Publication: Electrical Review
New York, NY, United States
Lava for Mechanical and Electrical Purposes.
The accompanying illustration shows a number of parts made up from the well-known material which has been designated as "lava." This material is not, as is frequently supposed, a natural product of volcanic origin. It is a material talc which has been machined in its natural condition and then baked under certain conditions of time and temperature until it has become thoroughly hard.
The material, being baked at a temperature of 2,000 degrees, is unaffected by subsequent temperatures short of that heat. This material fuses with difficult under a strong blast flame, and has exceptional stability under the electric arc. It is only slowly dissolved by hydrochloric acid, and is not easily affected by other acids or alkalies. It is free from metal oxides or other impurities, which promotes its insulating value.
The material, before being baked, is sawn, milled, drilled, turned and threaded in much the same manner as brass, and with practically the same character of tools. For most work and for pieces of bulk, the method of baking is much the same as with porcelain, where coal and coke ovens are used; while with pieces of moderate size, and especially where close control of temperature is desired for the purpose of extreme accuracy and uniformity, the electric furnace or gas blast furnace is employed.
Under tests for dielectric strength, made with transformers of large capacity, and with carefully calibrated electrostatic voltmeters, this material has demonstrated a uniform ability to withstand high potentials. Its dielectric strength is expressed as from 75 to 250 volts per thousandth of an inch thickness, depending upon the absolute thickness of the sample tested.
This material is being placed upon the market by the American Lava Company, Chattanooga, Tenn.