A.12.1 Equipment Overview
Screw air compressor motor power 37kW, working pressure 10bar (1bar=10⁵Pa), exhaust volume 5.6m³/min.
A.12.2 Accident Summary
The radial clearance between the main and auxiliary rotors in the compression chamber of the screw compressor is within 0.10mm. A slight deviation may cause the main and auxiliary rotors to be scratched or stuck. A certain company disassembled and reassembled a 37kW screw compressor and then ran it. The rotor was stuck. After disassembling the air compressor again, it was found that the rotor and the compression chamber wall had obvious scratches. What’s more serious is that the shaft of the main rotor at the suction end is sintered with the oil ring parts.
A.12.3 Cause Analysis
The inspection found that the shaft hole of the compressor body at the suction end was deformed to a certain extent, causing the oil ring part assembled in the shaft hole to be skewed. When touching the oil ring part and the body, there was a clear sense of concave and convexity. This shows that during the disassembly process of the compressor, the shaft hole on the body was deformed, resulting in poor coaxiality between the oil ring part and the rotor shaft. Since the oil ring part and the rotor are made of 45 steel, the friction between the two generates heat and forms sintering, resulting in the rotor being stuck.
A.12.4 Preventive measures
In order to avoid scratches and stuckness of screw compressors, effective improvement measures have been proposed in the design, processing and assembly aspects of compressor manufacturing to effectively prevent the occurrence of compressor scratches and rotor stuckness.
(1) Design.
1) Under the premise of not affecting the performance of the compressor, increase the gap between the parts, such as increasing the gap between the rotor shaft and the oil ring to about 0.08~0.01mm.
2) The oil ring and the rotor are made of different materials that are not easy to sinter. For example, the oil ring is made of tin bronze and the rotor is made of 45 steel. Copper and steel do not sinter. If the cost allows, the oil ring can be made of babbitt alloy.
(2) Manufacturing. Use precision processing equipment to strictly ensure the processing size requirements of parts.
(3) Assembly.
1) Use assembly tools to ensure assembly accuracy.
2) After assembly, perform an overall inspection of components and parts to check whether the clearance meets the design requirements.
3) Minimize the disassembly of compressor parts, especially the disassembly of the rotor, otherwise it will affect the size and assembly requirements of the parts.
