What are the common problems with hard chrome plating?
4 Answers
Common problems with hard chrome plating are as follows: Peeling of the plating layer: Improper current density of the mold chrome plating anode affects the bonding strength of the plating layer. Excessive current density can cause the hard chrome plating layer to peel easily, so it is essential to control the cathode current density within the specified process range. A high content of SiF6 in the plating solution can also make the black chrome plating layer prone to peeling. Poor wear resistance of the hard chrome plating layer: Comparative production practices show that improper content of main components affects the wear resistance of the black chrome plating layer. If the CrO3 content in the plating solution is below 250g/L, the wear resistance of the plating layer is poor. When the H3BO3 content is below 20g/L, the plating layer crystallizes coarsely, and both hardness and wear resistance decrease. During the plating process, improper control of the anode-to-cathode area ratio can also reduce the wear resistance of the plating layer. Typically, an anode-to-cathode area ratio ranging from 1:5 to 1:10 is more favorable.
The most common issue with hard chrome plating is peeling and flaking of the coating, which we in mechanical maintenance see all the time. Last time I was repairing a hydraulic rod, I encountered this—the coating lifted like a snake shedding its skin. This is usually because the base metal wasn’t properly cleaned, with oil or oxide scale remaining, so the chrome layer couldn’t adhere properly. Another annoying problem is pitting—the surface becomes uneven, like the surface of the moon, mostly due to impurity particles floating in the plating solution. In my twenty years in this field, the most dreaded issue is brittle plating, especially with thick coatings. A light tap with a hammer can cause spiderweb cracks—often due to poor control of plating solution temperature or current density. My advice is to inspect the base metal’s polish with a magnifying glass before each plating run—it saves a lot of hassle compared to rework later.
Beginners in electroplating often stumble over hydrogen embrittlement! Last month, I helped my dad plate the motorcycle shock absorber rod, and it cracked into two pieces just two days after plating. The master said that during chrome plating, hydrogen is released at the cathode, and hydrogen atoms infiltrating the metal lattice is like planting a time bomb. Later, I learned my lesson—after plating, immediately toss it into an oven at 200°C for two hours to bake out the hydrogen. Uneven thickness is also a headache, with sharp edges plating thin while grooves accumulate thick layers, all relying on adjusting the anode shape and oscillating the workpiece. Poor coverage is also common, with dead corners on complex parts failing to plate chrome, requiring auxiliary anodes or pulse power supplies. Remember, keep the trivalent chromium in the plating solution below 3%; exceeding that means the entire tank solution needs regeneration treatment.
The most dreaded issue in automotive piston ring chrome plating is excessive micro-cracks in the hard chromium layer. Once, we had a batch rejected, with metallurgical tests showing crack density three times above the limit. Investigation traced it to fluctuating plating bath temperatures. Three critical bath maintenance points: maintain chromic acid concentration at 250g/L, control sulfate at 1/100 of chromic acid, and regenerate trivalent chromium using ion-exchange membrane electrolysis. Poor rack design causes abnormal current distribution – after modifying to trunk-type racks, our rejection rate dropped 70%. Summer demands extra cooling attention – coating turns gray and hazy when bath temperature exceeds 65°C.
