Created on:2021-07-21 10:21

Maintenance of refining furnace_ Transformation of hydraulic system

Maintenance of refining furnace_ Transformation of hydraulic system

Hj90 / 130t ladle refining furnace is the key equipment of a company, which has long exceeded the normal overhaul period. The company requires to complete the overall overhaul of the refining furnace within three months. Hydraulic system is the core part of hj90 / 130t ladle refining furnace.

(1) Problems of hydraulic system before overhaul

During the nine years of operation before the overhaul, the problems and parts of the hydraulic system in the original design and use, such as high failure rate, inconvenient maintenance and leakage, have been improved to make it meet the requirements of production and process as much as possible. In order not to affect the normal production, there are still many problems to be solved in the overhaul.

① The main shut-off valve of vacuum has serious oil leakage, the gate is often opened and closed not in place, and there is no indication in place; The two-way cartridge valve and valve body of the control part have serious oil leakage, which is difficult to find and deal with. Sometimes it is linked with the lifting of the insulation cover.

② The pressure of the two bladder accumulators can't compensate the leakage, keep the pressure, absorb the pressure and relieve the hydraulic impact.

③ Some of the pressure gauges failed, and the oil level gauge was cancelled due to oil leakage at the root, which had been sealed with a screw plug. The oil level of the oil tank can only be observed from the top cover of the oil tank, and there is no minimum oil level alarm device and no oil temperature display.

④ The return oil temperature is high. The return oil temperature of the main hydraulic system is about 60 ℃, and the working temperature of the electro-hydraulic servo valve used to control the electrode lifting should be (40 ± 10) ℃. The original oil cooler is leaking.

⑤ When the two pumps are running, the noise is large, the oil pressure is unstable, and the temperature of the pump body is high.

⑥ The heating cover, vacuum cover, insulation cover and all hydraulic cylinders have serious oil leakage, especially the failure rate of two-way cartridge valve and manifold block in the control part is very high, the fault is not easy to investigate and deal with, and the valve core is often stuck. During operation, the control parts of the three covers have linkage phenomenon. When the boiler is shut down, the three covers will sink to the lowest point due to their own weight. The loose clamp part of the electrode is not flexible and in place.

(2) Measures and methods to solve the problem

① Transformation of vacuum main stop valve

a. Increase the diameter of hydraulic cylinder. The inner diameter is determined by φ 160mm to 160mm φ Under normal working pressure of 5MPa, the theoretical maximum thrust is 157kn.

b. Hydraulic cylinder is equipped with limit device. A push rod is added at the rear of the piston to connect with the piston. The rod end is equipped with a head to stop the movement after touching the fixed limit. There is an indicator light in the main control room to control the movement of the main stop valve.

c. Remove cartridge valve. The complicated two-way cartridge valve and manifold block are all cancelled and replaced with a two position four-way valve. The performance characteristic of two position four-way valve is that when the actuator moves forward and backward, its oil return mode is the same, which will not make the actuator stop moving at any position. Therefore, the phenomenon of opening and closing not in place can be avoided. The valve has the advantages of simple structure, convenient disassembly, easy maintenance and easy operation. After replacement, the volume of the valve is reduced, and the joint parts are less, so as to eliminate the leakage. Because of the short commutation time, series voltage and linkage with other mechanisms can be avoided.

② After cleaning, the two bladder accumulators are pressurized to 6Mpa and 2MPa respectively for energy storage and short-term oil supply. This kind of skin bag has small inertia, fast reaction, convenient maintenance, air and oil isolation, and oil is not easy to aging.

③ Replace the pressure gauge, replace all the pressure gauges, and add a switch in front of the gauge, which can be closed at ordinary times and opened in time, so as to prolong the service life of the pressure gauge. Restore the oil level gauge and install a liquid level signal sensor on the oil tank. It can display the oil level in the main control room and has the lowest oil level alarm function.

④ Replace the vane pump and renew the two single stage vane pumps. The new pump is easy to realize variable and direction changing, which is conducive to saving input power, compact structure, small size, smooth movement, low pulsation and noise.

⑤ Replacement of cartridge valve will replace the three sets of two-way cartridge valve and manifold block used to control the rise and fall of heating cover, vacuum cover and insulation cover with three three position four-way directional valves. The performance characteristics of the three position four-way valve are that when it is in the middle position, all the oil ports are closed, the oil does not flow, the system maintains the pressure, the hydraulic cylinder is closed and locked, and the pump does not unload; When the actuator moves left and right, the oil return mode is the same, which can make the actuator stop at any position. This kind of valve has fast reaction speed, stable starting and no impact; During the commutation process, the position is accurate and there is basically no leakage; It is reliable and easy to operate.

For the control part of the three-phase electrode unclamping device, the original four-way cartridge valve and valve seat are all cancelled and replaced with three two position four-way directional valves. Its performance characteristics are the same as that of the two position four-way directional valve which controls the movement of the main stop valve, and can ensure the safety of the valve φ 400mm electrode clamped or loosened.

(3) Precautions in operation

① Sealing is the premise to ensure the normal operation of the hydraulic system. The main reasons for system leakage are: low machining accuracy of moving pair and wide range of fit clearance; The fit between the valve core and the valve seat is not tight due to wear; The difference of the spring stiffness and the action of the pump are not synchronous; The static sealing quality of the joint surface of the components and accessories in the system is not high, the performance standard is reduced, and the sealing of the relative moving surface between the hydraulic cylinder and the piston is designed by the manufacturers themselves, which is lack of reliability test.

Compared with the above reasons, the measures taken in the overhaul are: Double nylon framework Y-shaped wear-resistant seal ring and standard parts for hydraulic cylinder; Simple and practical control elements are used; Improve the installation quality of the whole system. One barrel of oil should be added every week before the overhaul, and one barrel should be added 45 days after the overhaul, which greatly reduces the leakage.

② More than 70% of all kinds of faults in hydraulic system are related to the pollution of hydraulic oil. Therefore, it is an important work to improve the cleanliness of hydraulic equipment. If the sealing is not tight and the cleaning is not paid attention to during the maintenance, the external pollutants may enter the system. This will make the area of control oil port, throttle port, damping hole and pipeline decrease or even be blocked, resulting in increased energy loss and overheating of the system.

Therefore, use the dough to clean the dirt in the tank before use. In use, first of all, close the oil inlet, and check and test the oil quality before each refueling; The second is to regularly check and clean the magnetic filter screen, outlet filter element and fuel tank filter element; The third is to regularly check the oil quality, oil level, oil temperature and whether there are leakage points, and deal with the problems in time.

③ The oil temperature control in a reasonable range plays an important role in maintaining the good performance of the hydraulic system. In the overhaul, the original oil cooler was scrapped, two large oil coolers were made, and qualified components were selected to strengthen heat dissipation. In addition, softened water or domestic water should be used to prevent the blockage of dirt and the generation of scale.

After the hydraulic system of the equipment was reformed in the overhaul, there was no accident due to the problems of the hydraulic station, the failure rate was reduced, the operation procedure was simplified, the maintenance was convenient, and the leakage was reduced.

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