Improvements in electric furnaces
Реферат: 198,898. Wild, L. W., and Barfield, E. P. May 22, 1922. Resistance furnaces.-In an electric furnace a having heating elements consisting of rods, bars or plates of carborundum, b, the electrical connection to the heating elements is made by carbon rods c pressed against the carborundum by the action of gravity or springs so that the contact is automatically maintained as the carbons are consumed. The elements are made by fritting crushed carborundum crystals without any bonding material. Such elements are stated to have a specific resistance of 0.8 ohms per centimetre cube at 1400‹ C. In modifications, the heating element is situated in the roof of the furnace chamber and comprises a single plate or separate bars on either side of the chamber. Starting up is effected by applying an initial voltage many times greater than the normal, the supply being obtained from a transformer having suitable tappings. If a number of heaters are used starting up may be effected by first connecting them in parallel, then parallel series and finally full series. Alternatively the heating elements may be initially heated by a rod wound with a nickel chrome wire, or by the flame from a gas or liquid fuel burner. Stability of current and temperature is obtained by including a ballast resistance or choking coil and a regulating resistance in series with one or each of the heating elements. The ballast resistance may take the form of a wound muffle furnace used for preheating the work.
Improvements in or relating to Electric Furnaces.
Номер патента: GB191015168A. Автор: John Thomson. Владелец: Individual. Дата публикации: 1911-02-09.