Faults and Analysis of Hydraulic Lock of MS900 Rolling Mill

Abstract : Aiming at the problems encountered in the production of MS900 rolling mill , the failures and causes were analyzed mainly due to double locks instead of single locks, wrong installation positions of hydraulic locks, and inconsistent types of reversing valves used in conjunction with them.
Keywords : Strip mill ; hydraulic system ; hydraulic lock ; reversing valve

Hydraulic control check valves and double hydraulic control check valves are commonly referred to as single hydraulic locks and double hydraulic locks, referred to as single locks and double locks .
the MS900 rolling mill hydraulic system. Usually, the single lock is used to drag the load in the vertical direction, and the double lock is used to drag the load in the horizontal direction or the swing direction. The hydraulic motor circuit also uses double locks .
2 Hydraulic lock failure and analysis
In the MS900 rolling mill hydraulic control system , there are many reasons for the failure of the hydraulic lock. The following is a brief analysis .
2-1 Double lock instead of single lock causes failure
Usually the circuit with single lock can be replaced by double lock, but if the working environment of some executive components is special, sometimes single lock cannot be replaced by double lock . For example, the squeeze out anti-jump circuit ( as shown in Figure 1a ) is used to drag the squeeze roller to squeeze out the emulsion on the surface of the strip running at high speed and prevent the strip from jumping . When replacing the hydraulic lock , a double lock was used instead of a single lock ( as shown in figure 1b ) to improve the use effect , but the oil pipe burst occurred as a result .
The analysis shows that the squeeze roller will jump violently during operation ( although the amount of jump is small ) . If the squeeze roller jumps up, the piston of the hydraulic cylinder of the squeeze roller will be dragged to move upward passively, so that the volume of the rod chamber of the cylinder will increase to generate negative pressure oil. The liquid enters the rod chamber through the center lock of the reversing valve and the one-way valve of the speed regulating valve, and the volume of the rodless chamber of the cylinder decreases at the same time . Because the hydraulic lock has a locking function, the oil cannot be discharged and the pressure rises ; if the squeezed roller jumps down, the rodless chamber of the cylinder will absorb oil and the rod chamber will increase the pressure. Due to the locking effect of the double lock, the oil can only enter and cannot be discharged. The pressure in the rod chamber and the rodless chamber of the cylinder will rise alternately, eventually causing the oil pipe to burst .
2-2 Fault caused by wrong installation location
the valve parts on the MS900 rolling piece hydraulic valve group are installed in a superimposed manner . The installation positions from top to bottom are : reversing valve , hydraulic lock , speed control valve ( double one-way throttle valve ), pressure valve ( relief valve or safety valve ) and oil block .
When troubleshooting the trolley lifting circuit ( as shown in Figure 1c ) , the positions of the single lock and speed control valve were reversed by mistake . The role of the coiler is to take the coil from the saddle, lift it up and align the drum, and then move the coil laterally to the drum. As a result, it is found that the steel coil has a sinking action after the lifting action is completed .
resets after the rising action ends , and the pressure between the speed regulating valve and the reversing valve disappears quickly through the neutral position of the reversing valve . There is still a certain pressure between them , and the roll stops sinking . If the single lock is installed in the correct position , after the reversing valve is reset , the oil pressure controlled by the single lock will disappear quickly through the middle position of the reversing valve , the single lock is locked , and the rising action force makes the single lock open . Due to the self-weight of the steel coil, the steel coil sinks , and the pressure of the control single lock disappears .

The model of the supporting reversing valve is wrong, causing a fault
The function of the guide plate is to make the strip pass straight through after being lifted , and play a role in assisting the strip threading . However, after replacing the reversing valve of the swing circuit of the guide plate of the starter , it was found that the raised guide plate slowly descended . Checked for this , found that the model of the original reversing valve is : 4WE10J10, the middle position is "Y" type ( as shown in Figure 1e ), and the model of the replacement valve is : 4WE10E10, the middle position is "0" type ( such as As shown in Figure If ).
After analysis , the reason is : when the guide plate swings to a high position , the reversing valve loses power , the valve core is in the middle position , and the replaced reversing valve is in the "0" type , and there is a certain seal between the single lock and the reversing valve. The pressure that keeps the single lock in the open position . Since the reversing valve has a certain internal leakage , the guide plate will slowly descend under the action of its own weight .
24 The three-position reversing valve replaces the two-position reversing valve causing failure
MS900 rolling mill are different from the common lock circuits ( as shown in Figure 1g ). The single lock is used in conjunction with the two-position four-way solenoid valve , and the pressure oil is passed through the rod cavity , and the reel is in a tensioned state . The function of this circuit is : after the reel is rolled , the reel rises
( Continued from page 52 )
Extend to the side of the rolling wheel , and flatten the head so that the cooling water is sprayed directly onto the rolling wheel in a fan shape for cooling . The lubrication method adopts the intermittent lubrication method , and the lubricating oil is injected every 2 hours . The lubricating oil pipe is tightly connected to fix the steel coil , and then the tension can be built for rolling . After rolling , the diameter of the reel is reduced and the coil is unloaded , and this process is repeated .
When troubleshooting the stuck fault of the reversing valve core , the three-position four-way reversing valve was replaced by mistake , and the middle position was "Y" type ( as shown in Figure lh ). As a result, five coils of finished steel coils that were continuously rolled out were deformed .
According to the analysis , as the diameter of the coil increases during production , the pressure on the inner ring of the steel coil increases . Under the action of the hydraulic lock, the diameter of the coil cannot be properly reduced , resulting in deformity of the inner coil when the steel coil is unloaded. . If a two-position valve is used ( as shown in Figure 1g ), when the pressure generated by the steel coil on the reel is greater than the tension force provided by the hydraulic pressure , the reel will automatically shrink in a small amount to properly reduce the inner diameter because the check valve is always open. pressure on the circle . In the event of a failure to stop the pump , the pressure of the main oil circuit and control oil of the single lock will disappear quickly , and the single lock will act as a locking cylinder to prevent the strip from collapsing .
To the operation side of the rolling mill , it is convenient for workers to inject oil .

---