Vacuum-molded ceramic fiber electric radiant heating unit with resistance heating coils internally free of fibers

摘要

A vacuum-molded electrical radiant heating unit having a resistance heating coil embedded in a ceramic fiber body is prepared by a process in which a resistance heating coil (5) is placed on a sieve-like tray (1), above a suction box, and a slip is applied thereto composed of ceramic fibres, so that a ceramic fibre layer (4) builds up under the action of suction. Portions of the sieve-tray (1) are closed, in regions beneath the resistance heating coil (5) by means of spacing strips (11). These strips, which cover some of the perforations in the sieve-tray (1), are placed beneath the resistance-heating coil (5), in a manner such that the impervious regions of the sieve tray (1) are narrower than the width dimensions of the heating coil (5). These measures lead to the result that the space (8) inside the heating coil (5) remains free of fibre material during the vacuum-moulding operation, so that the temperature difference between the radiating side (6) of the heating coils (5) and the rear side (7), which lies within the composition forming the fibre block (4), is smaller than in conventional heating units of this type, in which there is a risk of crystallisation of the fibres forming the fibre block (4). The use of spacing strips (11) produces retaining webs (12) on the radiating side (9) of the fibre block (4), which ensure that the heating coils (5) are securely anchored.