Overview

This case study presents a recent investigation into fluctuating vibration levels and rubbing observed in a motor at both Drive End (DE) and Non-Drive End (NDE). The analysis provides valuable insights for engineers dealing with similar issues in rotating machinery.

Problem Description

- Fluctuating vibration levels at NDE and DE

- Stepping up of vibration amplitude

- Characteristics indicative of rubbing

Key Findings

1. Labyrinth Seal Clearance:

• Post-overhaul specification change resulted in reduced clearance
• Current clearance less than bearing clearance

2. Temperature Correlation:

• Vibration levels increased with:
  • Ambient temperature rise
  • Motor bearing temperature increase
  • Winding temperature increase
• Suggests thermal effects on system damping and motor's thermal vector

3. Rotor Dynamics:

• Post-overhaul changes in rotor orbit shape
• Indications of preload effects
• Evidence of narrow rotational clearance

4. Alignment Status:

• Motor-to-pump alignment within manufacturer's specifications

Root Cause Analysis

1. Primary Cause:

• Insufficient clearance in floating labyrinth seal post-overhaul

2. Contributing Factors:

• Thermal expansion not adequately accommodated
• Possible interaction between rotor dynamics and reduced clearances

Recommended Actions

1. Immediate Intervention:

• Shutdown motor to prevent potential rotor bending
• Inspect for evidence of rotor rubbing

2. Operational Continuity:

• Switch to alternate unit for continuous operation

3. Design Revision:

• Revert to original labyrinth seal specification
• Re-evaluate clearance requirements considering thermal expansion

4. Comprehensive Inspection:

• Record all clearances and internal diameters of sealing components
• Verify compliance with motor specifications for:
  • Floating labyrinth seals
  • Rigid labyrinth seals
  • Dust seals

5. Precision Alignment:

• If motor casing is dismantled or uncoupled, realign according to OEM instructions

6. Post-Implementation Monitoring:

• Analyze transient and vibration data after restart
• Monitor for recurrence of issues

Technical Insights

• The case highlights the critical nature of clearance specifications in high-speed rotating equipment
• Demonstrates the complex interplay between thermal effects and rotor dynamics
• Emphasizes the importance of comprehensive post-maintenance testing and monitoring

Further Information

For a detailed discussion of this case study or to explore our analytical methodologies, please contact Sales Team.