US2798921A

US2798921A - Thermally controlled safety switch

Info

Publication number: US2798921A
Application number: US556374A
Authority: US
Inventors: John W Haas
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-12-29
Filing date: 1955-12-29
Publication date: 1957-07-09
Anticipated expiration: 1974-07-09

Description

July 9, 1957 J. W. HAAS THERMALLY CONTROLLED SAFETY SWITCH Filed Dec. 29, 1955 Fi g1 JohnWHaas' Y NVENTOR.

2,798,921 Tirana/raux coNrnoLLnD SAFETY swirc John W. Haas, Rochester, N. Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application December 29, 1955, Serial No. 556,374

l3 Claims. (Cl. Zilli-423) This invention relates to a thermally controlled safety switch adapted to be used, for example, as a primary safety device in conjunction with ordnance fuses of the electrically-tired type.

With electrically fired fuses, such as those used as proximity fuses, it is highly desirable that the tiring circuit be rendered inoperative until such time as the fuse is ready for use. One way in which this may be done is by providing an electrical short across the tiring circuit, which short will only be removed upon energization of an auxiliary circuit.

It is an object of this invention to provide a safety switch which is particularly well adapted for use in such an environment.

A further object is to provide such a switch which is of relatively simple and foolproof construction and which may incorporate means for producing a predetermined time delay between energization of the auxiliary circuit and removal of the short circuit from the main control circuit.

Further objects will become apparent from the following specication and claims, particularly when considered in conjunction with the accompanying drawing wherein:

Fig. l is a sectional View of a switch according to my invention;

Fig. 2 is a similar sectional view of a slightly modified switch, also in accordance with my invention.

My improved safety switch comprises a suitable metallic casing 1, generally cylindrical in form, the opposite ends of which are closed by a pair of caps or plugs 2, 3 of insulating material to form a closed generally cylindrical housing. Extending through the plug 2 are a pair of spaced electrical conductors 4 and 5, the ends of which extend into the chamber 6 formed by a ring member 7. Connected between the ends of the conductors 4 and 5 is an electrically conductive, fusible bridge member 8 which serves normally to short circuit the conductors 4 and 5. These conductors 4 and 5 may, for example, be part of the main iiring circuit of a proximity fuse and, when shorted together will prevent firing of the fuse. The chamber 6 is filled with a charge of thermitic material 9 which, for example, may be a mixture of barium chromate and barium peroxide. This thermitic material, when ignited, produces extremely high temperatures and will quickly melt the bridge member 8, removing the short circuit between conductors 4 and 5.

In order to ignite the thermitic material 9, auxiliary electrically-controlled means are provided. To this end a second sleeve or ring 10 is provided adjacent the other cap or plug 3, the interior of which sleeve forms a combustion chamber 11, partially lled with an ignition charge 12, which may be any of the numerous compositions commonly used for such purposes in ordnance devices. A pair of

electrical conductors

13 and 14 extend through plug 3 and are bridged, at their inner ends, by

Avan electrical igniter 15, of any known construction.

Upon` application ofa suitable voltage across the

conductors

13 and 14, igniter 15 will ignite the ignition charge 12.

Where no appreciable time delay is desired the hot gases produced by the burning of this charge 12 would be permitted to directly ignite the thermitic material 9. However, it is frequently desirable to provide a time delay between the energization of the auxiliary circuit and ignition of the thermitic material. To this end Fig. 1 shows a delay charge 16, confined within the interior of a spacer ring17, located between the combustion chamber 11 and the thermitic charge 9. Upon ignition of the charge 12, the hot gases produced thereby will cause ignition of the delay charge 16. Burning will progress throughthischarge 16 at a predetermined rate, depending upon the particular delay charge employed, and at the end of the resulting delay period, will cause ignition of the thermitic material 9 to, in turn, cause melting of the bridge member 8.

Fig. 2 shows a slightly modified form of safety switch wherein the corresponding parts have been given the same reference numerals as in the Fig. l embodiment with the addition of a prime mark. In this form of the device a metal disk 18 is provided between the thermitic charge 9 and the bridge member 8 and conductors 4', 5'. Disk 18 therefore prevents the products of compositions from the thermitic material 9 from directly engaging the conductors 4 and 5', so that these combustion products cannot themselves produce a short circuit between conductors 4 and 5. As shown in Fig. 2 disk member 18 is in direct physical contact with the bridge member 8' so that the heat from the burning thermitic material will be directly conducted to the bridge member 8' causing the latter to melt. In order to guard against the possibility that the metal plate 18 might, upon melting of the bridge 8', itself form a short circuit between the conductors 4 and 5', the plug 2 may be provided, around its periphery, with a ilange 19', the axial dimension of which is slightly less than the thickness of the bridge 8'. Thus, after the bridge 8 has melted, iiange 19 will serve to space the disk 18 slightly away from the lower ends of the conductors 4 and 5. Operation of this form of the device is otherwise the same as that previously described with respect to the Fig. 1 embodiment.

While both of the forms of my invention which have been illustrated include a time delay charge, it is obvious that, where no appreciable time delay is desired, this charge can be omitted without otherwise affecting the operation of the device. It is also obvious that many changes can be made in the precise relationship of the elements to one another without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A thermally actuated electric circuit breaker comprising a generally cylindrical housing closed at both ends, one end wall thereof comprising a plug of insulating material, a pair of laterally spaced electrical conductors extending through said plug to the interior of said housing, a thermally-fusible, electrically-conductive, bridge member connecting said conductors together within said housing, a charge of thermitic material carried within said housing adjacent said bridge member, a shield member of high thermal conductivity separating said thermitic material from said bridge member and said conductors, and means including a charge of ignition material and an electrical igniter therefor for igniting said thermitic material to cause melting of said bridge member.

2. A thermally actuated electric circuit breaker comprising a generally cylindrical housing closed at both ends, one end wall thereof comprising a plug of insulating material, a pair of `laterally spaced electrical conductors` extending through `said plug to the vinterior of said housing, a thermally-fusible, electrically-conductive, bridge member connecting said conductors together within said housing, 'a charge `of thermitic 'material carried within said housing adjacent 'said bridge member, lmeans including a charge of ignition material and arr-electrical igniter therefor for Yig'niting sadfthermitic material to cause melting of said bridge member, and an ignition delay charge interposed between 'said ignition material and said 'thermitic material whereby to cause a predetermined time delay between Aignition of said ignition material and that of said 'thermitic material.

3. A thermally actuated electric circuitr breaker comprising a generally cylindrical housing 'closed at both ends, one end wall thereof comprising a plug of insulating material, a pair 'of laterally "spaced electrical conductors extending through said plug to the interior of fsad housing, a thermally-fusible, eleotricallyiconductive,

bridge member connecting said conductors together within said housing, a charge of thermitic material carried within said housing adjacent said bridge member, means including a charge of ignition material and an electrical igniter therefor for igniting said thermitic material to cause melting of said bridge member, a combustion chamber being provided Within said housing between said ignition material and said thermitic material.

References Cited in the tile of this patent UNITED STATES PATENTS 1,856,701 Gerdien May 3, 1932 2,202,719 Schmidt May 28, 1940 2,472,366 Brode June 7, 1949 2,725,821 Coleman Dec. 6, 1955 FOREIGN PATENTS 683,967 Germany 'Nov. 20, 1939