Created on:2022-03-29 10:31

Cause analysis and Countermeasures of multi-stage telescopic hydraulic cylinder

Cause analysis and Countermeasures of multi-stage telescopic hydraulic cylinder

1. Fault phenomenon

A two-stage sleeve telescopic double acting hydraulic cylinder is selected for a product. The piston and sleeve adopt thread nested type. The processing technology is the same as that of piston single acting oil cylinder. It is easy to ensure the quality and good reliability, but the structure is complex. After a jacking operation, it was found that the piston rod was strained and leaked; At the same time, the oil cylinder is blocked and the primary piston rod cannot retract. In order to avoid more serious accidents, the multi-stage oil cylinder was disassembled and inspected. It was found that the guide limit part had plastic deformation, the flat step edge was damaged, and the sharp iron filings scratched the chromium plating layer of the piston rod, further damaged the sealing ring and caused the leakage of the oil cylinder; At the same time, when the cylinder is retracted without load, the return oil back pressure is high and the pressure loss is great.

2. Cause analysis

The oil cylinder is analyzed. Considering the white body structure, the selection of cylinder diameter and piston rod diameter of multi-stage telescopic double acting oil cylinder is too large, as shown in Figure R. The cylinder diameter is one and the rod diameter is one respectively φ 200mm、 φ 190mm, secondary cylinder diameter and rod diameter are respectively φ l60mm、 φ 150mm。 There is only 5mm clearance on each side of each stage of oil cylinder. Generally, the oil cylinder extends step by step from the largest stage, i.e φ The 200mm oil cylinder moves first with the second stage sleeved in it. After the first stage stroke is fully extended, the next stage begins to extend; When retracting, after the smallest stage is fully retracted, the next stage begins to move and retract into the cylinder barrel step by step. Because the contact surface between each stage piston and the guide limit is very small, if the cylinder extends rapidly, the piston will collide with the limit. Long term collision will cause plastic deformation at the guide limit, resulting in card issuing of the piston rod and scratching of the chromium plating layer. Repeated expansion and contraction of the cylinder will further damage the sealing ring, resulting in jamming and leakage. The speed ratio of the first stage of the selected oil cylinder is 10.5 and the speed ratio of the second stage is 8.25. When the first stage is extended in place, the same flow enters the second stage, and its extension speed increases. However, the oil cylinder is not designed with a buffer device, and the rapidly extended piston will hit the guide part at the end of the stroke. This part is not specially treated, and the fault occurs after a long time. As for the high oil return back pressure during cylinder retraction, it is mainly caused by the large speed ratio of multi-stage cylinder. The same amount of oil enters the rod cavity, and the oil discharge from the rod cavity expands dozens of times. In the system design, it is mostly selected according to the oil supply of the pump, ignoring the increase of flow caused by speed ratio. The more the number of cylinder stages, the greater the impact, the greater the increase of system back pressure, Thus, the strange phenomenon that the engine throttle needs to be increased or power consumption occurs during no-load cylinder contraction.

3. Countermeasures

If you can reduce the extension speed of the oil cylinder and let it reach the end of the stroke smoothly, the collision problem can be solved. Therefore, the hydraulic principle is improved, and the principle is shown in Figure s.

When the multi-stage cylinder extends, the electromagnetic directional valve 3 is in the right position, and the throttle valve 2 first regulates the oil from the pump. The return oil with rod cavity returns to the oil tank through the one-way valve of one-way throttle valve 6. At the same time, the high-pressure oil closes the hydraulic control one-way valve 4 to control the extension speed of the oil cylinder and avoid high-speed impact. When the multi-stage cylinder retracts, 3 is in the left position. Throttle valve 2 regulates the oil from the pump first, and one-way throttle valve 6 regulates the flow twice according to the speed requirements. At the same time, the high-pressure oil goes to the control port of hydraulic control one-way valve 4, opens the hydraulic control valve and makes it flow in the opposite direction. The return oil without rod chamber returns to the oil tank through hydraulic control valve 4 and throttle valve 5, and throttle valve 5 can adjust the back pressure, Prevent the vacuum generated in the rodless cavity due to too fast retraction, resulting in system vibration and noise; The other hydraulic oil discharged from the rodless chamber can be returned to the oil tank through the solenoid directional valve and port T1.

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