Monday, April 7, 2008

Resizing of Nickel Plating

The long standing British practice of building up worn or mismachined parts by heavy nickel plating is in use in this country on a modest scale, particularly in connection with maintenance of trucks, buses, and airplane. There is nothing unusual about the nickel plating operation itself, the bath being selected to give deposits of the desired mechanical properties. Preparation of the basis metal to guarantee perfect adhesion, setting up the anodes, and stopping off or shielding the work to secure good metal distribution can be exacting.

There are numerous advantages in using nickel for salvage. It can be deposited rapidly, uniformly, and economically, the metal can be ground and, in addition, machined by conventional methods; it is corrosion resistant and tough, and it withstands shocks. Where heavy deposits with a hard surface are required, it is good practice to make up the major portion of the desired thickness with nickel and then finish with several micrometers of chromium.

Electroforming has inherent advantages over other processes of fabrication for parts which:
1. Require a very high surface finish, especially on internal surface contours.
2. Require high precision in certain dimensions.
3. Incorporate intricate details.
4. Needed in quantities too small for die casting run.

Sulfamate baths are increasingly used for electroforms because their deposits have low tensile stress. The Watts baths require the use of a stress reducer for low internal stress, and because of the sulfur content of such deposits. It is necessary to avoid temperatures above about 370 oC for such electroforms. At about this temperatures and higher, the sulfide containing nickel suffer severe reducers should be used at the lowest concentrations to accomplish minimum stress.

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