[Mechanical Equipment Technology Edition] Daily Question 20171012: The problem of seizure in screw compressors with injection systems
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This post was last edited by YORK Industrial Refrigeration on 2017-10-14 at 09:08. Starting from now, in order to enhance communication among users, we have launched the \"One Question per Day\" activity on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 points for active participation, 10-15 points for correct answers. This question is valid for two days; no scoring will be given after that period. A seized compressor is a nightmare for screw air compressors. What could cause a compressor to seize? (The image below shows a Hanbell compressor that has just seized.) 1. Poor clearance at the exhaust end of the compressor head. During one or two heavy-working days, if a jamming occurs, the fault can be easily identified by measuring the clearance values during disassembly and inspection. 2. Poor clearance at the air intake end of the machine head, causing jamming. Since the clearance at the intake end of the nose cone is determined by the manufacturer of the nose cone, and this intake clearance is much larger than the exhaust clearance, the likelihood of jamming at the intake end is relatively low. For most models, it is possible to visually check at the air inlet whether sintering has occurred at the intake side. The cause of this fault is mostly excessive wear of the exhaust-side positioning bearing due to oil issues, which leads to axial displacement of the rotor toward the intake side and results in an excessively small clearance at the intake side. It is also possible that the loosening of the positioning nut at the exhaust end causes the rotor to shift axially toward the intake end, resulting in an excessively small clearance at the intake end or even direct metal-to-metal contact (this is commonly seen in engines that have been repaired manually, due to an inappropriate locking torque for the positioning nut or an incorrect type of thread sealant). 3. Reverse jam. Since the vast majority of screw compressors are unidirectionally positioned, during normal operation, the conical thrust bearing bears the force exerted by the compressed air on the rotor in order to push it toward the intake side, thereby maintaining the exhaust clearance. When reversed, the thrust generated by compressed air pushes the rotor toward the exhaust side, causing metal contact and sintering, which leads to jamming. Although most heads are equipped with disc springs or similar elements that provide reverse floating positioning to counteract this thrust, they only allow short periods of no-load reversal to determine the correct direction of rotation. All complete machine manufacturers incorporate appropriate protection against reverse rotation, so it generally only occurs when the protection fails, or when the motor wiring is changed or the switch is replaced. 4. Reasons related to lubricating oil: a. Prolonged idling (including during transportation) results in insufficient oil inside the compressor’s components, leading to a sudden lack of oil and subsequent jamming. Therefore, for equipment that has been idle for a long time, it is necessary to fill the components with an adequate amount of oil before starting the equipment again ； b. Insufficient oil supply to the operating machine, including delayed replacement or addition of lubricant, or blockages and leaks in the oil circuit, resulting in the machine head running out of oil and getting stuck ； c. An excessively low oil level causes the bearings at both ends of the screw rotor to lose lubrication during operation, leading to severe wear of the bearings and resulting in frictional locking between the male and female screws. d. There are too many impurities in the lubricating oil. It may be due to reasons such as the user failing to change the oil in a timely manner, poor quality of the oil, mixing different types of oil, or overly dirty oil, which leads to poor cooling of the engine head. Oil carbon deposits cause the rotor to fuse together with the casing; this usually occurs at the exhaust end face of the rotor and the casing, or at the outer surface of the rotor shaft and the inner hole of the casing. Therefore, choosing the right lubricant and replacing it properly is crucial; using inferior lubricants or extending its usage period increases the likelihood of such accidents. 5. The compressor bearings are severely worn due to aging. To determine the degree of wear, one can try moving the needle rollers or balls 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 compressor operates for an extended period of time, the bearings in the compressor head undergo wear, which in turn leads to an increase in the 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 end surfaces. Such variations in the gap 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, serious consequences can occur when the bearings of the screw compressor accessories wear out and the clearance between the main components exceeds the allowable limits. 6. Foreign object has entered and caused jamming. It often occurs due to carelessness during maintenance, with foreign objects being drawn in through the air intake, resulting in jamming. In some cases, the oil filter is damaged as well; larger particles of debris can enter through the fuel injection ports and cause jamming. In the case of larger units with gears, these gears may get damaged, and the resulting debris can be drawn into the suction chamber via the oil return port, leading to rotor jamming. When repairing such heads, a copper mesh is generally installed at the oil return port to prevent the fault from worsening in case the gears are damaged. 7. Gears are stuck. Since the gears in the gear-driven head are lubricated and cooled by oil injected through specialized injection holes, poor quality oil can easily lead to carbon buildup in these injection holes, causing them to become clogged and thus preventing the gears from rotating. When a screw compressor head gets stuck, the first step is to disconnect the motor from the compressor head, and then check whether the head can rotate on its own to determine if it is indeed stuck. This is a serious issue, and it is recommended that users do not attempt to disassemble it themselves; instead, they should contact the distributor or manufacturer promptly to find a solution for repair. Performing maintenance on screw compressors helps to extend their service life. The maintenance of air compressors is also an important expense; therefore, it should be carried out by professional compressor operators. The main solutions for a stuck compressor head include: (1) disassembly and inspection after cleaning with chemical agents ； (2) Manual disassembly and inspection ； (3) Hydraulic disassembly and inspection ； (4) Disassembly by electrolysis. ================================ High-quality promotions: Mechanical equipment---Maintenance procedures for York screw compressors http://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment---Upgrading of York Quinton control centers http://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment---Major repairs for GEA Grasso screw compressors http://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment---Disassembly and maintenance of British HOWDEN screw compressors http://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment---Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors http://bbs.hcbbs.com/forum.php?mod=viewthread&tid=1786445
Insufficient lubricant amount, rotor deformation, bearing aging, and severe wear
1. Lubricant issue. Insufficient lubricating oil inside the compressor head leads to a sudden lack of oil, which in turn causes jamming; therefore, it is necessary to ensure that there is enough lubricating oil inside the compressor head before starting it. Failure to replace or add lubricant in a timely manner results in a lack of oil supply. Or blockages or leaks in the oil circuit can cause the engine head to run out of oil and seize. There are too many impurities inside the engine head, causing phenomena such as carbon buildup and coking. Never use low-quality lubricant or extend the usage period of lubricant, as this increases the likelihood of such failures. 2. Reasons related to the rotor and bearings. The rotor makes direct contact and locks up. Wear of the main engine bearings causes axial and radial movement of the screw to increase, and this change leads to alterations in the gaps between the screws, as well as between the screw and the main engine housing and its front and rear end faces. The bearing is aged and severely worn. As the air compressor operates for longer periods of time, these are inevitable. Therefore, it is important to carry out regular maintenance on the air compressor. The compressor head is the core compression component of a screw air compressor; its internal parts are exposed to high temperatures and pressures for extended periods, and coupled with high-speed operation, there is an inevitable tendency for these parts to deform over time. Factors in the operating environment also contribute to component deformation. Natural air contains dust and impurities, and over time these tiny particles can accumulate and form larger solid masses. Such masses may cause the male and female rotors to deform, increase the gaps between them, and in severe cases, lead to the machine getting stuck.
Ageing of air compressor bearings makes it more likely for the main unit (compressor head) to jam when inferior lubricating oil is used or the equipment is operated beyond its recommended lifespan. Insufficient lubricating oil
1. Poor clearance at the exhaust end of the head. During one or two heavy-working days, if a jamming occurs, the fault can be easily identified by measuring the clearance values during disassembly and inspection. 2. Poor clearance at the air intake end of the machine head, causing jamming. Since the clearance at the intake end of the nose cone is determined by the manufacturer of the nose cone, and this intake clearance is much larger than the exhaust clearance, the likelihood of jamming at the intake end is relatively low. For most models, it is possible to visually check at the air inlet whether sintering has occurred at the intake side. The cause of this fault is mostly excessive wear of the exhaust-side positioning bearing due to oil issues, which leads to axial displacement of the rotor toward the intake side and results in an excessively small clearance at the intake side. It is also possible that the loosening of the positioning nut at the exhaust end causes the rotor to shift axially toward the intake end, resulting in an excessively small clearance at the intake end or even direct metal-to-metal contact (this is commonly seen in engines that have been repaired manually, due to an inappropriate locking torque for the positioning nut or an incorrect type of thread sealant). 3. Reverse jam. Since the vast majority of screw compressors are unidirectionally positioned, during normal operation, the conical thrust bearing bears the force exerted by the compressed air on the rotor in order to push it toward the intake side, thereby maintaining the exhaust clearance. When reversed, the thrust generated by compressed air pushes the rotor toward the exhaust side, causing metal contact and sintering, which leads to jamming. Although most heads are equipped with disc springs or similar elements that provide reverse floating positioning to counteract this thrust, they only allow short periods of no-load reversal to determine the correct direction of rotation. All complete machine manufacturers incorporate appropriate protection against reverse rotation, so it generally only occurs when the protection fails, or when the motor wiring is changed or the switch is replaced. 4. Reasons related to lubricating oil: a. Prolonged idling (including during transportation) results in insufficient oil inside the compressor’s components, leading to a sudden lack of oil and subsequent jamming. Therefore, for equipment that has been idle for a long time, it is necessary to fill the components with an adequate amount of oil before starting the equipment again ； b. Insufficient oil supply to the operating machine, including delayed replacement or addition of lubricant, or blockages and leaks in the oil circuit, resulting in the machine head running out of oil and getting stuck ； c. An excessively low oil level causes the bearings at both ends of the screw rotor to lose lubrication during operation, leading to severe wear of the bearings and resulting in frictional locking between the male and female screws. d. There are too many impurities in the lubricating oil. It may be due to reasons such as the user failing to change the oil in a timely manner, poor quality of the oil, mixing different types of oil, or overly dirty oil, which leads to poor cooling of the engine head. Oil carbon deposits cause the rotor to fuse together with the casing; this usually occurs at the exhaust end face of the rotor and the casing, or at the outer surface of the rotor shaft and the inner hole of the casing. Therefore, choosing the right lubricant and replacing it properly is crucial; using inferior lubricants or extending its usage period increases the likelihood of such accidents. 5. The compressor bearings are severely worn due to aging. To determine the degree of wear, one can try moving the needle rollers or balls 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 compressor operates for an extended period of time, the bearings in the compressor head undergo wear, which in turn leads to an increase in the 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 end surfaces. Such variations in the gap 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, serious consequences can occur when the bearings of the screw compressor accessories wear out and the clearance between the main components exceeds the allowable limits. 6. Foreign object has entered and caused jamming. It often occurs due to carelessness during maintenance, with foreign objects being drawn in through the air intake, resulting in jamming. In some cases, the oil filter is damaged as well; larger particles of debris can enter through the fuel injection ports and cause jamming. In the case of larger units with gears, these gears may get damaged, and the resulting debris can be drawn into the suction chamber via the oil return port, leading to rotor jamming. When repairing such heads, a copper mesh is generally installed at the oil return port to prevent the fault from worsening in case the gears are damaged. 7. Gears are stuck. Since the gears in the gear-driven head are lubricated and cooled by oil injected through specialized injection holes, poor quality oil can easily lead to carbon buildup in these injection holes, causing them to become clogged and thus preventing the gears from rotating. When a screw compressor head gets stuck, the first step is to disconnect the motor from the compressor head, and then check whether the head can rotate on its own to determine if it is indeed stuck. This is a serious issue, and it is recommended that users do not attempt to disassemble it themselves; instead, they should contact the distributor or manufacturer promptly to find a solution for repair. Performing maintenance on screw compressors helps to extend their service life. The maintenance of air compressors is also an important expense; therefore, it should be carried out by professional compressor operators. The main solutions for a stuck compressor head include: (1) disassembly and inspection after cleaning with chemical agents ； (2) Manual disassembly and inspection ； (3) Hydraulic disassembly and inspection ； (4) Disassembly by electrolysis.
1. Lubricant-related issues: Firstly, there may not be enough oil inside the machine head, especially during temporary shutdowns (including transportation), which can lead to a sudden lack of oil and subsequent jamming. Therefore, equipment that is shut down temporarily should have an adequate amount of oil added to its machine head before it is restarted. Another issue is the untimely replacement or addition of lubricant, resulting in a shortage of oil supply. Or the oil circuit may become blocked or leaky, resulting in a lack of oil in the engine head and subsequent jamming; another cause is an excessive amount of impurities, carbon deposits, and coking. Therefore, it is crucial to choose the right lubricant and to replace it regularly; using low-quality lubricants or using them beyond their expiration date increases the likelihood of such incidents. For the issue of the nose cone getting stuck at this time, the solution is to disassemble it for inspection; soaking it in a cleaning agent for five hours will restore normal function. 2. Rotor-related causes include: those that lead to direct contact between the rotors and resulting explosion. Wear of the main engine bearings causes axial and radial movement of the screw to increase, and this change leads to alterations in the gaps between the screws, as well as between the screw and the main engine housing and its front and rear end faces. Such variations in the gap are normal and acceptable throughout the bearing’s service life, and the resulting decrease in the air compressor’s output volume as well as the increased load on the drive motor are also normal and acceptable. The bearings are aged and severely worn. To determine the degree of wear, one can try to move the needle rollers or balls on the lower side of the bearing without removing it – if they can be moved easily, then it’s time to replace the bearing. As the air compressor continues to operate over time… Severe consequences may occur. However, when the bearing wears out and the clearance between the main components exceeds the allowable limit. Even a piece of iron scrap 1 millimeter thick getting in will cause it to get stuck. Specifically, a foreign object fell in and caused a jam. Friction occurs between the screw inside the host and its front and rear end surfaces, as well as between the screw and the host housing. Firstly, the motor load increases sharply; the most severe consequence of this is the screw getting stuck or even the entire machine being damaged. If motor maintenance is not carried out promptly or fails, it may lead to the motor burning out. There is a significant decline in the air production volume of the air compressor. Secondly, it may affect the normal production of the gas-consuming units.
The main reasons are: 1. Poor clearance at the exhaust end of the nozzle； 2. Poor clearance at the air intake end of the machine head, resulting in jamming ； 3. Reverse jam ； 4. Lubricant issues ； 5. The compressor bearings are severely aged and worn out ； 6. Foreign object has entered and caused jamming ； 7. Gear jamming, etc.
Insufficient viscosity of the compressor oil, as well as a low pour point, can lead to engine damage; the viscosity of the compressor oil is extremely low