Testing

Plating metal onto another metallic substrate can offer benefits such as corrosion protection, increased wear resistance and enhanced appearance — but only if the metal coating properly adheres to the surface. There are tests that can indicate the level of coating adhesion with a relatively high degree of accuracy. Here is a look at some of the more common plating testing processes used to determine adhesion:

• Bend Test: Using a mandrel, bend away the part with the coated surface until its two legs are parallel. The mandrel diameter should be a minimum of four times the thickness of the sample. Examine the sample under low magnification to detect signs of flaking or peeling.
• Chisel-Knife Test: To test plating process adhesiveness using this method, use a sharp, cold chisel to penetrate the metal coating. If you’re able to remove the deposit, proper adhesion has not occurred.
• File Test: Begin by sawing off a portion of the plated part and look for signs of detachment at the deposit or substrate interface. Then raise the sawed edge with a coarse mill file. Evidence of lifting or peeling is an indication of poor adhesion.
• Impact Test: Use hammer or other blunt object to pound the coated part. Signs of exfoliation or blistering indicate insufficient adhesion.
• Peel Test: Solder a strip of brass or steel to the plated metal part, then attempt to peel the strip off at a 90-degree angle. Improper adhesion is present if there is failure at the deposit or substrate interface.
• Burnishing Test: Use a smooth-edged tool to rub a small section of the coated part for approximately 15 seconds, while being careful not to dig into the coating. Peeling, blistering or lifting of the coating are all signs of insufficient adhesion.
• Heat-Quench Test: Heat the plated parts in an oven at a temperature suitable for the substrate or metal coating combination. After heating, submerge the parts in room-temperature water to cool. Evidence of blistering or flaking indicates improper adhesion.
• Scribe-Grid Test: Use a hardened steel tool to scribe a grid pattern on the substrate surface. Inadequate adhesion is evident if any portion of the coating between the scribed lines breaks away.

It is important to select a testing procedure that is suitable for use with the particular substrate and metal coating to ensure reliable results and prevent damage to the part. Some steel plating testing processes, for instance, may not be appropriate for use with softer, less durable materials.