US2392099A - Manufacture of glass sealed contact units - Google Patents

Description

Ian l 1946- c. E:. POLLARD, JR 2,392,099

MANUFACTURE 0F GLASS SEALED CONTACT UNITS Filed Ju1y29, 1943 ROD ATTORNEY Patented Jan. l, 1946 MANUFACTURE F GLASS SEALED CONTACT UNITS Charles E. Pollard. Jr., Hohokus, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 29, 194s, serial No. 496,561

2 claims (01.49-89) This invention relates to processes of annealing and chemically cleaning and applies particularly to processes employed in the manufacture of electrical apparatus.

The object of the invention is primarily to eil'ect a cleaning of electrical apparatus sealed in glass envelopes after assembly and to remove impurities and accumulations of matter resulting from previous manufacturing steps. The process of the present invention is particularly applicable to the manufacture of a piece of apparatus known as theEllwood unit which is disclosed in Patent No. 2,289,830, granted to W. B. Ellwood on July Y i4, 1942, though it will apply as well to the manufacture of other similar apparatus and to electronic devices.

The Ellwood unit compared to other types of magnetic switches or relays, has certain unique characteristics. It is an assembly of specially stable elements bound to each other entirely by fusion. The parts themselves and the mechani-l cal bonds between them are practically unaffected by humidity and are stable with respect to ordinary temperature variations. This results in a high degree of stability of adjustment, compared, for instance, to spring pile-ups molded or clamped in plastic or other insulating materials. No adjustment after assembly or while in service is possible and therefore it is necessary to employ methods vof manufacture which will result in a high degree of uniformity in the product. Each manufacturing step -must be characterized by nicety of controla These units are made with a metal tube as a terminal at one end which is used after assembly for removing air and substituting therefor some non-corrosive gas and the tube which is copper plated on its inner surface is finally sealed with solder. The tube is composed of an alloy of nickel and iron which has a temperature coefficient of expansion almost exactly equal to the temperature coeiiicient of expansion of the lead glass used as the body of the unit. The fbond between the glass and the magnetic alloy is made simply by the application of heat, the surface tension of the molten glass being the only force involved in bringing the elements into contact. As this force is relatively small, it is possible in assembling to hold the parts of -the switch in a desired position with respect to each other and then to ilx this position permanently simply by applying heat to the glass. The metal oxide formed during the sealing-insures wetting of the metal by the molten glass and a tight seal is characterized by a homogeneous dark gray color due to this oxide.

Heretofore removal of extraneous matter from electronic apparatus has been practiced by heating the apparatus while maintaining a partial vacuum within. Heretofore also certain cleaning operations have been performed by heat treating in an atmosphere of hydrogen but in the present case certain special problems have had to be met. It is necessary to completely clean the parts of the switch unit without discoloring the unit, without changing the relative position of the parts and without destroying the metal oxide in the seal between the glass and the magnetic alloy. Heat treatment in an atmosphere of hydrogen at too high a temperature will tend to reduce the composition of the glass and to produce discoloration through reduction of the lead silicates and the formation of metallic lead. At

too high a temperature the oxide of the seal will b e attacked. At too low al temperature the hydrogen in its commercial formwill have little if any cleaning eiect. A feature of the invention,

then, is a process which involves the purification of the hydrogen to a point where it will affect the desired cleaning at a temperature which will not. affect the assembly or the adjustment of the parts thereof.

Another feature of the invention is a process which results in the simultaneous annealing of the glass to remove stains from the seals and the cleaning of the inside surfaces of the device. The metal tubulation is copper plated to render the solder seal tight and this annealing and cleaning operation must clean the copper inside surface of the metal tube so that the solder will thoroughly wet such surface in order to produce the requisite seal.

In accordance with these features two processes are combined and carried out in a single operation. It is necessary to anneal the glass which forms the body of the contact unit after the reeds have been sealed in and the adjustment of the parts has been made without altering and such adjustments. It is also necessary to condition such apparatus so that after the final seal is made and while in service the operation will be stable and dependable and will not be affected by any foreign substance on the parts left there by previous manufacturing steps. Applicant has' cordance with other materials. It is dictated by subjected to a temperature of 420, C. the boat is the fact that higher temperatures are to be moved, as indicated by the boat in outline 9, to avoided in 'order to speed the cleaning process. the comparatively cool part of the furnace. The

The temperature mentioned is therefore in the function of the heavy boat is to limit the rate of nature of a range since certain deviations in temperature change in the glass, particularly on either direction may be allowed without departcooling. A safe maximum rate of cooling is coning from the spirit of the invention. sidered to be about 100 C. per minute.

Other features will appear hereinafter, 'I'he period of treatment may be adjusted toA The drawing consists of a single sheet having the particular furnace used. It has been found three figures as follows: 10 thatif inspection with polarized light shows a Fig. 1 is a sectional view of a sealed reed consubstantial reduction in strain as the result of tact unit; the annealing, the switches will be satisfactory. Fig. 2 is a fragmentary sectional view greatly Darkening of the glass is an eiective indicator of enlarged of the `end o such a unit in which the over annealing, although switches showing 'slight metal tube is sealed showing the copper plating l5 darkening do not appear to be objectionable and the solder seal which is made after the anotherwise. Precise and reliable control of temnealing and cleaning operation; and perature is particularly desirable.

Fig. 3 is a diagram showing how the anneal- The hydrogen from container I o used in the ing and cleaning operation is carried out. furnace is puriiied by passing it through palladil 'I'he contact unit as shown in Fig. 1 comprises 20 um coated asbestos Il heated by means l2 at aI glass body portion i having therein two over- 300i50 C., then through two liquid air-traps lapping reeds 2 anda of magnetic material. The I3 and l5 in SereS- The palladium acts 8S a reed 2 is welded to a wire d of magnetic material' catalyst to combine free oxygen With hydrOgeD. which is sealed in one end of the glass tube and the resultant water vapor being removed along the reed e is welded tc a tube s of similar matewith other moisture in the traps. This puririal which is sealed in the other end of the glass cation of -the hydrogen greatly increases the eitube i. y fect of the heat treatment in reducing oxides in In manufacture. after the parts are assembled the switch. Actually the cleaning effect oband sealed togetheras shown in Fig; 1, the parts tained at this relatively low temperature of l420 inside the tube and the surfaces of the tube 5 30 C. with commercial hydrogen has been found to are cleaned in an atmosphere of puriiled hydrobe negligible. gen and the assembly is simultaneously annealed After the above-described annealing and at an elevated temperature. `Since the relative cleaning operation the contact units are placed adjustment of the parts cannot be allowed to upright in an iron basket, evacuated, nlled with alter during heat treatment and since commerpuriiied hydrogen and sea-led withvsolder. The cially available hydrogen is inenective at a lower tube *5 is copper p lated on the outside for a short temperature, it has been found that eective andistance from the bottom and on the inside for nealing and eiective cleaning can be secured at a greater distance as shown in Fig. 2. The a temperature which will not soften the parts cleaning operation prepares this inside Asurface sumciently to cause deformation thereof in an 4o for the soldering operationin which the said iron atmosphere of specially puriied hydrogen. basket is lowered to the point where the tubes The assembled switches are heat treated 'at enter a pool of molten solder up to a specified 420 C. with puriied. hydrogen in a quartz tube depth. With the inside copper-plated surface furnace. In Fig. 3, a quartz tube g is shown as clean the outside pressure of the hydrogen atextending through an electrically heated furnace mosphere is raised and the solder'slowly rises in 7. This temperature is below that usually used the tube 5, cooling as it rises above the outside to anneal the glass but is eiective in removing level thereof and reaching the solid state before' strains from the seals and the puriiied hydrogen it reaches the Seal t0 the glass tube 9. The

at this temperature will clean the copper surface bucket' and the switches are then raised above on the inside oi the tube 5 so that solder used 5@ the level of 'the solder and the assemblyis allowed later to seal this tube will properly wet the surto cool.

face and adhere thereto, will also remove possi- What is claimedis:

ble traces of oxide4 and volatile matter from the l. In the manufacture of electrical apparatus electrical contact surfaces and will remove onde consisting `of glass sealed magnetic and electrical coatings which m ght tend to ilake o inside the elements, the step of heat treating such appa- SWiChvratus in an atmosphere of puriiled hydrogen at This annealing temperature is onewhich not a temperature of 420 C.

only will avoid changes in adjustment of the 2. In the manufacture of electrical apparatus Aswitch due to softening of the glass but will also consisting ogf glass sealed magnetic and electrical avoid blackening of the glass by the hydrogen. conducting elements, the step of heat treating At and above the annealing temperature (431 C. such apparatus at a temperature of approxil.

as recommended by the' manufacturer of the mately 420 C. for a period of approximately 15 glass) hydrogen tends to reduce the lead silicates minutes and then cooling such apparatus at a in' the glass to metallic lead. rate oi approximately 100` C. per minute, in an The switches in batches are placed in a. heavy atmosphere oi purified hydrogen.

I copper boat e and inserted in the oven. After ifteen minutes in the position where they are C E. POLLARD, Jn.

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