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In addition to the cylinder barrel tube and piston rod we mentioned earlier, the key components of the hydraulic cylinder include cylinder head, piston, guide sleeve, connecting parts etc. Today we will learn about the materials used in these key components.
01. Common materials for pistons
The cylinder piston is the main component that converts hydraulic energy into mechanical energy. Its commonly used materials are cast iron, gray cast iron, steel and aluminum alloy. The coaxiality tolerance of the piston and piston rod should be 0.03mm.
The piston in a non-standard steel cylinder is usually made of steel, such as carbon steel CK45 (1045). Or other alloy steel materials depending on the structure of the cylinder.
Pistons made of cast aluminum alloys have the advantages of light weight and good thermal conductivity. Most pistons are made of die-cast or gravity-cast aluminum alloys. Cast aluminum alloys light weight, good structural integrity, low manufacturing cost. The light weight of aluminum reduces the total mass and force required to start and maintain piston acceleration.
Cast iron has the advantage of higher strength and continues to be used in pistons because of its high strength and economy.
The main criteria for selecting the piston material are the thermal conductivity and fatigue life of the material. If the expansion exceeds the provided clearance, the piston may seize. However, in some cases, due to the hardening process or the provided clearance is less than the required clearance. Combining these factors, the most common material for the piston is aluminum alloy.
Secondly, the piston material can be selected according to the structural form of the piston: for pistons (with support rings), 20#, 35# and 45# (also called CK45, or 1045) high-quality carbon steel are commonly used. For pistons without support rings, high-strength cast iron HT200-300, wear-resistant cast iron, ductile iron and aluminum alloy are mostly used. For some pistons that require high durability for continuous work, the outer surface can be treated with long-burned tin bronze alloy or sprayed nylon.
02. Common materials for cylinder heads
Common materials for hydraulic cylinder heads are 35#, 45# (also call CK45, or 1045) forged steel or ZG35, ZG45 cast steel or HT200, HT300, HT350 cast iron, etc. Generally, castings are used for low pressure, HT300 gray iron is used for medium and low pressure, and 35#, 45# (also call CK45, or 1045) steel is used for medium and high pressure.
When the cylinder head itself is also the guide sleeve of the piston rod, cast iron is used for the cylinder head. At the same time, brass, bronze or other wear-resistant materials should be melted on the guide surface. If the guide sleeve is pressed into the cylinder head, the guide sleeve should be wear-resistant cast iron, bronze or brass.
03. Common materials for guide sleeves
The guide sleeve guides and supports the piston rod. It requires high matching accuracy, low friction resistance, good wear resistance, and the ability to withstand the pressure, bending force, and impact vibration of the piston rod. Therefore, the hardness of the guide sleeve is crucial.
The material of the guide sleeve was first selected abroad brass, which has excellent properties such as wear resistance, low hardness, pressure resistance, small thermal expansion coefficient, and corrosion resistance.
The second generation chooses wear-resistant cast iron, ductile iron to replace expensive brass, but some of them have poor performance. Most of the materials are QT400-18 and QT450-10, and the lower the relative hardness, the better.
Now mainly choose suitable non-metallic materials, which are superior to brass in wear resistance, hardness, thermal expansion coefficient, corrosion resistance, etc., and will not scratch the cylinder, are light in weight, and are simple to produce and manufacture. They are ideal materials with good quality and low price.
04. Common materials for connecting parts
According to the different installation methods of hydraulic cylinders, commonly used connecting parts include flanges, earrings, ear shafts, etc.
The flange plate of the hydraulic cylinder must be made of hard material, usually cast steel, the earrings are mostly made of 35# steel and 45# (also called CK45, or 1045) steel, and the ear shaft is often made of 45# (also called CK45, or 1045) steel and cast steel.
