Maintenance of hydraulic system of common construc

2022-07-23
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Talking about the maintenance of hydraulic system of common construction machinery for mechanized construction enterprises, the good technical condition of construction machinery is a direct factor for the normal production of enterprises. As far as the construction machinery with hydraulic transmission is concerned, the normal operation of the hydraulic system is a major symbol of its good technical status. Qualified hydraulic oil is the guarantee of reliable operation of hydraulic system, and correct maintenance is the foundation of reliable operation of hydraulic system. Therefore, according to the work practice, the author makes a rough discussion on the maintenance of the hydraulic system of construction machinery in the general working environment

1 select appropriate hydraulic oil

hydraulic oil plays the role of pressure transmission, lubrication, cooling and sealing in the hydraulic system. Improper selection of hydraulic oil is the main reason for the early failure and durability decline of the hydraulic system. The hydraulic oil shall be selected according to the brand specified in the attached operation manual. If it is necessary to use alternative oil under special circumstances, its performance shall be the same as that of the original brand. Hydraulic oils of different brands shall not be mixed to prevent chemical reaction and performance change of hydraulic oil. The dark brown, milky white and smelly hydraulic oil is deteriorated oil and cannot be used

2 prevent solid impurities from mixing into the hydraulic system

clean hydraulic oil is the life of the hydraulic system. There are many precision coupling parts in the hydraulic system, some have damping holes, some have gaps, etc. If the solid impurities invade, the precision coupling will be strained, stuck, and the oil passage will be blocked, which will endanger the safe operation of the hydraulic system. The ways for general solid impurities to invade the hydraulic system are as follows: the hydraulic oil is dirty; Dirty refueling tools; Careless refueling, repair and maintenance; Desquamation of hydraulic components, etc. The following aspects can be taken to prevent impurities from invading the system, which is a beneficial factor for manufacturers to raise prices:

2.1 during refueling, the hydraulic oil must be filtered and filled, and the refueling tools should be reliable and clean. Do not remove the filter at the fuel filler of the fuel tank in order to improve the refueling speed. Refueling personnel shall use clean gloves and work clothes to prevent solid impurities and fiber impurities from falling into the oil

2.2 during maintenance

remove the oil filler cap, filter cap, inspection hole, hydraulic oil pipe and other parts of the hydraulic oil tank, so as to avoid dust when the system oil duct is exposed. The removed parts must be thoroughly cleaned before opening. For example, when removing the hydraulic oil tank filler cap, remove the soil around the oil tank cap first. After loosening the oil tank cap, remove the sundries left at the joint (do not flush with water to prevent water from penetrating into the oil tank). Open the oil tank cap only after confirming that it is clean. If wiping materials and hammers are required, wiping materials without fiber impurities and special hammers with rubber attached to the striking surface shall be selected. Hydraulic components and hydraulic hoses shall be carefully cleaned and assembled after drying with high-pressure air. Select the genuine filter element with intact packaging (the inner packaging is damaged, although the filter element is intact, it may also be dirty). Clean the filter while changing the oil. Before installing the filter element, carefully clean the dirt at the bottom of the filter housing with wiping materials

2.3 cleaning of hydraulic system

the cleaning oil must be the same brand as the hydraulic oil used in the system. The oil temperature is between 45 ~ 80 ℃, and the impurities in the system shall be taken away as much as possible with a large flow. The hydraulic system shall be cleaned repeatedly for more than three times. After each cleaning, it shall be completely discharged from the system when the oil is hot. After cleaning, clean the filter, replace the filter element, and then add new oil

3 prevent air and water from invading the hydraulic system

3.1 prevent air from invading the hydraulic system

under normal pressure and normal temperature, the hydraulic oil contains air with a volume ratio of 6 ~ 8%. When the pressure decreases, the air will be separated from the oil, and the bubble will burst, causing "cavitation" of the hydraulic components and generating noise. A large amount of air entering the oil will aggravate the "cavitation" phenomenon, increase the compressibility of the hydraulic oil, make the work unstable, reduce the work efficiency, and cause the actuator to "crawl" and other adverse consequences. In addition, air will oxidize the hydraulic oil and accelerate the deterioration of the oil. The following points shall be noted to prevent air intrusion:

1. After maintenance and oil change, the air in the system shall be removed according to the provisions of the accompanying operation manual before normal operation

2. The oil suction pipe orifice of the hydraulic oil pump shall not expose the oil surface, and the oil suction pipe must be well sealed

3. The seal of the oil pump drive shaft shall be good. It shall be noted that the "double lip" genuine oil seal shall be used when replacing the oil seal, and the "single lip" oil seal shall not be used instead, because the "single lip" oil seal can only seal the oil in one direction and does not have the function of sealing the air. After the overhaul of a Liugong ZL50 loader, the hydraulic oil pump made continuous "cavitation" noise and the oil level in the oil tank increased automatically. After inquiring about the repair process of the hydraulic oil pump, it was found that it was caused by the misuse of the "single lip" oil seal in the oil seal of the drive shaft of the hydraulic oil pump

3.2 prevent water from invading the hydraulic system

excessive water in the oil will make the hydraulic components rusted, the oil emulsion deteriorated, the strength of the lubricating oil film reduced, and accelerate the mechanical wear. In addition to preventing moisture intrusion during maintenance, pay attention to tighten the cover of the oil storage barrel when it is not in use, and it is best to place it upside down; The oil with large water content shall be filtered for many times, and the dried filter paper shall be replaced once each time. When there is no special instrument for detection, the oil can be dropped onto the hot iron plate. Only when there is no steam emerging and burning immediately can the oil be filled with high-strength chemical resistance

4 precautions during operation

4.1 mechanical operation shall be gentle and smooth

rough mechanical operation shall be avoided, otherwise impact load will inevitably occur, which will cause frequent mechanical faults and greatly shorten the service life. The impact load generated during operation, on the one hand, causes early wear, fracture and breakage of mechanical structural parts, on the other hand, causes impact pressure in the hydraulic system, and the impact pressure will cause damage to hydraulic components, premature failure of oil seals, high-pressure oil pipe joints and rubber hoses, oil leakage or pipe explosion, frequent action of overflow valve, and oil temperature rise. Our company once purchased a new uh171 shovel excavator. During the operation, the Doumen oil pipe would leak or burst every 4 to 6 days. The oil pipe is a pure genuine product imported randomly, and there is no quality problem after testing. Through on-site observation, it was found that it was caused by the strong impact on the limit block and door frame when the bucket door was opened and closed. To effectively avoid impact load: the operating procedures must be strictly implemented; The hydraulic valve shall not be opened or closed too fast; Avoid strong impact when the components of the working device move to the limit position; The hydraulic equipment without impact function cannot impact the working object violently with the working device (such as the bucket of the excavator) to achieve the purpose of crushing. There is also a noticeable problem: the operator should be stable. Because the free clearance of each equipment control system is different, the clearance is different due to the different wear degree of the connecting parts, and the output of the engine and hydraulic system is also different. These factors give the equipment personality. Only the operators who use the equipment carefully explore and correct their own operation actions to adapt to the personality of the equipment. After long-term operation, they can develop good operation habits that conform to the personality of the equipment. The general machinery industry adheres to the fixed personnel and machine system, which is also one of the factors

4.2 pay attention to cavitation and overflow noise

pay attention to the sound of the hydraulic pump and overflow valve at all times during operation. If the hydraulic pump has "cavitation" noise, which cannot be eliminated after venting, the reason shall be found out and the fault shall be eliminated before use. If an actuator moves slowly without load and there is overflow sound of overflow valve, it shall be shut down immediately for maintenance

4.3 strictly implement the shift handover system

when the shift handover driver parks the machinery, it is necessary to ensure the safety of the shift handover driver and check the accurate oil level. Whether the system leaks, whether the connection is loose, whether the piston rod and hydraulic hose are bruised, whether the low-pressure oil inlet pipe of the hydraulic pump is connected reliably, whether the oil level of the oil tank is correct, etc. are the key points for the shift driver to inspect the hydraulic system. For the atmospheric oil tank, the vent hole of the oil tank shall be checked and cleaned to keep it unblocked, so as to prevent the oil tank vacuum caused by the blockage of the vent hole and the hydraulic oil pump from being damaged due to the difficulty of oil absorption

4.4 maintain appropriate oil temperature

the working temperature of the hydraulic system should generally be controlled between 30 ~ 80 ℃ (dangerous temperature ≥ 100 ℃). Too high oil temperature of the hydraulic system will lead to: the viscosity of the oil, such as the use of fixtures and the failure to tighten screws, will be reduced, which is easy to cause leakage and reduce efficiency; The strength of lubricating oil film decreases, which accelerates the wear of machinery; Formation of carbides and sludge; Oil oxidation accelerates the deterioration of oil quality; Premature aging of oil seal and high-pressure hose, etc. In order to avoid 1. The concept temperature of the experimental machine is too high: do not overload for a long time; Note that the radiator fins should not be contaminated by oil, and the heat dissipation effect will be affected by the attachment of dust-proof soil; Maintain sufficient oil quantity to facilitate oil circulation and heat dissipation; Do not work all day in hot summer. Avoid the high temperature time at noon. When the oil temperature is too low, the oil viscosity is large, the fluidity is poor, the resistance is large, and the working efficiency is low; When the oil temperature is lower than 20 ℃, the hydraulic motor, valve, pipeline, etc. may be damaged by sharp turning. At this time, it is necessary to warm up the engine, start the engine, idle at no-load for 3 ~ 5min, increase the engine speed with the medium speed throttle, control the handle to make any action of the working device (such as excavator bucket) to the limit position, and keep it for 3 ~ 5min to make the hydraulic oil temperature rise through overflow. If the oil temperature is lower, it is necessary to appropriately increase the warm-up operation time

4.5 control of air pressure and oil quantity of hydraulic oil tank

pay attention to the air pressure of the oil tank at any time during the operation of the pressure type oil tank, and its pressure must be kept within the range specified in the attached operation manual. If the pressure is too low, the oil pump is easy to be damaged due to insufficient oil absorption. If the pressure is too high, the hydraulic system will leak oil, and the low-pressure oil circuit is easy to burst. For the equipment after maintenance and oil change, after exhausting the air in the system, check the oil level according to the provisions of the accompanying operation manual, stop the machine at a flat place, and recheck the oil level after the engine is shut down for 15min, and supplement it if necessary

4.6 other precautions

prevent falling stones from hitting hydraulic cylinders, piston rods, hydraulic oil pipes and other components during operation. If there is a small click injury on the piston rod, the edges around the small point shall be removed with an oilstone in time to prevent damage to the sealing device of the piston rod. It can continue to be used without oil leakage. For equipment that has been shut down continuously for more than 24h, before starting, oil shall be injected into the hydraulic pump to prevent damage caused by dry grinding of the hydraulic pump

5 precautions for regular maintenance

at present, some hydraulic systems of construction machinery are equipped with intelligent devices, which have warning functions for some hidden dangers of the hydraulic system, but their monitoring scope and degree have certain limitations. Therefore, the inspection and maintenance of the hydraulic system should combine the monitoring results of intelligent devices with regular inspection and maintenance

5.1 250h inspection and maintenance

check the attachments on the filter. If there is too much metal powder, it often indicates that the oil pump is worn or the cylinder is pulled. For this, it must be diagnosed and corresponding measures must be taken before starting the machine. If the filter is damaged or dirt accumulates, it shall be replaced in time, and the oil shall be replaced at the same time if necessary

5.2 500h inspection and maintenance

the filter element should be replaced regardless of its condition, because it is difficult to detect the small damage of the filter element with the naked eye. If it is operated at high temperature for a long time, the filter element should be replaced appropriately in advance

5.3 1000h inspection and maintenance

clean the filter, replace the filter element, clean the hydraulic oil tank and replace the hydraulic oil. The oil change time for long-term high-temperature operation shall be properly advanced. Of course, if the oil quality test and analysis can be used to guide the oil change

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