US2790877A - Switch - Google Patents

Description

April 30, 1957 R, C, EVANS ET AL SWITCH Filed July V21., 1955 FIG I 'lll/11111111111.

INVENTORS RICHARD C.

EVANS NORMAN H. ROSENBERG av ffl/cfm, fea/m4103549 d f ATTORNEY United States Patent O SWITCH Richard C. Evans, Hamden, and Norman H. Rosenberg,

New Haven, Conn., assiguors to Olin Mathieson Chemical Corporation, New Haven, Conn., a corporation of Virginia Application July 21, 1955, Serial No. 523,564

7 Claims. (Cl. 200-142) This invention relates to electric switches and more particularly to a switch that is actuated by a chemical change of a mixture of materials arranged in an electric circuit.

Within a suitable container, we arrange two leads forming a part of a circuit with a gap between them and this gap is filled with a mixture of two or more materials which is electrically conductive and which is capable of 'combustion when a required amount of heat is supplied, and which, on burning, produces an electrically non-conductive mass without substantial evolution of gas.

Such a switch may be used advantageously in many installations. For instance, it may be employed in a projectile fuze for arming it at a desired time. Many mixtures of materials, consisting of an oxidizer and a fuel, are available which will react or burn without substantial evolution of gas when brought to an elevated temperature. Such temperature may be produced by an electric igniter, which in a specic form, may be a high resistance wire or connector between the leads, or by a percussion cap. Initial electrical conductivity may be obtained by providing an electrically conductive metal powder, such as copper, silver or aluminum in the mixture in a proportion of at least about 35 to 40% by weight.

Various mixtures of materials may be employed in the construction of the switch. The preferred composition consists of a mixture of powdered zirconium, powdered copper and powdered barium peroxide, not necessarily in stoichiometric proportions but rather proportions which provide enough metal to insure conductivity before burning and enough oxidizing agent to insure rapid burning and oxidation of the metals present, so as to insure loss of conductivity upon burning. The preferred composition consists of l parts by weight of powdered zirconium, 40 parts by weight of copper and 50 parts by weight of barium peroxide, all ingredients being somewhat finer than 300 mesh. In addition to controlling the burning rate by using an excess of one ingredient, it is also possible to increase the burning rate by decreasing the particle size and to decrease the rate by increasing the particle size.

Many other similar mixtures may be employed. We may use any mixture of two or more materials that are preferably in powdered form, the mixture being initially substantially electrically conductive, the materials being reactive at a temperature such as may be obtained by passing an electric current through a resistance element in contact therewith and the product formed by combustion being a non-conductor of electricity.

Thus, we may use a mixture of powdered zirconium, copper, and potassium perchlorate although in this case, the nal electrical resistance is not as high as in the cornposition mentioned previously. The iirst composition had an electrical resistance between cylindrical lead wires separated by 1A@ inch of mixture of about 0.1 ohm or less before combustion and about 100 megohms after combustion. The second composition had an electrical ice resistance of 0.1 ohm or less before combustion and about 3000 ohms after combustion.

In the accompanying drawing, we have illustrated one embodiment of the invention. In this showing:

Fig. 1 is an end view of a switch constructed in accordance with the invention; and

Fig. 2 is a sectional view on line 2 2 of Fig. l.

Referring to the drawing, the switch is mounted in a casing 2 which may be of any suitable size and shape, and which may be made of any suitable material, such as metal, or a. plastic having the ability to withstand rough handling and usage. The ends of the casing may be closed by seals 4 preferably formed of an insulating material, such as glass contained in cylinder 3 of Kovar metal. Within the casing between the seals we place a lling 6 of the powdered mixture. As stated, this may be a mixture of powdered zirconium, powdered copper and powdered barium peroxide. A pair of terminals or connections 8 and 10 extends through one of the seals and are connected as desired in the circuit which is to be controlled.

One means of raising the temperature of the mixture 6 to a point that will cause the necessary reaction is by passing an electric current through a resistance wire or element in the powdered mixture. For this purpose a pair of lead wires 12 extend into the casing, for instance, through one of the seals 4 as shown in Fig. 2. These lead wires are arranged in tubes 14 of Kovar metal which is bonded to the glass seal. The tubes 14 are sealed to lead wires 12 by solder 16. A resistance wire 18 extends between the ends of the leads 12.

It is at times advantageous to provide an ignition charge 20 which burns without substantial evolution of gas in contact with the main charge 6 and surrounding the ignition wire 18. The ignition charge may consist of a mixture of 25% by weight of finely divided zirconium and by weight of barium chromate, or any of the other ignition compositions used in gasless electric detonators. When the metal component of charge 6 is highly reactive, one such as zirconium, the ignition mixture may have the same composition as charge 6 but in uncompressed or slightly compressed form.

The unit is assembled by crimping in place the seal containing terminals 8 and 10. Then, the required amount of charge 6 is added as a loose powder and compressed. The ignition powder is then added and lightly compressed by insertion of the seal, which is crimped in place. Both seals may then be waterproofed by application of a suitable layer of wax, plastic, or lacquer.

When a current is passed through leads 12, the wire 18 being of much smaller cross-section and being formed of an alloy that is normally used in resistance elements becomes heated to red heat. This causes combustion of the ignition mixture 20 which in turn causes the ingredients of the conducting mixtures to react. In this action, the conducting element or compounds, such as copper, is converted to a non-conducting oxide. Such an oxide is a poor enough conductor to disrupt the current path between leads 8 and 10 of the circuit being controlled, thus effecting the desired result.

The switch thus formed has 4a number of advantages. It is not afected by extremes of temperature =which cause inoperativeness or idiiculties in connection with many forms of mechanical switches. It is very durable and shock-resistant, thus being particularly useful in artillery shells, where the set-back forces frequently lare a source of trouble with switches of known construction. Its components are all very stable producing a switch of indefi- -nite life. As it contains no moving parts, it is less apt to become disabled than various forms of conventional Patented Apr. 30, 1957- switches. The simplicity of the switch is also clearly apparent. i

We claim:

1. A switch comprising a casing, a pair of terminals extending into the casing and spaced from each other, a mixture of a powdered conductive metal and an oxidizing argent in the casing bridging the space between the ends of the terminals, the mixture bein-g a relatively good conductor of electricity, but being such that an increase in temperature will cause combustion and the prcduction of a mixture that is a relatively poor conductor of electricity to thereby disconnect the terminals from each other, land means for raising the temperature of the mixture.

2. A switch comprising a casing, a pair of terminals extending into the easing and spaced from each other, a mixture of a powdered `conductive metal and an oxidizing -agent in the casing bridging the space between the ends of the terminals, the mixture being a relatively lgood yconductor of electricity, but being such that an increase in temperature wil-1 cause combustion and the production of a mixture that is 4a relatively poor conductor of yelectricity to thereby disconnect the terminals from each other, an electrical resistance clement in the mixture, and leads connected to said element.

3. A switch comprising a casing, a pair of terminals extending into the casing and spaced from each other, a mixture of powdered zirconium, powdered copper and barium peroxide in the casing bridging the space between the ends of the terminals, and means for raising the temperature of the mixture to oxidize the zirconium and .Copper and produce a non-conducting mixture between the terminals.

4. A switch comprising a casing, la pair `of terminals extending into the casing and spaced from each other, a mixture of powdered zirconium, powdered copper and potassium chlorate in the casing bridging the space be 4 tween the ends lof the terminals, and means for raising the temperature of the mixture to oxidize the zirconium and copper and produce ya non-conducting mixture between the terminals.

5. A switch in accordance with claim 3 in which the mixture consists of substantially l() parts of copper, 40 parts of zirconium, and 50 parts of barium peroxide.

6. A switch comprising a casing, a pair of terminals extending into the c-asing and spaced from each other, a mixture of ia powdered conductive metal and `an oxidizing agent in the casing bridging the space between the ends of the terminals, the mixture being a relatively good conductor `of electricity, but being such that an increase in temperature will cause combustion and the production of a mixture that is a relatively poor conductor `of electricity to thereby disconnect the terminals from each other, tain `electrical resistance element in the mixture, leads `connected to said element, Iand an ignition mixture in the `casing surrounding the resistance element.

7. A switch comprising a casing, a seal of insulating material in the easing, a pair of terminals extending through the seal and spaced from each other, ya mixture of a powdered conductive meta-l and an oxidizing agent in the casing bridging the space between the ends of the terminals, fthe mixture being a relatively good conductor of electricity, but being such that an increase in temperature will cause combustion yand the production of a mixture that is a relatively poor conductor of electricity to thereby disconnect the terminals from `each other, and means for raising the temperature of the mixture.

References Cited in the file of this patent UNITED STATES PATENTS

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