The function of the components of the oil-injected screw air compressor is introduced, and the working principle of the components is analyzed. Precautions in maintenance and analysis and elimination of individual faults.
lubricating oil
Lubricating oil has lubricating, cooling and sealing functions.
1) Pay attention to the oil level of the lubricating oil. Lack of oil will cause high temperature and carbon deposition of the unit, and it will also cause accelerated wear of the moving parts and damage the service life of the unit.
2) To prevent condensed water in the lubricating oil, the operating oil temperature should be around 90°C, and resolutely prevent the oil temperature during operation from being lower than 65°C.
Lubricating oil composition: base oil + additives.
Additives have the following functions: anti-foam, anti-oxidation, anti-corrosion, anti-solidification, wear resistance, descaling (rust), more stable viscosity (especially at high temperature), etc.
The lubricating oil can be used for at most one year, and the lubricating oil will deteriorate if the time is too long.
Two-screw air compressor components function
▌Air filter function
The most important task is to prevent impurities such as dust in the air from entering the air compressor system. Filtration accuracy: 98% of 0.001mm particles are filtered out, 99.5% of 0.002mm particles are filtered out, and 99.9% of particles above 0.003mm are filtered out.
▌Oil filter function
All wear-causing impurities and dirt are removed from the oil without separating the special additives added.
Filter paper precision: 0.008mm size particles filter out 50%, 0.010mm size particles filter out 99%. The counterfeit filter paper has not been tested by heating lubricating oil, has fewer folds, greatly reduces the filter area, and the spacing of the folds is uneven.
If the air in the air inlet is dusty, after the lubricating oil has been used for a period of time, the filter paper will be severely clogged, and the filter will hinder the flow of lubricating oil. If the pressure difference of lubricating oil entering the oil filter is too large (cold start or filter blockage), the oil circuit will lack oil, and the lubricating oil temperature will rise, which will damage the rotor.
Three oil and gas separator working principle
▌Function of oil and gas separator
It is mainly to separate the compressor lubricating oil from the oil-air mixture, and continue to remove the lubricating oil particles in the compressed air.
Entering the oil and gas barrel (composed of oil and gas separator, minimum pressure valve, safety valve and container shell), the oil and gas mixture undergoes three kinds of separation: centrifugal separation, gravity separation (oil is heavier than gas) and fiber separation.
Separation process: the oil-gas mixture enters the oil-gas barrel along the tangential direction of the outer wall of the oil-gas separator, 80% to 90% of the oil is separated from the oil-gas mixture (centrifugal separation), and the remaining (10% to 20%) oil sticks in the oil-gas separator The surface of the outer wall of the device is separated (gravity separation), and a small amount of oil enters the interior of the oil-gas separator (fiber separation), and is pressed back into the screw host cavity through the oil return pipe.
▌The gasket of the oil and gas separator is conductive
Since air and oil pass through the glass fiber, static electricity will be generated between the two separation layers. If the two metal layers are charged with static electricity, there will be a dangerous situation of electrostatic discharge accompanied by electric sparks, which may cause oil and gas The separator exploded.
Good oil and gas separator accessories ensure the electrical conduction between the separator core and the oil and gas barrel shell. The metal components of the air compressor have good electrical conductivity, which can ensure that all static electricity can be exported in time to prevent the generation of electric sparks.
▌The adaptability of the oil-gas separator to the pressure difference
The pressure difference that the design of the oil-air separator can bear is limited. If the filter element of the separator exceeds the maximum value, the oil-air separator may rupture, and the oil in the compressed air cannot be separated, which will affect the air compressor or cause separation. The core is completely damaged, and the high pressure drop of the oil-gas separator may also cause the separator to catch fire.
There may be the following 4 reasons for the excessive high pressure difference: the oil separator is blocked due to dirt, the reverse flow of air, the internal pressure fluctuates greatly, and the core of the oil-gas separator is counterfeit.
▌The metal of the oil and gas separator is normally electroplated and usually will not be corroded
Depending on the ambient conditions (temperature and humidity) and the operating conditions of the compressor, condensation may form inside the air-oil separator. If the oil-gas separator is not electroplated, a corrosion layer will be formed, which will have a damaging effect on the antioxidant of the compressor oil, and will significantly reduce its service life and the flash point of the oil.
▌Measures to ensure the service life of the oil-gas separator
Accumulated dust, residual oil, air pollutants or wear can reduce the service life of the oil separator.
① The air filter and oil filter can be replaced in time and the oil change time can be observed to limit the dust entering the compressor oil.
② Use the correct anti-aging and water-resistant lubricating oil.
Three-screw air compressor points for attention
▌The rotor of the screw air compressor must not be reversed
The rotor is the core component of the screw air compressor. The surfaces of the female and male screws do not touch, and there is a gap of 0.02-0.04mm between the male and female screws. The oil film acts as a protection and seal.
If the rotor is reversed, the pressure cannot be established in the pump head, the screw in the pump head has no lubricating oil, and the lubricating oil cannot be circulated. Heat is accumulated in the pump head instantly, resulting in high temperature, which deforms the inner screw and the shell of the pump head, and the female and male screws bite. Locking, the end face of the rotor and the end cover stick together due to high temperature, resulting in serious wear of the end face of the rotor, and even component defects, resulting in damage to the gearbox and rotor.
How to check the direction of rotation: Sometimes the phase sequence of the incoming line of the factory will change, or the incoming power supply of the screw air compressor will change, which will cause the phase sequence of the motor of the screw air compressor to change. Most air compressors have phase sequence protection, but To be on the safe side, the following inspections should be made before the air compressor runs:
① Press and hold the cooling fan contactor with your hand to see if the fan wind direction is correct.
② If the power line of the fan has been moved, manually jog the main motor momentarily to see if the rotation direction of the motor coupling is correct.
▌Screw air compressor rotor can not deposit carbon
(1) Causes of carbon deposition
①Use low-quality lubricating oil that is not genuine from the original manufacturer.
② Use a fake or damaged air filter.
③Long time high temperature operation.
④The amount of lubricating oil is small.
⑤ When replacing the lubricating oil, the old lubricating oil is not drained or the old and new lubricating oil are mixed.
⑥ Mixed use of different types of lubricating oil.
(2) Check the carbon deposition method of the rotor
①Remove the intake valve and observe whether there is carbon deposit on the inner wall of the pump head.
② Observe and analyze whether the lubricating oil contains carbon deposits from the surface of the oil filter and the inner wall of the lubricating oil pipeline.
(3) When checking the pump head, it is required
Non-professionals are not allowed to disassemble the screw air compressor pump head casing, and if there is carbon deposits in the pump head, only the professional and technical personnel of the manufacturer can repair it. The gap between the female and male screws in the pump head of the screw air compressor is very small, so be careful not to enter any impurities in the pump head during maintenance.
▌Regularly add motor bearing grease
Use a special oil gun to add, specific steps:
① On the opposite side of the oil nozzle, open the vent hole.
②The oil nozzle of the oil gun should be matched with the motor.
③Lubricating grease is divided into high-speed motor grease and low-speed motor grease, and the two cannot be mixed, otherwise the two will react chemically.
④ The amount of oil in the oil gun is 0.9g per press, and 20g is added each time, and it needs to be pressed several times.
⑤If the amount of grease is added less, the grease is on the oil pipeline and does not play a lubricating role; if it is added too much, the bearing will heat up, and the grease will become liquid, which will affect the lubrication quality of the bearing.
⑥ Add once every 2000 hours of operation of the air compressor.
▌Main motor coupling replacement
The coupling must be replaced in the following situations:
① There are cracks on the surface of the coupling.
② The surface of the coupling is scorched.
③The coupling glue is broken.
Fault Analysis and Elimination of Four-screw Air Compressor
▌A 40m³/min screw air compressor caught fire during operation in a certain company
The screw generates high temperature during the compression process, and the lubricating oil is sprayed to take away the heat, thereby reducing the temperature of the machine head. If there is no oil in the screw, the machine head will be locked instantly. The oil injection point is different for each head design, so the oil products of various screw air compressor manufacturers are not the same.
The screw air compressor in operation caught fire, and the machine was scrapped for the following reasons:
1) The flash point of lubricating oil is around 230°C, and the ignition point is around 320°C. Use inferior lubricating oil. After the lubricating oil is sprayed and atomized, the flash point and ignition point will be lowered.
2) The use of inferior wearing parts will cause the air compressor oil circuit and air circuit to be blocked, and the temperature of the air circuit and oil circuit components will be too high for a long time, which will easily generate carbon deposits.
3) The gasket of the oil-gas separator is not conductive, and the static electricity generated by the oil-gas separator cannot be exported.
4) There is an open flame inside the machine, and there are leaking fuel injection points in the oil circuit system.
5) Combustible gas is inhaled at the air inlet.
6) The residual oil is not drained, and the oil products are mixed and deteriorated.
It was jointly confirmed by relevant experts and engineering technicians that the machine used poor-quality lubricating oil and poor-quality wearing parts during maintenance, and the static electricity generated by the oil-gas separator could not be exported, causing the machine to catch fire and be scrapped.
▌Screw air compressor vibrates violently when it is unloaded and there is a fault of oily smoke
The head of the screw air compressor shakes when it is unloaded during operation, and the air filter alarm occurs every 2 months, and cleaning the air filter with high-pressure air does not work. Remove the air filter, oily fume is generated in the suction pipe, and the oily fume mixes with dust to seal the air filter tightly.
The intake valve was disassembled and the seal of the intake valve was found to be damaged. After replacing the intake valve maintenance kit, the screw air compressor operated normally.
▌The screw air compressor runs for about 30 minutes, and the new V-belt is broken.
The pre-tightening force required by the V-belt of the screw compressor is set before leaving the factory. When replacing a damaged V-belt, the operator loosens the lock nut to reduce the automatic tension in order to save effort and facilitate the installation of the V-belt. tight system tension. After replacing the V-belts, the lock nuts were not returned to the original running position (at the corresponding color mark). Due to the looseness, wear and heat of the V-belts, the newly replaced 6 V-belts broke again.
Five conclusions
The operator of the screw air compressor should always pay attention to the precautions in the maintenance when maintaining, and it is very necessary to understand the functions of the main components of the air compressor. Personnel in the equipment management and operation departments purchase the wearing parts of the original manufacturer to prevent the occurrence of inferior lubricating oil and inferior parts, and prevent unnecessary failures and incidents.