A series of faults caused by insufficient repair of synchronization gears

1. Case background

A customer's self-repaired Roots blower experienced abnormal vibration and noise during startup and operation, and was forced to shut down, which affected production. Preliminary inspection of the equipment showed that the vibration value on the drive side seriously exceeded the standard. The customer then sent the equipment to our company for in-depth disassembly and repair.

2. Fault phenomenon and preliminary judgment

After the equipment arrived at the factory, our maintenance engineers conducted a preliminary operation test (under the premise of ensuring safety), and found that the vibration at the drive end was large, far exceeding the standard value. Based on experience, our engineers determined that the root cause of the failure was likely to be the failure of the rotor dynamic balance, bearing damage, or rotor meshing, and decided to immediately disassemble and inspect the equipment.

3. In-depth disassembly and fault analysis

Cause of failure: After disassembly, it was found that the root cause of the equipment failure was that the customer's previous repair process for the synchronization gear was not in place or the repair solution was technically undesirable.

Evidence of failure: After disassembling the synchronizing gear, it was found that the synchronizing gear had signs of repair. The fundamental fault point is that the concentricity of the gear cone surface failed to meet the design accuracy requirements during repair and processing.

The reason why the gear repair plan is undesirable: When adopting the plan to repair the inner cone surface of the gear, it is impossible to obtain the positioning datum plane, because the gear processing technology uses the inner cone surface positioning to process the tooth surface. In turn, the inner cone surface cannot be repaired based on the tooth surface. This is the fundamental reason why the gear inner cone surface cannot be repaired.

The effects of gear concentricity difference: First, it causes huge unbalanced centrifugal force during high-speed transmission, which causes abnormal vibration of the entire gear transmission system. At the same time, the abnormal vibration will also cause the positioning pin to gradually loosen until it loses its positioning ability. After the positioning pin loses its positioning ability, it will further cause the positioning of the rotor in the cylinder to deviate, which will mainly cause friction between the sealing line of the master and slave rotors and the cylinder. This will generate a huge radial impact force, further causing a large amount of movement in the axial positioning bearing. Eventually, the driven rotor will move toward the gear end and contact the friction gear end side plate, and the active rotor will move toward the drive end and contact the friction drive end side plate. The second is that when dynamic balance testing is performed in the later stage, the dynamic balancing process is difficult, and the workload is increased and inefficient. The third is that it affects the meshing gap adjustment of the main and slave rotors during the assembly process, which increases the difficulty of maintenance, increases the cost of maintenance man-hours, and reduces work efficiency.

4. Repair plan and implementation

In response to this failure, we have developed a repair plan:

1. Core component replacement:

Synchronous gear: The inner cone surface of the gear was severely strained. Due to gear processing technology considerations, the gear no longer had a repair standard, so it was decided to replace the synchronized gear to ensure the concentricity and matching accuracy of the transmission gear;

Master-driven rotor: At the same time, due to damage to the cone journal of the rotor gear and wear of the seal profile, it was decided to replace the master-driven rotor.

1. Key parts replacement :

Bearing group sealing group: In order to avoid potential hazards, the bearing group sealing group is preventively replaced;

Locating pin: To ensure the connection rigidity and positioning accuracy between the gear and the shaft, replace the locating pin.

3. Assembly and adjustment: Accurately adjust the meshing clearance between the rotors, gear backlash and bearing clearance to ensure that all parameters are restored to the best factory condition.

4. Trial operation: After completing the assembly, conduct a trial operation in the test room to monitor key parameters such as vibration, temperature, noise, etc., and ensure that all indicators meet the standards before delivery to the customer.

5. Enlightenment and Summary

This failure brought profound enlightenment to both us and our customers:

1. Be careful when 'repairing': The repair of core precision components must be completed by a professional team with high craftsmanship and quality standards. Otherwise, it may seem like a cost saving, but in fact it will cause huge hidden dangers.

2. Diagnostic thinking is crucial: When faced with complex equipment failures, it is necessary to trace the root cause and find the starting point of the failure, rather than just solving the final symptoms.

3. Preventive maintenance: Regular maintenance and monitoring of equipment can detect problems such as loose positioning pins and abnormal wear in advance to prevent small problems from turning into catastrophic failures.

Keywords: fan maintenance, synchronization gear failure, rotor friction