The 'invisible patron saint' of oil-free screw compressors: axial force balancing device

The 'invisible patron saint' of oil-free screw compressors: axial force balancing device

01 Case background

Recently, our company received feedback from customers that an oil-free screw compressor had a rotor jamming failure during operation. After disassembly and inspection by our maintenance engineers, it was found that the internal damage of the main engine was serious. The details are as follows:

1. Air intake side panel part:

1. The inner end surface of the side plate and the rotor end surface are seriously scratched, and the wear depth of the end surface exceeds 0.5mm;

2. The joint between the two seat holes and the rotor journal is worn. Two cracks appear in the left seat hole and one crack appears in the right seat hole, both of which penetrate;

2. Yin and Yang rotor part:

1. The end face of the rotor and the end face of the intake side plate wear each other and the materials adhere due to high friction;

The journals at both ends of the rotor and the seat holes at both ends are worn, and the seal gears are seriously worn;

The sealing surface between the rotors is seriously worn and some parts are missing;

3. Cylinder part:

1. Different degrees of wear occur between the rotor body and the inner wall of the cylinder;

2. A crack occurred in the seat hole on the right side of the cylinder, but it has not penetrated;

4. Bearing pressure plate part:

The end surface of the bearing pressure plate and the bearing fitting surface are worn;

Failure cause analysis & modification measures:

According to the analysis of the damage phenomenon after the equipment was disassembled, the root cause of this failure is the axial movement of the male rotor, and the main factor causing the axial movement of the rotor is the damage of the axial positioning bearing; factors affecting the life of the bearing include the reduction of lubrication performance, excessive bearing temperature, abnormal axial force leading to bearing failure, etc.;

Further investigation revealed that the on-site process required the compressor to operate at close to full speed for a long time, which resulted in the continuous high speed of the male rotor of each compressor. The load on the bearings at both ends of the male rotor increased, and the failure rate increased significantly. Once the positioning bearings deviated, the axial position of the rotor would shift, thus causing the above-mentioned damage.

In response to the above problems, our company upgraded the main engine and installed an axial force balancing device on the rotor shaft head. This device introduces the exhaust pressure of the compressor itself to generate a balancing force in the opposite direction to the axial force. The balancing force automatically adjusts with the fluctuation of the exhaust pressure, thereby effectively reducing the abnormal axial load on the bearings and extending the service life of the main engine.

02 The necessity of axial force balancing device

In an oil-free screw compressor, gas will generate axial force during the compression process. The higher the exhaust pressure, the greater the axial force. The male rotor has a larger pressure-bearing area and bears much greater axial force than the female rotor, so it is the main stressed component.

Although the axial force balance device does not directly participate in gas compression, as a key component connecting the bearing and rotor, its performance is directly related to the overall life and operational reliability of the main engine. This device is usually installed on the suction end of the male rotor and consists of a balanced piston and a piston cavity. It works in a purely mechanical adaptive manner and can effectively offset the core axial load, protect the bearings and rotor, and stabilize operating conditions. It can be called the 'invisible guardian' of the oil-free screw host.

03 Technical advantages of Aertrans axial force balancing device (patent applied for)

Currently, the axial force balancing devices commonly used in the industry are mainly divided into two types: pneumatic drive and hydraulic drive, but both have certain application limitations.

In order to overcome the shortcomings of traditional solutions, Aerotrans has developed a new axial force balancing device. Its innovations are:

1. Power source: The stable oil pressure generated by the compressor's own lubricating oil pump is used to push the balance piston to move in the reverse direction to offset part of the gas axial force;

2. Control method: The compressor's own exhaust pressure is used as a regulating signal to control the lubricating oil flow and pressure, so that the axial force generated by the balancing device changes in real time with the fluctuation of the exhaust pressure, while ensuring that the bearings always bear a fixed minimum axial force to avoid fretting wear of the bearings at low loads.

This device has the following advantages:

1. No exhaust waste, sealed and no leakage

2. Adaptive adjustment - the axial force generated changes with the fluctuation of exhaust pressure

3. Minimum load protection--under the minimum exhaust pressure, the bearing still maintains the minimum load to prevent light load damage

4. Maximum load limit - under the maximum exhaust pressure, the maximum load borne by the bearing is controlled within the allowable range to ensure safety

5. No additional power consumption

6. Automatic control, simple and maintenance-free

04 Summary

Through this upgrade, the Aerotrans axial force balancing device effectively solved the rotor movement problem caused by the failure of the positioning bearing, providing a reliable guarantee for the long-term stable operation of the oil-free screw compressor under high speed and high load conditions. This solution is both economical and practical, and is an important technical path to improve host reliability.

Industry information is continuously updated, focusing on Aertrans oil-free screw technology!