Patent GB-338487-A (GB)
Title: Improvements in the electro-deposition of metals
IPC: C25D5/22
Filed: 1929-05-15
Abstract: 338,487. Coles, S. O. Cowper-. May 15, 1929. Electrodes, moving; preparing surfaces; treatment after electrolysis; copper, nickel, cobalt, and - other metals, depositing. - Metal is deposited on a cylindri. cal mandrel 1, shown in plan in Fig 3, rotated about a horizontal axis at a speed resulting in turbulence of the electrolyte sufficient to break up the film of exhausted electrolyte in proximity to the mandrel. 400 feet per minute is a suitable speed. The deposit is consolidated by rollers or discs 18 which are free to revolve and also capable of a limited movement in the circumferential direction of the mandrel ; the latter movement is permitted by the provision in the rollers of central appertures larger in diameter than the spindle 19 on which they are mounted. The spindle may be provided with a bush and the space between this and the inner circumference of the roller filled with sponge rubber. The rollers may be of glass or metal e.g. ferrosilicon. Grit is removed from the mandrel before passage under the rollers by a wiper 23. The rollers are supported on bars 20 mounted on a pivot bar 21 which is given an axial movement along the mandrel by a cam and lever mechanism not shown, and returned by means of a weight. During the return movement, which may be more rapid, the rollers are raised out of contact with the mandrel by a tipping bar 40 operated by a second cam and lever mechanism. In a modification the pivot bar 21 is stationary and the frame 20 is provided with a pair of halfnuts which rest on one or other of a pair of oppositely rotating threaded rods so as to traverse the frame axially. Transfer from one threaded nut to the other is effected by a rocker mechanism operated by end stops. Semicircular baffles 15 having a portion projecting between the cathode and the mandrel are supported by rods 16 axially adjustable on the bearings 4 of the mandrel which are situated above the vat and are themselves vertically adjustable. The baffles may be of insulating material or of an inert conductor such as lead when it is desired to prevent excessive deposit at the ends; or they may be of the metal to be deposited if thickening at the ends is desired. The bearings 4 are open-topped and are watercooled and lubricated with an electrically conductive material such as graphite. To relieve pressure on the bearings the mandrel may be made hollow and water-tight. The anode 13, comprising a copper casting or sheet or a series of copper bars disposed in arc formation is supported by a cradle 14 which rests on the edge of the cell. A rapidly rotating brush may be passed over the mandrel after a slight deposit has taken place and before application of the rollers. In the apparatus shown in Fig. 8, there are two mandrels 1, 1<a>, each provided with a set of rollers 18 of the type specified, carried by a common frame 60 resting on a pivot bar 21 the frame being tilted on the return stroke of the traversing movement by a tipping bar 40. To compensate for the weight of the rollers 18, a third set of rollers 61 is provided beneath the mandrels; these are supported by a rod 62 sliding through the frame 60 provided with a wing-nut 63 acting against a spring 64. The rod 62 is provided with a collar 65 having an inclined surface engaging a similar surface on a loose sleeve 67 bearing against a fixed abutment 68. At the moment of tilting the frame 60, an arm 69 on the sleeve 57 engages a fixed pin, not shown, thereby rotating the sleeve 67 and depressing the roller 61; the roller is raised in a corresponding manner at the end of the return stroke. The mandrel is preferably of welded steel or iron sheet or cast-iron which is turned and polished. To allow detachment of the deposit in tubular form the mandrel is first made passive by treatment with nitric acid and then polished and treated with a stripping preparation. It may be provided with a transverse groove or an insulating insertion to facilitate removal of the deposit in the form of a sheet or with a helical groove for detachment of the deposit as strip, which afterwards mav be drawn to form wire. A suitable electrolyte for depositing copper consists of a nearly saturated solution of sulphate of aluminium or magnesium to each gallon of which is added 5 oz. of copper sulphate and a volume of sulphuric acid of about the same weight. A current of 100 amps per sq. ft. at 0.8 volts and a temperature of 90' C. are employed. An anode of lead, carbon, ferrosilicon or other inert metal may be employed using as electrolyte a solution or suspension of a compound of the metal to bs deposited. In an example, a concentrated sulphide ore of copper from which any oil has been removed is mixed with 10 per cent sodium chloride solution and the suspension passed through the annular space between the mandrel and the anodes. A current density of 200 amps per sq. ft. is employed. The electrolyte is maintained in a cuprous state. A sulphide ore containing 9 per cent copper, 4 per cent nickel and 2 per cent cobalt is roasted to sulphate and leached first with water and then with 10 per cent. sulphuric acid, the temperature not being allowed to rise above 30' C. The solution containing copper and cobalt adjusted to contain 6 per cent. free acid is electrolyzed at 30 C. with a current density 10 amps per sq. ft. using an insoluble anode: cobalt is deposited on the rotating cathode. When all the cobalt has been removed another rotating cathode is substituted and the current density raised to 30 amps per sq. ft. the temperature to 60 C. and the acidity to 9-10 per cent free acid and copper is deposited. Iron compounds present are crystallized out from time to time. The residual ore after the first acid leaching is again leached with 10 per cent sulphuric acid at 90 C. and the solution electrolyzed for deposition of nickel at a current density of 60 amps per sq. ft. and a temperature of 80 C. Zinc and silver may also be deposited according to the invention. Copper deposited raccording to the invention is stated to have a breaking stress under tension of over 25 tons per sq. in. and a hardness factor of over 100 on the Brinell scale. Specifications 21974/98 and 21568/04 are referred to.