Causes and solutions for abnormal noise in screw air compressors

Screw compressors are a type of power equipment widely used in the fields of petrochemicals and industrial production. Their safe and reliable operation is of great significance to production, so it is necessary to focus on them.
A pair of mutually meshing spiral yin and yang rotors are arranged in parallel in the main cylinder of the screw compressor. There is a very small gap between the rotors and between the casing and the rotors. In theory, there is no metal contact during operation. Therefore, from a structural principle, screw compressors have the characteristics of stable operation and low noise compared to traditional piston compressors.
However, many screw compressor users will encounter abnormal noises during equipment operation, such as metal collisions, uniform knocking, friction whistling, etc. Due to different causes of faults, the external manifestations of abnormal noises and the locations of occurrence are also different. This article briefly analyzes the different causes of abnormal noises in compressors and provides corresponding solutions for reference by compressor peers only.
1. Cause of abnormal noise: The belt is too loose, and the groove type of the active and passive belts is too large to cause slippage and whistling (belt drive type). The compressor belt slippage can be judged and confirmed from the following aspects: (1) When approaching the equipment, you can smell a burning smell of the belt. If you observe carefully, you will find belt debris on the ground near the belt; (2) There is an abnormal friction sound between the pulley and the belt; (3) Due to uneven load, the current swings greatly. Solution: Rotate the adjustment bolt to adjust the belt to the appropriate tightness, with a deformation of less than 5mm, but not too tight. After readjustment, run with load. If it still slips, you need to replace the belt. The belt replacement and belt adjustment procedures are basically the same, but it should be noted that when replacing the belt, you cannot only replace one belt, otherwise the new belt will be damaged after replacement due to different belt tensions. At the same time, be careful not to splash lubricating oil on the belt or pulley to prevent the belt from slipping. 2. Cause of abnormal noise: The screw compressor lacks oil during operation, causing the male and female screws to bite directly without lubricating oil, and the dry friction of the metal produces a whistling sound. The oil-injected screw compressor does not have a synchronous gear structure. The male rotor directly drives the female rotor to rotate, but there is no direct contact between the two. The lubricating oil injected into the machine head establishes an oil film to act as an isolation. Therefore, for screw compressors, the role of lubricating oil is very important. If the screw compressor is "lack of oil", it will cause the screw rotor to directly contact, abnormal noise, bearing damage and other faults.
However, "lack of oil" in the machine head does not necessarily mean that the total amount of lubricating oil is insufficient. There may be other reasons that cause local oil shortage and low lubricating oil pressure.
Direct causes include: oil separation failure, oil cooler, oil pipeline blockage, loose oil pipe joints and oil leakage;
Indirect faults may include: minimum pressure valve failure, use of unqualified compressor lubricating oil, irregular design of oil and gas separation tank, damage to oil return check valve, improper installation of oil return pipe, large gas consumption, overload and low pressure use (or the oil separation treatment volume selected before the machine leaves the factory is too tight with the machine exhaust volume), etc.
Solution: Check the oil level, replace the oil filter, handle the faulty part and adjust the system configuration. When adding lubricating oil to the compressor main engine, at least let the oil soak to 3/4 of the rotor. It should be noted that in actual operation, some people only know that the operation of the equipment will cause the screw compressor to lack oil due to untimely addition. In fact, for those screw compressors that have been shut down for a long time, the amount of oil inside the head is often insufficient. At this time, if you start the machine rashly, it is easy to cause instantaneous oil shortage. Therefore, the screw compressor that has been shut down for a long time should first add enough oil to the head before starting it.
3. Cause of abnormal noise: The intake valve is not closed tightly, the leakage is large, and the intake valve check valve vibrates. The noise generated by the vibration of the check valve mainly comes from the lifting check valve. Generally, a check valve is installed at the outlet of the compressor. Its purpose is to prevent high-pressure gas from returning to the system when the compressor is stopped.
Solution: Replace or adjust the faulty valve. When assembling the valve components after inspection and repair, the following points should be noted:
(1) The screw compressor intake valve components should be clean;
(2) The contact between the valve plate and the valve seat, the radial clearance between the valve plate and the lift limiter, the valve plate's jump amount, the spring specifications, etc. should meet the design requirements;
(3) When replacing internal parts (such as valve plates, buffer plates, springs, etc.), all of them must be replaced at the same time.
(4) Leak test: Leak test is required before installing the valve.
4. Cause of abnormal noise: motor bearing failure
Solution: (1) When the motor is running, you can use a screwdriver with the tip against the outer cover of the bearing and put your ear close to the wooden handle of the screwdriver to listen to the sound of the bearing. If there is a faint rolling sound between the inner and outer rings of the rolling body, and the sound is monotonous and uniform, which makes people feel relaxed, it means that the bearing is good and the motor is running normally. If you hear an abnormal sound, you should analyze the cause and deal with it;
(2) If you hear obvious rolling and vibration sounds of the rolling elements, it means that the bearing clearance is too large or severely worn and needs to be replaced;
(3) If the rolling elements make a hoarse sound and the tone is heavy, it means that the bearing grease is too dirty and impurities have invaded. You need to clean the bearing with kerosene and replace it with new lubricant;
(4) If the rolling elements make irregular impact sounds, it means that some rolling elements in the bearing are broken and need to be replaced;
(5) If a whistling sound is mixed with the rolling sound of the rolling elements, it means that the bearing lacks grease or the lubricant is not properly selected. You need to add clean lubricant or replace it with a suitable lubricant.
5. Cause of abnormal sound: host failure. Foreign objects enter the host, causing the yin and yang screws to collide and produce a whistling sound; the clearance between the yin and yang screws and the bearing end face is too large; the host bearing is damaged.
Solution: Overhaul the host and readjust the host clearance. According to industry research data, generally speaking, the clearance ratio of screw compressors should be controlled between 0.8 and 1.2 threads. When the screw compressor rotates at high speed, due to factors such as thermal deformation of the tooth shape and wear of the gear tooth surface, the chase surface gap tends to decrease and the non-chase surface gap tends to increase. In order to ensure the long-term reliable operation of the compressor, the chase surface gap should be adjusted a little larger and the non-chase surface gap should be adjusted a little smaller during maintenance, so that the ratio of the chase surface gap to the non-chase surface gap is more reasonable between 1.0 and 1.2.
6. Cause of abnormal noise: Damage to the silencer system. The silencer system of the screw compressor is mainly composed of chassis, brackets, frames, door panels, silencer cotton, sealing strips and other parts.
Solution: Check whether the main body of the effect system is intact and whether the connecting bolts are loose. During operation, the compressor will be subjected to loads such as gas force, inertia force, friction force, etc., which will stimulate the vibration of components such as the compressor casing, the whole machine chassis, the pipeline system and the supporting structure. If these vibrations are not restricted by appropriate measures, they will cause abnormal noise.