Friday, April 18, 2008

Maintenance and Control of Nickel Baths

Maintenance and control should start with the installation of the tank and its auxiliary equipment. Satisfactory thoroughly tested tank linings and internal heating elements are available. Heating the solution by means of an external heat-exchanger is much preferred. As materials for internal heating elements, lead was at one time used almost exclusively. It has been replaced by either impervious carbon or glass in order to avoid the possibility of metallic contamination. Since lead is soluble in high chloride nickel baths, lead coils should not be used where the nickel chloride content is higher than 60 g/l. They should also not be used in baths containing organic acid that form soluble lead salt such as acetic and formic acids, or in baths with high concentrations of sulfonic acids. They can't be used in sulfamate, flouborate, all-chloride, or high-chloride baths.

Impervious carbon heating elements are widely used in such baths, and since they have good heat transfer properties, they may be employed in any type of nickel plating solution. The one disadvantage of such heating elements is their fragility. Special precaution is required to place them in the tank so that danger of physical damage is minimized. Glass heating coils avoid both metallic contamination and stray electrical current, but have the disadvantage of a relatively poor coefficient of heat transfer.

Since insulated defects may be the direct cause of poor adhesion and may result in current loss or poor plate distribution, tanks should be mounted on positive insulator such as glass or glazed ceramics. All piping connections for water, steam, and air exhaust should be equipped with permanent insulating joint in order to avoid electrical grounds and short circuits. All anode and cathode bats, racks, and contact points should be kept reasonably free from encrusted salts for good electrical contact. Contamination of the bath with copper must be avoided. Wrapping the anode bars with polyethylene sheeting is a step in that direction.