Seals brazed

Brazed seals have been the subject of extensive research and development, with only limited success to date. Normally, brazing involves application of elevated... 

K.S. Weil, C.A. Coyle, J.T. DarseU, et al.. Effects of thermal cycling and thermal aging on the hermeticity and strength of silver-copper oxide air-brazed seals. Journal of Power Sources, 152 (2005) 97-104. 

The anodes most suitable for burying in soil are cylindrical anodes of high-silicon iron of 1 to 80 kg and with diameters from 30 to 110 mm and lengths from 250 to 1500 mm. The anodes are slightly conical and have at the thicker end for the current lead an iron connector cast into the anode material, to which the cable connection is joined by brazing or wedging. This anode connection is usually sealed with cast resin and forms the anode head (see Fig. 7-2). Ninety percent of premature anode failures occur at the anode head, i.e., at the cable connection to the anode [29], Since installation and assembly costs are the main components of the total cost of an... 

Hermetic Seal—an impervious seal made by the fusion of metals of ceramics, which prevents the passage of gas or moisture. The seal can be achieved by brazing, soldering, welding, fusing glass or ceramics. 

Hermetically Sealed. A hermetically sealed device shall be sealed against the entrance of an external atmosphere and the seal shall be made by fusion, e.g., soldering, brazing, welding, or the fusion of glass to metal. 

This is the most common test method employed to qualify the leak characteristics of a new seal material. The test method involves applying the seal between two ceramic discs or between a ceramic and a metal disc, pressurizing the cavity formed by the seal and monitoring the pressure decay as a function of time.22 Alternatively, a metal tube and a ceramic disc can also be used [34], Typically, the cavity is pressurized to about 2 psi and the leak rate is determined by the pressure decay as a function of time. These tests can be done at room temperature or elevated temperatures. Similar test arrangement has also been used to test a plastically deformable brazed metal seal between fuel cell anode material and Haynes 214 washer [35], The cavity is pressurized to measure the rupture strength of the seal material. 

Certain alloys of iron, nickel, and cobalt (Kovar, Fernico, etc.) have thermal expansion curves which nearly match those of borosilicate glasses, and a good bond may be formed between the two. Kovar is similar to carbon steel in its chemical properties. For example, it oxidizes when heated in air and is not wet by mercury. It may be machined, welded, copper brazed, and soft soldered. Silver solders should not be used with Kovar since they may cause embrittlement. At low temperatures Kovar undergoes a phase transformation, and the change in expansion coefficient below this temperature may be sufficient to cause failure of a glass-to-Kovar seal. The transformation temperature usually is below... 

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