US2101115A

US2101115A - Electric switch of the fluid flow type

Info

Publication number: US2101115A
Application number: US47299A
Authority: US
Inventors: Warren R Walker
Original assignee: General Electric Vapor Lamp Co
Current assignee: General Electric Vapor Lamp Co
Priority date: 1935-10-29
Filing date: 1935-10-29
Publication date: 1937-12-07
Anticipated expiration: 1954-12-07
Also published as: US2142152A; US2142151A; DE674913C; GB466258A; US2153000A; US2073529A; US2142154A; US2101093A; DE682879C; US2047931A; US2142156A; DE670428C; GB462527A; DE664792C; GB471087A; FR830093A; US2155244A; GB466257A; GB467068A; US2142153A

Description

Dec. 7, 1937. w. WALKER ELECTRIC SWITCH OF THE FLUID FLOW TYPE Filed Oct. 29, 1935;

INVENTOR UNITED STATES PATENT OFFICE 2,101,115 emc'rarcswrrcn or'ruu FLUID FLOW me Warren E. Walker, Short Hills, N. 1., asslgnor to General Electric Vapor Lamp Company, Hoboken, N. 1., a corporation of New Jersey Application October 29, 1935, Serial No. 47,299

6 Claims. 01. (200-152).

The present invention relates. to electric switches of the fluid flow type, and particularly to switches employing mercury to close the circuit therethrough. 5 A particular object of the invention is to provide a fluid flow switch having an extremely low The invention consists in the new and novel structure hereinafter set forth and claimed.

15 In general the current rupturing capacity of a fluid flow switch considerably exceeds the current which the same switch can continuously carry with an approved temperature rise, and the rating of the switch is therefore necessarily limgo ited to the smaller value imposed by the latter of these considerations. This limiting temperature rise within the switch is, of course, a direct function of the internal resistance of the switch, and hence any decrease in this resistance is im- 5 mediately reflected .in an increased rating for the switch. Accordingly a great deal of effort has been expended in an attempt to reduce the internal redstance ofthese switches.

Recently considerable attention has been directed toward the development of switches having a metal envelope, in which different portions of this envelope serveas the electrodes. This construction has'provided electrodes having a very considerable area in contact with the mercury 35 commonly used as the fluid in these switches, and has thus tended to produce a switch having a low internal resistance. This general idea of a metal envelope switch has, of course, been toyed with for many years, but it isonly since the recent 40 development of switches of this type having vitreous seals, such as disclosed in an application by John H. Payne, Jr., Ser. No. 759,927, filed December 28, 1 934,'whereby they are hermeticallysealed for the first tim'e, that a successful commercial 45 structure has been attained. The production of these vitreous seals, however, requires the use of a fusing heat and this heat, while essential to the production of a successful tends to pro.- duce an oxide film on the surface of any of the 50 metals which it is practicable to-use for these envelopes. The presence of this film is indicated by the fact that the resistance of these switches. while very low, is sometimes above that which would be obtained with a clean metal surface 55 which would be we by the mercury. Furthermore I have found that many of the metal alloys which are commonly used in combination with soft glass, such as the various chrome-iron alloys which it is known can be sealed to the soft glasses, are not wet by mercury even when perfectly clean.

I have now discovered that the resistance of any of these switches is maintained at a constant low value by providing 'the inside of the metal shells forming the switch with a surface consisting of platinum, which I have found to be unique in possessing two essential characteristics for this contact surface. Thus first of all the platinum does-not oxidize during the heating"-opera:'---- tions which are necessary to fuse together the various elements of the switch, so that a clean metal surface is presented to the mercury. Even more important this clean platinum surface 'is readily wet by the mercury to produce an exceptionally good electrical contact therewith, but is not dissolved away to any appreciable extent by the mercury, due to its low solubility therein, sothat an extremely thin film can be depended upon throughout the long life of the switch. It is not essential, or even desirable, that the platinum cover the entire inner surface of the metal shells, since I have found that a very small area there:

' of located on each shell where it will make contact with the mercury when the circuit through the switch is closed is entirely adequate to give an extremely low resistance, and that by heat? ing these areas somewhat toward the open circuit position of the switch the angle of tilt required to open and close the circuit is diminished.

The desired platinum surface is produced in any of a variety of ways. Thus in the preferred case a small piece of sheet iron coated with a thin film of platinum on the exposed side is welded' in place in the metal shells. Or a fine wire sheathed in platinum, of the order of 10 mils in 40 diameter, is welded end on to the metal shell and clipped oi! as short as possible. In either of these cases, of course, pure platinum can also be used, but the use of an iron base for the platinum coatings permits the use of larger pieces at the same small cost, and thus not only simplifies the handling problem, but also exposes a larger surface to the mercury for a given quantity of platinum than would otherwise be convenient. Likewise the'platinum may be coated on other base metals 'which will not contaminate the mercury, if desired, although iron has been found to be especially valuable for this use. As an alternative to this welding the coating of the platinum is produced by depositing the metal out of a sus- Eli pension or solution of a salt thereof by any of the well known methods, or it can be plated on the shell.

In any of the above cases a small contact surface of platinum is formed at a point which is below the mercury in the closed circuit position of the switch which is not only free of oxide, but which is slightly wetted by the mercury, although it does not dissolve therein to any appreciable extent. This wetting of the contact surface results in an unusually constant and good electrical conduction from the platinum to the mercury, and as a result the internal resistance of the switches constructed in this novel manner is exceptionally low.

For the purpose of illustrating my invention I have shown a preferred embodiment thereof in the accompanying drawing, in which i Fig. 1 is an elevational view of a mercury switch having a hermeticallysealed metal envelope,

Fig. 2 is a sectional view of the switch of Fig. 1,

Fig. 3 is an internal view of one of the metal sides of the switch of Fig. 1 before assembly showing a. piece of platinum or platinum coated iron welded thereto,

Fig. 4 is an elevational view of the refractory dividing member shown in the position in which it is placed in the metal part shown in Fig. 3.

Fig. 5 is an enlarged section of a part of the metal side shown in Fig. 3 showing the preferred mode of attaching the platinum,

Fig. 6 is a similar view to Fig. 5 showing a modification of the structure thereof using wire, and

Fig. 7 is a side view of the switch of Fig. 1 showing the relation of the various parts thereof within the switch by means of dotted lines.

As shown in this drawing my novel switch, which is of the type disclosed in my co-pending application, Serial No. 28,560,1iled June 26, 1935, has two dished metal members i and 2 which areidentical, save that the member i has a filling opening therein. Between said members i and 2 there is positioned a refractory dividing member 3' with a thin coating of glass 4 hermetically sealing the members i and 2 to each other and to the member 3. Within said switch there is a body of mercury 5 which is adapted to close the circuit between the members i and 2 through an opening 6 in the refractory 3 at' mercury 5 whenever said mercury extends through the opening 6, and preferably at a point which is not quite opposite said opening, as best shown in Fig. 7, a piece of sheet metal 8, which consists of platinum or platinum coated iron, is welded to each of the 'metal members I and 2. In practice these metal strips are of the order of 2 by 4 millimeters in size, and are oi 10 mil iron on which there has been rolled or otherwise placed a coating of platinum of the order of .2 mil in thickness.

In the alternative form of Fig. 6 a platinum or platinum sheathed wire I of the order of 10 mils in diameter is welded end on to each of the metal shells, and the free end thereof then resistance and at the same time economizeson the use of the platinum. In some cases the wire 8 is welded on its side against the members I and 2, but in general better results are obtained with the structure shown for a given mass of platinum.

In the manufacture of these switches the

platinum contacts

8 or 8 are welded in place, as

shown, or an equivalent coating of the metal is deposited thereon from solution or suspension, by plating, or in any other suitable manner, and the switch then assembled and fused together, preferably in the manner described in Payne's application or in my co-pending application, referred to hereinbefore. The contacts 8 or 8' remain unoxidized, of course, despite the heating to which the members i and 2 are necessarily subjected during the fusion step, due to the characteristics of the platinum. After the switch has been evacuated it is given its filling of mercury 5 and hydrogen and then sealed-off by fusing the closure l in place.

The switch is then heated to a temperature of the order of C. while in such a position that the mercury E is in contact with the contacts 8 or d, either by placing it in an oven or by passing a suitable current therethrough. This heating greatly facilitates the wetting of the platinum by the mercury, with a resultant de crease in the contact resistance therebetween.

The contacts 8 or 8' are preferably positioned a little out of alignment with the opening 6, as shown, since in this position these contacts remain below the surface of the mercury as the switch is rotated between its open and closed clr cuit position. This prevents the attraction between the mercury and the wetted platinum from 1 exerting a drag on the mercury on either movement of the switch, and thus results in operation of the switch with a minimum angular movement thereof.

While I have described my invention by refer ence to a particular embodiment thereof it is to be understood that various changes, omissions and substitutions within the scope of the ap pended claims, may be made therein without departing from the spirit of my invention.

I claim as my invention&-

1. An electric switch comprising, in combination, a pair of metallic members hermetically sealed together to form a substantially all metal envelope, said members being insulated from each other, mercury within said envelope in contact with said metallic members over an extensive area, said envelope having a relatively high con tact resistance with said mercury despite said large contact area, a refractory member dividing said envelope into two chambers, said refractory member having an opening therein to permit mercury flow therethrough in the closed circuit position of said switch to electrically connect said metallic members, and a coating of platinum of relatively small area in electrical contact with each of said metallic members and with said mercury when said switch is in said closed circuit position to reduce the electrical resistance between said members and said mercury.

2. An electric switch comprising, in combination, a pair of metallic members hermetically sealed together to form a. substantially all metal envelope, said members being insulated from each other, mercury within said envelope in con-' tact with said metallic members over an extensive area, said envelope having a relatively high contact resistance with said mercury despite said duce the electrical resistance between said memlarge contact area, a refractory member dividing said envelope into two chambers, said refractory member having an opening therein to permit mercury flow therethrough in the closed circuit position of said switch to electrically connect said metallic members, and a coating of platinum of relatively small area in electrical contact with each of said metallic members and with said mercury when said switch is in said closed circult position, said platinum coatings being wetted by said mercury to make good electrical contact therewith to reduce the electrical resistance between said members and saidmercury,

3. An electric switch comprising,in combination, a pair of metallic members hermetically sealed together. to form a substantially all metal envelope, said members being insulated from each other, mercury within said envelope in contact with said metallic members over an extensive area, said envelope having a relatively high contact resistance with said mercury despite said large contact area, a refractory member dividing said envelope into two chambers, said refractory member having an opening therein to permit mercury flowtherethrough in the closed circuit position of said switch to electrically connect said metallic members, and a coating of platinum of relatively small area in electrical contact with each. of said metallic members and-with said mercury when said switch is in said closed circuit position, said coatings being so positioned in an offset relation with respect to the opening in said refractory member that they are completely below the surface of said mercury in both the open and closed circuit positionof said switch to rebers and said mercury.

4. In combination, a body of mercury, a metallic member of oxidizable metal in extensive contact therewith, said memberhaving a relatively high contact resistance with said mercury despite said extensive contact area, and a coating of a non-oxidizable metal on a relatively small portion of said member as compared to the' portion thereof in direct contact with said mercury, said coating being in contact with said mercury to re-' duce thev resistance of the electrical path from said member to said mercury.

-5. In combination, a body of mercury, a metallic member of oxidizable metal in extensive contact therewith, said member having a relatively high contact resistance with said mercury despite said extensive contact area, and a coating of platinum on a relatively small portion of said member as compared to the portion thereof in direct contact with said mercury, said coating being in contact with said mercury to reduce the resistance of the electrical path from said mem-, her to said mercury.

6. A sealed device consisting in part of vitreous material, mercury within said device, a metallic member of oxidizable metal sealed to said vitreous material and in extensive contact with said mercury, and acoating of platinum aflixed to a relatively small portion of said member as compared with the portion thereof which is in direct contact with said mercury, said coating being in contact with said mercury to .reduce the electrical resistance of the path from said memberto i said mercury.

WARREN R. WALKER.