GB1108523A - Improvements in and relating to astronomical reflectors - Google Patents

Abstract

1,108,523. Moulding reflectors; laminates. Z. HERPAY. 17 March, 1966 [19 Jan., 1966], No. 2404/66. Headings B5A and B5N. [Also in Division G2] A method of constructing an astronomical reflector, comprises the steps of using a silversteel, glass or other rigid tool to make a base having a surface of complementary shape to that desired for the final reflector and having an accuracy at least equal to a wavelength of the light used with the reflector, stretching a refleeting film or skin over the base, depositing a multiplicity of separate backing layers on the film or skin, each layer being deposited in the form of a liquid or plastic layer after the preceding layer has set rigidly, at least one of the layers having reinforcing fibres therein, finally placing thereon a prefabricated rigid skeleton and then removing the finished reflector from the base. The base may consist of a brick foundation on which thin layers of thixotropic material, such as blue ball clay or china clay are deposited, then layers of gesso provided with a French polish and finished with two or three coats of shellac, each coat being sandpapered under the guidance of the rigid tool. The surface is brought to the required optical precision using several silicone layers as varnish. A thin polymeric reflective film on a ring is then stretched on this base and a very fine layer of epoxy resin mixed with a hardener and accelerator applied to the film. When set, this secures the reflective film without much shrinkage and successive layers are then sprayed on, which are somewhat thicker and incorporate glass fibres and asbestos as fillers. The prefabricated skeleton which is adhered to the last layer by a glass and asbestos filled silicone modified epoxy resin is a honeycomb structure. In modifications the backings are formed of Portland cement, cast polyester reinforced with powdered steel and fired ceramic.