US2572662A

US2572662A - Electrical contact

Info

Publication number: US2572662A
Application number: US604600A
Authority: US
Inventors: Linwood T Richardson; Merle R Swinehart
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1945-07-12
Filing date: 1945-07-12
Publication date: 1951-10-23
Anticipated expiration: 1968-10-23
Also published as: GB614372A

Description

Oct. 23,1951 L. 'r. RICHARDSON EI'AL 2,572,652

' ELECTRICAL CONTACT Filed July 12, 1945 MIXTURE OF INDIUM Oxujz AND A METALLIC SALT.

METAL. OF 6000 ELECTRICAL. CONDUCTIVITY.

wxa y mwlw Mme Patented Oct. 23, 1951 ELECTRICAL CONTACT Linwood T. Richardson, Wauwatosa, and Merle R. Swinehart, Milwaukee, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application July 12, 1945, Serial No. 604,600

4 Claims.

This invention relates trical contacts.

An object of the invention is to provide for use of indium oxide in the composition of contact tips of the general character herein referred to,

to improvements in elecwith unexpectedly improved results of the character hereinafter specified.

Another object is to provide for use of indium oxide in a contact composition, either with or without the addition of a suitable relatively small proportion of a metallic salt.

Another object is to provide for. attainment of certain desirable and important results by combining a metallic salt with the indium oxide.

Other objects and advantages of the invention will hereinafter appear.

The single figure of the accompanying drawing is a fragmentary sectional view, highly magnified, of an electrical contact embodying our invention.

In producing an electrical contact of the aforementioned character composed essentially of silver powder and indium oxide, we prefer to employ precipitated silver powder (which is characterized by a fibrous texture, extreme whiteness, and an unusual ability to cold weld under pressure to a tough solid of considerable tensile strength) and a commercial form of indium oxide which may initially be of such fineness as to pass through a 325 mesh screen. The indium oxide is densified by pressing, or by pressing and heat sintering operations, and thereafter ground in such a manner that at least fifty per cent of the powder which passes through a 100 mesh screen will be retained upon a 300 mesh screen. The pressure employed for densifying the indium oxide (InzOs) may be varied throughout a wide range; as for example, from 40,000 pounds per square inch to 100,000 pounds or more per square 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 thus substantially increases the range of currents which such contacts will make and break. Such a metallic salt or salts when thus employed likewise insures a more even wear of the contacts, and consequently substantially increases the length of useful life of the latter.

The aforedescribed granular powder composed of indium oxide (either with or without the aforesilver powder, and such mixture of powders is inch. In the example hereinafter given a moldthen cold molded at a pressure of about 40,000 pounds per square inch to provide disk-shaped preforms of approximately three-fourths of an inch in diameter. Thereafter said preforms are subjected to a temperature of about 1600 degrees F. for about twenty minutes. After such heat treatment said preforms are subjected to a molding pressure of about 100,000 pounds per square inch to produce the finished contacts.

We have found that a contact consisting of per cent by weight of silver powder, of the character aforedescribed, and 15 per cent by weight of indium oxide, when subjected to the aforedescribed method of treatment, had non-sticking and non-transferring characteristics substantially like or equivalent to those of a silver-cadmium oxide contact similarly produced. However, the contact resistance of the silver-indium oxide contact of the present invention was substantially lower than that of the contact having similar proportions of silver and cadmium oxide. Moreover, we have found that a set of contacts produced in the manner aforedescribed and consisting of only silver powder and as little as 7.5 per cent by weight of indium oxide will not transfer to any appreciable extent when operated tomake and break a 200 ampere, 28 volt direct current resistance load. In contrast, we have found by experiment that at least 10 per cent by weight of cadmium oxide is-required, in the aforementioned silver-cadmium oxide contacts of the Swinehart Patent No. 2,425,052, to provide for attainment of a substantially similar result.

Although we have herein specified examples involving use of 7 .5 per cent and 15 per cent, by

scale for purposes of illustration, of an electrical contact embodying our invention. In this-sectional view, the numeral 6 designates the base or matrix material, which consists of a metal of good electrical conductivity, such asv precipi tated silver powder; and the numeral? designates particles or granules of a mixture of indium oxide and a metallic salt (of the group consist:-

ing of silver iodide, silver bromide, silver chloride,.

cadmium chloride and cadmium sulphate). The materials in powder form are treated in the manner 'afbredescribed to produce the final article.

One example of contacts produced in accordance with our invention i'sas followsi Contacts three-fourths of an inch in diameter, formed under heavy pressure and heat s-intered, may be composed of an intimatemixture of 8-2 per cent by weight of precipitated silver powder-i 14.5 per cent of indium oxide prepared as aforedescribed; and' 3.5 per cent of silver iodide.

Such contacts will have substantiallythe same utility for use in the control of alternating current circuits involving relatively hi h amperage, as would be provided by contacts of otherwise similar composition but having a corresponding percentage of cadmium oxide substituted for the indium oxide above-mentioned. However, as aforeindicated, when said contacts involving use of indium oxide are to be used in direct current circuits they afford certain' very definite advantages, in respect of minimizing the contact resistance of the contacts.

' The aforementioned beneficial action of the added metallic salt (of the groupaforementioned) in preventing sticking of the contacts and in their ability to extinguish very heavy alternating current arcs, is present in respect of contacts of the character herein contemplated involving use of silver powder and indium oxide, it appearing:

1. That the volatilized metallic salt produces an ionized atmosphere at the operating surface of at least one of the cooperating contacts of a pair. Such ionized atmosphere effects spreading of the arc at the arc feet, which inh rently 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-pointformations of molten silver upon the contact or contacts, which pin-point formations, if numerous; might cause welding or sticking of the cooperating contact surfaces upon subsequent operations.

2. That the condensation of the metallic salt or salts as a thin film un on the surface or surfaces acts to prevent bonding or sticking of the silvers of the cooperating contact faces in subseouent operations.

, 3. That the aforementioned. silver halides (silver iodide, bromide or chloride), in addition tacts when in operation, likewise act to prevent the contact resistance from increasing throughout the life of the contact, and in most cases actually result in a decrease in contact resistance. It is thought that such reduction in contact resistance may be due to the presence of additional silver upon the surface of the contact or contacts as a result of decomposition of the particular metallic salt employed, and also to the action of such metallic salt in weakening the. exposed indium oxide particles so that they may be more readily broken up by mechanical and arcing action as aforedescribed.

While we have herein disclosed our invention fibrous texture, and from: about seven and one 2. A pressure molded and heat sintered powder composition electrical contact consisting of a mixture of about eighty-two per cent by weight of fine silver, aboutfourteen and onevhaif per cent of indium oxide, and about three and one-r half per cent of a metallic salt of the groupconsisting of silver iodide, silver bromide, siiver chloride, cadmium chloride and cadmium sulphate, said indium oxide and said metallic salt being in the form of a composition densified by heat sintering, at least one-half of saidlast mentioned composition being in the form of par ticles larger than those which will pass through a 300 mesh screen and small enough to pass through a 100 mesh screen, said particles being dispersed throughout the mass of fine silver which serves as a matrix therefor.

3; A pressure molded silver base powder composition electrical contact consisting of fine silver of fibrous texture, indium oxide, and a silver halide, said indium oxide being present in an amount of not less than seven and one-half" per cent nor more than twenty-one and one-fourth per cent by weight of the entire mass, and said silver halide being present in an amount. of not less than one-half of one per cent nor more than three and three-fourths .per cent by weight of the entire mass.

4. A pressure molded and heat sintered silver base powder composition electrical contact, said contact consisting of approximately eighty-two per cent by weight of fine silver of fibrous. texture, approximately fourteen and one-half per cent by weight of indium oxide,. and approximately three and one-half per cent by weightof silver iodide, said indium oxide and silver iodide being jointly in the form of dense, heat sintered' particles all of which will pass through a 100" mesh screen,

to preventing sticking of the cooperating conthe majority of. which D w be retained upon a 300 mesh screen, said particles being dispersed throughout the mass of fine silver which serves as a matrix therefor, and said contact having non-sticking and low contact resistance characteristics.

LINWOOD T. RICHARDSON. MERLE R. SWINEHART.

REFERENCES CITED The following references are of record in the 10 Number Name Date Zickrick Oct. 13, 1936 15 Number Name Date 2,157,933 Hensel et a1. May 9, 1939 2,200,854 Ruben May 14, 1940 2,200,855 Ruben May 14, 1940 2,288,122 Cox June 30, 1942 2,307,668 Cox Jan. 5, 1943 2,425,052 Swinehart Aug. 5, 1947 OTHER REFERENCES LeBlanc et a1.: Electron Conductivity of solid oxides of varying balances, Chemical Abstract, v01. 26, page 12.

Claims

1. A PRSSURE MOLDED AND HEAT SINTERED POWDER COMPOSITION ELECTRICAL CONTACT CONSISTING OF A MIXTURE OF A QUANTITY OF PRECIPITATED SILVER OF FIBROUS TEXTURE, AND FROM ABOUT SEVEN AND ONEHALF PER CENT TO FIFTEEN PER CENT B WEIGHT OF THE ENTIRE MASS OF INDIUM OXIDE, SAID INDIUM OXIDE BEING IN THE FORM OF PARTICLES ALL OF 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, SAID PARTICLES OF INIDIUM OXIDE BEING DISPERSED THROUGHOUT THE MASS OF SILVER WHICH SERVES AS A MATRIX THEREFOR.