US1184813A - Compression-type seal. - Google Patents

Description

W. T. BIRDSALL. COMPRESSION TYPE SEAL. APPLICATION FILED MAY 4. 1915.

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WITNESSES AT'TORNEY UNITED STATES PATENT OFFICE.

WILFRED '1. IBIRDSALL, 0F MONTGLAIR, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORA- TION OF PENNSYLVANIA.

COMPRESSION-TYPE Specification of Letters Patent.

Patented May 30, 1916.

Application filed May 1915. Serial No. 25,865.

to provide a device of the character described that will be simple, inexpensive and rugged in construction.

Referring to the accompanying drawing, Figure 1 is a side view, partially in section and partially in elevation, of a seal embodying my invention; and Figs. 2 and 3 are plots illustrating and indicating the relation of the different coefficients of expan sion in my seal. Hitherto, when it has been desired to introduce electric current into evacuated containers of vitreous material, it has been necessary to fuse the conductor to the wall and the material which-has been used with most success as a sealing-in conductor has been platinum. When it is desired to employ platinum, however, inlarge amounts, as is 36 necessary for large-capacity rectifiers, its

cost'becomes prohibitive.

I have found, by surrounding a leadingin wire of any material, such, for example, as iron or tungsten by a mass of elastic material such, for example, as glass, and by surrounding said glass by a band of material having high tensile strength, said band of material being shrunk on so that the mass of glass is at all times maintained under compression, I am enabled to provide, in difl'erent annular zones of the glass, apparent coefficients of expansion which vary uniformly from that of the wire to that of the surrounding band. By choosing, therefore, a. compressing band the coefiicient of expansion of which, with respect. to the coefficient of the wire, lies beyond the coefiicient of .the material in the container, I i am enabled to provide a zone of glass having an apparent coefficient which is substantially that of the container and, by fusing the container wall to said zonein any well known manner, I am enabled. to obtain a vacuum-tight joint between the container Wall and the leading-in wire, in spite of great divergencies in the coeificients of expansion therebetween.

Referring to the accompanying drawings -for a more detailed understandingof my invention, I have shown a leading-1n wire at 4 in Fig. 1. The leading-in wire 4 is surrounded by, and supports, a mass of elastic material 5 formed, preferably, of glass. A band of material 6 surrounds the body of glass 5 and is formed of material having high tensile strength, such, for ex ample, as steel or brass. The band 6 is shrunk upon the body of glass .5 and is of such tensile strength that it will maintain the body in a state of compression throughout a wide range of temperature variation.- Under these conditions, the body 5 will not follow the ordinary law under which all of its component portions would exhibit the same coefficient "of linear expansion, butv the zone lying adjacent to the wire 4 will be forced to assume an apparent coefiicient' of expansion closely approximating to that of the wire 4. In like manner, the zone of the mass 5 lying adjacent to the band 6 will be forced to assume an apparent coefiicient of expansion closely approximating that of the material composing the band 6. All zones lying between the wire 4 and the band 6 will exhibit different apparent coefficien'tsof expansion, there being a radual transition from the value exhibite ad jacent the wire 4 to the value exhibited adjacent the band 6. The neck of the container of. a vapor electric device is shown at 7 and the coefiicient of the band 6 is so chosen with respect to the coeflicient of the wire 4 that it lies beyond the coeficient of the material composing the container 7. For example, if the material of the container 7 has a lower coeflicient than that of the wire 4', the material ofthe band 6 will be chosen to have a still lower 'coefiicient, and vice versa. As there is a gradual transition in the body 5 from an apparent coeflicient approximating that of the wire. 4 to that approximating the coeflicient of the band 6, 'a certain zone will be found having .an apparent coefilcient of expansion closely this zone, there will be no difierential expansion tending to rupture the seal, and a vacuum-tight connection may be readily provided between the container 7 and the wire 4.

In order to compute the necessaryradius for the neck of the container 7 to satisfy the above-described conditions, recourse may be had to a simple graphic treatment, as

illustrated in Figs. 2 and 3. Let the distances CD and CF be laid out on an ordinate to correspond, respectivel to the radii A and B of the wire 4 and 0 the inner surface of the band 6 at any arbitrary temperature. In like manner, let the distances GH and GK represent the respective radii of said .two members at' a different temperature.

' tainer 7 to the same scale as has been used dinate DF at a point geometry that any hne in plotting the coefficients of the members 4 and 6. The line MJ will intercept the or- E and the distance OE will be the desired radius X for the neck of the container 7 to the proper scale. To prove this, consider a particle in the mass 5 lying at distance X from the wires. If the mass 5 is homogeneous, as must be assumed, this particle will always divide the distance between the wire-and the outside band in the same ratio. In Fig. 2 we measure this distance as DF. Then we know by drawn through M will divide similar llnes, such as HK, in the same ratio that it divides DF. If the radius X is CE in Fig. 2, it follows that points of intersection with the different ordinates by the line MJ will give the radii of the particle of glass under compression at the temperatures respmtivel corresponding on the diagram to each ordmate. But the position of the line MJ is bound to indicate the raneck of the container 7 at each temperature. It will also indicate the position of the particle of the mass 5 at all temperatures and the coefiicient of the zone in the mass 5 at the radius X must be the same as that of the container 7. It therefore follows that a tube the mean radius of which is determined as above can be sealed directly to the wire 4 without danger of rupture.

If a seal is to be made without the central wire 4, then, in Fig. 2, the line MDH will be omitted and the point M will become the intersection of the line FK with the horizontal axle.

dius of the In the specific case when the wire 4 and the band 6 have the same coefficient, the point Mwill lie at infinity and, since the line MEJ must pass through this oint, it would be parallel with FK and D in each case. That is, the coeflicient of the container 7 must-be the same as that of the wire and of the band.

Referring to the diagram shown in Fig. 3, the conditions are exactly the same as shown in Fig. 2 except that the coefiicient of the band 6 is less than that of the wire 4 and, accordingly, the computation must be made on opposite sides ofthe point of intersection. Particular attention, should be paid to the fact that the values of the coefficients of the wire and of the clamping band should always be so chosen that they lie on opposite sides of the coefficients of the material of the container.

While, throughout this case, I have described the band 6 as being composed of metal, it may .very well be composed of glass or of any other material having suitable properties.

I have described the external band '6 as exerting pressure upon the mass5 but, within certainlimits determined by the coherence of the joints, the member 6 may exert tension on the mass of the member 5, establishing forced coefiicients of expansion in the intermediate zones thereof in the same manner as under conditions of pressure.

Many materials, such, for example, as compound metals, have an expansion line which is curved or which comprises two relatively straight lines meeting at an angle.

If the seal is raised to a temperature where the external forces acting upon the intermediate mass 5 are modified, the different zones will obey new laws, following an expansion line between the lines of the members 4 and 6. If either the member 4 or the member 6 entirely other laws, the apparent coeflicient belng raised if the wire 5 first releases and being lowered if the band 6 is the first to cease operation.

With certain combinations ofmaterials,

a seal having excellent manufacturing characteristics, such, for example, as cheapness, ease of manipulation, and great mechanical strength, may be produced in accordance with my invention but may exhibit a tendceases to act upon the mass 5, the intermediate zones of the latter will follow from the spirit thereof that no limitations comprising a massof material having a plu-- rality of different forced coefficients of expansion in different zones thereof, a seal between said wire and a zone of said mass of corresponding coefficient, and a seal between said tubular member and a zone of said mass of corresponding coefficient.

3. In a seal, the combination with two members between which a tight connection is to be made, of a third member, means for forcing said third member into close contact with one of said first named members and for imposing upon different portions of said third member different apparent coefiicients of expansion, and means for attaching the other of said first named members to a portion of said third member corresponding to its own coeflicient of expansion.

4. A seal between a tubular member and a wire extending therethrough and having a difierent coeflicient of expansion therefrom comprising a mass of material surrounding said wire, means for forcing said mass into intimate contact with said wire and for causmg the outer portlon of said mass to assume difi'erent coeflicients of expansion such that the coefiicient of the tubular member is between those of the wire and of the outer,

portion of said mass, and a seal between said tubular member and an intermediate zone in said mass having a coefficient of expansion corresponding to its own.

5. The combination with a wire, of a mass of elastic material mounted thereupon, a clamping member surrounding said mass and forcing the portions thereof adjacent said wire to assume a coeflicient of e ansion similar to that of the wire while orcing annular zones in said mass of larger radius from said wire to assume coeflicients of expansion differing by continuously increasing amounts from that of the wire, and a tubular member having a coefiicient of expansion differing from that of the wire and sealed to a zone in said mass having a coefficient corresponding to its own.

. 6. The combination with a wire, of a mass of glass mounted thereupon, a metallic band shrunk around said mass of glass so that said mass is maintained in compression throughout a wide temperature range and is forced to assume apparent coefficients of expansion in the portions adjacent to said wire and to said band of values corresponding, respectively, to those ofthe wire and band and in intermediate zones to assume apparent coefiicients of expansion of intermediate values, and a member composed of material having a coeflicient between those of the wire and of the band and sealed to a portion of said mass having a coeflicient corresponding to its own.

7. The method of joiningtwo members having different -coeiiicients of expansion which comprises imposing upon different portions of a third member a lurailty of different apparent coeiiicients 0? expansion, and sealing .each of said first named members to a portion of said third member having a coefiicient corresponding to its own.

8. The method of joining two members having different coefficients of expansion which comprises imposing upon difi'erent portions of a third member of elastic material a plurality of different apparent coeflicients of expansion by continuously applied external force and sealing each of said first named members to a portion of said third member having an apparent coeflicient corresponding to its own coefficient.

In testimony whereof, I have hereunto subscribed my name this 28th day of April,

WILFRED T. BIRDSALL. Witness:

ALFRED H. Enem

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