GB409311A - Improvements in or relating to the production of play balls - Google Patents

Abstract

Balls, such as tennis balls, are produced by introducing into hollow spherical moulds predetermined amounts of aqueous dispersions consisting of or containing rubber, gutta percha, balata or similar vegetable resins occurring naturally or artificially obtained, such dispersions being capable of gelling on the application of heat, closing the moulds, subjecting the moulds to rotation about a variable axis and effecting total gelling of the dispersions, such gelling preferably taking place while the moulds are still in rotation. Inflation may be obtained by providing the mould with a one-way valve through which gas at a predetermined pressure can be forced into the mould after closing and before gelling: in another modification the ball without inflation is stored in a compressed gas, subsequent leakage being reduced by treatment with a rubber solution that may also be used to secure a coating of felt or other material; in a further modification the mould is provided with a fine pointed wire carrying a filling plug that is secured to the wall of the ball and through which a hypodermic needle is subsequently inserted to permit air to be forced and also, if desired, a gas retaining p lining, e.g. a mixture of gelatine and glycerine. Substances used for making the dispersions gel on the application of heat are sodium or potassium silicofluoride, ammonium persulphate, or mixtures such as zinc oxide and ammonium sulphate. Specifications 219,635 and 290,313, [both in Class 70], are referred to. In a specific example a latex mixing of the following composition is prepared: rubber (as latex) 87.7, sulphur 1.5, tetramethyl thiuramdisulphide .30, mineral oil 5, lamp black 1, and gas black .5 all in parts by weight; the mixing is cooled to about 5 DEG C. and to each 100 grams of mixing 2.4 grams of 50 per cent zinc oxide dispersion is added with 4 c.cs of a 25 per cent aqueous solution of ammonium sulphate. The mixture is introduced into the ball mould and a capsule of paraffin containing a moist mixture of sodium nitrite and ammonium chloride also inserted; the mould is closed and placed on a rolling machine comprising two cylindrical rollers revolving in the same direction and at the same time moving backwards and forwards in opposite directions along their horizontal axes. The mould after rotation for 15 to 20 seconds is heated by steam for two minutes and after a further period of rotation for one minute is cooled under water and opened. The ball is dried at 45 to 50 DEG C., placed in a mould and heated in a steam pan. The mould is removed, cooled in water, opened and the vulcanized ball removed.