Patent GB-316596-A (GB)
Title: Improvements relating to gramophone records
IPC: G11B3/70
Filed: 1928-04-27
Abstract: 316,596. Cooper, W. F. April 27, 1928. Moulding gramophone records. - An annular conical record of hard composition with a deep groove is made by forming a matrix from an original record, impressing the composition into the matrix, and separating the record and matrix by cooling and shrinking. The diameter of the record is preferably 10 inches or more. For the production of the matrix by electrodeposition, the original wax record may be clamped between rubber pads 3, Fig. 9, or paraffin wax, backed by ebonite plates 1, 2 drawn together by ebonite bolts and nuts 6, 7. The plates 1, 2 have large central holes to allow of rapid sinking in the electrolyte, or, as shown, the central holes may receive a shaft, insulated from the electrolyte, so that the mould can be rotated during deposition. Contact with the plumbago coating may be made by a loop of wire 8, the ends of which are lightly twisted together, or by a ring of copper foil placed on one of the rubber pads and dusted with plumbago, the matrix then being formed with a flange. When the mould is rotated, it may be supplied with current by a brush extending the full width of the metal. Before the coating is complete, one or more copper strips may be placed against it so as to become embedded. A layer of nickel may be deposited before the copper. For separation of the matrix from the original record and subsequently from the reproductions, there may be employed a cooling device as shown in Fig. 4. This comprises a box 10 and lid 11 lined with slag wool 12 or the like and an inner chamber with two annular partitions 15, 16 between which the record &c. can be placed, the inner and outer chambers separated by the partitions containing brine or calcium chloride solution, in which coils 17, 18 are immersed. Carbon dioxide or other cooling medium is passed through the coils. A ring 19 of asbestos or the like supports the record. Cooling may be effected to -10‹ or -50‹ C. when deposition is done at ordinary temperatures; if deposition is at higher temperatures less cooling may suffice, especially with large records. For small ones it may be necessary to use solid carbon dioxide or liquid air. After separation the matrix may be backed with type metal, say from “ to ¢ inch thick for a matrix from <1>/32 to <1>/16 inch thick. A spirally-coiled tube may be cast in the backing, for the subsequent passage of a cooling or a heating medium. The backed matrix is placed in a conical pan 30, Fig. 5, widened at 33 for ease of insertion &c. An outer jacket 31 is shown, but may be dispensed with when the matrix itself is provided with the embedded coil. The bottom of the pan is cut away centrally. A ring 36 supporting the matrix rests on spacing blocks 37 on the bottom of the pan, and a ring 35 is placed over the matrix, within which is a truncated cone of moulding composition 38. There is then inserted a hydraulic press shown in Fig. 7. A central chamber 60 in the press is partly filled by a block 61 and opens into radial cylinders containing hydraulic pistons 45, which have reduced outer portions 53 to allow them, after being forced outwards, to be returned by hydraulic pressure applied through a circular row of passages 54. Theses passages terminate in a tapering groove 55 closed by a tapering ring 56. Conical segments 46 are attached to the outer ends of the pistons by means of pins 52 passing loosely through holes in projections on the pistons which fit loosely within recesses on the segments; thus the divergence of the two rows of radial pistons attached to each segment is allowed for. The segments have overlapping flanges, and the residual gaps between them are covered by their steel strips. The matrix and composition are heated before expanding the hydraulic press. The record may be provided internally with labels, or with a lining of felt or strengthening material.