US 3122321 A
Description (OCR text may contain errors)
Feb. 25, 1964 c. K. WILSON ETAL FLAME SPRAY GUN NOZZLE EXTENSION CHARLES K WILSON Filed July 8, 1960 gal w INVENTORS ARTHUR R SHEPARD WALTER A. S/EBE/N FERDINAND J D/777EJCH A ORN 5 United States Patent 3,122,321 FLAME SPRAY GUN NOZZLE EXTENSEGN Charles K. Wilson, East Williston, Arthur P. Shepard,
Flushing, Walter A. Siebein, Smithtown, and Ferdinand Ll. Dittrieh, Bellmore, N.Y., assignors to Metro, lire,
a corporation of New Jersey Filed July 8, 1960, Ser. No. 41,624 11 Claims. (Cl. 239-84) This invention relates to a new and improved nozzle extension for a flame spray gun.
A flame spray gun is a device in which a heat-fusible material is melted, or at least heat-softened, by the heat produced from a flame and then propelled in finely divided form, as for example against a surface to be coated.
In flame spray guns of the wire type the heat-fusible material, in the form of a rod or wire (the term wire being used generically to define both of these elements herein and in the claims), is fed into a heating zone where heat is produced by a flame and in which the tip of the wire is melted or at least heat-softened. A blast gas is directed against the tip of the wire thus heated in order to atomize fine particles from the wire and propel the same in the form of a spray.
The most common commercially utilized flame spray guns of the wire type utilize a combustion flame for the heating. Thus, for example, the heat in the heating zone may be generated by burning a fuel gas, such as acetylene or propane, with air or oxygen. The blast gas used to atomize the heat-fusible wire may, for example, be an, nitrogen or the like.
A conventional flame spray gun is, for example, described in US. Patent 2,340,903 of February 8, 1944. This gun is provided with a nozzle having a central wire feeding conduit or orifice surrounded by a multiple number of annularly positioned burner jets and has an air cap surrounding the nozzle in spaced relationship thereto. A combustible mixture, as for example acetylene and oxygen, propane and oxygen, acetylene and air, propane and air, or the like, is fed through the burner jets and ignited in front thereof, forming a heating zone. A wire of heatfusible material to be sprayed, as for example a metal wire or a rod of refractory material, is fed through the central wire feeding orifice into the flame. A blast gas, such as air, is passed through the blast gas cap, causing a gas impingement on the tip of the wire which is being melted in the flame, atomizing fine particles from this tip, and propelling the same away from the gun.
In accordance with newer constructions the flame Which produces the heat for melting or heat-softening the wire, is a plasma flame, i.e., a flame in the energy state above the gas state, with electrons being stripped from the atoms of the material forming the gas. The plasma is usually generated by means of an electric arc, and most commonly a constricted arc.
For various purposes it is often necessary or desirable to use flame spray guns which are provided with nozzle extensions. Nozzle extensions are simply elongated tubes connecting the nozzle and the remainder of the gun body, so that in eflect the nozzle is positioned on the end of an extension and has a longer reac and may be inserted in places which would not be accessible without such an extension. Thus, for instance, in the spraying of the interior of tubes and cylinders, it has been the general practice to use nozzle extensions and angularair caps. The nozzle extension allows the insertion and manipulation of the spraying nozzle in the interior of the tube or cylinder, and the angular air cap deflects the spray, directing the same against the side wall of the tube or cylinder. In most constructions the nozzle extension is in the form of an outer extension of air tube, one end of which is 3,122,321 Patented Feb. 25, 1964 ice connected to the gun proper, with the nozzle being mounted on the other end. The normal blast gas conduit from the gun body leads to this tube and the nozzle is so mounted on the end of the tube that the blast gas passing through the tube will pass through the blast gas cap in the conventional manner. Axially positioned within the center of this air tube is a concentrically mounted tube, usually constructed of metal, which coaxially interconnects the wire feed orifice of the nozzle and the Wire feed orifice of the gun body proper. Parallel tubes are positioned on either side of this central tube and interconnect the fuel and combustion supporting gas passages of the gun body and nozzle. It was the general practice to rigidly connect all of these tubes to the gun body and nozzle. In operation, however, a good deal of trouble was encountered, caused by warpage of the entire assembly due to differential expansion of the tubes.
In the operation of the flame spray gun with the nozzle extensions, difficulties were also encountered due to the condensation of water in the central wire guide tube. In order to obtain eflicient melting and spraying it was necessary that some of the heat from the flame be blown back, at least a short distance, into the nozzle around the wire. With a suflicient blow-back to obtain the necessary preheating, the combustion products would condense, forming water. The formation of this water would often interfere with eflicient spraying and would sometimes spurt out of the gun and spoil the work.
en spraying brittle =wire, such as ceramic rods, the rods would often break and/or crack as the same were passed through the nozzle. This breaking and cracking would seriously interfere with operation and successful spraying.
One object of thi invention is a novel nozzle extension for a flame spray gun which avoids the above mentioned disadvantages.
A further object of this invent-ion is a novel nozzle extension which prevents the previously encountered rod breakage during spraying.
These and still further objects will become apparent from the following description read in conjunction with the drawings in which:
FIG. 1 is a partial vertical section of an embodiment of a flame spray gun with a nozzle extension in accord auce with the invention;
FIG. 2 is a cross-section of the embodiment shown in FIG. 1;
FIG. 3 is a further cross-section of the embodiment shown in FIG. 1; and
PEG. 4 is an elevation partially in section showing a further embodiment of a wire guide tube for the nozzle extension in accordance with the invention.
The nozzle extension to which the invention is directed is a nozzle extension for a flame spray gun of the type having a tube defining a wire feed passage,'i.e., a wire guide tube extending axially therethrough. In accordance with the invention it has been surprisingly discovered that the prior art difiiculty of wire breakage, particularly refractory rod breakage, can be avoided while at the same time avoiding other disadvantages, if the wire guide tube is an insulated tube having a heat conductivity of not more than 360 B.t.u./hr./ F./sq. ft. and if means are provided for heating the inner surface of this tube at the outlet end portion thereof. The heat conductivity of the insulated tube is preferably less than B.t.u./hr./ F./sq. ft. and generally around 25 B.t.u./hr./ F./ sq. ft. The means for heating the inner surface of the tube at the outlet end portion is preferably means for causing a portion of the flame to be blown back into the nozzle around the wire, the degree of blowback being controlled by at least one bleeder hole extend ing through the nozzle communicating the .wire guide orifice and the space within the air cap through which the blast gas is directed. Thus the air cap may be so constructed that it is possible to maintain a positive pressure therein, and this positive pressure in conjunction with the bleeder hole causes a portion of the flame to be blown back a controlled short distance into the nozzle around the wire in the manner described in US. Patent 2,361,420.
In accordance with a further embodiment of the invention, in order to prevent previously encountered warpage, the wire guide tube is only rigidly connected at one end and provided with a sliding fit at the other end, as for example with the use of gaskets, such as rings. Thus, the wire guide tube may be rigidly connected to the nozzle as, for instance, by a brazed or screw fit and mounted in the gun body with a sliding fit, for example by being sealed by a silicone rubber O-ring. This latter construction is particularly desirable in connection with the insulated wire feed tube as the same may have a tendency to be more brittle than conventional uninsulated tubes and/ or the expansion differential as compared with other elements may be greater than with an uninsulated tube.
Referring to the embodiment shown in the drawings, 1 represents the flame spray gun body proper, 2 the nozzle extension and 3 the nozzle proper. The flame spray gun body proper is of the well known and conventional construction and has means (not shown), for example conventional feed rolls, driven for instance by a gas turbine, electric motor or the like, for feeding a wire through the orifice 4. Oxygen or air from a suitable pressure source is fed through the passage 5 and a fuel gas, such as acetylene or propane, is fed through the passage 6. The pressures and rates of flow may be controlled in the conventional manner by valves (not shown) provided on the gun body or separate therefrom. A blast gas, such as air, is passed through the passage 7. The extension is held in place by means of the screw cap 8 and consists of an outer tube body 9, of metal, often referred to as an air tube. A central coaxial tube 10, referred to as a wire guide tube, a tube 11 for the combustion supporting gas, such as air or oxygen, and a fuel gas tube 12 are positioned within the air tube 9. The rear end of the nozzle extension is provided with the disc 13, to which the tubes 11 and 12 are rigidly connected, as for example by brazing. This disc 13 has a passage 14 which mates with the tube 11 and a passage 15 which mates with the tube 12. The rear end of the disc 13 is machined flat and pressed in contact with a correspondingly flat, machined surface 16 on the gun head. The wire guide tube extends through the disc 13 into the gun body with a sliding fit and is sealed at its inner end by means of the silicone rubber O-ring 45. The oxidizing gas passage 5 communicates with a passage 17 extending through the gun head, which in turn communicates with the passage 14. The fuel gas passage 6 communicates with a passage 18 in the gun head, which in turn communicates with the passage and tube 12. The cap 8 holds the extension tube in place due to contact with the flange 19 riveted to the air tube. One or more passages 20 communicate the space within the interior of the cap 8 and the interior of the air tube 9, so that a blast gas passed through 7 will flow through the openings 20 and through the interior of the air tube 9.
The nozzle assembly 3 on the other end of the nozzle extension consists of the air cap body 21, the angular air cap 22, the nozzle body 23 provided with the burner jets 24 and central wire feed orifice 25. A nozzle connecting body 26 is provided on the forward end of the extension. This nozzle connecting body is not directly attached to the air tube 9 but is connected to the tubes 10, 11 and 12, as for example with brazed joints. This nozzle connecting member corresponds to the gun head construction which is mounted directly on the gun against the face 16, when an extension is not used. The connecting member is provided with the passage 27 which is in flow communication with the oxidizing gas tube 11, and which leads to an annular groove 28. The connecting member is also provided with a passage 29 connected to the fuel gas tube 12 which leads to the groove 30. A central wire guide orifice 31 is connected as an extension of the wire guide tube 10. A multiple number of passages 32 extend radially to the groove 28 and a multiple number of radial passages 33 extend to the groove 30. Small jet passages 34 interconnect these radial passages and lead to the combustible mixture passage 35, which terminates at the groove 36, at the forward flat face of the connecting member. The nozzle body 23 is screwed against the forward flat face of the connecting member by means of the nut 37, so that the groove 36 mates with the burner jets 24. The air cap 22 is screwed in place by means of the air cap body 21, which in turn is screwed to the air tube 9. The grooves 28 and 30 are sealed to form closed passages by means of the sleeve 38, which is slid in place and held in a gas-tight manner by means of the O-n'ng gaskets 39. The SlfiBVf is prevented from sliding out of place by means of the set screw 40. A bleeder hole 42 connects the wire guide orifice 31 and the interior of the 7 air cap body 21.
The wire guide tube 10, as shown, is formed of a stainless steel tube 43 insulated with asbestos cement 44, so that the same has a heat-conductivity of not more than 360 B.t.u./hr./ F./sq. ft.
The heat-conductivity of any material may be expressed in terms of B.t.u./hr./ F sq. ft. of area/inch of thickness. The heat-conductivity of the structure as a whole may thus be obtained by dividing this heat-conductivity value of the material by the actual thickness of the tube, and it is this value which the not more than 360, and preferably not more than B.t.u./hr./ F./sq. ft. represents. This value is for the total actual structure which may be insulated in any manner. Thus, for example, in place of the plain insulated tube, a double tube, as is shown in FIG. 4 with an insulating air space therebetween, may be used, and the value is the value for the composite structure.
In operation the heat-fusible material wire to be sprayed, as for example a metal or ceramic rod or wire, is fed through the passage 4 in the conventional manner, for instance by feed rolls driven by a gas-driven turbine, electric motor or the like, passes through the wire guide tube 10, through the passage 31, and wire guide orifice 25, to in front of the nozzle body. An oxidizing gas, such as air or oxygen, is passed through the passage 5, passes through the passages 17 and 14, through the tube 11, the passage 27, the groove 28 and through the jet passage 34. A fuel gas, such as acetylene or propane, is passed through the passage 6, passes through the passages 18 and 15, through the tube 12, through the passage 29 to the groove 30. The stantially high velocity through the jet passage 34, picks up the fuel gas by venturi action, forming a combustible mixture which passes through the passage 35 and burner jets 24, being ignited in the form of a burner flame in front of the nozzle body 23, melting the tip of the wire. A blast gas, such as air, is passed through the passage 7, passes through the opening 20, through the interior of the air tube 9, the air cap body 21, the openings 46 and through the air cap 22, impinging on the tip of the melting wire, atomizing and propelling the molten heat-fusible material in the form of a spray. The angular air cap 22 deflects the spray at an angle of about 45 so that, if the gun nozzle at the end of the nozzle extension is inserted in a tube or cylinder, the interior wall of this tube or cylinder may be sprayed in the conventional manner. In place of the angular air cap 22 a conventional straight air cap may be used if it is not necessary to defleet the spray, or any other known angular air cap may be used, as for example the air cap described in United States application, Serial No. 38,031, filed June 22, 1960.
Very surprisingly, with the construction in accordance oxidizing gas, passing at sub with the invention, the prior art difiiculties are not encountered. Thus, with the new construction in accordance with the invention, brittle wire, such as rods of alumina or zirconia, may be sprayed without the previous difficulty of cracking or breaking. Furthermore, the formation of water in the wire guide tube is avoided, along with the avoidance of the difiiculties caused by the formation of this water. With the sliding fit of the wire guide tube the problems of Warpage are completely avoided.
The construction in accordance with the invention, with the provision of the sleeve 38 which forms with the grooves 28 and 30 the enclosed, sealed annular gas flow passages, allows the construction of the extension to be kept to a minimum size and greatly facilitates construction and maintenance as compared with prior art construction. Cleaning is thus greatly facilitated by the easy removal of the sliding fit, whereas in the prior art constructicn portions which now become available by removin g the sleeve, were inaccessible.
By way of a specific example given for purposes of illustration and not limitation the wire guide tube is constructed of type 304 stainless steel having a outer diameter and .305" inner diameter. Prior to assembly a braided asbestos sleeve woven from approximately 5 diameter asbestos cord is slipped over the wire guide tube 10 and loosely held in place during silver brazing of the entire assembly, including tubes 11 and 12, which are constructed of A outer diameter brass tubing. After the brazing of the assembly the asbestos sleeve is stretched taut and the braid filled with commercial zirconium base low expansion cold-set refractory cement (Sauereizen #29). The total thickness of the insulating layer, including both the braided asbestos cord sleeve and the refractory cement, is to While the invention has been described in detail with reference to certain specific embodiments, various changes and modifications which fall within the spirit of the invention and scope of the appended claims will become apparent to the skilled artisan. The invention is therefore only intended to be limited by the appended claims or their equivalents, wherein we have endeavored to claim all inherent novelty.
1. In a nozzle extension for a flame spray gun having a tube defining a wire feed passage extending axialy therethrough, the improvement which comprises said tube being an insulated tube having a heat-conductivity of not more than 360 B.t.u./hr./ F./ sq. ft. and means for heating the inner surface of said tube at the outlet end portion thereof.
2. Improvement according to claim 1 in which said tube has a heat-conductivity of not more than 100 B.t.u./hr./ F./sq. ft.
3. Improvement according to claim 1 in which said tube has a heat-conductivity of about B.t.u./hr./ F./ sq. ft.
4. Improvement according to claim 1 in which said means for heating the inner surface of said tube at the outlet end portion thereof is means for blowing back a portion or" the flame from a nozzle of a flame spray gun in connection with which the nozzle extension is used.
5. Improvement according to claim 4 in which said means for blowing back a portion of the fiarne includes at least one bleeder hole extending through said tube.
6. Improvement according to claim 5 in which the heatconductivity of said tube is less than B.t.u./hr./ F./sq. ft.
7. Improvement according to claim 1 in which said tube is a double-walled tube having an insulating space between said double walls.
8. Improvement according to claim 1 in which said nozzle extension comprises a cylindrical outer air tube with said insulated tube concentrically coaxially positioned therein, and with an axially extending oxidizing gas tube positioned at one side of said insulated tube and an axially positioned fuel gas tube positioned on the other side of said insulated tube.
9. Improvement according to claim 1 in which said tube is rigidly mounted in said extension at one end portion and slidably mounted for axial movement upon expansion and contraction at the other end portion.
10. Improvement according to claim 1 in which said extension has a nozzle attaching member at its forward end defining a first and second gas flow passage, flowcommunicated at a peripheral groove defined in said memher, and a sleeve mounted for sliding removal surrounding said groove, forming therewith an enclosed, sealed annular gas flow passage.
11. Improvement according to claim 10 in which said nozzle attachment member defines an axially extending fuel gas and oxidizing gas passage therein, the oxidizing gas passage leading into a first annular groove defined in said member, a multiple number of axially extending jet flow passages defined in said member, in flow communication with said first annular groove and leading into an axially extending combustible gas mixture passage defined in said member, the fuel gas passage leading into a second annular groove defined in said member, flow connected with the outlet ends of said jet flow passages and inlet end of said combustion gas mixture passage, and a sleeve mounted for sliding removal surrounding said first and second grooves, forming therewith enclosed, sealed annular gas flow passages.
References Cited in the file of this patent UNITED STATES PATENTS 1,725,012 Meurer Aug. 20, 1929 2,040,030 Snyder et al May 5, 1936 2,340,903 Shepard Feb. 8, 1944 2,361,420 Shepard Oct. 31, 1944 2,643,955 Powers et al June 30, 1953 2,659,623 Wilson Nov. 17, 1953