US3372054A - Method of flame spraying and powder - Google Patents

Description

United States Patent Office 3,372,054 Patented Mar. 5, 1968 This invention relates to the flame spraying of metal powders upon metal surfaces, and it more particularly relates to the simultaneous spraying and bonding of such coatings.

It has been customary in flame spraying metal powders upon metal surfaces to utilize particle sizes finer than 100 mesh and preferably 150 mesh and smaller. Nominal 150 mesh particle size powders normally incorporate a distribution of finer particle sizes ranging down to 325 mesh with a minor percentage of even finer. These fine powders have been considered necessary to insure sufficient heating during passage through the flame to bond with the preheated metal surface upon which they are impinged. The alloy compositions suggested for such powders have melting temperatures ranging approximately from 360 F. to 2200 F. They include lower melting temperature metals and alloys such as lead, aluminum, bronze, brass, silver base alloys, zinc, cadmium and the various nickel and cobalt base alloys in the upper portion of the aforementioned range and primarily between -l800 'F. and 2200" F.

The metals and alloys in the lower portion of the abov; range and below l800 F. are highly susceptible to volatilizing and fuming when sprayed in the fine particle size previously deemed essential. This fumes away critical constituents to the detriment of the deposited coating. The fumes of certain of these volatile metals such as lead, zinc and cadmium are also highly toxic and are liable to poison an operator.

Alloy compositions in the higher melting temperature range from 1800 to 2200 'F., when sprayed in the heretofore conventional fine particle size, are highly sensitive to particle size and distribution and configuration. Deviation from prescribed particle size distribution is likely to interfere with the deposit of suitable coatings, and particles of spherical shape are recommended for optimum results. This makes such powders difiicult to prepare and quite expensive.

An object of this invention is to provide a method and powder for flame spraying that minimizes the elfect of particle size distribution and configuration and any tendency of the powder composition to volatilize.

Another object is to provide such a method and powder that flame spray volatile metal powders without fuming.

In accordance with this invention the particle size of approximately 75100% by weight of metal powder compositions having melting temperatures ranging approximately from 360 F. to 2200 F. is maintained approximately between -60 to +100 mesh passes through and is retained). The remainder of the powder may be of smaller or larger particle size no greater than 40 mesh, and a particularly effective particle size distribution is as follows.

mesh.

Mesh size: Example in percent by wt. 40 +60 1 60 40 -80 50- 100 9 The amount less than 100 mesh is predominately mesh.

This powder is flame sprayed upon a metal surface within an oxy-fuel gas flame to plasticize the powdered metal without volatilizing it. The plasticized powder is impinged upon the preheated metal surface with which it coalesces and bonds to form a smooth continuous coating.

This invention, for reasons that are not completely understood, remarkably minimizes the effect of particle size distribution and configuration and any tendency of the powder composition to volatilize to such an extent that such effect and tendencies are eliminated for all practical purposes. Relatively economical and easily prepared powders can thus be efficiently sprayed at remarkably high recovery rates in any size distribution within the recited range and in any particle configuration-angular, spherical or otherwise. The prevention of fuming is highly important with metals that melt in the range of from 360 to 1800 F. because many of them such as lead, aluminum, zinc and cadmium are highly subject to volatilizing,

and the fumes of lead, zinc and cadmium are toxic. The

flame spraying of volatile metal powders without any loss of critical constituents from the ultimate coating or-emission of poisonous fumes is thus remarkably facilitated.

A particularly effective torch 'for'use in conjunction with this invention is of the general type described in a copending, commonly assigned application for US. Letters Patent entitled Flame Spraying Torch, S.N. 297,844, filed July 26, 1963, now Pat. No. 3,220,068. For effectively performing the method of this invention, such a torch utilizes acetylene as the combustible gas, supplied at a pressure ranging approximately from 2 to 14 p.s.i. and preferably from 8 to 12 p.s.i. Oxygen is most efficiently used as the combustion supporting gas, supplied at a pressure ranging approximately from 16 to 50 p.s.i. and preferably from 24 to 32 p.s.i. Highly efficient supply pressures of acetylene and oxygen are respectively 9 p.s.i. of acetylene and 28 p.s.i. of oxygen. The exit area of the torch tip ranges from that of a No. 48 size orifice to that of a No. 30 size orifice with a No. 34 size providing highly effective performance. A multiple orifice tip with three No. 50 size orifices also provide highly effective performance. The aforementioned tip or orifice size numberscorrespond to those of standard U.S. twist drills. The flow rates of acetylene and oxygen are made substantially equal to each other by the configuration of passages for them within the torch. The torch is thus operated under what is conventionally referred to as equal pressures to provide a neutraloxy-acetylene flame. The temperature of oxygen-acetylene flames of varying proportions range from 5550 'F. to 6000 F., and a neutral flame has a temperature of approximately 5850 F.

With a No. 34 size tip upon a torch to which 9 p.s.i. of acetylene and 28 p.s.i. of oxygen are applied, approximately 68 cubic feet per hour of acetylene and 70 cubic feet per hour of oxygen are burned. With a multiple tip having three No. 50 size orifices, the corresponding flow rates of acetylene and oxygen are respectively 74 and 80 cubic feet per hour. Minimum effective flow rates of acetylene and oxygen within the indicated ranges of pressures and tip sizes are approximately 10 and 14 c.f.h. Maximum effective flow rates of acetylene and oxygen within the indicated ranges of pressures and tip sizes are approximately 851 and 100 c.f.h. At pressures of8-12 p.s.i. of acetylene and 2432 p.s.i. of oxygen and a No.

34. size tip, approximately 6080 c.f.h. of acetylene and 60-90 c.f.h. of. oxygen are effective flow rates.

For supplying powder of the required particle size to a gas flame provided by the aforementioned parameters, the diameter of a powder passage of substantially circular cross section may vary from approximately 0.050 of an inch to 0.080 of an inch and preferably from 0.065 to 0.075 an inch. Highly efficient powder flow is provided by a substantially circular passageway having a 0.070 of an inch diameter. This provides a flow of metal powder to the aforementioned flame ranging approximately from pounds per hour to pounds per hour with? an eflicient range of 6 to 7 pounds per hour and ahighly efiicient rate of 6 /2 pounds per hour.

The powders of this invention may have any composition that melts in the range between 360 F. and 2000" F. In the lower 360 F. to 1800 F. range are'found the metals and alloys (such as tin, lead, silver, antimony, cadmium, zinc and aluminum) that have relatively high vapor pressureswhich make them susceptible to volatilization-at normal flame-spraying temperatures. Although the temperature of aneutral oxygen-acetylene flame is approximately 5850 F., the powder sprayed through it is not heated to that temperature because of their relatively great mass and short passage time within the flame.

Inthe'torch; of the aforementioned copending application for. US. Letters Patent, S.N. 297,844, filed July 26', 1963, they powder is entrained in the oxygen by gravity flow and the differential in pressure between-the low" pressure in the restrictedintroduction portion of the oxygen passage and the higher pressure in the powder container. The powder laden oxygen is then mixed with acetylene and the mixture burned when it is discharged from the'tip. The powder accordingly flows in the burning stream of gases of the flame spray. The rapidity and force of the flame spray helps coalesce the heated par ticles withthe preheated metal surface. This coalescence is facilitated by the pool of molten metal deposited by previously impinged particles that spreads over the surface: of the preheated metal surface. Even though the sprayed particles are so large and massive that they are: merelyplasticized during. their transit through the ame spray, the force of impingement and dissolution in the previously deposited molten pool effectively bonds them to the preheated metal surface and coalesces them therewith. All'of, these factors cooperate with each other to form a smooth metal coating upon a. preheated metal surfacedespite the relatively great mass of the particles ofthis invention which previously would have been considered too large to allow sufficient heating to bond them with a metal surface through flame spraying. These relatively massive particles are so little affected by the heat that plasticize-d. them that no discernable volatilization occurs of compositions having melting temperatures from 360 to 2000 F. This avoids the serious fuming problem' associated with more volatile metals, suchas tin, lead, antimony, zinc andJcadmium and for the first time makes it possible'to flame spray compositions including them without any danger of poisoning. Other volatile metalsisuch as aluminum may also be flame sprayed without any toxic effects. or loss from the ultimate deposit.-

A composition that can be flame sprayed with remarkable-eifectiveness and absence of fuming through this invention isasilver base alloy having a solidus temperature of 1125 F. The composition ofsuchpa silver base alloy is for example an AWS BAg-1 type as describedin the Brazing Manual of the American Welding Society, Inc., copyright 1963, and in AWS Specification for Brazing Filler Metals, AWS A--5.8, ASTM B260. All alloys designated herein as AWS refer to the aforementioned publications.

Thisopens upthe field. of spraying to a wide variety of silver solder and silver brazing alloys that contain volatile constituents such as zinc and cadium whose loss would seriously detract from the physical properties of the ultimately deposited coating and whose fumes are toxic. The same applies to soft solders of the tin/ lead type having a solidus of 361 F. and to tin/zinc systems having a solidus of 390 F. Other lower melting range systems can also be flame sprayed with remarkable absence of volatilization. These include the following having the indicated solidus temperatures: tin/ antimony 452 F., tin/silver 430 F., lead/silver 579 F., cadium/ silver 640 F., cadium/zinc 509 F. and zinc/ aluminum 720 F.

A typical brass alloy that is flame deposited with complete carryover of all constituents and with lack of fuming of this invention has for example an AWS BCu Zn A type composition.

Despite the great susceptibility of zinc to fuming, the above composition is totally flame deposited by this invention Without any appreciable loss of zincor significant emission of its poisonous fumes.

As previously discussed, this invention is also quite advantageous for higher melting temperature powders between 1800 and 2200 F. to complete the overall applicable range of 360 F. to 2200 F. This invention.

makes these high melting powders. insensitive to the effect of powder distribution and configuration. With heretofore used powders of finer particle size, a particular particle distribution had tobe maintained very carefully throughout the range from 150 through 325 mesh. This was considered mandatory for suflicient heating and melting during flame spraying. It was also thought critical that the powder configuration be maintained sub.- stantially spherical. This invention makes eflicient flame spraying insensitive to both particle size distribution and configuration.

A typicalnickel base alloy having a melting temperature of between 1800" F. and 2000 F. is. an AWS BNi2 type composition. Cobalt base alloys incorporating nickel and chronium constituents melt between 2000 F. and 2200 F. and also are flame sprayed in accordance with this invention with remarkable effectiveness.

The effectiveness of this invention in flame spraying.

and particularly its elimination of fuming when spraying alloys that are highly susceptible to fuming is highly remarkable in view of the inability of all previous modes of flame spraying to minimize fuming let alone completely. eliminate it. Even when finer powders are propelled at relatively high velocities through a flame spray, such as by a compressed air propellant, substantial fumingstill: occurs. It is thus highly remarkable that powder compositions having relatively low melting temperatures :and whichare highly susceptible to volatilization do-not fume to any significant. extent.

What is claimed is:

1. Amethod. of flame spraying metal powders that minimizes the effect of particle size distribution and configuration and any tendency of thepowder composition to volatilize comprising the selection of a metal powder. compositionhaving a melting temperature ranging approximately from 360 F. to 2200 F., maintaining the particle size of said powder less than 40 mesh andapproximately 100% by weight thereof approximately from -60 to mesh, preheating said metal surface approximately to its bonding temperature with said heated metal powders whereby coalescence therewith is achieved, and flame spraying saidpowdered metal upon.

said metal surface within an oxy-fuel gas flame to plasticize said powdered metal without volatilizing it and to impinge it upon said preheated metal surface whereby it.

coalesces and bonds therewith to form a smooth continuous coating upon said metal surface.

2. A method asset forth in claim 1 wherein a metal powder composition is selected that has a meltingtemperature ranging approximately from 360 F. to 1800 F.

wherein many of said compositions are highly susceptible" to volatiiizing when heated during passage within a flame spray, and said method preventing said compositions from volatilizing and fuming whereby loss of constituents and emission of toxic fumes during flame spraying are avoided.

3. A method as set forth in claim 1 wherein said oxyfuel gas flame incorporates a burning mixture of a combustible gas and oxygen issuing to atmosphere from a torch to which they are supplied under pressure, said combustible gas being supplied at a pressure ranging approximately from 2 to 14 p.s.i., said oxygen being supplied at a pressure ranging approximately from 16 to 50 psi, the exit area of said torch ranging approximately from that provided by a No. 48 to a No. 30 tip size, and said powder flowing at a rate ranging approximately from 5 lbs. to lbs. per hour.

4. A method as set forth in claim 3 wherein the temperature of said flame ranges approximately from 5550" F. to 6000 F.

5. A method as set forth in claim 3 wherein said powder is entrained within said burning mixture and flows at substantially equal velocity therewith within said flame toward said metal surface.

6. A metal powder for flame spraying that is relatively insensitive to particle size and distribution and has a minimum tendency to volatilize comprising a metal composition having a melting temperature ranging from 360 F. to 2200 F., and the particle size of said powder ranging from 40 to +140 mesh.

7. A metal powder as set forth in claim 6 wherein the melting temperature of said composition ranges from 360 F. to 1800 F.

8. A method as set forth in claim 3 wherein said combustible gas and said oxygen respectively flow at rates ranging from 10-88 and 14100 cubic feet per hour.

9. A method as set forth in claim 1 wherein said particle size of said powder is distributed in the following ranges of percent by weight of said powder:

Mesh-- Percent by wt.

References Cited UNITED STATES PATENTS 3,055,769 9/1962 Herron et al. 1l746 X 3,071,678 1/1963 Neely et a1.

3,077,659 2/1963 Holzwarth et al. 29197 3,091,029 5/1963 Davis et al 117105 X 3,285,769 11/1966 Cape 117 22 3,318,730 5/1967 Kreiselrnaier 117--105 X ALFRED L. LEAVITT, Primary Examiner.

I. H. NEWSOME, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,372,054. March 5, 1968 Frederick T. Wishnie et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 35, for "3,220,068" read 3,226,028

Signed and sealed this 15th day of July 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, IR.

Claims (1)

1. A METHOD OF FLAME SPRAYING METAL POWDERS THAT MINIMIZES THE EFFECT OF PARTICLE SIZE DISTRIBUTION AND CONFIGURATION AND ANY TENDENCY OF THE POWDER COMPOSITION TO VOLATILIZE COMPRISING THE SELECTION OF A METAL POWDER COMPOSITION HAVING A MELTNG TEMPERATURE RANGING APPROXIMATELY FROM 360*F. TO 2200*F., MAINTAINING THE PARTICLE SIZE OF SAID POWDER LESS THAN 40 MESH AND APPROXIMATELY 75-100% BY WEIGHT THEREOF APPROXIMATELY FROM -60 TO +100 MESH, PREHEATING SAID METAL SURFACE APPROXIMATLEY TO ITS BONDING TEMPERATURE WITH SAID HEATED METAL POWDERS WHEREBY COALESCENCE THEREWITH IS ACHIEVED, AND FLAME SPRAYING SAID POWDERED METAL UPON SAID METAL SURFACE WITHIN AN OXY-FUEL GAS FLAME TO PLASTICIZE SAID POWDERED METAL WITHOUT VOLATILIZING IT AND TO IMPING IT UPON SAID PREHEATED METAL SURFACE WHEREBY IT COALESCES AND BONDS THEREWITH TO FORM A SMOOTH CONTINUOUS COATING UPON SAID METAL SURFACE.