Factors influencing the life of hydraulic cylinder of four-column hydraulic press

1, processing and manufacturing

Due to the stress concentration of the flange transition area and the bottom of the cylinder block, if the inner surface of the bottom transition area of the four-column hydraulic press or the outer surface of the transition area of the flange roughness is large, there are obvious knife marks, it is more sensitive to stress concentration. Reduce fatigue strength. In particular, the inner surface of the transition arc at the bottom of the cylinder of the four-column hydraulic press is deep inside the cylinder, and the processing is very difficult. It should be noted that the roughness should not be too high and generally should not be greater than Ra3.2μm. The damage of cylinder wall is mostly caused in the manufacturing process, such as the whole forging or the casting blank itself has serious defects; The welding quality in the cracked welded structure is not good, and the heat treatment of the new air purifier after welding is not suitable. The distance between the circumference welding position and the base of the cylinder should be no less than 1.5r2 (r2 is the outer radius of the cylinder), the distance from the upper surface of the flange should be no less than (1.5-2) r2, and the weld must be in the nearby heat affected zone to take appropriate measures to eliminate the thermal stress and adverse crystal structure caused by the welding process. The same process must be performed when using repair welding.

2. Design

It can be seen in the design introduction of the hydraulic cylinder of the four-column hydraulic press that the design is also based on the purpose and working conditions of the host. The energy plunder violates the structure layout, resulting in the unreasonable design of the structure size. For example, the height of the flange is too small or the outside diameter of the flange is too large, and the comprehensive stress is too high to be destroyed. For example, the flange height of a 20MN forging hydraulic press is only 1.1 times the thickness of the cylinder wall, and the calculated stress of the flange is greater than 250MPa. After 1-2 years of operation, two cylinders broke at the flange. When replacing the new cylinder, the flange height increases, the outside diameter of the flange decreases, and the use of many years is also good.

The structural design of the transition area from the cylinder wall to the flange is unreasonable, which will also cause stress concentration, such as the working cylinder of the 6300kN hydraulic press. Since the radius of the flange transition arc is only designed to be 4mm, it will be used soon. Cracks appear in the blue area, and the cracks expand, causing the entire flange to break. In order to avoid the above situation, the transition line of the flange can be optimized to select an optimized line that can reduce the stress concentration factor.

3, installation and use

The contact surface of the hydraulic cylinder flange and the beam should be more than 80% of the close contact area. Due to the long-term use of some hydraulic presses, the accuracy of the contact surface is damaged and local contact is formed, and the supporting reaction force of the beam at the local contact point increases sharply, resulting in early failure. The unreasonable degree or unreasonable arrangement of the rib in the beam mounting hydraulic cylinder may also lead to the uneven distribution of the reaction force at the contact surface of the flange and excessive working stress.

The connection bolt between the cylinder flange and the beam is usually loose. If it is not tightened in time, it will cause the cylinder block to move and collide, and the contact surface of the beam will continue to collapse and form local contact. It is recommended to tighten the bolts of the new air purifier when the hydraulic cylinder is pressurized. Some small hydraulic presses use clasp rings or keys to secure the cylinder and beam to the bottom of the cylinder in case the cylinder becomes loose.

The working fluid tends to corrode the cylinder wall and reduce its fatigue strength. Therefore, it is necessary to pay attention to the composition and preparation of the emulsion. Do not use direct water as the working medium of hydraulic machines. The hydraulic oil used in the hydraulic press should have good anti-rust performance. Both should stick to their pH levels.

Hydraulic frame press