Abstract
THE construction recently of 62-in. searchlight reflectors at the Bart Laboratories, New Jersey, shows, according to the Electrical Review of April 11, that satisfactory progress is being made in modern electro-forming methods. An electro-formed nickel-surfaced mould is first of all made and a coat of nickel 0-003-0-005 in. thick is applied to the outer passivated nickel face. Then follows a coating of copper, to which a pre-formed bronze ring is applied, and the assembly is given a heavy deposit of copper. These firmly bonded layers are stripped from the mould in the form of a bi-metal reflector with copper on the convex face and nickel on the inner polished face. To prevent the introduction of copper into the rhodium bath, a protective mask is fitted on the copper side. The reflector is now ready to receive its rhodium-plating, and in this instance a ‘flash’ of rhodium 30 millionths of an inch thick appears satisfactory.
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