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Basic knowledge of hydraulic cylinder for hydraulic cutting machine

Apr 03, 2018

With the development of modern industry, hydraulic transmission technology has been greatly applied and developed in many industries around the world, such as loaders of engineering machinery, bulldozer and roller, and so on; forklift trucks, belt conveyers and car cranes for heavy transportation machinery, pile driving machines and hydraulic jack of construction machinery, hydraulic jack and so on; agricultural machinery, automobile industry, mine machinery, metallurgical machinery, etc.


The hydraulic transmission equipment is usually composed of four components, such as power, execution, control and assistance. And hydraulic cylinder as a straight line reciprocating motion or less than 360. The hydraulic mechanism of reciprocating swinging movement is simple in structure and reliable in work. It is also the most widely used component in the hydraulic system. It is the liquid pressure energy produced by the mechanical energy in the hydraulic system, and then it can be directly driven by the load to carry on the reciprocating motion or less than 360. An energy conversion device for reciprocating oscillating mechanical energy. To understand the hydraulic cylinder, we must know the following basic knowledge.


Classification and composition of hydraulic cylinders

The hydraulic cylinder can be divided into four types: piston cylinder, plunger cylinder, swinging cylinder and special cylinder. According to the rated pressure, it is divided into high pressure and ultra-high pressure hydraulic cylinders, medium and high pressure hydraulic cylinders and medium and low pressure hydraulic cylinders...

1, cylinder: cylinder is the main part of the hydraulic cylinder, and it forms a closed cavity with parts such as cylinder head, piston and so on, and promotes piston movement. There are 8 kinds of commonly used cylinder structures, which are usually selected according to the connection form between cylinder and end cap. Materials generally require sufficient strength and impact toughness, and also have good welding performance for welding, so the commonly used materials are: 25, 45, ZG200~400, 1Cr18Ni9 and so on. Cylinder billets are mostly cold drawn or hot-rolled seamless steel tubes, so the process is usually quenched and tempered (to ensure the strength of the cylinder, so that it can withstand the oil pressure without deformation and destruction) - honing or boring rolling (to ensure the roughness, roundness, cylindricity and straightness, etc. of the cylinder bore, so that the sealing property of the piston is unchanged after a long period of reciprocating movement) - the vehicle (the design size requirements, such as cylinder length, etc.) Drilling (processing oil outlet, ensuring inlet and outlet).

2, cylinder head: the cylinder head is installed at both ends of the hydraulic cylinder, and the cylinder cavity is closely coupled with the oil cylinder. There are usually welding, thread, bolt, card key and pull rod and so on. It is generally chosen according to the working pressure, the connection mode of the oil cylinder, the use of the environment and so on.

3, piston rod: piston rod is the main component of hydraulic cylinder's transmission force. The material generally chooses medium carbon steel (such as steel 45). When the cylinder works, the piston rod is subjected to thrust, tension or bending moment and so on. It is necessary to ensure the strength of the piston rod. And the piston rod is often slid in the guide sleeve. It should be suitable, too tight, high friction and too loose. It is easy to cause the phenomenon of stagnation and single side wear, which requires the proper surface roughness, straightness and roundness. Therefore, the technology of the piston rod is usually coarse car, quenching and tempering, semi-finished car to quenching, pre grinding, chromium plating, after grinding and fine turning.


4, piston: piston is the main element to turn hydraulic energy into mechanical energy, and its effective working area directly affects the force and speed of hydraulic cylinder. Piston and piston rod are connected in many ways. They usually have clasp ring, shaft sleeve and nut type. When there is no guide ring, the piston is made of high strength cast iron HT200~300 or ductile iron. When the guide ring is used, the piston is made of high quality carbon steel 20, 35 and 45.

5, guide sleeve: guide sleeve plays the role of guiding and supporting the piston rod. It requires high precision, small friction resistance, good wear resistance, and can withstand the pressure, bending force and shock vibration of the piston rod. A sealing device is installed to ensure the seal of the cylinder with a rod cavity, and the outside is equipped with a dustproof ring to prevent impurities, dust and water from being brought to the sealing device and damage the seal. The metal guide sleeve usually uses small friction coefficient, good wear resistance bronze, gray cast iron, spheroidal graphite cast iron and oxidized cast iron, and non metal guide sleeve can use polytetrafluoroethylene and poly (three fluorochloroethylene).

6. The cushioning device: the piston and the piston rod have great momentum when they are driven by the hydraulic pressure. When they enter the end cover and the bottom part of the cylinder, it will cause a mechanical collision and produce a lot of shock pressure and noise. A buffer is adopted to avoid such collision. The principle of the work is to make the oil (all or part) of the cylinder low pressure (all or part) to convert the kinetic energy into heat by throttle, and the heat energy is taken from the circulating oil to the hydraulic cylinder. The structure of buffer is divided into two parts: constant throttling area buffer and variable flow buffer.