Patent GB-1115221-A (GB)
Title: Manufacture of asbestos products by electrophoretic deposition
Inventor: HERON GORDON FREDERICK
IPC: C25D1/12
Filed: 1963-05-28
Abstract: An anionic aqueous dispersion of asbestos fibres, with or without other constituents, is passed between two electrodes across which a voltage is applied whereby solid constituents of the dispersion move towards the anode and are deposited on the anode or an ion-permeable membrane in the path to the anode, and the deposit is continuously removed from the dispersion. The dispersion may also contain a water-soluble soap so that if the anode is of a metal that corrodes during the process a water-soluble soap is also included in the deposit thereby improving its wetstrength. To maintain the composition of the dispersion constant, the dispersion which is preferably continuously or periodically circulated in a separate circuit through a reservoir from which dispersion is fed by a metering pump to and through the electro-deposition bath is replenished periodically or continuously, e.g. with undispersed constituents which are dispersed by a pump in the reservoir circulation.  The solid constituents of the dispersion may be chrysotile asbestos alone or with fibres of amosite or crocidolite or undispersed chrysotile asbestos, slag wool or chopped glass fibre rovings and/or synthetic rubbers, thermoplastic resins such as polythene, polyvinyl chloride, polystyrene or polyester resins, thermosetting resins or mixtures thereof and/or finely divided particles of graphite, colloidal silica, clay or bentonite, the latter acting also as a subsidiary dispersing agent.  Examples of anionic dispersing agents are alkyl aryl sulphonates, alkyl sulphosuccinates or sulphated higher alcohols.  Corrodible anode metals specified are Al, Zn, Cu, Pb or Fe while non-corrodible anodes of Pt or carbon may be used.  As described an asbestos tape with good wet strength is formed (Fig. 1) by withdrawing the anodic deposit formed on one wall of a box comprising two aluminium sheets separated by insulating block spacers, the dispersion which includes soap being fed in through the bottom block which is hollowed out for the purpose and provided with a removable door for access for cleaning.  Excess dispersion passes out of the top of the box over a weir on the cathode side while acid generated adjacent the anode passes out over a weir on the anode side.  In another arrangement (Fig. 3), the anode is a drum with insulating side cheeks rotatable about a horizontal axis over a concentric part cylindrical cathode cover by a nylon cloth diaphragm which prevents cathodically evolved gas from entering the body of the dispersion.  The dispersion is fed in over a weir to pass between the cylinder anode and the cathode diaphragm, the deposit is withdrawn vertically from the drum as a tape, and the excess dispersion overflows a weir on the exit side of the drum together with acid formed between the deposit and the drum and escaping around the tape formed, while cathodic alkaline liquid is separately withdrawn from between the curved edges of the diaphragm and cathode.  The tape withdrawn may be twisted or slit and then twisted to form a yarn. Instead of a drum, the anode may be an endless metal belt (Fig. 4) which carries the deposit out of the bath and through a drier before the tape is stripped from it. A tubular deposit may be formed on a rotating anode of tapered form (Fig.5), the deposit collapsing into a tape and being twisted on withdrawal and thus formed into a yarn. Asbestos-coated copper wire may be formed by feeding bare wire as anode through the waxed cork bottom of a tubular plastic container provided with an internal aluminium cathode surface (Fig.6). An asbestos coating may be formed in a similar way on a graphite coated paper strip.