GB1563930A

GB1563930A - Flame spray torch

Info

Publication number: GB1563930A
Application number: GB3957976A
Authority: GB
Original assignee: Eutectic Corp
Current assignee: Eutectic Corp
Priority date: 1976-09-23
Filing date: 1976-09-23
Publication date: 1980-04-02

Description

(54) FLAME SPRAY TORCH (71) We, EUTECTIC CORPORATION, a corporation organized and existing under the laws of the State of New York, U.S.A. with an office at 40-40 172nd Street, Flushing, New York, U.S.A., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to flame spray torches and, in particular, to an improved nozzle construction for said torches.

It is known to spray metal powder by means of an oxyacetylene flame wherein the metal powder is deposited in the flame and the powder propelled thereby to a metal substrate, the metal powder melting or fusing in flight such that it bonds to the metal surface to form a metal coating thereon having desired properties, such as resistance to corrosion, resistance to wear and other useful chemical and physical properties.

The powder generally has a particle size range and may involve an alloy powder or a heterogeneous mixture of two or more powdered metals. Thus, where the powder is heterogeneous and/or has a particle size range, the powder spray should be as uniform as possible to minimize segregation in flight since this adversely affects the spray pattern and hence the quality of the deposited metal coating.

The manner in which the powder is dropped into the flame is important and this is brought out in U.S. Patent No. 3,352,492 in the name of Arthur T. Cape, said patent having issued on November 14, 1967. In this patent, the nature of the oxyacetylene flame is discussed, the flame being described as being constituted of an inner cone of unburned gases and an outer relatively cool zone in which all the carbon is consumed and the color of which is bluish. In feeding the powder into the flame, it is preferably dropped into the bluish cone at a point about one-third of the distance from the end of the nozzle or tip to the end of the bluish cone. This enables the powder to be carried by the flame to a maximum distance to the receiving metal substrate with the desired spray pattern. When the powder is dropped into the flame outside of the aforementioned flame region, the distance of travel of the powder is reduced.

The purpose of controlling the position of feed of the powder into the flame is to provide a more uniform or equal distribution of powder with respect to the flame and with respect to the metal substrate receiving the coating.

Over the past several years, the trend has been in the development of various types of powders for specific uses in powder metal spraying. Such powders generally had different flow characteristics which had an effect on spray pattern and density of the powder spray. In order to compensate for the differences in powder characteristics and assure the desired spray pattern, attempts were made to develop torches to enable the use of a wide variety of powders that could be fed in a direct and simple amnner by gravity to the proper location in the flame under conditions to inhibit segregation of the powder during transport to the flame.

A torch which was developed having the foregoing characteristic is described in U.S.

Patent No. 3,620,454 (issued November 16, 1971) which is assigned to the same assignee.

This torch is capable of handling powders of different characteristics, including powder mixtures which react exothermically and generate heat during metal spraying. Such powders are particularly useful in producing a bond coat which serves as a foundation layer for receiving and anchoring other metal powders used in producing a final coat. It is important that the powder used for the bond coat be applied with the right spray pattern to assure maximum bonding over the area of the metal substrate being coated.

Flame characteristic is another important variable in achieving the desired spray pattern. Thus, there should be a relatively smooth flow of gases with minimum turbulence which will smoothly carry the powder to and firmly apply it to the metal substrate without adversely affecting the spray pattern in flight. A disrupted or turbulent spray pattern may re sult in less than adequate adhesion to the metal substrate, particularly with regard to the application of a bond coat using powder mixtures which react exothermically in the flame during flight to the metal substrate.

Present day nozzles are designed to provide as smooth a flame as possible. Such nozzles generally have a plurality of gas flow orifices at the tip of the nozzle, the tip terminating into a flat face through which the orifices emerge. While such nozzles have been very successful, they are subject in the field to flashback when the top, through inadvertence, is caused to touch a workpiece or an element of a workframe or bench such that the orifices are blocked off, whereby flashback may occur which can be dangerous to the operator. The reason flashback can occur is that the fuel gas and oxygen are mixed in the nozzle chamber before the gas mixture is ignited. Thus, when the flame outside the nozzle is blocked off, the flame recedes or backs up into the mixing chamber and becomes hazardous. Thus, an improved torch should include the added feature of being substantially flashback-proof.

While the torch described in U.S. Patent No. 3,620,454 has been a marked improvement in achieving some of the foregoing objectives, further improvement in flame control, flashback, spray pattern and the like would be desirable, particularly with regard to spray powders which have been developed for use in a variety of applications.

It has now been found that the foregoing can be achieved by the use of nozzle construction which provides better flame control, which is designed to prevent flashback and which improves spray pattern as evidenced by the quality of bond coat obtained.

Thus the invention provides a flame spray torch comprising means for supplying powdered metal through a flame from a gas nozzle to a workpiece, the torch having a gas nozzle having a hollow cylindrical body defining a gas chamber and a converging generally frustoconical nose, there being a plurality of gas-conducting passages passing through the nose from the gas chamber and terminating in the conical surface of the nose as orifices which lie in a ring axially of the nozzle, and the torch further comprising means for supplying combustible gas to the gas chamber.

We have found that the nozzle used in the torch of the invention gives improved flame stability, and helps in preventing flashback during use. The nozzle gives improved powder spray pattern during use and improved laminar flow.

The intersection of each of the emerging orifices with said surface may define either a circle or substantially an elliptical opening.

For example, the conical nose may have an annular step or shoulder transverse to the axis of said nozzle at which the orifices terminate, each of said orifices defining a circle.

It has been found that by having the gasconducting passages terminating in the conical surface of the nose of the nozzle and not in the flat end of the nose, a smoother, more stable and quieter flame is obtained.

The invention will be further described below with reference to the accompanying drawings, wherein: Figs. 1 to 3 are illustrative to one embodiment of the improved nozzle used in the invention; Figs. 4 and 5 depict a prior art nozzle which tends to cause flashback during use when the tio thereof inadvertently contacts a workpiece or an element of a workframe or bench; Fig. 6 is a cross-section of part of a nozzle nose used in the invention Fig. 7 is a cross-section of part of a nozzle nose having a conical surface with a step or shoulder therein and Fig. 8 shows one embodiment of a metal spraying torch of the invention.

Referring to Fig. 1, a hollow nozzle 10 is shown having a tapered nose 11 as shown, said nozzle having an inner bore 12 located axially therein which communicaes with and defines a gas chamber with an outer bore 13 of slightly larger diameter which is connectable to a stem (not shown) through which the gas mixture is fed into nozzle 10. The nozzle which is preferably made of tellurium copper has a series of annular grooves or fins 14 at the coupling end thereof to serve as cooling radiators to control the temperature of the nozzle.

The frustoconical nose 11 has a flat end 1 lA, which constitutes a flat circular face as shown. The end wall 16 of the bore including nose 11 is fairly thick relative to the size of the nozzle and it is through this end wall and the nose that gas-conducting passages 15 pass.

The thick end wall also behaves as a heat sink in conducting heat away from the nose of the nozzle. The gas-conducting passages are disposed radially about the axis of the nozzle and pass through the conical surface a short distance A short of end 1 1A to form elliptical orifices on the conical surface as shown in Fig. 1. In the end view shown in Fig. 2 looking towards the tip end 11A, it will be noted that the orifices in the conical surface of the nose of the nozzle lie substantially in a circle.

Thus, when an oxyacetylene gas mixture enters the gas chamber defined by bores 12 and 13 and passes through the orifices and is ignited as shown in Figure 3, a plurality of uniform jets 19 is formed, each jet having an inner cone 17 of unburned gas and an outer cone 18 having a bluish color. By having the jets emit from the inclined face of the nose rather than directly from the end as is the practice, a more stable flame is provided which is not extinguished when the end 1 lA of the nose of the nozzle touches an interfering surface, since the orifices are back from the end. It is also believed that the conical surface provides a more streamlining effect of the air aspirated along flame edges as compared to eddy currents which are apt to occur using a flat-tipped surface for the orifices as shown in the prior art nozzle depicted in Fig. 4, which shows a similar nozzle 20 having cooling fins 21 and a conically shaped nose 22 which terminates into a flat end having a plurality of orifices 24.

The nozzle 10 of Figs. 1 to 3 is also fairly thick-walled at 1 0A to provide a good path together with end wall 16 for the heat generated by the gas jets during spraying so that the temperature of the nozzle does not rise to above critical limits. The orifices 15 in the conical face of nose 11 are positioned a distance A from the end I IA according to the length C of the conical nose. Thus, the distance A from the end measured along axial length C of the nose may range from about 8% to the limit imposed by the diameter of the gas chamber, and, more preferably, from about 10% to 25% of the axial length of the nose.

The angle B made by the surface of the nose with the axis of the nozzle is preferably about 45". However, the angle may range from about 20 to 60 and, more preferably, from about 30 to 50". A typical nozzle is one measuring in total length about 1-642 inches, with the length C of the nose measuring about 0-230 inch, the angle B of the nose being about 45". The diameter of the nozzle is about 0 750 inch, the inner bore about 0-468 inch in diameter, the large bore about 0 504 inch in diameter, the circular flat and or face 11A having a diameter of about 0 343 inch.

The orifices each have a diameter of about 0-031 inch, eight regularly spaced passages being drilled through the end wall 16 and being either parallel to or at an angle to the axis of the nozzle.

Reference is made to Fig. 6 which shows a fragment of a nozzle 10B in cross section showing passages 1 5A passing generally axially through the nozzle but being inclined towards axis A-A thereof as shown.

In Fig. 7, a nozzle fragment 10C is shown with the conical nose 11 B interrupted by an annular step or shoulder at which the passages terminate, the step being shown at right angles to the axis B-B of the nozzle.

A particularly useful flame spray torch shown in Fig. 8 The flame spray torch 25 shown is adapted for gravity feed of metal powder directly to the flame issuing from the nozzle.

The torch has a housing in the shape of a five-sided polygon with one leg of the polygon arranged as a handle portion 27, another leg as a base portion 28, a further leg as a feed portion 29, and another leg of the polygon as the top portion 30 of the torch. The housing 26 has coupled to it a powder feed assembly 31 and a flame assembly 32 to which is coupled the nozzle 33.

The top portion 30 is provided with a fitting 34 adapted to receive a receptacle 35 for holding the alloy powder, a metering device being employed to control powder feed comprising a feed actuator plate 36 slidably mounted in a slot 37 located in the housing top port 30 below fitting 34. Feed plate 36 is provided with a knob 38 which protrudes upwardly above the housing and permits the sliding of feed plate 36 reciprocally toward and away from housing feed portion 29.

It is known that metal powders used in metal spray torches vary in composition and in particle size from approximately 25 mesh to finer sizes and that such powders have different flow rates. Optimum powder spray results for particular applications are obtained within specific powder spray densities which are determined by powder flow rates.

Best results are obtained by direct gravity flow which are determined by experimentation for each powder. Thus, it has been found that powder flow and spray rates for powderflowingby gravity unhindered through circular orifices in sizes ranging from 0 075 to 0-120 inch for different alloy powders can be maintained substantially constant over a mesh size range of minus 50 to plus 400 mesh.

In achieving the desired flow rate, feed plate 36 is selectively aligned with powder flow orifices 39 to control variably the flow rate of the powder from receptacle 35 through flow orifice 39 through conduit 40 and through variable spray control assembly 41.

Assembly 41 has a housing 42 which holds a powder feed tube 43 and having a central core hollow cylinder 44 slidably and telescopically fitted within feed tube 43 and communicating directly with powder flow conduit 40 to deliver powder directly by gravity to feed tube 43 through discharge end 45. A portion of the outer surface of feed tube 43 is provided with indexing means or grooves 46 which through latching assembly 47 enables the setting of powder feed tube 43 in order to locate discharge end 45 at the correct distance from the flame end of nozzle 33. The latching assembly comprises a holding pin 48 that is normally urged toward one of the indexing grooves 46 by spring 49, the holding pin 48 being actuated by rod 50 in making the setting. Thus, by depressing rod 50, the pin is moved out of contact with one of the indexing grooves and tube 43 set according to the desired position. This position can be set at the factory and may not require further setting later.

The flame assembly 32 is supported by sliding element 51 which can be lockingly moved along a track 52 located at the bottom leg of housing 26, a locking pin 51A being provided as shown. Gas flow tube 53 is fixedly held by sliding element 51 and may be factory set, one end of the tube having a connector 54 for attaching to a source of oxygen and acetylene.

By employing the nozzle 33 of the invention with a gavity feed torch of the foregoing type as one example of use, it being understood that the nozzle may be used with other powdered metal torches as well, unexpected results are achieved which add to the inherent advantages of this type of torch. This will be apparent from the following test conducted with the torch arrangement shown in Fig. 8.

Several tests were conducted, (1) with a prior nozzle shown in Figs. 4 and 5 hereinafter referred to as the standard nozzle, and (2) with the nozzle used in the invention illustrated in Figs. 1 to 3.

In a first test, a standard oxyacetylene flame was produced as would normally be used for flame spraying, except that powder was not fed through the flame for use in the flashback test. In the case of the standard nozzle (Fig.

4), the tip thereof was touched against the surface of the workpiece which resulted in an immediate flashback when the orifices were blocked off. In the case of the nozzle used in the invention, the same test showed no flashback whatever and, moreover, the flame did not extinguish but stayed lit at the end of the tip where it should be.

The so-called standard nozzle (Fig. 4) had the same number and size of orifices discussed hereinabove with regard to the nozzle used in the invention, that is, eight orifices having a diameter of about 0-031 inch. In comparing the flames of each nozzle before metal spraying, the flame issuing out of the nozzle used in the invention and under the same gas-flow conditions was quieter. The noise level of the standard tip or nozzle was measured at about 93 decibels while that of the nozzle used in the invention was 85 decibels. This is a large improvement (approximately 102o less noise) when it is considered that the spray pattern of the powder is very sensitive to flame conditions.

Although the flame envelope of the nozzle used in the invention is the same length, it is narrower, more symmetrical and tends to be less divergent, that is, does not tend to spread out as much. The flame appears more stable and tends to flutter less, particularly with respect to the tips of the inner zone. The nozzle does not show the pulsating action of the standard nozzle.

Morever, the inner cores are more pointed and decidely less bulbous, which characteristic is an indication of stability and balance.

The temperature of the nozzle in service is essentially similar to the aforementioned standard nozzle. After one minute of use, the nozzle temperature is about 1800F; after 3 minutes, about 240"F; and after 8 minutes, it attains a maximum steady state temperature of 280"F, which temperature did not exceed 280"F after 15 minutes.

Another test conducted was the spray test.

In this test, a rate and deposition efficiency was determined using a gas regulator setting of 4 psi C2H2 and 8 psi 02, the gases being fed to the nozzles at a flow rate of 23 C. F.H.

(cubic feet per hour) of 2 and 36 C.F.H. of C,H2.

A bond coat powder was sprayed comprising a mixture of nickel powder and an exothermic reacting metal powder onto a roughened mild steel plate using the standard nozzle in one test and the nozzle used in the invention in another test. Because of the nature of the powder, a reaction occurs in the flame which results in an increase in spray temperature of the nickel particles which deposit on and bond to the steel surface. After the bond coat is applied, an aluminum bronze powder is then sprayed over the bond coat.

The final coating produced with the nozzle used in the invention exhibited a better quality than the coating with the standard nozzle.

The nozzle used in the invention also provided improved bonding of the bond coat of over about 5% which adds further to the final quality of the coating. The rate and deposition efficiency was 90% at a spray rate of 581 Ibs/hour.

WHAT WE CLAIM IS: 1. A flame spray torch comprising means for supplying powdered metal through a flame from a gas nozzle to a workpiece, the torch having a gas nozzle having a hollow cylindrical body defining a gas chamber and a converging generally frustoconical nose, there being a plurality of gas-conducting passages passing through the nose from the gas chamber and terminating in the conical surface of the nose as orifices which lie in a ring axially of the nozzle, and the torch further comprising means for supplying combustible gas to the gas chamber.

2. A torch as claimed in claim 1, wherein the conical surface of the nozzle makes an angle with the axis of said nozzle ranging from 20' to 60".

3. A torch as claimed in claim 2 wherein said angle ranges from 30 to 50 .

4. A torch as claimed in any one of the preceding claims wherein the orifices in the nose are at a distance in from the end of the nose ranging from 8% of the axial length of the nose to the limit imposed by the diameter of the gas chamber.

5. A torch as claimed in claim 4, wherein the orifices are at a distance in from the end

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

sliding element 51 which can be lockingly moved along a track 52 located at the bottom leg of housing 26, a locking pin 51A being provided as shown. Gas flow tube 53 is fixedly held by sliding element 51 and may be factory set, one end of the tube having a connector 54 for attaching to a source of oxygen and acetylene.

By employing the nozzle 33 of the invention with a gavity feed torch of the foregoing type as one example of use, it being understood that the nozzle may be used with other powdered metal torches as well, unexpected results are achieved which add to the inherent advantages of this type of torch. This will be apparent from the following test conducted with the torch arrangement shown in Fig. 8.

Several tests were conducted, (1) with a prior nozzle shown in Figs. 4 and 5 hereinafter referred to as the standard nozzle, and (2) with the nozzle used in the invention illustrated in Figs. 1 to 3.

In a first test, a standard oxyacetylene flame was produced as would normally be used for flame spraying, except that powder was not fed through the flame for use in the flashback test. In the case of the standard nozzle (Fig.

4), the tip thereof was touched against the surface of the workpiece which resulted in an immediate flashback when the orifices were blocked off. In the case of the nozzle used in the invention, the same test showed no flashback whatever and, moreover, the flame did not extinguish but stayed lit at the end of the tip where it should be.

The so-called standard nozzle (Fig. 4) had the same number and size of orifices discussed hereinabove with regard to the nozzle used in the invention, that is, eight orifices having a diameter of about 0-031 inch. In comparing the flames of each nozzle before metal spraying, the flame issuing out of the nozzle used in the invention and under the same gas-flow conditions was quieter. The noise level of the standard tip or nozzle was measured at about 93 decibels while that of the nozzle used in the invention was 85 decibels. This is a large improvement (approximately 102o less noise) when it is considered that the spray pattern of the powder is very sensitive to flame conditions.

Although the flame envelope of the nozzle used in the invention is the same length, it is narrower, more symmetrical and tends to be less divergent, that is, does not tend to spread out as much. The flame appears more stable and tends to flutter less, particularly with respect to the tips of the inner zone. The nozzle does not show the pulsating action of the standard nozzle.

Morever, the inner cores are more pointed and decidely less bulbous, which characteristic is an indication of stability and balance.

The temperature of the nozzle in service is essentially similar to the aforementioned standard nozzle. After one minute of use, the nozzle temperature is about 1800F; after 3 minutes, about 240"F; and after 8 minutes, it attains a maximum steady state temperature of 280"F, which temperature did not exceed 280"F after 15 minutes.

Another test conducted was the spray test.

In this test, a rate and deposition efficiency was determined using a gas regulator setting of 4 psi C2H2 and 8 psi 02, the gases being fed to the nozzles at a flow rate of 23 C. F.H.

(cubic feet per hour) of 2 and 36 C.F.H. of C,H2.

A bond coat powder was sprayed comprising a mixture of nickel powder and an exothermic reacting metal powder onto a roughened mild steel plate using the standard nozzle in one test and the nozzle used in the invention in another test. Because of the nature of the powder, a reaction occurs in the flame which results in an increase in spray temperature of the nickel particles which deposit on and bond to the steel surface. After the bond coat is applied, an aluminum bronze powder is then sprayed over the bond coat.

The final coating produced with the nozzle used in the invention exhibited a better quality than the coating with the standard nozzle.

The nozzle used in the invention also provided improved bonding of the bond coat of over about 5% which adds further to the final quality of the coating. The rate and deposition efficiency was 90% at a spray rate of 581 Ibs/hour.

WHAT WE CLAIM IS: 1. A flame spray torch comprising means for supplying powdered metal through a flame from a gas nozzle to a workpiece, the torch having a gas nozzle having a hollow cylindrical body defining a gas chamber and a converging generally frustoconical nose, there being a plurality of gas-conducting passages passing through the nose from the gas chamber and terminating in the conical surface of the nose as orifices which lie in a ring axially of the nozzle, and the torch further comprising means for supplying combustible gas to the gas chamber.
2. A torch as claimed in claim 1, wherein the conical surface of the nozzle makes an angle with the axis of said nozzle ranging from 20' to 60".
3. A torch as claimed in claim 2 wherein said angle ranges from 30 to 50 .
4. A torch as claimed in any one of the preceding claims wherein the orifices in the nose are at a distance in from the end of the nose ranging from 8% of the axial length of the nose to the limit imposed by the diameter of the gas chamber.
5. A torch as claimed in claim 4, wherein the orifices are at a distance in from the end

of the nose ranging from 10% to 25% of the length of the nose.
6. A torch as claimed in any one of the preceding claims wherein the gas-conducting passages are parallel with the axis of the nozzle.
7. A torch as claimed in claim 1 and substantially as described herein with reference to any one of Figures 1 to 3 and 6 to 8 of the accompanying drawings.