US3366463A - Sintered shaped structure formed of penetration-bonded metal, particularly for arcing electric contacts - Google Patents

Description

HREINER 3,356,453

F ED OF PENETRATION'BONDED FOR ING ELECTRIC CONTACTS July 14, 1966 Jan, 30, 1968 sc SINTERED SHAPED STRUCTURE METAL, PARTICULARLY Filed Fig.3

Fig. 2

United States Patent Ofifice 3,366,463 Patented Jan. 30, 1968 3,366,463 SINTERED SHAPED STRUCTURE FORMED F PENETRATION-BONDED METAL, PARTICU- LARLY FOR ARCING ELECTRIC CONTACTfS Horst Schreiner, Nuremberg, Germany, assignor to Siemens-Schuckertwerke Aktiengesellsehaft, Berlin and Erlangen, Germany, a corporation of Germany Filed July 14, 1966, Ser. No. 565,146 Claims priority, application Germany, July 20, 1965, S 98,310 2 Claims. (Cl. 29-1821) ABSTRACT OF THE DISCLOSURE An electric arcing contact. This contact comprises a sintered, shaped structure of a penetration-bonded metal, consisting essentially of at least one higher and one lower melting metal. The pores of a compressed body, reinforced by sintering of at least one higher melting metal have a surface roughness of l-30 m. The pores are filled with a lower melting metal. The body has on the surface thereof a layer of the impregnating metal 1-10 ,um. thick.

Make and break contacts for carrying high-current must be resistant to the electric arcs of switching operations. The contacts should simultaneously have the highest possible electrical and heat conductivities. These requirements are satisfactorily met by known bonded materials such as tungsten/copper and tungsten/silver.

In the production of these contacts as penetration compound metals, a porous skeleton is first of all produced by pressing and sintering the metal powder of the high melting components. The skeleton is then filled in by impregnation of the lower melting component. The metal skeleton is located in a graphite mold during impregnation. A raw work piece is obtained, which is larger than the finished shaped structure. These contacts receive their final shape by turning or polishing on a lathe. This usually entails considerable waste of valuable contact material. Difficulties also occur during galvanic silver plating of the surfaces, machined by chip-removing tools. To obtain a satisfactory galvanic silver plating, it is necessary first to dissolve the tungsten particles from the surface. This requires several immersions in an etchant bath with intermediary rinsing. It was frequently found that 20 ,um. thick silver layers, produced according to the galvanic method, cannot withstand hardening by means of a rollingmill treatment and that they scale off.

The object of the invention is a sintered, shaped structure formed of penetration-bonded metal, which is particularly suitable for electric arcing contacts and which is not afllicted with the above-mentioned disadvantages.

According to this invention, a high melting metal powder or preferably, a metal powder mixture which contains at least one higher melting and one lower melting component is first pressed and sintered into a skeleton having a surface roughness between 1 and 30 m. Subsequently, the skeleton is saturated with a lower melting metal component and simultaneously provided with a thin, uniform coating of a lower melting component. In other words, in addition to a complete saturation of the pores of the skeleton, a thin, uniform cover layer of the impregnating metal-is obtained over the entire surface of the skeleton, at a surface roughness of 1 to 30 m.

Considerable advantages of this invention are that no further measures are required to produce an adhesive, homogeneous metallic surface layer and that shaped structure contacts may be obtained from the penetrationbonded metal without the necessity of after-treatment at the outer contours. When using copper as an impregnating metal if a silver surface is desired, one merely galvanically silver plates the copper layer without additional measures. Where silver is used as the impregnating metal, the surface layer already consists of silver.

According to a particularly favorable embodiment of the invention, the initial powder mixture with the very evenly distributed metal powder components is compressed at such a high pressure that the volume of pores corresponds to the desired volume of impregnation. The sinter shrinkage occurring during the :sintering of the skeleton is thereby taken into account. The linear sinter shrinkage amounts to approximately 0.5 to 2%. The stability of the sinter skeleton lies between 5 and 10 kp./ mm?.

The grain size distribution of the initial metal powder mixture is preferably so selected that the central surface pores of the sinter skeleton are smaller than 50 ,um. in diameter and that the surface roughness amounts to l to 30 m. A particularly favorable copper layer several m. thick is obtained with the impregnating metal copper at a temperature between 1150 and 1250 C. This layer gives the penetration-bonded metal the appearance of a galvanically copper-plated compact body. The copper layer adheres very well to the skeleton since it is a continuation of the impregnating metal.

In the drawing, FIG. 1 relates to the structure build up; and

FIGS. 2 and 3 show electrical pre-contacts of penetration-bonded metals.

The structure build up is illustrated in FIG. 1 which shows a micro-diagram of a section through the sintered, shaped structure. 1 is the impregnating metal and 2 the tungsten skeleton. 3 is the surface layer which extends directly into the pores of the skeleton filled with impregnating metal and 4 is the outer surface layer deposited on 3.

The metal powder for the production of the sinter skeleton may consist of pure tungsten, pure molybdenum or of a powder mixture. Metal powder mixtures which are particularly favorable comprise tungsten, molybdenum, rhenium or mixtures thereof as arcing resistant components with copper or silver and one or two components of the metals, nickel, cobalt, chromium or iron. Copper or silver is present up to 2 to 10% whereas the share of nickel, cobalt, chromium, iron is 0.5 to 5%.

It is preferred to add such metals, which in a fluid state, wet the surface of the high melting metal and coat it with a thin film. The metal powder may be utilized in the form of reduction powders (W, Mo, Re), electrolyte powders (Cu, Ag, Fe), carbonyl powders (Ni, Co, Fe), or mechanically broken up powder (Cr).

It is particularly advantageous to use an initial powder containing a small amount of nickel as this affords satisfactory wetting and thereby an impregnation completely free of cavities, and a uniform cover layer results on the surface pores with the indicated dimensioning.

FIG. 2 illustrates an arcing point and FIG. 3 an arcing ring with 4, the surface layer.

The following examples erve to further illustrate the invention:

Example 1 Reduction tungsten powder of a grain size 25 ,um. was compressed into a shaped structure with Mp./cm. the compression density was 11.3 g./cm. The compressed body was sintered at 1700 C., in a vacuum or in hydrogen, for the duration of an hour, to give a sintered density of 11.5 g./cm. During sintering, a linear shrinkage of 0.6% occurred. Impregnation of the sinter skeleton occurred using copper in an amount calculated to fill the pores and provide an excess of 1.5 g. copper. This was at 1200 C. for A of an hour, in a hydrogen atmosphere or in a vacuum. An additional, linear shrinkage of 0.7% occurred during saturation. The total shrinkage of 1.3% was added as an excess of the compressed body. The density of the saturated sinter skeleton amounted to 14.8 g./cm and the surface of the shaped structure was entirely covered with a several a thick copper layer.

Example 2 A powder mixture of 99.5% by weight of reduction tungsten powder (W of grain size 250 ,um. and 0.5% by weight carbonyl-Ni powder of grain size m was compressed after intensive mixing with 2 Mp./cm. into a shaped structure; the pressure density amounted to 11.4 g./cm. After sintering for an hour at 1300 C. in hydrogen or in a vacuum, a sinter density of 11.6 g./cm. was obtained at a shrinkage of 1.2%. Following saturation of the sinter skeleton with copper under conditions described in Example 1, an additional shrinkage of 0.6% was obtained; the density of the impregnated bonded metal amounted to 14.7 g./cm. This shaped structure is also coated at its surface by a shining, pure copper layer.

In Examples 1 and 2 the surface roughness of the sinter skeleton amounts to between 1 and 30 ,um.

Example 3 A powder mixture of 07.8% by weight reduction tungsten powder of grain size 200 am. (median grain size 60 ,um.), 2% by weight electrolyte copper powder of grain size 200 ,um. (median grain size 40 ,wm.), and 0.2% by weight carbonyl-Ni powder of grain size 5 m. was compressed after intensive mixing with 2 Mp./cm. into a shaped structure. The compression density was 11.2 g./cm. The diameter of the pressed portion, according to FIG. 2, amounted to 20.20i0.04 mm. Sintering occurred at 1300" C. in hydrogen or in a vacuum, for one hour, whereby the diameter amounted to 20.04i0.06 (sintering density 'ys:11.4 g./cm. Following saturation with pure electrolyte copper, a contact form structure was obtained which was coated all over by a smooth, thin, shiny copper layer. The diameter was 19.94i0.06 mm.

4 It lies within the required tolerance of the fit 20 hll, that is to say, the diameter lies between 19.87 and 20.00 mm. The density of the saturated bonded metal amounted to 14.6 g./cm. The median depth of roughness of the surface of the sinter skeleton was 16 ,wIn.

Similarly, the structure of FIG. 3 was prepared as above. Following one hour of sintering at 1300 C. in hydrogen or in a vacuum, a sinter density of 11.6 g./cm. was obtained at a shrinkage of 1.2%. After impregnating the sinter skeleton with copper under conditions described in Example 1, an additional shrinkage of 0.6% was obtained; the density of the saturated bonded metal amounts to 14.7 g./cm. This shaped structure is also coated by a shiny, pure copper layer at its surface.

I claim:

1. An electric arcing contact comprising a sintered, shaped structure of a penetration-bonded metal, consisting essential-1y of a compressed body of at least one higher and one lower melting metal, wherein the pores of a compressed body, reinforced by sintering of at least one higher melting metal, have a surface roughness of 1-30 rn, said pores are filled or impregnated with a lower melting metal, and said body has on the surface thereof a layer of the impregnating metal 1-10 m. thick.

2. The contact of claim 1, which contains 30 to vol. percent of the lower melting metal.

References Cited UNITED STATES PATENTS 2,313,070 3/1943 Hensel 29182.1 2,633,628 4/1953 Bartlett 29182.1 X 2,669,008 2/1954 Levi 29182.1 X 2,851,381 9/1958 Hoyer 29182.1 X 2,922,721 1/1960 Tarkan 29182.1 X 3,107,418 10/1963 Gorman 29-1821 X CARL D. QUARFORTH, Primary Examiner.

BENJAMIN R. PADGETT, Examiner.

A. J. STEINER, Assistant Examiner.

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