| After the extruding of the20,000tons extruder is finished, the working cylinder will return. If without fully and reasonably unloading, huge hydraulic shock will occur, and it will bring harm to equipment and manufacture. At present, unloading ways are backward, unloading law lacks theoretical basis,and factors of hydraulic shock are not recognized fully. Then it is difficult to achieve accurate proportional control of unloading process and make it stable and fast. So it is necessery to study the high-pressure and large-flow proportional unloading technology.In this paper, the main research work, methods and conclusions are summarized as following:(1) The unloading circuit of working cylinder of20,000tons extrusion press was designed. By comparing different valves, proportional cartridged throttle is used as unloading valve, its core has a displacement sensor. Moreover, mathematical modeling, parameter calculation and component selection are finished.(2) Through unloading mechanism analysis, it is presented that the essence of unloading is the release process of stored energy and the volume increment of oil. Based on the principle of uniform release of stored energy and the volume increment of oil, unloading law was studied, and two unloading curves were obtained. Through a simplified AMESim test model, unloading effect was contrasted with different unloading curves and different unloading time. Results indicates that the unloading process is smoother by increasing unloading time and using "first-slow-then-quick" unloading curves. It is also found the unloading curve based on the principle of energy uniform release makes the unloading time reduced to less than1second. It makes the unloading process stable and fast.(3) By theory and simulation analysis to factors of unloading shock, the relationship between shock and the factors was researched. The sensitive factors that affect unloading shock had length and diameter of pipes, volume modulus of oil and the frame stiffness. In addition, the hydraulic shocks were contrasted with unloading circuit or not. Results showes that hyhraulic shock is smaller when unloading circuit is added.(4) Based on unloading essence, the experiment plan was designed. And then, the unloading way and rule were verified by experiment. The results indicates that the unloading way is feasible, the theoretical analisis and simulation are correct, and the experiment way is reasonable. |
