Hydraulic Cylinder
The hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy, performing linear reciprocating (or oscillating) motion. It has a simple structure and reliable operation. When used to achieve reciprocating motion, it eliminates the need for a speed reduction device and has no transmission clearance, ensuring smooth movement. Therefore, it is widely used in hydraulic systems of various machines. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference on both sides; the hydraulic cylinder mainly consists of the barrel and cap, piston and piston rod, sealing device, buffer device, and exhaust device. The buffer device and exhaust device depend on specific application scenarios, while other components are essential.
The hydraulic cylinder is an actuator in the hydraulic transmission system, converting hydraulic energy into mechanical energy. The hydraulic motor achieves continuous rotary motion, while the hydraulic cylinder achieves reciprocating motion. There are three main types of hydraulic cylinder structures: piston cylinders, plunger cylinders, and oscillating cylinders. Piston and plunger cylinders achieve linear reciprocating motion, providing output speed and thrust. Oscillating cylinders achieve oscillating motion, delivering angular velocity (revolutions per minute) and torque. In addition to being used individually, hydraulic cylinders can also be combined in pairs or multiples with other mechanisms to perform special functions. Hydraulic cylinders have a simple structure and reliable operation, making them widely used in the hydraulic systems of machine tools.
There are various structures of hydraulic cylinder, and various classification methods: it can be divided into linear reciprocating motion and rotary swing, single action, piston, plunger, gear, rack, and 16Mpa, 25Mpa, 31.5Mpa according to the pressure grade.
Piston
The single-piston rod hydraulic cylinder has a piston rod at only one end. As shown in Figure 1, there is a single-piston hydraulic cylinder. Both ends of the import and export oil ports A and B can pass the pressure oil or oil return to achieve two-way movement, so it is called A double-action cylinder.
The piston can only move in one way, and its movement in the opposite direction should be completed by external forces. But its stroke is generally larger than the piston-type hydraulic cylinder.
Piston type hydraulic cylinder can be divided into single rod type and double rod type two structures, its fixed way by the cylinder block fixed and piston rod fixed two kinds, according to the action of liquid pressure has single action type and double action type. In the single-acting hydraulic cylinder, the pressure oil only serves one cavity of the hydraulic cylinder, the cylinder moves in one direction, the opposite direction by external force (such as spring force, dead weight or external load), and the double-acting hydraulic cylinder piston is moved in the two direction by the action of fluid pressure.
As shown in Figure 2 is a schematic diagram of the single rod double action piston hydraulic cylinder. It only has a piston rod on one side of the piston, so the effective action area of the two cavities is different. With the same oil supply, the piston is different. When the load force to be overcome is the same, different cawill require different oil supply pressure, or after the pressure of the system.
Plunger type
(1) plunger hydraulic cylinder is a single action hydraulic cylinder, by liquid pressure can only achieve one direction of movement, plunger return to rely on other external forces or the weight of the plunger;
(2) The plunger is only supported by the cylinder liner and does not contact with the cylinder liner, so that the cylinder liner is easy to process, so it is suitable for the long stroke hydraulic cylinder;
(3) the plunger is under pressure, so it must have sufficient stiffness;
(4) the plunger weight is often larger, 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.
telescopic
The telescopic hydraulic cylinder has two or many stage pistons, the telescopic hydraulic cylinder piston protruding sequence from large to small, and the order of no-load retraction is generally from small to large. The telescopic cylinder can achieve a longer travel, while the retracted length is shorter, and the structure is more compact. This kind of hydraulic cylinder is commonly used on construction machinery and agricultural machinery. There are multiple pistons, and the output speed and output force are changed.
Swing type
Swing-type hydraulic cylinders are actuating elements that output torque and achieve reciprocating motion, available in single-blade, double-blade, and spiral swing forms. In the blade type: the stator block is fixed on the cylinder body, while the blades are connected to the rotor. Depending on the direction of oil flow, the blades will drive the rotor to oscillate reciprocally. The spiral swing type is further divided into single-spiral and double-spiral types; currently, the double-spiral type is more commonly used. It relies on two screw pairs to convert the linear motion of the piston inside the hydraulic cylinder into a compound motion of linear and rotational movements, thereby achieving oscillating motion.
Swing type
The wing hydraulic cylinder is the execution element of output torque and realize reciprocating motion, including single blade, double blade, spiral swing and so on. 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 oil intake, the blade will drive the rotor to swing repeatedly. 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 movement of the piston in the hydraulic cylinder is transformed into the compound movement of linear movement and rotation movement, so as to realize the swing movement.
buffer unit
In hydraulic systems, hydraulic cylinders drive mechanisms with certain masses. When the cylinder reaches its stroke limit, it possesses significant kinetic energy. If no deceleration measures are taken, the piston will collide mechanically with the cylinder head, causing impact and noise, which can be destructive. To mitigate and prevent such hazards, a deceleration device can be installed in the hydraulic circuit or a buffer device can be set up inside the cylinder.
Cylinder processing
The cylinder barrel, as a key component of hydraulic cylinders, single-piece supports for mining, hydraulic supports, and blast pipes, has its processing quality directly impacting the lifespan and reliability of the entire product. The requirements for cylinder barrel processing are stringent; the internal surface roughness must meet Ra0.4~0.8&um standards, with strict demands on coaxiality and wear resistance. A fundamental characteristic of the cylinder barrel is deep-hole machining, which has long been a challenge for processors.
Using rolling processing, due to the residual compressive stress in the surface layer, it helps the sealing of tiny cracks on the surface, and hinders the expansion of erosion. Thus improve the surface corrosion resistance, and can delay the generation or expansion of fatigue crack, thus improve the fatigue strength of cylinder. Through rolling forming, 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 and avoiding burns caused by grinding. After rolling, the surface roughness value reduction, can improve the coordination properties.
The cylinder is the most critical component of construction machinery. Traditional machining methods include: turning the cylinder body —— precision boring the cylinder body —— grinding the cylinder body. The roller pressing method involves: turning the cylinder body —— precision boring the cylinder body —— roller pressing the cylinder body, which consists of three processes. However, in terms of time: grinding a 1-meter cylinder takes about 1-2 days, while roller pressing a 1-meter cylinder takes approximately 10-30 minutes. In terms of investment: a grinding machine or hobbing machine (tens of thousands —— millions), and roller pressing tools (1 thousand —— tens of thousands). After roller pressing, the surface roughness of the hole decreases from Ra3.2~6.3um before rolling to Ra0.4~0.8&um, and the surface hardness of the hole increases by about 30%, with the fatigue strength of the inner surface of the cylinder tube improving by 25%. If the service life of the cylinder is considered only based on the cylinder tube, it can be increased by 2 to 3 times. The efficiency of the boring and roller pressing process is about three times higher than that of the grinding process. The above data indicates that the roller pressing process is highly efficient and can significantly improve the surface quality of the cylinder tube.
After the cylinder is rolled, the surface has no sharp small edge, and the long time of motion friction will not damage the sealing ring or seal, which is particularly important in the hydraulic industry.
