US3492611A - Electromagnetically operated mercury switch - Google Patents

Description

' Jan. 27, 1970 R. KOLB 3,492,611

ELECTROMAGNETICALLY OPERATED MERCURY SWITCH Filed Aug. 15. 1968 INVENTOR: Rudolf Kalb mammal T gm ATTORNEL'SS United States Patent 3,492,611 ELECTROMAGNETICALLY OPERATED MERCURY SWITCH Rudolf Kolb, 28 Leiblstrasse, Nuremberg 85, Germany Filed Aug. 15, 1968, Ser. No. 752,817 Claims priority, application Germany, Feb. 10, 1968,

Int. (:1. H6111 29/00 US. Cl. 335-49 6 Claims ABSTRACT OF THE DISCLOSURE A mercury switch which is moved to and held in its on position when a magnet coil is energized which surrounds a float of a magnetizable material which is immersed in mercury in a contact tube and carries on its upper end a cylindrical control cup which likewise contains mercury. When the switch is in its on position, the lower end of a stationary pin-shaped electrode extends from above into the mercury in the contact tube above the control cup. When the magnet coil is switched off,/the buoyancy of the float in the mercury of the contact tube lifts the float together with the control cup, whereby the electrode passes into the control cup and displaces a part of the mercury therefrom which, while the control cup moves upwardly to its off position, flows over the upper edge of the control cup and to the mercury in the contact tube.

The present invention relates to improvements in an electromagnetically operated mercury switch of the type as disclosed in the British Patent No. 857,392, which comprises a contact tube which is partly filled with mercury, a magnet coil surrounding this tube, a float of a magnetizable material which is immersed in the mercury of the contact tube and carries on its upper end a cylindrical control cup which has a closed bottom and an open upper end and consists of an insulating material and likewise contains mercury, a pin-shaped upper electrode which is adapted to be immersed into the mercury in the control cup, and a lower electrode which is electrically connected to the mercury in the contact tube. When the switch is in its on position, the float together with the control cup is held by the energized coil in its lowest position in which the mercury in the contact tube extends above the control cup and surrounds the lower end of the upper electrode. When the coil is then switched oif, the float together with the control cup is lifted by its buoyancy in the mercury, and due to this upward movement of the control cup, the upper electrode passes more and more deeply into this cup and thereby displaces a part of the mercury therefrom which spills over the upper edge of the control cup until the latter has been lifted to a position in which it projects above the mercury in the contact tube.

When this mercury switch is switched off and the control cup while moving upwardly breaks through the upper surface of the mercury in the contact tube, an arc is formed which is extinguished when the upper edge of the control cup has reached a certain distance from the upper surface of the mercury in the contact tube. This known mercury switch has, however, the disadvantage that during the further upward movement of the control cup the upper electrode is immersed still more deeply into the control cup and thereby continues to expel the mercury therefrom which then flows downwardly along the outer wall of the control cup. This aditional mercury while flowing down may produce a conductive connection between the mercury in the control cup and that in the contact tube so that a dangerous back-arcing will then occur within the switch.

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It is an object of the present invention to improve the mercury switch as above described in a manner so as to prevent absolutely such a back-arcing.

According to the invention, this object is attained by providing at the inside of the contact tube a ring of insulating material which is concentric to the control cup and surrounds the latter with a very small clearance when the switch is in its off position, and which is provided with an annular recess in its upper side for collecting the mercury which is displaced from the control cup by the immersion of the upper electrode when during the disconnecting movement the upper end of the control cup passes upwardly through the insulating ring. Instead of flowing along the outer wall surface of the control cup to the mercury in the contact tube, this expelled mercury will be collected in the annular recess in the insulating ring since it cannot possibly penetrate through the small clearance between the insulating ring and the outer wall surface of the control cup. Consequently, the part of the outer surface of the control cup which extends from the inner upper edge of the insulating ring to the upper surface of the mercury in the contact tube will be entirely free of any mercury during the disconnecting movement and will thus absolutely prevent any back-arcing within the switch.

It is a further object of the invention to accelerate as much as possible the upward movement of the control cup to the position in which it passes through the insulating ring and thereby prevents any further flow of current within the switch and thus also any back-arcing.

For attending this object, the invention further provides that the insulating ring floats on the upper surface of mercury in the contact tube and is slidable in the vertical direction within the switch housing and that its movement in the upward direction is limited by a suitable stop against which the insulating ring is pressed by the mercury in the contact tube when the switch is in its on posit-ion. As soon as the disconnecting movement begins, the control cup is lifted by the float and thereby lowers the level of the mercury in the contact tube. The insulating ring floating on the upper surface of the mercury in the contact tube is thereby likewise lowered and this ring and the control cup are thus moved in opposite directions toward each other so that the control cup will pass very quickly into the insulating ring. In order to perm-it the control cup to slide easily into the insulating ring, the inner wall of this ring is made of a conical shape increasing in diameter toward its lower level.

The insulating ring may be easily produced by making its annular recess of an angular cross section and by making the inner wall of this angular recess of a shorter length than its outer wall. This recess is therefore made of a relatively great depth and is thus capable of holding a considerable quantity of mercury. The outer wall surface of the control cup when sliding upwardly through the insulating ring engages with the upper edge of the inner wall of the recess and further increases the capacity of the latter.

The mercury switch according to the invention is provided like the known mercury switch as previously described with a so-called switch dome of insulating material which covers the inner side of the upper part of the contact tube and the upper wall of which has a central bore through which the upper electrode extends. According to another feature of the invention, the lower part of the wall of the switch dome which is open at its lower end is made of a larger inner diameter than the 'upper part and serves as a guide surface along which the insulating ring is slidable in the vertical direction. The inner shoulder which is formed between the upper and lower parts of the switch dome then serves as a stop Patented Jan. 27, 1970 against which the insulating ring abuts when the mercury switch is in its on position. By this design of the switch dome the advantage is attained that despite the additional provision of the insulating ring, the outer diamensions of the mercury switch according to the invention do not have to be larger than those of the known mercury switch as previously described.

The features and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which FIGURE 1 shows a vertical axial section of a mercury switch according to the invention in its on position; while FIGURE 2 shows a similar view of the same mercury switch, but in its off position.

The mercury switch according to the invention comprises a murcury contact tube 1 and a magnet coil 2 surrounding this tube 1. The housing of the contact tube 1 consists of a bell-shaped upper part 3 and a tubular lower part 4 which is surrounded by the coil '2. A pin shaped electrode 5 and a connecting terminal 6 are secured and electrically connected to the upper wall of the bell-shaped upper part 3, and another connecting terminal 7 is electrically connected to the bottom 8 of the tubular lower part 4. The upper part 3 and the lower part 4 of the housing are mechanically connected to each other by a layer of insulating material 9 and in addition by switch dome 10 which likewise consists of insulating material and extends along the entire length of the upper housing part 3. The switch dome 110 and the lower housing part 4 are separated from each other by a disk 11 which is provided with apertures through which the mercury 12 may pass from one part to the other. When the mercury switch is in its on position as illustrated in FIGURE 1, the mercury 12 fills out the lower housing part 4 and also a part of the switch dome 10. Immersed into the mercury 12 is a hollow float 13 which consists of a magnetizable material, and a cylindrical control cup 14 which consists of an insulating material and is secured to the inner wall of the upper part of the float 13. The wall of float 13 is provided underneath the control cup 14 with a bore 15 through which the mercury may pass to the inside of the float so as to reduce the lift which is produced by the mercury 12 to the required extent. On its lower end, float =13 is provided with lateral guide projections 16. T he control cup 14 which is rigidly secured to the float 13 is vertically slidable in a central guide bore in disk 11. The switch dome -10 'as well as the control cup 14 may consist of a ceramic material. It is of particular advantage to make the control cup 14 of aluminum oxide which permits this mercury switch to remain fully operative for a very long time and to be used for carrying out an extremely large number of switching operations.

The lower part 17 of the inner wall of the switch dome 10 is recessed so as to have a larger inner diameter than the upper part. A ring 18 consisting of an insulating material, for example, a ceramic material, is inserted into this lower part 17 and is slidable therein in the vertical direction. On its upper side, this insulating ring 18 is provided with an annular recess 19 of an angular cross section which is defined by an outer wall 20 and an inner wall 21 which has a shorter length than the outer wall. Ring 18 has a central bore 22 of a diameter which is only slightly larger than the diameter of the cupshaped member 14 so that, when the latter passes into the bore 22, the outer surface of the control cup 14 will be spaced from the wall of bore 22 by a clearance which is too small to permit any mercury to penetrate. Underneath the short cylindrical part of bore 22, this bore increases conically in diameter in the downward direction, thereby forming a conical bore 23. The lower wider part 17 of the inner wall of the switch dome 10 is separated from the narrower upper part by an annular shoulder 24 which serves as a stop for the ring 18. When the mercury switch is in its on position as illustrated in FIGURE 1, the insulating ring 18 floating on the mercury 12 will be pressed by the latter against the annular shoulder 24. In this on position of the switch, the mercury 12 which is contained in the lower housing part 4 and in the lower part of the switch dome 10 is directly connected with the mercury 12 which is contained in the control cup 14, and the lower end of the electrode 5 is immersed into the mercury 12 so that the two terminals 6 and 7 are electrically connected to each other through the electrode 5, the mercury 12, and the bottom 8 of the lower housing part 4. The float 13 will then be held in a fixed position by the lines of force of the magnetic field of coil 2. The lower housing part 4 may consist either partly or entirely of a nonmagnetic material so that the magnetic lines of force may pass through the lower part 4 into the float 13.

When coil 2 is switched off, the buoyancy of float 13 in the mercury 12 will move this float upwardly together with the control cup 14. This results in a lowering of the level 12 of the mercury and also of the level of ring 18 which is floating on the surface of the mercury. Since the control cup 14 and the insulating ring 18 are thus moved simultaneously in opposite directions, the control cup 14 will engage very quickly into the bore 22 and then extend through the latter. Due to the upward movement of the control cup 14, the electrode 5 passes into the mercury in this cup and thereby displaces the mercury therefrom which flows over the upper edge of cup 14 and then into the annular recess 19 as soon as the upper edge of cup 14 projects through the bore 22. Since the clearance between the walls of bore 22 and the control cup 14 is too small to permit the mercury to penetrate, the outer surface of the part of the control cup between the bore 22 and the mercury surface 12 will be entirely bare of mercury so that no back-arcing can possibly occur.

Although my invention has been illustrated and described with reference to the preferred embodiment thereof, I wish to have it understood that it is in no way limited to the details of such embodiment but is capable of numerous modifications within the scope of the appended claims.

Having thus fully disclosed my invention, what I claim 1. An electromagnetically operated mercury switch having a contact tube partly filled with mercury, a magnet coil surrounding said tube, a float of a magnetizable material immersed in the mercury in said contact tube and carrying on its upper end a cylindrical control cup consisting of an insulating material and having a closed bottom and an upper open end and likewise containing mercury, a stationary pin-shaped upper electrode adapted to be immersed from above into the mercury in said control cup by the upward movement of said cup, and a lower electrode electrically connected to the mercury in said contact tube, said coil when energized holding said float together with said control cup in its lowest position in which the mercury in said contact tube extends above said control cup and surrounds the lower end of said upper electrode, whereas when said coil is deenergized, said float together with said control cup is lifted by its buoyancy in the mercury in said contact tube and, due to this upward movement of said control cup, the upper electrode then passes more and more deeply into said cup and thereby displaces a part of the mercury therefrom which spills over the upper edge of said cup until the latter has been lifted to a position in which it projects above the mercury in said contact tube, a ring of insulating material concentric to said control cup at the inside of said contact tube, said control cup being slidable with a small clearance through said insulating ring when moving upwardly to its off position, said insulating ring having an upper side to receive the mercury which during said movement is expelled from said control cup by the immersion of said upper electrode, said clearance between said in sulating ring and the outer surface of said control cup being so small as to prevent any passage of mercury from the upper side of said ring in the downward direction.

2. A mercury switch as defined in claim 1, in which said insulating ring is sildable in the vertical direction and floating on the upper surface of the mercury in said contact tube, and further comprising a stop for limiting the extent of the upward movement of said ring.

3. A mercury switch as defined in claim 2, in which the central bore of said insulating ring increases conically in diameter toward its lower end.

4. A mercury switch as defined in claim 1, in which said insulating ring has an annular recess in its upper side for collecting said expelled mercury.

5. A mercury switch as defined in claim 4, in which said annular recess has an angular cross section defined by an inner and an outer wall, said inner wall being of a shorter length than said outer wall.

6. A mercury switch as defined in claim 2, in which the upper part of said contact tube has an inner covering of insulating material forming a switch dome, said switch dome being open at its lower end and having an upper wall with a central bore through which said electrode extends, the lower part of said switch dome having a larger inner diameter than the upper part and thereby forming an inner shoulder, said insulating ring being disposed within said lower part and being guided by the inner wall surface of said lower part so as to be slidable in a vertical direction along said surface, said shoulder forming said stop for limiting the extent of the upward movement of said insulating ring.

References Cited UNITED STATES PATENTS 2,288,089 6/1942 Hedin 33549 2,367,498 1/1945 Hedin 33549 2,658,124 11/1953 Weirner 33549 FOREIGN PATENTS 857,392 12/1960 Great Britain.

BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner

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