Research on improving the pressure bearing capacity of ultra high pressure hydraulic cylinder

In the design of the current ultra-high pressure hydraulic cylinder, the calculation formula of the thick-walled cylinder is usually used to determine the wall thickness of the cylinder. The wall thickness of the cylinder calculated by this method is increased with the increase of the working pressure in the cylinder. Not only the volume and weight of the cylinder are enlarged, but also the research and experiment of prestressing the cylinder material can not be fully utilized.

Force analysis of thick-walled cylinders When a single-layer thick-walled cylinder is subjected to internal pressure, its cylinder wall is subjected to radial compressive stress tangential tensile stress and axial tensile stress, where tangential tensile stress. The pressure bearing capacity of the cylinder is most affected, and the stress varies unevenly along the radial direction of the cylinder. 1; the inner wall of the cylinder is small. According to the material mechanics, the ratio of the inner and outer circle radius of the cylinder is the moxibustion left factory. The hydraulic cylinder, the ratio of the tangential tensile stress on the inner wall is visible. When the value of 4 is larger, the inner wall of the inner and outer wall is 16 and the material is 45 steel. The working pressure in the cylinder For example, according to the calculation formula of thick wall cylinder, the cylinder wall is 1 , the inner wall 1 tensile stress 7.1 and the outer wall tangential tensile stress, the ratio is 2.225, that is, the internal stress is 1.22 times larger than the external stress, such as 1; Underutilized. Moreover, it can be proved that when the female value is larger than a certain value, the increase is the wall thickness, and the pressure bearing capacity of the cylinder bore is not significantly improved.

To solve the problem of cylinder stress distribution + uniformity. A large pressure can be pre-applied in the cylinder to plastically deform the inner layer of the cylinder, while the outer cylinder is still in the deformation range of the magazine, and the jade force is removed. The wall of the cylinder tube has residual stress, such as the cabinet. It can be seen that the plastic deformation of the factory produces a constant tangential compressive stress on the inner wall of the cylinder, while a small tangential pull is generated on the outer wall of the cylinder. The size of the value should be set according to the needs.

If the pre-stressed cylinder is filled with pressurized oil, the shear stress change of the wall of the 1 cylinder of the shell is offset by the tangential compressive stress of the inner wall of the cylinder as the pressure in the cylinder increases, and then becomes Pulling stress. Still in the above example, in the case where the wall thickness of the cylinder is constant, when the cylinder pressure reaches 5, the inner wall is pulling stress, + goods. The external wall coffee 1 tensile stress is large, plus, the ratio of internal and external stress. 4, the internal stress is 0.14 times larger than the external force, and the final stress is 1. It can be seen that the tangential stress distribution of the cylinder wall is basically uniform, the material strength is fully utilized, and the pressure bearing capacity can be increased by more than 40. If the working pressure inside the cylinder is constant, the wall thickness can be greatly reduced.

In the previous example, the wall thickness can be reduced from 68 to 45. The wall thickness is reduced by 34, and the experiment proves that the value is correct.

3 Method of applying pre-stress As described above, the purpose of applying pre-stress to the cylinder is to produce the inner wall of the cylinder. The tangential deformation is obtained, and the tangential compressive stress is obtained. In order to offset the cylinder tube, it is necessary to engage in the maximum tangential tensile stress of the inner wall of the scientific research and teaching work in hydraulic technology, so that the stress distribution of the cylinder tube over the entire wall thickness is substantially uniform. The principle of prestressing is the principle of work hardening of materials. The prestressing methods are as follows: 1 cold extrusion method, cold extrusion method, roller rolling ball rolling single ring extrusion. Multi-ring extrusion, etc., the most commonly used is ball rolling, such as the depth of the part of the force is 2.5 cylinders, the degree can be increased by 50, and the rolling tools are not too complicated, the rolling pressure is low, the cylinder The deformation is small, and the cylinder surface roughness is very low after rolling, so it is widely used.

2 The hydraulic high-pressure deformation method 21 is small, and the cover is used to seal both ends of the cylinder, and the super-high pressure hydraulic source is input under the pressure of 4 according to the required pre-stress. Moreover, the connection strength between the cylinder head and the cylinder tube is also sufficient, so it is suitable for a long cylinder and a large pre-stressed cylinder.

Percol cold extrusion 祛 离 离 用法 用法 Usage 3 Explosion deformation method This method uses a special explosive as an energy source, and uses a shock wave generated by explosive detonation attached to the inner wall of the cylinder to deform the cylinder. Compared with the first two methods, the blast deformation method is simple and does not require any equipment and equipment. The equipment is quickly arranged and the explosive process can be completed in a few minutes. The cost is a cold extrusion method of about 150, which is a high pressure deformation method. The left and right flexibility is not limited by the length of the cylinder diameter, and the ratio of the amount of deformation to the amount of explosive is easy to control, so the effect is remarkable.

4 Conclusion In the design of the overpressure hydraulic cylinder, the work hardening principle caused by metal deformation is used to pre-stress the cylinder wall of the cylinder tube. When the high pressure liquid is filled, the pre-stressing can be offset to make the cylinder The shear stress of the outer wall is basically uniform, and the mechanical properties of the material are rationally utilized. The wall thickness of the cylinder is reduced by 30 or more without increasing the wall thickness.

1佚摩辛何. Material strength 7. Call. Beijing Science and Technology Publishing Department. I97A 3 Zheng Mingxin. Engineering Materials. Beijing Tsinghua University Press. Ming 2.

3 Shao Guohua. Ultra-high pressure container design elbow. Shanghai Science and Technology Press. 1995.

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