we expert produce the piston for hydraulic machine and aluminnum profile extrusion press machine.the material is chilled alloy cast iron.the surface hardness is between HRC 45 to HRC 52. the surface of piston is very smoothly. we expert produce the piston for hydraulic machine and aluminnum profile extrusion press machine.the material is chilled alloy cast iron.the surface hardness is between HRC 45 to HRC 52. the surface of piston is very smoothly.