GB757338A - Improvements in or relating to catadioptric lenses - Google Patents

Abstract

757,338. Making moulding dies. ELASTIC STOP NUT CORPORATION OF AMERICA. Aug. 18, 1953 [Aug. 22, 1952], No. 22748/53. Class 83 (2). [Also in Groups V and XI] A die for moulding (see Group V) a circular catadioptric lens (see Group XI), e.g. of thermoplastic, comprises two separable blocks 44, 46 for mounting in an injection or die-casting machine for movement to and from each other, with a gate opening 52 for injection of the material into the space 50 between the blocks. Block 44 comprises a part 54 with a highly polished spherical surface 56 forming the lightemitting face of the lens and surrounded by a part 58 with a die surface 60 forming the flange portion of the lens, the block 44 being preferably in separate parts 54, 58 for facilitating forming the surfaces 56, 60. Block 46 comprises a baseplate 62 to which is rigidly fixed a central core 70, as by a screw stud 78, and closely fitted telescoped tubular elements 72 held in fixed axial relation to each other and to the core 70 by a dowel pin 74, the end faces of these elements being shaped to produce the central portion of the lens and surrounding these elements are the closely fitted, telescoped elements 64, the upper ends of which are shaped to produce the catadioptric elements of the lens, these elements being held against axial displacement by dowel pins 76 and the group of elements 64 being secured to the base 62 by the shortened outer one of elements 72 clamping down on a thickened base portion 64a of the innermost of the elements 64. An outer die element 80 seats against a shoulder 82 of the outermost of the elements 64 and provides die surfaces 84 for the marginal flange portion of the lens. The member 80 has axially extending bores 86 registering with the flange portion of the die cavity 50 and receives stripping pins for stripping the lens from the face of the die block after the mould is opened. Preferably, the die surfaces 66, 68 when required to produce diffusing lens faces are first precision finished to the desired area contour and highly polished and the highly polished face then subjected to a liquid honing operation or the polishing operation may take place after the honing operation to remove the tops of the myriad of projections so that in the moulded lens they form " valleys " or depressions of polished non-diffusing refracting surface areas interspersed by raised roughened diffusing refracting surface areas.