US2094482A - Art of uniting metals - Google Patents

Description

p 1937- w. J. WEDER 2,094,482

ART OF UNYITIING METALS Filed July 16, 1936 3 Copper amajgam Alloy of copperand s/'/rer amagam silver amalgams sin/28F si/Veramq/gam a co er ama/ am Alloy of copper and pp 3 silver amalggmy' ll copper Inventor:

Wi I li am J. We der,

Patented Sept. 28, 1937 'eATEN ART? OF UNXTHNG METALS New Yorla Application .liuly M5, 1936; Serial No. 982

- lit tllairns.

This invention relates broadly to the art of uniting metals, and more particularly to the art of uniting metallic elements and alloys thereof which will amalgamate with mercury. The invention is particularly directed to various improvements and modifications in the process of uniting metals of the class described, which involves placing a coating of mercury upon the surfaces to be united and then applying heat and prewure to vaporize excess mercury and bond the metals. This invention is especially applicable to uniting silver to copper and its alloys, hereinafter for brevity collectively designated as copper, and for bonding copper to copper.

It is a main object of this invention to provide articles of manufacture, comprising metals, such as copper, silver and the like, rigidly and strong-. ly 'joined together by a process that is rapid, economical and effective.

Other objects of the invention will be apparent to those skilled in the art as a reading of this specification proceeds.

Before the action of current on metallic solutions was known (by means of which certain metals can be plated from solutions on a given surface) amalgams were used for gilding and silverlng. The article to be coated was covered by the amalgam and the excess mercury volatilized by heat, the gold or silver remaining on the surface as a strongly adhering coating. Later, it was proposed to apply heat and pressure simul taneously to the mercury-coated surfaces to form a union of the metals. Unions of lead to lead,

tin to tin, lead to tin. or either lead or tin to I any other metal which may be provided with a tinned surface, made by a so-called "mercury cementation" process, are old and well known.

I have found that in order to obtain a .practically eilective union of high tensile strength between metals oi the class hereinbefore mentioned, it is necessary to follow a procedure substantially as hereinafter described. The extremely strong and improved unions produced by my invention are due in large part to the fact that I treat the metal surfaces to be united both to provide substantially clean surfaces of the starting metals and for the removal of air bubbles after the parts have been initially assembled, and upon the further fact that, after the assembled parts have been placed'in a press having heated platens for simultaneous subjection to pressure and vaporization of excess mercury, I provide a cushion of a suitable material, such as sheet aluminum, pressboard, heavy paper or thelike, over the assembled parts to compensate for irregularities in one or the other, or both, of the metals being joined and thereby insure intimate contact over the wholesurface.

The novel features which are characteristic of my invention are set forth in the appendedclaims. The invention itself, however, will best be understood from reference to the following specification when considered in connection with the accompanying drawing in which the single figure is a micrograph (magnification 350 diameters) of a cross-section of a part of a union produced in accordance with the invention and illustrative thereof.

Referring to the drawing, i, i denotes two copper members; 2, an intervening layer of silver; 3, 3', layers of strata of copper amalgam in contact with each of the metallic copper surfaces; i, l, layers or strata of silver amalgam in con tact with each of the metallic silver surfaces; and 5, 5', layers or strata of. an alloy of copper and silver amalgams separating the copper amalgams fromthe silver amalgams and in cont-act therewith.

The drawing will also aid in understanding other embodiments -oi this invention such, for instance, as when merely uniting one metal to. another, for'example, metallic silver. to metallic copper.

Much of the strength of a union such as is produced by this invention is thought to exist in the alloy 5, 5 of the two amalgams. Thisalloy forms under the heat and pressure em-' ployed in practicing my invention. A characteristic of amalgams is that when initially formed and slightly heated they are soft and easily workable, but when set become very hard. There would therefore be some reason to expect that an alloy of, for example, copper and silver amalgams, when solidified, might form an unusually strong bond. That such is actually the case is indicated by the fact that, on tensile-strength tests, breaking of unions produced in accordance with this inventionpccurred in the silver layer and not at the silver-copper surfaces. I have recognized the practical importance of obtaining and mainver to copper is illustrative of how this invention may be practiced:

The surface of the copper article, for example,-a piece of flat copper, is treated to render it substantially clean, said treatment comprising, for example, acid dipping or scrubbing with, for instance, pumice. The part of the copper to which the silver-is to be applied is coated with mercury in the following manner:

Over an area of the copper surface a little larger than the piece of silver to be applied, a small amount of an aqueous. solution of mercuric nitrate and sodium cyanide is swabbed with a pad made of chamois skin, or metallic mercury and sodium cyanide may be similarly applied, in either case subsequently rubbing the surface until the mercury is thoroughly amalgamated with the copper. The metallic mercury is filtered through a chamois skin as it is applied to the copper surface. The surplus mercury and cyanide solution are removed and the article set.

aside to dry for about one-half hour. The resultant surface is polished with a dry pad of chamois skin. Next, fresh mercury is applied asaforedescribed and the surplus is subsequently removed.

A strip of silver of the desired thickness, for example, 3 mils thick, and of the shape and size required, is brushed or wiped clean, and the cleaned silver strip is then immersed in a bath of metallic mercury until it'is coated. The amalgamated silver strip is removed from the mercury bath and brushed to remove excess mercury and any particles of dirt or other foreign impurities adhering thereto.

The mercury-coated silver strip is now placed upon the previously marked-off spot on the mer cury-coated copper surface, and pressed and fixed thereon by hand. It adheres readily to'the amalgamated copper surface.

The assembled article, if flat, is now passed slowly and with considerable pressure through rubber rolls such, for instance, as those of an ordinary clothes wringer. When this is impractical due to the shape of the piece, the silver may be patted down with a stiff wire brush, starting the patting operation at one end and continuing to the other end. The object of such operations is to remove any entrapped gas such as air bubbles from the joint. Such bubbles, if not removed, cause blisters to appear in the union and a consequent weakening thereof.

The assembled parts are now placed in a press having heated platens. Sufiicient work is spread on the platen so that the pressure will be uniformly distributed andwill not crush the copper parts. Steel spacers are used at the sides of the pieces to prevent crushing, that is, deforming, the copper. A cushion of compressible material, for example, a sheet of aluminum, pressboard (about its inch thick), or heavy paper, is placed over the entire area of the assembled parts. compressible material sufficiently large to cover the silver, at the point where it is bonded tothe copper, may be used. Such a cushion compensates for irregularities in the copper surface and insures intimate contact of the copper andsilver throughout their entire adjoining surface areas. Without a cushion of the kind described, the copper must be squeezed to the flow point to get uniform contact with the silver. For economic and other reasons use of pressures no higher then necessary to obtain a strong bond is preferred.

The temperature of the platens is maintained If desired, small individual pieces of such below about 290 C., advantageously between about 225 and 250 C., by any suitable means, for instance, by electric heating units. Temperatures above about 290 C. have a harmful eflect upon the copper, for example, detrimentally affecting its hardness. The purpose of applying heat is to remove excess mercury and to assist in the formation of 'a strong union between, the silver and the copper.

The particular pressure employed depends upon the surface irregularities of the copper and the resistance of particular pieces to displacement, that is, to effecting intimate contact. Too little pressure gives a weak joint. Too high a pressure may set up strains within-a metal such as copper sufficient to weaken it materially. Depending upon the size of the article and other influencing factors the pressures used may vary widely, for

example, between about 500 and 40,000 pounds per square inch, the lower limit in most cases being about 1,000 pounds. Pressures ranging between about 1,000 and 4,000 pounds per square inch, for example, about 3,000 pounds per square inch, in most cases are effective in producing the desired results and are generally satisfactory in bonding silver to copper by the above-described process. The period of time the united parts are subjected to.-pressure depends to a large extent upon the size of the individual pieces. In any event, the pressure should be applied long enough for the piece to become uniformly -:.heated throughout. For pieces about 1-inch square, about three minutes is required. The press is Provided with suction orifices at both sides of the press and in front for withdrawing the mercury as it is vaporized from between the joint.

After pressing, the bonded pieces are removedfrom'the press and the excess mercury brushed on over a suctionhood. If desired, the articles may then be placed in a curing oven held at a temperature of about 225 to 250 C., for removal of further amounts of mercury.

In the process hereinbefore described, coating the metal surfaces with a film of mercury formsa copper amalgam on the copper and a silver amalgam on the silver. when pressure is applied to form an alloy of said amalgams. panying drawing, appears in the union as a practically rupture-free layer (5, 5 separating the copper and silver amalgains and in contact therewith. The superior quality of the unions produced by a process such as described isdue in largepart to the eliminationof "blisters from the union and the consequent obtainment of a practically rupture-free layer of an alloy of the amalgams of the source metals. The formation of such blisters and other defects in the union were particularly noticed 1) when cloth was employed in connection with the'application of the mercury to the metals; (2) when little or no care was taken in cleaning the metal surfaces; ('3) when the united parts were not treated for the removal of air bubbles; and (4) when no cushion was employed during the pressing oper-' lint (used prior to my invention in cleaning the metal surfaces and in applying the mercury) becoming trapped between the silver and copper surfaces during cleaning and assembling. --When These amalgams unite This alloy, as shown in the accom-- the assembled parts were placed in a hydraulic press and heated, water vapor and fixed gases were liberated by the lint, thereby forming blisters within the union. I discovered that by not using a lint-producing material at any stage of the process, but by using a material such as chamois skin for cleaning the surfaces and in applying the mercury, one cause of blister formationwithin the union was eliminated. Anecond cause of blister formation was removed by thoroughly cleaning the metal surfaces, especially the copper surfaces when making a silver-copper union. 1 have found that most satisfactory and uniform results are obtained if the surfaces are cleaned chemically clean. By the term chemically clean I mean a surface freed of impurities to the degree acceptable by chemists, and used in the chemical literature, as descriptive of a surface substantially freed of adhering foreign bodies. A third cause of blister formation was eliminated by removing air bubbles from the union prior to subjecting the same to heat and pressure by passing the united metals through rubber rolls or by patting with a wire brush, as hereinbefore has been set forth. Use of a compressible cushion upon the work during the pressforming an amalgam with a thin sheet or strip of a metal capable of'so doing, for example, a silver sheet or strip about 3 mils thick, and inserting it between the pieces of metal to be joined, forinstance, between two pieces of copper. In all cases the metals to be joined must be capable of amalgamating with mercury. By means of pressure and heat a bond is formed which varies in strength with the metals other than mercury employed in the process. A particularly strong union of copper articles is obtained when sheet silver and mercury are used as bonding metals.

The following description of the preparation of test pieces consisting of copper bars united by means of sheet silver and mercury as bonding metals, and the results of tests on such pieces, is illustrative of this embodiment of my inven.--

tion. Y

Copper bars with a rectangular cross-section of 2 by inches were beveled so that they could be fitted together with a Z inch length of lap. The beveled surfaces were coated with mercury and placed together with a 0.002 inchthick piece of silver between. A' pressure of about .40,000 pounds per square inch and, a temperature of about C. were applied to the bars for about 5 minutes. After removing the bars from the press, they Wereheated inan oven for approximately 12 hours at about 110 C. to vaporize any further amounts of excess mercury and to increase the strength of the bond. A tensile strength test was made on the union thus made. A pulling force of twelve thousand pounds was required to break the union at the joint.

A second test sample was made in the same form and manner as the one just described. Flight thousand to eleven thousand amperes were put through the joint about thirty times, the temperature of the joint rising to about C.

during the process. There was no damage to the joint. The test piece was then vibrated at 60 cycles per second for 384 hours without damage to the joint. The piece was then pulled in tension and broke through the copper bar at 16,950 pounds. The joint was intact. The joint was then. broken apart by driving a chisel between the copper bars. Both sides of the copper were coated with silver, showing that the break was through the silver layer.

Thin laminations of silver were "mercury bond to copper bars. They were then placed in a furnace maintained at an elevated temperature. lfter the barshad reached a temperature of 700 @232, they were removed from the furnace and quenched in water. This treatment had no apparent detrimental efiect upon the bond.

Lead, tin, silver and copper amalgamated with mercury have Wen used for bonding the same or other metal articles with varying strengths ofthe resultant bonds. For bonding copper articles, sheet silver amalgamated with mercury has given the greatest strength in the union. Among the other elements and alloys of these elements which will amalgamate with mercury are barium, bismuth, cadmium, chromium, gold, magnesium manganese, potassium, sodlum strontium and iron. The practical utility of many such elements in a process of the kind herein disclosed depends upon their cost, the ease or dimculty with which they form amalgams, and the strength and other service requirements of the resultant bonded article. For example, when copper bars are amalgamated and then pressed together, a bond is formed; but a union so made is not sufllciently strong for use in many manufacturing operations, for example, in electrical switch stud construction.

The table shows results obtained in uniting copper to copper using lead, tin and silver amalgamated with mercuryas bonding metals:

Tobie Pulling force required to break the Joint Test sam- Description of Bonding (tensile strength) in pie No. test sample medium pounds. (Note: In each instance the bars broke in the Joint.)

l Copper bar l Sheet lead, 25

inch by 1 two mils inch by 56 thiclaamah inch thick g cm a t e d oined to a with merar oi like cury. dimensions. 2 do Sheet tin, 910

three mils thick, amalg a m a t e d with merw cury. 3 "do Sheet silver, 2150 three mils thick, amalg a m a t e d with mercury. 4; Rod brass bar Shsetsilver, 5 13,500 I (80% copper, mils thick,

0. zinc) amalga 1% inchby mated with 1 inch by mercury.

nch thick oine'd to a er of like dimensions.

The results oi the foregoing tests show that in joining articles of copper and its alloys, a siland accurate comparison with the other samples cannot be made, however, due to the fact that the test bars in this case were slightly larger in area inbefore described, in comparison with a joint soldered with 60-40 lead-tin solder, were performed as follows:

A ltd-inch copper stud had a slotmilled in it to a depth of 1 inches. In this slot was inserted a 's-inch copper tongue, contacting surfaces of both the stud and the tongue having been coated with mercury, as hereinbefore described, and a sheet of silver foil having been placed between contacting surfaces of the tongue and the stud. This assembly was then placed between two steel blocks and the whole placed between the heated platenspf a hydraulic press.

Pressure and heat were then simultaneously applied, as previously described herein, until practically all the excess mercury had been vaporized and a firm and permanent bond hadbeen formed. A pulling force of-10,000 pounds. per

square inch was required to break the bond .made

in the manner described.

An assembly of a copper stud and a copper I tongue joined with 60-40 lead-tin solder, and subsequently sweated, pulled apart under a tension of 5,100 pounds per square inch. One advantage of the use of a mercury-silver cementation process in joining articles such as copper. is thus shown. The thicknessof silver or metal used for bonding purposes is important where strength is required. Bonding can be done with thin and thick material, but for most work material 3 mils in thickness gives the most generally satisfactory 4 results. The time and temperature of heating are also important. An amount of heat sumcient to soften one or another, or both, of the metals being joined, must be avoided. On the other hand, insumcient heat or heating for too 45 short a period of time does not give a practically satisfactory bond. .The time and temperature of heating will vary with parts of different size. In general, when bonding 'copper to copper with a silver amalgam, the temperature for effective 50 bonding should not exceed about 290 C., and advantageously may be maintained between about 225 and 250 C. Bonding of such parts can be done at a temperature as low as 100 0., but at such a temperature pressure must be applied for 55 a much longer period of time. A practically sat-' isfactory joint depends upon the pressure, heat,

and length of time the work is subjected to pressure, and upon following the procedures hereinbefore described for eliminating blister-forming 1. .In an article of manufacture, a union of at least two' diflerent metals the surfaces of. which will form an amalgam with mercury, said union (5 comprisingamalgamsof the. respective metals What I claim as new and novel and desire'to secure ,by Letters Patent-of the United States is:

in contact with the saiddifferent metals and a practically continuous layer of an alloy of the amalgams separating said amalgams and in contact therewith, and said union being the resultant of simultaneously subjecting the joined, amalgamated surfaces to a heat treatment sumcient to volatilize excess mercury and to a pressure of at least about 500 pounds per square inch.

2. In an article of manufacture, a union of silver and copper articles comprising silver amalgam in contact with the silver article, copper amalgam in contact with the copper article, and a practically continuous layer of an alloy of copper and silver .amalgams separating said amalgams and in contact therewith.

3. In an article of manufacture, a joint uniting metallic copper to metallic copper, said joint comprising an intervening layer of silver, copper amalgam in contact with each of the metallic copper surfaces, silver amalgam in contact with each of the metallic silver surfaces, and practically continuous layers of an alloy of copper and silver amalgams separating said amalgams and in contact therewith.

4. A method of uniting metal articles the surfaces of which will form an amalgam with mercury which comprises applying a film of mercury to the clean surfaces to be united, bringing the amalgamated surfaces into initimate contact with each other to join the articles, treating the joined articles for the removal of any entrapped gas, cushioning said articles with a compressible material to compensate for any surface irregularities therein, and subjecting the cushioned articles to a simultaneous pressure and heat treatment willcient to remove excess mercury and to firmly and permanently unite the .articles without detrimentally affecting the physical properties thereof.

5. A method of uniting metal articles the surfaces of which will form an amalgam with mercury, which comprises amalgamating the clean surfaces to be joined without introducing thereupon solid foreign contaminants, bringing the amalgamated surfaces into intimate contact with each other to join the articles, treating the joined articles for the removal of any entrapped gas,

cushioning said articles with a compressible'material to compensate for any surface irregularities therein, and subjecting the cushioned articles to a simultaneous pressure and heat treatment, said pressure being suillciently high to provide intimate contact of the articles throughout their entire adjoining surface areas and to firmly and permanently bond the amalgamated metals, and said heat being sufficiently high to vaporize excess mercury from the metal surfaces without detrimentally affecting the physical properties of the metals.

8. A method of uniting metallic copper members which comprises applying a film of mercury to clean facing surfaces of said members at the point of subsequent union, applying a film of mercury to front and back surfaces of a thin sheet of metallic silver, bringing said amalgamated sheet of metallic silver into contact with the copper members at their amalgamated surfaces, and subjecting the whole simultaneously to pressure and heat, said pressure being sufliciently high to provide intimate contact of the members throughout their entire adjoining surface areas and to firmly and permanently bond adjoining amalgamated surfaces, and said heat being sunlciently high to vaporize excess mercury from the metal surfaces without detrimentally affecting the physical properties of the metals.

till

l. A method of uniting meic copper mem bers which comprises app a oil more to clean racing surfaces oi suici members st the point of subsequent union. applying u i or user cury to front and back suriaces of a thin sheet oi metallic silver 01' a size suficient to cover the copper surfaces at thepoint of subsequent union. bringing said amalgamated sheet or metallic sil ver into contact with the copper members st their amalgamated surfaces, and cup pressure and heat simultaneously thereto, said pressure being between about 1,000 and some pounds per square inch and said hect being between ubcut 100 and 290 C.

8. A method oi uniting metallic copper reenabers which comprises applying a film of mer- 1 to clean facing surfaces oi said members at th point of subsequent union, applying a of ercury to front and back surfaces of a time sheet of metallic silver or a size sumcient to cover the copper surfaces at the point of subsequent union, bringing saidv amalgamated sheet of metallic silver into contact with the copper members at their amalgamated surfaces, treating the union thus formed for the removal of any entrapped g, and applying heat and pressure simultaneously thereto, said pressure being sufllclently high to form a firm and permanent union of the members and said heat being suflicientlyhim to vapor-ice exeach other to join the articiestrcutins the Joined articles for the removal or any entrapped ces, anu subjecting saicl urtlcles to a simultsneous pr 1; anci best treatment, said pressure being between about oco sncl euccc poimclsuer square inch end said heat being between cbout lii0 ancl 1s. A method of ting silver and p per articles which comprises smeisemcti the clean surfaces to be joined without intrcrluc thereupon solid foreign continents, bringing smeissmated surfaces into contact with each other to loin the articles; trestinn the joined artlcies lies the removal of any entrapped gas, cioninc snicl articles with a compressible mate to compensate for :any surface irregularities therein, and subjecting the cushioned articles to a simultaneous pressure and heat treatment, said pressure being between about 1,000 and 40,000 pounds per square inch and said temperature being between about 100and 2M? (2.

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