Mechanical Cleaning, Polishing, and Buffing
Mechanical Cleaning, Polishing & Buffing
As a general rule, a plated surface will not look any better than the surface finish of the substrate. Many times parts will have scale, rust, burrs or other artifacts of heat treating, manufacture and machining, and may need mechanical cleaning. FPW has several methods of blasting, and a wheelabrator machine. Parts to be plated must be clean and free of dirt, corrosion, and defects before plating can begin. To clean and protect the part during the plating process a combination of heat treating, cleaning, masking, pickling, and etching may be used. Cleanliness is essential to successful electroplating, since molecular layers of oil can prevent adhesion of the coating. ASTM B322 is a standard guide for cleaning metals prior to electroplating. Cleaning processes include solvent cleaning, hot alkaline detergent cleaning, electro-cleaning, and acid treatment etc.
The most common industrial test for cleanliness is the water break test, in which the surface is thoroughly rinsed and held vertical. Hydrophobic contaminants such as oils cause the water to bead and break up, allowing the water to drain rapidly. Perfectly clean metal surfaces are hydrophilic and will retain an unbroken sheet of water that does not bead up or drain off. ASTM F22 describes a version of this test. This test does not detect hydrophilic contaminants, but the electroplating process can displace these easily since the solutions are water-based. Surfactants such as soap reduce the sensitivity of the test and must be thoroughly rinsed off.
For ultra decorative work, the part may need to be buffed and polished. Coatings such as EN can actually magnify minor surface defects, so frequently a part is polished and/or buffed to make the substrate smooth and defect free prior to plating.