[Mechanical Equipment Technology Edition] Daily Question 201801010: Common Faults in Refrigeration Systems (5.2)
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This post was last edited by YORK Industrial Refrigeration on 2018-1-12 at 15:34. Starting from now, in order to enhance communication among users, a 【Daily Question】 activity has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth points for active participation, 10-15 wealth points for correct answers. This question is valid for two days; no score will be given after that period. What effects can bearing aging in a screw refrigeration compressor have? Answer: It will cause axial and radial displacement of the screw! Causes of compressor wear ============================== High-quality promotions: Mechanical equipment---York screw compressors – maintenance procedures https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment---Upgrading York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment---Overhaul of GEA Grasox screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment---Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment---Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
Bearings do not experience aging; the modes of failure include pitting, wear, plastic deformation, and fracture.
The compressor bearings are aged and severely worn. To determine the degree of wear, it is possible to try moving the needle rollers or balls located on the lower side of the bearing without removing it; if they can be moved easily, then the bearing needs to be replaced. As the air compressor operates for longer periods of time, the main bearings will inevitably wear out, which in turn leads to increased axial and radial movement of the screws. This change results in alterations in the gaps between the screws, as well as between the screws and the main housing and its front and rear surfaces. Such variations in the clearance are normal and acceptable throughout the bearing’s service life, and the resulting decrease in the compressor’s gas production volume and increase in the load on the drive motor are also normal and acceptable. However, when the bearing wear and the clearance between the main components exceed the allowable limits, serious consequences may occur. Specifically, foreign objects getting stuck can cause problems. An air filter paper – a piece of iron shrapnel 1 millimeter thick – getting inside can also lead to blockages. Firstly, within the Shanghai Atlas air compressor, friction occurs between the screw and the front and rear end faces, as well as between the screw and the compressor housing. This leads to a sharp increase in the motor’s load; in the worst cases, the screw can get stuck or even the entire compressor can be damaged. If the motor protection system does not respond properly or fails, it may result in the motor burning out.
Metals will experience fatigue. Under an environment where bearings are continuously subjected to cyclic stress, they will eventually experience deformation, cracking, wear, and other issues. The manufacturer provides a standard: the theoretical service life of the bearing is 100,000 hours. If they can specify such a lifespan, can’t they also indicate the rate of aging? Why is preventive maintenance necessary for compressors?
Bearings do not experience aging; the modes of failure include pitting, wear, plastic deformation, and fracture.
The aging of bearings leads to an increase in the bearing clearance, greater vibration between the rotating part of the bearing and the raceway, changes in the clearance between the male and female rotors, which causes vibration and even seizure； The axial clearance also changes, which in turn leads to changes in the amount of intake and exhaust air
Wear and damage to the bearings can lead to an increase in the bearing clearance, greater vibration between the rotating parts of the bearing and the sliding surfaces, as well as changes in the clearance between the male and female rotors, which in turn causes vibration. This results in abnormal noise from the refrigeration unit, and in severe cases the bearings may even seize, causing the compressor system to shut down.
Wear of the bearings causes the support for the screw to deviate from its original center, resulting in an axis deviation. This leads to a reduction in the clearance between the screw and the bearing housing on one side, thereby disrupting the lubricating effect of the oil film. Additionally, bearing wear reduces the precision with which the screw is positioned axially and radially, causing it to shift. This in turn leads to wear on the compression chamber and the high-pressure end face of the compressor, as well as issues such as shaft binding or rubbing, which increase noise levels during operation.
The compressor bearings are aged and severely worn. To determine the degree of wear, it is possible to try moving the needle rollers or balls located on the lower side of the bearing without removing it; if they can be moved easily, then the bearing needs to be replaced. As the air compressor operates for longer periods of time, the main bearings will inevitably wear out, which in turn leads to increased axial and radial movement of the screws. This change results in alterations in the gaps between the screws, as well as between the screws and the main housing and its front and rear surfaces. Such variations in the clearance are normal and acceptable throughout the bearing’s service life, and the resulting decrease in the compressor’s gas production volume and increase in the load on the drive motor are also normal and acceptable. However, when the bearing wear and the clearance between the main components exceed the allowable limits, serious consequences may occur. Specifically, foreign objects getting stuck can cause problems. An air filter paper – a piece of iron shrapnel 1 millimeter thick – getting inside can also lead to blockages. Firstly, within the Shanghai Atlas air compressor, friction occurs between the screw and the front and rear end faces, as well as between the screw and the compressor housing. This leads to a sharp increase in the motor’s load; in the worst cases, the screw can get stuck or even the entire compressor can be damaged. If the motor protection system does not respond properly or fails, it may result in the motor burning out.
Ageing of the bearings in a twin-screw refrigeration unit can lead to an increase in clearance or a greater radial movement range, resulting in increased gaps or friction between the rotors, between the rotors and the casing, and between the rotors and the front and rear end faces. Friction generates abnormal noises, and the presence of small particles falling off can cause sticking or even complete locking of the rotating parts. The temperature of the bearings may rise, triggering alarms; in severe cases, this can lead to damage to the motor as well. As the clearance (radially) increases, it may lead to air leakage or insufficient exhaust volume, resulting in a reduced cooling effect of the system and increased power consumption. Since this is a gradual process, the fault symptoms may appear gradually and intensify over time. Therefore, it is particularly important to carry out planned maintenance or regularly replace wear and tear parts as well as components that have reached the end of their useful life.