Large-scale hydraulic cylinders are divided into two categories: large-bore large-scale hydraulic cylinders and large-tonnage large-scale hydraulic cylinders. They are characterized by large cylinder diameters, long strokes (individually), large volumes, and large own weights. The pulling force or thrust provided is also large. It is difficult and expensive to process large hydraulic presses. Therefore, before designing and manufacturing such hydraulic cylinders, the selection of materials is extremely critical. Once the selection of materials is wrong, it will cause great economic losses.
1. Material requirements for each part
Large hydraulic cylinders are mainly composed of hydraulic cylinder barrels, cylinder bottoms, cylinder heads, hydraulic piston rods, pistons, earrings or flanges, and mounting bases.
1. Generally speaking, in the absence of special working environment, the materials of each part of the large hydraulic cylinder are:
1) Hydraulic Cylinder barrel, also known as hydraulic cylinder tube: 1020 seamless steel pipe, ST52.3 seamless steel pipe, 1045 seamless steel pipe; for extra large hydraulic cylinder, 1045 steel or higher strength steel as SAE 4140 steel are required to make hydraulic cylinder barrel.
2) Hydraulic Piston rods: 1045 steel and St52 steel are generally used. When the impact and vibration of the hydraulic cylinder are big, alloy materials such as 27SiMn steel or 4140/42CrMo can be used.
3) Piston:
Integral pistons: Most use 1035 steel and 1045 steel.
Assembled piston: gray cast iron, wear-resistant cast iron, aluminum alloy, etc. are often used. For special needs, bronze, brass and nylon wear-resistant sleeves can be installed on the outside of the steel piston blank.
4) Cylinder head:
When the working pressure is P10MPa, use high-strength cast iron (HT200), when P20MPa, use seamless steel pipe, when P20MPa, use cast steel or forged steel.
2. Special working conditions and special working environment
1) Cylinder barrel: ST52, 1045 steel or higher is generally used; Cylinder barrel is made of honed tubing, the surface roughness of the cylinder barrel can reach 0.4, the surface of the inner hole forms a uniform grid honing pattern, and the piston forms a uniform oil film on the surface of the cylinder barrel during the reciprocating motion.
2) Piston rod: Generally, it should be quenched, quenched and tempered to HB241-286, and the surface should be plated with hard chrome, the thickness should reach 0.03-0.05, or meet the requirements of HRC55-65; it also needs to be polished to make the surface clean，making its surface cleanliness to 0.4um~0.2um.
