Created on:2021-07-20 09:58

Heating furnace_ Failure of proportional control for horizontal hydraulic cylinder of walking beam furnace

Heating furnace_ Failure of proportional control for horizontal hydraulic cylinder of walking beam furnace

(1) Proportional control of horizontal hydraulic cylinder in walking beam furnace

The load driven by horizontal cylinder of walking beam furnace is large and has great inertia. In order to prevent the impact, slow acceleration is carried out when the horizontal cylinder of the walking furnace is just started, and two-stage deceleration is carried out before the running is finished. The ideal velocity curve is shown in Figure s.

In order to meet the requirements of horizontal cylinder movement speed, the pump source is fe25cio type two-way plug-in displacement electric feedback electro-hydraulic proportional throttle valve (with the advantages of controlling large flow, high power hydraulic system and high steady-state accuracy) is adopted. The electro-hydraulic proportional system diagram of walking furnace is shown in Figure T, and the electro-hydraulic proportional control block diagram of horizontal cylinder speed is shown in Figure U.

S1T1U1.jpg

The control principle is as follows. The liquid flow at the port of two-way cartridge valve is equivalent to the flow form of small hole. Its flow rate is related to the flow coefficient (generally constant), pressure difference and overflow area, while the overflow area is related to the area gradient and spool displacement. The formula of flow rate is q = cdwxv, and there is a linear relationship between valve core displacement XV and the current of proportional electromagnet. Therefore, as long as the pressure difference between the inlet and outlet of the valve is constant (the constant differential pressure reducing valve system with pressure compensation function is adopted) and the flow rate of the valve port is linear with the given current of the proportional electromagnet, the ideal horizontal cylinder motion speed curve can be obtained as long as a certain electric control signal is given to the proportional amplifier.

(2) Typical symptoms and causes of control failure

When the fault occurs, the movement deceleration is not obvious, but the movement speed is low, or even does not move. The analysis shows that the fault is either from the electronic control system, including amplifier, proportional electromagnet, displacement sensor, etc; Or from the hydraulic system, including proportional throttle system, differential pressure reducing valve system.

(3) Troubleshooting procedures

Firstly, the current of the given proportional electromagnet and the electrical signal of the main spool displacement sensor are detected to ensure its normal operation. Secondly, the constant pressure reducing valve is inspected and disassembled to check whether the valve core is within the normal wear range and whether the rigidity of the return spring is good; Whether the wear of the cone valve core of the control cover plate is within the normal range, whether the rigidity of the return spring is good, and whether the damping plug in the cover plate is unblocked. In addition, clean the two-way cartridge proportional throttle valve block to ensure that its control oil passage and damping plug are unblocked, and properly adjust the differential pressure of constant differential pressure reducing valve.

After taking the above measures, the proportional valve can restore the speed control function, and the movement speed of the horizontal cylinder can be ideally controlled.

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