Maintenance and Repair Guide – Fault Analysis of Screw Air Compressor Rotors

Sep 24, 2024

I. What are the general fault phenomena of the yin and yang rotors of screw compressors?

1. Normal mechanical wear and aging

1.1 Wear of the outer diameter of the yin and yang rotor teeth;

1.2 Normal wear of the rotor cylinder.

2. Man-made mechanical damage

2.1 Scratches on the outer diameter of the yin and yang rotor teeth;

2.2 Scratches on the rotor cylinder;

2.3 Scratches on the sides of the rotor intake and exhaust end covers;

2.4 Wear of the intake and exhaust end bearings and the inner circle of the bearing end cover;

2.5 Wear of the shaft diameter of the rotor bearing position;

2.6 Deformation of the yin and yang rotor shaft ends

3. General parts of scratches or jams

3.1 Scratches and jams (bites) between the female and male rotors;

3.2 Between the outer diameter of the rotor and the inner wall of the machine body;

3.3 Between the exhaust end face of the rotor and the exhaust bearing seat;

3.4 Between the shaft neck at the suction end of the rotor and the shaft hole of the machine body;

3.5 Between the shaft neck at the exhaust end of the rotor and the shaft hole of the exhaust bearing seat.

Ⅱ. What are the common causes of screw compressor failures?

1. The air filter element of the screw air compressor is not replaced in time, resulting in poor air intake quality and serious rotor wear; the random replacement of lubricating oil and the mixing of different brands often lead to crosstalk and rotor wear;
2. The compressor oil model used by the air compressor is unqualified or not replaced in time as required, and the impurities in the oil exceed the standard, causing scratches on the rotor and cylinder;
3. The exhaust temperature of the air compressor is too low during operation, resulting in excessive moisture in the oil and gas. Long-term operation will cause oil emulsification, which will cause the inlet and exhaust end bearings to not be effectively lubricated during high-speed and heavy-load rotation, causing heat damage, resulting in rotor stringing, deformation and jamming;
4. The VSD fixed screw air compressor is deformed at the drive coupling end of the shaft head due to the meshing clearance of the drive coupling gear or the gear key connection failure;
5. Abnormal damage caused by the bearing quality of the permanent magnet variable frequency air compressor. The above faults of the air compressor are generally caused by human factors. In daily inspection and maintenance work, as long as the operation and maintenance are carefully carried out in accordance with the use and maintenance procedures, the above faults can be completely avoided.

In short, the shaft journals of the suction and exhaust ends of the screw compressor rotor are supported by the bearings on the compressor body and the exhaust bearing seat respectively. If the coaxiality of the compressor body, the exhaust bearing seat and the rotor does not meet the design requirements due to machining or assembly, it is easy to cause scratches between the rotors, between the rotor and the body, and between the rotor and other parts, or the rotor is stuck. Generally, the coaxiality of the shaft hole and the rotor compression chamber is required to be within 0.01-0.02mm.

The clearance between the parts in the compression chamber of the screw compressor is generally measured in wires or mm. The parts in the compression chamber are dynamic fits. If the designed clearance value is too small, coupled with the error in the manufacturing process, the rotor is prone to scratches or jams. The clearance between the rotor and the body is generally about 0.1mm, and the clearance between the rotor exhaust end face and the exhaust bearing seat is 0.05-0.1mm.

During the disassembly process of the screw air compressor, because the bearing and the rotor shaft are tightly matched, if the disassembly force is too large, it will cause the parts to deform and the coaxiality of the parts themselves will be reduced.

After the air compressor is assembled, the overall coaxiality of the assembly parts needs to be checked. If the coaxiality exceeds the tolerance, it will also cause scratches between parts or the rotor will be stuck.

Ⅲ. How to detect the rotor of the screw air compressor?

During the normal operation of the air compressor, if there are abnormal sounds, increased vibrations, long-term high exhaust temperature, and current overload, it is necessary to stop the machine for careful inspection. The air compressor bearing should be checked for damage and the end of the rotor shaft should be checked for deformation. If the damage to the rotor end bearing can be detected in time and the machine is shut down immediately, the bearing will not be heated and stuck, and major mechanical parts will not be damaged. If the damage to the air compressor air end cannot be detected in time, the screw air compressor will run for a long time. Generally, the inner circle of the bearing and the rotor installation bearing position will rub and slide. In severe cases, the rotor bearing position will turn blue, be roughened, or the bearing of the rotor end cover will be stuck due to the inner circle, causing the outer circle of the bearing to rotate, thereby enlarging or losing the roundness of the end cover bearing hole. There may even be a direct deformation of the rotor under the action of high power due to bearing damage, which will damage the coaxiality of the rotor.

The inspection of the yin and yang rotors of the screw air compressor generally depends on the wear and scratches of the rotors. The meshing wear shall not be less than 0.5mm-0.7mm of the nominal diameter. The scratch area shall not be greater than 25mm2, the depth shall not be greater than 1.5mm, and the misalignment of the rotor shaft end shall not be greater than 0.010mm.