US3502465A - Contact alloys for vacuum circuit interrupters - Google Patents

Description

United States Patent Int. Cl. C22c 9/00 US. Cl. 75153 1 Claim ABSTRACT OF THE DISCLOSURE In order to decrease the chopping current upon interrupting the vacuum type of circuit interrupters as Wel as improving the property of resisting to welding of contacts, the disclosed contact alloys comprise from 10 to 20% by weight of cobalt, from 0.1 to 1.0% by weight of bismuth and the balance copper except for small amounts of incident impurities. Contact alloy suitable for use as materials for contacts of vacuum circuit interrupters adapted to interrupt relatively low currents have also been disclosed comprising from to less than by weight of one element selected from the group consisting of bismuth, tellurium and lead, and the balance copper except for small amounts of incident impurities. These contact alloys are relatively low in chopping current characteristics and good in property of resisting to welding.

This invention relates to contact alloys for use as materials for electric contacts of vacuum circuit interrupters operative to interrupt a flow of current through the associated circuit through opening of the contacts in a high vacuum established within the interrupter.

It is Well known that if electric contacts for use in vacuum circuit interrupters are composed of copper that such copper contacts have an ability to interrupt a high magnitude of alternating current. However it is also known that they are disadvantageous in high magnitudes of chopping current resulting in an abnormal voltage induced in the associated circuit upon interruption. There has been previously prevailing the concept that the chopping phenomenon is associated with a metallic vapor or vapors evolved upon arcing across electric contacts and that any metal high in vapor pressure or low in thermal conductivity has a low magnitude of chopping current. Therefore, upon the basis of that concept there has been proposed the addition of a large amount of a suitable metal high in vapor pressure to another metal such as copper high in thermal conductivity in order to decrease a magnitude of chopping current for the resulting contact alloy. For example, an alloy including 20% by weight of bismuth and the balance copper could be utilized as electric contacts for use in vacuum circuit interrupters.

However it is difiicult to seal alloys of the type containing a large amount of metal high in vapor pressure into the associated vacuum container. Also since low boiling point elements are generally low melting point elements, brazing of those alloys causes such a low melting point element to be diffused into the associated brazing material during the brazing operation leading to the difficulty with which a sound brazed part is formed.

Therefore if any alloy containing a large amount of a low melting point element is used as a material for electric contacts which are, in turn, heated to an elevated temperature and subject to evacuation treament to be held in a high vacuum space and which have applied thereto repeated impact forces during service, then troubles that might be caused from the use of such an alloy is particularly significant.

Accordingly, it is an object of the invention to provide a new and improved copper base alloy for use as 3,502,465 Patented Mar. 24, 1970 "ice a material for electric contacts of vacuum circuit interrupters having a low magnitude of chopping current without the necessity of adding a large amount of a low melting-point element thereto as well as having' the improved property of resisting to welding.

Briefly, the invention accomplishes the above object by the provision of a copper base alloy comprising from 10 to 20% by weight of cobalt, from 0.1 to 1.0% bY weight of bismuth and the balance copper except for small amounts of incident impurities.

It is another object of the invention to provide a new and improved copper base alloy for use as a material for electric contacts of vacuum circuit interrupters adapted to interrupt relatively low current, which alloy is good in property of resisting to welding and also has the relatively low chopping current characteristics.

To this end, there is provided a copper base contact alloy comprising from 5 to less than 10% by weight of one element selected from the group consisting of bismuth, tellurium and lead, and the balance copper except for small amounts of incident impurities.

These and other objects and advantages of the invention will become apparent from the following detailed description.

The addition of a low melting point element such as bismuth, antimony or the like, in an amount of 10% or more based upon the weight of the resulting alloy to copper is known effective for decreasing a chopping current for such an alloy.

Extensive tests for the so-called chopping phenomenon were conducted with copper base alloys containing one element selected from the group consisting of bismuth, tellurium and lead, in a varying amount. Electric contacts made of such alloys were operated to interrupt alternating currents having an eifective magnitude of 10 amperes at 80 volts and an effective magnitude of 20 amperes at 160 volts in a vacuum of from 1 10- to 5X1O- torr. For each pair of electric contacts, a chopping magnitude of arc current occurring upon interruption was measured ten times and both the average of ten measured magnitudes and a maximum magnitude are tabulated in the following Table I. In Table I, for purpose of comparison data for copper are included.

TABLE I.--EFFECT OF ADDITION OF LOW MELTING ELE- MENTS UPON CHOPPING CURRENT FOR COPPER Chopping current in A upon interrupting alternating current of specified efieetive magnitude Alloy in Average Maximum Average Maximum percent wt. in in in A in A From the above Table I it will be seen that the addition of one of bismuth, tellurium and lead in an amount of 1% or less based upon the weight of the alloy did not materially affect the magnitude of the chopping current for copper.

On the other hand, in order to determine the effect of TABLE IL-EFFECT OF ADDITION OF LOW MELTING ELEMENTS UPON WELDING POWER OF COPPER Separating force in kg. after passage of current having specified peak magnitude in ka.

Alloy in percent wt. 10 12 14 15 As seen in Table II, all the low melting elements do not always decrease the welding power. For example, copper-antimony alloys are inferior in property of resisting to welding to pure copper. However Table II indicates that the addition of bismuth, tellurium or lead to copper improved the property of resisting to welding of the resulting alloys. It also indicates that an increase in amount of bismuth, tellurium or lead added to copper tends somewhat to increase the welding power of the resulting copper base alloy. Thus it has been found that bismuth, tellurium or lead is preferably added in an amount of at most 1% by weight to copper.

According to the invention, one element selected from the group consisting of bismuth, tellurium and lead is added in a small amount to copper only for the purpose of improving the property of resisting to welding and a decrease in chopping current relies upon the use of another element. The chopping current tests were conducted with numerous binary alloys containing copper and iron, cobalt or nickel in a varying amount respectively in the same manner as previously described in conjunction with Table I. Their results are tubulated in the following Table III. For purpose of comparison Table III include further data for iron, cobalt and nickel.

TABLE III.-CHOPPING CURRENT FOR COPPER BASED ALLOYS CONTAINING ONE OF IRON, COBALT AND NICKEL Chopping current in A upon interrupting alternating current of specified effective magnitude Alloy in I percent wt. Average Maximum Average Maximum From the above Table III it will be seen that from 10 to 20% by weight of cobalt is effectively added to copper for purpose of decreasing the chopping current for the resulting alloy and that the addition of iron or nickel similar in properties to cobalt is not so effective as the addition of cobalt. As will be well known, nickel is higher in vapor pressure than cobalt and copper-nickel alloys are less in thermal conductivity than copper-cobalt alloys. Also a binary copper-nickel alloy including approximately 50% of nickel based upon its weight has a minimum thermal conductivity. Nevertheless the chopping current decreases monotonously as the content of nickel increases. Thus it has been found to be incorrected that the magnitudes of chopping current of such alloys are estimated simply and easily on the basis of both the properties of each of the elements composing the alloys and the general physical characteristics of the alloys.

While cobalt is effective for decreasing the chopping current as above described it has been found that the same is disadvantageous in an increase in welding power. However this disadvantage has been eliminated through the addition of bismuth in a small amount to the coppercobalt alloys as seen in the following Table IV. The figures listed in Table IV were obtained in the same manner as already described in conjunction with Table II. Table IV also includes data for a Cu-10% Co alloy and a Cu-20% Co alloy for purpose of comparison.

TABLE IV.WELDING POWER OF COPPER-COBALT ALLOY CONTAINING ONE OF BISMU'IH, TELLURIUM AND LEAD Welding power in kg. after passage of current having specified peak magnitude in ka.

Alloy in percent wt. 10 12 14 15 Cu, 10 O0 100 100 100 100 Cu, 10 Co, 0.01 Bi 19 77 67 100 Cu, 10 G0, 0.1 B 9 18 28 100 Cu, 10 CO, 0.5 B 14 18 12 22 Cu, 10 CO, 1 Bi 22 18 26 30 Cu, 10 Co, 3 Bi 9 15 38 48 Cu, 10 C0, 5 Bi 36 38 33 54 Cu, 10 Co, 0.01 Pb 100 100 100 100 Cu, 10 Co. 0.1 Pb... 66 29 69 100 Cu, 10 Co, 0.5 Pb, 24 56 86 81 Cu, 10 C 1 Pb 2 63 100 100 Cu, 10 C 3 Pb 19 29 35 69 Cu, 10 C 1 Te 36 36 86 100 011, 10 O0, 3 Te 36 59 100 100 Cu, 20 C0 100 100 100 100 Cu, 20 G0. 0. 24 43 100 100 Cu, 20, 0- Bi 8 4G 21 17 Cu, 20 C 0.5 B1. 10 12 35 24 Cu, 20 C 1 Bi--. 18 32 16 20 Cu, 20 0 .3 Bi 8 59 23 28 Cu, 20 oo, 1 Te- 24 1s 97 100 Cu, 20 O0, 3 Te 29 61 62 100 From Tables II and IV it is noted that tellurium as added to copper to form binary alloys effectively decreases the welding power thereof whereas tellurium as added to copper-cobalt alloys is less efiective. From Table IV it will be also seen that, in order to decrease the welding power of the copper base alloy lead is required to be added to the alloy in a large amount as compared with bismuth. However the elfect of lead is not so definite as the effect of bismuth added to the alloy. It has been found that a content of bismuth required for improving the property of resisting to welding of the contact alloys should range from 0.1 to 1.0% based upon the weight of the alloy. The content of bismuth in excess of the magnitude just specified does not improve such property and instead only adversely aifects the workability of the resulting alloys.

The invention also contemplates to provide binary copper base alloys containing bismuth, tellurium or lead respectively and especially suitable for use as materials for electric contacts of vacuum circuit interrupters adapted to interrupt relatively low currents which contacts are relatively good in property of resisting to welding and relatively low in chopping current characteristics.

As understood from Table I, the copper-bishmuth, copper-tellurium and copper-lead alloys each are unsuitable for decreasing the chopping current, provided that the alloys contain copper in an amount exceeding based upon the weight of the alloy. On the other hand, it will be apparent from Table II that in order to improve the property of resisting to welding the content of bismuth should be less than 10% by weight for copperbismuth alloys whereas the content of tellurium may range from 1 to 10% by weight and if desired, may exceed 10% for copper-tellurium alloys. Also, for copperlead alloys, the content of lead may range from 1 to 10% by weight or more.

It has been found that for the binary copper-bishmuth alloys, the optimum composition should contain from 5 to less than by weight of bismuth and the balance copper. Only considering the chopping current characteristics and the property of resisting to welding coppertellurium and copper-lead alloys may be sufficiently uti lized including at most 90% by weight of copper. As previously described, however, the use of a high vapor pressure element such as tellurium, lead or the like in a large amount leads to various harmful effects. Therefore copper-tellurium and copper-lead alloys should also include from 5 to less than 10% by weight of tellurium and leads respectively and the balance copper.

It is to be understood that the present alloys are allowed to include small amounts of incident impurities provided that they do not exhibit the adverse effects upon the electric contacts of vacuum circuit interrupters as gaseous elements.

From the foregoing it will be appreciated that the invention provides contact alloys comprising from 10 to by weight of cobalt, from 0.1 to 10% by weight of bismuth and the balance copper except for small amounts of incident impurities, which alloys are low in chopping current, excellent in property of resisting to welding enough to be used as materials for heavy current contacts and also suitable for use as materials for contacts of vacuum circuit interrupters adapted to be used in producing envelopes of electron tubes.

The ternary copper-cobalt-bismuth alloys were tested in the same manner as previously described in conjunction with Table I for chopping current and the results are given in the following Table V.

TABLE V.CHOPPING CURRENT OF TERNARY ALLOY OF INVENTION Chopping current in A upon interrupting alternating current of specified electric magnitude 10A 20A Alloy in percent wt. Average Maximum Average Maximum The alloys of the invention are produced by vacuum melting followed by vacuum cooling.

Copper-cobalt alloys are generally liable to segregate during solidification and a content of cobalt in excess of 20% is diflicult to provide a homogeneous alloy. It has, however, been found that this segregation can be advantageously utilized to braze the electric contacts of the present ternary alloys to the associated members. More specifically, upon producing the ternary alloys comprising from more than 20% to 50% by weight of cobalt and bismuth in an amount as above specified, the resulting ingot will have an initially solidified surface layer enriched in cobalt but short of copper and containing no bismuth. This surface layer can then be utilized to effect brazing of contacts in easy manner. If desired, a part of cobalt may be replaced by iron.

Also since the solubility of carbon to the alloy increases with the content of cobalt, carbon may be used to remove oxygen from the alloy during the vacuum melting operation whereby an alloy very low in contents of gases can be more easily provided.

What I claim is:

1. An electrical contact for use in a vacuum circuit interrupter consisting of from 10 to 20% by weight of cobalt, from 0.1 to 1.0% by weight of bismuth, and the balance copper except for small amounts of incident impurities.

References Cited UNITED STATES PATENTS 2,975,255 3/1961 Lafferty 153 X 2,975,256 3/1961 Lee et al. 200166 X 3,246,979 4/1966 Lafierty et al 75153 X FOREIGN PATENTS 6,614 3/1965 Japan.

CHARLES N. LOVELL, Primary Examiner US. Cl. X.R. 200144, 166