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

1. Processing and manufacturing

Due to the stress concentration in the circular transition area of the flange and cylinder bottom, if the inner surface of the cylinder bottom transition area or the outer surface of the flange transition area of the four-column hydraulic press is machined with large roughness and obvious knife marks, it will be sensitive to stress concentration and reduce fatigue strength. In particular, the four-column hydraulic press cylinder bottom transition arc inner surface, in the deep inside the cylinder, processing is quite difficult, more attention should be paid to the roughness should not be too high, generally should not be greater than Ra3.2μm. The damage of the cylinder wall is mostly caused in the manufacturing process, such as the overall forging or casting blank itself has serious defects; The welding quality of the broken welding structure is not good, and the heat treatment of the new air purifier after welding is inappropriate. The distance between the position of the circumferential weld and the bottom of the cylinder should be as far as possible not less than 1.5r2(r2 is the outer radius of the cylinder), and the distance from the top surface of the flange should not be less than (1.5-2) r2, and corresponding measures must be taken to the heat affected zone near the weld to eliminate the thermal stress and adverse crystallization structure caused by the welding process. In the use of repair welding, the same treatment should be carried out.

2. Design

In the design introduction of the hydraulic cylinder of the four-column hydraulic press, it can be understood that the design is also designed according to the use of the host and working conditions, if the grasp of the design performance violates the structural layout, it will cause unreasonable structural size design, such as the flange height is too small or the outside diameter of the flange is too large, so that the comprehensive stress is too high and damaged. For example, a 20MN forging hydraulic press, its flange height is only 1.1 times the thickness of the cylinder wall, the calculated stress at the flange exceeds 250MPa, and after 1-2 years of work, two cylinders have broken at the flange. When the new cylinder is replaced, the height of the flange is increased, and the outside diameter of the flange is reduced.

The structural shape design of the transition area from the cylinder wall to the flange is unreasonable, and it will also cause great stress concentration, such as the working cylinder of a 6300kN hydraulic press, because the transition arc radius of the flange is only designed to be 4mm, cracks appear at the flange soon after use, and after the crack expansion, the whole ring flange breaks off. In order to avoid the above situation, the transition shape line at the flange can be optimized to select the optimized shape line which can reduce the stress concentration coefficient.

3, installation and use

Hydraulic cylinder flange and beam contact surface should require more than 80% of the area close contact. Some hydraulic press due to long-term use, the accuracy of this contact surface is damaged, the formation of local contact, local contact beam support reaction force increases sharply, resulting in early damage. The insufficient rigidity of the beam or the unreasonable arrangement of the reinforcement plate at the installation of the hydraulic cylinder will also lead to the uneven distribution of the reaction force on the contact surface of the flange, resulting in excessive working stress.

The connecting bolt of the cylinder flange and the beam is often loose, if not tightened in time, it will cause the cylinder to move and impact, so that the contact surface of the beam is constantly compressed, forming local contact. The bolt connecting to the new air purifier is best tightened under the pressure of the hydraulic cylinder. Some small hydraulic press in the bottom of the cylinder with a clamp ring or key to tighten the cylinder and the beam, to prevent the loosening of the cylinder has a certain effect.

The working liquid often has a corrosive effect on the cylinder wall, which will reduce its fatigue strength, so it is necessary to pay enough attention to the composition and preparation of the emulsion, and it is never allowed to use water directly as the working medium without treatment in the hydraulic machine. And the hydraulic oil used in the oil press should have good rust resistance. Both should adhere to their pH.