s.i. gauge.

The powdered material is placed in the gun hopper. The gun is lighted, as previously described, and the iiarne adjusted to be approximately neutral. The carrier gas valve is opened to approximately 6 clicks of the detent.

A 4 square by 1A" thick mild steel plate, which is to be coated on one surface, is first grit-blasted, using a 50%-50% mix-ture oif SAE G 25 and SAIE G 40 steel grit, lusing a suction blast gun in the conventional manner and a blasting air pressure orf approximately -80 psi.

The clean surface orf the plate is pre-heated, using the gun to a temperature of approximately 250 iF.

The powder feed trigger off the gun is then operated to produce powder flow and the gun used to spray the coating of the alloy. The gun nozzle is held .about 6" from the surface of the plate.

'It is -desired in this case to have a finished thickness of .015.

The spraying speed w-as 2%. pounds per hour of matenial, and the deposit efficiency, which is the ratio of the weight of the solid material fed into the iiame to the weight otf the deposited coating, was '86%. A strong hard coating resulted.

With previous constructions operated exactly as described in the albove example, zirconia of a 'particle size tfrom 10 to 40 microns would have been required and a deposit efhciency of only 46% would have been obtained and a spraying speed of only 11/2 pounds per hour would have resulted. More skill would have ibeen required by the operator to produce the hard coating produced in Example 1 without spatter.

f' The nozzle construction 1n accordance with th1s invention is highly satisfactory (for spraying finely divided metals as well as ceramic materials.

EXAMPLE 2 A self-fiuxing boron-silicon-niokel base alloy composition is provided in powdered iform, with lparticle size such that all will pass through a 120 mesh U.S. standard screen and not over 30% will pass through a 325 mesh U.S. standard screen:

A gun as described above and illustrated in the drawing is attached to a source olf acetylene ata pressure of 15 lbs. per square inch gauge and a source of oxygen gas at a pressure orf lbs. per square inch gan-ge.

The powdered alloy is placed in the gun hopper. The gun is lighted, as previously described, and the flame adjusted to be approximately neutral. The carrier gas valve is opened to approximately 10 clicks of the detent.

A 4 square by 1A thiok mild steel plate, which is to be coated on one surface, is first grit-blasted, using a 50%- 50% mixture of SAE G 25 and SAIEl G 40 steel grit, using a suction blast gun in the conventional manner and a blasting air pressure olf approximately y p.s.i.

The clean surface of the plate is pre-heated, using the gun to a temperature of approximately 250 F.

IThe powder feed trigger of the gun is then operated to produce powder iiow and 4the gun used to spray the coating of the alloy. The gun nozzle is held about l0 from the surface olf the plate.

It is desired in this case to have a [finished thickness after final grinding orf .030. The coating is applied until it is between .045 and .050 thick.

The coating, which in this case will not get hotter than a few hundred degrees, is allowed to cool in air to near room temperature.

The surface is then ground to the desired thickness, using a silicon carbide wheel in the conventional manner.

The above examples are given to illustrate the invention and not lto limit the same.

The foregoing specific description is 'for purposes of illustration and not of limitation and it is therefore my intention that the invention be limited only by the appended claims or their equivalents wherein I have endeavored to claim broadly all inherent novelty.

We claim:

1. In a spray gun for spraying finely divided, solid heatfusible material, a discharge nozzle defining a central conduit and means connected thereto adapted to supply a stream of gas-borne, finely divided, solid material thereto, a series of jets at least partially surrounding said central conduit, and means connected thereto adapted to supply a stream of combustible gas mixture thereto to produce a sheath of flame at least partially surrounding the projection of said central conduit, the improvement which comprises said central conduit terminating as an annular, angularly outwardly directed discharge outlet with its walls terminating within the outward projection of said jets to outwardly diffuse said stream of gas-borne solid material into the space occupied by said sheath.

2. A spray gun according to claim 1 in which said central conduit is flared outwardly and provided with a central cone which defines with said flare, said annular, angularly outwardly directed discharge outlet.

3. Improvement according to claim 2 including an air bleeder c-omprising an annular groove surrounding said central conduit, and at least one duct connecting said groove with the side of said nozzle.

4. Improvement according to claim l including an air bleeder comprising an annular groove surrounding said central conduit, and at least one duct connecting said groove with the side of said nozzle.

5. In a spray gun for spraying finely divided, solid heat-fusible material, a discharge nozzle defining a central conduit, and means connected thereto adapted to supply a stream of gas-borne, finely divided, solid material thereto, a series of jets at least partially surrounding said central conduit, and means connected thereto adapted to supply a stream of -combustible gas mixture thereto to produce a sheath of iiame at least partially surrounding the projection of said central conduit, the improvement which comprises a transverse screen in the discharge end of said central conduit adapted to outwardly diffuse said stream of gas-borne solid material into the space occupied by said sheath.

6. Improvement according to claim 5 in which said central conduit is of enlarged diameter adjacent said screen.

7. Improvement according to claim 6 including air bleeder means extending from the side of said nozzle into the space at the discharge end of said nozzle between said central duct and said sheath, adapted to aspirate air into said space.

8. Improvement according to claim 7 in which said air bleeder means includes an annular groove surrounding said central conduit and at least one duct connecting said groove with the side of said nozzle.

9. Improvement according to claim 5 including air bleeder means extending from the side of said nozzle into the space at the discharge end of said nozzle between said central duct and said sheath, adapted to aspirate air into Said space.

10. Improvement according to claim 9 in which said air bleeder means includes an annular groove surrounding said central conduit and at least on'e duct connecting said groove with the side of said nozzle.

12 11. Improvement according to claim 1 including air bleeder means extending from the side of said nozzle into the space at the discharge end of said nozzle between said central duct and said sheath, adapted to aspirate air into said space.

References Cited by the Examiner UNITED STATES PATENTS 2,510,143 6/1950 Sandora et al. 239-79 3,111,267 11/1963 Shepard 'et al. 239-85 FOREIGN PATENTS 545,275 5/ 1942 Great Britain.

EVERETT W. KIRBY, Primary Examiner.

Claims (1)

1. IN A SPRAY GUN FOR SPRAYING FINELY DIVIDED, SOLID HEATFUSIBLE MATERIAL, A DISCHARGE NOZZLE DEFINING A CENTRAL CONDUIT AND MEANS CONNECTED THERETO ADAPTED TO SUPPLY A STREAM OF GAS-BORNE, FINELY DIVIDED, SOLID MATERIAL THERETO, A SERIES OF JETS AT LEAST PARTIALLY THERETO ADAPTED TO SUPPLY CONDUIT, AND MEANS CONNECTED THERETO ADAPTED TO SUPPLY A STREAM OF COMBUSTIBLE GAS MIXTURE THERETO TO PRODUCE A SHEATH OF FLAME AT LEAST PARTIALLY SURROUNDING THE PROJECTION OF SAID CENTRAL CONDUIT, THE IMPROVEMENT WHICH COMPRISES SAID CENTRAL CONDUIT TERMINATING AS AN ANNULAR,

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