US2960274A

US2960274A - Wire guide for heat-fusible material spray guns

Info

Publication number: US2960274A
Application number: US835145A
Authority: US
Inventors: Arthur P Shepard
Original assignee: Metco Inc
Current assignee: Metco Inc
Priority date: 1959-08-20
Filing date: 1959-08-20
Publication date: 1960-11-15
Anticipated expiration: 1977-11-15
Also published as: GB876473A; DE1184680B

Description

Nev. 15, 150

A. P. SHEPARD 2,6,274 wmz GUIDE FOR HEAT-FUSIBLEI MATERIAL SPRAY GUNS Filed Aug. 20, 1959 /J I 4 f l5 2.) L 7 tr/6 IN VENTOR ARTHUR P. SHEPARD ATTORNE S WIRE GUIDE FOR I-llEAT-FUSEBLE MATERIAL SPRAY GUNS Shepard, Flushing, N.Y., assignor to Metco Filed Aug. 20, 1959, Ser. No. 835,145

18 Claims. (Cl. 233-83) This invention relates to an improved wire guide for heat-fusible material spray guns. The invention, more particularly, relates to an improved construction for the guide, generally in the form of a bushing, which guides the wire into the heating zone in a heat-fusible material spray gun of the wire type.

- Heat-fusible material spray guns are devices, in which a heat-fusible material is fed into a heating zone where the same ismelted or at least heat-softened and then propelled in finely divided form, as for example against a surface to be coated.

In a heat-fusible material spray gun of the wire type, the heat-fusible material in the form of a rod or Wire (the tenn wire being used generically to define both of these elements) is fed into a heating zone, 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 propelthe same in the form of a spray.

. The most common commercially utilized heat-fusible material spray guns of the wire type are heat-fusible material spray guns utilizing a combustion flame for the heating and a blast gas for atomizing and propelling. Thus,for example, the heat in the heating zone could be generated by the burning of a fuel gas, such as acetylene or propane with air or oxygen, and the blasting could be effected with a blast gas, as for example air, nitrogen or the like.

lnaccordance with one conventional construction, as s'hownin United States Patent No. 2,340,903 of February 8, 1944, the heat-fusible material spray gun is provided witha nozzle having a central wire feeding orifice surrounded by a multiple number of annularly positioned burner jets and has an air cap surrounding the nozzle spaced relationship thereto. A combustible mixture, for example acetylene and oxygen, propane and oxyg'enQace'tyIene. 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 or rod of the heat-fusible material to be sprayed, as for example a wire or rod ofmetalor refractory material, is fed through the central wirefeeding orifice into the flame forming the heating zone. 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.

' Another'less common construction does not provide a blast gas, but the expanding combustion gases are additionallyutilized as a blast gas by allowing the same to expand from a confined combustion zone through a throttle nozzle of to expand through an elongated nozzle or the like.-

' In accordance with newer constructions, the heat for melting or heat-softening the wire is produced by a plasma flame, i.'e. a flame in the energy state above the gas state, with electrons being actually stripped from the'atoms of the material forming the gas. The plasma Patented Nov. 15, 1960 ice is most commonly generated utilizing an electric arc and most commonly a constricted arc. The plasma flame may be used for the spraying in a manner similar to the combustion flame, and a separate blast gas may be used for atomizing and propelling the material being sprayed, if desired.

Other modes have also been known or proposed for generating the heat for the heat-fusible material spray guns. These include electric heating, as for example electric resistance heating or induction heating and ordinary. arc heating. With the use of an ordinary electric arc, two separate heat-fusible material wires may be fed forward at a converging angle and an electric arc struck therebetween. A blast gas may then be propelled against the arc, atomizing the wires as they are consumed and melted in the arc and propelling the atomized material away from the arc in the form of a spray. Alternately, the wire may for example be fed forward through an electric are formed from separate electrodes, as for example consumable carbon electrodes.

In all heat-fusible material spray gulns of the wire type, a guide has to be provided to support, guide and direct the wire as it is fed into the heating zone. This guide is generally in the form of a wire-guiding orifice leading into the heating zone. The wire-guiding orifice has a diameter substantially corresponding to the outer diameter of the wire and is generally in the form of a wire'guide bushing, positioned adjacent the heating zone. The wire is fed forward at the desired feed rate, generally by means of feed rollers driven by any conventional drive means, as for example electric or turbine .drive means, which are usually governed as to the rate of speed. The wire passes through the wire guide bushing into the heating zone and is thus supported as the same is fed forward and accurately positioned in the heating zone, such accurate positioning being necessary for uniform and efficient heating and satisfactory utilization of the blast gas.

In order to provide the necessary guiding, the orifice, such as the bore of the bushing, could not be made too, oversize, and its inner diameter would have to substantially correspond to the outer diameter of the Wire without too much clearance.

In order to ensure an even feeding and prevent sticking and excessive wear of the guide orifice, such as the bushing, the wires are generally provided with a lubricant coating, as for example of oils or soaps. Thus, the lubricant which is inherently present on the wire, as for example that used in the final drawing operation of the wire, could be used for this purpose or the wire could be coated with a separate lubricant. Additionally, many heat-fusible material wires, as for example conventional metallizing wires, are provided with a coating, as for ex ample a natural coating or a special corrosion-preven tion coating. Thus, molybdenum wire, used for metallizing, is furnished with a coating of molybdenum oxide, steel Wire is furnished with a copper plating to prevent rusting, and aluminum and zinc wires have thin coatings of their natural oxides, as do most other materials.

In the operation of the heat-fusible material spray guns of the wire type, after a certain period of operation, the wire would stick and jam in the wire guide orifice, such as the bushing. This would necessitate a shutdown, a removal of the wire and a cleaning out of the bushing, and in some cases a complete'replacing of the nozzle containing this bushing.

The operational period prior to sticking of the wire might vary from a few seconds to several hours. Factors, which influence the tendency to stick, include type of Wire, type of wire finish, wire temper or stiffness; amount of wire lubricant, amount of clearance between wire and nozzle and back-pressure in the heating zone,

Even when all of these factors are kept under dilignet control, wire sticking has been a serious problem in the past, and no satisfactory solution has been found. It was believed by many that this sticking is caused by an accumulation of foreign material, as for example the wire coating or lubricant building up and plugging and jamming the wire intothe guide orifice, such as the orifice of the bushing.

This view seemed to be supported by the observation of a scraping 01f and building up of material behind the orifice. Attempts to overcome this problem by wiping the wire off prior to entrance into the orifice and/ or providing additional lubricant, as for example by tying an oily rag around the rod behind the gun, did not prove satisfactory. In some situations, the sticking problem is somewhat alleviated, but still is a serious one. Thus, for instance, when spraying aluminum wire, the tying of an oily rag behind the gun around the wire could in crease the spraying time between shut-downs, but the sticking and shut-down is not eliminated.

One object of this invention is to overcome the abovementioned difficulties.

A further object of this invention is a novel construction for a wire guide orifice, as for example the orifice through a wire guide bushing, which will prevent the wires sticking or at least substantially increase the time period during which spraying can be effected without sticking. These and still further objects will become apparent from the following description, read in conjunction with the drawings in which Fig. l is a vertical section of the forward portion of a heat-fusible materialspray gun of the wire type having an embodiment of a wire guiding orifice in accordance with the invention;

Fig. 2 is a front elevation of the nozzle of the heatfusible material spray gun shown in Fig. l; and

Fig. 3 is a diagrammatic vertical section on an enlarged scale of an embodiment of a wire guide bushing in accordance with the invention.

In accordance with the invention, I have surprisingly discovered that the long-standing problem of wire-sticking in the operation of heat-fusible material spray guns of the wire type may be substantially, and in most cases completely, eliminated if the outlet end of the wire guiding orifice leading into the heating zone of the spray gun, as for example defined by the wire guide bushing, diverges outwardly in the direction of the heating zone to an increased diameter at its outlet end of D which is equal to K L -i-D wherein D is equal to the normal diameter of said orifice, i.e. a diameter corresponding to the outer diameter of the wire to be used in the gun, L is the length of the divergent portion and K is a value between about 0.035 and 0.54, preferably between about 0.05 and 0.1, and most preferably about 0.07.

The length of the divergent portion L should be at least equal to about /2 D should preferably be about /2 to 1 /3 D and most preferably about equal to D The over-all length of the wire guiding orifice, such as the wire guide bushing, may be conventional and the untapered straight portion of its length, i.e. its total length L -L need only be sufficient to provide the support and guidance required for the wire. For this purpose, a minimum over-all length of at least of an inch is usually required, but in order to prevent undue wear, a length of at least about A; of an inch should generally be provided. An over-all length for L of about 7 of an inch is generally convenient for most conventional metallizing wire sizes.

Referring to the embodiment shown in the drawing, 1 represents the nozzle of a conventional heat-fusible material spray gun of the flame combustion type for spraying heat-fusible material fed in the form of a wire or rod. The nozzle has a central mis wire feeding orifice 2 provided with the wire guide bushing 3, which is pressed or sw-aged in place, and a multiple number of converging, burner jets 4. An annular groove is cut in the rear face of the nozzle and intersects these burner jets 4. The rear face of the nozzle 1 is machined flat at 6 and pressed against a corresponding fiat surface of the gun head 11 by means of the nut 7. The gun head 11 has an annular groove 8 which corresponds to and mates with the groove 5 in the nozzle. A gas feed passage 9 leads into the groove 8. The head 11 also has an axial bore or orifice 10 which corresponds to and mates with the wire feeding orifice 2. Surrounding the head. is a housing 12 and screwed onto the housing is a blast gas cap 13. T he gas blast cap surrounds the nozzle 1 forming the annular blast gas passage 14 therewith.

The bushing 3 is constructed of conventional material, as for example steel, tungsten carbide or ceramic material, and, in accordance with the invention, has the shape as shown in Fig. 3. Thus, the end portion of the wire guiding orifice, defined by the bore of said bushing, diverges outwardly at 15 in the direction of the heating zone. This outward divergence is such that an increased diameter D is formed at the outlet end. This increased diameter in accordance with the invention must be equal to the value K L +D D is the normal inner diameter of the wire guiding orifice, i.e. of the bushing 3, which should correspond to the outer diameter of the wire or rod in connection with which the nozzle is to be used. While this diameter D cannot be under-sized with respect to the diameter of the wire, it may be and is generally preferably several thousandths of an inch oven sized with respect to outer diameter of the wire. length L is the length of the diverging portion as shown in Fig. 3 and should generally be at least /2 D preferably at least /2 to 1% D and most preferably about equal to D K, is a value between about 0.035 and 0.54 and preferably between about 0.05 and 0.1 and most preferably about 0.07.

While, as shown, the divergence at 15 is a straight an gular divergence, i.e. a uniform increase in diameter, the divergence portion may be curved, as for example inwardly or outwardly curved. The shape of the divergence is thus unimportant, so long as the diameter, as increased, would substantially fall within the value K L -i-D wherein L is the length from the beginning of the divergence to any particular point at which the diameter increase in measured or wherein a substantial portion of the divergence will fall within the values given above.

In operation, a rod or wire 16 of heat-fusible material, as for example a conventional metallizing rod or rod of refractory material or the like, is fed through the gun through the orifice 10, the wire feeding orifice 2 and the Wire guiding orifice defined by the wire guide bushing 3 and through the heat zone formed in front of the nozzle 1. The feeding of the wire may be effected in any known or conventional manner, as for example by feed rolls driven by any known or conventional drive means, such as a gas turbine actuated by the blast gas, an electric motor or the like. A combustible gas mixture of, for example, actylene and oxygen, actylene and air, propane and air, propane and oxygen or the like is fed, as for example from a mixing chamber, through the fuel passage 9 and passes into the annular groove 8, whence it passes from this annular groove 8 to the annular groove 5 and thence through the burner jets 4, where the same is ignited in front of the nozzle 1 forming the heating zone. The flame from the jets 4 impinges on the tip of the rod 16 melting the same. A blast gas, such as compressed air, is fed in through the space 17 and passes through the space 18 into the annular passage 14, directing the gas against the tip of the rod 16, atomizing material from this melting tip and propelling the same in the form of a fine spray away from the gun, as for example against a surface to be coated.

With the conventionally constructed wire guide bushings not having the divergence 15, after a period of'operation the wires would stick and jam in the bushing,

The

necessitating a shut-down and cleaning or even replacement of the entire nozzle.

In accordance with the invention, with the provision of the diverging portion 15, this sticking is eliminated or so reduced that operation can be effected for long periods without such sticking causing shut-downs.

It is interesting to note that, if the diverging portion of the bushing is cut off so that the length L is removed, the sticking problem will again arise in the identical manner as if the divergence had not been provided. With the diverging portion cut off in this manner, the area of contact with the wire is no greater than where the diverging portion is provided, and the area where jamming could occur is even less.

The following examples are given by way of illustration and not limitation:

Example 1 In this example, a metallizing gun having a construction corresponding to that shown in Fig. 1 and commercially sold by the Metallizing Engineering Co., Inc. of Westbury, L.I., New York, as a Model K gun was used. The gun was provided with a bushing corresponding to bushing 3, but without the diverging portion 15. The inner diameter of the bushing D was of an inch+.003 of an inch over-size and the ove-all length of the bushing of an inch.

The gun operated with oxygen at 41 p.s.i. and 88 cu. ft./hour, acetylene at 15 p.s.i. and 42 cu. ft./hour and air as the blast gas at 43 p.s.i. A molybdenum wire, 7 of an inch size, provided with a molybdenum oxide coating on which graphite had been rubbed in its final drawing operation was used. Upon spraying, the wire could only be sprayed for intervals varying between about 3 and 15 minutes without sticking. At the end of each of these intervals, the Wire stuck, necessitating removal and cleaning of the bushing.

Example 2 Example 1 was repeated exactly, except that the bushing 3 was of identical construction to that shown in Fig. 3 of the drawing. The bushing had an over-all length L ,i L D =0.191", D =0.200".

In this experiment, the molybdenum rod was sprayed four hours continuously without showing any tendency to stick. Thereafter the experiment was discontinued.

The experiment was again repeated with a bushing identical to the bushing used above in length and size, except without being provided with the diverging portion 15. Here again, as in Example 1, the wire stuck in the nozzle regularly at intervals varying between about 3 and 15 minutes.

Similar experiments, repeated with zinc and aluminum wire of 75 of an inch size and with various other wires of varying sizes, indicated that, when using the bushing constructed in accordance with the invention, there was no tendency of the wire to stick.

While the above specific embodiment has been described in connection with a metallizing gun of the flame combustion type, the invention is equally applicable to any other known heat-fusible material spray gun of the wire type, in which the wire is fed into a heating zone through a wire guiding orifice. Thus, the orifice, specifically the bushing construction in accordance with the invention, may be used with plasma flame guns, are guns and other guns operated with wires or rods in which the wire or rod is fed into the heating zone in which it is melted, through a wire guiding orifice.

While the invention has been described in detail with reference to specific embodiments shown, various changes and modifications will become apparent to the skilled artisan, which fall within the spirit of the invention and scope of the appended claims. The invention is, therefore, only intended to be limited by the appended claims or their equivalents, wherein I have attempted to claim all inherent novelty.

I claim:

1. In a heat-fusible material spray gun of the Wire type having a heating zone and means defining a wire guiding orifice leading into said heating zone, the improvement which comprises the end portion of said wire guiding orifice adjacent said heating zone being outwardly diverging in the direction of said heating zone to an increased diameter at its outlet end of D which is equal to the value K L +D wherein D =the diameter of said orifice L =the length of said diverging portion and K is a value betwene about 0.035 and 0.54.

2. Improvement according to claim 1, in which K is a value between about 0.05 and 0.1.

3. Improvement according to claim I, in which K is a value of about 0.07.

4. Improvement according to claim 1, equal to at least /2 D 5. Improvement according to claim 1, in which L is equal to about /2l% D 6. Improvement according to claim 1, substantially equal to D 7. In the nozzle construction of a wire-feeding heatfusible material spray gun, with a wire-feeding orifice provided with a wire guide bushing, the improvement which comprises the bore of said bushing being outwardly diverging at its outlet end portion to a diameter D which is equal to a value K L -l-D wherein D equals the diameter of the bore of the bushing, L equals the length of the diverging portion of the bushing and K is a value between about 0.035 and 0.54.

8. Improvement according to claim 7, in which K; is a value between about 0.05 and 0.1.

9. Improvement according to claim 7, in which K is a value of about 0.07.

10. Improvement according to claim 7, in which L equals at least /2 D 11. Improvement according to claim 7, in which L equals /21% D 12. Improvement according to claim 7, in which the nozzle construction has a multiple number of burner jets substantially surrounding the axis of said orifice and a blast gas cap surrounding the nozzle.

13. A wire guide bushing for a heat-fusible material spray gun having a bore outwardly diverging at one end thereof to an increased diameter, D which is equal to the value K L -i-D wherein D is the diameter of said bore, L is the length of the diverging portion and K is a value between about 0.035 and 0.54.

14. A bushing according to claim 13, in which K equals 0.05 to 0.1.

15. A bushing according to claim 13, in which K equals about 0.07.

16. A bushing according to claim 13, in which L equals at least /2 D 17. A bushing according to claim 13, in which L equals /2-133 D 18. A bushing according to claim 13, in which L is substantially equal to D in which L is in which L is References Cited in the file of this patent UNITED STATES PATENTS 2,340,903 Shepard Feb. 8, 1944 2,397,165 Shepard Mar. 26, 1946 2,648,567 Brennan Aug. 11, 1953 FOREIGN PATENTS 568,641 Great Britain Apr. 13, 1945