US2201717A - Sealed electrical device - Google Patents

Description

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Examine} CROSS REFERENCE COATING OR, PLASTIC s 4 y] May 21, 1940. I w. pAwu-u. ErAL SEALED ELECTRICAL DEVICI Filed m. 22; 1938 hi2: E 21 m I Inventors: Walther- Dawihl. I Wo|f3an g' Thoureo, Q3 e. him

Them Attorng Patented May 21, 1940 UNITED STATES PATENT OFFICE SEALED ELECTRICAL nnvrcn Application January 22, 1938, Serial No. 186,420 In Germany February 1, 1937 2 Claims.

acid content, the disadvantage is often noticed" that the seals around the current-supply wires become colored and do not remain air tight after a certain length of time. This phenomenon for many years was considered to be due to the diiferences in the coeillcients of expansion of the metal and glass, and therefore it was believed that it was possible to prevent-the seals from leaking by the use of special alloys or by the use 01' intermediate glasses with coefficients of expansion between those of the metal and the glass. Actually the reason for the leaks at the seals is an oxidation 01' those parts of the lead-in wires 25 which extend outward from the sealing point and are'therefore exposed to air. When the lamp is placed in operation, the lead-in wires are heated considerably and the said outer portions become oxidized. This oxidation cannot be observed 30 with the naked eye and was determined only by means of many microscopic examinations and glass analyses. This detrimental oxidation 0! the external part of the lead-in wire, which was unobserved up to the present, advances into the 35 seal as time goes on and then leads to leaks.

According to the invention it is possible to effectively avoid the leaks in the sealing points of lead-in wires or strips of tungsten or molybdenum for bulbs consisting of quartz or of glasses 40 with a high silicic acid content, by covering the parts of the leads which protrude outward with a cement which consists of a mixture of a material which oxidizes readily at higher temperatures, such as tungsten, molybdenum, magnesium, carbon or sulphur, a binding medium such as waterglass, and a filling material such .as feldspar,

kaolin or quartz. The oxygen of the surrounding air is bound by the readily oxidizable material in the cement coating which rapidly solidifies after 50 it is applied to the external part of the lead-in wire. The oxygen is bound at the temperature which the lead-in wire and the cement coatin assume in operation and is prevented from reaching the enclosed part of the lead-in wire. However, since the external parts of the lead-in wires do not become incandescent during operation but are heated to temperatures of, at most, several hundred degrees centigrade, and since, in addition, the particles of the readily oxidizing material are finely distributed in the cement coating. the binding of the atmospheric oxygen will of course take place extremely slowly so that even after a. thousand hours oi operation and more, the part of the cement consisting of readily oxidizing materials is not completely oxidized and particles 01' those materials are still available for binding oxygen from the air. Tests which have been carried out with the new cement coatin have shown in any case that the sealing points of the lead-in wires are still tightly sealed after more than a thousand hours oi operation and their'appearance is unchanged.

The part of the mixture consisting of readily oxidizing materials may be from twenty to eighty per cent of the total quantity. Preferably, however, the mixture consists of approximately one half of pulverulent, readily oxidizing material while the other half consists of a binding medium and a filler.

The invention can be utilized to advantage in metal-vapor discharge lamps and also in discharge vessels of other types, as well as high capacity electric incandescent lamps.

' The drawing illustrates how the cement may be applied to the lead-in conductors in accordance with our invention. Fig. 1 is a longitudinal sectional view of a stem having its leads coated in accordance with our invention. and Fig. 2 is a sectional view of a portionot an envelope for an electric discharge lamp or similar device with leads sealed therethrough and also coated in accordance with our invention.

The stem shown in Fig. l .is of the conventional so-called tipless construction adapted to be sealed in and constitute part of a suitable bulb and comprises a stern tube III and exhaust tube II which are fused and compressed at their upper ends l2 around portions of lead-in conductors iI-l3 which have outer leads I 4- welded thereto. The tubes i0 and H may be made of a glass having a high silica content, while the inner leads lI--l3 may be made of tungsten or molybdenum and the outer leads ll-ll of copper. In accordance with our invention, the portions of the leads l3-l3 extending to the outside from the stem press I! are provided with coatings l5-i5 of the cement described above and containing a readily oxidizable powdered material which traps oxygenin the air and prevents oxidation of the portian: o! the leads lS-IS sealed in the press I! which would lead to the development of cracks.

In Fig. 2, the quartz or high-silica glass envelope ii of a discharge lamp or similar device has the lead-in conductors Il-ii sealed through an end thereof, the external portions or said leads adjacent to the envelope being provided with the cement coatings ll-II.

A very useful cement to be used according to the present invention may consist of 50 parts by weight of molybdenum powder and 50 parts of ield ar powder; to t mixture is added about 30 parE of liquid water lass in such a manner that an easily EeaaaBle plastic cement mass is obtained which is easily applied by hand upon the wire parts to be covered.

-What we claim as new and desire to secure by Letters Patent oi the United States is:

1. In a sealed electrical device comprising an envelope of vitreous material of high silica con-' tent having at least one metallic lead-in conductor of a metal of the group consisting of tungsten and molybdenum fused therein and extending outwardly from said envelope, a coating of cement on the said outwardly extending portion of said conductor adjacent to said envelope, the portion of said conductor sealed in said envelope being free from the cement, said cement comprising a finely divided readily oxidizable metallic material. a binder and a filler, said oxidiz'able material being finely distributed throughout the mass oi. cement.

2. In a sealed electrical device comprising an envelope of vitreous material of high silica content having at least one lead-in conductor of a metal of the group consisting of tungsten and molybdenum fused therein and extending outwardly from said envelope, a coating of cement on the said outwardly extending portion of said conductor adjacent to said envelope, the portion of said conductor fused in said envelope being frec'from the cement, said cement comprising a mixture of a binder, a filler and a finely divided readily oxidizabie metallic material finely distributed in the cement and constituting not more than about eighty per cent of the mixture.

WALTHER DAWIHL. WOLFGANG THOURET.

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