US2197394A - Electric contact - Google Patents

Description

Patented Apr. 16,1940

PATENT OFFICE EIEUIRIC CONTACT UNITED STATES poration of Delaware No Drawing. Application June 5, 1939, Serial No. 277,494

6 Claims.

This invention relates to a new silver electric contact and is concerned more particularly with an electric contact which has improved physical and electrical characteristics.

It is one of the objects of the invention to provide a silver base contact material which can be used for an electrical make and break contact; retaining low contact resistance, having low material transfer and having increased resistance 10 to welding and sticking under electrical loads.

. Another object of the invention is to provide a new silver base contact alloy which has improved physical properties, such as hardness and tensile strength, and retains a high ductility.

It is a further object to provide a material which shows considerable improvements as far as corrosion resistance is concerned.

Other objects of the invention will be apparent from the following description taken in connec- 0 tion with the appended claims. The present invention comprises a combination of elements, methods of manufacture and the product thereof, brought out and exemplified in the disclosure hereinafter set forth, the scope of the inventio being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements, without departing from the spirit of the invention.

The present invention comprises an electric contact of silver with beryllium, and a third element, taken from the same group, to which 35 beryllium belongs, namely, magnesium, zinc and cadmium.

In the formation of the new contact alloy, it is preferable to provide a composition of the mate- 0 rials specified in the following proportions:

} Per cent Beryllium; .05- 4 Metal taken from the second group of the periodic system, comprising magnesium,

45 zinc and cadmium Silver Substantially the balance titanium, zirconium,

located at approximately .97% of beryllium, an alloy of this composition having a melting point of 881 degrees C. The alpha solid solubility of beryllium in silver is quite small and at the eutectic temperature, does not exceed .35% ii beryllium. This solid solubility furthermore decreases with temperature which indicates that the alloys of this type can be improved by heat treating as far as electrical conductivity is concerned, and also as far-as hardness and tensile properties are concerned. The increase in properties, however, with such small percentages of beryllium present, is comparatively small. The fact that the system is of an eutectic nature, however, results in a material which retains a rather high electrical conductivity, because the electrical conductivity is lowered primarily if a solid solution is formed; therefore, in our tests, we have found that a material of almost the eutectic composition and which contained .94% b beryllium, balance silver, showed in the as cast condition, an electrical conductivity of 67.2% I. A. C. S. With an increase of the beryllium content, the solidus curve is raised very steeply and an alloy containing about 4% beryllium has 25 a solidus which is located above 1000 degrees C. The elements which are contemplated as additions in the present disclosure, arecadmiurn, magnesium and zinc. There is considerable similarity in the diagrams of silver-cadmium, silver-magnesium and silver-zinc. All three of these metals, namely, magnesium, zinc and cadmium, form an alpha solution with silver, the alpha range being the smallest in the silvermagnesium system, and the highest in the silvercadmium system. In addition to the alpha range, a number of other phases are'formed that are usually identified by such letters as beta, gamma, delta, and in the case of silver-cadmium and silver-zinc, epsilon, and eta. The present inven- 40 tion, however, considers the addition of the elements of magnesium, .cadmium and zinc,

primarily in their alpha range or possibly in the beta range. a

In preparing the alloys, it is desirable to add beryllium in the. form of a silver-beryllium master alloy containing approximately 4-6% of beryllium. The master alloys which were used in the present experiments contained, in one case, 4% of beryllium, and had a Rockwell F hardness of -81, and in the other case, 5% of beryllium, which alloy had a Rockwell F hardness of 86. The materials of the second group of the periodic system, namely, magnesium, zinc and The master alloys were prepared either by melting or by pressed powder methods.

We have investigated a. series of compositions and have found that the following alloys, which are given by way of example only, have shown good physical properties and also good electrical properties:

Per cent (1) Beryllium .05- 4 Metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium .1 5 Silver Balance (2) Beryllium .05- 4 Metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium 1- 8 Silver Balance (3) Beryllium .05- 4 Metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmiumc 1-25 Silver Balance (4) Beryllium .05- 4 Metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium 5-25 Silver Balance (5) Beryllium .75- 2 Metal of the second group of the periodic system, comprising magnesium, zinc and cadmium 1- 10 Silver Balance An alloy containing about .91% beryllium and 6-7% cadmium, showed in the cast condition 40% electrical conductivity and a cast hardness of 17 Rockwell F. After swaging, 25%, this hardness was increased to 89 Rockwell F. This material showed a very high density in the as cast condition.

An alloy containing approximately .9-1% and 3 4% zinc, showed an electrical conductivity in the cast condition of 26.1%, a cast hardness of 37 Rockwell F, which was raised to 92- Rockwell F by 25% cold swaging.

An alloy approximately beryllium and /z%-3% of magnesium, showed an electrical conductivity in the as cast condition of 22.7%, a cast hardness of 43 Rockwell F, which was increased to Rockwell F, by 25% cold swaging. This latter alloy had a specific gravity of approximately 9 grams peT cc., which is considerably below that of fine silver, the specific gravity of which is 10.5. This is due to the lower specific gravity, both of magnesium and beryllium.

In adding cadmium, zinc and magnesium to the alloys of the present invention, more consistent results are obtained if the substitution of elements is carried out by volume percentage, rather than weight percentage. This automati= cally indicates that a smaller percentage of magnesium added, corresponds to a higher percentage of, for instance, cadmium, because the speciilc gravities of the two materials are quite different. The specific gravity of magnesium, for instance, is 1.74, while the specific gravity of cadmium is 8.648. This is a ratio of about 1:5. In other words, in order to have the same volume percentage of magnesium and cadmium present, in the alloys of the present invention, it would be necessary, in one case, to add about 3 weight per cent of magnesium and in the other case, 15 weight per cent, of cadmium. The specific gravity of zinc is 7.14 and the ratio of speciflc gravities of magnesium to zinc, corresponds to approximately 1:4. The constitutional diagrams are usually plotted in weight per cent. By changing the weight percent to volume percent, it can be found that the alpha solid solutions of magnesium in silver, or zinc in silver, or cadmium in silver are very nearly-the same if they are plotted in volume percent rather than in weight percent.

The corrosion resistance of silver alloys is highest in the alpha solid solution range, and therefore it is desirable to add beryllium to the alpha solid solutions of magnesium in silver, zinc in silver and cadmium in silver.

A comparison test was conducted, wherein contacts of similar physical dimensions were tested on a resistive inductive circuit at 470 cycles per minute and wherein current flowing in the circuit was increased periodically to obtain definite current values in the nature described above in comparison with contact materials produced in the prior art. The amount of material transfer of one contact to another was found to be considerably less' than materials of the prior art, not containing a combination of beryllium and a metal taken from the group of magnesium, zinc and cadmium.

At the same time, it was found that after completion of the tests, the contact resistance of the material was quite low. The actual tests showed a contact resistance after completion of the tests, of .40 milliohm, in the case of the beryllium-cadmium alloy. In the case of the beryllium-zinc alloy the contact resistance was .70 milliohm after completion of the tests, and in the case of the beryllium-magnesium alloy the contact resistance was .80 after completion of the test. The beryllium-cadmium alloy showed the highest critical current values at which the material would not stick.

The alloys of the present invention have been found to have excellent free machining properties for the production of commercial parts where high speed production and corrosion resistance are required. r While the present invention as to its objects and advantages has been described herein as carriedout in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover. the invention broadly, within the spirit and scope of the appended claims.

What is claimed is:

1. An electric contact consisting of beryllium, .05-4%, 3. metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium, .1-25%, silver, substantially the balance.

2. An electric contact consisting of beryllium, 05-4%, and a metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium, .1-5%, silver substantially the balance.

3. An electric contact consisting of beryllium, 05-4%, and a metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium, 1'-8%, and silver, substantially the balance.

4. An electric contact consisting of beryllium,

.054%, and a metal taken from the second group of the periodic system, comprising magnesium, zinc and cadmium, 1-25%, silver substantially the balance,

5. An electric contact consisting of beryllium,

.054%, and a metal taken from the second group group of the periodic system, comprising magof the periodic system, comprising magnesium, nesium, zinc and cadmium, 140%, silver subzinc and cadmium, 5-25%, silver substantially stantially the balance. the balance. FRANZ R. HENSEL.

5 6. An electric contact consisting of beryllium, KENNETH L. EMMERT. 5

.75-2%%, and a metal taken from the second JAMES W. WIGGS.