US2207710A - Switch - Google Patents

Description

J"137716, 1940 P. s. BEAR l 207,710

SWITCH Filed Nov; 1v,y 193s 2 sheets-shane f'g. g5 )a5 92 I I xg? l 5f if /05 //0 ATTORNEY Patented July i6, i940 PATENT or-Flc'ls';I

SWITCH Paul S. Bear, Elkhart, Ind., assignor to Bucklan- Bear Laboratories, Inc., Elkhart, Ind., a corpov ration ot Indiana Application November 17, 1938., Serial No. 240,885

14 claims.

This invention relates to switches, and more particularly is directed to mercury switches of the metallic envelope type adapted to be operated by longitudinal tilting of the switch to flow a body 6 ofmercury into` and out of contact with a second body of mercury retained against an electrode.

More specically, the present invention is directed to certain detailed improvements in switches of the typeishown generally in my copending application, Serial No. 745,862, lled Septemberl 28, 1934.

The present invention is directed particularly to a switch assembly comprising a cup-shaped electrode formed of metal having an enlarged open end in which is seated a ceramic or refractory insert which centers and supports an electrode and is sealed in position within the switch by means of suitable resilient gasket means.

In such switches there is considerable diiiiculty in providing a tight seal, and also in providing a construction which will allow for' the rapid distribution of heat generated within the sealed envelope due to the making and breaking arcs as the'switch is tilted in opposite directions.

One of the main features of the present invention resides in a construction for insuring the retention of a body of mercury in contact with the secondary electrode and in a position so that a mercury to mercury contact is effected when the .switch is tilted. 'Ihis retained body of mercury is preferably so related to the second-aryelectrode as to have an appreciable surface ,contact therewith in order to reduce materially the resistance to the flow of current.

Still another feature `of the present invention is the provision ofa compression insulator de-v such a construction, the spinning operationf which produces a slightly radially inwardl thrust on the comprsion insulator, will not cause the insulator to crack or be damaged due to the fact that a slight clearance around the shank of the electrode is provided.

Still, another feature of the invention is the provision of av switch in'which the switch envelope is filled with either a liquid or a gas capable of producing a reducing atmosphere. This may, if desired, comprise a filling of hydrogen =gas or a liquid illling of triethanolaminediethanolamine, or any other anhydrous alkaline liquid. It is de- .sirable that some such reducing 'atmosphere be 53 provided within the lswitch envelope in order to keep the metallic parts clean and bright, and also to act as a medium for preventing the formation of oxides on the surface of thel mercury. In addition the liquid iill, as described above, has the characteristic of increasing the normalmeniscus height of the mercury so that a greater surface contact is effected when the switch is tilted toward'closed position. It also acts as an enveloping lm over the moving mercury body and over the retained body of mercury, and serves as a iioatation medium within which is suspended impurities which may be picked up from the mercury or from the walls of the envelope.

One great dimculty attendantupon the use of hydrogen in the metal envelope switch of this type is the fact that ordinary soft iron cannot conne hydrogen gas. 'I'he hydrogenapparently penetrates through the pores of the metal and escapes from within the switch envelope. 'I'his inability to retain the hydrogen in iron and similar ferrous bodies is a distinct problem, as otherwise, hydrogen would| be a desirable reducing at-l mosphere within the switch envelope.

It is to be understood that therev is a distinct difference between the use of an inert atmosphere and the use of a reducing atmosphere of this type. Obviously, with an inert atmosphere there is no tendency to keep the walls of the switch clean and bright or to prevent any possible oxidation within the envelope. On the other hand,

with the reducing atmosphere, oxidationis positively prohibited, and the walls of the envelope are maintained in a highly polished condition.

lIn order to employ hydrogen ina sealed.l metal envelope switch of this type, I have found it necessary to provide an enclosure of metal impervious to'hydrogen. For this reason I have found that a clad metal is best suited for a switch envelope if a hydrogen vatmosphere is to be used therein. In/a preferred form of the invention this comprises a metal envelope having aninternal -surface composed of steel of thetype similar to SAE-1010, which has thereabout a coating of copper or a similar metal impervious to hydrogen. Preferably, copper is employed because of its low resistance to the passage of electrical current, thereby reducing the resistance through the switch. This copper layer may be of sumcient thickness to provide the proper strength of shell to resist internal pressures that may be developed, and can be used for' preventing any possible escape of hydrogenl through the relatively thin steel lining withinthc shell. l'

`Also, I have found that pure iron does not unite with the mercury, nor does it even wet with mer-y cury in the manner that stainless steel is wetted when contacted by a body ofmercury. This produces a certain resistance in the contact between the two metals. While nickel wets with mercury, it apparently has about the saine resistance in contact therewith and repeated flashing of mercury in the presence of a nickel surface causes Va stickiness of the mercury, showing a certain chemical reaction being produced between the mercury and the nickel. (f

I-have found that hot rolled sheet formedof an ironA alloy, better known as SAE-1010, draws into body shapes for useA in mercury switches much better than iron. Also, during the draw-v ing operations, this metal polishes in such a manner that the contact resistance, as the metal and mercury lie in contact, is appreciably reduced. An examination of the contact surface ofl this metal shows that the entire surface is composed of closely spaced minute points which have been wetted with the mercury. 'Ihis does not produce an amalgamation, nor does it produce a surface wetting such as produced when a vnickel steel is employed. The surface apparently looks clean, but. the plurality of minute points are wetted with the mercury and a much closer afiinity between the mercury and lthe hot rolled l sheet metal is produced which results in a reduced contact resistance between the two; such as to provide a much coolei` operating switch due to the reduction of resistance therethrough,

vand the consequent reduction in heat generated by such current. Preferably the composite envelope formed of the SAE-1010 lining and the copper coating is so designed that approximately 5to 10 percent of the wall thickness is composed of the hot rolled sheet iron, while the remaining 90 to 95 percent of the wall is composedl of copper, which greatly reduces the resistance '-an inch. The operating angle within this range through the switch.

In switches of the type where speed of operation is not essential, such as lused on calibrated instruments, control devices and the like, where the switch cuts in or cuts out at certain prede- -termined points. I have found that a certain relationship exists between the operating angle of v the switch and the length of the body of mercury which is retained against the electrode. The

Vdecreases substantially directly with the decrease in the length of the retained body. f

Another feature of the present switch isthe design of an electrode and its shank in such manner as to form adequate heat dissipation from the face of the electrode Ato the external part ofthe switch. 'This may be accomplished by providing finned ribs or other heat dissipating means for increasing the rate of heat dissipation from the electrode face. I

Still another feature 'of the present invention' is the provision of an auxiliary ceramic of the Alundum type for forming the sharp cutting edge over which contact is made and broken. This is ahighly thermally refractive material which will not beetched or eroded under repeated high tension arcs.

Other objects'and advantages of the present invention will be more apparent from the following detailed'description which, taken in conjunction with the accompanying drawings, will disclose to those skilled in theart the particular construction and operation of a preferred form of the present invention.

In the drawings:

Figure 1 is a sectional view through one form of switch embodying the present invention;

Figure 2 is a corresponding sectional view of a modified form of switch;

Figure 3 shows the use of an auxiliary insert to provide the sharp cutting edge over which contact is made and broken in the switch;

Figure 4 shows one form of compression insulator that may be employed;

Figure 5 shows a modification of this form;

Figure 6 is a sectional view through `a switch with a modied electrode construction;

-Figure '7 is a sectional view through another form of electrode;

Figure 8 is a sectional view through a still further modied form of electrode; and

Figures 9 and 10 are sectional views of other lmodified electrodes.

thereof. The closed end of the envelope is tapped.

as indicated at 8 to receive a tapered fill plug,

, which will be described in `detail hereinafter.

Disposed within the enlarged-end l of the envelope is a ceramic insert 9 which may be formed of. Isolantite or a similar ceramic material, and which is provided with a radially inwardly directed ange portion I having the rounded delining edge II. The flange IIJ forms with the body of the insert 9 la shouldered portion against which electrode I2 is seated. The electrode I2 preferably has a cup-shaped face I3, the anged edge I4 thereof abutting against the radial surface defining the angeli) of the insert. The shank I I of the electrode extends outwardly from the end of the envelope and is suitably threaded as will be described in detail hereinafter.

It will be noted that the 'axial length of the electrode I2 is such that the rear face 'thereof lies substantially coplanar with the outer end of the insert 9. Disposed against these surfaces and sealing the annular crack therebetween is a gasket member I which may be formed of synthetic rubber, such as Neoprene or the like. The gasket I5 is adapted to be axially compressed by means of a compression washer I6, preferably formed of a ceramic material and lhaving an axially directed reduced portion Il fitting about the shank I I of the electrode. Upon the outer vportion of the ceramic compression washer I5 is a retaining ring I8 formed of metal and having an external diameter substantially identical with the internal diameter of the enlarged portion I 'of the shell 5. When the parts have been positioned as shown in Figure 1, the extending edge of the enlarged portion 'I ofthe shell is spun over as indicated at IS, the gasket I5 being maintained under compression in a manner such as described in detail in my'copending application, Serial No. 211,420, filed June 2, 1938. Threaded on the'shank II of the electrode is a washer 20 and a nut Z'Iwhereby a Asuit- 75 able terminal conductor may be connected thereto.

It will be noted that by reason' of the cup shape of the electrode face an annular space or groove is provided between the shoulder formed by the ilange I0 and the face I3 of the electrode. Within this groove is disposed a body of mercury 22, the groove being ofv a width such that the body is retained permanently therein as described in my copending application, Serial No. 53,146, filed December 6, 1935. Also, a second body of mercury 23 is disposed in the main body portion of the shell 5, this mercury being adapted to move up the surface of the insert bore to contact with the retained body portion 22 when the switch is tilted toward circuit closing position. Disposed over the mercury is a liquid film, indicated at- 2d, which may comprise any anhydrous'alkaline liquid such as triethanolamine, or a liquid of this class which. when vaporized, will produce a reducing atmosphere. The liquid film serves to prevent oxidation of the mercury and also floats the impurities which may remain in the envelope so that fresh clean mercury is employed for the contact at all times. e

In the assembly of the switch,.the parts disposed within the enlarged body portion I are placed in position and then maintained under a suitable pressure, while the spun-over edge I@V is rolled into position to lock the parts against displacement. This compresses the gasket both axially and radially forming a positive seal about the electrode shank and also within the enlarged portion 'I of the shell. With the parts thus placed in position, the interior yof the envelope is evacuated through the opening B and the mercury and the liquid illl are introduced therein. With the envelope still in evacuated condition the interior thereof is sealed by means of a tapered ll plug 25 threaded into the tapered opening 8 and then further sealed by means of a globule of solder 26 or the like. This provides a positive seal for the interior of the envelope and prevents the admission of gas or moisture thereinto. It will be noted that with this construction the retained body of mercury 22 has a substantial surface contact with the face I3 of .the electrode I2, which reduces to a considerable extent the resistance to now of current. from the retained body into the electrode.

By using hot rolled strip of the type specified I am able to obtain a greater contact between the mercury and the metal wall of the envelope vdue, I believe, to the factthat the surface of the metal forms an infinite number of very line pointsV which .are wetted by the'mercur'y in thel same manner as nickel steel is wetted, and which thus decrease the contact resistance between thev mercury and the metal. This also reduces the electrical resistance through the switch, resulting in a cooler operating switch regardless ofthe lspeed of operation thereof. The present switch may also be operated by rapid axial reciprocating movement which drives the shoulder of the insert boreunder the body of mercury 23, and due to the inertia of the body of mercury, causes the making or breaking of contact over the shoulder.

-or lining surface of the shell is of a ferrous metal similar to that used in the shell 5 but this metal f is clad with a coating or body of copper. The

lining in the shell, which is of a'ferrous metal,

the insert 34 corresponding to the insert 9 of Figure 1, except that in place of the rounded surface of the flange, itis provided with a frusto=l conical opening deiined by theA surface 35 and terminating in an abrupt acute angled edge dened by theradially extending wall 3E. The insert 35 is counterbored to receive the electrode I2 which ts into the recess and isl maintained against the radial surface 36 by means of the gasket I5. The remaining portions ofthe end construction of the switch are asdescribed in connection with Figure l, and corresponding reference numerals have been applied thereto. The spun-over edge of the shell 30 indicated at 3l' 'locks these parts in compressed sealing position,

and a retained body of mercury 22 and a movable body of mercury 23 are introduced in the switch in the same manner as previously described. However, after the switch envelope has been evacuated, hydrogen gas is forced thereinto through the opening d. and preferably is maintained in the envelope under a pressure of 2 or3 atmospheres. Inasmuch as the gasket I5 is impervious to hydrogen, an effective seal for the back face of the electrode I2 and the insert 34 is provided to prevent escape of hydrogen `therethrough, while the cross sectional area of the shank II is relatively small, it is desirable that this shank be rendered. impervious to the escape of hydrogen therethrough, and consequently the shank may be made of copper if so desired, which is also of advantage in that the conductivity therethrough is increased between the electrode I2 and the terminal connected beneath' the Washer 20 to the shank. With an acute angled cutting edge 3l Aas shown in Figure 2, a very positive operating switch is provided which will open and close the circuit therethrough at predetermined angular inclinations. This is what is termed repeat performance; that is, the switch will continue to close the circuit at a certain angle and to open the circuit at a certain angle. The included anglebetween the on and off position of the switch which is considered the operating angle of the switch, varies directly withA the length of the retained body `22. "For example, if the length of this body is 2 mm. the operating angle for the switch of the type shown isapproxlmately 31/2 degrees. If the length of the retained body o i mercury is increased to '3 mm., the operating angle increases 'to 4 degrees. It appears that with further increases in length of the retained body, the operating angle increases about l@ a degree for. each 1/4 mm. increase in length in a very definite and regular manner until the length of the stable body reaches a point exceeding the stability point, which is about 7@ of an inch.,

Considering now the form of the invention shown in Figure 3, the hot rolled strip which forms the shell lli is provided with a frusto'- conical section 42 terminating in the enlarged cylindrical portion 43. The ceramic insert 6B is similarly provided with a frusto-conical external surface whereby this insert may seat directly against the corresponding portion of the shell. The insert is also preferably provided with a rear face parallel with the rear face of the electrode 66, but provided with an axially recessed peripheral portion into which the ange portion 53 of the resilient gasket 54 is adapted to extend. This increases the leakage distance from the electrode to the interior of the shell 43, and also provides for an increased sealing eiect of the gasket upon axial compression to prevent possible leakage of pressure outwardly past the insert or the electrode.

Preferably, a suitable compression insulator 5| is provided for producing axial compression of the gasket 54 when the edge of the shell 43, as indicated at 55, is spun over the retaining ring 56. It will be noted that the retaining ring 56 is of an internal diameter such as to extend radially inwardly of. the external periphery of the electrode. The purpose of this construction is to prevent possible shear action due to internal pressure on the electrode from shearing the gasket or compression insulator, since the radial overhang prevents any possible shear stresses of this nature.

'Ihe interior of the invelope 40 may be provided with a liquid fill or with a gas fill, but in the event that a reducing gas is employed, it is obvious that the shell 40 will be made of the two metals, as described in connection with Figure 2. The internal bore of the insert 60 is molded in such manner as to provide a truste-conical recess 62, which has a shoulder portion 63 adapted to receive the annular wedge shaped refractory insert-64 held thereagainst by the flanged lip 65 of a cup-shaped electrode 66. The refractory insert 64 is preferably formed of a highly thermally refractive material such as Alundum, which has the characteristic of not being etched or eroded under high electric arcs', and which is capable of withstanding appreciably more abuse than the material 60' which may be of the type known as Isolantita The retaining body of mercury 68 is disposed in the annular groove formed between the rear face of the insert 64 andl the electrode cup formed by the flange on the electrode face 66. It"will be noted that the insert 64 provides a cut-back so that when the switch is stood on end, only a small part of the mercury will escape from the, annular groove, and consequently, when the switch is turned into its proper position there will be a sufcient retained body collected in the lower arcuate portion o f the groove to provide the proper mercury to mercury contact. It will also be noted that by this construction a very appreciable surface of the retained body is in contact with the electrode 66, thus decreasing the resistance therebetween.

In 'Figurcs 4 and 5 dI have illustrated a modied form of. compression insulator, the form vshown in Figure 4 having the main body portion provided with the extended axial shoulder portion 82 which serves to space the electrode shank and insulate the same from the metallic retaining ring such as the ring I8 or 56. 'I'he member 80 is provided in this form of the invention with a tapered bore 83 which ts about the electrode shank and allows a slight amount of movement of the compression insulator during the spinning operation to prevent buckling of the outer part of the insulator due to possible radial compression stresses thereon. This same fe-sult can be produced by the compression insulaton 85 shown in Figure 5 having the axially directed shoulder portion 86 and provided with a bore 81 having the shoulder portion 89 therein. With such a construction the shoulder portion 88 fits Vclosely about the electrode shank for centering molded more easily for such a construction.

Considering now the form of. the invention shown in Figure 6, I have provided a cup-shaped envelope or shell 90 having the radial shoulder 92 on the enlarged open'end portion 93. Seated against the 'shoulder 92 within the enlarged vend 93 is a ceramic insert 94 having the frusto-conical bore 95 therein which terminates in the sharp cutting edge 96 and the cut-back annular groove 91.

An electrode 98 is provided having the annular flange portion 99 disposed within and forming the annular outer wall of the cut-back recess .91.

i The face of the electrode is spaced from the cutting edge 96 a distance such as to retain the body of mercury |00 therebetween in contact with the electrode and projecting above the cutting edge in such manner as to provide for mercury to mercury making and breaking of. contact with the movable contactor |02.

The electrode 98 is provided with a cylindrical extension |03 around which is disposed the resilient sealing gasket 04 adapted to be com-v pressed by the annular compression washer |05 which has seated thereagainst the retaining ring |06 disposed beneath the spun over edge |01 of the shell. The compression washer |05 radially encloses the extending portion of thel cylindrical extension |03 of the electrode and serves to insulate the electrode from the retaining ring |06 and the end portion 93 of the shell 90 forming the otherv electrode. The electrode 98 within the cylindrical extension |03 is provided with an integral axially extending post construction |08 which is tapped at its outer end to receive the terminal screw |09 by which the conductor or terminal lug |0 is secured to the electrode. With this construction the conduction of heat from within the switch envelope through the electrode is facilitated due to the annular cylindrical portion |03 forming a metallic path for the escape of this heat which provides for a much more rapid rate of heat dissipation than if the heat had to be dissipated through a rubber gasket and ceramic compression member. Also, with this construction there is provided an annular opening ||2 about the post |08 insuring removal of the heat from the metal through the circulation of air in this opening.

For switches which are operated many times per minute, such as sign flashing, advertising, or oscillating mechanisms, a constructionl of this type is desirable to .prevent the building up of heat within the switch envelope and to insure a suicient dissipation of heat to prevent'the pos-,.

sibility of destroying or deteriorating the resilient sealing member |04 or the surface of the ceramic insert` 94 due to high temperatures being continually impressed thereon.

In Figures '7 to 10, inclusive, various forms of` electrodes are disclosed which all have as their primary purpose a construction which will facili- 35 ltate this dissipation o'f the heat. For example, in Figure 7 the electrode ||3 is provided with the cup-shaped recess III withinwhich the retained body of mercury is disposed and is provided with,

also directed axially rearwardly in planes passing through the axis of the electrode. 'I'he electrode is preferably tapped, as indicated at H6,

for the' reception of the terminal screw.

In Figure' 8 a modied construction is shown in which the electrode ||1 has a serrated cupshaped surface ||8 for contact with the retained body of mercury, the serrations in the surface increasing the contact area between the retained body and the electrode surface to reduce the resistance therebetween. The outwardly extending portion of this electrode is provided with an annular cylindrical extension ||9 to which are joined integral ribs which diverge outwardly J from the rear face of the electrode ||1 in such entirely open or recessed axially to provide access to the tapped opening |28 for receiving the ter-- minal screw. Similarly, the electrode-|30 in Figure 10 has a solid cylindrical section |32 extending rearwardly thereof for facilitating heat dissipation, and is provided with the centrally disposed tapped opening |33 for the reception of the terminal screw.

It is to be understood that in all embodiments of the invention in place of a single metallic envelope, a bimetallic envelope may be employed using hot rolled strip for the inner lining surface, and' having copper or a similar metal enclosing the same to prevent escape of hydrogen if the switch is of the gas-filled type. Also, the ceramicv inserts may be provided with "Alundum portions s at the annular contact making and breaking pointsf to prevent breaking down of the insert edge under repeated high temperatures and arcs, as shown clearly in Figure 3 of the drawings.

It is therefore believed that I have provided a novel type of switch construction vdesigned to meet the particularoperating requirements of such switches and capable of long, continued rapid operation vwithout any appreciable building up of the operating temperature to a point such as to destroy the life of the switch.

I am aware that various changes may be made in certain of the details of the constructions illustrated and described, and I therefore do noi'.

intend to be limited except as defined by the scope and spirit of the appended claims.

I claim:

1. A metal envelo /e mercury switch having an insert in one end ca rying an electrode, a hydrogen atmosphere within the envelope, and a movable body of mercury in contact" with the envelope, said envelope comprising a ferrous lining with an external covering of copper impervious to the passage of hydrogen therethrough.

2. A metal envelope for a mercury switch of the metal envelope type. comprising a cup-shaped shell having a lining of ferrous metal and a covering of a metal impervious to hydrogen.

3. The envelope of claim y2 wherein said lining comprises 10% or less of i the thickness of said envelope.

4. A metal envelope mercury-switch comprising an electrode shell open at one end, an insert in said ends, an electrode centered in said insert and having an outwardly projecting shank, a resilient gasket about said shank within said open end of said shell, and a ceramic compression member abutting the outer face of said gasket and having an aperture receiving said electrode shank, said aperture having radial clearance about said/shank increasing toward the outer end thereof, said sheell having its edge spun radially inwardly to lock said compression member and gasket in lposition and to impose axial pressure thereon.

5. In `a metal envelope mercury switch having a ceramic insert in one end thereof, an electrode centeredin said insert and having an axially projecting shank, a resilient gasket aboutsaid shank sealing the outer faces of said electrode and insert, al compression member fitting closely in the envelope against the outer face of said gasket and having an outwardly tapered bore receiving said shank, and means for exerting axial compression on said member to compress said gasket into sealing engagement about said shank and against the internal surface of the envelope.v

' 6. The combination of .claim 5 wherein said Acompression member has an axial extension about said shank projecting beyond the end oi' said env I velope.

of said electrode extending axially outwardly, a resilient sealing gasket engaging the outer faces of said insert and electrode, and a refractoryv ceramic compression member engaging the outer radial face of said gasket and having a tapered bore fitting about said electrode.

v 8. A metal envelope mercury switch comprising a cup-shaped electrode shell having a ceramic insert in the open end thereof, said insert having a lfrusto-conical recess opening into the shell, a cup-shaped electrode centered in the insert adjacent the small end -of said recess, and a ring of a highly refractive ceramic material forming the inner end of said recess, the peripheral. edge ofsaid electrode having abutment against both said ring and said insert. 9. The switch of claim"8 wherein said ring material comprises Alundumz 10. A ceramic insert for `a` metal envelope mercury` switch comprising a body portion having an axial frusto-conical recess extending into one end thereof, a coaxial cylindrical bore extending y into the opposite end thereof of a greater diameter than the small end of the recess and overlapping the sainey to form an annular groove thereabout, the material forming the portion between said groove and recess being more highly refractive and less thermally conductive than the remaining portion ofsaid body portion and being supported on an angle surface of said insert preventing movement thereof toward the outer edge of said recess.

1l. A metal envelope mercury switch compris! ing a cup-shaped electrode shell having an enlarged open end, a ceramic insert in said end having a frusto-conical axial recess, a cup-shaped 10 electrode in said insert closing the small end of the recess and having an outwardly projecting shank of a diameter substantially equal to that of the large end of said recess.

12. The switch of claim 11 wherein said shank is axially recessed and provided with a central portion thereof.

PAUL S. BEAR.

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