GB566927A - Improved method of and means for heating articles in a high frequency electric field - Google Patents

Abstract

566,927. Electric induction heating. JABLONSKY, B. May 14, 1943, No. 7712. [Class 39 (iii)] A die 1 is fitted with an electrode 3 and a die 2 with electrodes 4, 5, 6, each with a separate connector so that three separate fields can be produced when high-frequency potential is applied to the electrodes. The electrodes 4, 5, 6 can be fed simultaneously or successively by the same generator or by individual generators. The article heated between the electrodes may be a laminated air-screw blade constructed as described in Specification 563,900, [Group XXXIII], and the areas of the electrodes can be selected in relation to the material and its thickness so that the capacities are approximately equal. The periods of connection are so chosen that sufficient heat for bonding the material is generated in each section, i.e. longest for electrode 4. Connection may be effected by hand or automatically, and sparking at the change over may be reduced by reducing the voltage or interrupting the current in a low voltage circuit of the generator. A change-over mechanism may comprise a movable contact arranged to connect the electrodes 4, 5, 6 consecutively to a counter contact while it is shifted along an insulated threaded spindle. Contact for the electrode 6 is longest and for the electrode 4 shortest. The frequency can be suited to the loss factor of the material, a higher frequency being applied to portions having a lower loss factor. Specification 563,912, [Group XXIII], also is referred to. The Provisional Specification describes the heating of various parts of an article by moving an electric field along it. A short coil may be moved along a steel shaft or over a steel surface, for hardening it, while for non-conductors two movable electrodes arranged on opposite sides and energized by a high-frequency supply may be moved over the article, or one of the electrodes may be stationary and larger, e.g. the size of the article. The electrodes may be moved by hand or mechanically, and their speed may vary with the cross-section of the article. The article may be compressed between dies faced with conducting zones or condenser plates, which may be energized in succession by a moving member rolling or sliding over them. The width of the conducting zones and spaces may be varied to control the heating effect. The article treated may be of bonded laminated fibrous material, the binder being a natural or synthetic glue or resin, which may be chosen to influence the intensity of the high-frequency field.