Created on:2021-07-16 09:03

Speed out of control fault of hydraulic system of steel coil transport trolley

Speed out of control fault of hydraulic system of steel coil transport trolley

Steel coil lifting carriage is widely used in steel rolling industrial production line. Its normal operation directly affects the transportation and installation of steel coil, thus affecting the normal operation of equipment and the normal production of products. The following is the fault analysis of the hydraulic system of the steel coil lifting transport trolley in a steel plant.

Symptoms: when the car is no-load, there is abnormal vibration in the transverse forward and backward direction. When the car is descending longitudinally, the electromagnet still crawls down slightly after losing power. After loading (20t steel coil is placed on the trolley platform), the trolley moves forward and backward in transverse direction; When the solenoid valve is not switched to the down state, the weight will slowly drop with the platform, and it can not be positioned, which is completely not in line with the action requirements.

Analysis: from the field fault situation, it can be concluded that the hydraulic circuit, hydraulic components or problems. The hydraulic system diagram is shown in Figure o.

① After the coil car is loaded, the reasons that affect the car's transverse advance and retreat are as follows.

a. The opening degrees of the two one-way throttle valves (4 and 5 in Figure o) in the oil return circuit of the hydraulic motor are not suitable. The flow rate is directly proportional to the speed of the hydraulic motor. The higher the flow rate is, the faster the speed is. Two one-way throttle valves are installed in the oil return circuit of the hydraulic motor in the hydraulic circuit to control the lateral advance and retreat of the car, forming the oil return throttle speed regulation. The opening size of the two one-way throttle valves determines the oil intake of the hydraulic motor, and thus determines the speed of the rotation of the hydraulic motor, that is, the speed of the lateral movement of the car.

b. Under the condition that the set pressure (12MPa) of the system pressure regulating valve (6 in Figure o) remains unchanged, the relief valve at the front end of the hydraulic motor inlet (7 and 8 in Figure o) is also the key element to determine the transverse advance and retreat of the trolley. If the pressure of the relief valve is set too high, the hydraulic motor will operate under high pressure, and it is easy to generate heat, thus reducing the service life; If the pressure is too low, the hydraulic motor will not turn. The two relief valves are also used to limit the maximum impact pressure produced by the hydraulic motor during reverse and forward rotation respectively, so as to play the role of brake buffer. If the pressure is set too high, the hydraulic motor brake too hard, it will cause impact and vibration.

Based on the above reasons, the troubleshooting method is: first, set the pressure of two relief valves in the inlet and outlet of the hydraulic motor to 10.3MPa (according to the design requirements), then adjust the throttle opening size of the return throttle throttle valve, according to the user requirements until the optimal speed of the steel coil car's lateral entry and retreat is adjusted.

② The analysis process is as follows: the coil car rises longitudinally after loading, stops and drops down slowly.

Specification of hydraulic cylinder: piston diameter d = 170mm, piston rod diameter d = 127mm, stroke L = 8lomm; The system pressure is 1MPa.

F=pS (4-13)

Where p is the system pressure; F is the maximum thrust of hydraulic cylinder; S is the piston area.

F=pπD2/4≈270 (kN)

When 20t steel coil is placed on the working platform, the hydraulic cylinder drives the working platform to rise smoothly and the speed is normal. According to the calculation results, the maximum upward thrust of the hydraulic cylinder is 270kn. It can be seen that the system circuit of the car's longitudinal rise is OK, that is, the system pressure regulating valve (6 in Figure o) and the hydraulic pump (13 in Figure o) are OK. There are only two reasons for the failure

a. The hydraulic cylinder (11 in Figure o) has internal leakage or external leakage (it is eliminated after identification);

b. The pressure valve and check valve in the balance valve are faulty.

The pressure in the lower chamber of the hydraulic cylinder is sealed by the one-way valve in the balance valve (9 in Figure o) to stop the movement of the hydraulic cylinder. Only when the pressure at the remote control port is greater than the pressure setting value of the pressure valve in the balance valve, can the balance valve be opened. At this time, the pressure in the lower chamber of the hydraulic cylinder is released and the platform is lowered. The current situation is that there is no pressure at the remote control port, the pressure valve in the balance valve is not opened, and the oil flows out of the balance valve. It is obvious that the one-way valve in the balance valve is damaged (the valve core is worn and stuck), or the pressure valve core in the balance valve is worn and leaked, as shown in Figure P.

Troubleshooting: in the case of invalid regulating balance valve, replace the balance valve. If there are no spare parts, in order to ensure the normal operation of the main line, the balance valve on the coil car of the auxiliary line can be installed as a spare part.

③ There are three possible reasons why the car doesn't move in longitudinal descent.

a. The pressure setting value of the pressure valve in the balance valve is too high or closed, the pressure of the remote control port is not enough to open the pressure valve in the balance valve (9 in Figure o), so that the pressure oil in the lower chamber of the hydraulic cylinder is sealed by the one-way valve in the balance valve, and the hydraulic cylinder cannot move downward.

b. The three position four-way (9 in Figure o) has electrical fault, the electrical plug is loose, the contact is poor, the line is not connected well, connected wrong, disconnected, etc., which can cause the electromagnet not to act, so that the solenoid valve does not change direction.

c. The opening of the throttle valve in the return oil one-way throttle valve (3 in Figure o) is too small or the throttle valve is closed, so that the pressure oil in the lower chamber of the hydraulic cylinder can not return to the oil tank through the throttle valve, but is blocked in the pipeline, and the hydraulic cylinder can not move downward.

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