Adhesive Wear and Galling
Two metal surfaces sliding under load micro-weld and tear material from each other. The result is a torn surface, seizure, seal damage and leakage.
Symptoms
- Torn surface, smeared material and metal transfer from one surface to the other
- Seizure, stiff movement or sudden locking of sliding parts
- Scratches on piston rods and resulting seal leakage
- Loss of sealing on valve balls or seats
Typical Parts
Two surfaces of similar material micro-weld under insufficient lubrication and high contact pressure. Stainless and austenitic materials are particularly prone to galling. Surface roughness is also decisive.
Why Piston Rods Fail and How HVOF Solves It
From seal damage to leakage, hard chrome vs HVOF WC-CoCr, and our workshop sequence: grit blasting, robotic HVOF, diamond grinding, superfinishing and inspection.
Turkish narration on screen, English subtitles.
Which Process for Which Case?
The goal is a hard, smooth surface that does not "weld" to its counterpart.
| Solution | Material System | Typical Thickness | When Is It the Right Choice? |
|---|---|---|---|
| HVOF + superfinish | WC-CoCr, WC-Co | 150–300 µm | Piston rods, sliding shafts; an alternative to hard chrome |
| HVOF | Cr₃C₂-NiCr | 150–300 µm | Sliding surfaces with elevated temperature or corrosion |
| PTA overlay | Stellite (Co-based) | 1.5–3 mm | Valve seats, high contact load and temperature |
| Grinding / polishing | — | Ra ~0.1–0.4 µm | Final surface roughness; critical for seal life |
Values are typical ranges; the final choice is made after the part, base material and operating conditions have been seen.
The final surface matters as much as the coating
Even a hard coating will wear the seal and cause leakage if left rough. On sliding surfaces we measure final roughness and record it in the report. A coated area must not be turned afterwards; this can cause edge cracking and spalling.
FAQ
Can HVOF tungsten carbide replace hard chrome?
In many piston rod and sliding surface applications, yes. It contains no hexavalent chromium (Cr6+) and offers high wear resistance. The choice depends on operating conditions and the customer specification.
How smooth is a coated piston rod?
With precision grinding and superfinishing, Ra 0.1–0.4 µm is targeted depending on the application, and measured and reported.
Do you coat valve balls?
Yes; depending on the application with HVOF tungsten carbide or Stellite-based PTA overlay, followed by grinding and lapping.
Let’s Talk About Your Part
Take a photo of the damaged area and send it by e-mail or WhatsApp, or call us directly. On the phone we identify the mechanism together and give a suitable process and a rough cost/lead-time indication in the same call.
- Close-up and overall photo of the damaged area
- Diameter / length or a technical drawing
- Operating conditions: temperature, medium, particles, speed