1. The hazard of excessively high temperature of hydraulic oil ① The viscosity, volumetric efficiency and working efficiency of hydraulic system are all reduced, the leakage is increased, and even the mechanical equipment cannot work normally.
②The parts of the hydraulic system expand due to overheating, which destroys the original normal clearance of the relative moving parts, resulting in increased frictional resistance and easy seizure of hydraulic valves. The precision mating surfaces of motors, etc., become invalid or scrapped due to premature wear.
③ Accelerate the aging and deterioration of rubber seals, shorten the life, and even lose their sealing performance, causing serious leakage of the hydraulic system.
④The oil vaporizes and the water evaporates, which is easy to cause pitting corrosion of the hydraulic components; the oil oxidizes to form gel deposits, which is easy to block the small holes in the oil filter and hydraulic valve, so that the hydraulic system cannot work normally.
Therefore, excessively high hydraulic oil temperature will seriously affect the normal use of the machine, reduce the service life of hydraulic components, and increase the maintenance cost of construction machinery. 2. Reasons and precautions for excessive temperature of hydraulic oil
(1) Improper oil selection
The brand, quality and viscosity grade of the oil do not meet the requirements, or the mixing of hydraulic oils of different brands results in the hydraulic oil viscosity index being 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.
Precautions: The selection of oil should be determined according to the brand recommended by the manufacturer and the working environment and temperature factors of the machine. For some machines with special requirements, special hydraulic oil should be used; when the maintenance of hydraulic components and systems is inconvenient, anti-wear hydraulic oil with good performance should be selected.
(2) Serious pollution
The environment on the construction site is bad. With the increase of the working time of the machine, impurities and dirt are easily mixed in the oil. The contaminated hydraulic oil enters the matching gap of the pump, motor and valve, which will scratch and destroy the precision and roughness of the matching surface To increase leakage and increase oil temperature.
Precautions: generally change oil after more than 1000 hours of cumulative work. When changing the oil, pay attention not only to drain the old oil in the tank, but also to replace the old oil in the entire system pipelines and working circuits. The oil has sufficient circulating cooling conditions. In case of sudden failure caused by hydraulic oil pollution, it is necessary to filter or replace the hydraulic system oil. For example, a YZT14G road roller has a fault 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 operation returns to normal.
(3) The oil level in the hydraulic tank is too low
If the amount of oil in the hydraulic oil tank is too small, the hydraulic system will not have enough flow to take away the heat generated, resulting in an increase in oil temperature.
Precautions: During actual operation and maintenance, strictly abide by the regulations on hydraulic oil level in the operating regulations. For example, a PC2003 hydraulic excavator, after working for a period of time, the hydraulic oil temperature is too high. Check the hydraulic oil tank and find that the oil level is much lower than the specified value. It can fully stand for heat dissipation, and the oil temperature rises. After adding enough hydraulic oil as required, the temperature of the hydraulic oil will immediately drop to the normal range.
(4) Air is mixed in the hydraulic system
The air mixed into the hydraulic oil will escape from the oil and form bubbles in the low-pressure area. When they move to the high-pressure area, these bubbles will be crushed by the high-pressure oil, and will be rapidly compressed to release a lot of heat, causing oil temperature. Rise.
Precautions: Always check the sealing of the seals such as the inlet pipe joints to prevent air from entering; at the same time, the air in the system should be exhausted after each oil change. For example, the hydraulic oil temperature of a PY184 grader is too high, accompanied by hydraulic noise; the inspection found that the hose connected to the hydraulic pump inlet is slightly damaged, and the air is sucked in, resulting in excessive oil temperature. In good condition.
(5) The oil filter is clogged
Abrasive particles, impurities and dust will be adsorbed on the filter element of the oil filter when it passes through the oil filter, resulting in an increase in oil absorption resistance and energy consumption, resulting in an increase in oil temperature.
Precautions: Regularly clean and replace the oil filter. For the oil filter with a clogging indicator, the filter element should be cleaned or replaced as indicated; the performance, structure and validity of the filter element must meet its use requirements. For example, when a TY220 bulldozer is operating, the oil temperature alarm continuously alarms, and at the same time it is found that there is burnt smell of oil smoke and oil at the torque converter, the oil level in the steering oil tank is low; This failure is caused by the clogging of the oil suction filter. The filter is full of deposits, so that the oil leaked from the torque converter cannot be pumped back to the steering tank in time. The more the accumulation, the greater the resistance of the torque converter and the heat generated by friction Increased, and eventually caused the oil temperature to rise too fast; after cleaning the filter, the oil temperature returned to normal. As another example, a CATD8N crawler bulldozer hydraulic transmission system issued a high temperature alarm, and there was an abnormal noise in the transmission part; the oil filter was disassembled and the filter element was found to contain a large amount of powdery dirt; after the filter element was replaced, the fault disappeared.
(6) The hydraulic oil cooling circulation system is not working well.
Generally, water-cooled or air-cooled oil coolers are used to compulsorily lower the oil temperature of the hydraulic system. The water-cooled cooler will reduce the heat dissipation coefficient due to the dirty fins or the poor water circulation; the air-cooled cooler will block the gap of the heat sink of the cooler due to excessive oil pollution, and it is difficult for the fan to cool it The oil temperature will increase.
Precautions: Regularly check and maintain the hydraulic oil cooling circulation system. Once a fault is found, it must be stopped immediately to eliminate it. For example, a CPCD60D hydraulic drive forklift, after working for a period of time, the driving force of the torque converter is insufficient, and the steering wheel turns heavily (a pump is used in combination with the hydraulic transmission and power steering); it has been discovered after several inspections that it is air-cooled The clogged ventilation holes of the oil cooler caused the oil temperature to be too high, and the fault was eliminated after the dredge. As another example, after a K-702 loader cooler starts to work for less than 3 hours, the oil temperature warning indicator of the torque converter on the instrument panel flashes, indicating that the hydraulic oil temperature is too high. Check the oil quantity and oil quality first, the result is that the oil quantity is sufficient and the oil quality is good; then check the oil filter, not dirty; then check the cooler, it is found that the oil sludge has blocked part of the cooler and the oil hole. After cleaning the cooler, everything is normal.
(7) Serious wear of parts
The gears of the gear pump and the pump body and side plates, the cylinder and valve plate of the plunger pump and motor, the cylinder hole and the plunger, the valve stem and valve body of the reversing valve, etc. are all sealed by the gap. Wear will cause an increase in internal leakage and an increase in oil temperature.
Preventive measures: timely repair or replacement of excessively worn parts Carry out maintenance in time. Otherwise, the operation will be basically normal when the machine is cold, but after working for 1-2h, the movement speed of each mechanism of the system will obviously slow down. It needs to be stopped to continue working after the oil temperature is reduced. For example, after a WY160 hydraulic excavator appeared the above failures, the working pressure of each mechanism was obviously low after testing. Dismantle and inspect the main safety valve first, there is no abnormal phenomenon; after dismantling and inspecting the main pump, it is found that the spherical surface of the valve disc is seriously worn. After grinding the valve plate, re-assemble and adjust the gap, the installation operation is good. As another example, a ZL50 loader moves slowly and weakly, the pressure of the tested system is low, and the gear pump feels very hot. It is suspected that it is caused by internal leakage of the internal wear of the gear pump; The clearance of the gear end face is excessive. After replacing the gear pump, the problem was solved.
(8) The ambient temperature is too high
Ambient temperature is too high, and the use of high load for a long time will make the oil temperature too high.
Precautions: Avoid long-term continuous and heavy-load work; if the oil temperature is too high, the equipment can be turned around at no load for about 10 minutes, and then work after the oil temperature drops.
