Created on:2021-07-14 10:51

MXA-300 shearer hydraulic failure

MXA-300 shearer hydraulic failure

(1) Characteristics of hydraulic transmission system

MXA-300 is a domestic high-yield and high-efficiency hydraulic haulage double drum shearer with an annual output of 1 million tons, but it still has a big gap compared with the foreign similar products. After more than ten years of production and use, more than 80% of the faults of this kind of shearer occur in the hydraulic system, among which the hydraulic system of traction part and cutting part is the most prominent. The hydraulic transmission system of traction part is shown in Figure e, and that of cutting part is shown in Figure F.

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In the hydraulic system of MXA-300 shearer, the pressure is greatly affected by the load. When the working resistance is large, the pressure in the hydraulic system is large, and the pressure loss and leakage also increase. The hydraulic transmission system is connected by oil pipes, and the hydraulic energy is converted into mechanical energy by hydraulic oil. Pipelines and other hydraulic components are fastened by connecting screws, which are sealed by seals or gaps to reduce and eliminate leakage. Therefore, the connection is not tight, the installation position is not correct, will produce leakage, and leakage will seriously affect the performance of the system. The working medium of hydraulic system is hydraulic oil, and the oil temperature has a great influence on the system, which will cause the change of oil viscosity.

MXA-300 shearer hydraulic components have high manufacturing accuracy and small fit clearance. Most of them are sealed by clearance, especially for the main components such as, etc. they not only require good sealing performance and flexible action, but also need to use oil film to reduce metal friction. This requires that there should be no moisture, air, mechanical impurities in the transmission medium - oil, otherwise the components will be damaged, stuck, and failure will occur. The hydraulic system of the shearer is equipped with overload and undervoltage protection system. The adjustment value of the hydraulic components of the protection system must be accurate and reliable, otherwise it will affect the normal work of the machine.

(2) Analysis and elimination of common faults

According to practical experience, the procedure to judge the fault of MXA-300 shearer hydraulic system is listening, touching, looking, measuring and comprehensive analysis. Listen: the driver on duty introduces the status and symptoms before and after the failure. Touch: the shell of the occurrence point, judge the temperature change, and touch the hydraulic system for leakage. Look at: operation log, use and replacement time of main hydraulic components, hydraulic system diagram and oil test sheet, and observe the changes of high and low pressure of hydraulic system, and whether the filtration and connection are reliable when the machine is running. Measurement: measure the flow and temperature, check the changes of high and low pressure in the hydraulic system, grease pollution, leakage of main hydraulic pump and hydraulic motor and oil temperature changes, and check whether the servo mechanism, high and low pressure safety valve, back pressure valve and protection system are normal. According to the comprehensive analysis of the materials obtained from the above inspection, the method of dissecting layer by layer is adopted to find out the fault point, find out the cause of the fault, put forward the feasible treatment scheme, and eliminate the fault as soon as possible.

① High and low pressure abnormal shearer hydraulic system is divided into high pressure and low pressure two parts, high pressure increases with the increase of load, low pressure is stable, not affected by load.

a. The low pressure is normal and the high pressure drops. When the load increases, the high pressure decreases. This shows that there is leakage in the hydraulic system, and the leakage point is at the high pressure side of the main oil circuit, so it should be stopped for inspection.

b. High pressure normal, low pressure down. It indicates that there is leakage in the low pressure system or oil make-up system. Check the low pressure side of the main oil circuit, auxiliary pump and oil make-up system.

c. The high pressure drops and the low pressure rises. Explain the hydraulic system of high and low pressure collusion, should check the high pressure safety valve, bypass valve, shuttle valve whether there is leakage, resulting in high and low pressure collusion.

② The causes of this kind of fault phenomenon are generally considered from the following aspects: 1

a. Serious leakage of main hydraulic pump or hydraulic motor; b. Serious leakage of high pressure safety valve or check valve; c. Servo mechanism failure, such as servo valve or control cylinder does not act; d. Motor constant power speed regulation failure, such as power speed regulation piston stuck in V-groove;

e. Hydraulic automatic speed control device failure, such as hydraulic cylinder leakage or spring damage, etc; f. High pressure safety valve failure, such as low adjustment pressure or spring damage, etc; g. The bypass valve and shuttle valve are not closed tightly, resulting in high and low pressure collusion.

③ Two way non traction (low pressure system pressure) causes this kind of fault phenomenon from the following aspects: A. auxiliary hydraulic pump leakage serious or damaged; b. The coarse oil suction filter of auxiliary hydraulic pump is blocked, the oil supply is difficult, and the pressure loss is large; c. The oil tank of the traction part is seriously short of oil, which makes the auxiliary hydraulic pump suck air, resulting in the oil pressure drop or instability; d. High pressure safety valve failure, valve leakage is serious; e. Back pressure valve stuck or damaged; f. The low pressure side joint of shuttle valve leaks seriously; g. Leakage of back suction valve; h. Under pressure protection failure, serious leakage of under pressure protection valve, etc.

④ The causes of this kind of failure are generally considered from the following aspects: a. the servo mechanism acts in one direction, such as the follow-up valve acts in one direction, so that the main hydraulic pump can only swing in one direction; b. There is a side pipe joint leakage in the main oil circuit; c. The shuttle valve operates in one direction, one end of the valve body is damaged, and the valve core can only operate in one direction; d. One or one side of the high pressure safety valve leaks; e. There is leakage on one side of the bypass valve.

⑤ The causes of this kind of failure are generally considered from the following aspects: a. the main hydraulic pump has leakage, generally the leakage is not serious, but if it continues to develop, it will cause no traction; b. The main oil system pipe joint leakage, generally for the joint seal is not tight, resulting in more leakage; c. High oil temperature causes serious leakage. The possible reasons for high oil temperature are too high viscosity of oil, oil pollution, hydraulic system leakage, etc; d. Servo mechanism action failure, such as servo valve or control hydraulic cylinder leakage, resulting in the main hydraulic pump can not be locked, etc.

⑥ According to statistics, about 600% of the faults of shearer hydraulic system are caused by oil pollution. Therefore, oil pollution must be analyzed frequently.

a. The normal oil temperature of the traction part is 60 ~ 70 ℃. If the oil is emulsified after mixing with water, the viscosity of the oil will decrease, the system leakage will increase, and the oil temperature will rise rapidly. If it is not handled in time, it will cause the failure of the hydraulic system. Treatment method: observe whether the oil level of the traction oil tank rises; Take oil sample to observe whether there is precipitation; The oil decomposes quickly after entering the water. The upper part is oil and the lower part is water. In this case, the oil should be changed immediately.

b. When the oil is mixed with air, cavitation will occur in the hydraulic system, and the hydraulic pump will make abnormal sound. If it is not handled in time, the main pump and the hydraulic system will be damaged. Treatment method: check whether the filter is blocked; Whether there is leakage in the oil suction pipe; Check whether the liquid level in the fuel tank of the traction part is too low. These are the main factors that cause the system to absorb air, which should be dealt with in time.

c. If the oil is mixed with mechanical impurities, the filter will be blocked. If the filter is not cleaned frequently, the mechanical impurities will enter the hydraulic system through the one-way valve, causing damage to some hydraulic components and causing leakage of the hydraulic system. Treatment method: the filter should be checked and cleaned every shift; Take oil samples regularly for observation and test.

d. The slow action of servo mechanism is also caused by oil pollution. The oil is polluted, which increases the leakage of the hydraulic system and reduces the pressure and flow of the hydraulic system.

⑦ The main hydraulic pump pressure is abnormal, the hydraulic motor does not rotate or the output torque is low. The main hydraulic pump of MXA-300 shearer mostly adopts axial piston pump, and the hydraulic motor basically adopts two types, one is axial piston or radial piston hydraulic motor, the other is cycloid hydraulic motor. The main hydraulic pump and hydraulic motor are the key hydraulic components of the traction part and the heart of the hydraulic system of the shearer. The failure will stop the production of the whole fully mechanized mining face. If the failure analysis is not accurate, it will cause a vicious circle.

a. The main hydraulic pump pressure is low. The symptom is that the traction force and traction speed of the shearer are reduced, and there is pulsation when pulling the bow I. The causes of this kind of failure should be considered from two aspects: one is the local wear of the matching surface between the oil distribution plate and the cylinder block of the main hydraulic pump, resulting in the leakage of the matching surface; Second, the clearance between piston and cylinder block is large, which causes the hydraulic oil leakage from the clearance when the piston discharges oil.

b. The main hydraulic pump pressure suddenly drops to zero. The symptom is that the high and low pressure of the shearer suddenly drop to zero during operation, which indicates that the oil distribution plate of the main hydraulic pump and hydraulic motor is seriously worn or damaged.

c. There is no pressure in the main hydraulic pump. The symptom is that the high pressure is zero and the shearer does not pull. This is mainly due to the main hydraulic pump body fracture or piston fracture, resulting in the main hydraulic pump does not rotate.

d. The hydraulic motor does not rotate. The reason is that the matching surface of oil distribution sleeve and oil distribution shaft is worn, and the motor is locked up due to the increase of oil temperature.

e. The output torque of oil motor is low. The symptom is low traction. The causes of this kind of failure should be considered from the following aspects: the mating surface of oil distribution sleeve and oil distribution shaft is worn, and the pressure oil leaks; There is wear on the matching surface of piston and cylinder block, and the pressure oil leaks when the piston moves back and forth; Some springs or expansion rings of the motor are damaged, and some pistons do not reciprocate.

(3) Measures to reduce faults of shearer hydraulic system

① Strictly implement the "four inspection" system, that is, the compulsory maintenance system of shift inspection, daily inspection, ten day inspection and monthly inspection, and timely repair and treatment.

② The driver of the shearer should choose a reasonable traction speed according to the working coal quality, roof, floor and other geological conditions, not overload operation, strictly implement the operating procedures, put an end to blindly seeking output and illegal operation, and strictly implement the reward and punishment system.

③ In some places, the market of shearer accessories is chaotic, the quality of accessories is rough, and the maintenance, quality inspection and guarantee system is not perfect. Near the large coal machinery factory, there is even a phenomenon of coal machinery accessories street, which seriously affects the use of shearers. Therefore, it is necessary to establish the manufacturer's maintenance responsibility system to eliminate unqualified parts and ensure the quality of product maintenance and renovation.

④ At present, some standards in the manufacture and maintenance of shearers in China are strictly enforced. For example, the explosion-proof standard is close to that in Britain, which is stricter than that in the United States. Some standards are loose, which is one of the reasons why the quality of shearer is not high. High quality products come from high standards. Standard is the technical basis of product quality. Considering the situation of national conditions, users and manufacturers, the standard should be appropriately raised by 1-2 levels to improve the quality of shearer products. The maintenance of shearer shall be carried out in strict accordance with the procedures. For the shearer after minor repair and major repair, the user unit shall have special acceptance personnel. The maintenance unit shall issue the necessary certificate and experimental report, identify the responsible person, and file the relevant data for future reference.

⑤ The oil for shearer shall be managed by special personnel, and the trial implementation rules for oil management of fully mechanized mining equipment issued by the former Ministry of coal shall be strictly implemented. There should be a special person and special barrel to transport oil to the well. Pollution prevention measures should be taken when injecting oil into the well. Oil should be injected according to the oil injection chart specified in the product manual. The filter should be checked or cleaned once a shift, and the hydraulic oil of traction department should be tested and analyzed once a month.

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