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From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
The method for chromium plating car cylinder bores for a 6-cylinder Bentley block.

Identifier  ExFiles\Box 132\4\  scan0239
Date  16th October 1939
  
This is a Copy

Rm{William Robotham - Chief Engineer}/Mr.Salt. HL./EA. 1/JM.{Mr Morley} 16.10.39. Laboratory.

Chromium Plating of
Car Cylinder Bores.

For your information details are given below of the method employed in carrying out the above operation on the 6 cyl. Bentley block. Will you please treat these as confidential at the moment.

Preparation of the Block.

The block is degreased, preferably, but not essentially, in a Trichlorethylene degreaser.

The cylinder bores are wiped well by hand, using a cloth, wetted with water and sprinkled with pumice powder. This is particularly necessary to remove slight carbon deposit if the block has been run.

The special insulated anode jig (EJJ's drawing No: J21402) is bolted on the block top joint face. This jig contributes largely to the success of the job, as it is designed to give even current distribution, and the anodes are adjustable so that any desired length of the cylinder bores can be plated. In the case of the blocks already plated, the projection of the anodes into the bores was 1 3/4".

The whole assembly is then lowered into the plating solution, by means of a pulley, until the top joint face of the block is approx. 1" under the solution. Suitable connections, previously fixed to the anodes and to the block, are securely fastened respectively to the anode and cathode bus bars of the vat. During this operation the current supply to the vat is cut off.

Plating is carried out as follows:-

Solution - Chromic Acid 250 grammes/litre.
Sulphuric Acid 0.037N.
Temperature - 53/55 degrees C.
Current - 600 amps.
Time - 30 minutes.

Afterwards the assembly is removed from the vat, the jig disconnected and the block thoroughly washed in running water, particularly the water passages. It is then dried off in boiling water and the bores are immediately wiped with a cloth soaked in neat soluble cutting oil, to prevent rust.

Hl/EA.
  
  


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