PLATING AND ANODIZING: CORROSION TESTING IMPROVING PLATING PERFORMANCE Salt Spray Testing: What it is and how to maximise your plating results BY MAXWELL GEORGE fter plating, there is a wide variety of methods that can determine the efficacy of the plating finish. You can visually inspect the part for pitting, blisters, or voids. There are porosity tests using copper sulfate to determine if the plating has tiny pores invisible to the human eye. You can measure the thickness of the plating using XRF, and you can test adhesion using tape or bending. But above all others, a long-held standard in the industry is the use of salt spray testing to determine how well a plating performs in a corrosive environment before rusting. But what is salt spray, and how can it maximise plating results? What is Salt Spray? The typical standard used in salt spray testing in the plating industry is the ASTM B117 method. This standard involves placing your plated panels and parts into a controlled corrosive environment to determine how long the parts will last in 24-hour increments before showing signs of white or red rust. The atmosphere in this salt spray chamber is a five per cent sodium chloride solution that has a monitored pH between 6.5 - 7.2 and temperature range between 33- to 37-degrees C. The panels and parts are placed in the chamber on racks at a 15-degree to 30-degree angle from the vertical. Companies will use this test to determine the efficacy of the coating in preventing rust and corrosion in the real world. Many adhere to OEM specifications or their own internal specifications for how long a part should last inside the salt spray chamber before rust appears. For a chromated zinc or cadmium plated part, one would expect the parts to last 24 to 168 hours in salt spray before the appearance of white rust and 24 to over 336 hours before the appearance of red rust when used with a chrome passivate. For a hard chrome part, you could expect to see rust in 24 hours to 100 hours, while a decorative chrome part should last between 24 hours to 336 hours. March/April 2024 23 A