Once the screw compressor head gets stuck, the compressor is on its way to being scrapped! All the preventive measures are here

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1. Fault case: At 10:30 on August 25, 2017, the oil-injected screw air compressor J-6001A in the instrument air system of the air compression station tripped due to interlock failure, resulting in an urgent need to switch to a backup unit. Upon on-site inspection, it was found that the temperature of the machine head was high (150°C as measured), the current was high at the moment of shutdown, and the machine could not be rotated. 2 Cause analysis On August 26, 2017, the Mobile Maintenance Center organized fitters and specialized technical personnel to carry out maintenance work. Inspection revealed that the unit could not be rotated, and one of the bearing brackets on the air compressor shaft was broken, as shown in Figure 2. This causes the bearing to lose its original fit accuracy, resulting in an increase in the axial movement and radial clearance of the screw. It also leads to changes in the clearances between the screws themselves, as well as between the screw and the main housing and its front and rear end faces, which in turn causes the screws at the machine head to lock together. Therefore, this was a serious equipment failure in which the compressor head screw got stuck due to a crack in the bearing support frame. Causes of head jamming failure in 3-stage compressors and preventive measures: It is well known that head jamming failure in screw air compressors is a very serious equipment fault; it can lead to damage to the equipment, poses significant safety risks, results in high repair costs, and causes substantial economic losses. Therefore, having a thorough understanding of the causes of jamming in the screw air compressor head is of great significance for quickly resolving equipment failures and avoiding or preventing such serious problems as head jamming in air compressors. The common reasons for the jamming of the air compressor head include the following: (1) Aging and severe wear of the compressor bearings. The service life of the air compressor head is determined by the service life of its bearings, and these bearings have a significant impact on the overall service life of the compressor head. As the air compressor operates for extended periods of time, the large bearings in its head will inevitably wear out, which 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 clearance are normal and acceptable throughout the bearing’s service life, and the resulting decline in the air compressor’s output volume as well as the increased load on the drive motor are also normal and acceptable. However, when the bearing wear and the clearance between the main unit components exceed the allowable limits, it leads to an increase in the axial and radial movement of the screw. This change results in alterations in the clearances between the screws themselves, as well as between the screw and the main unit housing and its front and rear end faces, which may cause the machine head to get stuck. Precautionary measures: Regularly inspect, maintain, and service the air compressor units; during these maintenance tasks, special attention should be paid to the bearings. Check the bearing clearance for any wobbling or wear; if abnormalities such as wobbling or wear are detected, the bearing should be replaced promptly. (2) Insufficient oil supply or too low oil level during the operation of the air compressor can cause the compressor head to seize due to a lack of oil. Insufficient oil supply or low oil level in the compressor unit, which may be caused by delayed replacement or addition of lubricant, or by blockages or leaks in the oil circuit, can result in the bearings at both ends of the screw rotor losing lubrication during operation. This leads to severe wear of the bearings, causing the male and female screws to rub against each other and seize. Precautionary measures: Carry out regular and routine maintenance of the engine unit; conduct daily inspections, check the oil level on time, and top up the lubricating oil promptly to prevent the engine head from seizing due to lack of oil. (3) Insufficient lubricating oil in the compressor head: When a screw compressor remains shut down for an extended period of time, the amount of oil in its internal components, especially in the head, decreases. If the machine is started without paying attention to this, there will be a sudden shortage of oil, which can cause the head to get stuck. Precautions: For screw air compressor units that have been out of use for a long time, it is necessary to fill the compressor head with an adequate amount of oil before starting it; also, turn the compressor manually several times before initiating its operation. (4) Oil quality issues: Due to failure to change the oil in a timely manner, or because the oil quality is poor with too many impurities; the lubricating oil contains impurities, carbon deposits, coking, and rust spots ； Using low-quality lubricant or using it beyond its expiration date causes a decline in various performance parameters of the lubricant ； Poor cooling and lubrication of the engine head can be caused by the use of mixed oils or overly dirty oils; oil carbon deposits can cause the rotor to fuse together with the casing. This often 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, leading easily to jamming of the main engine (engine head). Precautionary measures: Use high-quality lubricating oil specifically designed for air compressors, carry out maintenance in strict accordance with the regulations for replacing such lubricant, and regularly take samples of the lubricant to analyze it, thereby ensuring its quality. (5) Jamming due to foreign objects: When foreign objects are drawn in through the air inlet, it is very likely to cause jamming. Precautions: Regularly inspect and maintain the air filters to ensure that the air supply to the air compressor is clean. (6) Unit reversal jamming: When a screw air compressor reverses, the thrust generated by the compressed air pushes the rotor toward the exhaust side, causing metal contact and sintering that results in jamming. So, it generally only occurs when protection fails, or when the motor wiring is replaced, the switch is replaced, etc. Precautionary measures: Carry out regular maintenance tasks to ensure the proper functioning of the instruments and equipment. Follow the established procedures carefully when replacing motor connections or switches, in order to avoid problems such as the air compressor rotating in the wrong direction and getting stuck. If you have anything to say, feel free to leave a message to communicate!