GB537688A - Improvements in and relating to the production of laminated fibrous material - Google Patents

Abstract

537,688. Synthetic resin compositions. GONDA, D. Dec. 27, 1939, Nos. 32874/39 and 1220/40. [Class 2 (iii)] [Also in Groups VIII and XI] A compound sheet material is made by treating a plurality of fibrous sheets with a thermo-setting synthetic resin, one or some, but not all of the sheets being perforated, superposing the sheets so that cavities are formed by the perforating, filling the cavities with thermo-setting synthetic resin and uniting the assembly by heat and pressure. The fibrous sheets may be of paper, cardboard, cellulose pulp, fabric or asbestos and the synthetic resin may be a phenol-, cresol- or urea-formaldehyde resin. The synthetic resin used for filling the cavities may contain a filler, e.g. paper, asbestos, textile or wood fibres, silica or mica. The structure may comprise an imperforate sheet 7, Fig. 3, between perforated sheets 9, 10 with outer imperforate sheets 6, 8. The perforations in sheets 9, 10 may be staggered in relation to one another. The cavities formed by the perforations may be of different axial section. The product may be used in making an electrical heating unit (Figs. 9, 10) in which the resistance wire 64 is wound in a flat helix on strip 63 formed from sheets of fibrous material impregnated with synthetic resin similar, but perforated, sheets 65, 66 are arranged on opposite sides of the strip 63 and together with further superposed sheets 69, 70 enclose terminal bars 67, 68. The apertures formed by the perforations are filled with synthetic resin having a filler of powder or flake mica and imperforate sheets 71, 72 form exterior surfaces. Terminal bars 67, 68 of adjacent elements are interengaged in a rabeted portion 73 and a terminal box 74 is provided on one element.