Developments in
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The Finishing of Metals
Plating, Lacquering, Colouring and Rust-proofing Among the Different Treatments that are Discussed and Analysed by a
Metallurgical Authority
THE days when metal had to be finished to resemble wood as closely LS possible are over. To-day, metal is ;iven a variety of finishes, each pos,essing distinctive advantages and none neventing the metal from looking like
netal. The importance of finish is )eing increasingly recognized as a sales eature. in both the general and the ;ommercial automobile fields.
One development worthy of mention s the commercial plating of steel with durninium, producing a finish which is >oth resistant to rust and capable of vithstanding a high degree of heat. Intil quite recently, this class of platug was only a laboratory process. The flectrolytic deposition of copper on tee is another process which is being isecl to a growing extent. New lectro-galvanizing processes for the leposition of zinc have also been ntroduced.
An invention that is bound to have important repercussions on the finishng of parts is the Schneider method of providing a non-conductive surface vith an extremely thin film of a conflicting substance, which enables lectro-plating to follow. The confactor employed is a special solution; -his is blown on by a compressed-air lin with two converging nozzles, so hat two solutions impinge, at the ame time, on the surface to be
prayed. The special solution turns olid the moment that it strikes the urface, and spreads out to constitute thin adhesive layer—said to be about ,000,000th of an inch thick.
The Plating and Lacquering of Die Castings.
The fufishing'of die castings has been reatly improved. Jr. the United tates it has already been found posble to plate zinc-alloy die castings ith nickel and chromium in such a ay that ordinary weather conditions m be resisted for a relatively long eriod. For example, radiator grilles ave been manufactured as die castigs, because of the ability to give hem a nickel-chromium plating, with lich has been effectively combined an narnelling treatment.
Bare die castings have also been sacassfully lacquered by giving them a reliminary cleaning treatment, the ffect of which is to modify the surface I the zinc alloy by a moderate etchig, accompanied by the deposition of ertain metallic salts.
Again, there has been discovered a ew chemical process for colouring teel. It is claimed that a brilliant
black can be obtained by merely lunging the steel in a bath at a rein-. .vely low temperature for a period of pproximately five minutes. The bath self is of welded steel, and contains ,ater in which certain salts have been E48
dissolved. Steam, gas or oil is used to heat the bath to about 95 degrees C.
One interesting point is that this black finish is not in any way a deposit or thickening of the metal, the size and thickness of which remain unaltered, but constitutes an integral part of the steel itself. The colour can be given to surfaces that have been subjected to a high degree of polish.
Bright nickel-plating is another process which is increasing in employment, and has made great strides. It furnishes so great a contrast with the former electro-galvanizing process, in which zinc figured, that it has become a great favourite in industry. De posits up to in. thick, and having a great brilliancy, can be obtained. By its aid buffing can be dispensed with. The deposit can be heat treated.
A New Coating Process.
A new process of coating steel and a number of base metals has found its way into commercial use. Here, again, the compressed-air gun is employed for spraying the metal to be treated with aluminium or whatever suitable metal is used for coating. When the coating is complete, the part is given a heat treatment to ensure complete union between coating and surface.
Two methods of chromium plating, which do not infringe current patents, are in existence in England. In one, a secret salt is added to chromicacid, producing a liquid having better " throwing "power than has previously been found possible. The second method is called brush plating ; the brush employed closely resembles the type used by painters, but it has a metal anode in the centre of the bristles. A jelly like solution of chromic acid is employed.
An electrolytic means for the treatment of steels and other metals, known as the Webb rust-proofing process, has recently beer; introduced, and has as its objective the protection of these metals against corrosion. The feature of the method lies in coating or " im pregnating," as it is called. the parts to be dealt with, with an alloy.
In the fabrication of semi-finished steel, descaling of the billets is an essen tial process. A new and extremely easy way of achieving this has been invented, and consists in the use of a specially constructed gas-burner which throws the flames against the surface of the billet.
The heat lifts up the scale formed by the original heating of the billet, after which compressed air is employed to blow awa_.y this scale, leaving a clean surface. Water has also been used for a similar function, use being made of a high-velocity jet, a hydro-pneumatic accumulator, and a pump.
The Electrical Engineering Department of the University of Michigan has brought out an improved process for electro-plating non-corrosive chromium on Other metals. The inventor is Dr. Schneidewind, who uses complicated organic. chemicals to secure the necessary " spreading " effect for the elec tricity. With the chemicals in the electro-plating bath, the electric current no longer coats only the high spots, hut also plates the hollows.
Etching on Metals—A New British Apparatus.
An English concern has produced a simple and useful apparatus for etching on divers kinds of metal. Current for working it can be had from a.c. mains, or a battery. A static transformer is enclosed in a metal case, and one of the secondary terminals is united by a clip to the metal, upon which letters, figures or words are to be engraved.
The other terminal is joined to a "pen," made up of a light holder with a stylus point at the end. When the point is brought into contact with the metal surface to be engraved it vibrates, and an intense spark is created between the point and the metal, the vibration being caused by a small solenoid within the holder. ' After a little practice, letters, figures or words can be etched on the metal ,and the depth of the etching can be controlled.
A new preparation for the protection of aluminium which, at the same time, furnishes a base for paint, lacquer or enamel finishes, has been produced by a British concern. It is manufactured in powder form and is a mixture of several chemicals which, when dissolved in boiling water, forms a solution and reacts quickly upon aluminium, converting the surface into a non-metallic film of complex basic oxides, which is highly resistant to corrosion.