Problems and Corrective Procedures

Faulty operation of a chromium-plating solution can result in slow plating speed or deposits with undesirable characteristics. The problems encountered in hard chromium plating are similar for all three chemistries. Possible causes and suggested corrective procedures include:

Poor coverage

• Low chromic acid content

• Low ratio of chromic acid content to total catalyst content. Correct by adding chromic acid or by precipitating sulfate, if too high, with barium carbonate.

• Temperature too high

• Current density too low

• Passive or scaled anodes. Correct by cleaning and reactivating anodes, using high current density until uniform gassing is obtained, and checking for good anode contact.

• Rack contacts too heavily built up with metal, causing rack to rob plate

• Thieves too large or too close

• Open holes preventing uniform plate in adjacent areas. Correct by using nonconducting plugs in holes.

• Gas entrapment preventing plating solution from reaching some areas. Correct by positioning parts in solution so that all gases can escape or by agitating parts while they are plating.

Burnt deposits

• Ratio of chromic acid to total catalysts too high. Correct by adding necessary catalyst or by lowering chromic acid content.

• Current density too high

• Temperature too low

• Large parts were colder than solution temperature when plating began.

• Some parts, in a load of different parts, receive too much current. Correct by adjusting anodes and contacts to ensure that each part receives correct current density.

• Excessive amount of anode within a given area for the part being plated. Correct by eliminating all excess anodes in the tank, designing the shape of conforming anodes to minimize current density at high-density areas, and, if necessary, using nonconducting shields at these areas.

Slow plating speed

• Chromic acid content too high

• Ratio of chromic acid to total catalyst too high

• Temperature too high

• Current density too low

• Scaled anodes

• Insufficient or inadequate sizes of conductors in anode or cathode circuits

• Thief obtains too much current. Correct by redesigning thief or by removing nodules from thief.

• Single phasing of rectifier caused by partial burnout. Correct by repairing rectifier.

• High contact resistance on busbars, racks, or jigs. Correct by cleaning contacts to lower contact resistance. Do not always rely on voltage for control, because it does not indicate the conditions present on the part; instead, control by amperage.

• Large variety of parts in same tank prohibiting proper current density for each part

• Tank overcrowded with parts

• High content of metallic impurities. Correct by discarding a portion of solution; readjust after dilution. Nodular deposits

• Insufficient etching before plating in relation to thickness of deposit. Correct by increasing etching time.

• Rough surface before plating

• Chromic acid content too high. Correct by removing portion of solution; dilute the remainder and adjust.

• Low temperature

• Low sulfate content

• Current density too high

Pitted deposits

• Marking dye not completely removed

• Material suspended in solution. Correct by filtering out suspended material.

• Surface-activating agents caused deep pits when plating thick deposits. Correct by discarding as much of the solution as necessary to eliminate pits and replace with fresh solution. Prevent by discontinuing use of mist suppressors. Plastic parts that decompose, such as floats, can form decomposition products that also create pits.

• Gas bubbles adhering to part. Correct by improving surface finish before plating and by agitating part occasionally during plating.

• Part is magnetized. Correct by demagnetizing.

• Magnetic particles in the solution. Correct by removing particles with magnet.

• Insufficient cleaning prior to plating

• Particles falling on work from anodes or thieves. Correct by improving design of anodes and thieves and by cleaning both regularly to remove loose particles.

• Carbon smut on surface. Correct by scrubbing before plating.

• Excessively etched surface during reverse-etch or stripping operation

Poor adhesion

• Insufficient or no etching before plating

• Contaminants not completely removed from surfaces during cleaning

• Excessive grinding rate at edges or sharp projections, where base metal fractures and it may appear that plated material did not adhere

• Single phasing of rectifier caused by partial burnout. Correct by repairing rectifier.

• Current interruption during plating

• Cold solution

Macrocracks

• Highly stressed base metal; cracks are visible during grinding or when heat is applied. Correct by relieving stresses in base metal.

• Grinding at too fast a rate (heat checks)

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