US2887984A

US2887984A - Apparatus for gas plating continuous length of metal strip

Info

Publication number: US2887984A
Application number: US439075A
Authority: US
Inventors: Folsom E Drummond
Original assignee: Commonwealth Engineering Company of Ohio
Current assignee: Commonwealth Engineering Company of Ohio
Priority date: 1954-06-24
Filing date: 1954-06-24
Publication date: 1959-05-26
Anticipated expiration: 1976-05-26

Description

APPARATUS FOR GAS PLATING CONTINUOUS LENGTH OF METAL STRIP Filed June 24, 1954 May 26, 1959 F. E.'-DRUMMOND 2 Sheets-Sheet 1 INVENTOR FOLSOM 5. ORUMMOND VACUUM PUMP ATTORNEYS May 26, 1959 F. E. DRUMMOND APPARATUS FOR GAS PLATING CONTINUOUS LENGTH OF METAL STRIP 2 Shgets-Sheet 2 Filed June 24. 1954 VACUUM PUMP United States Patentc) APPARATUSYFOR. GAS PLATINGCONTINUQUS LENGTH OF'METALSTRIP Folsom-E; 'Drummond, Washington; 'D.C.,'-' assignor to The Commonwealth Engineering Company of Ohio, Dayton, Ohio, a corporation of Ohio Application June 24, 1954, Serial'No. 439.975 If;

1 Claimw c1. 11s-4s This invention; relates to the art of gaseous deposition of metals. The invention more particularly is concerned I with the preparation of gaseous plated'metal products and improved processes for carrying osition.

out gaseous metal depln the preparation of coatings-as obtained for exam 'le -by gaseous metal deposition-of metal'carbonyls, it-has beenproposed to produce-such metal coatings by treat-' ing the base metal, in the form of a strip or other article,

-which has been mechanically or chemically -'clea ned,- to gaseous-metal deposition by heating'the material in an atmosphere containing the heatdecomposable gaseous metal compound and thereafter subjectingthe gaseous metal treated article to heating-to produce -a relatively smooth, uniform; coherent continuous metal coating. The

present invention distinguishes from the priorprocesses in that the metalbase ormaterial to be plated "is sub jected to a pre-treatment to produce adry, 'deaer-ated metal surface for receiving the-gaseous metal coating.

The invention thus makes it possible for the first time "to produce a metal coating which is interlocked withthe base metal in such a manner as to produce a substantially integral product. The product thus distinguishes from so-called wet-plating of metal surfaces, e.g;, aS-inelectrosurface. -Heretofore it has-been knownthat such pores and sub-microscopic depressions of the-surface" metal a could notbe plated utilizingthe so-calledwet processes,

wherein solutions containing the l'saltslxof the metal to be plated are utilized with,orswithout electrical means.

By the present invention a. product; is produced wherein the metal plate iscarried out utilizinglgaseou's heat/decomposable metals andlwhereby the metal to be .platedris initially heated todrive off all occluded gases: and While thus heated is subjected tozvacuum-or. reduced pressure .conditions. so as .to expunge the metal surface to be plated of all gases and permit the gases containing'the'gaseous metal to enter the pores and sub-microscopic.depressions .in the metal surface, andzdepositthe metal therein to .thus

forman interlocked substantially integral metal product.-

It vis the principal object ,of the: present invention-to produce a gaseous metal coated product wherein the metal product produced is made up .of a metal base and .a

\ coating which is substantially integral therewith.

Another object of the invention is toprovide an.;im-- proved method of plating, utilizing gaseous :metal com= pounds and wherein the gaseous metal deposition is-carthe base metal than has heretofore been effected-by-wet and dry methods of plating.

:It I is another object of the invention to -provide an improvedmethod of producing metal coatings whichcan withstand elevated temperatures andbending stresses' with- {887,984 a n ed Me? to 195 ice out @causing blistering or peeling-"oftliefmetal coating.

' It is a further object-of the invention to"provided 1 method of producing metal coat'ed articles rhavin' a' co- 5 1 here'ntinterlocked metal -surface*coating o'ver the metal "It is a still further object of the invention to provide a' product comprising a base metal '-"material"" which "is coated with uniformly deposited metal wherei'n the'i'net'al coating is made to penetrate deeply-into='theihaselnetal I -and diffuse therein so as to become substantially integral with the'base metal. p F

Theseand other objects arid'advdntages'tvill become apparent as the description proceeds, and taknin conjunction with thef'drawing'sforming apart of this specification, wherein:

Figure 1 illustrates diagr'arnr'naticallyandpictorially an 1 apparatus for carrying out 'the' gaseous 'me'tal' 'platingfin =.a'c ordance with this invention;

i Figure 2 is a'verticalcrosssectional View taken substantially on the Iine"2+2 of Fi'gure'zl and" lookingfin thedi'rection ofthe arrows; r

Figure 3 is a similar cross-sectionalviewms inFigure ---2, taken substantially on the line 3 3 banium: l, and

l'ookingin the direction of the arrows; v Figure '4 is a cross-sectional view through the gaseous --"rnetal' plating chamber, taken" substantiallyF on tlie line arrows; Y Figure '5 is an 'enlargedfview showing 'a -nretal-article plated by the wet plating method;

Figure '6 is a similar View illustrating '-a like "cross-sectionof a metal strip plated in accoi'dance"with this in- -vention; w Figure-7 is a similar'viewin perspectiveas in Figure 1, illustrating amodification of the apparatus and process therein,'and wherein the metal strip tobecoated' is heated by means ofaclosed coil and the'deaeratibnchamher is substantially integral with the'gaseous deposition chamber,'providing amore-compact apparatns;'

I Figure 8 is a cross sectionalview' taken on-tl1e line 1 8-'-8 of Figure-1', and'slooking in the dirction of the -arrows; V 3 Figure v.9 is' a. somewhat eiilarg'ed -cross sectional view taken on the line '9'-9 of Figure? l'g and" lookingin the direction of the arrows; 1 r a i Figure" 10 'is a similar sectional iview'take n substantially on theline 10- 10 of Figure 9; and Io'Qking -in-the; direcition of'tthe-arrows; and

Figure 11 is a similar sectional view on a somewhatcnboularged scale taken onthe'linei 11+1r'or Figuredfand looking in the direction of thearrowsi i l In the preferred process 'ofithe inventionfand which ewwill be described with particular re'ferenceito the plating :of'a. continuous length metal strip-,uit'is undrstoo d that ::the'invention is not to be restricte'dto th 'shapeorsize of the base metal to be plated. For examplwthe gaseous continuous process. In the embodiment shown. in Figures 1%:4 ofthdraw- 60. ingsya metal strip 10, which. may comprise:steel;aluminum, copper, etc.,' and whichhas been-previously 'cleaned vas by electro.chemical.or'isand't'blasting':ortthe like, is passed over the roll 12 and thencefintothe cleaning bath .14,being drawn under. the. spaced rolls :15 arranged in the :1 bottom of the cleaning tank 16. 3

l The cleaning bath 14 may comprise 'rinsewaten'or'ganic volatile solvent, :e.'g., ethyl: acetate, acetone; petroleum solvent,-or mixtures thereofg'towashtliestripi-and remove anycgreaseand-foreign particles or 's'pre cleaning' solution. 70. As the metal strip 10 is drawn upwardly and over the roll18'itis subjected to an air. blast z-2'2.:w-hi'ch preferably comprises hot air as supplied from: the blower- 24iltlie metal ,platingimay. be carrieduout" as a continuous. ordisair beingidrawn into the is drawn upwardly and over the roll 18 and thence into theheating chamber 20, the strip being moved along and centrallybetween the vertically spaced electrical heating elements,- or. resistance coils 30. The heating elements 30 are connected to a source of electrical current by.

suitable conductors 32. The heating chamber 20 comprises an elongated compartment having insulated inner walls34 and a slot opening 36 for the entrance of the metalstrip 10, and a similar exit opening 37 at the opposite end, the heating chamber being suitably fabricatedfrom two halves which are bolted together, as at 38 as shown in Figures 1 and 2.

. Joined to and communicating with the exit opening v37 of the heating chamber 20 is a gas lock gate means 40 which comprises an I-shaped member having a longi-.

tudinal slot opening 42 therethrough which is adapted to register with the exit opening 37 so as to accommodate the passage of the metal strip 10. Communicating with the opening .42 of the gas lock 40 are tubular conduits vide the gaseous gate interlocked between chamber 20 and the deaerating chamber 47.

The deaerating chamber 47, as shown, preferably comprises an elongated cylindrical chamber which is fitted 1 44 and 45-. throughwhich is passed the inert gas to pro- 1 chamber 86 which is constructed and operated similarly as the heating chamber 20. The finished plated strip'is drawn from the heat treatment chamber 86, and after cooling in the air, is wound up on the storage roll 88, as illustrated in Figure 1.

In a modification shown in Figures 7-11, the metal strip being treated, as shown at 10, is passed through a heating chamber 92, which chamberin this instance is heated by the helical coils 94' through which heated fluid, such as steam, hot water or the like fluid, is passed. Strip 10 is supported and drawn centrally of the coils 94 so as to be evenly heated.

Conduits

96, 97 are connected to the chamber 92 and the coil 94 for passing heated fluid through the coil.

After the strip 10 has passed through the pre-heating chamber 94 it is conducted into the vacuum or low pressure chamber 99 and thence into the gas plating chamber 100, and finally through the post heatingor annealing chamber 102, after which the finished gas plated metal strip 10 is rolled up on the storage roll 104.

. The low pressure chamber 99 is provided with a pressure gauge 106, and the conduit 108 which is in communication with the interior of the chamber is provided,

the conduit being connected to a vacuum pump or evaouatingprime mover whereby the chamber 99 is kept under reduced pressure. Provision is made at the inlet and exit of the strip for properly sealing the openings.

with apressure gauge 48 and

conduits

50 and 52 for ,the admission and withdrawal of gas from within the chamber147. ,Arranged within the chamber 47 are cooperating pairs of guide rolls 54 and 56 which are arranged to guide and support the metal strip 10 as the As ilsame is drawn therealong through the chamber.

lustrated, the conduit 50 is open at its inner end 57 and communicates with the chamber 47 the conduit being connected to a vacuum pump or the like to provide a vacuum or reduced pressure chamber for drawing off any occluded as nitrogen, helium, carbon dioxide, etc., where it is desired to introduce the same while subjecting the strip to reduced pressure conditions. In this manner a gaseous washing effect may be produced simultaneously with the low pressure conditions as effected by the vacuum pump.

valve 58 is provided in the line .52 so that the same may gasesfrom the surface of the metal strip before subjecting the same to gaseous metal plating. The conduit 52 is .prOVided for introducing inert gas or washing gases, such be sealed 011 where it is desired to use only the vacuum for low pressure treatment in chamber 47.

v From'the deaerating chamber 47 strip 10 passes through gthfigdSfiOllS gate interlock 60 which is of similar construction and operation as gas lock gaseous gate interlock 40. i

' Thestrip isithus passed from thechamber 47 into the .the introduction the the heat decomposable gaseous metal plating compound. At the opposite end a conduit 70 is provided. The gaseous metal compound is preferably introduced through the conduit'69 and after circulating through the chamber and in contact with the metal strip is withdrawn. through the exit conduit 70.

To assist in the even distribution and circulation of the gaseous metal compound in the chamber 65, the

same is provided with helical-shaped baflies 74 and .76.

. An important aspect of applicants invention is the I municates with the plating chamber at one end permits In this instance the gates 11 0,and 111 comprise sponge rubber seals which function as a squeegee to seal the strip as the same moves into and out of the chamber 99. Appropriate guide rolls 113 are arranged on the standard 114 and which support and guide the strip 10 through the -low,pressure chamber.

1 In the gaseous

plating chamber conduits

116, 118 are provided through which the heat decomposable gaseous metal compound is introduced and discharged respectively, as shown more clearly in Figure 9. A pressure gauge 120 is provided for observing thefluid pressure in the gaseous plating chamber.

In order to circulate the gaseous metal compound in contact with the moving sheet or strip 10,

suitable baffies

112, 123 are spacedly arranged longitudinally of the plating. chamber, as illustrated in Figure 9. The gaseous metal compound is admitted through the'conduit 116' at one end of the chamber 100 and passes downwardly and upwardly about the

baffles

112, 123, as, indicated by arrows at 125, the exhaust gases and unused decomposition products are drawn 011 through the conduit 118at the opposite end of the gaseous plating chamber.

The strip 10 after passing through the gaseous metal plating chamber is drawn outwardly through the exit gate 127 and into the post heating chamber 102,. and after cooling in the air is stored on the roll 104.

provision of a vacuum or low pressure pre-treatment following the heating of the strip or metal article to be gaseous metal plated.

The vacuum pressures used may vary depending upon the particular metal being plated, in each being sutficiently high to produce a perfectly dry metal surface being free of moisture and water vapor and wherein the pores and sub-microscopic depressions-in the metal surface are free of all occluded gases.

- about the production of a metal product having a metal Guide rolls 78 and 79 are arranged in the chamber 65.

and-adapted to support and guide the strip 10 therealong similarly as-guide rolls 54 and 56 of chamber 47.

.After the metal strip 10 is passed through the gaseous which is of similar construction and operation as gas .10cks40 and.- 60,- and thence through the heat treating coating layer which penetrates into the base metal to provide the same with a layer of metal which is interlocked with the base metal thus forming a substantially integral metal layer therewith. 5

The invention accordingly provides a method of dry 'platin'g metal articles' in a manner to provide the same with a coating-metal layer which adheres tenaciously to thebase metal forming a coherent, substantially integral .;;body.,. As. is-xwell: known, .in wet'zelectroplating, it has ,been: the practice to applya flash coating ofmetal, such as copper over the base metal to improvethe cohesion of the platedmetal. Such practice becomes, entirely un necessary with gaseous metal platinglin accordance with -55 applicants invention.

. In carrying out the gaseousmetal plating in accordance with applicants process, leakage of gas from one compartment to another is efiectively prevented by the use of inert gas gatelocks, such as shown at 40,and 60 in Figurenlo 2, the inert gas medium used in this instance being carbon dioxide, nitrogen or the like, ,the pressure being maintained slightly higher than thechamber to be protected so as to cause leakage of the inert vapor into the chamber rather, than leakage of the gas outwardly of the chambenk:

In this process a stream of gaseous material is conducted into the gaseous platingchamber and'circulated about the heated metal strip. The gaseous plating atmosphere may be formed by mixingan inert gas with the I vapors of a volatile metal compound or by atomizing aL-='20 liquid metal compound into a blast of hot inert gas or 1 other equivalent method.

Carbon dioxide, helium,.nitrogen, hydrogen, the gaseous product of controlled burning ofhydrocarbon gases free of oxygen, and the like, have been utilized as a car- 2 rier medium or inert gas medium.

In some instances the use of hydrogen is.preferred, as for example, in the Cleaning anneal chamber where its ability to act as a reducing agent may be put to advantage to remove the oxide film or rust from iron or metal strip being plated.

' .iron, chromium, molybdenum, cobalt, and mixed carbonyls. 40

Illustrative compounds of other groups are the nitroxyls, such as copper nitroxyl; nitrosyl carbonyls, for

example, cobalt nitrosyl carbonyl; hydrides, such as antimony hydride, tin hydride; metal alkyls, such. as chromyl chloride; and carbonyl halogens, for example osmium carbonyl bromide, ruthenium carbonyl chloride, and the like.

Each material from which armetal may be plated has a temperature at which decomposition is complete. However, decomposition may take place slowly at a lower temperature or while the vapors are being raised in temperature through some particular range. For example, nickel carbonyl completely decomposes at a temperature in the range of 375 F. to 400 F. However, nickel carbonyl starts to decompose slowly at about 175 F. and therefore decomposition continues during the time of heating from 200 F. to 380 F.

A large number of the metal carbonyls and hydrides may be eifectively and efficiently decomposed at a temperature in the range of 350 F. to 450 F. When working with most metal carbonyls we prefer to operate in a temperature in the general decomposition range of the volatile compounds.

- If the metal is,for example, hot drawn strip, the hot stripupon cooling to the plating temperature range after deaeration may be led directly to plating chamber with or without an annealing stage therebetween. If an anneal is desired, the operation within the apparatus may be carried out in amanner similar to that used when starting with cold metal. The metal strip may be raised to and 70 maintained at desired temperatures by causing the metal to conduct electricity or by induction heating.

The temperatures in preheating and post heating cham- .;-ber sare;considerably;;higherthan plating temperatures,

i.e., in the range of 4 0Q-jF.,-to 1200" F.

'solutely dry metal surface.

. 1 Preparatory to coating the -;strip qtheztmetallic material may be cleaned by employingconventional methods used in. the art, comprising electro-chemicallyzcleaning by moving the same through abath of alkali-.or:acid= electrolyte wherein the strip is made the cathode or anode.

Pickling of the metal with hydrochloric, sulfuric: or

I nitric acid, or a combination of acids-,mayyalso be made as apart of the cleaning process, and the strip thoroughly rinsed-or washed prior -to introduction ,intotheplating apparatus.

However, if the metal strip is in good condition a cleaning anneal may suffice, in-which event the strip may be heated just prior to-entering thevacuumtreatmentcham ber. a

In a cleaning anneal any'grease and the like will be burned away by bringing the strip, to red heat.

The invention will be more clearly understood from the following description of.:one -embodiment 'ofithe. ap-

. paratus and its mode of operation. I

By subjecting the ymetal to beplated .to aipre-heatin treatment prior to the vacuum or low pressure treatment, occluded gases are more readily removed and at a lower vacuum pressure. Thisvacuum deaeration treatment prior to gaseous metal plating constitutes an essential step of the processin order to :produce an ab- The presence of hydrogen, oxygen or water vapor entrapped or occluded in the pores or irregularities over thesurface of the metal is avoided by the present process and a thoroughly coherent metal coating produced.

The post heat treatment of the gaseous plated metal may be omitted if desired, but is preferred inmost cases to produce a more even textured and smoother plating film or coating. The post heat treatment also is advantageous in preventing the entrainment of moisture. To further assist in this, it is, preferable to carry out the post heat treatment inthe presence of inertgas, e.g., helium, argon, nitrogen, carbon dioxide or the like, This may also be accomplished by allowing a controlled amount of gas leakage of waste gas to take place from ,the plating chamber or by circulating a small amount of the rela- Lrvely spent or inert gases through the post heating cham The post heating temperatures employed will varyfor dilferent metal platings and base metals. treated as aforementioned. Generally the post temperature is the same or somewhat higher than the pre-plating heattreatment, the latter being governed by the temperature required to effect substantially complete removalof gaseous occlusions in the surface depressions of the base metal under the reduced pressure conditions. The postjheating, of the plated product inaddition to degassing the stripmay be controlled to efiect annealing of the strip. U The duration of heating in both pre-heating chamber and post heating chamber may be suitably varied to provide for a heat treatment of from ten to twenty minutes as desired.

The following examples are illustrative but not limitative of the invention.

EXAMPLE I Nickel-coated steel strip A steel strip which is to be coated andwhich has been chemically cleaned in the conventional manner is passed through the rinsing bath and air dried byhot air blast. The strip is then moved along through the pre-heating chamber and subjected to a temperature, of:525? F.', the strip being moved along at a uniformrate and such that the plating time allowed is approximatelytwo to'three minutes. The heated strip then passes directly: into the 4 low pressure or vacuum chamber where it: is subjected to a vacuum of approximately 1 mm. Hg after which the strip is passed along and through the gaseousmetal plating chamber. Nickel carbonyl in theform of vapor and admixed withcarbon dioxide carrier gasis-fed' to the plating chamber. Approximatelyfiye cubic feet ofinickel carhonylrcarhon dioxideqmixture Per, hour.-.is ;fed;.through the plating chamber, the metal carbonyl being present in the mixture of vapor is nickel carbonyl and carbon dioxide in the proportionate amount of about five ozs. of carbonyl per cubic foot of carbon dioxide. The temperature in the plating chamber and strip is approximately 400 F.

For a plating exposure of two and one-half minutes, this provides a coating of nickel of approximately 0.002- inch which interlocked and penetrated into the micropore surfaces of the metal is provided. After gaseous plating the strip is moved from the plating chamber through the post heating chamber where it is subjected to a temperature of approximately 700 F. in the presence of carbon dioxide.

' EXAMPLE II Nickel coated aluminum Aluminum metal strip is substituted for steel strip material and processed as in Example I, except that both preheating and post heating treatments are carried out at about 500 F.

EXAMPLE III Cobalt coated steel Steel strip in this example is processed as in Example I, utilizing cobalt carbonyl as the heat-decomposable gaseous metal compound.

The cobalt carbonyl is introduced at a rate of approximately one pound of carbonyl (liquid) per minute. Gaseous plating temperature is maintained at approximately 425 F. and nitrogen gas used as the carrier in place of carbon dioxide.

EXAMPLE IV Antimony coated copper metal Copper sheet is coated with antimony by first preheating copper strip material free of foreign matter in an atmosphere of helium at 525 F. The heat treated strip is then passed into a vacuum chamber where the hot metal strip is subjected to a vacuum pressure of 50 mm.

Hg and in an atmosphere of carbon dioxide. The strip is then immediately passed to the gaseous metal plating chamber where it is subjected to a gaseous atmosphere of antimony hydride heated to 400 F. to effect decomposition and plating out of antimony metal onto the copper strip. The post heat treatment is carried out at a temperature of 475 F. to produce a final coherent antimony coating on the copper metal base strip, being integrally united with the copper metal.

While the foregoing examples are given to more particularly point out how the invention may be practiced, it will be understood that the invention is not to be specifically limited thereby. The essence of the invention is the provision of a pre-treatment so as to deaerate or de-gas the metal to be gaseous plated so as to provide a perfectly dry, water-vapor and hydrogen free metal surface for receiving the gaseous metal plating. The process provides a finished product as aforementioned, wherein the plating or metal coat is interlocked with the base metal so as to form a substantially integral metal product.

In this connection, Figures and 6 illustrate in enlarged section, the essential difference in structure between 'Wet plated metal products and gaseous or dry plated metal products. As illustrated in Figure 5, metal coating is applied over conventional treated metal as generally indi- :section a gaseous metal coated structure as produced in In this instance, asqg accordance with this invention.

shown, the base metal and metal coating 156 are interlocked to provide a substantially integral structure. The microscopic pores at the surface of the metal are freed of gas occlusions and gaseous metal allowed to enter and thus penetrate into the body of the base metaLdeposition of metal taking place to thus provide an interlocking of the metal coating or. plating with the base metal. I

The foregoing description of a method of gaseous metal plating and product obtained thereby is accordingly distinguished from conventional wet plated products and methods. Whereas the method and apparatus disclosed herein are susceptible to various changes and modifications without departing from the principle and spirit of this invention, it is intended that such modifications as are required to adapt the invention to different conditions and uses are contemplated as within the scope of the invention except as restricted in the appended claim.

What is claimed is:

In apparatus for gas plating metal strip of long continuous length, means comprising cooperating rolls for supporting and moving a metal strip lengthwise, a plurality of chambers arranged in tandem and through which said metal strip to be gas plated with metal is moved, said chambers comprising a heating chamber having an inlet and outlet opening for the passage of said metal strip lengthwise therethrough, means for heating said chamber comprising elongated heating coils arranged in vertically spaced relationship and between which said metal strip is moved, a deaerating chamber connected to the outlet of said heating chamber, said deaerating chamber consisting of an elongated cylindrical enclosure which is fitted to and arranged to receive said metal strip as the same moves from the heating chamber, said deaerating chamber having inlet and outlet openings for passage of said metal strip, means comprising a vacuum pump connected to said deaerating chamber for evacuating the same, inert gaseous interlocks disposed at opposite ends of said deaerating chamber to provide a gaseous seal for the deaerating chamber from the surrounding atmosphere, a gas plating chamber directly connected to the outlet of said deaerating chamber and adapted to receive the metal strip after passing through the deaerating chamber and convey it along centrally through said plating chamber, inlet and outlet openings in said gas plating chamber, means for introducing a heat-decomposable gaseous metal compound consisting of gaseous nickel carbonyl admixed with carbon dioxide carrier gas into said plating chamber and discharging the waste products therefrom, said plating chamber including helical-shaped bafile means spacedly arranged lengthwise of said plating chamber for distributing said gaseous metal compound evenly in said plating chamber, and means comprising a heating and annealing chamber directly connected to said gaseous metal plating chamber and arranged to receive the resultant gas plated metal strip as the same passes therefrom to provide a finished gas plated metal strip.

References Cited in the file of this patent UNITED STATES PATENTS 1,497,417 Weber June 10, 1924 1,987,577 Moers Jan. 8, 1935 2,382,432 McManus et al. Aug. .14, 1945 2,516,058 Lander July 18, 1950 2,576,289 Fink Nov. 27, 1951 2,656,283 Fink et al. Oct. 20, 1953 2,656,284 Toulmin Oct. 20, 1953 2,685,535 Nack Aug. 3, 1954 2,793,609 Shen et al. May 28, 1957 FOREIGN PATENTS 589,966 Great Britain July 4, 1947 OTHER REFERENCES Steel, Gas Plating Offers Versatility, vol. ,113, No. 16, October 19, 1953, pages 120, 121 and 124..