Study On The Rigidity Of Overload Protection Devices Of Large Mechanical Presses

Hydraulic overload protection devices of slide are essential for large mechanical presses, which can protect presses and mold from damage, and at the same time guarantee high productivity. For overload protection devices, connector plays critical roles, which connects the hydraulic unloading circuit through liquid cushion. The rigidity of the connector and that of the cushions have great impacts on the unloading of the overload-protection system as well as on the precision of products. Study of the rigidity of the connector and the liquid cushion is important for studying the overload protection system.This paper has done some systematic studies of the rigidity of connector and liquid cushion, by the means of theoretical analysis, numerical computing and simulation.The model of connector is simplified to some extent, namely, using two springs to replace the connector and the liquid cushion. Then the relationship of rigidity of the connector, the liquid cushion, the unloading pressure and the critic pre-stress pressure is gotten through deduction. Influences caused by the change of rigidity of the connector, the liquid cushion, the unloading pressure and the pre-stress pressure are analyzed by figure. Some conclusions are gained:Increasing rigidity of the connector can increase the transmitting force.Build a proper FEA model of the connector and using FEA software to simulate deformation of the connector under load. The equal rigidity of the connector is computed. The analysis shows that the model of the connector cannot be over simplified, and the model should include the slide and the worm gear box, otherwise rigidity of the connector will turn to be lower.Deduct the relationship between the liquid pressure and the compression according to the volume elastic modulus’s definition equation. The relationship shows that compression of liquid is related to the volume of liquid as well as the rigidity of the container, ignoring the air content of liquid. Compression of liquid would be more obvious if pressure is higher and that will be the same if the volume is larger. Meanwhile, simulation shows that deformation of the connector’s cylinder has impacts on the liquid cushion’s rigidity, which decrease rigidity of the liquid cushion. And analysis of the pipes shows that pipes influence rigidity of the liquid cushion because of its volume, and deformation of pipes has little influent. The critic pre-stress pressures under different cases are computed in this paper, and the ratios between pre-stress pressure and unloading pressure are also gotten. The regularity of pre-stress pressure with the length of pipe is gained by the way of curve fitting.Parts that have great impacts on rigidity of the connector are found through simulation, among which the rings and the piston play more important roles. The influence that caused by the radial dimension of cylinder is studied and it can be ignored. The influence that caused by the change of ring’s dimension and structure are studied and thus a proper dimension and structure are found. Study also shows that piston with a high Young’s Modulus can improve the rigidity of the connector.