US3106628A

US3106628A - Cylindrical forged tungsten electrical contact

Info

Publication number: US3106628A
Application number: US680452A
Authority: US
Inventors: William G Chiswell
Original assignee: Fansteel Inc
Current assignee: Fansteel Inc
Priority date: 1957-08-27
Filing date: 1957-08-27
Publication date: 1963-10-08
Anticipated expiration: 1980-10-08

Description

1963 w. G. CHISWELL 0 CYLINDRICAL FORGED TUNGSTEN ELECTRICAL CONTACT Aug. 27, 1957 n 19 i INN I" n 16 4/. 20 Ill 21 19 V 23 @f' -2 24 I W 11 /f9 11 30 22 31 L 30 31 s 4 3,106,628 CYLINDRICAL FORGEB TUNGSTEN ELECTRICAL CONTACT William G. Chiswell, Waukegan, lll., assignor to Fansteel Metallurgical Corporation, a corporation of New York Filed Aug. 27, 1957, Ser. No. 680,452 2 Claims. (Cl. 200-166) The present invention relates to electrical contacts and a method of making electrical contacts. It particularly relates to electrical contacts and a method of making electrical contacts of the type used in devices such as relays and voltage regulators, etc.

The electrical contacts used in devices such as relays and voltage regulators must carry high currents and are subjected to high current densities. They are also subjected to frequent circuit opening and closing operation. As a result, these contacts must withstand high temperature, due to arcing, and must have a high wear resistance because of the frequency with which they are opened and closed. The contacts also must have a surface configuration that will resist wear and that aids in breaking arcs that occur between adjacent contacts.

For these purposes, contacts of this type have been made of material such as tungsten or other similar metals having high melting points. Although lower melting point metals have been used, tungsten is the most commonly used material. The present invention is not, however, concerned with the particular material used for makin the contact.

To reduce arcing and to reduce the effects of mechanical wear, it has been the practice to make contacts of this type with a crowned or segmental spherical face which may or may not, as desired, having a slight fiat portion at the center of the crown.

Crowning of these contacts is important to the wear and are resistance characteristics. However, crowning has been a costly and time-consuming operation since it is generally accomplished by hand grinding. The hand grinding is not only inefiicient, but subject to inaccuracies. The grinding of the crowned faces of the contacts also leaves grinding streaks or marks on the face of the contact. These grinding streaks reduce the efficiency of the contact by giving the face a rough and irregular surface and by promoting oxidation and increasing the surface resistance of the contact.

By the present invention these difficulties are overcome and face of the contact is provided with a smooth crowned configuration that is segmentally spherical. The contacts of this invention are also given a concave back face which permits more efiicient and easier mounting thereof on the backing and supporting member to which it is brazed.

In accordance with this invention contacts are made by cutting cylindrical segments from a rod made of contact material, such as tungsten. The pieces are cut to have an appropriate contact thickness. As an example, a tungsten rod is cut in a diamond disc cutoff machine that operates automatically to cut off disc blanks at a thickness of about 0.030 inch. The rod has a diameter of about 0.147 inch. Contacts made from these discs may be used in an automotive voltage regulator. The disc blanks are then placed in a forging machine, on an appropriately configurated die of a diameter of about inch with a concave die face having a diameter of 0.180 inch and a 0.700 inch radius of curvature.

With tungsten, the disc blank is then heated by such means as an induction heater or an cry-acetylene torch to a temperature of from about 1600 F. to about 1800 F., substantially below the melting point of the metal but high enough to permit forge shaping and crowning of the metal disc. The disc is then struck by a male die operated Patented Oct. 8, 1963 from a pneumatic or hydraulic ram. The ram is pneumatically or hydraulically operated so that it may cornpe-nsat-e for slight variations in thickness of the disc.

The male die, in this example, has a diameter of about 0.125 inch and is provided with a segmental spherical face having a radius of about 0.670 inch.

After the disc is struck, it is ejected from the forging machine by an air blast. The slight resilience of the disc is sufiicient to provide the disc with a final outer surface radius of from about 0.750 inch to about 0.800 inch, and a substantially identical inner concave surface radius. The external surface of the disc is smooth since it was forced against a highly polished die surface.

The advantages and features of the invention, the details thereof and variations therein will become clear to those skilled in the art and others from the following detailed description of the invention and an embodiment thereof, from the claims, and from the accompanying drawings in which each and every detail shown is included as a part of this specification, in which like reference numerals refer to like parts, and in which:

FIGURE 1 is a fragmental partly sectional view of a die portion of a forging machine with a contact disc therein;

FIGURE 2 is a sectional view of a contact disc embody ing this invention and mounted on a backing and mounting pin;

FIGURE 3 is an elevation view of a contact disc blank prior to being forge crowned;

FIGURE 4 is a vertical sectional view of a forge crowned contact disc embodying this invention and made by the method of this invention;

FIGURE 5 is a plan view of the mounting face of the contact disc of FIGURE 4; and 0 FIGURE 6 is a plan view of the contact face of the contact disc of FIGURE 4.

Contact discs embodying this invention are cut in any convenient manner from rods of contact material, such as rods of tungsten. The manner of cutting the discs is not critical to this invention; however, the discs may be cut manually, semiautomatically, or automatically by appropriartely jigged mechanisms. The discs'cut from the rods are slightly smaller in diameter and slightly smaller in thickness than the final contact discs.

After the disc blanks are cut from the rod they are fed, in any convenient manner, manually or automatically, into a forging or modified punching machine shown in part in FIGURE 1. Therein it is shown that the machine has a base 12 appropriately recessed, as at 13, to receive a female die 14 on which the disc blank is placed. The die 14 has a spherically curved and polished concave face 15, the radius of curvature of which is appropriate to allow for spring-back of the disc material after forg-. ing so that the disc will have the desired spherical face. In one example of such a die and disc, if the disc is to have a radius of curvature of from about 0.750 inch to about 0.800 inch, and is to be made of tungsten, with the forging operation being effected at a temperature of from about 1600' F. to about 1800 F., then the radius of curvature of the face 15 on the die 1-4 will be about 0.700 inch. The disc 11 is held coaxially over the face of the die 14 by any convenient chuck arrangement such as the resilient holding fingers 16. These fingers hold the disc in place for heating and forging.

The heating of the discs is effected in any convenient manner such as by an induction heater 17 disposed above the fingers 16 and about the disc 11. It is also suificiently spaced from the die 14 and supporting block 12 to permit the finished disc 11 to be air blast ejected from the mechanism. Further, the induction heater 17 shown in FIGURE 1 is a single-turn heater with a sufiiciently large \J inner diameter to permit the upper movable punch or die 18 to pass therethrough without engaging the heater.

When the heater 17 is energized, the disc 11 will be heated to a sufficient temperature to permit forging. Then a pneumatic or hydraulic ram 19 will drive the punch or male die 18 downwardly to strike the upper surface of the disc blank. The bottom face 20' of the die 18 is provided with a segmental spherical configuration which, in this example, has a spherical radius of about 0.670 inch. The diameter of the die 18, in this example, is about 0.125 inch.

After the blank is struck by the male die it is transformed from the configuration of blank shown in FIGURE 3 to the configuration of disc shown in FIG- URE 4. It is then ejected from the machine by an air blast emanating from a nozzle 21 connected to any appropriate source of air and controlled in any convenient manner so that air will blast from the nozzle 21 after the die 18 is retracted by the ram 19.

The disc expands slightly under the force of the male die striking the disc so that it is enlarged slightly in diameter and is enlarged slightly in rim thickness. This latter effect is due to the fact that the male die is made slightly smaller in diameter than the diameter of the disc. The effect of using a smaller diameter die than disc also provides the disc with a fiat rim 22 about the face of the disc that is struck by the male die and provided with a concave central spherical curved portion 23.

The face 24 of the disc 11, which face was in contact with the face of the female die 14, is now convexly curved with a spherical radius that is substantially the same as the radius of the concave face 23. This curvature has a slightly greater radius than the radius of the dies due to resilience of the material.

However, both the concave and the convex face are substantially perfectly formed and smooth since they were formed against highly polished dies. They do not have grinder marks or other similar marks thereon such as might occur in hand grinding and the contacts are uniformly made so that they are freely substitutable and interchangeable.

The fiat rim 22 about the concave curved portion of the disc 11 provides an alignment aid and brazing aid for mounting of the disc on a contact backing pin. The relation between the concave face of the disc and a mounting pin is shown in detail in FIGURE 2 wherein a complete assembly is shovsm in section.

The contact mounting pin 25 has a mounting shank 26 for mounting the assembly on a relay arm. To position the shank on the relay arm, the shank carries a radial shoulder 27 that may be hexagonally contigurated to be held by a wrench or other appropriate mounting tool. Beyond the shoulder portion 27, the mounting pin has a head 28 onto which the disc 11 is secured coaxially with the pin.

The face 29 of the head 28 is spherically curved to a radius slightly greater than the radius of spherical curvature of the concave face 23 and the convex face 24 on the disc 11. This provides a slightly greater brazing gap at the center of the disc that at the inner edge 30 of the rim 22 on the disc 11. In the example given the radius of curvature of the face 29 of the head is about 0.900 inch.

By providing a centrally enlarged gap between the disc and the pin head 28 and a radially expanding gap between the rim 22 and the face 29 of the head, more etlicient brazing is facilitated and the members permit brazing material such as is shown at 31 to fill the gap and be accepted between the two parts to hold the parts together. Without this enlarged gap the brazing material would be squeezed out of various areas between the disc and the pin so that voids would occur in the brazing area. Such voids are highly undesirable since they reduce the electrical contacting efficiency and increase the contact resistance of the members.

Devices embodying this invention provide efiicient contacts that have long life in operation as well as on the shelf. Since there are no irregularities on the actual contact face 24 of the disc 11, oxidation of the face is minimized and sparking and arcing are substantially reduced.

From the foregoing it will be seen that numerous modifications and variations may be effected without departing from the true spirit and scope of the novel concepts and principles of this invention.

1 claim:

1. An electrical contact comprising a substantially cylindrical tungsten disc formed of a homogeneous metallic composition and having an annular outer surface and a pair of opposed transverse surfaces, the opposed surfaces of said disc being smooth to increase the efficiency of the disc as a contact member and being substantially spherically curved, one of said opposed surfaces being convex to reduce arcing and to reduce the effects of mechanical wear, and the other of said opposed surfaces being concave, said opposed surfaces having substantially the same radius of curvature, the curvature of said concave surface terminated inwardly from the periphery of the disc whereby the disc is provided with a flat rim between the concave curved portion of said other surface and the outer periphery of the disc.

2. An electrical contact comprising a substantially cylindrical forged tungsten metal disc of unitary structure, the opposed faces of said disc being spherically curved, one of said faces being convex and the other of said faces being concave, the curvature of said concave face terminating inwardly from the periphery of the disc whereby the disc is provided with a fiat rim between the concave curved portion of said other face and the outer periphery of the disc.

References Cited in the tile of this patent UNITED STATES PATENTS 1,046,823 McBerty Dec. 10, 1912 1,220,886 Pfanstiehl Mar. 27, 1917 2,181,083 Fayette Nov. 21, 1939 2,439,570 Hensel et ai. Apr. 13, 1948 2,468,888 Mekelburg May 3, 1949 2,624,820 Fayette Jan. 6, 1953 2,646,613 Enzle r July 28, 1953 2,737,708 Rollfinke Mar. 13, 1956

Claims

2. AN ELECTRICAL CONTACT COMPRISING A SUBSTANTIALLY CYLINDRICAL FORGED TUNGSTEN METAL DISC OF UNITARY STRUCTURE THE OPPOSED FACES OF SAID DISC BEING SPHERICALLY CURVED, ONE OF SAID FACES BEING CONVEX AND THE OTHER OF SAID FACES BEING CONCAVE, THE CURVATURE OF SAID CONCAVE FACE TERMINATING INWARDLY FROM THE PERIPHERY OF THE DISC WHEREBY THE DISC IS PROVIDED WITH A FLAT RIM BETWEEN THE CONCAVE CURVED PORTION OF SAID OTHER FACE AND THE OUTER PERIPHERY OF THE DISC.