Mechanical plating is becoming a preferred option as OEMs seek safer and more sustainable coating solutions.
Denis Rainbird, General Manager at WEP, said mechanical plating offers several advantages in certain applications, including the elimination of hydrogen embrittlement, uniformity of coating, good adhesion, conductivity and its compatibility with further treatments and top coats.
Mechanical plating is a cold coating process that applies a protective metal layer, typically zinc or alloy layers such as tin zinc, onto steel parts using a tumbling action with glass beads and metal powders.
Denis said: “Mechanical plating is often overlooked, but there is renewed interest as it can be a safer and more environmentally friendly choice for critical applications where part integrity is essential and hydrogen embrittlement is a concern.”
Suitable applications include structural bolts, anchors and fixings for the construction and infrastructure industry and track fasteners and brake and coupling components for the rail sector.
Mechanical plating does not use electricity to deposit the coating or generate hydrogen, making it ideal for high strength fasteners across many industries. The process delivers a uniform matte finish and excellent corrosion protection, even on complex shapes.
Mechanical plating also offers clear environmental benefits compared to traditional electroplating methods. The process uses very little electricity, operates at room temperature and eliminates the need for hazardous chemicals.
Denis added: “This reduces energy consumption, chemical waste and water usage throughout production. Because it generates less effluent and minimises air and water pollution, mechanical plating supports cleaner manufacturing practices and helps companies meet increasingly strict environmental and sustainability standards.”
The process begins with thorough cleaning to remove oils, dirt and scale. A mild acid or conditioning treatment then lightly etches the surface to promote bonding. A thin flash coat of copper is first deposited to improve adhesion between the steel and zinc, enhance corrosion resistance and ensure a uniform final finish.
Next, zinc powder, glass beads, water and chemical promoters are added to a tumbling barrel. The glass beads mechanically peen the zinc onto the copper coated surface, forming the primary protective layer. The parts are then rinsed and dried, with optional sealants applied for additional corrosion protection.
Mechanical plating typically produces slightly thicker matte coatings, usually between 5 and 25 microns and up to 50 microns for heavy duty applications.
“If hydrogen embrittlement is a concern for high strength parts under load, mechanical plating should be a serious consideration as a preferred coating process,” said Denis.