1. Easy failure and causes
1) Leakage
Although the leakage of hydraulic components has been greatly reduced with the continuous improvement of processing technology and material properties, the leakage failure of the hydraulic system still accounts for a high proportion in the specific working environment of iron and steel enterprises.
Leakage refers to the external leakage of the system, which is directly reflected in the reduction of the total amount of oil in the system. The occurrence point is mainly in the actuator (such as a hydraulic cylinder) and its connecting pipeline, close to the red blank. Because these components are completely exposed to the strong infrared radiation of the casting blank, it is easy to cause the aging of the rubber hose and the sealing failure of the tubing and hydraulic cylinder joints; The second is in the continuous casting operation area and the equipment field maintenance operation area of the cross operation area, here not only interwoven with a variety of mechanical, electrical and hydraulic equipment, but also the casting billet tail processing place, the cross operation of various types of work, if the coordination is not good, it is easy to collide and cause accidents, for the hydraulic system is the damage of components and external leakage.
Internal leakage mainly occurs in the pump body, cylinder block, and valve body. The leakage in the cylinder is mainly because the hydraulic cylinder, as the actuator, is relatively close to the casting billet or ladle, and the strong thermal radiation causes the high temperature aging of the seal on the piston, resulting in the oil pumping of the high and low pressure two chambers, so that the pressure of the high pressure chamber is reduced. Its direct performance is that the hydraulic cylinder lifting and contraction are slow, weak, and cannot even complete the specified action in serious cases. At this time, the noise of internal oil pumping can be obviously heard close to the cylinder wall. Because the pump and valve are mainly installed in the special hydraulic pump room, their internal leakage is mainly caused by the wear of the moving parts, which is a long, slow change process. To go through the running-in period, stable period, and rapid wear period of these three stages, the first two stages are for the quantitative change accumulation stage. The third stage is the qualitative change stage. At this time, the pump and valve operating noise increases, and the pump outlet pressure drops in serious cases, resulting in insufficient pressure supply to the entire system. If the internal discharge of the constant-pressure variable pump in use increases, the amount of oil discharged through the pump housing increases. If the flow cannot be discharged in time, the oil pressure at the housing will increase, and the hydraulic pump will be damaged in serious cases. The leakage in the valve may cause the mechanism to misoperate. Internal leakage is a kind of hidden fault, and from quantitative change to qualitative change, it is not easy to find in time, and the harm is greater than the leakage.
2) Oil pollution
Oil pollution is another important factor that causes a variety of hydraulic system failures, the direct result in valve damping hole plugging and valve core stuck, resulting in misoperation. The former mainly occurs in the pilot type pressure control valve, which has a long damping control hole (diameter of about 0.8 ~ 1.2mm) from the main stage to the pilot stage in the structure, which is used to adjust the pressure difference of the main valve core movement, if blocked, it can not be adjusted; The latter mainly occurs in electromagnetic directional valves with slide spool. Especially in the use of a period of time in the reversing valve more likely to occur, this is due to the frequent action of the spool and the valve body clearance between the larger.
3) Use maintenance processes
The process of use and maintenance is also the process that causes faults. The causes of these failures are more complex, but a large part of them are due to the operation and maintenance personnel did not operate according to the relevant procedures. Such as the installation of the pump, because the driving shaft of the hydraulic pump can not bear the radial force and axial load in the structure, the shaft of the pump and the motor should be strictly aligned during installation. However, in the on-site installation of the maintenance personnel lack of necessary installation, testing equipment and technical guidance, the installation process is rough, can not meet the design requirements, although generally to compensate for the coaxial error of the pump and motor shaft, most of the elastic coupling flange connection, it is still unable to avoid the serious consequences of this rough installation. A continuous casting machine uses a Vickers vane pump; the hydraulic medium is water-glycol. The original pump of the system was replaced for half a year, and the replaced pump was only used for less than half a year, which shows the serious consequences. If the components are replaced without the necessary test, the user of the party knows that the replacement is still bad, or the closed ball valve is not opened after the maintenance is completed, resulting in misoperation. And the intermediate ladle through the ladle, the overflow of molten steel splatters to control the sliding water port on the hydraulic components, causing damage to the components also occur.
2. Fault classification and solution
1) Natural factors
Such factors exist objectively, and only measures can be taken to reduce their impact, but they cannot be completely eradicated. The failure and leakage of seals and pipe fittings caused by high temperature radiation, the unavoidable oil pollution and related consequences on the site, as well as the normal wear of components and the aging of seals, are of this kind.
The solution to the high temperature is to add cooling water spray device. Set up from the cooling water main of the secondary cooling chamber to the cooling branch pipe of pulling straightening and stripping, and make full use of the water pressure of the secondary cold water to spray the cooling water directly to the relevant equipment through the nozzle to cool down. This is low cost, and less water diversion will not affect the cooling effect of the secondary cooling chamber. After adding cooling water, the pipe explosion and leakage failure can be reduced from the original 1.5 pieces /2 days to l ~ 2 pieces /3 ~ 4 weeks. The hydraulic cylinder is replaced due to internal leakage, is replacement from less than 3 months to annual inspection replacement or even longer.
The following measures can be taken to reduce oil pollution: a) Remove the protective packaging of the component when it needs to be replaced to reduce the time exposed to the site; b) Arrange oil replenishment in the pump room as far as possible, and wrap the oil replenishment pipe after the completion of oil replenishment, do not expose; c) Provide a protection plate at the extension of the piston rod of the hydraulic cylinder to block part of the dust, but can not hinder maintenance; d) The focus is still on strengthening the filtration of oil - return oil filtration and circulation cooling system filtration, frequently change the filter element; e) For systems using water-glycol medium, it is best to use stainless steel pipes as tubing to prevent corrosion of tubing by water in the medium. The tank should be cleaned regularly. If the dirt causes the valve failure, the pressure valve can first close the ball valve of the oil inlet, so that the pressure drops to zero, and then suddenly open the ball valve, using the impact of the pressure oil to remove the blockage, can be repeated operation; If the reversing valve is stuck, it can be removed by pushing its manual control lever directly, and if it fails, the component can only be replaced and cleaned.
Single electromagnet reversing valve because the spring is easy to jam, resulting in reversing failure, and hydraulic parts do not act, it is best to use a double electromagnet reversing valve.
2) Maintenance management factors
Such factors are caused by mistakes in decision-making, maintenance, and use, and can be avoided as much as possible. The fundamental solution is to strengthen management, strengthen the sense of responsibility, and carry out necessary and practical operational training for employees. Large iron and steel enterprises should set up a hydraulic repair center, which should have more perfect equipment and technical force, to carry out operations such as the replacement of various commonly used hydraulic pumps, valve cleaning and simple repair, repaired components for detection, to avoid the occurrence of some failures. Second, waste utilization can save outsourced funds.
3) Design factors
The design idea does not consider practicality, and the result is a high failure rate. Two continuous casting machines were put into operation in a steel mill. Machine No. 4 is the first large billet continuous casting machine put into production, and it is the first continuous casting machine that uses a hydraulic system except for the crystallization vibration part, which was relatively advanced at that time, but it is not satisfactory in practice. The main problem is that the operation of hydraulic shear and hydraulic casting is extremely unstable, resulting in a serious abnormal shutdown. The reason is that the hydraulic cylinder and cylinder connecting tubing of the two systems are too close to the casting blank for operation, and the strong thermal radiation causes serious leakage of the cylinder and tubing, and failure. It was made to use spray cooling, but the effect was not ideal, and eventually removed and replaced with flame cutting and mechanical pushing of steel. After putting into operation is the continuous casting machine with the new electric furnace steelmaking; Due to the previous experience of flame cutting and mechanical push steel, the failure rate is very low and the production is stable. The layout of the hydraulic system pipeline in the field, originally used in the lower part of the production surface, the surface looks clean, but it has brought extreme trouble to spot inspection and maintenance. The pipe network below is densely covered, and it is extremely difficult for maintenance personnel to go in for maintenance The pipeline is easily buried by the steel slag rushed down by the second cooling chamber and cut by the working face, and cannot be replaced. Eventually, it had to be routed down from the operating platform instead.
