US3162731A

US3162731A - Explosion proof switch

Info

Publication number: US3162731A
Application number: US269230A
Authority: US
Inventors: Magnus V Braunagel
Original assignee: SMALL BUSINESS ADMINISTRATION
Current assignee: SMALL BUSINESS ADMINISTRATION
Priority date: 1963-02-11
Filing date: 1963-02-11
Publication date: 1964-12-22
Anticipated expiration: 1981-12-22

Description

Dec. 22, 1964 M. v. BRAUNAGEL 3,162,731

EXPLOSION PROOF SWITCH Filed Feb. 11, 1965 2 Sheets-Sheet 1 INVENTOR.

MAGNUS v BRAUNAGEL ATTORNEY 1954 M. v. BRAUNAGEL 3,162,731

EXPLOSION PROOF SWITCH Filed Feb. 11, 1963 2 Sheets-Sheet 2 INVENTOR. MAGNUS V. BRAUNAGEL.

ATTORNEY and, if desired, the actuating shaft.

with the contact surfaces of the electrical leads.

mally there are a plurality of sets of leads spaced periph- United States Patent 3,162,731 EXPLOSION PROOF SWETCH Magnus V. llraunagel, Littleton, (3010., assignor, by mesne assignments, to Small Business Administration, an agency of the United States Government Filed Feb. 11, 1963, Ser. No. 269,230 14 Claims. (Cl. Milt-11) This invention relates to an electrical switch and more particularly to a totally enclosed switch having various features which cooperate to make it explosionproof. 7 There are many environments in which there is a considerable possibility of leakage of inflammable or explosive substance and in which a fire or explosion is more than ordinarily serious, usually resulting in disaster. Among such environments are surface and undersea ships, fuel and chemical plants, missile installations and the like. While every possible precaution is taken to prevent leakage of such substances the possibility of leakage remains and therefore it is also essential to avoid open fires and sparks of any kind.

Electrical switches, especially when carrying heavy currents, normally produce an. arc upon opening the circuit. This arc, or spark, will ignite combustible mixtures unless it is shielded from them in some way. Hence it is'desirable to provide electrical switches which produce minimum sparks and which provide shielding of some kind for the sparks which are produced. Various switches have been proposed and made available in the past to satisfy this need but none is known which solves the problem as Well as might be desired.

The switch of the present invention includes a construction and arrangement which reduce arcing to a remarkable degree and provide means for completely preventing access of combustible substance to such spark as may be produced. In general the switch includes a completely enclosed casing into which electrical conductors or leads are introduced through hermetically sealed openings. The casing, when assembled, has only one opening leading to the exterior, through which passes the actuating shaft for the switch. Sealing is completed by a bellow-like flexible sleeve which surrounds the handle The outer end of the sleeve is sealed to the handle or shaft, and the inner end is sealed to the casing. Consequently, in normal working conditions there can be no interchange of gases or liquids between the interior and exterior of the case.

To further enhance this safety feature means are pro vided to insert an inert gas within the casing and to purge any air or combustible material which may be present before the switch is put into use. A pressure gauge is mounted in or on a Wall of the casing to indicate the gas pressure. If the indication falls below a predetermined level this serves as a Warning to the operator not to use the switch until it has been repaired.

In the preferred form of the invention a disk-like rotor is mounted for rotation about its axis in the casing and carries a contact member for conducting engagement Norerallyabout the generally cylindrical interior of the casing and the rotor carries a corresponding number of contact members similarly spaced near its periphery. 'An

actuator is mounted in the casing for rotation about an the actuator and rotor.

ing of the circuits.

axis substantially coincident with that of the rotor and has an actuating shaft passing through an end wall of the rotor where it is sealed by the flexible sleeve in the manncr described above.

The rotor and actuator are both rotatable through arcs of about the same extent, their travel being limited to approximately thirty to sixty degrees in the present instance by suitable stops. Normally the actuator has a somewhat greater angular travel than the rotor. In one extreme position of the rotor the contact members are in engagement with the contact surfaces and in the other extreme position they are substantially spaced therefrom. When the actuator and rotor are at rest they are in angularly opposite extreme positions. This is accomplished by the use of several expansible force units which are spring devices with their ends attached respectively to The points of attachment are so arranged that when the rotor and actuator are in angularly opposite extreme positions the force axis of the force unit extends at a substantial angle between them and has force components extending in opposite directions to hold them against their stops. The unstressed length of the force unit is substantially greater than the distance between the rotor and acuator and it exerts a considerable force when compressed.

When it is desired to change the rotor position. the actuator is rotated toward the position of the rotor. This action compresses the force unit more and more until it reaches a position extending directly across the shortest path between them. Continued movement of the actuator brings the force unit over center and it then expands very rapidly, driving the actuator against its stop in the direction in which it was being moved manually and driving the rotor to the opposite extreme position with a snap action which produces a quick open- The leading edges of the contact member and contact faces are formed so that they extend generally laterally across the path of their relative movement and at an angle to each other in the plane of the rotor. Consequently, when the contact member moves away, even though it is moving rapidly, the edges separate gradually and gradually increase the resistance to current flow, concluding with a point contact separation and reducing the spark to a minimum. This feature combined with the gas-tight sealing of the casing makes the switch usually safe in operation in explosive environments.

A further safety feature consists in the provision of a latching means which is held inoperative by the pressure of the gas within the casing so long as that pressure remains above a predetermined level. If, through damage of any kind, the gas pressure drops below the predetermined level the latching means will engage a portion of the actuator or rotor to prevent operation of the switch.

FIG. 3 is an elevational view in perspective of the actuator and rotor removed from the casing and showing the arrangement of the force units;

FIG. 4 is a fragmentary View in elevation of portions of the actuator and rotor with the force unit in oncenter position;

FIG. 5 is a fragmentary perspective view of a portion of the rotor and of a contact face showing the contact member of the rotor in non-contact position; and

FIG. 6 is a similar view showing the contact member in contact position.

The general arrangement of the working parts of the switch is illustrated in FIGS. 1 and 2, in which the casing 10 consists of a generally cylindrical cup shaped main casing portion 12, a generally cylindrical auxiliary casing portion 14 and a back plate 16. These components are secured together in gas-tight relation by any suitable means. Electrical conductors or terminals 18 pass through one or more walls of the casing and are hermetically sealed to prevent passage of any combustible material. At their inner ends they are provided with contact faces 20, described in more detail below, which are aligned with each other in spaced relation.

The main casing portion 12 is provided at its free edge with a counterbore 22 which cooperates with the adjacent edge of casing portion 14 to form a bearing channel for the reception of the perimeter of the disk-like rotor 24. The rotor is formed of any suitable insulating material but is preferably ceramic to provide strength, rigidity, and dimensional stability. It is thus mounted for rotation about an axis which is substantially coincident with that of the generally cylindrical interior. of the casing and is rotatable between two extreme positions by virtue of a stop member or pin 26 extending radially through the casing wall and a peripheral slot 28 in the peripheral surface of the rotor. Contact member 30 extends through the thickness of the rotor and has surfaces flush with each end face thereof although they may protrude slightly in some cases. In one extreme position of the rotor the contact member 30 engages contact faces 20 to complete a circuit and. in the other extreme position it is clear of them in non-contact relation. There may be a plurality of contact members and pairs of contact faces as indicated in FIG. 3 to simultaneously actuate a corresponding number of circuits.

An actuator 32 includes a main body 34 which is of about the same thickness as the rotor. Its periphery may be of any suitable form but is preferably cylindrical as shown. Shaft members 36, 38 extend axially fore and aft to mount the actuator for rotation in the casing and to provide for the desired control by means of handle 40. The latter is limited to two extreme positions of angular movement by projection 41 on the handle which engages alternately with stops 43 extending from the outer wall of the casing. Shaft 36 is seated in bearing 42 of boss 44 carried by the back plate 16, and shaft 38 extends through a bearing opening 46 in boss 48 carried by casing portion 12. An auxiliary hollow boss 50 is mounted on the front face of casing portion 12 and is provided with a lateral opening 52 to permit angu-' lar movement of handle 4% A flexible bellows or sleeve 54 fits loosely around the handle and its outer end is secured thereto in sealing engagement. The inner end of the bellows is sealed to boss 50 around opening 52. This completes the hermetic sealing of the casing to prevent the entry of any combustible material which might be ignited by a spark from the switch.

In order to further enhance the safety of the switch, means are provided to fill the casing with an inert gas such as argon, helium or the like. An inletfitting 56 is mounted in the front wall of easing portion 12 for entry of inert gas into the casing. In order to purge the interior, a removable screw plug 58 is provided at the outer end of bellows 54. When this is r moved S cient inert gas can be injected from a gas bottle, not shown, and passed through to insure that all combustible substances have been expelled. Thereupon plug 58 is replaced and additional gas is injected to raise the internal pressure to the desired value. For this purpose fitting 56 is provided with a typical spring loaded bell check valve. Pressure gauge 60 is mounted in or on the casing wall toindicate the gas pressure in the casing at all times.

Referring now to FIG. 3, it will be seen that the actuator and rotor are interconnected for cooperative interaction by one or more, preferably three, force units 62. Each force unit consists in the preferred form of a plurality of serpentine springs 64 secured at their ends to journal pins 66. The shape of one such spring and its relation to the journal pins is clearly illustrated in FIG. 4. The two journal pins of a given force unit are mounted respectively in bearings 68 in the inner wall of the rotor and 70 in the outer wall of the actuator. In the positions shown the springs 64 are compressed and exert a substantial expansive force along the force axis passing through

pins

68 and 70, producing force components acting tangentially in opposite directions on rotor 24 and actuator 32 as indicated by arrows A and B. Since handle 40 at this time is against its right hand stop 43 the rotor is forced counter-clockwise so that one end of slot 28 engages pin 26 and contact member is in conducting engagement with contact faces 20.

When it is desired to open the circuit or circuits handle 40 is swung counter-clockwise, moving the actuator in the same direction. As the actuator approaches the position shown in FIG. 4 the force unit is further compressed and stores up additional energy reaching its maximum at'the on-center position shown in this figure. Further movement of the actuator oauses the force unit to move over-center, whereupon the tangential force components indicated at A and B reverse their direction forcing the actuator to complete its travel and swinging the rotor to its opposite extreme position with a very forceful snap action which opens the contacts rapidly and breaks the circuit. The same type of action occurs in reverse when the handle 40 is swung to close the circuit.

To guard against the possibility that a spring may break and parts of it fall into positions where they could close normally open circuits or damage any of the parts, a pair of guard rings 71 are fixed coaxially to the front and rear faces of the actuator body 34 and movably overlap the inner periphery of the rotor 24 as illustrated a part of the casing.

The are reducing character of the contacts is best illustrated in FIGS. 5 and 6 in which it will be seen that a contact face 20 includes a pair of re-curved

spring contact blades

72 and 74 having convex faces for engagement' with contact member 30 in circuit closing position. Blade 72 has a leading edge 76 which is angled laterally with respect to the direction of relative travel between it and the rotor. The leading edge 78 of the rotor is likewise angled with respect to the direction of travel and the two leading edges include a substantial angle between them in the plane of their contact. As the two members are moved apart separation begins at one side and travels laterally across to the other. A small arc is produced as they begin to separate and travels across from the first side to the second side thus greatly reducing erosion of any one part. As the total contact decreases, resistance is built up to reduce the current flow with the result that only a small spark occurs as the last points separate, reducing the possibility of ignition of any combustible substance.

A further safety factor has been introduced in the form of a device to prevent operation of the switch it the pres-- sure of the inert gas drops below a predetermined safe level. Turning again to FIG. 2, one form of such device has been illustrated including a bracket 80 mounted on an inner wall of the casing and providing a rigid support for a sealed bellows type capsule 82 which is rigidly mounted at one end thereto. At its movable free end the capsule carries a latch pin or detent 84 which is adapted to slide axially in passage 86 in boss 48. Shaft 38 of the actuator is provided with a pair of detent receiving depressions or keepers 88 only one of which is shown. These depressions are peripherally spaced around the shaft so that one of them is in alignment with passage 86 in each extreme position of the actuator. When the pressure of the gas in the casing is above a predetermined safe level the capsule 82 is axially compressed to such an extent that the free end of pin 84 is retracted within passage 86 and does not interfere with operation of the switch. However, if the pressure falls below the safe level the capsule will expand and pin 84 will extend into depression or keeper 88 and prevent any rotation of the actuator. If the pressure falls during movement of the actuator the pin will ride the shaft surface until the actuator has completed its movement, whereupon it will drop into the appropriate depression. The latching device can be adapted to act directly on the rotor but the construction shown is preferred.

It will thus be seen that the switch of the present invention is simple, compact and rugged and incorporates various fail-safe features so as to practically eliminate any possibility of danger when used in explosive atmospheres.

It will be apparent to those skilled in the art that various changes and modifications may be made in the construction and arrangement of parts as disclosed without departing from the spirit of the invention and it is intended that all such changes and modifications shall be embraced within the scope of the following claims.

I claim:

1. An electrical switch comprising: a support; a plurality of electrical conductors fixedly carried by said support and having contact faces for conducting engagement by a contact member to complete a circuit; a rotor mounted for rotation about its axis on said support for movement between two extreme positions of contact and non-contact and provided with a contact member for engagement with said contact faces in one of said extreme positions; an actuator mounted on said support for rotation about an axis substantially coincident with that of said rotor and movable between two extreme positions angularly opposed to those of said rotor; and an expansible force unit having its ends attached to said actuator and said rotor at selected points angularly spaced about said axis of rotation when said actuator and rotor are in their opposed extreme positions, its force axis passing through said ends and having angular 'force components urging said actuator and rotor to their opposed extreme positions; said actuator being movable through a sufiicient angle to carry its point of attachment angularly beyond the rotors point of attachment and reverse the angular direction of application of the force components; expansion of the force unit urging said actuator and said rotor to their alternate opposed extreme positions.

2. An electrical switch as claimed in claim 1 in which said force unit comprises at least one serpentine spring.

3. An electrical switch as claimed in claim 1 in which said force unit comprises a plurality of serpentine springs having journal pins secured to their ends; and said points of attachment on the actuator and rotor comprise bcarings to receive said pins.

4. An electrical switch as claimed in claim 1 in which there are a plurality of force units evenly peripherally spaced to provide a balanced force application.

5. An electrical switch comprising: a casing having a generally cylindrical hollow interior including a pair of end walls joined by a surrounding wall; a pair of electrical conductors extending into the casing and having contact faces for engagement by a contact member to complete a circuit; a disk-like rotor mounted for rotation about its axis in said casing for movement between two extreme positions of contact and non-contact and provided with a contact member for engagement with said contact faces in one of said extreme positions; an enlarged axial opening in said rotor; an actuator passing through said opening and mounted in said casing for rotation about an axis substantially coincident with that of said rotor and mov able between two extreme positions angularly opposed to those of said rotor; and an expansible force unit located in the general plane of said actuator and rotor and having its ends attached to the outer wall of said actuator and the inner wall of said rotor at selected points angularly spaced about said axis of rotation when said actuator and rotor are in their opposed extreme positions, its force axis passing through said ends and having angular force components urging said actuator and rotor to their opposed extreme positions; said actuator being movable through a sufficient angle to carry its point of attachment angularly beyond the rotors point of attachment and reverse the angular direction of application of the force components; expansion of the force unit urging said actuator and said rotor to their alternate opposed extreme positions.

6. An electrical switch as claimed in claim 5; said conductors extending into said casing through one of said Walls with their inner ends in alignment with each other and with their contact faces spaced apart substantially the thickness of the rotor; said contact member extending through the thickness of the rotor near its periphery and having faces substantially flush with the faces of the rotor for engagement with said contact faces in one extreme position of the rotor.

7. An electrical switch as claimed in claim 5; said surrounding wall having a bearing channel formed therein; and said rotor having its peripheral rim journaled for rotation in said channel.

8. An electrical switch as claimed in claim 5; said force unit comprising a plurality of serpentine springs.

9. An electrical switch as claimed in claim 8; said actuator and said rotor being of substantially the same axial thickness; and a pair of guard rings secured to the faces of said actuator and movably overlapping the faces of said rotor to confine said springs and segregate them from other parts of the casing in the event of breakage.

10. An electrical switch comprising: a casing having a generally cylindrical hollow interior including a pair of end walls joined by a surrounding wall; a pair of electrical conductors extending into the casing in sealing relation therewith and having contact faces for engagement by a contact member to complete a circuit; a rotor mounted for rotation about its axis in said casing for movement between two extreme positions and provided with a con tact member for engagement with said contact faces in one of said extreme positions; an actuator mounted in said casing for rotation about an axis substantially coincident with that of said rotor and movable between two extreme positions angularly opposed to those of said rotor; said actuator having a control shaft passing through a wall of said casing; yieldable means sealingly connected to said wall and said shaft to provide for actuation of said shaft while preventing passage of gas through said casing wall; and an expansible force unit extending between and secured to said actuator and rotor and movable to alternate over-center positions in response to movement of said actuator to force said rotor to its opposed alternate positions with snap action to open and close said circuit; the sealing of said casing preventing access of combustible gas mixtures to sparks extending between said contact member and said contact faces.

11. An electrical switch as claimed in claim 10; the leading edges of said contact member and contact faces lying substantially laterally of the line of relative move ment in closing and opening the circuit and extending at a substantial angle to each other in the general plane of said member and faces; whereby said edges disengage gradually to produce a gradual increase in resistance to current flow even during rapid rotor movement and conclude their disengagement with substantially point contact to minimize sparking.

12. An electrical switch as claimed in claim 10; said control shaft having a laterally extending handle; and said yieldable means constituting a flexible envelope surrounding a portion of said handle and having one end sealed to said handle and the other end sealed to the casing Wall.

13. An electrical switch as claimed in claim 10; said casing containing an inert gas to render the switch explosion-proof; and means for supplying an inert gas under pressrr to the interior of said casing.

14. An electrical switch as claimed in claim 13; and a pressure gauge in a Wall of said casing to indicate the pressure of the inert gas within said casin No references cited.

Claims

1. AN ELECTRICAL SWITCH COMPRISING: A SUPPORT; A PLURALITY OF ELECTRICAL CONDUCTORS FIXEDLY CARRIED BY SAID SUPPORT AND HAVING CONTACT FACES FOR CONDUCTING ENGAGEMENT BY A CONTACT MEMBER TO COMPLETE A CIRCUIT; A ROTOR MOUNTED FOR ROTATION ABOUT ITS AXIS ON SAID SUPPORT FOR MOVEMENT BETWEEN TWO EXTREME POSITIONS OF CONTACT AND NON-CONTACT AND PROVIDE WITH A CONTACT MEMBER FOR ENGAGEMENT WITH SAID CONTACT FACES IN ONE OF SAID EXTREME POSITIONS; AN ACTUATOR MOUNTED ON SAID SUPPORT FOR ROTATION ABOUT AN AXIS SUBSTANTIALLY COINCIDENT WITH THAT OF SAID ROTOR AND MOVABLE BETWEEN TWO EXTREME POSITIONS ANGULARLY OPPOSED TO THOSE OF SAID ROTOR; AND AN EXPANSIBLE FORCE UNIT HAVING ITS ENDS ATTACHED TO SAID ACTUATOR AND SAID ROTOR AT SELECTED POINTS ANGULARLY SPACED ABOUT SAID AXIS OF ROTATION WHEN SAID ACTUATOR AND ROTOR ARE IN THEIR OPPOSED EXTREME POSITIONS, ITS FORCE AXIS PASSING THROUGH SAID ENDS AND HAVING ANGULAR FORCE COMPONENTS URGING SAID ACTUATOR AND ROTOR TO THEIR OPPOSED EXTREME POSITIONS; SAID ACTUATOR BEING MOVABLE THROUGH SUFFICIENT ANGLE TO CARRY ITS POINT OF ATTACHMENT ANGULARLY BEYOND THE ROTOR''S POINT OF ATTACHMENT AND REVERSE THE ANGULAR DIRECTION OF APPLICATION OF THE FORCE COMPONENTS; EXPANSION OF THE FORCE UNIT URGING SAID ACTUATOR AND SAID ROTOR TO THEIR ALTERNATE OPPOSED EXTREME POSITIONS.