SURFACE QUALITY OF PISTON RODS AND CYLINDER RUNNING SURFACES
Hardening, grinding, hard chrome plating
The service life of hydraulic cylinders depends on the quality of the piston rod, among other things. Hardened rods have a significantly thicker case depth, which significantly increases its resistance to wear – and especially to impact effects.
For optimal surface adjustment, the hardened rods are polished and if necessary also hard chrome plated.
At AHP Merkle, almost all piston rods are hardened and polished. For long-stroke cylinders the piston rods are additionally hard chrome plated.
The hardening process gives the piston rod material a case depth in the range from 0.5 to 2.5 mm (0.019 to 0.098 inches). This reaches a hardness value of up to 57 HRC. Hard chrome plating the surface increases the hardness value to up to 67 HRC, increasing the durability of the piston rod.
As a result, the hardened piston rods are much more resistant to impact, scratches and other wear. This increases their life, and also the life of the seals.
As an alternative to thermal, chemical and other processes for surface hardening, roller burnishing is also used for cylinder running surfaces. This burnishing process is a non-cutting surface treatment that creates a high- precision, high-strength cylinder running surface.
For example, at AHP Merkle the housings of the block cylinders are given a more „refined“ quality by the roller burnishing process. This increases the percentage contact area of the piston running surface, which provides optimal values in relation to wear and life of the cylinder.