Hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and makes linear reciprocating motion (or swing motion). It is simple in structure and reliable in work. When it is used to realize reciprocating movement, the deceleration device can be removed, and there is no transmission gap, and the movement is smooth, so it is widely used in various mechanical hydraulic systems. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference between the two sides; The hydraulic cylinder is basically composed of cylinder and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device. Buffer device and exhaust device depending on the specific application, other devices are essential.
Classification of hydraulic cylinders
The structure of the hydraulic cylinder is various, and its classification method is also various: according to the motion mode can be divided into linear reciprocating motion type and rotary swing type; According to the action of liquid pressure can be divided into single action type, double action type; According to the structure form can be divided into piston type, plunger type, multistage telescopic sleeve type, rack and pinion type, etc. According to the installation form can be divided into tie rod, earrings, foot, hinge shaft, etc.; According to the pressure level, it can be divided into 16Mpa, 25Mpa, 31.5Mpa and so on.
1. Piston type
Single piston rod hydraulic cylinder only one end of the piston rod, the two ends of the import and export oil ports A and B can pass pressure oil or oil return, in order to achieve two-way movement, so it is called double acting cylinder
The piston can only move in one direction, and its reverse movement needs to be completed by external force. But its stroke is generally larger than the piston hydraulic cylinder.
Piston type hydraulic cylinder can be divided into single rod type and double rod type of two structures, the fixed way by the cylinder fixed and piston rod fixed two kinds, according to the action of the liquid pressure of the single action and double action. In the single acting hydraulic cylinder, the pressure oil is only for one chamber of the hydraulic cylinder, and the cylinder can move in a single direction by the hydraulic pressure, and the reverse direction movement is achieved by the external force (such as spring force, dead weight or external load). The double acting hydraulic cylinder piston two directions of the movement through the two chambers alternate oil intake, by the action of liquid pressure to complete.
2. Plunger type
(1) The plunger hydraulic cylinder is a single acting hydraulic cylinder, which can only achieve one direction of movement by liquid pressure, and the return of the plunger depends on other external forces or the dead weight of the plunger;
(2) the plunger is only supported by the cylinder liner and does not contact with the cylinder liner, so the cylinder liner is easy to process, so it is suitable for long stroke hydraulic cylinder;
(3) when working, the plunger is under total pressure, so it must have enough stiffness;
(4) the plunger weight is often large, and it is easy to sag because of its weight when placed horizontally, resulting in unilateral wear of seals and guides, so its vertical use is more favorable.
telescopic
The telescopic hydraulic cylinder has two or multiple stages of piston, telescopic hydraulic cylinder piston out of the sequential type from large to small, and the sequence of no-load retraction is generally from small to large. The telescopic cylinder can achieve a longer stroke, and the retraction length is short, the structure is more compact. This kind of hydraulic cylinder is often used in construction machinery and agricultural machinery. There are multiple pistons in one motion. When each piston moves successively, its output speed and output force are changed.
3. Swing type
Swing hydraulic cylinder is the output torque and realize reciprocating movement of the executive components, there are single blade, double blade, spiral swing and other forms. Vane type: The stator block is fixed to the cylinder block, and the blade and rotor are connected together. According to the direction of oil intake, the blade will drive the rotor for reciprocating swing. Spiral swing type is divided into two kinds of single spiral swing and double helix. Now the double helix is more commonly used. The linear motion of the piston in the cylinder is transformed into the composite motion of linear motion and rotation motion by the two spiral pairs, so as to realize the swing motion.
Two, the working principle of the hydraulic cylinder
Hydraulic cylinder is the executive component of hydraulic transmission system. It is the energy conversion assembly that converts hydraulic energy into mechanical energy. The hydraulic motor realizes the continuous rotary motion, while the hydraulic cylinder realizes the reciprocating motion. Hydraulic cylinder structure type has piston cylinder, plunger cylinder, swing cylinder three categories, piston cylinder and plunger cylinder to realize reciprocating linear motion, output speed and thrust, swing cylinder to realize reciprocating swing, output angular speed (speed) and torque. In addition to the use of a single hydraulic cylinder, can also be two or more combined or combined with other institutions to use. To accomplish a special function. The hydraulic cylinder is simple in structure and reliable in work, and has been widely used in the hydraulic system of machine tools.
