How to choose the hydraulic cylinder of the hydraulic press

The typical structure of the hydraulic cylinder of the hydraulic press is shown in Figure 4-1 and Figure 4-3. Figure 4-1 is the structure of the double-rod piston hydraulic cylinder, and Figure 4-3 is the structure of the single-rod piston hydraulic cylinder. The structure of the hydraulic cylinder can be divided into five basic parts: the connection between the piston and the piston rod, the connection between the cylinder and the cylinder head, the sealing device, the buffer device and the exhaust device.

buffer device

In order to prevent the piston of the hydraulic press from hitting the cylinder head at both ends of the stroke, the hydraulic cylinder is generally equipped with a buffer device. The principle of buffering is to increase the oil return resistance when the piston is close to the cylinder head, thereby reducing the speed of the piston. Commonly used buffer devices are shown in Figure 4-13.

(1) Cylindrical annular buffer device: as shown in Figure 4-13(a). When the buffer plunger enters the inner hole of the cylinder head, the enclosed oil must pass through the gap to be discharged, thereby increasing the oil return resistance and reducing the piston speed. Since the throttling area of ​​this structure remains unchanged, the buffering effect is gradually weakened with the decrease of the piston speed.

(2) Conical annular gap buffer device: as shown in Figure 4-13(b). The buffer plunger is changed to a conical type, and its throttling area decreases with the increase of the buffer stroke, and the buffer effect is better.

(3) Variable throttling groove buffer device: as shown in Figure 4-13(c). There is an axial triangular groove on the buffer plunger, the throttling area gradually decreases with the increase of the buffer stroke, and the buffer pressure changes smoothly.

(4) Adjustable orifice buffer device: as shown in Figure 4-13(d). The buffer pressure is controlled by adjusting the size of the orifice to meet the buffer requirements of different loads. When the throttle screw is adjusted, it can work like an annular gap type and have similar characteristics. When the piston moves in the opposite direction, the high-pressure oil enters the hydraulic cylinder from the one-way reading, which will cause a slow start.

5. Exhaust installed straight

The hydraulic cylinder of the hydraulic press often has air infiltration to affect the stability of the movement. In severe cases, the system cannot work normally. Therefore, when designing the hydraulic cylinder, the discharge of air must be considered.

For hydraulic cylinders with low requirements, the hydraulic press often does not have a special exhaust device, but the oil port is placed at the highest point at both ends of the cylinder body, which can also use the liquid flow to bring the air to the oil tank for discharge. However, for hydraulic cylinders with high stability requirements, special exhaust devices, such as exhaust valves, exhaust plugs, etc., are often installed at the highest part of the hydraulic cylinder. Figure 4-14 shows the vent plug. Loosen the screw to exhaust, and then tighten the screw after exhausting the air, and the hydraulic cylinder of the hydraulic press can work normally.

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