The piston rod is used in tough surrounding and corrosive condition; consequently a high quality protecting layer is essential. Currently EHC, electroplating hard chromium (hard chrome) is a widespread method for piston rod coating due to powerful performance
Piston Rod Coating
a) Toughness
Toughness is an essential characteristic for piston rod coatings. Coatings demonstrating poor toughness or being not tough enough could not absorb much energy during the angular stone or hard grit strike the piston rod, surface damage then happens easily, the hydraulic cylinder will in turn fail to work immediately due to coating delamination or flaking.
b) Corrosion resistance
Due to poor working environment, the corrosion resistance is very important for hydraulic cylinder piston rod coating. Salt spray test is a conventional standardized test method used to check corrosion resistance of hydraulic cylinder piston rod coating; it is an accelerated corrosion resistance test and the appearance of corrosion products is evaluated after a period of time.
c) Wear resistance
Bearing the above parameters in mind, the piston rod plating thickness is usually in the range of 22-30 microns. If a piston rod is to be repaired, the plating generally is higher at around 50 microns. This is because the rod will have to be reground to remove any pittings and marks on the surface. Hence additional plating will be required to bring the rod back to its original size.
d) Hardness
Particular care should be taken that the manufacturer regularly audits and maintains the plated rod coating hardness. This is important as the plated rod is one of the main moving parts in a hydraulic cylinder and shows significant wear and tear over multiple years of usage. Wear and tear on the piston rod spoils the seals quicker thereby reducing the life of the hydraulic cylinder.