US2425052A - Electrical contact materials and contacts and methods of making the same - Google Patents

Description

Aug. 5, 1947. M. R. SWINEHART ELECTRICAL CONTACT MATERIALS AND CONTACTS AND METHODS OF MAKING THE SAME Filed March 8, 1944 MIXTURE OFA METALLIC OXIDE AND AMETALLIC SALT.

CONDUCTIVITY.

Patented Aug. 5, i947 ELECTRICAL CONTACT MA'EMIALS AND CONTACTS AND METHODS OF MAKING THE SAME Merle a. Swinehart, Milwaukee, Wis, assignor to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation oi. Delaware Application March 8, 1944, Serial No. 525,606

30 Claims. i

Another object is to provide electrical contacts formed of powdered mixtures of materials of such composition that attainment of a high degree of density thereof by sintering or heat treatment is facilitated.

Another object is to provide a powder composition electrical contact wherein formation of a film or layer of a material different from the main current carrying metal upon the operating surface of the contact is insured when in use.

Another object is to provide for inclusion in the contact composition of a relatively small percentage of an ingredient which acts to provide a surface film adapted to assist in preventing bonding or sticking of the cooperating contacts.

Another object of the invention is to provide a powder composition contact including a metallic salt whereby the length of life and other operating characteristics thereof are greatly improved. I

Another object is to provide an electrical contact having a novel form'and arrangement of at least one ingredient thereof with respect to another whereby the desirable characteristics of each are accentuated.

Another and more specific object of the invention is to provide a powdered silver base contact embodying arelatively small quantity of a silver halide whereby the current controlling capacity and life of the contact ar greatly increased.

The single figure of the accompanying drawin is a fragmentary sectionalview, highly magnified, of an electrical contact embodying my invention.

Although I will herein describe that phase of my invention relating to particle size of the oxide as specifically applied to the improvement of electrical contacts composed essentially of silver and cadmium oxide, it is to be understood that the invention inthis respect is applicable to the improvement of substantially all types of composition contacts made by the methods of powder metallurgy or otherwise.

Heretofore it has been proposed to use amor. phous cadmium oxide to coat and thus separate 2 the individual metallic ticles of such composition contacts to prevent the cooperating contacts from welding or sticking together during operation.

As the result of extensive experiments I have iound that it is not necessary or desirable to separate the metallic particles throughout the body of the contact to prevent welding or sticking; but that it is only necessary to provide a film of cadmium oxide upon the active surface of at least one of the cooperating contacts.

In a contact produced in accordance with my invention such a surface film is continuously produced by disintegration of relatively large and dense particles of cadmium oxide embedded in a matrix of fine silver. As the embedded particles are exposed at the surface of the contact by wearing down of the latter, such particles are broken up and'spread over the surface of the contact both by mechanical action and arcing action.

As will be apparent to those skilled in the art, a contact of the character herein disclosed has the advantage, over known contacts of this general type, of greatl increased electrical and thermal conductivities, which are due to the presence of many unbroken paths of fine silver throughout the depth or thickness of the contact. Furthermore such inner structure or character of the contact material facilitates densification thereof, because of its inherently greater response to sintering or heat treatment.

In producing a contact of the aforementioned character composed essentially of silver powder and cadmium oxide, I prefer to employ Merck's precipitated silver powder and a commercial form of cadmium oxide which is initially of such fineness as to pass through a 325 mesh screen. As set forth in Patent N 0. 2,307,668, granted Jan. 5, 1943, to I. W. Cox, Mercks precipitated silver powder is characterized by a fibrous texture, extreme whiteness, and unusual ability to cold weld under pressure to a tough solid of considerable tensile strength. Such cadmium oxide is then densifled by pressing, or by pressing and heat sintering operations, and thereafter ground in such a manner, or to such an extent, that at least fifty per cent of the powder which passes through a mesh screen will be retained upon a 300 mesh screen. The pressure employed fordensifying the cadmium oxide may vary throughout a wide range, as for example, from 40,000 pounds per square inch to upwards of 100,000 pounds per square inch In the particular examples herein-' (silver, for instance) par- 3 pounds per square inch was employed to produce slugs of cadmium oxide having a diameter of one and one-eighth inches, said slugs being thensubjected to a temperature of 1600 degrees F, for a period of one hour.

However, prior to application of the aforementioned densifying process to the cadmium oxide I prefer to add thereto and intimately mix therewith a suitable metallic salt; as, for example, silver iodide, silver bromide, silver chloride, cadmium chloride or cadmium sulphate.

The addition of one or another of such metallic salts (or combinations of two or more thereof) improves to a marked degree the anti-welding or non-sticking characteristics of the particular contact, and thereby substantially increases the range of currents which such contact will make and break. Such metallic salts when thus employed insure a more even wear of the contacts, and consequently prolong the life-of the latter.

The aforedescribed granular powder composed v; of cadmium oxide and a metallic salt is intimately mixed with a given quantity of silver powder (such as Merck's precipitated silver powder), and such mixture of powders is then cold molded at a pressure of about 40,000 pounds per square inch to provide preforms of approximately threefourths of an inch in diameter. Thereafter said preforms are subjected to a temperature of approximately 1600 degrees F. for about twenty minutes. After such heat treatment said pref-orms are subjected to a molding pressure of approximately 100,000 pounds per square inch to produce the finished contacts.

In the single figure of the drawing the numeral 5 designates a fragment, on a greatly enlarged scale for purposes of illustration, of an electrical contact embodying my invention. In thissectional view, the numeral 6 designates the base or matrix material, which consists of a metal of good electrical conductivity, such as silver; and the numeral 1 designates particles or granules of a mixture of a metallic oxide (such as cadmium oxide) and a metallic salt (such as silver iodide). The materials in powder form are treated in the manner aforedescribed to produce the final article.

The following examples of contacts produced in accordance with my invention indicate the non-welding characteristics thereof, and show other advantages thereof over contacts of the priorart.

(a) A set of contacts, three-fourths of an inch in diameter, formed under heavy pressure and heat sintered, composed of an intimate mixture of 87.5 per cent of Mercks precipitated silver powder, 11.86 per cent of cadmium oxide (of the character aforedescribed), and 0.64 per cent of silver iodide, will make and break 5000 amperes of a 30 volt direct current resistance load approximately one hundred times before sticking occurs. On the other hand, the most promising contacts of the prior art for such a purpose will fail at once on such a load, and such prior art contacts will make and break only 2000 ampere of a 30 volt direct current resistance load for the same contact life; namely, one hundred operations.

(1)) A set of contacts three-fourths of an inch in diameter, formed under heavy pressure and heat sintered, composed of an intimate mixture of 82 per cent of Mercks precipitated silver powder, 16.2 per cent of cadmium oxide prepared as aforedescribed, and 1.8 per cent of cadmium sulphate, will make and break 2600 amperes of a 250 volt alternating current, 60 cycle, 50 per cent lagging power factor load at least one hundred times; whereas no known contacts of the prior art are in anywis'e dependable for such service.

(0) A set of contacts three-fourths of an inch in diameter. formed under heavy pressure and heat sintered, composed of an intimate mixture of '75 per cent of Merck's precipitated silver powder, 21.25 per cent of cadmium oxide prepared as aforedescribed, and 3.75 per cent of silver chloride, will properly make and break 4000 amperes of a 260 volt alternating current, 60 cycle, 40 per cent lagging power factor load at least ten times. Such a performance is not possible with any known contacts of the prior art. Substantially the same novel result may be obtained by substituting for the silver chloride a corresponding amount of silver bromide, the proportions of the other ingredients remaining the same.

In the foregoing examples the given proportions of the ingredients are by weight. Although I prefer to employ Mercks precipitated silver powder where a silver base contact is to be produced, it is to be understood that other silver powders may in some cases be found entirely suitable, and less expensive. Moreover, it will be apparent to those skilled in the art that the speciflc proportions of the various ingredients may be varied within relatively wide limits without sacrificing the important advantages of my invention, according to the particular use contemplated for the contacts.

While I have herein disclosed my invention as specifically applied to the improvement of socalled silver-base contacts produced from powdered materials, it is to be understood that it is in nowise limited to use with powdered silver. Thus the main ingredient of the powder used in forming the contact may consist of a suitable alloy of silver; or powdered copper, nickel, gold, etc. may be employed.

Although I do not know the exact reasons for the beneficial action of the added metallic salts in preventing sticking of the contacts and in their abilityto extinguish very heavy alternating current arcs, the following novel characteristics thereof are indicated:

1. It appears that the volatilized metallic salt produces an ionized atmosphere at the operating surface of at least one of the cooperating contacts. Such ionized atmosphere effects spreading of the are at the arc feet, which inherently results in lower current density and reduced heating of the contact surface or surfaces by the arc. Such decreased heating by the arc involves a reduction of pin-point formations of molten silver upon the contact or contacts, which pinpoint formations, if numerous, might cause welding or sticking of the cooperating contact surfaces upon subsequent operations.

2. The condensation of the metallic salt or salts as a thin film upon the contact surface or surfaces is believed to act to prevent bonding or sticking of the silvers of the cooperating contact faces in subsequent operations.

3. The aforementioned silver halides (silver iodide, bromide, or chloride) in addition to preventing sticking of the cooperating contacts when in operation, likewise act to prevent the contact resistance from increasing throughout the life of the contact. In a large percentage of many life tests conducted upon such contacts by me it was found that the contact resistance actually decreased as the respective tests progressed. It is thought that such additional beneficial action of the silver halides (in reducing contact resistance) may be due the presence of additional silver upon the surface of the contact or materials comprising from sixty per .cent to ninety-three per cent by weight of a metal of good electrical conductivity, a second ingredient consisting of cadmium oxide, and a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, said contact having nonsticking and substantially constant contact resistance characteristics when in use.

2. An electrical contact formed of powdered materials comprising a metal of good electrical conductivity, a second ingredient consisting of cadmium oxide, and a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, said cadmium oxide being present in the amount of about seven to forty per cent of the entire mass, and said metallic salt being present in the least useful amount up to about ten per cent of said mass, said contact having nonsticking and substantially constant contact resistance characteristics when in use.

3. An electrical contact formed of powdered materials comprising a metal of good electrical conductivity, a second ingredient consisting of cadmium oxide, and a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, said cadmium oxide being present in the amount of about seven to forty percent of the entire mass, said metallic salt being present in the amount of one-tenth ofone per cent to about ten per cent of said mass, and at least fifty per v cent of the amount of said cadmium oxide consisting of particles of a size greater than that which will pass through a 300 mesh screen.

silver powder of fibrous texture, from seven to forty per cent of cadmium oxide, and from onetenth of one per cent to ten per cent of a silver halide, all of said cadmium oxide being in the form of denslfied particles which will pass through a. 100 mesh screen, and the major portion of said particles being of a size greater than that which will pass through a 300 mesh screen.

8. A pressure molded and heat sintered contact composed of a mixture of approximately eighty-seven and one-half per cent by weight of precipitated silver powder of fibrous .texture, approximately eleven and eighty-six one-hundredths per cent of cadmium oxide, and approximately sixty-four one-hundredths per cent of silver iodide.

9. A pressure molded and heat sintered contact composed of a mixture of ingredients in about the following proportions by weight: eighty-two per cent of precipitated silver powder of fibrous texture, sixteen and two-tenths per cent of cadmium oxide, and one and eight-tenths per cent of cadmium sulphate.

10. A pressure molded and heat sintered con- I tact composed of a mixture of ingredients in about the following proportions by weight: seventy-five per cent of precipitated silver powder of fibrous texture, twenty-one and twenty-five one-hundredths per cent of cadmium oxide, and

4. A pressure molded and heat sintered contact composed of a mixture of from sixty per cent to ninety-three per cent by weight of the entire mass of silver powder, a substantially smaller proportion of the mass consisting of cadmium oxide, and a still smaller proportion of the mass consisting of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate.

5. A pressure molded and heat sinteredcontact composed of a mixture of from sixty to ninety-three per cent by weight of precipitated silver powder of fibrous texture, from seven to forty per cent of cadmium oxide, and from onetenth of one per cent to ten per cent of a silver halide.

6. A pressure molded and heat sintered contact composed of a mixture of from sixty to ninety-three per cent by weight of precipitatedsilver powder of fibrous texture, from seven to forty per cent of cadmium oxide, and from onetenth of one per cent to ten per cent of a silver halide, the major portion of said cadmium oxide being in the form of densifled particles of a size greater than that which will pass through a 300 mesh screen.

'7. A pressure molded and heat sintered contact composed of a mixture of from sixty to ninety-three per cent by weight of precipitated three and seventy-five one-hundredths per cent of silver chloride.

11. A pressure molded and heat sintered con-- tact composed of a mixture of ingredients in about the followin proportions by weight: seventy-five per cent of precipitated silver powder 'of fibrous texture, twenty-one and twenty-five one-hundredths per cent of cadmium oxide, and three and seventy-five one-hundredths per cent of silver bromide.

12. A contact of the character set forth in claim 8, wherein the cadmium oxide is in such form that all of its particles will pass through a 100 mesh screen but less than half of the same will pass through a 300 mesh screen.

13. A contact of the character set forth in claim 9, wherein the cadmium oxide is in such form that all particles thereof will pass through a 100 mesh screen but less than half of the same will pass through a 300 mesh screen.

14. A contact of the character set forth in claim 10, wherein the cadmium oxide is in such form that all particles thereof will pass through a 100 mesh screen but less than half of the same will pass through a 300 meshscreen.

'15. A contact of the character set forth in clai 11, wherein the cadmium oxide is in such form that all particles thereof will pass through a 100 mesh screen but less than half of the same will pass through a 300 meshscreen.

16. An electrical contact formed of thoroughly mixed powdered materials, one of-said materials consisting of from sixty per cent to ninety-three per cent by weight of a metal of good electrical conductivity, another of said materials comprising relatively large particles of cadmium oxide, and said metal beingadapted to act as a matrix for said cadmium oxide, whereby, the electrical tity of cadmium oxide a major portion of which is in the form of relatively large particles, and

another of said materials consisting of a stillsmaller quantity of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride, and cadmium sulphate, said first mentioned material being adapted to act as a matrix for said second mentioned material, whereby the electrical conductivity of the former is substantially unaffected by the presence of the latter, and said third mentioned material acting at the operating surface of the contact to decrease heating thereof due to arcing when in use and to prevent bonding or sticking of such surface to a contact surface cooperating therewith.

18. A pressure molded and heat sintered electrical contact formed of intimately mixed powdered materials, one of said materials consisting of a relatively large quantity of metal of good electrical conductivity, another of said materials consisting of a relatively smaller quantity of cadmium oxide a major portion of which is in the form of relatively large particles, and another of said materials consisting of a still smaller quantity of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, said first mentioned material being adapted to. act as a matrix for said second mentioned material, whereby the electrical conductivity of the former is substantially unaffected by the presence of the latter, and said second and third mentioned materials acting jointly to provide a film at the operating surface of the contact to decrease heating thereof due to arcing when in use and to prevent bonding or sticking of such surface to the surface of a substantially similar, contact cooperating therewith.

19. A pressure molded and heat sintered electrical contact composed of intimately mixed powdered materials, one of said materials consisting of from sixty to ninety-three per cent by weight of silver powder, another of said materials consisting of from seven to forty per cent of cadmium oxide, and another of said materials consisting of from one-tenth of one per cent to'ten per cent of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, a major portion of said cadmium oxide being in .he form of particles of a size greater than that which will pass through a 300 mesh screen, said silver being adaptedtc act as a matrix for said cadmium oxide, whereby the electrical conductivity of the former is substantially unaffected by the presence of. the latter, andsaid cadmium oxide and metallic salt acting jointly during use of the contact to provide a film at the operating surface thereof, said film acting to decrease heating of such surface as an incident to arcing and to prevent bonding or sticking of such surface to a contact surface cooperating therewith.

20. An electrical contact formed of powdered.

materials comprising-a metalof good electrical conductivity, a second ingredient consisting of cadmium oxide, and a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride, and cadmium sulphate, said second ingredient being present in an amount corresponding to seven to forty per cent of the entire mass, said metallic salt being present in an amount corresponding to one-tenth of one per cent to ten per cent of said mass, at least fifty per cent of the amount of said second ingredient consisting of particles of a size greater than that which will pass through a 300 mesh powdered silver, cadmium oxide and a silver halide, said cadmium oxide being present in an amount of not less than seven per cent nor more than forty per cent, and said silver halide being present in an amount of not less than one-tenth of one per cent nor more than ten per cent.

22. An electrical contact consisting of fromseventy-flve per cent to eighty-seven and onehalf per cent by weight of metal of good electrical conductivity, and a relatively smaller proportion of cadmium oxide, the major portion of said cadmium oxide being in theform of particles of a size greater than that which will pass through a 300 mesh screen dispersed throughout the mass of said metal which serves as a matrix therefor.

23. A pressure molded electrical contact consisting of a mixture of from seventy-five per cent to eight-seven and one-half per cent by weight of powdered metal of good electrical conductivity, and a relatively smaller proportion of cadmium oxide densifled by heat sintering, the major portion of said densified cadmium oxide being in the form of particles of a size greater than that which will pass through a 300 mesh screen dispersed throughout the'mass of said metal which serves as a matrix therefor.

24. A pressure molded and heat sintered electrical contact comprising a mixture of from sixty percent to ninety-three per cent by weight of fine silver powder, a relatively smaller proportion by weight of cadmium oxide, and astill smaller proportion by weight of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride and cadmium sulphate, said cadmium oxide and said metallic salt being jointly in the form of powder densified by heat sintering, the major portion of said last mentioned powder being in the form of particles of a size greater than that which will pass through a 300 mesh screen dispersed throughout the mass of said metal which serves as a matrix therefor.

25. The method of producing an electrical contact having improved non-welding characteristics when in use, which consists in dispersing throughout a quantity of metal of good electrical conductivity a substantially smaller quantity of cadmium oxide,'th'e major portion of said cadmium oxide being in the form of particles of relatively large size, whereby said metal is adapted to act as a matrix for said cadmium oxide without substantially affecting the electrical conductivity of the former.

26. The method of producing an electrical contact having improved non-welding characteristics when in use, which comprises intimately mixing a relatively small quantity of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride, and cadmium sulphate with a relatively larger quantity of cadmium oxide, molding said mixture and sintering the same by application of heat to substantially increase the density thereof, then grinding said molded mixture to form a granular powder the major portion of which consists of particles of a size greater than that which will :pass through a 300 mesh screen, intimately mixing said powder with a substantially larger quantity of a powdered metal of good electrical conductivity, and then molding said last 27. The method of producing an electrical contact having improved non-welding characteristics when in use, which comprises intimately mixing a relatively small quantity of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride, and

cadmium sulphate with a relatively larger quantity of cadmium oxide, sintering said mixture by application of heat to substantially increase the density thereof, then grinding said mixture to form a granular powder the major portion of which consists of particles of a size greater than that which will pass through a 300 mesh screen,

intimately mixing said powder with a substan-.

tially larger quantity of a powdered metal of good electrical conductivity, then molding said last mentioned mixture under high pressure to provide an article of a desired shape, and then subjecting said article to a sintering heat.

28. The method of producing an electrical contact having improved non-welding characteristics when in use, which comprises intimately mixing a relatively small quantity of a metallic salt of the group consisting of silver iodide, silver bromide, silver chloride, cadmium chloride, and cadmium sulphate with a relatively larger quantity of cadmium oxide, sintering said mixture by ap 'ication of heat to substantially increase the de .ty thereof, then grinding said mixture to form a granular powder the major portion of which consists of particles of a size greater than that which will pass through a 300 mesh screen, intimately mixing said powder with a substantially larger quantity of a powdered metal of good electrical conductivity, then molding said last mentioned mixture under high pressure to provide an article of a desired shape, then subjecting said article to a sintering heat, and thereafter subjecting said article to a higher molding pressure to provide the finished article.

29, The method of producing an electrical contact having improved non-welding characteristics when in use, which comprises intimately mixing a relatively small quantity of a silver halide with a relatively larger quantity of cadmium oxide, sintering said mixture by application of heat to substantially increase the density thereof,

10 then grinding said mixture to form a granular powder adapted to pass through a mesh screen, the major portion of said powder consisting of particles of a size greater than that which will pass through a 300 mesh screen, intimately mixing said powder with a substantially larger quantity of precipitated silver powder of fibrous texture, then forming said last mentioned mixture under a pressure of approximately forty thousand pounds per square inch in a mechanical molding press into an article of a desired shape, and then subjecting the molded article to a heat treatment for sintering thereof.

30. The method of producing an electrical contact having improved non-welding characteristics when in use, which comprises intimately mixing a relatively small quantity of a silver halide with a relatively larger quantity of cadmium oxide, sintering said mixture by application of heat to substantially increase the density thereof, then grinding said mixture to form a granular powder adapted to pass through a 100 mesh screen, the major portion of said powder consisting of particles of a size greater than that which will pass through a 300 mesh screen, intimately mixing said powder with a substantially larger quantity of precipitated silver powder, then forming said last mentioned mixture under a pressure of approximately forty thousand pounds per square inch in a mechanical molding press into an article of a desired shape, then subjecting the molded article to a heat treatment for sintering thereof, and thereafter subjecting said article to a molding pressure of approximately one hundred thousand pounds per square inch to produce a finished contact.

MERLE R. SWINEHART.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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