1. The hazard of excessive temperature of hydraulic oil
1 Hydraulic oil viscosity, volumetric efficiency and hydraulic system work efficiency are reduced, leakage increases, and even mechanical equipment can not work properly.
2 The parts of the hydraulic system expand due to overheating, which destroys the original normal fit clearance of the relative moving parts, resulting in increased frictional resistance and easy to get stuck in the hydraulic valve. At the same time, the lubricating oil film becomes thinner and the mechanical wear increases, resulting in pumps, valves, The precision mating surface of the motor or the like is disabled or scrapped due to premature wear.
3 Accelerate the deterioration of the rubber seals, shorten the service life, and even lose its sealing performance, causing serious leakage of the hydraulic system.
4 oil vaporization, water evaporation, easy to make the hydraulic components cavitation; oil oxidation to form a gel-like deposit, easy to block the oil filter and small holes in the hydraulic valve, so that the hydraulic system can not work properly.
Therefore, the excessive temperature of the hydraulic oil will seriously affect the normal use of the machine, reduce the service life of the hydraulic components, and increase the maintenance cost of the construction machinery.
2. Reasons for the excessive temperature of hydraulic oil and oil and preventive measures
(1) improper selection of oil products
The brand, quality and viscosity grade of the oil do not meet the requirements, or different grades of hydraulic oil are mixed, resulting in a hydraulic oil viscosity index that is too low or too high. If the viscosity of the oil is too high, the power loss increases and the oil temperature rises; if the viscosity is too low, the leakage increases and the oil temperature rises.
Precautionary measures: The selection of oil should be determined according to the grade recommended by the manufacturer, the working environment in which the machine is located, and the temperature factor. For some machines with special requirements, special hydraulic oil should be used; when the hydraulic components and system are inconvenient to maintain, the anti-wear hydraulic oil with good performance should be selected.
(2) Serious pollution
The construction site has a bad environment. As the working time of the machine increases, impurities and dirt are easily mixed into the oil. The contaminated hydraulic oil enters the matching gap between the pump, the motor and the valve, which will scratch and damage the precision and roughness of the mating surface. To increase leakage and increase oil temperature.
Precautionary measures: Generally, the oil is changed after more than 1000 hours of accumulated work. When changing oil, pay attention not only to drain the old oil in the fuel tank, but also to replace the old oil in the whole system pipeline and working circuit; when refueling, it is best to use a filter mesh of 120 mesh or more, and increase the amount of oil according to regulations. The oil has sufficient circulating cooling conditions. In the event of a sudden failure due to contamination with hydraulic oil, be sure to filter or replace the oil used in the hydraulic system. For example, a YZT14G roller has a problem that the hydraulic oil temperature is too high and the vibration force is insufficient. The inspection found that the hydraulic oil is milky white, has deteriorated, and the viscosity has decreased. After the hydraulic oil is replaced, the roller is returned to normal operation.
(3) The oil level in the hydraulic tank is too low
If the amount of oil in the hydraulic tank is too small, the hydraulic system will not have enough flow to take away the heat it generates, causing the oil temperature to rise.
Precautionary measures: In the actual operation and maintenance process, strictly observe the regulations on the hydraulic oil level in the operating procedures. For example, a PC2003 hydraulic excavator has a problem of excessive hydraulic oil temperature after working for a period of time; check the hydraulic oil tank and find that the oil level is lower than the specified value. Because the hydraulic system is excessively short of oil, the hydraulic oil is circulating too fast. The heat can be fully rested, and the oil temperature rises; after the hydraulic oil is added according to the regulations, the temperature of the hydraulic oil drops to the normal range.
(4) Air is mixed into the hydraulic system
The air mixed in the hydraulic oil will escape from the oil and form bubbles in the low pressure zone. When it moves to the high pressure zone, the bubbles will be crushed by the high pressure oil, which will be compressed rapidly and release a large amount of heat, causing the oil temperature. Raise.
Precautions: Always check the tightness of the seals at the inlet pipe joints to prevent air from entering; at the same time, drain the air from the system after each oil change. For example, the temperature of a hydraulic oil of a PY184 grader is too high, accompanied by hydraulic noise; inspection found that the hydraulic pump inlet hose is slightly damaged, inhaling air, causing excessive oil temperature, replacing the hose after the grader It is in good working condition.
(5) Oil filter blockage
When abrasive particles, impurities and dust pass through the oil filter, they are adsorbed on the filter element of the oil filter, causing an increase in oil absorption resistance and energy consumption, causing an increase in oil temperature.
Precautions: Clean and replace the oil filter regularly. For oil filters with clogging indicators, clean or replace the filter element according to the instructions. The performance, structure and expiration date of the filter element must meet the requirements for use. For example, a TY220 bulldozer continuously alarms when the oil temperature alarm is in operation, and at the same time, it is found that the torque converter has the burning smell of oil smoke and oil, and the oil level in the steering tank is low; the inspection result is that the torque converter return pump The oil filter filter blockage caused this failure, because the filter is full of deposits, so that the oil leaking from the torque converter can not be pumped back to the steering tank in time, the more accumulated, the torque converter placed resistance increased, the heat generated by friction Increased, and finally caused the oil temperature rise too fast; after cleaning the filter, the oil temperature returned to normal. Another example is a CATD8N crawler dozer hydraulic drive system that emits a high temperature alarm and an abnormal sound in the transmission part; the filter is removed and the filter element is found to contain a large amount of powdery dirt; after the filter element is replaced, the fault disappears.
(6) The hydraulic oil cooling circulation system is not working properly.
Typically, water-cooled or air-cooled oil coolers are used to forcefully cool the oil system's oil temperature. The water-cooled chiller will reduce the heat dissipation coefficient due to the dirty heat sink or poor water circulation; the air-cooled chiller will block the gap of the fin of the cooler due to excessive oil pollution, and the fan is difficult to dissipate heat. Causes the oil temperature to rise.
Precautions: Regularly inspect and maintain the hydraulic oil cooling circulation system. Once a fault is found, it must be stopped immediately. For example, a CPCD60D hydraulic transmission forklift, after working for a period of time, the torque converter drive force is insufficient, the steering wheel is heavy (the hydraulic transmission and the power steering use a pump together); after several inspections, it is air-cooled. The venting of the oil sump has caused the oil temperature to be too high, and the fault is eliminated after dredging. Another example is that a K-702 loader cooling machine works less than 3 hours after startup, and the oil temperature alarm indicator of the torque converter on the instrument panel flashes, indicating that the hydraulic oil temperature is too high. First check the oil quantity and oil quality, the result is sufficient oil and good oil quality; check the oil filter again, not dirty; check the cooler afterwards, and find that the sludge has blocked some of the cooler and oil hole. After cleaning the cooler, everything is ok.
(7) Serious wear and tear of parts
The gear of the gear pump and the pump body and the side plate, the cylinder block of the piston pump and the motor and the valve plate, the cylinder hole and the plunger, the valve stem of the reversing valve and the valve body are sealed by gaps, and these components are Wear will cause an increase in internal leakage and an increase in oil temperature.
Precautionary measures: timely repair or replacement of excessively worn parts. According to statistics, under normal circumstances, after five or six years of operation of imported hydraulic pumps and motors, the wear of domestically produced products is quite serious after two or three years of work. Prompt maintenance. Otherwise, the operation will be basically normal when the machine is cold, but after 1-2 hours of operation, the movement speed of each mechanism of the system will be obviously slower, and it is necessary to stop the oil temperature before it can continue to work. For example, after a fault occurs in a WY160 hydraulic excavator, the working pressure of each unit tested is obviously low, which is suspected to be caused by the main safety valve or the main pump. First remove the main safety valve, there is no abnormal phenomenon; after the main pump is dismantled, the spherical surface of the distribution plate is seriously worn. After the grinding plate is ground and reassembled and the gap is adjusted, the installation operation is good. Another example is that a ZL50 loader is slow and weak, and the pressure of the test system is low. The hand-gearing gear pump feels very hot. It is suspected that the internal wear of the gear pump is caused by internal leakage. After the disassembly inspection, the gear pump side plate is found. The gap at the end of the gear is out of tolerance. After replacing the gear pump, the problem was solved.
(8) The ambient temperature is too high
If the ambient temperature is too high and the high load is used for a long time, the oil temperature will be too high.
Precautionary measures: Avoid long-term continuous heavy load work; if the oil temperature is too high, the equipment can be idling for about 10 minutes, and then work after the oil temperature drops.
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