Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H1/00—Contacts
  • H01H1/02—Contacts characterised by the material thereof
  • H01H1/021—Composite material
  • H01H1/023—Composite material having a noble metal as the basic material
  • H01H1/0233—Composite material having a noble metal as the basic material and containing carbides
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S75/00—Specialized metallurgical processes, compositions for use therein, consolidated metal powder compositions, and loose metal particulate mixtures
  • Y10S75/95—Consolidated metal powder compositions of >95% theoretical density, e.g. wrought

Definitions

• the invention provides electrical contact members especially adapted for heavy duty service consisting essentially of nickel and titanium carbide together with (1) a metal of the group silver and copper, and (2) a metal of the group molybdenum and tungsten.
• the contacts consist essentially of, by volume, 15 to 60 percent of silver, 30 to 55 percent of titanium carbide, 8 to 40 percent of nickel, and 0.1 to 10 percent of molybdenum.
• the cont-acts are made by pilling those constituents and then sintering the compacts, and they are characterized by the fact that their density is at least 95 percent of the theoretical density.
• This invention relates particularly to electrical contacts especially suitable for heavy duty use in, for example, circuit breakers.
• Such devices are frequently used as switches, for instance in to ampere service.
• the contacts are commonly of silver-tungsten, silver-molybdenum or copper-tungsten.
• circuit ice tions even though they might be supposed to behave rather similarly to the Cu-Ni-W compositions just mentioned.
• the literature shows that such compositions as silver-tungsten and copper-tungsten cannot be pressed and sintered to density even approaching 90 percent of theoretical; the same thing is true for molybdenum based contacts, as well as for contacts in which the copper in the Cu-Ni-W would be replaced by silver.
• the following table represents the results of tests in which the compositions listed were pilled under the conditions stated and then sintered at 1600 C.
• breakers provided with such contacts are used as switches with frequently repeated make-and-break operation there is a tendency for the contacts to become heated with consequent damage to the contact surfaces, and the temperature rise may even be great enough to result in catastrophic failure.
• Acceptable density can be obtained by infiltrating the compacts, as with silver, or by hot pressing or hot coining. Hot pressing and hot coining are not looked upon with favor by the manufacturers of these articles because of the unfavorable economics of those procedures. For the same reason the trade would like to eliminate the infiltration step. However, those practices have been followed down to the present time because it has not been possible to achieve the desired density by simple pilling and sintering of the most desirable compositions.
• Cu-Ni-W contact compositions can be made at close to theoretical density by pilling and sintering for prolonged lengths of time, of the order of hours, and the same thing is true of a few other compositions, but the lengthy sintering needed is an economic burden. Oddly enough that practice does not suffice for most other contact composi- The data of the table show that the densities of pilled and sintered contacts of the compositions commonly used as heavy duty contact materials are substantially below the minimum of theoretical) believed to be essential for acceptable performance.
• a major object of this invention is to provide electrical contacts particularly adapted for the type of service alluded to above, which are characterized by having density at least and preferably 98 percent of theoretical, and which can be made without the usual step of infiltrating sintered compacts.
• Another object is to provide such contacts characterized by especially low temperature rise in use, especially in frequently repeated make-and-break operation, which are of less expensive composition than the contacts conventionally used for such service, and which may be made easily by powder metallurgy methods without using the infiltration step, hot pressing or hot coining such as have been necessary up to the present time in order to produce acceptable maximum density with the most favored compositions.
• the contacts consist essentially of, by volume:
• a preferred composition consists of, by volume, 30 percent of silver, 46 percent of titanium carbide, 19 percent of nickel, and percent of molybdenum. Furthermore, optimum results are achieved when the volume percentage of silver plus nickel is in the range 40 to 70 percent.
• compositions within the foregoing ranges give good performance in the type of service contemplated, and perform satisfactorily in all phases of the Underwriters Laboratories tests.
• High contents of nickel are unusual in contacts because they do not contribute to electrical conductivity or to suppress welding, but these contacts perform well even so.
• compositions outside of these ranges have been found to be unsatisfactory. From an economic standpoint the compositions of this invention are important also because the amounts of silver and molybdenum used, which are expensive materials, are significantly reduced beneath the levels commonly required in silver-tungsten and silver-molybdenum contact grades.
• a blend of, by weight, 40 percent of silver, 30 percent of titanium carbide, 22.5 percent of nickel, and 7.5 percent of molybdenum, all in the form of minus 325 mesh powders is lubricated with a suitable binder to facilitate pilling, as by adding a dry wax to the dry powders.
• the wax and the powder blend are thoroughly mixed and the mixture is pilled at tons per square inch.
• the contact is sintered 5 minutes in a non-oxidizing atmosphere at 1375 C.
• the density of the product is in excess of 95 percent of theoretical, i.e. 7.4 to 7.5 g./cc. In this case the theoretical density was 7.6 g./cc., the molded density was 5.5 g./cc. (73% of theoretical), and the shrinkage due to sintering was 17%.
• the superiority of the contacts of this invention in comparison with the presently available commercial contacts for service of the type contemplated is demonstrable by a test used by some circuit breaker manufacturers for evaluating contacts for such service.
• the breakers are subjected to continuous make-and-break action for 1,000 cycles after which they are left in the make condition until the temperature has equilibrated, normally about two to three hours, and the temperature rise above ambient is determined. This operation is repeated for six cycles of 1,000 operations each. It is desired that the maximum temperature rise in these tests be 50 C.
• Cycle 1 4 tests 63-97 Cycle 2, 4 tests 90-115 Cycle 3, 4 tests -120 Cycle 4, 4 tests 67-90 Cycle 5, 4 tests 85-120 Cycle 6, 4 tests "a 75-115 Contacts this invention Cycle 1, 2 tests 15-18 Cycle 2, 2 tests 18-25 Cycle 3, 2 tests 20-25 Cycle 4, 2 tests 70 Cycle 5, 2 tests 55-62 Cycle 6, 2 tests 55-60 MANUFACTURER NO. 2 Standard equipment contacts C.
• the maximum temperature was only 70 C. and in most instances it was below the desired maximum of 50 C. Furthermore, the contacts in accordance with the invention exhibited a stronger tendency to repair themselves in use and resist catastrophic failure, that is, temperatures in excess of 75 C. above ambient.
• An electric contact consisting essentially of, by volume, a sintered body of about '15 to 60 percent of a metal of the group copper and silver, about 30 to 55 percent of titanium carbide, about .8 .to 40 percent of nickel, and about 0.1 to 10 percent of a metal of the group tungsten and molybdenum, thedensity of the sintered contact being at least about percent of theoretical.
• a contact according to claim 1 consisting essentially of, by volume, about percent of silver, 46 percent of titanium carbide, 19 percent of nickel, and 5 percent of molybdenum, the density of the sintered contact being at least 95 percent of theoretical.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Composite Materials (AREA)
• Materials Engineering (AREA)
• Contacts (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24880379

Family Applications (1)

Country Status (3)

Cited By (3)

Families Citing this family (2)

Citations (5)

• 1968
  • 1968-03-28 US US717016A patent/US3482950A/en not_active Expired - Lifetime
• 1969
  • 1969-01-30 GB GB5163/69A patent/GB1214961A/en not_active Expired
  • 1969-03-04 DE DE19691910965 patent/DE1910965A1/de active Pending

Patent Citations (5)

Also Published As

Similar Documents