Created on:2021-09-04 14:30

Port equipment_ Hydraulic failure of luffing mechanism of cantilever bucket wheel reclaimer

Port equipment_ Hydraulic failure of luffing mechanism of cantilever bucket wheel reclaimer

Cantilever bucket wheel reclaimer is the key equipment for port material handling. Two 6000t / h cantilever bucket wheel reclaimers in a port are designed and manufactured by Mitsubishi Corporation of Japan.

(1) Working principle of hydraulic system of luffing mechanism

The hydraulic system of luffing mechanism is a balance circuit, and its principle is shown in Figure v. The luffing of the cantilever bucket wheel reclaimer is realized by two parallel hydraulic cylinders 11 and 12. The boom counterweight, bucket wheel and other components in the luffing mechanism constitute the overload of the telescopic elbow of the hydraulic cylinder piston assembly. In order to prevent the boom counterweight, bucket wheel and other components from overturning or falling due to their own weight, a one-way sequence valve 8 and 8 are connected in series with the oil ports a and B of 7 9. The valve acts as a balance valve. The two-way luffing speed of the boom is set by the electro-hydraulic proportional speed regulating valve 3, and its luffing direction is controlled by the electro-hydraulic directional valve 7.

When the two cantilever bucket wheel reclaimers are delivered, the hydraulic locks 10 and 13 in Figure V are not set. During commissioning, the boom cannot be accurately positioned at any position and has serious sliding phenomenon. Japanese experts added components such as hydraulic lock 10 and electromagnetic directional valve 13 in Figure V, the fault phenomenon was alleviated, but there was still a little sliding when the boom stopped moving.

(2) Faults and analysis in use

After the two cantilever bucket wheel reclaimers were put into operation, the luffing mechanism has been in a normal working state. However, in the high temperature season, when the site temperature is about 43 ℃, both reclaimers vibrate in the process of downward amplitude variation, and the amplitude at the bucket wheel reaches 2m. In addition, the phenomenon of a little sliding when the boom stops moving is more serious. By judging the system noise, it is found that the change frequency of oil flow noise at balance valve 9 is consistent with the vibration frequency. Therefore, it is judged that the vibration fault in the luffing process is caused by balance valve 9. The balance valve 9 is set to prevent the bucket wheel and other components from falling due to their own weight. It controls the damping on the oil circuit, that is, it reflects that the opening pressure is set by the overload formed by the bucket wheel and other components. When the ambient temperature is low, the oil viscosity is high, the damping on the control oil circuit of balance valve 9 increases and the opening pressure increases. When the bucket wheel drops, the back pressure on the oil return pipeline of the hydraulic cylinder increases; Therefore, the whole boom runs smoothly. On the contrary, when the ambient temperature is high, the oil viscosity becomes low and the damping becomes small. When the bucket wheel descends, the back pressure on the oil return pipeline of the hydraulic cylinder becomes low, the bucket wheel and other components accelerate to decline due to their own weight, and the pressure in the oil inlet chamber of the hydraulic cylinder decreases. When the pressure drops to the opening pressure of the balance valve, the balance valve closes, the bucket wheel and other components "temporarily" stop moving, and the pressure in the oil inlet chamber of the hydraulic cylinder rises. When the pressure rises to the opening pressure of the balance valve, the balance valve opens, and the bucket wheel and other components accelerate to decline. In this way, the balance valve is opened and closed repeatedly, that is, chattering occurs. As the balance valve in Figure V adopts a one-way sequence valve, the one-way sequence valve itself has internal leakage, resulting in poor locking. For this purpose, a hydraulic lock 10 is connected in series between valves 8 and 9 and the hydraulic cylinder. The function of hydraulic lock 10 is to "lock" the hydraulic cylinder and position it accurately when the hydraulic cylinder stops moving. When the boom stops moving, the sliding phenomenon occurs because the back pressure valve 15 is installed on the control oil circuit of hydraulic lock 10, so that the one-way valve in hydraulic lock 10 cannot be closed and locked in time, that is, the so-called "lag locking" phenomenon occurs.

(3) Troubleshooting measures

In order to completely eliminate the vibration and sliding faults of luffing mechanism, the following measures are taken. As shown in Figure w, before the balance valve 9 controls the one-way throttle valve on the oil circuit, an adjustable flow valve 16 is connected in series (structurally, a superimposed plate for throttling is added under the original combined valve), so as to adjust the opening and closing time of balance valve 9. The length of this time is appropriate to avoid chattering. In addition, when the electromagnetic directional valve 13 is not powered on, the control oil circuit and leakage oil circuit of the hydraulic lock 10 are directly connected back to the oil tank without passing through the back pressure valve, so that the control oil circuit does not maintain pressure and is closed in time to avoid the phenomenon of so-called "lag locking". The scheme can completely eliminate the vibration and sliding faults of the luffing mechanism.

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As shown in figure x, remove the hydraulic lock 10 and electromagnetic directional valve 13 in Figure V, and replace the one-way sequence valves 8 and 9 with balance valves; Two one-way throttle valves 17 and 18 are connected in series on the oil circuit between balance valves 8 and 9 and the hydraulic cylinder. Adjust the opening of the one-way throttle valve, so as to adjust the back pressure. The back pressure should not produce chattering. The scheme can also completely eliminate the vibration and sliding of the luffing mechanism.

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