Pointers on Chromium Plating
Page 57
If you've noticed an error in this article please click here to report it so we can fix it.
Some Notes Made During a Tour of the Wellequipped Premises of The Harris Plating Works, Ltd.
THERE is far more in chromium plating than is thought by those who have nortried to overcome the difficulties which confront the beginner ; even such well-qualified platers as Messrs. E. W. Harris and A. Pranks, the partners in The Harris Plating Works, Ltd., of 12, Glasshouse Yard, London, E.G 1, studied the subject for more than two years before adding this department to
the company's works. They actually visited America to obtain details of the latest practice, and now they can be counted as amongst the most successful operators in. the industry.
We recently spent several hours at the above works, where we saw a huge number of parts in course of treatment, these including radiators, bumpers, Tedalemit grease guns, A.A. badges, licence holders, mascots, etc.
In chromium plating, grease is the deadliest enemy, and all parts must be taken completely to pieces before treatment, this even applying to radiators. After cleaning and polishing, small work is wired on to a thick copper frame or cradle, which prevents small articles from being " burned," i.e., over-plated. _ After wiring 4, the ,parts are hung., in
caustic-soda or cyanide, and sulphuric acid baths to clean off the grease. All old plate must, of course, be removed, the deplating being effected by reversing the polarity of the current. Many articles are ground and all are polished before plating.
It is not essential to copper-plate first, but parts must always be nickelled. Curiously enough, iron and steel stand up better than anything else to chromium plating.
For chromium work, the nickel deposit must be thick and homogeneous and every hole must be plugged, otherwise there would be no chromium deposit for about a in. around it. The current must be carried practically all the way to the metallic surface, consequently the anodes have to be jigged to follow the contours of the articles. Grid anodes insulated by glass beads are employed for cylindrical articles.
Chromium objects to going into corners, and the more acute the angle the closer must be the anode. The
metal will, not go into cracks, and there must be no crevices for gas to enter. Cracks and joints should be soldered.
With iron and articles of fine quality the copper plating to 1-64-in, depth takes 24 hours, and the nickel plating one hour. The chromium requires 150 amps. to the square foot, and is deposited very rapidly. Chromium for ornamental purposes must be deposited heavily or it " spangles."
Anodes made 'Of mere bits of wire, as used in ordinary plating, are not sufficient. They must be very heavy conductors and insulated, except where the articles are attached, so that as much metal as possible is deposited actually on the articles. A chromium plating tank 6 ft. by 3 ft. by 3 ft. requires 3,000 amps., compared with the 250 amps, required for nickel.
The best ehromic-acid solution so far found is a German product. The fumes are collected and condensed.