US 3111267 A
Description (OCR text may contain errors)
Nov. 19, 1963 A. P. SHEPARD ET AL 3,111,267
APPARATUS FOR APPLYING HEAT-FUSIBLE COATINGS ON SOLID OBJECTS Filed April 18, 1957 4 Sheets-Sheet l INVENTOR ARTHUR I? SHEPARD FERDINAND J. D/TTR/Ch' BY g Dulu v p ATTORNEYS APPARATUS FOR APPLYING HEAT-FUSIBLE COATINGS ON SOLID OBJECTS Filed April 18, 1957 Nov. 19, 1963 A P. SHEPARD ETAL 4 Sheets-Sheet 2 INVENTORS ARTT/UR F. SHEPARD FERDINAND J. D/TTR/C BY flap, D@(1. o$ }m ATTORNEY 1963 A. P. SHEPARD ET AL 3,111,267
APPARATUS FOR APPLYING HEAT-FUSIBLE COATINGS 0N SOLID OBJECTS Filed April 18, 1957 4 Sheets-Sheet 4 I EFWWM/ PRIOR ART /403 T ar=:.l4.-
INVENTOR ARHVUR P SHEPARD FERDINAND J DlTTR/CH ATTORNEYS United States Patent 3,111,267 APPARATUS FOR APPLYING HEAT-FUSIBLE COATING-S 0N SDLID OBJECTS Arthur P. Shepard, Flushing, and Ferdinand J. Dittrich, Bellmore, N.Y., assignors to Metco Inc, a corporation of New Jersey Filed Apr. 18, 1957, Ser. No. 653,662 3 Claims. (Cl. 239-85) This invention relates to an apparatus for applying heat-fusible coatings on solid objects from heat-fusible materials in divided, such as powdered, form. The invention more particularly relates to a gun construction for spraying heat-fusible material, using a fuel gas and a combustion supporting gas where said material is fed into the gun in finely divided, solid form.
Heat-fusible material spray guns of the powder type are devices in which powdered material is fed 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 a hopper to the heating zone by a stream of gas, in which the finely divided powdered material is entrained.
Such guns are most commonly used for spraying metal powders and hence are frequently referred to as 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 fundamental 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 alloy metals and refractory ceramic materials, including alumina and zirconia.
These guns, which are satisfactory for higher melting point materials, differ from previous powder spray guns it. that they supply the powdered material to the center of the flame at a relatively low velocity and do so by using a relatively small amount of carrier gas in proportion to the solid material carried.
All previously known heat-fusible material spray guns and spraying methods have 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 flow of solid powdered material to be sprayed must be adjusted and controlled very accurately to produce satisfactory coatings. This requires a well trained, highly skilled operator, since it is extremely difiicult 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 if 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 gun adjusted properly. Some operators have been unable to consistently produce satisfactory coatings.
Another limitation of even the most etlicient previously known guns is that they require very accurate grading in 3,1 l 1,26 7 Patented Nov. 19, 1963 a narrow range of the particle size of the material to be sprayed. For instance, with such guns alumina must be graded to a particle size range of from 10 to microns, and zirconia must be graded from 10 to 40 microns. Even when accurately so graded, materials of this type give the ditliculties 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 only 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 to spray refractory powdered materials (including refractory metsis and refractory ceramics) so that consistent hard coatings can be produced without spatter by unskilled operators.
The construction and method in accordance with this invention makes it possible for the first time to spray refractory powdered materials comprising a relatively wide range of particle sizes and particularly finer materials than previously have been sprayable. For instance, when sprayed in accordance with this invention, alumina of a particle size of from 2 to 60 microns, and zirconia of a particle size of from 2 to microns, may be successfully sprayed commercially.
In accordance with this invention carrier gas containing finely 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 the cross-section of said flame.
The spray gun nozzle for effecting the method in accordance with this invention has means for passing a combustible fluid and a combustion supporting fluid, such as gases, with a substantial forward linear velocity for flame combustion from the tip of said nozzle, a carrier gas conduit terminating substantially adjacent said tip of said nozzle, said conduit being positioned and adapted for introduction of carrier gas into the central zone of said flame, and diffuser means in said conduit cooperatively positioned with respect to 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 limitation, the invention will be described in further detail with reference to several preferred constructional embodiments, as shown in the drawings in which:
P16. 1 is a side elevation of one embodiment of a heatfusible material spray gun in accordance with this invention;
FIG. 2 is a vertical longitudinal section of the embodimerit of FIG. 1;
FIG. 3 is an enlarged partial cross-section of FIG. 2;
FIG. 4 is a front elevation of the showing in FIG. 1;
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 77 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. 10 is a cross-section of the nozzle of a heat-fusible material spray gun showing a preferred embodiment of the invention;
FIG. ii is an end view taken in the direction lit-11 of the showing of FIG. ltl;
FIG. 12 is a cross-section of the nozzle of a heat-fusible material gun showing an alternative embodiment of the invention;
FIG. i3 is an end view taken in the direction l3.l3 of the showing of FIG. 12;
FIG. 14 is a schematic diagram illustrating the flame of a previously known heat-fusible material spray gun; and
FIG. 15 is a schematic diagram illustrating the flame of a spray gun in accordance with this invention.
Referring to the drawings, 1 shows the body of the spray gun, on which is mounted the inclined, tubular material hopper 2. Material hopper 2 is held by a saddle 3 (FIG. I) fastened to body 1 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 duct 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 10 and screws 11. A packing washer 12 is provided around nipple 9.
A small piece of rubber tube 13 fits over the lower projecting end of nipple 9 and is held in place by a rubber ring 14. 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, flanged plug is fitted into the bore 20 with a sliding fit and has a flange extending over the end of body 1. 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 39 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 dowell pin 34 is provided between body 1 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 1. 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 with annular groove 36. Body 1 is provided with duct 49 which communicates with hole Body 1 is provided with duct 41 for combustion supporting gas and duct 42 for combustible gas. These duets can be seen by referring to FIG. 5 which also shows more clearly the connecting ducts between ducts 41 and 4 with duct 45).
The connecting duct between 4! 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 oi" these ducts with small steel screws at 45 and 46. Valves 47 and 43 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 5i and 52 respectively.
A valve 53 is provided and mounted on body 1 by means of screws 5-4. The details of this valve construction can best be seen in FIG. 3. A cylindrical bore 55 is provided in body 1 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 64 into which the needle of the needle valve 57 fits. 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 d2 or a similar hole may be provided into duct 41.
Referring to FIG. 2, a 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 defines 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 see tion 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 flow through the rubber tube.
In the open position of rubber tube 13, powder is permitted to flow by gravity from hopper 2 through hole 5, duct 6, the passage in nipple 9, through rubber tube 13, through valve chamber and into powder chamber 19.
When trigger 70 is pulled rearwardly toward 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 additional 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 of cam 92 engages the rear terminus 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 86. 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 85a, 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 for- Ward 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 S 6, and after riding over this projection the spring 78 will cause the cam to snap back, with its lower projection in the cutout 85. The spring 80 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 48 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 first 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 3-7. While the flow of air through holes 38 is very small, it is suificient 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 38 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 flows from conduit 42 through hole 64, through the valve 53, and past neec'ile as, 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 flow through jet hole 31 in jet screw 36. This jet of fuel gas extends across groove 29 and exhausts out through powder conduits 2S and 27 to the center of the flame.
To start the powder feeding, the operator pulls back on tri ier 7%, which opens the powder feed valve as hereinahotc 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 90 from horizontal to practically vertically down.
The end or tip of nozzle 26- (FIGS. 6 and 7) has a counter-bored section 60 1 which comprises a continuation of an enlargement of conduit 27. At the tip of the nozzle and at the terminus of conduit 601 is wire screen 692. Screen 662 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 fit or brazing. Screen 60?. may be of a mesh size of from 20 to but is preferably of a mesh size of from 30 to 50, and is most preferably a 40 mesh screen made from .06 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 837. In this embodiment, however, the internal construction of the nozzle differs from that shown in FIGS. 6 and 7. In this embodiment the nozzle 326 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 counter-bore 001, so that annular passage 803 is provided between plug 802 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 826.
Nozzle 826 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 005 so as to provide an annular conical groove or passage 800. 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 004, 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 P165. 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 H63. 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 100]. 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 be 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 with the 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 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 efficiency of a much higher order, as previously described. Materials of melting points as high as those of molybdenum, among the metals, and alumina and zir conia, among the ceramics, can be satisfactorily sprayed. Another result is substantially increased deposit efliciency.
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 H6. 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 com trary the carrier gas rapidly diffuses into the flame, carry ing 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 1052.
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, afcr 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 flame so that each particle is heated by the flame for a longer per od 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 diificulties that result from uneven carrier gas velocities by providing a substantially even velocity across the cross-section 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 efficiency. 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 finely divided powdered form is provided with a particle size of from 2 to 50 microns. A gun in accordance with the preferred embodiment, as described above, and with a nozzle illustrated in FIGS. 10 and ii, is attached to a source of acetylene, at a pressure of i5 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 flame adjusted to be approximately neutral. The carrier gas valve is opened to approximately 6 clicks of the detent.
A 4" square by /4" thick mild steel plate, which is to be coated on one surface, is first grit-blasted, using a 50%50% mixture of SAE G25 and SAE G40 steel grit, using a suction blast gun in the conventional manner and a blasting air pressure of approximately 80 p.s.i.
The clean surface of the plate is pre-heated, using the gun to a temperature of approximately 250 F.
The powder feed trigger of 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 was 2V2 pounds per hour of mate rial, and the deposit efficiency, which is the ratio of the weight of the solid material fed into the flame to the weight of the deposited coating, was 86%. A strong hard coating resulted.
With previous constructions operated exactly as described in the above example, zirconia of a particle size from 10 to 40 microns would have been required and a deposit efficiency of only 46% would have been obtained and a spraying speed of only 1 /2 pounds per hour would have resulted. More skill would have been required by the operator to produce the hard coating produced in Example 1 without spatter.
The nozzle construction in accordance with this invention is highly satisfactory for spraying tinciy divided metals as well as ceramic materials.
sition is provided in powdered form, with particle size such that all will pass through a 120 mesh U.S. standard screen and not over 30% will pass through a 325 mesh US. standard screen:
A gun as described above and illustrated in the drawing is attached to a source of acetylene at a pressure of lbs. per square inch gauge and a source of oxygen gas at a pressure of lbs. per square inch gauge.
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 /4-thick mild steel plate, which is to be coated on one surface, is first grit-blasted, using a 50%50% mixture of SAE G and SAE G steel grit, using a suction blast gun in the conventional manner and a blasting air pressure of approximately p.s.i.
The clean surface of the plate is pro-heated, using the gun to a temperature of approximately 250 F.
The powder feed trigger of 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 10" from the surface of the plate.
It is desired in this case to have a finished thickness after final grinding of .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 to limit the same.
The foregoing specific description is for purposes of illustration and not of limitation and it is therefore our intention that the invention be limited only by the appended claims or their equivalents wherein we have cn deavored to claim broadly all inherent novelty.
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 mi ure thereto to pro udce a sheath of flame at least par t. lly surrounding the projection of said central conduit, said central conduit terminating in a number of radially divergent passages to outwardly diffuse said stream of gas-borne solid material into the space occupied by said sheath.
2. 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 flame at least partially surrounding the projection of said central conduit, said central conduit terminating in a number of radially divergent passages to outwardly diffuse said stream of gas-borne solid material into the space occupied by said sheath, and comprising, in addition, 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.
3. In a spray gun for spraying finely divided, solid heat-fusiblc 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. 21 series of jets at least partially surrounding said central conduit, and means connected thereto adapted to sup ply 21 stream of combustible gas mixture thereto to produce a sheath of flame at least partially surroundIng the projection of said central conduit, said central conduit terminating in a number of radially divergent passages to outwardly diffuse said stream of gas-borne solid material into the space occupied by said sheath, and comprising, in addition, an air hleeder including an annular groove UNITED STATES PATENTS Brierly May 19, 1953 Charlop et al Jan. 21, 1958 FOREIGN PATENTS Great Britain May 18, 1942 Great Britain Jan. 16, 1952