The hydraulic cylinders working life by many factors, must be combined with specific analysis of the circumstances, but can be summarized in the following areas.
1, the design of reasons. Structural size of the design is unreasonable, such as flange height is too small or flange outside diameter is too large, comprehensive stress too much damage. 20MN forging such as a hydraulic machine, the flange height of only 1.1 times the cylinder wall thickness of the flange calculation of stress over 250MPa, after 1-2 years of work, two-cylinder has ruptured in the flange. Replaced with a new tank, increasing the flange integrated oil press, reducing the outer diameter flange used for many years is not bad.
From the cylinder wall to the flange structure of the transition zone shape design is unreasonable, will cause a lot of stress concentration, such as 6300kN hydraulic machine working cylinder flange at the transition radius is only designed for 4mm use soon in France Lan at the cracks, crack propagation, resulting in the whole circle of the flange breaking off. In order to prevent such a situation, you can optimize the design of the transition line of the flange to select the optimization shaped line can reduce the stress concentration factor.
2, processing and manufacturing reasons. Flange and Bottom arc transition zone of stress concentration, if the processing roughness of the outer surface of the inner surface of the Bottom of the transition zone or flange transition zone, there are obvious marks, will stress concentration sensitive, reduce the fatigue strength . Especially Bottom transitional arc surface, deep in the tank, the processing is very difficult, but also should be noted that the roughness should not be too high, generally should not exceed Ra3.2μm. Tube wall of the cylinder part of the damage is mostly in the manufacturing process, such as the overall forging or casting blank itself is seriously flawed; broken weld structure welding quality is not good after welding Yat air purifier heat treatment is not appropriate. Circumferential weld location with the Bottom of the distance should be not less than 1.5r2 (r2, cylinder outer radius), and the upper surface of the flange distance should not be less than (1.5-2) r2, and be sure to the vicinity of the weld heat affected zone to take appropriate measures to eliminate the thermal stress caused by the welding process and unfavorable crystal structure. When using welding, but also for the same treatment.
3, the installation of use reasons. The hydraulic cylinder flange and the beam contact surfaces should be more than 80 percent of the area in close contact. Long-term use of some hydraulic machine, the accuracy of this contact surface destruction, the formation of local contacts, local contact at the beam support reaction force increases rapidly, leading to early destruction. The beam stiffness is not enough to install the hydraulic cylinder at the rib layout is unreasonable, will lead to flange contact surface of the reaction force is unevenly distributed, causing too much work stress.
Cylinder flange beams, bolts often loose, if not tightened, will cause the cylinder traverse and impact, so that the beam contact surfaces continue to sag, the formation of local contacts. Join Yat new air cleaner bolt is the best in the hydraulic cylinder under pressure, tighten. Some small hydraulic press in the Bottom card ring or key cylinder and beams fastened to prevent the cylinder loose a certain effect.
Working fluids are often corrosive effect on the cylinder wall, it will reduce its fatigue strength, adequate attention must therefore be of emulsion composition and preparation, in a hydraulic press will never allow direct water as the working medium rather than to address them. The hydraulic pellet packing machine used in the hydraulic machine should have a good rust resistance. Both should adhere to its pH.