US2101114A - Fluid flow electric switch and method of and apparatus for manufacture of same - Google Patents

Description

, 1937. w R. WALKER 2,101,114

FLUID FLOW ELECTRIC SWITCH AND METHOD OF AND APPARATUS FOR MANUFACTURE OF SAME Filed June 26, 1935 2 Sheets-Sheet 1 .INVENTOR 28/ G2. IX/Mm TORNEY Dec. 7, 1937. w. R. WALKER FLUID FLOW ELECTRIC SWITCH AND METHOD OF AND APPARATUS FOR MANUFACTURE OF SAME Filed June 26, 1935 2 Sheets-Sheet 2 I? %f a? 5 INVENTOR Patented Dec. 7, 1.937

UNITE-o STATES PATENT err-" ce FLUID FLow ELECTRIC swr'ron Ann mz'rnop OFAND APPARATUS son. MAN- UFACTURE OF SAME Warren R. Walker-,Short Hills, N. J., assignor to" General Electric Vapor Lamp Company, Ho-' boken, N. J., a corporation of New Jersey Application June 2c, 1935, Serial No. 28,560

12 Claims.

vide a fluid flow switch havingan extremely low internal resistance. Another object of my 'in-.

vention is to provide a compact fluid flow switch which willv have a long useful life. Another object of my invention is to provide a fluid flow switch requiring only a small angular movement to secure operation thereof. A further object of my invention is to provide a novel method and apparatus for the manufacture of a fluid flow switch. Still other objects and advantages of my invention will appear from the following detailed specification or from an inspection of the accompanying drawings.

The invention consistsin the new and novel structure and apparatus, and in the novel steps of the method, as hereinafter set forth and claimed.

It has long been the goal of those interested in the development of mercury switches to produce a switch which not only would combine the strength of a substantially all-metal envelope with the many well known advantages of the hermetically sealed vitreous envelope type nowon the market, but which would also be adaptable to mass production by automatic machinery. Many efiorts have been made heretofore to develop such a switch,but none of theseprior efforts has resulted in commercial success, 'due to the many difliculties involved.

One of these difliculties is the high internal resistance resulting from the oxidation of the metal inleads during the fabrication of the switch.

Where the vitreous portion of the envelope vastly exceeds the metal; as in the switches now on the market, this oxide is easily eliminated bycleaning the inleads after'they have been sealed into the envelope and then finally closing the envelope at a point remote from the metal inleads,.but as the relative proportion of the metal to glass in- 1 creases this elimination of oxide becomes increasingly diflicult. Thus when the vitreous portion of the envelope has been reduced to the minimum consistent with proper insulation of the 1 parts and the inleads have been expanded in area until they form virtually the entire envelope, as in the preferred case, it'is obviously impossible to use this cleaning method of the prior art. The oxide which thus remained in the finished switch has greatly increased the internal resistancethereof', and has necessitated special and. expensive treatment of the switch to even partially renovel materials.

necessary to use the more refractory glasses for duce' this resistance to the value that would be obtainable with unoxidized'electrodes.

I 'have nowdiscovered thatthis difficulty is overcome by constructing my fluid flow switch of Thus heretofore it has been the envelopes of mercury switches and the like.

I have now found, however, that with the novel switch structure which I employ extremely satis factory results are produced with a glass having a low melting point, far below that of any glass heretofore used for mercury switches, due to the fact that this'glass is here almost completely shielded from, the arc. With this low meltin point glass the switch is fused together ,at' a temperature below that at which any appreciable oxidation of the electrodes is produced. Other thermoplastic materials of low fusing point may likewise be used with this novel construction with similar results. As a further precaution I prefer to place the portion of the metal housing which is destined to make contact with the mercury in good thermal contact with a body of large thermal capacity, during the fusion process,

whereby these parts are maintained at an even lower temperature than that at which the fusion of the parts occurs.

virtually free of oxide and hence have an extremely low resistance.

the glass seal is made relatively long, ascompared to the actual separation of the metal portions, and at the same time the amount of said seal which is exposed either on the interior or As a result of this novel structure, and procedure my novel switches are f In the novel'structure which I preferably use the exterior of the switch is kept very small. -I- have found that with this novel construction the switch remains effectively sealed, even after long periods of hard usage, despite the low melting point of the glass employed. A convenient way ofv producing this result is to form the refractory dividing memberwhich is commonly used with a rounded edge of substantially the same diameter as the thickness of said membenthe metal parts also being formed with a flange of the same curvature. the refractory member along this entire curved The metal parts are then sealed to surface by means of the low melting point glass,

the result being a very'thin seal of a length at any point which is of the order of three fourths the thickness of the refractory member. This long seal is. obtained with this novel construction without an objectionable increase in the dimensions of the 1 switch. Furthermore, due to the shape of the seal this novel structure is unusually'strongand resistant to shocks, since it is well adapted to resist stresses inany direction. t I have found that the thin coating of-glass' which is thus employed between the-refractory member and the metal parts is very conveniently produced in a novel manner by rotating said member with the edge thereof immersed in a molten bath of the desired glass. This produces a very thin coating, with some of the glass penetrating the pores of the refractory member, which has been found to give exceptionally good results. In some cases, however, this refractory member is entirely covered with a glaze which can be used to fuse the metal members thereto, this glaze being produced in any suitable manner.

In any of these switches where the size is reduced as much as possible in the interest of compactness there is an objectionable tendency to increase the angle of rotation necessary to produce operation of the switch. I have found that this difficulty is overcome by placing the opening in the refractory member as close to the outside edge of the mercury retaining chamber as is consistent with the necessary strength of the member, and by further providing this opening with a novel shape. Thus the outside edge of this opening is preferably made to substantially follow an are drawn about the axis of the refractory member, while the remainder of the opening extends in any desired shape to a point above the level attained by the mercury when it is all on one side of the member, whereby gas can always readily flow therethrough to permit equalization of the mercury level on opposite sides of said member. I have furthermore found that the refractory member is more resistant to strain if the corners of this opening are rounded slightly, and that this desirable result can be attained without in any way affecting the sensitivity of the switch by making the radius of curvature at the ends of the arcuate section conform to theshape naturally assumed by the mercury because of the high surface tension thereof. In general I prefer to make the sides of this opening symmetrical since this greatly facilitates the manufacturing procedure, the preferred opening being roughly triangular.

For the purpose of illustrating my invention I have shown a preferred embodiment, together with the novel apparatus used in the manufacture thereof, in the accompanying drawings, in which Fig. 1 is a sectional view of my novel switch,

tional views of the apparatus used to assemble the switch, and

Fig. 8 is a sectional view of one of the work holding chucks showing the manner in which the switch parts are supported therein.

As particularly shown in Figs. 1 to 4 my novel switch is formed of two dished metal members I and 2, which are identical save that the member I has an opening therein, a refractory dividing member 3, mercury 6, a metal ball 5 welded into the opening in the member I, and a thin coating 6 of glass or other thermoplastic material between the refractory 3 and the metal members I and 2. These metal members are each preferably drawn from sheet metal and have a short cylindrical section, say inch long and inch in diameter, one end of which is closed with a flat wall having a reentrant boss therein whichis adapted to cooperate with the mounting means, while the other end is flared outwardly in an arc of approximately 90 with a radius of approximately of an inch, as shown in Figs. 1 and 4. i The refractory member 3 is made in the form of fractory member 3, said opening extending close to the rounded portion thereof.

Said opening is roughly triangular in shape, although the corners are slightly rounded, with a radius of say inch, and the edge thereof which is adjacent the rim of the refractory member 3 follows an arc of approximately 50 which is concentric with the refractory member 3. Since the chord deviates but little from the arc with this angle and radius, I find that the chord may be followed by this opening with substantially the same resuits, and I include this variation in the claims when I refer to the rim of this opening as being substantially arcuate. As shown the apexof this opening does not quite reach the center of the member 3, although the exact position thereof is not extremely important, so long as it is far enough from the edge to permit free flow of the mercury under all conditions.

The glass 8 which is used to fuse the foregoing parts together preferably consists of a glass having an extremely low softening temperature, so that the metal members I and 2'will not be oxidized during the fusion process. It likewise must have a suitable coefficient of expansion and must wet the metal members I and 2 so as to form a good seal. Thus when the metal members I and 2 are made of an alloy produced by the Allegheny Steel Company and known as Allegheny 55, this being a 26% chrome-iron alloy with a typical analysis as follows:-

Carbon -Junder- .25 Manganese do 1.00 Sulphur do .025 Phosphorus do .025 Silicon do .60 Chromium 26.00-30.00 Nickel -under- .60

it has been found that a glass having the following composition gives exceedingly good results:

Percent SiOz 27 N320 8 02.0 2 MgO 1 A1203 -Q 1 PbO 44 B203 17 This glass has a softening temperature of less than 450 C., so that the switch can be fused together therewith without heating the metal even to a red heat, the oxidation thereof during the fusion process thus being virtually eliminated. Furthermore the coefiicient of expansion of this glass almost exactly matches that of the metal, so that no strains are produced in the switch which might result in breakage thereof. With this'combination of metal and glass I prefer to make the refractory member 3 of the following composition:

Percent MgO '15 Ball clay j Feldspar 10 After this has been fired at 1155 C. for 120 hours this refractory has a coefflcient of expansion which closely matches that of the glass and the metal. I a

In place of this low melting point glass other thermoplastic materials, such as vinyl acetate and related compounds may also be used with spindle III of the apparatus shown in Fig. 5.

This spindle is driven by a motor II through suitable reduction gearing and the belt I2. Said sp ndle has an axial opening therethrough which is connected through the cooling coil I3 and the tube I4 to a. vacuum system, whereby said spindle serves as a vacuum chuck, a lug being provided on the end thereof which engages the opening 8 in therefractory member 3 to accurately position sa d member on said spindle. Air is conveniently supplied through the nozzle I5 to cool the coil I3, and fins I6 are likewise provided on the spindle III to keep the support bearings cool. A crucible ll of molten glass is mounted within the electric furnace III which is supported on a cam Is. Said cam is connected to a handwheel 20, and is adapted upon rotation to raise the crucible I'I until a refractory member 3 on the spindle I0 will rotate with its rounded edge immersed therein. A support 2I rotatably carries a set of gas, jets 22 which are adapted to impinge upon a refractory member 3 carried by the spindle Ill, and upon the surface of the glass in the crucible I! when the latter is in its'elevated position. whereby the re fractory is kept at such a temperature that the glass flows evenly over the edge thereof, as shown in Fig.3.

After the refractory member 3 has been placed upon the spindle III the latter is rotated and the jets 22 are adjusted to impinge thereon. As soon as said member is sufficiently hot the handwheel is operated to raise the crucible II until the entire rounded edge of said member has been immersed therein to produce the coating 6, after which the crucible is again lowered. In practice the member 3 is allowed to continue rotating for a short intervalin the flames from the jets 22, while the glass coating sinks somewhat into the pores ofthe refractory member 3, since this has been found to give better results.

While the refractory isthus being coated the metal members I and 2 are placed in the chucks 25 and 26 of the apparatus shown in Figs. 6 and '7. Said chucks are similar except that the upper chuck 26. has an opening 2-1 therethroughwhich is connected in a. suitable manner with a vacuum system, whereby the member 2 is retained were ',in by suction. As particularly shown in Fig. 8

these chucks are relatively massive and make a snug fit with the cylindrical portion of the metal therebetween. The'chuck 25 is mounted on a horizontal arm28 which is in turn carried. by the vertical slide member 29. The latter member operates in suitable channels in the vertical support 30,and has a rack 3| thereon which cooperates with a pinion 32 operated by the handwheel 33. The chuck 26 is carried by a. similar horizontal arm 34 which is in turn attached to the member 35 which slides in suitable channels in the slide member 29, sufiicient friction being provided therebetween to cause said members 29 and 35 to move together in response to the operation of the hand-wheel 33. A handgrip 36 is provided on the member 35 to provide a method of moving the chuck 25 with respect to the chuck 26, while a parallel handgrip 31 on the slide member 29 provides a convenient means to exert considerable pressure between the aforesaid chucks when said handgrips are both grasped by the same hand and squeezed together. A vertical support 38 carries at its upper end a horizontal arm 39 which slidably supports the member 40, the latter in turn carrying theburner 4| having a series of jets converging from all sides toward a common point.

Theparts I and 2 are loaded into the chucks 25 and 26 while this burner 4| is in the position shown in Fig. 6, after which this burner is slid to the position shown in Fig. '7. The hand-wheel 33 is then moved to bring'the metal shell I into range of the flames from the burner 4|, and a coated refractory member 3 with the glass coating 6 still soft is almost immediately laid thereon, a vacuum wand having a pick-up portion similar to the end of the spindle Ill preferably'being used for this purpose. The handgrip 36 is then moved to bring the metal shell 2 down into contact with the coating Ii on this refractory member. After a short heating period the handgrips 36 and 31 are squeezed together to put pressure on the metal shell 2, forcing the parts of the switch into the intimate contact shown in Fig. 1. The handwheel 33 is then operated to lower the switch assembly until the burner 4| can pass above the chuck 26, after which said burner is retracted to the position shown in Fig. 6, and the switch removed; In some cases this assembly is then annealed in a suitable furnace in order to eliminate the possibility of strains.

The assembled switch is then evacuated in any suitable manner through the opening in the metal shell, and the desired quantity of mercury insorted therethrough, together with an arc suppressing atmosphere such as hydrogen or anhydrous ammonia at a pressure of the order of one or two atmospheres, although when desired the device can be left evacuated and successfully used bled with the indents opposite each other and at a given angle of rotation with respect to the opening 8 in the refractory member 3. Ihis assembly is greatly facilitated by providing the chucks 25 and with internal bosses which engage these indentsand thus ensure a fixed position of the metal shells therein.

Due to the unusually low. temperature required to fuse the glass 6, and to the presence of the chucks of high thermal capacity, which serve to restrict the temperature rise, the cylindrical and end portions of the metal shells l and 2 are. not appreciably Oxidized during the fusion of the elements, so that the internal resistance thereof is extremely low. The use of this low melting point glass does not in any way reduce the useful life of these switches, however, due to the fact that with my novel structure only an extremely small portion of the long vitreous seal is exposed to the arcs therein. The working temperature of these switches furthermore seldom, if ever reaches 100 C., so that there is no danger of the glass softening during operation. As a further advantage of this structure only a small amount of this glass is exposed on the exterior of the switch, although the seal itself is relatively long, as compared to the amount thus exposed.

The angular movement necessary to operate my novel switchis relatively small, of the order of only 30, in spite of its compact size, due to the shape and location of the opening 8 in the refractory member 3. As a result of these two features, which have heretofore never been attained .together, my novel switch is especially adapted for use in wall switches and other similar places where mercury switches have not been extensively used heretofore because of their bulkiness.

While I have described my invention by reference to a specific embodiment thereof it is to be understood that various changes, substitutions and omissions, within the scope of the appended claims, may be made in the structure and in the steps of the method without departing from the spirit of my invention. I

I claim as my invention:

1. An electric switch comprising the combination of an apertured disc, a pair of metallic members whose rims are shaped to closely fit the edges of said disc for an' appreciable distance without making contact with each other, a thin coating of thermoplastic insulating material between the overlapping portions of said disc and each of said metallic members, whereby the fore going elements comprise a hermetically sealed envelope having two chambers connected by the aperture in said disc, said thermoplastic material having a composition which is workable to hermetically seal said envelope at a low temperature, and mercury within said envelope to connect said metallic members through said aperture in one position of said switch.

2. An electric switch comprising the combination of an apertured disc of refractory material, the edges of said disc being rounded, a pair of dished metallic members whose rims are shaped to fit the rounded edges of said disc without making contact with each other, a coating of thermoplastic insulating material between the overlapping portions of said disc and each of said metallic members, said coating covering the entire rounded surface of said disc whereby the foregoing elements comprise a hermetically sealed envelope having two chambers connected by the aperture in said disc, and mercury within said envelope to connect said metallic members through said aperture in one position of said switch.

3. An electric switch of the fluid flow type comprising the combination of an apertured ceramic disc, a pair of dished metal members on opposite sides of said disc and fused thereto by a thin layer of glass, the coefficients of expansion ofsaid disc, said metal members and said glass being similar, said glass being of a composition which is workable to hermetically seal said switch at a temperature at which said metal members are not appreciably oxidized in air, and a quan tity of mercury sufficient to close a circuit through the aperture in said disc between said metal members.

4. The method of producing the casing of anelectric switch of the fluid flow type which comprises dipping the periphery of an apertured ceramic disc into a bath of molten thermoplastic material to produce a coating of said material thereon, and fusing a metal member to said material onopposite sides of said disc to form an envelope having two chambers connected by the aperture in said disc.

5. The method of producing the casing for an electric switch of the fluid flow type which comprises coating the periphery of an apertured ceramic disc with molten glass, and fusing a dished metal member to said glass on opposite sides of said disc while said glass is still molten to form an envelope having two chambers connected by the aperture in said disc.-

6. The method of producing the casing for an electric switch of the fluid flow type which comprises coating the periphery of an apertured ceramic disc with molten glass, fusing a dished metal member to said glass on opposite sides of said disc to form an envelopehaving two chambers connected by the aperture in said disc, and restricting the temperature rise of a portion of said metal members during the aforesaid fusion process to prevent oxidation of the interior surface thereof.

7. The method of producing a casing for an electric switch of the fluid flow type which com prises fusing two dished metal members to a ceramic disc with a thermoplastic material, and restricting the temperature rise of a portion of each of said metal members during said fusion process to prevent oxidation of the interior surface thereof.

8. In apparatus for producing an electric switch of the liquid flow type, in combination, means to support a pair of dished metallic members in such a position that a glass coated ceramic disc can be laid upon one of said members, means to move the other of said members into contact with the coating on said disc, and means to heat the coating on said disc and the portion of said metal members in contact therewith to perfect the fusion of said parts to form a switch envelope, said supporting means having an appreciable thermal capacity and being recessed to permit the snug insertion therein of substantially all of said metal members except that portion thereof which is being fused to said glass, whereby oxidation of the interior of said switch envelope during the fusion process is substantially prevented.

9. In apparatus for producing an electric switch of the liquid flow type, in combination,

' means to dip an apertured ceramic disc into a path of molten glass to coat the edge thereof with said glass, means to support a pair of dished metallic members in such a position that said coated disc can be laid upon one of said members, means to transfer said coated disc to said member while the coating thereon is still molten, means to move the other of said members into contact with the coating on said disc, and means to heat said coating and the metal in contact therewith to perfect the fusion of said parts to form a switch envelope.

:10. An electric switch comprising the combination of an apertured refractory body, a pair of metallic members whose rims are shaped to closely fit said body for an appreciable distance away from the edge of said members without making contact with each other, a thin coating of thermoplastic material between the overlapping portions of said body and each of said metallic members, whereby the foregoing elements comprise a hermetically sealed envelope having two chambers connected by the aperture in said body, said thermoplastic material having a composition which is workable to hermetically seal said envelope at a low temperature, and mercury within said envelope to connect said metallicmembers through said aperture in one position of said switch. v

11. An electric switch comprising the combination of an apertured refractory bodina pair of metallic members whose rims. are shaped to closely fit said body for an appreciable distance away from the edge of said members without making contact with each other, a thin coating of thermoplastic material between the overlapping portions of said body and each of said metallic members, whereby the foregoing elements comprise a hermetically sealed envelope having two chambers connected by the aperture in said body, and

mercury within said envelope to connect said metallic members through said aperture in one position of said switch, said body having abutments on either .side thereof against which the edges of said metallic members rest to determine both the separation of said metallic members and the thickness of the thermoplastic coating between each of said members and said body.

12., An electric switch comprising the combination of an apertured body whose thickness adjacent the rim thereof decreases progressively in the direction of the rim, 9, pair of metallic members whose rims are shaped to closely fit the edges of said body for an appreciable distance away from the rim thereof, a thin coating of thermo-' plastic -material between each of said metallic members and said body throughout the area where they closely fit each other, whereby the foregoing elements comprise a hermetically sealed envelope having two chambers connected by the aperture in said body, and mercury within said envelope to connect said metallic members through said aperture in one position of said switch, said refractory body having abutments on either side thereof against which the edges of said metallic members rest to determine both the separation of said metallic members and the thickness of the thermoplastic coating between each of said metallic members and said body.

WARREN R. WALKER.

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