| [Image: hard chrome coating] |
| [Image: tungsten carbide coating] |
| [Image: comparison of hard chrome and tungsten carbide] |
Hydraulic cylinder rods have traditionally been coated with highly polished hard chrome. This surface provides reasonable corrosion resistance and good sealing in hydraulic cylinders, but the material can corrode. If a machine is parked with cylinder rods extended and exposed to the atmosphere, pitting and corrosion can occur due to micro-cracks in the chrome plating. When that happens, the pitting and corrosion rapidly ruin the hydraulic cylinder seals. Approaches taken to reduce this problem include storing equipment inside, storing equipment with cylinder rods retracted, and coating the rod surface with grease when rods must be exposed.
Alternate approaches now used on some new equipment, including loader cylinders on compact tractors, include a sprayed-on tungsten carbide coating and hard chrome plating over an impervious coating of nickel. The tungsten carbide coating is sprayed on as a powder that is melted and blown onto the surface. The hard chrome over nickel coating is plated on. After application, the surfaces are polished. The resulting surfaces have significantly better corrosion resistance than the traditional hard chrome.
These new coatings should extend cylinder life and dramatically reduce corrosion of cylinder rods.