The hydraulic cylinder rod is typically a hard chrome-plated piece of cold-rolled steel that attaches to the piston and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment. The piston rod is highly ground and polished so as to provide a reliable seal and prevent leakage.
The cylinder rod is the only external part that can’t be painted. Because of this, it has to be protected in other ways. In order for the cylinder to work well the coating has to be completely smooth. The cylinder rod needs to be highly resistant to pitting, corrosion or wear. Any cracks can scrape on seals, causing contamination to enter the hydraulic fluid and leading to eventual hydraulic system breakdown. Therefore, the materials and coating of the hydraulic cylinder is of the utmost importance. Most commonly, the cylinder rod is made of steel or stainless steel and is then coated with Hard Chrome Plating (HCP). However, a number of even more hard-wearing coatings have been developed, including COREX – a specialised coating developed by Apex Hydraulics which can be up to ten times less porous than HCP, with hardness of up to 1400Hv; double that of HCP. Extreme environments may require different materials, such as Inconel, which is particularly corrosion resistant.