CONTACT MATERIAL FOR VACUUM CIRCUIT BREAKER

Abstract: A contact material for a vacuum circuit breaker having excellent properties, which consists essentially of copper, molybdenum, one member selected from the group consisting of niobium and tantalum, and one or more kinds of low melting point materials.

Description: This present invention relates to a contact material for a vacuum circuit breaker, which is excellent in its large current breaking property. The vacuum circuit breaker has various advantages such that it is free from maintenance, does not bring about public pollution, is excellent in its current breaking property, and so forth, on account of which the extent of its application has become broadened very rapidly. With this expansion in its utility, demands for higher voltage withstand property and large current breaking capability of the vacuum circuit breaker have become increasingly stringent. On the other hand, the performance of the vacuum circuit breaker depends, to a large extent, on those factors to be determined by the contact material placed within a vacuum container for the vacuum circuit breaker. For the characteristics of the contact material for the vacuum circuit breaker to satisfy, there may be enumerated: (1) large current breaking capacity; (2) high voltage withstand; (3) small contact resistance; (4) small melt-adhesive force; (5) low chopping current value; (6) good workability; (7) sufficient mechanical strength; and so forth. In the actual contact material, it is fairly difficult to satisfy all of these characteristics, and general circumstances at the present time are such that use is made of a material which meets particularly important characteristic depending on its use at the sacrifice of other characteristics to some extent. For instance, the contact material of copper-tungsten alloy as disclosed in Japanese Unexamined Patent Publication No. 78429/1980 is excellent in its voltage withstand capability, owing to which it is frequently employed for a load-break switch, a contactor, and so forth, although it has a disadvantage such that its current breaking property is inferior. On the other hand, the contact material of copper-chromium alloy as disclosed, for example, in Japanese Unexamined Patent Publication No. 71375/1979 has been widely used for a circuit breaker or the like owing to its excellent current breaking property, but its voltage withstand capability is inferior to that of the above-mentioned contact material of copper-tungsten alloy. Further, the contact material of copper-chromium-bismuth alloy as disclosed, for example, in Japanese Unexamined Patent Publication No. 147481/1979 has a low melt-adhesion and peeling force, which makes it possible to reduce the operating force of the vacuum circuit breaker with the consequent advantages such that the circuit breaker can be designed in a compact size, and the chopping current value can be made low. On the other hand, however, its voltage withstand capability and current breaking property are inferior to those of the above-mentioned contact material of copper-chromium alloy. Furthermore, the contact material of copper-molybdenum-niobium alloy as disclosed, for example, in Japanes Unexamined Patent Application No. 107 619/1986 is very excellent in its current breaking property and voltage withstand capability, owing to which it appears to be useful in wide range in future, although the contact material indicates its property of somewhat higher chopping current value and melt-adhesion and peeling force than those of the above-mentioned contact material of copper-chromium-bismuth alloy. A contact material for a vacuum circuit breaker which consists essentially of copper as the basic component, and, as the other components, 35% by weight or below of chromium and 40% by weight or below of niobium, the total quantity of chromium and niobium in said contact material being 10% by weight and above is disclosed in EP-A 0 109 088. As described in the foregoing, the conventional contact materials for the vacuum circuit breaker have so far been used in taking advantage of various properties they possess. In recent years, however, demands for large current breaking property and high voltage withstand capability of the vacuum circuit breaker have become more and more stringent with the result that such conventional contact materials tend to be difficult to satisfy the required performance. There has also been a demand for the contact material having more excellent performance against size-reduction in the vacuum circuit breaker. The present invention has been made with a view to improving the conventional contact material as mentioned in the foregoing, and aims at providing an improved contact materilal for the vacuum circuit breaker being excellent in its current breaking property; having higher voltage withstand capability; having low melt-adhesion and peeling force; and being small in its chopping current value and its power consumption at the contact points. The present inventors produced various alloy materials, on the experimental basis, by addition of various metals, alloys, and intermetallic compounds to copper base, and by assembly of these alloy materials in the vaccum circuit breaker, with which to conduct various tests. As the result of these tests, it was found out that the contact materials containing one or more kinds of low melting point metals such as bismuth, tellurium, antimony, thallium, lead, selenium, cerium and calcium in the alloy base of copper-molybdenum-niobium, were excellent in their current breaking property and voltage withstand capability, and had low melt-adhesion and peeling force, low chopping current value, and low power consumption at the contact. The contact material for the vacuum circuit breaker according to the present invention is characterized in that it contains, in the copper-molybdenum-niobium alloy base, one or more kinds of low melting point metals selected from bismuth, tellurium, antimony, thallium, lead, selenium, cerium and calcium. Various ways of carrying out the present invention will be described in detail hereinbelow with reference to several preferred examples thereof in reference to the accompanying drawing, in which:- Figures 1, 2 and 3 are graphical representations showing the current breaking property of the contact materials produced by the infiltration method according to one example of the present invention; Figures 4, 5 and 6 are graphical representations showing the voltage withstand capability or the contact materials produced by the infiltration method according to one example or the present invention; Figures 7 and 8 are graphical representations showing the current breaking property of the contact materials produced by the powder sintering method according to another example of the present invention; Figures 9 and 10 are graphical representations showing the voltage withstand capability of the contact materials produced by the powder sintering method accoding to another example of the present invention; Figures 11 and 12 are graphical representations showing the current breaking property of the contact materials produced by the vacuum hot press method according to other example of the present invention; and Figures 13 and 14 are graphical representations showing the voltage withstand capability of the contact materials produced by the vaccum hot press method according to other example of the present invention. Figures 15, 16 and 17 are graphical representations showing the current breaking property of the contact materials produced by the infiltration method according to one example of the present invention; Figures 18, 19 and 20 are graphical representations showing the voltage withstand capability of the contact materials produced by the infiltration method according to one example of the present invention; Figures 21 and 22 are graphical representations showing the current breaking property of the contact materials produced by the powder sintering method according to another example of the present invention; Figures 23 and 24 are graphical representations showing the voltage withstand capability of the contact materials produced by the powder sintering method according to another example of the present invention; Figures 25 and 26 are graphical representations showing the current breaking property of the contact materials produced by the vacuum hot press method according to other example of the present invention; and Figures 27 and 28 are graphical representations showing the voltage withstand capability of the contact materials produced by the vaccum hot press method according to other example of the present invention. [EXAMPLES] In the following, the present invention will be described in detail with reference to specific examples thereof. [EXAMPLE 1] (Production of Contact Materials) The contact materials were produced in accordance with the powder metallurgy using the three methods of "infiltration", "complete powder sintering; and "hot pressing". Production of the contact material according to the first method infiltration was carried out in such a manner that molybdenum powder having particle size of 3 µm in average, niobium powder having a particle size of 40 µm or below, copper powder having a particle size of 40 µm or below, and bismuth powder having a particle size of 75 µm or below were weighed at their respective ratios of 73.8 : 7.7 : 18.0 : 0.5, followed by mixing the ingredients for two hours; subsequently, this mixed powder was filled in a metal mold of a predetermined configuration and subjected to shaping under a pressure of 1 ton/cm²; thereafter, a mass of oxygen-free copper was placed on this shaped body, which was held for one hour in the hydrogen atmosphere at a temperature of 1,250°C to thereby obtain the contact material with the oxygen-free copper having been impregnated into the shaped bpdy. The ultimate compositional ratio of this contact material is indicated in Table 1 below, where it is indicated as "Sample No. N-Bi-18". Incidentally, this Table l lists other contact materials of various compositional ratios, which were produced by the same method as described above. Production of the contact material according to the second method of complete powder sintering was carried out in such a manner that molybdenum powder having an average particle size of 3 µm, niobium powder having a particle size of 40 µm or below, copper powder having a particle size of 75 µm or below, and bismuth powder having a particle size of 75 µm or below were weighed at their respective ratios of 38.1 : 1.9 : 59.9 : 0.1, followed by mixing the ingredients for two hours; subsequently, this mixed powder was filled in a metal mold of a predetermined configuration and subjected to shaping under a pressure of 3.3 tons/cm²; thereafter, this press-formed body was sintered for two hours in the hydrogen atmosphere at a temperature immediately below the melting point of copper, whereby the intended contact material was obtained. The ultimate compositional ratio of this contact material is indicated in Table 2, where it is indicated as "Sample No. N-Bi-89". By the way, this Table 2 also lists other contact materials of different compositional ratios, which were produced by the same method as described above. Production of the contact material according to the third method of hot pressing was carried out in such a manner that molybdenum powder having an average particle size of 3 µm, niobium powder having a particle size of 40 µm or below, copper powder having a particle size of 75 µm or below, and bismuth powder having a particle size of 75 µm or below were weighed at their respective ratios of 38.1 : 1.9 : 59.9 : 0.1, followed by mixing the ingredients for two hours; subsequently, this mixed powder was filled in a dice made of carbon and then subjected to heating in the vacuum for two hours at a temperature of 1,000°C, during which a pressure of 200 kg/cm² was applied to the mixed powder by means of the hot press device, thereby obtaining a mass of the contact material. The ultimate compositional ratio of the thus obtained contact material is shown in Table 3 below, where it is indicated as "Sample No. N-Bi-137". By the way, this Table 3 also indicates other contact materials of different compositional ratios, which were produced by the same method as described above. Also, for the purpose of comparing the properties with the contact materials according to the present invention, the compositional ratios of the contact materials which have heretofore been used are shown in Table 4 below. The same method of the complete powder sintering as described above was used for the production of these conventional contact materials. (Properties of Contact Materials) The above-described contact materials produced in accordance with each of the afore-described various methods in the powder metallurgy were machine-processed into electrodes, each having 20 mm in diameter. Each of these electrodes were then assembled into a vacuum circuit breaker to measure its electrical properties. The results of measurement are shown in Table 5 below. The measurements were carried out on the current breaking property, voltage withstand capability, chopping current value, melt-adhesion and peeling force, and power consumption at the contact points. The results are expressed in terms of magnification with the properties of the conventional Cu-25Cr alloy (the sample C-1 in Table 4) as the reference. For the current breaking capability, therefore, a higher magnification indicates superiority; and the contact point having its magnification of 1 or above indicates that it possesses more excellent current breaking capability than the conventional Cu-25Cr alloy. With regard to the voltage withstand capability, the same thing as that of the current breaking property can be said, i.e., a higher magnification indicates superiority. On the other hand, the chopping current value should desirably be lower in its magnification from the standpoint of its use, hence a lower magnification indicates superiority. In the same manner, a lower magnification of the melt-adhesion and peeling force may be advantageous from the view point of the operating machanism, and a lower magnification should also be desirable concerning the power consumption at the contact point; therefore, lower values of the magnification for both properties indicate superiority. From Table 5, it is seen that, with regard to the current breaking property, almost all of the contact materials according to the present invention which were produced by the infiltration method are superior to the conventional Cu-25Cr alloy contact material. For those contact materials having their current breaking property of 1 or below, when the Sample No. N-Bi-73, for example, is compared with Cu-Cr-Bi alloy material (Sample No. C-Bi-7 in Table 6 below) containing therein the same amount of bismuth (20% by weight) as in N-Bi-73, it is seen that N-Bi-73 has the magnification value of 0.6 (as compared with Cu-25Cr), while C-Bi-7 has the magnification value of 0.51 (as compared with Cu-25Cr), hence the contact material of the present invention is superior. Figure 1 is a graphical representation showing the current breaking property of the contact materials according to the present invention, in which the current breaking property is expressed in terms of the contact material produced by the infiltration method with the amount of Cu being approximately 60% by weight. In the drawing, the ordinate axis denotes the current breaking property with the property of the conventional Cu-25Cr contact material (Sample No. C-1) being made the reference, while the abscissa axis represents the adding quantity of Bi. In the drawing, a curve 1 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 4.7% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-1, N-Bi-13, N-Bi-25, N-Bi-37, N-Bi-49, N-Bi-61, N-Bi-73); a curve 2 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 9.4% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-2, N-Bi-14, N-Bi-26, N-Bi-38, N-Bi-50, N-Bi-62, N-Bi-74); a curve 3 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 18.9% by weight, wherein the adding quantity of Bi is varied (Sample Nos, N-Bi-3, N-Bi-15, N-Bi-27, N-Bi-39, N-Bi-51, N-Bi-63, N-Bi-75); and a curve 4 also indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 28.5% by weight, wherein the adding quantity of Bi is varied (Sample Nos, N-Bi-4, N-Bi-16, N-Bi-28, N-Bi-40, N-Bi-52, N-Bi-64, N-Bi-76). Further, in this drawing, a curve 5 (in dash line) indicates the current breaking property of the conventional Cu-25Cr alloy contact material (Sample Nos. C-1, C-Bi-1, C-Bi-2, C-Bi-3, C-Bi-4, C-Bi-5, C-Bi-6, C-Bi-7), to which Bi was added. Also, in the same drawing, a double-circle 6 indicates the current breaking property of the conventional Cu-Mo alloy contact material (Sample No. M-1). The results of the measurements on these conventional alloy contact materials are shown in Table 6 below. From Figure 1, it may be seen that the contact materials of the present invention with the added quantity of Nb relative to Mo being 9.4% by weight, 18.9% by weight and 28.5% by weight, respectively (the curves 2, 3 and 4 in the drawing) are superior to the conventional Cu-25Cr alloy contact material, even if the adding quantity of Bi is 20% by weight. Further, the alloy contact material of the present invention with the added quantity of Nb relative to Mo being 4.7% by weight (the curve 1 in the drawing) is also superior to the conventional Cu-25Cr alloy contact material, if the adding quantity of Bi is not exceeding 5% by weight, and this contact material is still excellent in comparison with the Cu-25Cr-Bi alloy contact material (the curve 5 in the drawing), even when the adding quantity of Bi is above 5% by weight. Figure 2 is a graphical representation showing the current breaking property of the contact materials according to the present invention, in which the current breaking property is expressed in terms of the contact material produced by the infiltration method with the amount of Cu being approximately 50% by weight. In the drawing, both axes of ordinate and abscissa represent the same entries as in Figure l. In the drawing, a curve 7 indicates the current breaking property of the contact material of the present invention with the added quantity of Nb relative to Mo being 4.7% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-5, N-Bi-17, N-Bi-29, N-Bi-41, N-Bi-53, N-Bi-65, N-Bi-77); a curve 8 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 9.4% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-6, N-Bi-18, N-Bi-30, N-Bi-42, N-Bi-54, N-Bi-66, N-Bi-78); a curve 9 is the current breaking property of the contact material with the added quantity of Nb relative to Mo being 18.9% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-7, N-Bi-19, N-Bi-31, N-Bi-43, N-Bi-55, N-Bi-67, N-Bi-79); a curve 10 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 28.5% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-8, N-Bi-20, N-Bi-32, N-Bi-44, N-Bi-56, N-Bi-68, N-Bi-80). From Figure 2, it may be seen that the contact materials of the present invention with their respective added quantity of Nb relative to Mo being 4.7% by weight, 9.4% by weight, 18.9% by weight, and 28.5% by weight (the curves 7, 8, 9 and 10) have more excellent current breaking property than that of the conventional Cu-25Cr alloy contact material, even when the adding quantity of Bi is 20% by weight. Further, in comparison with Figure 1, the contact materials of the present invention with the added quantity of Nb relative to Mo being 4.7% by weight and 9.4% by weight, respectively, show their improved current breaking property. Figure 3 is also a graphical representation showing the current breaking property of the contact materials according to the present invention, in which the current breaking property is expressed in terms of the contact material produced by the infiltration method with the amount of Cu being approximately 40% by weight. In the drawing, both axes of ordinate and abscissa denote the same entries as in Figure 1. In the drawing, a curve 11 indicates the current breaking property of the contact material according to the present invention with the added quantity of Nb relative to Mo being 4.7% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-9, N-Bi-21, N-Bi-33, N-Bi-45, N-Bi-57, N-Bi-69, N-Bi-81); a curve 12 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 9.4% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-10, N-Bi-22, N-Bi-34, N-Bi-46, N-Bi-58, N-Bi-70, N-Bi-82); a curve 13 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 18.9% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-11, N-Bi-23, N-Bi-35, N-Bi-47, N-Bi-59, N-Bi-71, N-Bi-83); and a curve 14 indicates the current breaking property of the contact material with the added quantity of Nb relative to Mo being 28.5% by weight, wherein the adding quantity of Bi is varied (Sample Nos. N-Bi-12, N-Bi-24, N-Bi-36, N-Bi-48, N-Bi-60, N-Bi-72, N-Bi-84). From Figure 3, it may be seen that the contact materials of the present invention with their respective added quantities of Nb relative to Mo being 9.4% by weight, 18.9% by weight, and 28.5% by weight (the curves 12, 13 and 14 in the drawing) have the superior current breaking property to that of the conventional Cu-25Cr alloy contact material, even when the adding quantity of Bi is 20% by weight. It may also be seen that the contact material of the present invention with the added quantity of Nb relative to Mo being 4.7% by weight (the curve 11 in the drawing) has the superior current breaking property to that of the conventional Cu-25Cr alloy contact material, provided that the adding quantity of Bi does not exceeds 11.5% by weight. It may further be seen that, even when the adding quantity of Bi is above 11.5% by weight, the contact materials of the present invention are still more excellent, in respect of the same adding quantity of Bi, than the Cu-25Cr-Bi alloy contact material (vide: the curve 5 in Figure 1). On the other hand, however, the current breaking property of the contact materials in Figure 3 is generally low in comparison with that in Figure 2. Further, when this Figure 3 is compared with Figure 1, the optimum current breaking property may be obtained on the alloy contact material with the Cu content being in the vicinity of 50% by weight. In Figures 1, 2 and 3, on the other hand, it is seen that the degree of lowering in the current breaking property of the contact material, when the adding quantity of Bi is increased, tends to be smaller with the Cu content of 40% by weight than other constituent elements. Incidentally, it is to be added that, when comparing the contact material of the present invention (Sample Nos. N-Bi-1, through N-Bi-84) with the conventional Cu-Mo contact material (Sample No. M-1), all of the contact materials according to the present invention have more excellent currentt breaking property than the conventional Cu-Mo alloy contact material. From the foregoing, it may be concluded that, when the added quantity of Nb relative to Mo is 9.4% by weight or above, the contact material of the present invention indicates more excellent current breaking property than the conventional Cu-25Cr alloy contact material within the Cu content ranging from 40 to 60% by weight, irrespective of the adding quantity of Bi; when the added quantity of Nb relative to Mo is 4.7% by weight, the contact material indicates more excellent current breaking property than the conventional Cu-25Cr alloy contact material with the adding quantity of Bi of up to 5% by weight in case the Cu content is 40% by weight, or with the adding quantity of Bi of up to 11.5% by weight in case the Cu content is 60% by weight; and when the added quantity of Nb relative to Mo is 4.7% by weight and the Cu content is 50% by weight, the contact material indicates more excellent current breaking property than the conventional Cu-25Cr alloy contact material, irrespective of the adding quantity of Bi. Therefore, when comparing the contact materials of the present invention with the conventional Cu-25Cr-Bi alloy contact material in respect of the same Bi content, all of the contact materials according to the present invention indicate their excellent current breaking property within the whole compositional range. Moreover, from Table 5 below, it will be seen that the contact material according to the present invention is superior to the conventional Cu-25Cr alloy contact material in respect of the voltage withstand capability. More specifically, in respect of the contact material having the voltage withstand capability of 1 or below, when the Cu-25Cr-1Bi alloy contact material (Sample No. C-Bi-4) containing the same amount of Bi (1% by weight) as in the contact material of the present invention (Sample No. N-Bi-37, for example) is compared with the N-Bi-37 alloy contact material, the latter has its voltage withstand capability of 0.55 (a ratio to Cu-25Cr), in contrast to which the C-Bi-4 alloy contact material has its voltage withstand capability of 0.3 (a ratio to Cu-25Cr). From this, it is seen that the contact material of the present invention indicates more excellent voltage withstand capability than that of the conventional contact material. The measurement of the voltage withstand capability of the contact material was done by repeating the following cycle of the steps in a number of times: (1) conduction of electric current; (2) no-load breaking; (3) application of high tension voltage; and (4) checking of presence or absence of electric discharge owing to application of high tension voltage. These four steps (1) to (4) are made constitute one cycle, and, by repeating this cycle in a number of times, a voltage withstand value was calculated from (the number of cycle, at which the electric discharge occurred)/(the total number of the cycle), based on which calculation the voltage application was adjusted so that the probability of the electric discharge may become 50%. Table 5 below indicates the voltage withstand value or the contact materials according to the present invention with the voltage value to bring about 50% discharge probability in the conventional Cu-25Cr alloy contact material as the refrence. In this measurement, the current conduction, the space interval between the contacts, and other conditions were set same. Figure 4 is a graphical representation showing the voltage withstand capability of the contact material according to the present invention produced by the infiltration method with the Cu content being 60% by weight, in which the ordinate axis denotes the voltage withstand capability of the contact material of the present invention with the voltage withstand capability of the conventional Cu-25Cr alloy contact material being made the reference, and the abscissa axis shows the adding quantity of Bi. Incidentally, it should be noted that, for the purpose of indicating variations in the voltage withstand capability owing to addition of varying amount of Bi, the graphical representation is divided into Figure 4-1 and Figure 4-2 at the point of the Bi adding quantity of l% by weight. In these divided graphical representations, the curves 1 to 5 and the double-circle 6 are for the same contact materials as those shown in Figure 1. From Figures 4-1 and 4-2, it may be seen that the contact materials of the present invention (the curves 1, 2, 3 and 4) are superior to the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may be seen further that, in comparison with the conventional Cu-25Cr alloy contact material, the contact materials of the present invention have their superior voltage withstand capability to that of the conventional Cu-25Cr alloy contact material, when the contact material has its added quantity of Nb relative to Mo of 4.7% by weight and the adding quantity of Bi is up to 0.2% by weight; when the contact material has its added quantity of Nb relative to Mo of 9.4% by weight and the adding quantity of Bi is up to 0.35% by weight; when the contact material has its added quantity of Nb relative to Mo of 18.9% by weight and the adding quantity of Bi is up to 0.5% by weight; and when the contact material has its added quantity of Nb relative to Mo of 28.5% by weight and the adding quantity of Bi is up to 0.65% by weight. Further, it may be seen from Figures 4-1 and 4-2 that the contact materials with more quantity of addition of Nb relative to Mo indicate a small degree of decrease in the voltage withstand capability owing to increase in the adding quantity of Bi. Figure 5 is a graphical representation showing the voltage withstand capability of the contact material according to the present invention produced by the infiltration method with the Cu content being 50% by weight, in which both axes of ordinate and abscissa denote the same entries as in Figures 4-1 and 4-2. It is to be noted that, same as in Figure 4, this graphical representation of Figure 5 is divided into Figures 5-1 and 5-2 at the point of the Bi adding quantity of l% by weight, and that the curves 7 to 10 are for the same contact materials as in Figure 2. From Figures 5-1 and 5-2, it may be seen that the contact materials of the present invention (the curves 7, 8, 9 and 10) are superior to the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may be seen further that, in comparision with the conventional Cu-25Cr alloy contact material, the contact materials of the present invention have their superior voltage withstand capability to that of the conventional Cu-25Cr alloy contact material, when it has the added quantity of Nb relative to Mo of 4.7% by weight and contains up to 0.3% by weight of the added Bi; when it has the added Nb relative to Mo of 9.4% by weight and contains up to 0.55% by weight of the added Bi; when it has the added quantity of Nb relative to Mo of 18.9% by weight and contains up to 8% by weight of the added Bi; and when it has the added Nb relative to Mo of 28.5% by weight contains up to 11.5% by weight of added Bi. Further, it may be seen from Figures 5-1 and 5-2 that the contact materials with more added quantity of Nb relative to Mo indicate a small degree of decrease in the voltage withstand capability due to increase in the adding quantity of Bi, as Figures 4-1 and 4-2 show. Moreover, when Figures 4-1 and 4-2 are compared with Figures 5-1 and 5-2, the latter graphical representations indicate, in general, a higher voltage withstand capability than the former, which appears to be due to the quantity of Cu in the contact materials according to the present invention. In other words, it may be said that the contact material having the Cu content of 50% by weight is more excellent in its voltage withstand capability than the contact material having the Cu content of 60% by weight. Figure 6 is a graphical representation showing the voltage withstand capability of the contact materials according to the present invention produced by the infiltration method with the Cu content being 40% by weight, in which both axes of ordinate and abscissa denote the same entries as in Figures 4-1 and 4-2, and the curves 11 to 14 are for the same contact materials as in Figure 3. In the same way as in Figure 4, this graphical representation of Figure 6 is divided into Figures 6-1 and 6-2 at the point of the Bi adding quantity of 1% by weight. From Figures 6-1 and 6-2, it may be seen that the contact materials of the present invention (the curves 11, 12, 13 and 14) are superior to the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may be seen further that, in comparison with the conventional Cu-25Cr alloy contact material, the contact materials of the present invention are superior in their voltage withstand capability, when it contains up to 0.32% by weight of the added Bi content against the added Nb content of 4.7% by weight relative to Mo; when it contains up to 0.75% by weight of the added Bi content against the added Nb quantity of 9.4% by weight relative to Mo; when it contains up to 12% by weight of the added Bi content against the added Nb content of 18.9% by weight relative to Mo; and when it contains up to 20% by weight of the added Bi content against the added Nb content of 28.5% by weight relative to Mo. Further, it may be seen from Figures 6-1 and 6-2 that the contact materials with more added quantity of Nb relative to Mo indicate a small degree of decrease in the voltage withstand capability due to increase in the adding quantity of Bi. Moreover, when Figures 5-1 and 5-2 are compared with Figures 6-1 and 6-2, the latter graphical representations indicate, in general, a higher voltage withstand capability than the former. When the above-mentioned comparison between Figures 4-1 and 4-2 and Figures 5-1 and 5-2 is taken together, it will be seen that the contact materials of less Cu content (i.e., the Cu content of 40% by weight) are superior in their voltage withstand capability. From Table 5 below, it will be seen that the contact materials of the present invention produced by the infiltration method (Sample Nos. N-Bi-1 through N-Bi-84) depend, in their chopping current value, on the adding quantity of Bi. The effect of addition of Bi emerges at about 1% by weight or so, and, thenceforward, the chopping current value decreases with increase in the adding quantity of Bi. The principal component which affects the chopping current value is Bi, the other components of Cu, Mo, and Nb having no remarkable influence on the chopping current value within their compositional ranges in the contact materials of the present invention. As for the melt-adhesion and peeling force, the contact materials of the present invention indicate considerable effect with the adding quantity of Bi of 0.1% by weight, beyond which the measured value thereof indicates zero (0). The measurement of the melt-adhesion and peeling force was done by first conducting electric current of 12.5 kA for three seconds in the state of the contacts of a vacuum switch which had been assembled in a circuit breaker being closed, and then the vacuum switch was removed from the circuit breaker to measure the melt-adhesion and peeling force between the contacts by means of a tension tester. In Table 5 below, the numeral zero (0) appearing in the column of "Melt-Adhesion and Peel Force" should be understood such that no melt-adhesion took place at the time of test by the tension tester, or the contacts were separated during their handling for the test owing to very small melt-adhesion and peeling force. As for the power consumption at the contact points, it is seen from Table 5 below that, irrespective of the adding quantity of Bi, the contact materials according to the present invention produced by the infiltration method are superior to the conventional Cu-25Cr alloy contact material. This superiority is considered due to the function of the component elements, in particular, Mo, Nb and Cu, constituting the contact materials. As the consequence, the contact materials according to the present invention exhibit their effect for the chopping current value at 1% by weight or above of the added Bi content, their effect for the melt-adhesion and peeling force at 0.1% by weight or above of the added Bi content, and their effect for the power consumption at the contact points with the compositional range of Cu, Mo, Nb and Bi contained in the contact materials as shown in Table l below (i.e., the Cu content ranging from 40 to 60% by weight; the Nb added quantity relative to Mo ranging from 4.7 to 28.5% by weight; and the Bi content ranging from 0.1 to 20% by weight). From the above, it is seen that the contact materials according to the present invention produced by the infiltration method exhibit good properties within their compositional range of Cu of from 40 to 60% by weight; Mo of from 28.6 to 57.2% by weight; Nb of from 1.9 to 17.1% by weight; and Bi of from 0.1 to 20% by weight. Table 5 below also shows, as Sample Nos. N-Bi-85 through N-Bi-132, various properties of the contact materials according to the present invention produced by the second method of powder sintering. As to the current breaking property, it will be seen clearly from Table 5 below that all the contact materials, except for Sample No. N-Bi-129, have their superior current breaking property to that of the conventional Cu-25Cr alloy contact material (Sample No. C-1). Even the contact material of Sample No. N-Bi-129 is seen to exhibit its superior current breaking property, when it is compared with the contact material of Sample No. C-Bi-7, on the basis of the same adding quantity of Bi. Figure 7 shows the current breaking property of the contact material according to the present invention produced by the powder sintering method with the Cu content of 75% by weight, in which the ordinate represents the current breaking property with the property of the conventional Cu-25Cr alloy contact material as the reference and the abscissa denotes the adding quantity of Bi. In the graphical representation of Figure 7, a curve 15 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 4.7% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-85, N-Bi-93, N-Bi-101, N-Bi-109, N-Bi-117, N-Bi-125); a curve 16 indicates the current breaking property of th contact materials, in which the added quantity of Nb relative to Mo is 9.4% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-86, N-Bi-94, N-Bi-102, N-Bi-110, N-Bi-118, N-Bi-126); a curve 17 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 18.9% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-87, N-Bi-95, N-Bi-103, N-Bi-111, N-Bi-119, N-Bi-127); and a curve 18 indicates the current breaking property of the contact materials, in which the added quantityt of Nb relative to Mo is 28.5% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-88, N-Bi-96, N-Bi-104, N-Bi-112, N-Bi-120, N-Bi-128). From Figure 7, it is seen that the contact materials of the present invention exhibit more excellent properties than the conventional Cu-25Cr alloy contact material in respect of the current breaking property, although the property thereof is seen to decrease with increase in the adding quantity of Bi. It is also seen that the contact materials of the present invention produced by the powder sintering method with the Cu content being 75% by weight have their superior current breaking property, with the added quantity of Nb relative to Mo being in a range of from 4.7 to 28.5% by weight and the adding quantity of Bi being up to 20% by weight. Figure 8 shows the current breaking property of the contact materials of the present invention produced by the powder sintering method with the Cu content being 60% by weight, in which the ordinate and the abscissa denote the same entries as in Figure 7. In the drawing, a curve 19 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 4.7% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-89, N-Bi-97, N-Bi-105, N-Bi-113, N-Bi-121, N-Bi-129); a curve 20 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 9.4% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-90, N-Bi-98, N-Bi-106, N-Bi-114, N-Bi-122, N-Bi-130); a curve 21 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 18.9% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-91, N-Bi-99, N-Bi-107, N-Bi-115, N-Bi-123, N-Bi-131); and a curve 22 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 28.5% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-92, N-Bi-100, N-Bi-108, N-Bi-116, N-Bi-124, N-Bi-132). From Figure 8, it may be seen that the contact materials according to the present invention having the added Nb content relative to Mo of 9.4, 18.9 and 28.5% by weight exhibit their excellent current breaking property in comparison with the conventional Cu-25Cr contact material, although their current breaking property decreases with increase in the adding quantity of Bi. It may also be seen that even the contact materials having the added quantity of Nb relative to Mo of 4.7% by weight show excellent current breaking property, if the quantity of addition of Bi does not exceeds 17% by weight. It may further be seen that the contact materials of the present invention having the added quantity of Nb relative to Mo of 4.7% by weight have sufficiently superior property when they are compared with the conventional Cu-25Cr-Bi alloy contact material (the curve 5) added with the same amount of Bi as in the above-mentioned contact material of the present invnetion. As to the difference in the current breaking property due to the difference in the Cu content, it may be seen from Figures 7 and 8 that the contact materials having the added Nb content relative to Mo of 4.7% by weight and 9.4% by weight exhibit their superior current breaking property with the Cu content of 75% by weight in the case of small adding quantity of Bi, and the difference in the current breaking property tends to be small with increase in the adding quantity of Bi, or to be substantially eliminated; on the other hand, the contact materials having the added Nb content relative to Mo of 18.9% by weight and 28.5% by weight exhibit their current breaking property which is equal to, or higher than, that of the conventional contact material, when the Cu content is 60% by weight. However, the contact materials having the Cu content of 60% by weight show a small degree of decrease in the current breaking property due to increase in the adding quantity of Bi. From the foregoing, it may be concluded that, if the added Nb content relative to Mo is 9.4% by weight or more, the contact materials of the present invention indicate superior current breaking property to the conventional Cu-25Cr contact material within a range of the Cu content of from 60 to 75% by weight, without depending on the adding quantity of Bi; also, when the added Nb content relative to Mo is 4.7% by weight, the contact materials of the present invention indicate superior current breaking property to the conventional Cu-25Cr alloy contact material with the Cu content of 75% by weight, without depending on the adding quantity of Bi; and when the Cu content is 60% by weight, the contact materials of the present invention indicate more excellent current breaking property than the conventional Cu-25Cr alloy contact material with the adding quantity of Bi of up to 17% by weight. When the contact materials of the present invention are compared with the conventional Cu-25Cr-Bi alloy contact material, in respect of the same Bi content, the contact materials of the present invention have their superior current breaking property to the conventional one in their whole compositional range. It may be further seen from Table 5 below that, with respect to the voltage withstand capability, the contact materials of the present invention produced by the powder sintering method, when the adding quantity of Bi is small, exhibit their superiority to the conventional Cu-25Cr alloy contact material. Figure 9 is a graphical representation showing the voltage withstand capability of the contact materials according to the present invention obtained by the powder sintering method with the Cu content of 75% by weight, in which the ordinate represents the voltage withstand capability with the capability of the conventional Cu-25Cr alloy contact material as the reference and the abscissa denotes the adding quantity of Bi. Incidentally, in the same manner as in Figure 4 above, the graphical representation of Figure 9 is divided into Figures 9-1 and 9-2 at the point of 1% by weight of the Bi content. In these graphical representations, the curves 15 to 18 are for the same contact materials as in Figure 7. From Figures 9-1 and 9-2, it may be seen that the contact materials of the present invention (the curves 15, 16, 17 and 18) possess their superior voltage withstand capability to that of the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may further be seen that the contact materials of the present invention having the added Nb content relative to Mo of 4.7% by weight are more excellent in their voltage withstand capability than the conventional Cu-25Cr contact material with the adding quantity of Bi of up to 0.25% by weight; the contact materials having the added Nb content relative to Mo of 9.4% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.23% by weight; the contact materials having the added Nb content relative to Mo of 18.9% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.35% by weight; and the contact materials having the added Nb content relative to Mo of 28.5% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.32% by weight. Further, from Figures 9-1 and 9-2, it may be seen that the contact material having more Nb content relative to Mo shows a small degree of lowering in the voltage withstand capability due to increase in the adding quantity of Bi. Figure 10 is a graphical representation showing the voltage withstand capability of the contact materials according to the present invention obtained by the powder sintering method with the Cu content of 60% by weight, in which both ordinate and abscissa denote the same entries as in Figure 9 above. Also, the graphical representation of Figure 10 is divided into Figures 10-1 and 10-2 at the point of the Bi content of 1% by weight. In these graphical representations, the curves 19 to 22 are for the same contact materials as in Figure 8. From Figures 10-1 and 10-2, it is seen that the contact materials of the present invention (the curves 19, 20, 21 and 22) have their excellent voltage withstand capability over that of the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may be further seen that the contact materials of the present invention having the added Nb content relative to Mo of 4.7% by weight indicate their superior voltage withstand capability to the conventional Cu-25Cr alloy contact material with the adding quantity of Bi of up to 0.22% by weight; the contact materials having the added Nb content relative to Mo of 9.4% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.35% by weight; the contact materials having the added Nb content relative to Mo of 18.9% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.65% by weight; and the contact materials having the added Nb content relative to Mo of 28.5% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.75% by weight. Further, from Figures 10-1 and 10-2, it may be seen that the contact material having more Nb content relative to Mo shows a small degree of lowering in the voltage withstand capability due to increase in the adding quantity of Bi. Moreover, upon comparison between Figures 9-1 and 9-2 and Figures 10-1 and 10-2, it may be seen that the contact materials with the Cu content of 60% by weight indicate the higher voltage withstand capability than the contact materials with the Cu content of 75% by weight. Furthermore, it may be seen from Table 5 below that the chopping current value of the contact materials according to the present invention produced by the powder sintering method (Sample Nos. N-Bi-85 through N-Bi-132) is dependent on the adding quantity of Bi. The effect of addition of Bi emerges at about 1% by weight or so, and, thenceforward, the chopping current value decreases with increase in the adding quantity of Bi. As for the melt-adhesion and peeling force, the contact materials of the present invention indicate considerable effect with the adding quantity of Bi of 0.1% by weight, beyond which the measured value thereof indicates zero (0). As for the power consumption at the contact points, the contact materials of the present invention obtained by the powder sintering method are not dependent on the adding quantity of Bi, but on the content of Cu and other components. Here, the contact materials of the present invention with the Cu content of 60% by weight show their excellent capability of the power consumption at the contact points, which is 0.2 to 0.3 times as low as that of the conventional Cu-25Cr alloy contact material, the capability of which is as equal as that of the contact material of the present invention obtained by the afore-mentioned infiltration method. On the other hand, the contact materials with the Cu content of 75% by weight have their capability of the power consumption at the contact points of 0.5 to 0.7 times as low as that of the conventional Cu-25Cr alloy contact material, from which it will be seen that, when the Cu content becomes less than 60% by weight, there can be observed not so conspicuous change in the power consumption at the contact points. When the contact materials of the present invention with the Cu content of 75% by weight are compared with the conventional Cu-25Cr alloy contact material or Cu-25Cr-Bi alloy contact material, the power consumption at the contact points of the contact materials according to the present invention is seen to be 0.5 to 0.7 times as low as that of the conventional contact materials, the difference of which is considered due to difference in the constituent elements of the contact materials. As the consequence of this, the contact materials of the present invention produced by the powder sintering method show their effect on the chopping current value with the adding quantity of Bi of l% by weight or above, their effect on the melt-adhesion and peeling force with the adding quantity of Bi of 0.1% by weight or above, and their favorable capability on the power consumption at the contact points with the Cu content in a range of from 60 to 75% by weight, the added Nb content relative to Mo in a range of from 4.7 to 28.5% by weight, and the adding quantity of Bi in a range of from 0.1 to 20% by weight. From the foregoing, it may be seen that the contact materials of the present invention produced by the powder sintering method indicate their favorable properties with the range of content of Cu being from 60 to 75% by weight, Mo being from 17.9 to 38.1% by weight, Nb being from 1.1 to 11.4% by weight, and Bi being from 0.1 to 20% by weight. Table 5 below also shows various properties of the contact materials according to the present invention produced by the third method of the vacuum hot press, as Sample Nos. N-Bi-133 through N-Bi-180. As to the current breaking property, it will be seen clearly from Table 5 that all the contact materials have their superior current breaking property to that of the conventional Cu-25Cr alloy contact material. Figure 11 shows the current breaking property of the contact materials according to the present invention obtained by the vacuum hot press method with the Cu content of 75% by weight, in which the ordinate represents the current breaking property with the property of the conventional Cu-25Cr alloy contact material being made the reference, and the abscissa denotes the adding quantity of Bi. In the graphical representation of Figure 11, a curve 23 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 4.7% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-133, N-Bi-141, N-Bi-149, N-Bi-157, N-Bi-165, N-Bi-173); a curve 24 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 9.4% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-134, N-Bi-142, N-Bi-150, N-Bi-158, N-Bi-166, N-Bi-174); a curve 25 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 18.9% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-135, N-Bi-143, N-Bi-151, N-Bi-159, N-Bi-167, N-Bi-175); and a curve 26 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 28.5% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-136, N-Bi-144, N-Bi-152, N-Bi-160, N-Bi-168, N-Bi-176). From Figure 11, it is seen that the contact materials of the present invention have more excellent current breaking property than the conventional Cu-25Cr alloy contact material, although the property thereof is seen to be lowered with increase in the adding quantity of Bi. It is also seen from Figure 11 that the contact materials according to the present invention produced by the vacuum hot press method with the Cu content of 75% by weight have their superior current breaking property, in case the added quantity of Nb relative to Mo is in a range of from 4.7 to 28.5% by weight and the adding quantity of Bi is up to 20% by weight. Figure 12 shows the current breaking property of the contact materials according to the present invention produced by the vacuum hot press method with the Cu content of 60% by weight, in which the ordinate and the abscissa denote the same entries as in Figure 11. In the drawing, a curve 27 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 4.7% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-137, N-Bi-145, N-Bi-153, N-Bi-161, N-Bi-169, N-Bi-177); a curve 28 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 9.4% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-138, N-Bi-146, N-Bi-154, N-Bi-162, N-Bi-170, N-Bi-178); a curve 29 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 18.9% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-139, N-Bi-147, N-Bi-155, N-Bi-163, N-Bi-171, N-Bi-179); and a curve 30 indicates the current breaking property of the contact materials, in which the added quantity of Nb relative to Mo is 28.5% by weight and the adding quantity of Bi is varied (Sample Nos. N-Bi-140, N-Bi-148, N-Bi-156, N-Bi-164, N-Bi-172, N-Bi-180). From Figure 12, it may be seen that the contact materials according to the present invention have their superior current breaking property to that of the conventional Cu-25Cr alloy contact material, although the property is lowered with increase in the adding quantity of Bi. Moreover, it may be seen from Figure 12 that the contact materials of the present invention produced by the vacuum hot press method with the Cu content of 60% by weight possess their excellent current breaking property with the added Nb content relative to Mo ranging from 4.7 to 28.5% by weight and the adding quantity of Bi of up to 20% by weight. As to the difference in the current breaking property due to the difference in the Cu content, it may be seen from Figures 11 and 12 that such difference tends to be higher, in general, with the contact materials having the Cu content of 60% by weight. From the foregoing, it may be concluded that the contact materials of the present invention having the Cu content in a range of from 60 to 75% by weight, the added Nb content relative to Mo in a range of from 4.7 to 28.5% by weight, and the adding quantity of Bi of up to 20% by weight have their excellent current breaking property in comparison with that of the conventional Cu-25Cr alloy contact material. It may be seen further from Table 5 below that, respect with to the voltage withstand capability, the contact materials of the present invention produced by the vacuum hot press method, when the adding quantity of Bi is small, exhibit their superiority to the conventional Cu-25Cr alloy contact material. Figure 13 is a graphical representation showing the voltage withstand capability of the contact materials according to the present invention obtained by the vacuum hot press method with the Cu content of 75% by weight, in which the ordinate represents the voltage withstand capability with the property of the conventional Cu-25Cr contact alloy material being made the reference, and the abscissa denotes the adding quantity of Bi. Incidentally, in the same manner as in Figure 4, the graphical representation of Figure 13 is divided into Figures 13-1 and 13-2 at the point of 1% by weight of the Bi content. In the drawing, the curves 23 to 26 are for the same contact materials as in Figure 11. From Figures 13-1 and 13-2, it may be seen that the contact materials of the present invention (the curves 23, 24, 25 and 26) have their superior voltage withstand capability to that of the conventional Cu-25Cr-Bi contact material (the curve 5). It may further be seen that the contact materials of the present invention having the added Nb content relative to Mo of 4.7% by weight are more excellent in its voltage withstand capability than the conventional Cu-25Cr alloy contact material with the adding quantity of Bi of up to 0.23% by weight; the contact materials having the added Nb content relative to Mo of 9.4% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.36% by weight; the contact materials having the added Nb content relative to Mo of 18.9% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.5% by weight; and the contact materials having the added Nb content relative to Mo of 28.5% by weight are more excellent than the conventional contact material with the adding quantity of Bi of up to 0.4% by weight. Further, from Figures 13-1 and 13-2, it may be seen that the contact material having more Nb content relative to Mo shows a small degree of lowering in the voltage withstand capability due to the addition of Bi. Figure 14 is a graphical representation showing the voltage withstand capability of the contact materials according to the present invention obtained by the vacuum hot press method with the Cu content being 60% by weight, in which both ordinate and abscissa denote the same entries as in Figure 13. Also, the graphical representation of Figure 14 is divided into Figures 14-1 and 14-2 at the point of the Bi content of 1% by weight. In these graphical representations, the curves 27 to 30 are for the same contact materials as in Figure 12. From Figures 14-1 and 14-2, it may be seen that the contact materials of the present invention (the curves 27, 28, 29 and 30) have their excellent voltage withstand capability over that of the conventional Cu-25Cr-Bi alloy contact material (the curve 5). It may be further seen that the contact materials of the present invention having the added Nb content relative to Mo of 4.7% by weight indicate their superior voltage withstand capability to the conventional Cu-25Cr alloy contact material, when the adding quantity of Bi is up to 0.22% by weight; the contact materials having the added Nb content relative to Mo of 9.4% by weight are more excellent than the conventional contact material, when the adding quantity of Bi is up to 0.4% by weight; the contact materials having the added Nb content relative to Mo of 18.9% by weight are more excellent than the conventional contact material, when the adding quantity of Bi is up to 1% by weight; and the contact materials having the added Nb content relative to Mo of 28.5% by weight are more excellent than the conventional contact material, when the adding quantity of Bi is up to 0.42% by weight. Further, from Figures 14-1 and 14-2, it may be seen that the contact material having more added Nb content relative to Mo shows a small degree of lowering in the voltage withstand capability due to addition of Bi. Moreover, upon comparison between Figures 13-1 and 13-2 and Figures 14-1 and 14-2, it may be seen that the contact material with the Cu content of 60% by weight indicates the higher voltage withstand capability than the contact material with the Cu content of 75% by weight. Furthermore, it may be seen from Table 5 below that the chopping current value of the contact materials according to the present invention produced by the vacuum hot press method (Sample Nos. N-Bi-133 through N-Bi-180) is dependent on the adding quantity of Bi. The effect of the addition of Bi emerges at about 1% by weight or so, and thenceforward, the chopping current value decreases with increase in the adding quantity of Bi. As for the melt-adhesion and peeling force, the contact materials of the present invention indicate considerable effect with the adding quantity of Bi of 0.1% by weight, beyond which the measured value thereof indicates zero (0). As for the power consumption at the contact points, the contact materials of the present invention are not dependent on the adding quantity of Bi, but on the content of Cu and other components. Here, the contact material of the present invention with the Cu content of 60% by weight indicate their excellent power consumption, which is 0.2 to 0.3 times as low as that of the conventional Cu-25Cr alloy contact material, as is the case with the contact materials of the present invention obtained by the powder sintering method, the capability of which is comparable with the property of the above-mentioned contact materials of the present invention. On the other hand, the contact materials with the Cu content of 75% by weight show their capability of the power consumption at the contact points of 0.5 to 0.7 times as low as that of the conventional Cu-25Cr alloy contact material, i.e. their capability is as equal as that of the contact materials obtained by the powder sintering method. From this, it wil be seen that, when the Cu content becomes less than 60% by weight, there is seen not so remarkable change in the power consumption at the contact points. When the contact materials of the present invention with the Cu content of 75% by weight are compared with the conventional Cu-25Cr or Cu-25Cr-Bi contact material, the contact materials of the present invention show their power consumption, which is 0.5 to 0.7 times as low as that of the conventional contact material, the difference of which is considered due to difference in the constituent elements of the contact materials. Therefore, the contact materials of the present invention produced by the vacuum hot press method show their effect on the chopping current value when the adding quantity of Bi is 1% by weight or above, their effect on the melt-adhesion and peeling force when the adding quantity of Bi is 0.1% by weight or above, and their favorable property on the power consumption at the contact points when the Cu content is in a range of from 60 to 75% by weight, the added Nb content relative to Mo is in a range of from 4.7 to 28.5% by weight, and the adding quantity of Bi is in a range of from 0.1 to 20% by weight. From the foregoing, it may be concluded that the contact materials of the present invention produced by the vacuum hot press method and having the Cu content in a range of from 60 to 75% by weight, the Mo content in a range of from 17.9 to 38.1% by weight, the Nb content in a range of from 1.1 to 11.4% by weight, and the Bi content in a range of from 0.1 to 20% by weight exhabit their favorable properties. In passing, it should be noted that, although, in the foregoing examples of the present invention, explanations have been given on the contact materials produced by addition of Bi to the base alloy of Cu-Mo-Nb, those elements such as Te, Sb, Tl and Pb may be used in place of Bi, in which case one or more kinds of these low melting point materials may be added to the base alloy. Table 7 below indicates various samples containing these elements. In this Table 7, the compositional ratio was determined in reference to the afore-described examples, and the adding quantity of the low melting point material, for the samples, was set to be 20% by weight at the maximum, based on which condition the contact materials of the present invention were compared with the conventional contact materials. The method for production of these contact materials is as follows: Sample Nos. 1, 2 and 3 are obtained by the infiltration method; Sample Nos. 4 and 5 are obtained by the powder sintering method; and Sample Nos. 6 and 7 are obtained by the vacuum hot press method. The shape of the contacts and the method of their testing are the same as in the afore-described examples. The results of the mesurement are shown in Table 8 below. From Table 8, it is seen that the contact materials of the present invention added with the low melting point component of Te, Sb, Tl, Pb, Se and Bi-Te in an amount of 20% by weight (Sample Nos. N-Te-2, N-Te-3, N-Te-5, N-Te-7, N-Sb-2, N-Sb-3, N-Sb-5, N-Sb-7, N-Tl-2, N-Tl-3, N-Tl-5, N-Tl-7, N-Pb-2, N-Pb-3, N-Pb-5, N-Pb-7, N-BT-2, N-BT-3, N-BT-5, N-BT-7) have more excellent current breaking property than the conventional contact material of Sample No. C-B-7, and that these contact materials of the present invention are also excellent in respect of their voltage withstand capability. It is further seen that, depending on the kind of the low melting point compact, the contact materials containing therein Bi and Te indicate a relatively small degree of lowering in their current breaking property, and the contact materials containing therein Pb are inferior in such property among the contact materials of the present invention. Further, more excellent current breaking property can be attained by adding 20% by weight in total of both Bi and Te together, each being at 10% by weight, rather than by adding 20% by weight of single Bi or Te. The same effect can be expected of the other low-melting point components. On the other hand, it is seen from Table 8 below that the chopping current value, the melt-adhesion and peeling force, and the power consumption at the contact points are not so much dependent upon the low melting point components to be added. Accordingly, the properties of the contact materials according to the present invnetion as shown in Table 8 are considered to be essentially same as the contact materials added with Bi which are shown in Tables 1, 2 and 3. That is to say, the contact materials produced by the infiltration method exhibit their excellent properties with the content of Cu in the range of from 40 to 60% by weight, Nb relative to Mo in the range of from 4.7 to 28.5% by weight (i.e., the Mo content of from 28.6 to 57.2% by weight and the Nb content of from 1.9 to 17.1% by weight), and one or more kinds of the low melting point materials such as Te, Sb, Tl, Pb, and Bi in the range of from 0.1 to 20% by weight; and the contact materials produced by the powder sintering method or the vacuum hot press method exhibit their ecxcellent properties with the content of Cu in the range of from 60 to 75% by weight, Nb relative to Mo in the range of from 4.7 to 28.5% by weight (i.e., the Mo content of from 17.9 to 38.1% by weight and the Nb content of from 1.1 to 11.4% by weight), and one or more kinds of the low melting point material such as Te, Sb, Tl, Pb and Bi of up to 20% by weight. In the foregoing, the explanations have been made as to the contact materials according to the present invention with the Cu content or from 40 to 75% by weight, the Mo content of from 17.9 to 57.2% by weight, the Nb content or from 1.1 to 17. 1% by weight, and one or more kinds of the low melting point materials of from 0.1 to 20% by weight. However, the compositional range of the practically useful contact materials is considered to be much broader. That is to say, there may be contemplated those contact materials having the Cu content of from 30 to 80% by weight, the Nb content relative to Mo of from 2 to 35% by weight (i.e., the Mo content of from 13 to 68.6% by weight and the Nb content of from 0.4 to 24.5% by weight), and the content of one or more of the low melting point materials of from 0.05 to 25% by weight, and any arbitrary alloy materials are able to be chosen within these compositional ranges depending on their use. As has been mentioned in the foregoing, since the first Example of the present invention utilizes the contact materials composed of Cu, Mo, Nb and one or more kinds of the low melting point materials as the electrodes for the vacuum circuit breaker, the resulting vacuum circuit breaker has excellent operating characteristics.

Claims: A contact material for a vacuum circuit breaker, comprising copper and niobium, characterized in that it is composed of copper, niobium, molybdenum and one or more kinds of low melting point materials selected from bismuth, tellurium, antimony, lead, thallium, selenium, cerium and calcium. The contact material for a vacuum circuit breaker according to Claim 1, characterized in that the copper content is in a range of from 30 wt.% to 80 wt.%, the molybdenum content is in a range of from 13 wt.% to 68.6 wt.%, the niobium content is in a range of from 0.4 wt.% to 24.5 wt.%, and the content of one or more kinds of the low melting point materials is in a range of from 0.05 wt.% to 25 wt.%. The contact material for a vacuumm circuit breaker according to Claim 1, characterized in that the copper content is in a range of from 40 wt.% to 75 wt.%, the molybdenum content is in a range of from 17.9 wt.% to 57.2 wt.%, the niobium content is in a range of from 1.1 wt.% to 17.1 wt.%, and the content of one or more kinds of the low melting point materials is in a range of from 0.1 wt.% to 20 wt.%. The contact material for a vacuum circuit breaker according to Claim 1, characterized in that the copper content is in a range of from 40 wt.% to 60 wt.%, the molybdenum content is in a range of from 28.6 wt.% to 57.2 wt.%, the niobium content is in a range of from 1.9 wt.% to 17.1 wt.%, and the content of one or more kinds of the low melting point materials is in a range of from 0.1 wt.% to 20 wt.%, and that said contact material is produced by the infiltration method. The contact material for a vacuum circuit breaker according to Claim 1, characterized in that the copper content is in a range of from 60 wt.% to 75 wt.%, the molybdenum content is in a range of from 17.9 wt.% to 38.1 wt.%, the niobium content is in a range of from 1.1 wt.% to 11.4 wt.%, and the content of one or more kinds of the low melting point materials is in a range of from 0.1 wt.% to 20 wt.%, and that said contact material is produced by the powder sintering method. The contact material for a vacuum circuit breaker according to Claim 1, characterized in that the copper content is in a range of from 60 wt.% to 75 wt.%, the molybdenum content is in a range of from 17.9 wt.% to 38.1 wt.%, the niobium content is in a range of from 1.1 wt.% to 11.4 wt.%, and the content of one or more kinds of the low melting point material is in a range of from 0.1 wt.% to 20 wt.%, and that said contact material is produced by the vacuum hot press method. The contact material for a vacuum circuit breaker according to Claim 1, 2, 3, 4, 5 or 6, characterized in that said low melting point material is selected from bismuth, tellurium, antimony, lead, and thallium.

Inventors: MIYAMOTO, SEIICHI MITSUBISHI DENKI K.K., NAYA, EIZO MITSUBISHI DENKI K.K., OKUMURA, MITSUHIRO MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1987
Main classification: H01H1
IPC codes: C22C1, H01H1, C22C9, H01H33