What components does the cylinder consist of? Super detailed analysis

The pneumatic actuator cylinder is mainly composed of cylinder barrel, piston rod, guide sleeve, seal and other components. The material composition and process working principle of these important components are explained below to better understand the operation of the cylinder.





Cylinder material and process


Generally, a cylindrical structure is used. Currently, square and rectangular special-shaped pipes and special-shaped pipes with rectangular or oval holes for anti-rotation cylinders are widely used. The cylinder material is cold-drawn high-carbon steel pipe, malleable cast iron, aluminum alloy die-cast high-strength aluminum alloy, brass (miniature cylinder), stainless steel and engineering plastic pipe. Most small and medium-sized cylinders use aluminum alloy tubes and stainless steel tubes. The cylinder barrel of the switch cylinder or the cylinder barrel used in a corrosion-resistant environment requires non-magnetic materials, such as stainless steel, aluminum alloy or brass. Heavy-duty cylinders used in metallurgy, automobile and other industries generally use cold-drawn precision-drawn steel pipes, and cast iron pipes are also used. Cast iron pipes should be artificially aged, and welded parts with flange cylinder structures need to be annealed.


In order to resist the wear of the piston movement, the surface of the material should have a certain hardness. The inner surface of the steel pipe needs to be chromium plated and honed to a thickness of 0.02mm. Aluminum alloy pipes require hard anodizing treatment, and the thickness of the hard oxide film layer is 30~50m. The dynamic matching accuracy of the cylinder barrel and the piston is H9 level, the cylindricity tolerance is (0.02~0.03)/100, the surface roughness Ra0.2~0.4m, and the perpendicularity tolerance of both ends of the cylinder barrel to the inner hole axis is 0.05~0.1mm. The cylinder barrel should be able to withstand the pressure test under conditions of 1.5 times the maximum working pressure and should not leak. The cylinder wall thickness is directly proportional to the maximum working pressure p and cylinder diameter, and inversely proportional to the allowable stress of the cylinder material. The cylinder wall thickness can be calculated according to the calculation formula of thin-walled tubes:









Where b: cylinder wall thickness, cm

D: cylinder inner diameter, cm

P: Maximum air pressure that the cylinder bore, MPa

[G] Allowable stress of cylinder material, MPa

The actual value of the cylinder wall thickness is approximately 7 times the calculated value for general-purpose cylinders and 20 times the calculated value for heavy-duty cylinders, and then is rounded to the standard pipe size.






Cylinder piston rod materials and processes


The piston rod is an important force-bearing component in the cylinder. It is required to withstand loads such as tension, compression, and vibration. The surface is wear-resistant and does not rust. Generally, carbon steel (35 steel, 45 steel), precision-rolled stainless steel and other materials are used. The steel surface requires chromium plating and quenching and tempering heat treatment. The piston rod protrudes outside the cylinder and is easily affected by dust, making the surface of the piston rod easily scratched. In dusty environments, a dust cover should be installed on the pole. Most of the materials are rubber-coated nylon cloth, and fiberglass cloth materials are also used in high-temperature situations.

During use, it should be noted that when the movement of a large inertia load stops, it is often accompanied by an impact. The piston rod head is easily damaged due to impact. Therefore, the inertia force of the load should be checked during use, and a blocking device and a buffer absorption device for load stop should be installed to eliminate the unreasonable force on the piston rod. In most cases, the piston rod bears thrust load, and the stability of the pressure rod of the slender rod must be considered. When the cylinder is installed horizontally, the head of the piston rod will droop due to its own weight when the piston rod extends out. Attention should be paid to the bending strength of the piston rod.


Cylinder piston materials and processes


The cylinder piston generates thrust due to air pressure and slides in the cylinder tube. In high-speed motion situations, the piston may hit the cylinder head. Therefore, the piston is required to have sufficient strength and good sliding characteristics. Full attention should be paid to the sliding performance of the piston used in the cylinder, especially the wear resistance and the absence of "cylinder biting" phenomenon. With the development of sealing technology, pistons are now made of integral type. The integral piston is made of aluminum alloy or ductile iron, which has good sliding properties, vibration damping and impact resistance. For magnetic switch cylinders, since a magnetic ring needs to be installed on the piston, it is generally made in two halves.







Figure 2 shows schematic diagrams of several piston structures. Figure 2 (a) shows the overall structure of the piston. Figure 2 (b) shows the piston structure with copper alloy welded on the sliding surface of the piston. Figure 2 (c) shows the structure of the piston. A guide ring structure made of polytetrafluoroethylene, polyurethane, cloth-covered synthetic resin and other materials is installed on the cut surface to improve the cylinder guideability. The piston with the structure shown in Figure 2 (b) and (c) has better sliding performance.

The width of the piston is related to factors such as the number of sealing rings and the form of the guide ring. Generally, the smaller the piston width, the shorter the overall length of the cylinder.