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Summary of rotor fault knowledge of screw air compressor

June 14,2023

First,Rotor component

Rotor components are composed of driving rotor (male rotor), driven rotor (female rotor), main bearing, thrust bearing, bearing gland, balance piston and balance piston sleeve.

1.General fault phenomenon of yin-yang rotor

1. Normal mechanical wear and aging

1.1 Wear of the outer diameter of the male and female tooth paths of the rotor;

1.2 Normal wear of rotor cylinder.

Second. Man-made mechanical damage

2.1 Scratches on the outer diameter of the tooth path of the male and female rotors;

2.2 Scratches on the rotor cylinder;

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

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

2.5 Wear of shaft diameter at rotor bearing position;

2.6 The shaft ends of the male and female rotors are deformed.

3. General parts that are scratched or stuck

3.1 Abrasion and seizure (occlusion) between the male and female 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 journal at the suction end of the rotor and the shaft hole of the machine body;

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

Third,the cause of the failure

1. The air filter element is not replaced in time, resulting in poor intake quality and serious rotor wear; Lubricating oil is more slippery at will, and the mixed use of different brands often leads to friendship and rotor wear;

2. The compressor oil used is unqualified or not replaced in time according to the regulations, and the impurities in the oil exceed the standard, resulting in scratches on the rotor and cylinder barrel;

3. The exhaust temperature is too low during operation, which leads to too high water content in oil and gas. Long-term operation will lead to emulsifying phenomenon of engine oil, which will lead to the failure of effective lubrication of the bearings at the inlet and exhaust ends during high-speed and heavy-load rotation, resulting in rotor shaft string and deformation seizure;

4. The shaft head of the rotor driving end is deformed due to the meshing clearance of the driving coupling gear or the failure of the gear key connection;

5. Abnormal damage caused by bearing quality. The above faults of air compressor are generally caused by human beings. In the daily maintenance work, the above faults can be completely avoided as long as the operation and maintenance procedures are carefully followed.

In a word, the 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 fails to meet the design requirements due to mechanical processing or assembly, it will easily lead to scratches between the rotors, between the rotors and the body, between the rotors and other parts, or the rotors will be stuck. Generally, the coaxiality between the shaft hole and the rotor compression cavity is required to be within 0.01 ~ 0.02 mm.

The gap between parts in the compression cavity of screw compressor is generally in the unit of thread or mm, and the parts in the compression cavity are in dynamic fit. If the designed gap value is small, coupled with the error in the manufacturing process, the rotor is prone to be scratched or stuck. The clearance between the rotor and the machine body is generally about 0.1mm, and the clearance between the exhaust end face of the rotor and the exhaust bearing seat is 0.05 ~ 0.1 mm..

When the compressor is disassembled, because the bearing and the rotor shaft are closely matched, if the disassembly force is too large, the parts will be deformed and the coaxiality of the parts will be reduced.

After the compressor is assembled, it is necessary to check the overall coaxiality of the assembly parts. If the coaxiality is out of tolerance, it will also lead to scratches between parts or the rotor is stuck.

Forth, the harm and detection of rotor damage

In the normal operation of the air compressor, abnormal sound, increased vibration, long-term high exhaust temperature and current overload occur, so it is necessary to stop the machine and check it carefully. Should focus on checking whether the air compressor bearing is damaged and whether the rotor shaft end is deformed. If the rotor end bearing damage can be detected in time and stopped immediately, it will not cause the bearing to heat up and jam, and will not cause large mechanical parts damage. If the rotor end bearing is not found damaged in time, and the air compressor runs for a long time, under normal circumstances, the bearing inner circle and the rotor mounting bearing position will rub and slide, and the rotor bearing position will turn blue and thin, or the bearing outer circle of the rotor end cover will turn because the inner circle is stuck, so that the bearing hole of the end cover will become larger or out of circle. Even the bearing damage will directly cause the rotor to deform under the action of high power and destroy the rotor coaxiality.

Generally, the detection of male and female rotors depends on the wear and scratches of the rotors, and its 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.

Seize is a brand manufacturer focusing on energy-saving air compressors, integrating R&D, manufacturing, marketing and service! The company is a high-tech and specialized new enterprise in Shanghai, with a certified energy efficiency laboratory. Its products all exceed the national first-class energy efficiency standard, and many products have won the National Energy Efficiency Star, a patent demonstration enterprise in Jinshan District, and won the title of industry leader. We have the invention patent of the whole machine and line of energy-savingair compressor,  and have a wide variety of air compressor models, which can meet most of the market demand.

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