Patent GB-995694-A (GB)
Title: Method and apparatus for making a curved surface
IPC: B29D11/00
Filed: 1963-12-05
Abstract: 995,694. Moulding three-dimenional curved surfaces. COMPUTING DEVICES OF CANADA Ltd. Dec. 5, 1963 [Dec. 5, 1962], No. 48170/63. Heading B5A. In the moulding of curved surfaces, e.g. paraboloidal surfaces, for, for example lenses and radiation reflectors, from liquid plastic material, the shaping is effected by a deformable membrane subjected to liquid pressure. In one example, Fig. 1, a membrane 18 is cleaned and clamped to the open end of a cylindrical chamber 10 and liquid is introduced into the chamber to a desired level thereby providing a pressure head deforming the membrane 18. A mould 23, 24 is filled with a hardenable liquid plastic material and brought into contact with the membrane 18. The membrane 18 assumes a curvature depending on the pressure differential and the apparatus remains in the position shown until the plastic material hardens. The liquid in the chamber 22 is then drawn off and the moulded article removed. It may or not be desirable for the membrane to form part of the finished article and the membrane is treated before assembly to ensure or prevent adhesion. If the curved surface is to be used as a reflector, a reflecting surface, e.g. a thin aluminized film, may be applied to the moulded article. This reflecting surface may be applied to the surface of the membrane facing the plastic material or the pressure liquid, when the membrane is to be part of the finished article, or to the finished curved surface of the moulded article. In an example wherein the mould cylinder is above the liquid chamber, the latter has an air bleed valve so as to prevent entrapment of air, the assembly being pivoted to a vertical position during bleeding and the membrane being protected by a retaining disc. The peripheral clamping of the membrane may be effected by angled flanges to ensure that it is uniformly tensioned. In a further example, Fig. 5, liquid plastic material introduced into a cylindrical mould 67 is provided with opposed curved surfaces by the membranes 69 and 76 under pressure heads in chambers 77 and 80 respectively. The apparatus is mounted for rotation about diametrically opposed bearings 85, 86, and the mould 67 and chamber 80 have bleed valves 81 and 82 respectively. With the apparatus as shown, the mould is filled with plastic material 78 and chamber 80 with liquid, under heads sufficient to fill them, and any air trapped therein is bled from the bleed valves 81 and 82 by rotating the apparatus to bring the bleed valves uppermost. The apparatus is then rotated to its original position and the heads in the chambers 77 and 80 and in the mould 67 are adjusted to give the desired curvature of the membranes 69 and 76. To ensure that the head of liquid in chamber 80 remains constant while the plastic material is hardening, it is provided with constant head means 97, 98, 100, 101. Similar means may be provided to control the heads in the chamber 77 and the mould 67. It is suggested that the plastic material and the pressure liquids may be treated before use to remove any dissolved gases. In Fig. 6, apparatus is shown by which the deformation of the membrane may be measured by the reflection of a beam of light from a reflecting membrane. The light from a projector 108 passing through a window 106, in the base 33a of a chamber, being reflected from the membrane on to a calibrated window 107. Temperature control of the pressure liquid may be desirable and this may be achieved with heat exchange coils mounted within the chamber or chambers. For the production of a paraboloidal surface it is stated that the densities of the liquid plastic material and the pressure liquid should be equal. It is suggested that the curved surfaces produced may be used as moulds for subsequent casting of objects having curved surfaces.