US1996845A - Electrical sealed container - Google Patents

Description

April 9,1935. c. J. WARNK E 1,996,845

ELECTRICAL SEALED GONTAIMFR Filed Oct. 31, 1931 Patented Apr. 9, 1935 ELECTRICAL SEALED COIN'I'AIN'ER' Carl J. Warnke,'Elkhart, ind" assignor, by direct.

and mesne assignments, to The Adams &

Westlake Company, Chicago, 111., a corporation of Illinois Application October 31, 1931, Serial No. 572,311

3 Claims.

My invention relates to electrical sealed containers, such as mercury switches, incandescent lamps of all types, radio tubes, rectifiers. mercury arc lamps, Roentgen tubes, power vacuum 5 tubes, and devices of this character generally in which an envelope of glass or vitreous material encloses a sealed space having conductors disposed therein and electrically communicating with an external power circuit through lead-in conductors which are embedded in and through the wall of the container, the disclosure in this application relating more particularly to mercury switches as illustrating the advantages of my container.

One object of my invention is to devise a vitreous container for electrical apparatus which is characterized by a high electrical resistance, an improved stability which makes the container more resistant to the deteriorating effects of age than the glasses now commonly used for such purposes, and in which the constituents of the glass comprising the container have been so selected and arranged as to provide for a substantially neutral glass through the balanced relation of the component substances.

A further object is to provide a container of the character indicated in which the percentage composition of the substances employed may be varied over a definite range for the purpose of adjusting the coeflicient of thermal expansion of the completed container in order to meet the requirements of any particular operating con dition, without sacrificing the advantages of the container in other respects.

A further object is to provide a mercury switch having an envelope which is composed of a-glass characterized by a melting point which is sufficiently low to permit an easy working of the glass, and a low coeflicient of thermal expansion relative to the lamp glass now used in the industry, and which is therefore capable of withstanding the ravages of the electric are that occurs when the circuit is completed or broken within the switch container.

A further object is to provide for a mercury switcher other types of electrical apparatus an envelope of the character indicated consisting of a glass which is substantially void of those materials, such as lead, tin, antimony and substances generally, which are decomposed under v and by the action of the electric arc and are A further object is to produce a glass for electrical sealed containers which is substantially void of any oxides which are reducible by hydrogen and is thereiore' superior to the so-called alkaline glasses in this respect.

A further and more particular object is the employement of a glass that may be classed generally as a'magnesium silicate glass which, in addition to the several advantages'noted above, is characterized by high tensile strength and toughness, a higher degree of resiliency than the lime glasses, ability to withstand and be substantially unafiected by rapid temperature fluctuations over wide ranges; and which, when used as the envelope of a mercury switch, facilitates the free rolling of the mercury mass, since there is no tendency on the part of the mercury to adhere to the container surface.

A further object is .to provide. a container formed of a glass which is characterized by a capacity for establishing a close aflinity with lead-in conductors, such as tantalum and molybdenum, when the material of the container is in a plastic or partially liquid condition and after cooling, to thereby effect a thorough wetting of the conductor surface and the creation of a tightseal therewith.

For the purpose of more particularly illustrating the details and advantages of my invention, the same will be illustrated and described as embodied in a mercury switch, but it will be understood that the invention is considered generically applicable to other types of electrical apparatus in which sealed containers are employed.

Mercury switches are generally in the-form of glass containers which may be filled with gases such as nitrogen, hydrogen, or carbon-monoxide for the purpose of assisting in the dissipation of heat created by the electric arc, and within which container rides a mass of mercury for bridging the space between a pair 01' electrodes disposed within the container and connected by means of lead-in conductors passing through the wall of the envelope with an external. source of electricity. By tilting the container in one direction, the body of mercury moves into electrical conducting relation with the electrodes and by moving the container in the opposite direction, the body of mercury flows away from one or both of the electrodes to break the circuit. Other modifications of this construction may include an arrangement in which a mercury to mercury contact is effected between separated pools of mercury by tilting the container to cause a portion of the mercury to flow between these pools. However constructed, switches of this character have been subject to many operating disadvantages, particularly where used in circuits bearing currents of considerable ampere strength and which are intended to make and break the circuit a large number of times over a considerable period.

When the electrical circuit is interrupted or is about to be completed as above described. the tendency of the current to break down the dielectric strength of the intervening air gap results in the creation of an electric arc of relatively high temperature which has a marked capacity for effecting deterioration of the switch. Glasses-which have heretofore been employed in the making of switch envelopes have generally been characterized by a relatively high coeiiicient of thermal expansion and a low melting point, so that the impingement of the electric are upon the glass of the envelope in the region adjacent the rupture of the electrical circuit frequently results in a breakdown of the glass at the indicated point, or close to the locality where the lead-in conductors are sealed in and through the envelope. This condition is particularly aggravated where a mercury switch is employed in an inductive circuit owing to the high voltage are which is induced at the breaking of the circuit and the resulting rapid changes of temperature which subsequently obtain within the switch envelope. This rise in temperature occurs within a relatively short period of time, as does the temperature recession downwardly therefrom to the normal temperature of the switch, so that the glass envelope is subjected to a highly destructive efiect in both instances, the glass being actually eroded with a consequent decrease in the wall thickness and excessive stresses being thereby established in the envelope which are in addition to and superimposed on the natural stresses present in the glass. The glass accordingly breaks at the indicated point and the switch is therefore removed from service. Similar rapid and temperature changes occur in such switches when employed in circuits subject to high current surges, that is, in inductive circuits through which the current flows intermittently and in which the loads are heavy, such as the lamp banks of advertising signs and similar installations. In both of the foregoing instances, mercury switches as now known are prone toearly failure in service owing to the deterioration and subsequent destruction of the glass envelope.

Other objections to glass envelopes as now used in mercury switches arise from the fact that the type of glass employed frequently embodies metallic substances, reducible oxides, or materials generally which, in the operation of the switch are decomposed by the high voltage arc, and are picked up by or amalgamate with the mercury. This decomposition of what, so far as the desired efllclent operation of the switch is concerned, are substantially in the nature of impurities, results in a lessening of the purified condition of the mercury with a consequent aifecting of its capacity for operating according to its primary purpose, or it may result in the formation of slag or film deposits on the interior surface of the envelope, or between the electrodes themselves, thus short-circuiting the switch.

As specific examples of the practice of the prior art'in the use of sealed containers for electrical apparatus, and more particularly mercury switches, it may be noted that it has been heretofore proposed to utilize the so-called hard glasses I in connection with tungsten lead-in wires. Where such a container is formed of a lead borosilicate glass, it has been ascertained that, while the tungsten lead-in wires may be readily sealed through this glass owing to the closeness in the numerical values of the coefficients of thermal expansion, the glass container will not withstand severe usage over long periods. As one solution of this particular difliculty, a bore-silicate glasscontaining an appreciable quantity of aluminum has been substituted for the lead bore-silicate glass, the former being the so-cailed pyrex glass, but the use of this particular glass requires the employment of a fusion zone of lead hero-silicate glass, through which the tungsten lead-in wires may be sealed, the lead glass being in turn united to the pyrex container. However, this fusion zone creates a region of weakness which is very susceptible to cracking with a result that the hermetic condition of the envelope is destroyed. Other modifications have contemplated the use of a quartz container, but this type of envelope is subject to the same disadvantages as discussed in connection with the pyrex container and to a greater degree. Still other attempts involved the employment of envelopes of relatively soft glass, but utilizing a protective element of arcresisting material which is supported in some manner within the container and out of contact therewith.

The principal object of the present invention is to overcome the foregoing disadvantages insofar as may be accomplished through changes in the character of the glass employed for the switch container and in the adoption of a metal which will operate satisfactorily as a lead-in conductor with particular reference to its capacity for establishing a gas-tight seal with the glass and in the maintenance of this seal throughout the working range of the switch, considered from the standpoint of temperature and the conductance of the electric current. For .this purpose, I have discovered that magnesium silicate glass, when made according to a'deflnite composition, possesses certain properties that are particularly useful under the special conditions found in mercury switch operation, and is generally advantageous for use in a variety of sealed containers for electrical apparatus. The outstanding characteristic of this glass is the balanced relation of its component parts, resulting in the formation of a glass which is substantially neutral or perhaps very slightly basic, as contrasted with the alkaline characteristics of the lime and soda potash glasses, and the acid properties of the well known bore-silicate glasses, whose disadvantages have already been discussed. In composition, my improved glass is constituted of silicon dioxide (S102), magnesium oxide (MgO), boric oxide (8:03) and sodium oxide (Na-.0).

I have ascertained that, when these substances are combined in certain definite percentages and within a given range, the resulting glass is not only substantially neutral or perhaps slightly basic, but is characterized by a high electrical resistance, a melting point which is sufllciently low to permit the glass to be easily worked, toughness, capacity for withstanding shock, a high degree of heat resistance, a substantial freedom from lead, tin, antimony, or substances which are de composed by the action of the electric arc, and is also substantially void of any reducible oxide in an atmosphere of hydrogen. In addition, this glass is stable, more resistant to age, does not shattereasily, and, as will presently be discussed, is capacitated for establishing a remarkably close amnity with lead-in wires, suchas tantalum and molybdenum. In the preferred composition, the

percentage of silicon dioxide may range from 68- to 71%, the amount of magnesium oxide employed varies from 10 to 14%, boric oxide from by the minimum coeflicient of thermal expansion which is approximately of the order of from 48 to 54- x-l0-, while the utilization of a 68% portion of silicon dioxide will produce a glass having the maximum coeflicient of thermal expansion, being approximately of the order'of from 58 to 64 x 10 As lead-in conductors for the foregoing kind of glass, it has been ascertained-that wire composed of tantalum 'of molybdenum -works very satisfactorily, owing to the capacity of these metals for being readily wetted by the glass and to maintain the seal thus obtained throughout the working temperature range of the container. For example, in the sealing of the above lead-in wires, it is believed that the acid oxide formed is substantially. dissolved in and by the glass while the latter is in a liquid,molten, or a semi-molten condition, thereby causing a very pronounced wetting action betweenthe glass and wire and,

resulting in an exceptionally tight seal. The strength of this seal is attested by the fact that there is no sharp dividing line between the leadin wire and the glass container, but that the seal is characterized by a graded nature and composed of the glass, the metal oxide, and the metal proper. The relation between the wetting characteristics of the tantalum and molybdenum erence being had to the accompanying drawing,

and the novel means by which said objects are efiectuated will be definitely pointed out in the claims.

In the drawing, the figure represents a longitudinal, sectional elevation of a. conventional form of mercury switch arranged in circuitbreaking position. J

The switch shown in the drawing is intended merely as illustrative of switches of this general character, and no claim is made thereto as regards the structural details of the switch, except to the extent as indicated more particularly hereinafter. sealed container l0 which is formed of magnesium silicate glass having the characteristics and composition noted above, and throughvthe walls of which pass lead-in conductors Ii and i2, composed of tantalum or molybdenum, which are connected externally of the container to any suitable source of electricity by means of con- Speciflcally, the switch comprises a.

tainer III, the lead-in conductors ll and- 12'- are connected respectively to electrodes and I8 which may be of any de'siredshape and material and bear any desired space relation to each other. The details of construction of the elements above described form no part of the present invention, except as regards the materials constituting the container l0 and the lead-in conductors. i i and i2, so that they may be arranged for the carriage of currents of any value and atany voltage over any desired period of time, the sealing of the lead-in conductors H and i2 withinth'e'walls of the container ill being such as to prevent leakage at these points. In the drawing, the numeral I1 is intended to designate the graded character of seal which obtains between the lead-in conductors and the material of the envelope.- The container III also encloses a body of mercury l8 which is shifted from end to end thereof-iassaid conductor is tilted by any approved means, the position of said mercury in the drawing indicating a circuit-breaking position and when said container is tilted in the opposite direction, the mercury l8 rolls along the bottom of said container to bridge the space between the electrodes iii and IE to thereby complete the circuitwithin the switch. At the time the switch is made, the air content originally within the container I0 may be evacuated and a predetermined quantity i of a heat dissipating and are suppressing gas, such ashydrogen, may be inserted therein at some approved pressure.

The outstanding characteristics of, a mercury switch constructed as above described, or, of any electrical apparatus which employs a container composed of the material set forth above,.is its ability towithstand hard usage. over extended periods of time without having its primary effectiveness continuously decreased andits capacity for remaining positively neutral so far as any tendency to promote any deteriorating action in the other parts of the switch. Accordingly, the switch is featured by a high degree of dependability and desirability for use under conditions which are not satisfactorily met by present type switches. The composition of my improved glass is sufficiently elastic to permit of any desired variations within the limits'outlined in order to secure a type of glass which will best suit operating conditions and with particular reference to any peculiar characteristics which the container should embody in order to satisfactorily meet the indicated condition, as regards coeflicient of thermal expansion, electrical resistance, toughness, nieltingpoint, and other factors.

While I have shown one set of combinations and elements thereof for efiectuating my. im-

proved sealed container, it will be understood that the same is intended for purpose of illustration only and in no wise to restrict the device to the exact forms and structures shown, for many changes may be made therein without departing from the spirit of my invention.

I claim:

1. A glass for use in mercury switches and the like composed of silica in excess of 68%, magnesia in the next largest proportion, and an oxide of an alkali metal to the extent of at least 7%, said glass being substantially free of lead, tin, antimony, and the like, and having a coeflicient of thermal expansion of 64 x 10- or less.

2. A glassfor use in mercury switches and the like composed of silica in excess of 68%, magnesia in the next largest proportion, and an oxide of an alkali metal to the extent of at least 7%, said glass being substantially free of lead, tln,'antlmany, and the like, and having a coefllclent or thermal exnanslon 01' 64 x 10- or less, and a tantalum or molybdenum conductor sealed therein. I 3. A glass for use in mercury switches and the like composed of silica in excess of 68%, magnesia in the next largest proportion, and an oxide of an alkali metal to the extent-of atleast 7%, said glass being substantially neutral to basic and having a coefllcient of thermal expansion of 5 64 x 10- or less. CARL J. WARNKE.

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