US2253401A - Circuit interrupter contact - Google Patents

Description

Patented Aug. 19, 1941 CIRCUIT INTERRUPTER CONTACT Joseph Slepian, Pittsburgh, Pa., assignoxto Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Penn- Sylvania Application October 9, 1937, Serial No. 168,225 4 20 Claims.

The invention relates to electrical circuit making and breaking devices, and more particularly to the relatively movable contacts thereof.

In electrical switches and circuit interrupters, difficulties have been experienced due to the adhering or welding together of the relatively movable contacts when subjected to high temperatures produced by arcingv or other causes. This adhering or Welding action has often prevented or at least retarded the separation of the contacts where breaking of the circuit becomes desirable cr necessary.

In order to avoid the tendency of the contacts to yadhere or weld together, it has heretofore been proposed and practiced to construct one or both of the contacts of specially constituted materials or compositions adapted to prevent or resist the said tendency. One such construction provides a Contact composed of finely divided silver and graphite intermixed and pressed into a block of the desired size and shape. The silver has a lowy resistance and the graphite functions as an antiflux to prevent the adhering or welding action. Another known construction utilizes a mixture of powdered silver and lead oxide pressed into a block and sintered in a special atmosphere. Contacts of these special materials and construction, while overcoming the tendency to weld, are relatively expensive to produce and are apt to be broken by the impacts imparted during operation of the breaker."

An object of the invention is the provision of improved electrical contacts of relatively low resistance which do not adhere or weld together when subjected to high temperature from arcing or other causes.

Another object of the invention is the provision of improved low resistance non-welding contacts that are sufficiently strong to withstand severe operating impacts substantially indefinitely with-` out breaking.

Another object of the invention is the provision of improved electrical contacts of the type menl tioned which are relatively inexpensive to pro- Fig. 3 is a bottom plan view of the movable contact;

Fig. 4 is a sectional view of the contact shown in Fig. 2 taken on the line IV-IV of Fig. 2;

Fig. 5 is a sectional view of a modified form of contact, and

Fig. 6 is an enlarged fragmentary sectional view of the Contact shown in Fig. 5.

Referring to Fig. 1 of the drawing, there is shown a pair of relatively movable contacts 5 and 1 constructed in accordance with the invention. The contacts 5 and I form the contact means of a circuit interrupter (not shown). The details of the structure and operating mechanism of.the circuit interrupter are not an important part of the present invention, and are not neces- -sary to a complete understanding thereof.` Any suitable circuit interrupter structure and operating mechanism may be used embodying the contacts of the present invention. One satisfactory structure and mechanism for the contacts is disclosed in Patent. No. 2,071,848 issued to Ture Lindstrom February 23, 1937,' and assigned to the assignee of this invention.

The stationary contact 5 is mounted on a suitable conducting support! and is secured thereto either by mechanical means or by brazing. The movable contact l is carried by a movable conducting switch arm Il and is secured thereto in o described above.

any suitable manner, as, for example, by mechanical means or by brazing as in the caSe of the contact 5. The switch arm Il is adapted to be moved to open and to closed circuit position by means of the operating mechanism ofthe breaker or interrupter to open or to close the contacts.

Each of the contacts 5 and I comprises a bOdy of metallic `conducting material the contact surface I3 of which is provided with a plurality of f closely spaced parallel recesses or slots I5. lThe recesses l5 are filled with a refractory material ,indicated at I1 which serves to prevent adhering or welding together oflthe contacts Sand 'I when they are subjected to high temperatures as a result of arcing orother causes. One refractory material for` filling the recesses I5, which has been found satisfactory for preventing sticking or welding of the contacts is finely divided or powdered graphite or other similar forms of' carbon which have a very high fusing or melting point. The powdered graphite is pressed into the recesses until its upper surface is substantially flush with the contact surface I3' of the contact. Another material which has been found satisfactory to prevent sticking or welding of the contacts is an intimate mixture of 'nely divided graphite, or similar forms of carbon and finely divided noble metal such assilver'orplatinum. which material is pressed into the slots of the contact the same as in the case of the graphite In either of the cases mentioned above, the finely divided graphite acts to prevent the drops of molten metal from coalescing into larger drops which, when frozen, would be of sufllcient size to cause the contacts to adhere or weld together. Other materials that have been found satisfactory in preventing sticking or welding of the contacts are lead oxide, thallium oxide and other metallic oxides, and these materials may be used to fill the recesses l5 of the contacts 5 and 'l in place of the nely divided `graphite or silver graphite mix previously mentioned.

The body portion of the contacts 5 and l may be composed of a number of different suitable conducting materials such as copper, noble metals, or alloys or compositions containing such metals. The noble metals such as silver and platinum have been foundV more satisfactory than copper because of the fact that corrosion has very little effect on the contact resistance of contacts formed of such materials and their conductivity is good. The body portion of the contacts 5 and 1 may be composed of suitable alloys containing noble metal such as silver or platinum, and either molybdenum or tungsten. Molybdenum or tungsten serves to increase the wear resisting quality of the contacts.`

The Width of the ribs and slots o f the contacts vary in accordance with the requirements of the 'contacts and the opening force applied by the breaker operating mechanism. In the case of small circuit interrupters in which the opening force of the breaker operating mechanism is small the ribs and slots are of very small width and very closely spaced. In such instance the width of the slots and ribs may be of the order of .010 of an inch or less. In the case of larger breakers having more powerful operating mechanism the width of the slots and ribs may be made greater. In any case the width of the slots The contacts 5 and 1 'are so disposed that the slots I5 of the movable contacts 'l are set at right angles to the slots I5 of the stationary contact 5. With the slots'arranged in this manner, both materials of each contact are in engagement when the contacts are closed and a continuous path for the current through the metallic con- -ducting material of the two contacts is provided. The relatively small width of the ribs formed by the slots I5 and the arrangement of the ribs of one contact at right angles to those of the other contact results in a contacting engagement between the contacts in the closed position of the interrupter which is small, so that the unit pressure of the engaging surfaces is-high.

A further modification of the invention is illustrated in Fig. 5 of the drawing. In this modication, the contact 2l is composed of a lami-` nated body consisting of alternate sheets 22 of a good conducting material and sheets 24 of a composition of conducting material and a refractory material which serves to prevent welding. Silver or an alloy containing silver has been found most satisfactory for the solid metallic sheets 22 although copper, gold, platinum, or other good conducting materials may be used. The sheets 24 may be made of a composition of pressed silver and graphite or a pressed mixture of any good Vconducting material such as copper, silver, gold or platinum, and a refractory material which prevents welding such as graphite, lead oxide, thallium oxide or other metal oxides. The metal- Y, lic sheets. are rolled from blocks to the desired thickness usually of the order of .010 of an inch. The composition sheets 24 are formed by mixing the powdered conducting material with the powdered material which prevents welding, pressing the mixture into a block, and then rolling the block into sheets of the desired thickness usually about .010 of an inch thick. The sheets 22 of conducting material and the composition sheets 24 are laid one upon the other in alternating fashion and the whole is then rolled further until a. substantially solid mass is obtained which contains `alternate layers of conducting material and layers of the composition material.

The final rolling operation reduces the thickness prevents welding or adhering of the contact thus formed to a cooperating contact.

In the appended claims the term antilux materialis intended to cover any material which serves to prevent adhering or welding together ofthe contacts.

It will be noted that in each of the embodiments of the invention the contact has portions of good conducting material which extend 'clear through the contact from its face to its back and the good conducting portions are separated at least at the face-of the contact by alternate layers of a refractory material. The good conducting portions provide the contact with a good electrical conductivity.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit of the invention. It is desired therefore that the language of the appended claims be given the broadest construction possible in the light of the prior art.

I claim as my invention:

1. A circuit interrupter including a pair of relatively movable contacts one of which comprises a body of metallic conducting material having its contact surface provided with' a relatively large number-of portions of a material which prevents adhering or welding of the contacts and which separate the metallic conducting material at the contact surface into a plurality of separate metallic portions, the other contact in the closed position of the contacts engaging a plurality of the metallic portions of the said one contact.

2. A circuit interrupter including a pair of relatively movable contacts one of which comprises a body of metallic conducting material .having its contact surface provided with a considerable number of closely spaced parallel slots gaging a plurality of the metallic portions of the said one contact which are separated by the slots.

3. A circuit interrupter including a pair of rel--A atively movable contacts one of which comprises a body of metallic conducting material having its contact surface /provided with a plurality of closely spaced recesses filled `with a refractory material which serves to prevent adhering or welding of the contacts, the4 other contact in the closed position of the contacts engagingla plurality of the portions of metallic conducting maf, terial of said one contact which are separated by the portions of refractory material.

4. An electrical contact comprising a body of conducting material having its contact surface provided with a plurality of closely spaced re cesses lled with an oxide of the group including lead oxide and thallium oxide.

5. A circuit interrupter including a pair of relatively movable contacts one of which comprises a body of conducting material having its con-` tact surface provided with a relatively large numberof closely spaced recesses filled with finely divided and compressed graphite, the other contact in the closed position of the interrupter en- 12. An electrical contact comprising a lamy inated body consisting of alternate layers of connated body consisting of alternate layers of congaging a plurality of the portions of conducting v f. material of said one contact which are separated by the graphite portions.

6. An electrical contact comprising a body` of metallic conducting material having its contact surface provided with a relatively large number of closely spaced recesses lled with a composiv tion consisting of an intimate mix of finely divided conducting material and finely divided anti-fiuxing material.

'7. A circuit interrupter including relatively movable contacts, each of which is comprised of a body of conducting material having its contact surface provided with a plurality of closely spaced parallel slots filled with material which serves to prevent adhering or welding together of the contacts, the slots of one of said contacts being disposed at an angle with respect to the slots of the other contact. 4

8. A circuit interrupter .including relatively movable contacts each comprising a body composed of an alloy containing a noble metal, said body having a contact surface provided with a plurality of closely spaced recesses filled with a material which serves to preventr adhering or welding together of the contacts,v both portions of said contacts being in engagement when said contacts are in engagement.

9. A circuit interrupter including a pair of relatively movable contacts one of which comprises a body of conducting material at least the contact portion of which is composed of a large number of relatively thin alternate layers of .conducting material and a material which prevents adhering or welding of the contacts, the edges of the layers terminating at-the face ofthe contact, the other contact in the closed position of the contact engaging a plurality of the layersof conducting material.

10. An electrical contact comprising a body of conducting material at least the contact portion of which is laminated, the laminations being ducting material and layers of a refractory material, the layers being disposed substantially perpendicular to the face of the contact.

l5. The method of making electrical contacts which consists in placing sheets of conducting material and sheets of a material which serves to prevent adhering or welding of the contact to a mating contact upon one another in alternating fashion, subjecting the pile of sheets to pressure to obtain a compact mass, and cutting contact blocks of the desired size from the mass.

16. 'Ihe method of making electrical contacts which consists in rolling blocks of silver, and

blocks of a pressed intimate mixture of silver and graphite into sheets of predetermined thickness, n

placing the sheets of silver and the sheets of silver graphite upon one another in alternating fashion, subjecting the pile of sheets to pressure to obtain a compact laminated mass, land cutting contacts of the desired size from the mass.

17. An electrical contact comprising a body having a contact surface composed of a plurality of parallel strips of good conducting material and a plurality of alternate strips of refractory material which prevent permanent welding or adhering of the contact to a cooperating contact.

18. A pair of relatively movable contacts one of which comprises a body having a plurality of portions of good conducting material extending clear through the contact from the face ofthe contact to th'e back of the contact, and having a plurality of portions of refractory materialI disposed between the good conducting portions at least at the face of the c ontact, the other contact in the closed position of said contacts engaging a plurality of the portions of good conducting material of said one contact which are separated by the portions of refractory material.

19. An electrical contact comprising a body having a plurality of portions of refractory material separated by a plurality of portions of a conducting material extending clear through the contact from its face to its back, said portions of refractory material serving to prevent permanent welding or adhering ofthe contact to a cooperating contact.

20. An electrical contact comprising a body composed of a pluralit*1 of parallel strips of good conducting material and a plurality of alternate strips of refractory material, the planes of the strips being perpendicular to the face of the contact and the strips of good conducting material extending clear through the contact from its face to its back, said strips of refractory material serving to prevent permanent welding or adher-v ing of the contact to a cooperating contact.

JosEP'rI SLEPIAN.

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