Patent GB-299071-A (GB)
Title: Improvements in the method of and apparatus for electrolytically depositing metal onthe interior of metal tubes
IPC: B28B21/12
Filed: 1927-04-22
Abstract: 299,071. Martin, F. G., and Ramsay, W. April 22, 1927. Electrodes; cells; electrolytes, cooling; chromium, depositing. - In coating metal tubes internally, flexible anodes are employed and are maintained in a central position by tensioning means which do not stress the tubes themselves. The invention is particularly applicable to the internal coating of long and narrow tubes such as condenser tubes with chromium. The end parts of the tubes may also be coated externally. In the apparatus shown in Fig. 1, the tubes a pass through tapered holes in a ring f, in which they are secured by split collets a<1> and nuts a<2>; the tubes also pass through guiding apertures in lower rings g. Alternatively the tubes may be secured by split collets a<3> entering tapered holes in one of the rings g no nut being necessary in this case. The lower end of each anode b is formed by knotting or otherwise with a button b<1> over which is fitted a tapered bush h<1> adapted to engage a tapered aperture in a ring h. The anodes are secured near the top by set-screws n<2> in insulating collars n<1> which are pressed upwardly by springs n abutting against insulating bushes e<1> set in a ring e. The flexible anodes may be of stranded copper cable highly compressed and covered with lead, or they may be of steel not covered with lead. The anodes may have rigid ends b<2> consisting, for example, of steel sleeves passed over the cable to assist threading through the tubes. The rings d - - h are mounted with spacing washers l on bolts i, formed with rounded ends serving as feet on which the frame so formed rests in the tank k. The top ring d which is smaller than the rest is provided with outwardly extending clips d<2> engaging the anodes b and also rods c supporting external tubular or ring-shaped anodes c<1>, c<2>. The ring d is provided with a terminal post d<3> and is insulated from the bolts and spacers l by washers d<1>. An extension o of one of the bolts i serves as negative terminal. The tank is provided with a cooling pipe or coil u. The ends of the tubes a may be provided with vulcanite caps v, Fig. 7, having apertures w for the passage of the anodes and apertures x for the circulation of electrolyte. Alternative methods of mounting the tubes and anodes on the rings and the rings on the bolts are described. In one modification, Fig. 3, the supporting and guiding rings &c. are replaced by horizontal bars f, g, h supported by end bars p. The frame is surmounted by a hood r connected by a pipe r<5> to a fan for the withdrawal of gases. The negative terminal r<2> is secured to the hood. The anodes b are secured in screw-threaded sleeves t and are tensioned by means of nuts t<1> abutting against a bus-bar s separated from the top of the hood r bv washers r<1>. The lower ends of the anodes are provided with lead covered buttons q. The external anodes c are also secured to the bus-bars s. The vertical part of the external anodes may have a steel covering; the rings may be of copper covered with lead. Means may be provided for supplying current to both ends of the flexible anodes. The tubes, mounted in the frames, may be pickled by dipping in waste chromic acid with or without sulphuric acid before plating and washed after plating, suitable lifting means being provided. When coating brass tubes with chromium, the frame may be lowered into the plating bath before the current is switched on; when iron or steel tubes are to be coated, the current should be switched on before immersion. Specification 299,100, [Class 64 (iii), Surface apparatus &c.], is referred to.