US2235048A - Cover switch - Google Patents

Description

March 18, 1941. H. F. SPENCER COVER SWITCH Filed June 13, 1939 2l Sheets-Sheet l INVENTOR.

' ATTORNEY.

Mar

Mal-l1 18, 1941 H. F. SPENCER covEa SWITCH Filed June 13, 1939 2 Sheets-Sheet 2 INVENTOR. may 7? 5,414.04

ATTORNEY.

Patented Mar. 18, 1941 UNITED STATES PATENT OFFICE COVER SWITCH ration of Pennsylvania Application June 13, 1939, Serial No. 278,868

4 Claims.

This invention relates to new and useful improvements in thermocouple switches for use in furnaces employing a movable cover in which is supported a thermocouple to indicate temperature conditions at the top of the furnace, such, for example, as soaking pit furnaces for heating steel ingots and the like.

It is among the objects of the invention to provide a switch mechanism for use with movable cover mechanisms of soaking pit furnaces which shall be efficient in establishing `and maintain- Y ing contact in a thermocouple circuit of a very low E. M. F.

Another object of the invention is the provision of a thermocouple switch which, when opened to disconnect the thermocouple, automatically short-circuits the instrument, such as a galvanometer. to prevent iiuctuation of the indicator arm.

Still another object of the invention is the provision of a switch of the above-described character in which the contacts are of a non-oxidizing metal such as stainless steel and are subjected to a wiping action in their circuit making and breaking movements.

These and other objects of the invention will become more apparent from a consideration of .the accompanying drawings constituting a part hereof in Which like reference characters designate like parts, and in which:

Fig. l is a side elevational View partially in section of a portion of a pit type furnace and movable cover with the thermocouple switch connected thereto embodying the principles of this invention;

Fig. 2 an end elevational View of a portion of the furnace wall cover and switch;

Fig. 3 a top plan view of the switch base with spring elements partially cut away;

Fig. 4 a side elevational view of the switch base; and

Fig. 5 an end elevational view thereof.

With reference to the several figures of the drawings the structure therein illustrated comprises the top portion of a soaking pit furnace wall designated by the reference character I having a recess 2 in the top thereof for receiving silica sand which forms a sand seal around the periphery of the furnace in which a sealing flange 3 of a cover 4 is embedded. The cover 4 is provided with a mounting bracket 5 that carries an outlet box 6 connected by conduit 'l to a thermocouple extending vertically downward through the furnace cover as indicated at 8, Fig. 1, the thermocouple being adapted to register the temperature at the top of the furnace chamb er. A plurality of spacer spools 9 of insulating material are carried by bracket 5 to support terminal plates, I-Ia which are electrically connected to the thermocouple conduits II and I2 extending through the outlet box 6 into the conduit l. Contact plates Ill-Illa are made of a non-oxidizing metal such as stainless steel.

Mounted on a support I3 directly beneath the contact plates IU is a switch base I4 having angle brackets I5 extending vertically thereon. The angle brackets I5 pivotally support bell crank levers I6 at Il, the horizontal arms of which support terminals I8-I8a also of stainless steel, which are adapted to engage the terminal plates Iii-Illa. Terminals I8-I8a have a long depending nger I9-I9a and are electrically connected by conduits 2li- 20a to an outlet box 2|, which is connected through conduit 22 leading to a recording or registering instrument, such as a galvanometer or potentiometer, the conductors 23 of the instrument being connected through the outlet box 2l to a pair of contact terminals 24-24a.

A pair of tension rods 25-25a extend through the vertical arms 2S--26a of the bell crank levers I6. The ends of rods 25-25a are perforated to receive the ends of coil springs 21--2'Ia, tension of the springs being adjustable by adjusting nuts 28-28a on the ends of the rods. Tension of the springs 21 is such as to normally bias levers I5 in the manner shown in dotted lines in Fig. 4.

The operation of the above described switch mechanism is briefly as follows:

Cover 4 is adapted for both vertical and horizontal movement, the cover being supported on a traversing carriage (not shown) and not essential to a description of the present invention.

Figs. 1 and 2, the cover is shown in its normal lowered position on top of the furnace wall with the sealing flange 3 projected into the sand holding recess 2 on top of the wall. In this position the thermocouple switch is as shown in Fig. 1 with the contact plates Ill- Illa in engagement with terminals I8-I8a of the switch base. When the cover is moved to expose a portion of the pit chamber for charging or removing ingots therefrom, it is first raised vertically, and as it moves upward tension of springs Z'I-Z'I'a tilts levers I6 to raise terminal contacts I8--I8a upward to maintain contact with plates Ill- Illa until ngers Ill- Illa engage the shortcircuiting terminals 24-24a so that the instrument connected to conduit 22 is short-circuited before or at the instant the thermocouple connection is broken at the terminals lillila and I8-l3a. This, as previously explained, prevents violent fluctuation of the indicator arm of the recording instrument. After the cover has been traversed and returned to its position in register with the sand seal of the furnace wall, it is again lowered, and as the plates lQ-la contact the tilted terminals l-ia the latter will be pressed downwardly, thereby breaking the circuit with terminals 2li and establishing the circuit between the thermocoupie and the recording or control instrument. It will be noted that because of the tilted position of terminals I8--l8a, the lowering of the cover will cause a wiping action of terminals i3 on plates lil, which is useful in maintaining a smooth and bright contact surface between the terminal members. As previously explained, stainless steel is used to eliminate oxidation incidental to the use of copper terminal members, and with the wiping action of the contacting terminals the surface is rendered smooth to obtain an eiicient electrical contact of the terminal members. This is essential because of the low E. M. F. of the thermocouple circuit which could not be efficiently transmitted through an oxidized copper surface.

It is evident from the foregoing description of the invention that a thermocouple switch made in accordance therewith maintains an eifective and efficient electrical connection between the thermocouple in a movable furnace cover and the controlling instrument for maintaining predetermined temperature conditions within the furnace chamber.

Although one embodiment of the invention has been hereinillustrated and described it will be apparent to those skilled in the art that various modications may be made in the details of construction without departing from the principles herein set forth.

I claim:

1. A cover switch for pit furnaces or the like comprising a switch base having a pair of terminal arms pivotally mounted thereon, spring means normally biasing said arms to an upward position, terminals mounted on said arms, each having a top contact and a depending iinger contact, a switch element movable with the cover having terminals for engagement with the top contacts of said arm terminals and stationary terminals on said base for engagement by the finger vcontacts of said arm terminals, said terminals being subjected to a wiping contact in the circuit making and breaking movements of the switch parts.

2. A cover switch for pit furnaces or the like comprising a switch base having a pair of levers pivoted thereon, stationary contacts on said base terminal contacts on said levers, springs joining said levers to bias the contacts normally upward and against said stationary contacts, and terminal contacts movable vertically with said cover and adapted for engagement with the terminal contacts on said levers.

3. A cover switch for pit furnaces or the like comprising a switch base, levers mounted on said base, terminals on said levers, said terminals having extending portions normally disposed vertically, spring means biasing said levers to raise the terminals, terminals disposed intermechate said first-named terminals adapted to be contacted by the extending portions of said firstnamed terminals in the raised position thereof, and terminal plates movable with said cover for engaging the nist-named base terminals.

4. A cover switch comprising a stationary switch base having an outlet box, levers pivotally mounted on said base and terminals on said levers, conductors connected to the terminals and extending through the outlet box, a plurality of short-circuiting terminals on said outlet box, spring means for actuating the levers to effect contact of the first-named terminals with the short-circuiting terminals, and a switch element movable with the cover for engaging the first-named terminals to displace the same against the tension of the spring, whereby to break the short circuit vand establish a normal circuit.

HOWARD F. SPENCER.

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