BETTER GLOW-PLUGS
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DiFFICULT1ES in the manufacture of insulating material for glow-plugs are mentioned in patent No. 876,300 which proceeds to describe an improved material and method. (Robert Bosch G.m.b.H., 4 Ereitscheidstrasse, Stuttgart, W. Germany.)
The central electrode forms one terminal, and a tubular member (1) the other, the filament being connected across them.
Both electrodes are insulated from their surroundings by layers shown in dotted lines at 2 and 3. These consist of a sprayed-on coating of ceramic material which is then fired. This provides the
actual insulation, but to ensure gastightness a softer material, such as talc, is applied on top of the ceramic. This, when pressed into assembly, can deform to accommodate irregularities and so create a seal. The ceramic is also appliei exposed portion (4) where it combustion products adhering.