Hard Chrome Plating: Industrial Process Control and Quality Guide
Applications and Thickness
Hard chrome plating for hydraulic piston rods (20-50μm), mold cores (30-80μm), valves (10-25μm) and printing rolls (100-500μm). Hardness 68-72 HRC (HV 850-1,100). Friction coefficient 0.15-0.2 against steel.
Low coefficient of friction for mold release. Corrosion resistance through dense, crack-free deposits.
| Application | Thickness | Purpose | Substrate |
|---|---|---|---|
| Piston Rods | 20-50μm | Wear+corrosion | 4140 steel |
| Mold Cores | 30-80μm | Release+wear | P20/420 SS |
| Hydraulic Valves | 10-25μm | Sealing | Steel |
| Printing Rolls | 100-500μm | Wear+dimension | Steel/copper |
Electroplating Control
Chromic acid 250g/L with sulfate 2.5g/L. Current 30-60 A/dm². Bath 50-60°C. Deposition 30-50μm/hour. Daily titration for bath chemistry. Rack design for uniform current. Masking with PVC or wax.
Current control ±1%. Temperature ±1°C. Chrome to sulfate ratio 100:1 for optimal deposition and hardness.
| Parameter | Target | Control Method |
|---|---|---|
| CrO3 | 250 g/L | Daily titration |
| Current | 40 A/dm² | ±1% rectifier |
| Temperature | 55°C | ±1°C |
| Deposition | 35μm/hr | Bath composition |
Post-Plate Processing
Hydrogen embrittlement bake at 190°C for 4h within 1h of plating. CBN wheel grinding to final dimensions (remove 5-15μm). Surface finish Ra 0.1-0.2μm. Quality tests: XRF thickness, micro-Vickers HV 850+, ferroxyl porosity.
Thermal shock adhesion test at 200°C. Salt spray 200-500h per ASTM B117 depending on thickness class.