GB391230A - Improvements in or relating to a process for the production of casting moulds of rubber - Google Patents

Abstract

391,230. Rubber moulds for reproducing sculpture &c. ANODE RUBBER CO., Ltd., 10, Lefebvre Street, St. Peter's Port, Guernsey.-(Assignees of Magyar Ruggyantaarugyar Reszvenytarsasag, Budapest.) Oct. 27, 1931, No. 29759. Conven. tion date, Dec. 6, 1930. [Class 87 (ii).] Sculptures &c. are reproduced by the use of rubber moulds formed by coating the model to be reproduced in one or several operations with one or more layers of an aqueous dispersion of rubber, guttapercha, balata, &c. and removing water from the rubber-containing layer or layers. The remaining coherent rubber layer may be vulcanized on the model itself. A liquid of small viscosity may be used for the first layer, subsequent layers being of greater viscosity, and after a desired thickness has been thus reached, raw or pre-vulcanized rubber sheets may be applied to complete the mould wall. The aqueous dispersion may be applied by spreading, dipping, spraying, casting, electrophoresis, &c., and may contain known compounding ingredients and may be in concentrated form. Aqueous dispersions or emulsions which can be rendered capable of gelling on the application of heat or to which substances can be added to cause the emulsion to gel in the cold after a definite and controllable time interval may also be used. A model 1 may be placed on a gypsum base 2 and coated with successive layers of the aqueous dispersion, the base 2 having an annular recess to form a positioning rib 3 on the mould part 4. A gypsum cover 5 is then applied, the base removed and the cover and mould inverted. Aluminium or graphite paste to prevent adhesion is applied to the border of the mould and aqueous dispersion is then applied to the exposed upper surface of the model and a gypsum backing applied. The rubber is then vulcanized and the gypsum backing and model removed bearing the two part mould 4, 4<1>, Fig. 5. Casting moulds consisting of only one part or of more than two parts may also be made. According to a modification, a box of wood or plaster of Paris may be charged with aqueous rubber mixture which may be frothed and which, under the influence of coagulant, e.g. sodium silicofluoride, sets within a controllable time interval. The model is partly dipped into the mixture and maintained in position until the rubber dispersion solidifies, after which the rubber is vulcanized. The box is then removed. Subsequently, the other part of the model is similarly treated. Specifications 332,525 and 332,526, [both in Class 70, Indiarubber &c.], are referred to.