TASK 70-45-03-330-004
1 . General.
A.The selective contact plating process is similar to brush plating. A carbon electrode or stylus is wrapped with an absorbent pad, which is then saturated with the desired stripping, activating, deoxidizing, or plating fluid, and connected as the anode to a direct-current power source. The work to be plated is connected to the power source as the cathode. Contact plating solutions, for the most part, consist of suspensions of organo-metallic chelates in water, adjusted to an appropriate pH value. Most contact plating fluids are relatively nontoxic.
B.A wide variety of metals is available for contact plating. These include cadmium, copper, nickel, chromium, cobalt, tin, zinc, silver and gold. These may be mixed or used in sequence to form "sandwich" layers to obtain multipurpose coatings for buildup of worn or undertolerance areas, corrosion/erosion or wear resistance, or to provide anti-fretting and gasketing surfaces. Contact plating should be performed only as directed by the Engine/Shop Manual, and the work should be done only by qualified, experienced operators.
2 . Advantages.
Subtask 70-45-03-330-041
A.Contact plating has several advantages over conventional immersion bath plating in shop applications. Selected areas can often be plated with minimal masking; assembled parts that are difficult or impractical to disassemble or immerse can be selectively plated; building up worn or out-of-tolerance areas can be done to close limits. In addition, deposits are characterized by low stress, very fine grain, negligible hydrogen embrittlement and porosity, and excellent adhesion. The rate of deposition is high and can be accurately controlled.
3 . Equipment.
Subtask 70-45-03-330-042
A.The following equipment and supplies are required for contact plating:
(1)Power pack having a controllable, metered (voltage and amperage) DC output.
(2)Special electrodes or styli applicable to the plating being performed.
(3)Appropriate fixtures, turntables, lathes, drip-feed mechanisms and mechanical agitators, as required.
(4)Rinse tank for overflowing demineralized water.
(5)(Optional). Covered dip tank for methyl or ethyl alcohol, if used to facilitate drying.
(6)A number of evaporating dishes, swabs, absorbent cotton batting, masking material, gauze, and nylon thread or string.
(7)Equipment may be obtained from the sources listed below:
4 . Materials.
Subtask 70-45-03-330-043
 
Consumable Product
No.
 
Dalic Plating Equipment and Solutions
C03-050  
 
LDC Plating Equipment and Solutions
C03-051  
5 . Procedure.
Subtask 70-45-03-330-044
A.Prepare parts for contact plating by grinding down damaged surfaces to a maximum depth of 0.0025 inch (0.0635 mm), then proceed as follows:
NOTE:
Many nickel base alloys require an anodic etch in the appropriate solution before starting the plating operation. Refer to Engine/Shop Manual for specific repair being performed.
(1)Parts to be cleaned and masked as required per the applicable Engine/Shop Manual section.
(2)Connect part to negative (-) pole of DC power supply, and attach plating electrode to positive (+) pole.
(3)Adjust operating voltage as specified by manufacturer.
WARNING:
OPERATOR SHOULD WEAR PROTECTIVE RUBBER GLOVES DURING THE DEOXIDIZING AND PLATING OPERATIONS.
(4)Saturate stylus (electrode-swab) with deoxidizing solution and rub it gently on the part to be plated until the part shows no water break when rinsed in clean tap water. The deoxidizing solution is indicated in Subtask 70-45-03-330-043, Materials.
(5)Adjust the operating voltage for plating as specified by the manufacturer of the plating solution to be used.
(6)Saturate a clean electrode-swab in the plating solution and rub it gently on the part to be plated. The plating solution is indicated in Subtask 70-45-03-330-043, Materials. Refer to the manufacturer's instructions on the container of plating solution for proper plating current, type of stylus, rate of movement, coverage, and thickness of deposit per minute of operation, and to the Engine/Shop Manual for any special instructions.
(7)Agitate the part in the rinse tank of overflowing demineralized water until all plating solution is removed. Withdraw and drain part, then return to rinse tank for 10-20 seconds. Agitate during second rinse. Drain.
WARNING:
METHYL AND ETHYL ALCOHOL ARE FLAMMABLE AND TOXIC. USE IN A APPROVED TANK KEPT IN A WELL VENTILATED AREA. TAKE PRECAUTIONS AGAINST FIRE.
(8)Air dry, or dip in reagent-grade methyl or ethyl alcohol for10-20 seconds to facilitate drying. Properly preserve and protect parts after drying.