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The cylinder is the main component of the hydraulic cylinder. The material and processing quality of the cylinder directly affect the life and reliability of the entire product.
01. Technical requirements of cylinder barrel tube
The cylinder barrel tube is the main body of the hydraulic cylinder and must withstand a large amount of hydraulic pressure. Therefore, it should have sufficient strength and rigidity.
The cylinder barrel tube, cylinder head, and sealing system device constitute the sealed working volume of a hydraulic cylinder, so the cylinder barrel must have reliable sealing.
Often, it is necessary to weld oil ports, flanges and other components onto the cylinder barrel tube of a hydraulic cylinder, which requires that the material of the cylinder barrel also have good welding properties.
02. Common materials for cylinder barrel tube
The cylinder barrel tube is made of steel; usually carbon steel. There is a range of different steels available in terms of strength, with higher pressures requiring stronger steel and thicker cylinder walls. The barrel can be painted with a variety of paints or coatings, and company logos are often displayed here.
The inside diameter of the tube does not usually require paint or chrome protection, as the hydraulic fluid protects it from corrosion. However, if the hydraulic fluid is a corrosive material (such as water, salt water), the inside of both the tube and the rod will be coated or chromed plated.
The materials of the hydraulic cylinder barrel are generally cast iron and seamless steel pipe.
1. Cast iron or forgings
Cast iron, commonly used are gray cast iron and ductile iron, which are ordinary cast iron without any alloy elements.
2. Seamless steel pipe
The cylinder barrel tube of the hydraulic cylinder is generally made of seamless steel pipe, which is a high-precision steel pipe material after cold drawing or hot rolling. It has the advantages of no oxide layer on the inner and outer walls, high pressure without leakage, high precision, high finish, no deformation during cold bending, expansion, and no cracks during flattening.
The chemical composition of the hydraulic cylinder steel pipe includes carbon C, silicon Si, manganese Mn, sulfur S, phosphorus P, and chromium Cr. Steel can be divided into low carbon steel, medium carbon steel and high carbon steel according to the carbon content. The carbon content of low carbon steel is generally less than 0.25%, the carbon content of medium carbon steel is generally between 0.25 and 0.60%, and the carbon content of high carbon steel is generally greater than 0.60%.
The commonly used materials for hydraulic cylinder barrel tubes are:
20# steel pipe: 20 refers to a carbon content of 0.2%, which is low carbon steel. This steel has low strength, good toughness, plasticity and weldability.
35# steel pipe: The average carbon content is about 0.35%, which is medium carbon steel.
45# steel pipe: The carbon content is about 0.45%, which is medium carbon steel.
ST52 steel pipe: non-alloy ordinary structural steel
Q355 steel pipe: low alloy high strength structural steel
The above materials achieve the purpose of improving material strength performance by increasing the carbon content.
In addition, 27SiMn and 25Mn are also the materials commonly used in hydraulic cylinder barrel tubes. They improve the heat hardness and wear resistance of steel by adding some alloy elements such as Mn, Si, Cr, Mo, Cu, etc.:
27SiMn (27 silicon manganese steel pipe) is one of the materials of seamless steel pipes. 27 represents the carbon content, and Si and Mn represent the restrictions on the content of Si and Mn in the steel pipe.
25Mn is an alloy structural steel with an average carbon content of 0.25%, a manganese content of about 2%, and a vanadium content of less than 1.5%.
03. Selection of hydraulic cylinder barrel tube material
In the selection of hydraulic cylinder materials, for the cylinder barrel tube, it is important to pay attention to the pressure resistance and the strength and rigidity standards. In addition, it should be able to withstand a certain working pressure for a long time without deformation or bending.
1. Cast iron
Mainly for cylinder barrel tubes with complex shapes, if the requirements are relatively high, ductile iron can be used, such as QT450-10, QT500-7 and QT600-3.
1. Seamless steel pipe
The blank of the cylinder barrel tube generally uses annealed cold-drawn or hot-rolled seamless steel pipes. There are semi-finished products with honed or finely processed inner holes on the market. You only need to cut the seamless steel pipe according to the required length. The materials are 20, 35, 45 steel and 27SiMn, 25Mn alloy steel.
The tensile strength of 20# steel pipe is 355~500MPa, the tensile strength of 35# steel pipe is ≥530MPa, and the tensile strength of 45# steel pipe is not less than 600Mpa. These steel pipes are honed or rolled, with a roughness requirement of 0.2-0.4μm.
The material of the hydraulic cylinder barrel tube can be selected according to the pressure of the working medium: low-pressure cylinders can use 20# steel pipes, ST52 steel pipe, and high-pressure cylinders use 45# steel pipes.
Select according to working conditions: For hydraulic cylinder barrels with working temperatures below -50℃, 35# steel pipes or 45# steel pipes or other low temperature resistant material must be used, and they must be quenched and tempered.
Whether welding is required: If the cylinder barrel needs to be welded with a cylinder head or flange, 20# steel pipes and 35# steel pipes and ST52 steel pipes can be selected, and they can be quenched and tempered after mechanical pre-processing, because their welding performance is better. For cylinder barrels that are not welded with other parts, use quenched and tempered 45# steel pipes.
