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COUNTERACTING WEAR BY IRON DEPOSITION.

9th March 1920, Page 22
9th March 1920
Page 22
Page 22, 9th March 1920 — COUNTERACTING WEAR BY IRON DEPOSITION.
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Great Progress is Being Made in this Nev Branch of Repair Work.

TNCREASING INTEREST is being

,taken in the building up of worn or under-sized parts by the electric deposition of iron. A considerable amount of this work was done in Fra.noe 'particularly at the large RoAelf. Base Repair Depot. The results obtained were most satisfactory, and thousands of parts, which would otherwise have had to have been scrapped through overmachining or wear, were made serviceable.

During the war several concerns in England endeavoured to apply the process, but in few cases did they succeed. The work requires extremely careful manipulation, and its success depends to a great extent upon the skill of the operators.

The benefits which accrue from the use of this method of rectification and repair, when successfully applied, cannot be over-estimated. Modern production methods to ,ensure interchangeability necessitate the maintenance of The onginal standard dimensions. If for any reason the dimensions of, say, the housings of ball races are exceeded, iron can be electrieklly deposited to the required thickness with perfect adhesion and a surface harder in many cases than the original material. The finish also is such that no further machining is necessary, unless the surface on which the iron is to be deposited is irregular or oval; in that case the thickness of the deposit is increased and the part ground out. We have recently examined some of the work which has been done by Thomas Fry and Son, Ltd., whose works and offices are at 37, Great Pulteney Street,. W. 1. The company are doing a considerable amount of delicate work for instance, many Le Rhone engine crankcases are being made serviceable by the building up of the ball-race housings, thus avoiding the necessity for scrapping valuable, highly machined parts.

The apparatus used for the work is of a very simple nature. It consists of a table on which is mounted a tube running the whole length of the table and supported in bearings; at either side of this tube project shorter tubes to which the anodes are attached. An electile motor of .h.p. operates a cam, by which n slight see-saw motion is given to the anode shafts.

The part on which the work is to be performed has to be very carefully prepared. Say, for instance, it is a bail-race

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housing, with a hole through its centre. To begin with, a Sheet...iron disc of a suitable size is placed over the hole; bees wax is then run over this disc and over the whole of the interior of the housing with the exception of the surface on which the deposit is to be made. Around the exterior of the housing is fitted a sheet-iron collar, this also being well bees' waxed. .

Before bees' waxing, the worn or undersized surface must be mechanically cleaned, and after the waxing it most be chemically cleaned by an electrolytic method. A copper anode is employed and the housing is filled with cyanide of potassium solution. The part to he cleaned is first connected up for two or three minutes as the anode. The. current, which has an E.M.F. of four volts, is then reversed, and the housing becomes the cathode. This action removes all grease and leaves the exposed surface chemically clean-.

The solution is then removed and the housing swilled out with water and filled with a copper cyanide solution, a thin film of copper being then deposited. This copper film has a thickness of .00325 in. The current employed for the deposition of copper is 15 amps. per sq. ft. The housing is again washed with water and afterwards filled with a special iron solution and pure iron deposited, using an iron anode and a current with an E.M.F. of one volt.

During all three operations the solutions are kept in constant agitation by the motion of the anodes.

The present plant permits of 20 parts being operated on at the same time. The

rate of deposit is fixed at .001 in. per hour. It is possible to build up to a thickness of .125 in., but this must be done by depositing alternate layers of copper and iron. With one layer only of copper and one of iron the building up can be safely taken to .005 in.

An interesting point is that housings, etc., need not be measured in order to ascertain the thickness of the deposit ; for instance, a part may be sent in with a request to reduce the diameter of a. housing by .002 in. Depositing in this ,instance is carried on for two hours. For depositions of iron at the atasidard rate the current consumed is 5-10 amps. per sq. ft. The surface obtained is wonderfully smooth, and though only iron is deposited, yet the result is ashard as 70-ton steel, owing to the presence of hydrogen in it. The main voltage used at the works is 220 but this is reduced to 5 by a converter. It is then further reduced to the E.M.F. required by resistances. The instrument beard carries a. voltmeter and an ammeter, which measure the current used over the whole 20 sets. Each set has to have its own resistances adjusted to suit the part on

W hich work is in progress. In future, by the addition of further plant, the company hope to be able to deposit iron direct on to steel parts which require subsequent heat treatment and hardening. Up to the present the iron deposits, whilst suitable for the purposes which we have enumerated, and for light 'Dearing surfaces, are not sufficiently hard for heavily loaded bearings, therefore this is a development which will be watched with much interest.

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