What is Hydraulic Cylinder


Hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and does linear reciprocating movement (or swing movement).It is simple in structure and reliable in its work.When it is used to achieve the reciprocating motion, it can avoid the deceleration device, and there is no transmission gap, and the movement is stable, so it is widely used in various mechanical hydraulic systems.The output force of hydraulic cylinder is proportional to piston effective area and the pressure difference on both sides; hydraulic cylinder basically consists of cylinder cylinder and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device.Buffering and exhaust devices depending on the application, other devices are essential.

Hydraulic cylinder is the actuator in the hydraulic transmission system, it is the energy conversion device to convert hydraulic energy into mechanical energy.The hydraulic motor realizes continuous rotary motion, while the hydraulic cylinder realizes reciprocating motion.The structural type of hydraulic cylinder has three categories of piston cylinder, piston cylinder, swing cylinder, piston cylinder and piston cylinder to achieve reciprocating linear movement, output speed and thrust, swing cylinder to achieve reciprocating swing, output angular speed (speed) and torque.Hydraulic cylinders can be used in two or more combinations or in combination with other mechanisms.To complete the special function.The hydraulic cylinder structure is simple and reliable, and is widely used in the hydraulic system of the machine tool.


The structure of hydraulic cylinder is varied: single action and double action, piston, plunger, gear rack, rod, earrings, foot, and 16Mpa, 25Mpa, 31.5Mpa according to pressure level.



The Single piston rod hydraulic cylinder has a piston rod at only one end.Figure 1 is a single piston hydraulic cylinder.Both the inlet and export oil ports A and B can pass through the pressure oil or return oil to realize two-way movement, so it is called a two-action cylinder.


The piston can only move in one way, and its reverse direction should be done by an external force.But its stroke is generally larger than the piston-type hydraulic cylinder.


Piston hydraulic cylinder can be divided into single rod type and double rod type two structures, its fixed by cylinder block and piston rod fixed two, according to the action of liquid pressure has single action and double action.In single-acting hydraulic cylinder, the pressure oil is only for one cavity of the hydraulic cylinder by liquid pressure in the opposite direction by external force (such as spring force, dead weight or external load), and the movement of the piston of hydraulic cylinder moves between the two directions by the action of liquid pressure.

A schematic diagram of a single rod double action piston hydraulic cylinder is shown in Figure 2.It only has a piston rod on one side of the piston, so the effective action area of the two cavities is different.When the oil supply amount is the same, the piston movement speed is different, in the load force to overcome is the same, different cavity oil, need different oil supply pressure, or after the system pressure adjustment, the two directions of the hydraulic cylinder can is different.


Plunger Type

(1) The plunger hydraulic cylinder is a kind of single-action hydraulic cylinder, by the hydraulic pressure can only achieve one direction of movement, the plunger return journey depends on other external forces or the weight of the plunger;

(2) The plunger is only supported by the cylinder sleeve and does not contact with the cylinder sleeve, so that the cylinder sleeve is easy to process, so it is suitable for making a long-stroke hydraulic cylinder;

(3) The plunger is always pressed at work, so it must have sufficient stiffness;

(4) The plunger weight is often large, and the horizontal placement is easy to droop due to the dead weight, resulting in unilateral wear of seals and guidance, so its vertical use is more favorable.



The telescopic hydraulic cylinder has two or multiple stage pistons, and the expansion hydraulic cylinder piston extends from the sequential type from large to small, and the no-load retraction sequence is generally from small to large.The telescopic cylinder can achieve a long stroke, while the retracted length is shorter, and the structure is more compact.Such hydraulic cylinders are commonly used in construction machinery and agricultural machinery.There are multiple once moving piston, each piston movement by motion, its output speed and output force are changed.


Swing Type

Swing hydraulic cylinder is the execution element that output torque and realizes reciprocating motion. There are several forms such as single blade, double blade, and spiral swing.Blade type: the stator block is fixed to the cylinder block, and the blade and the rotor are connected together.According to the direction of the oil intake, the blade will drive the rotor to reciprocate swing.The spiral swing type is divided into two kinds: single spiral swing and double spiral. Now the double spiral is more commonly used. The linear motion of the piston in the hydraulic cylinder changes into the compound movement of linear motion and rotation motion, so as to realize the swing movement.


Buffer Unit

In the hydraulic system, the hydraulic cylinder is used to drive a mechanism with a certain quality. When the hydraulic cylinder moves to the end of the trip, it has a large kinetic energy. If there is not a deceleration treatment, the hydraulic cylinder piston and the cylinder head will collide mechanically, causing impact, noise and destructive.To mitigate and prevent this hazard, a reducer can be provided in the hydraulic circuit or a buffer in the cylinder block.


Cylinder Processing

As the main component of hydraulic cylinder, mining single pillar, hydraulic support and gun pipe, the quality of its processing quality directly affects the life and reliability of the whole product.cylinder processing requirements are high, its inner surface roughness requirements of Ra0.4~0.8&um, coaxial, wear resistance requirements.The basic feature of the cylinder cylinder is deep hole processing, its processing has been troubling the processing personnel.

Rolling processing is used, because the surface has residual pressure stress in the surface layer, which helps in the sealing of tiny cracks on the surface, and hinders the expansion of erosion effect.Thus improve the surface corrosion resistance, and can delay the generation or expansion of fatigue crack, thus improve the cylinder fatigue strength.Through rolling molding, a cold hardening layer is formed on the rolling surface, which reduces the elastic and plastic deformation of the grinding auxiliary contact surface, thus improving the wear resistance of the inner wall of the cylinder cylinder while avoiding burns caused by grinding.After rolling, the surface roughness value decreases, which can improve the coordination properties.

Oil cylinder is the most important component of engineering machinery, the traditional processing method is: pull cutting cylinder block —— fine boring cylinder block —— grinding cylinder block.The rolling method is: pull cutting cylinder block —— fine boring cylinder block —— rolling cylinder block, the process is 3 parts, but the time comparison: grinding cylinder block 1 meter about 1-2 days, rolling cylinder block 1 meter about 10-30 minutes.Investment comparison: grinder or quilter grinder (tens of thousands of —— of millions), roller knife (1 thousand —— tens of thousands).After rolling, the surface roughness of the hole is reduced from Ra3.2~6.3um before rolling to Ra0.4~0.8&um, the surface hardness of the hole is increased by about 30%, and the inner surface fatigue strength of the cylinder cylinder is increased by 25%.If the service life of the cylinder only considers the influence of the cylinder cylinder, it is 2~3 times higher, and the boring and rolling process is about 3 times higher than the grinding process efficiency.The above data show that the rolling process is highly efficient and can greatly improve the surface quality of the cylinder cylinder.

After the cylinder rolls, the surface does not have a sharp small edge, and the long motion friction will not damage the sealing ring or seal, which is particularly important in the hydraulic industry.

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