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Examining the Root Causes of Gearbox Failure Leads to Longer Life

By Steve Luchetta


Coal Age October, 2002 — When equipment fails, often the biggest concern is how to get the equipment running again. Equally important, however, is discovering why the equipment failed and how such a failure can be prevented.


Preventive maintenance is defined as the regular performance of equipment maintenance practices to avoid future equipment problems. An important first step in any preventive maintenance program is learning to identify the causes of equipment failure. Once the cause of failure is determined, one can take steps to avoid the problem in the future.


If there is potential metal-to-metal contact, effective lubrication is extremely critical. Maintenance professionals have several tools for diagnosing gearbox lubrication problems. One of these tools, oil analysis, plays a crucial role in not only preventing such problems, but in assessing the overall health of equipment. By analyzing particulate content and concentration in the oil, engineers are able to monitor the condition of an operating gearbox.

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Vibration is a key indicator in the diagnosis of machine faults. Each machine fault generates a specific vibration profile, and a single vibration measurement provides information concerning multiple components. By analyzing shaft vibration, engineers are able to determine whether the cause of the machine fault is imbalance, misalignment, general looseness or wear, bearing defects, gear defects, or some other unforeseen problem.


Preventive maintenance measures are taken not only to ensure equipment is kept running; these efforts are also made to keep equipment running at peak output levels. This often means up-rating a gearbox for optimum output based on its application. By performing a detailed review of a gearbox and its application, engineers can determine the equipment's up-rate potential, and in many instances, a gearbox can be up-rated by up-grading rotation elements, without adversely affecting existing gearbox interface requirements.


In contrast, lack of preventive maintenance often results in the opposite. Equipment in use from different manufacturers, and maintained irregularly, often is not operating at peak levels, or worse, is used at levels exceeding maximum output recommendations. In these cases, preventive maintenance practices can be taken to calibrate machinery so that it is operating at optimum levels — before it becomes a problem.


As potentially damaging as equipment failures, environmental factors often place equipment under strains that it was not designed for — whether it is corrosion from a humid environment, or lack of maintenance due to inaccessibility.



While identifying the cause of equipment failure can sometimes be as simple as looking closely at the damage, discovering the root cause of a problem is often more difficult. Most plants do not have the sophisticated equipment needed to identify shaft-vibration anomalies or analyze oil samples for foreign materials. Outsourcing preventive maintenance functions to an outside service provider is certainly an option.


When selecting a preventive maintenance provider, there are several key services that should be included in any agreement. Repair and overhaul services are a necessity, as ultimately all equipment will need maintenance at one point or another. The key is to plan that maintenance downtime so that it does not negatively affect production. Such services should cover breakdowns, scheduled maintenance, parts reconditioning, service upgrades, reverse engineering, alignment and balancing, and on- or off-site diagnostic services. Providers should be thoroughly skilled in performing gearbox failure root cause analysis.


Troubleshooting is also another necessary service. Such troubleshooting duties include engineering assistance in the identification, and swift resolution of operational problems.


Any good preventive-maintenance contract should include a strong warranty on all equipment serviced. Such warranties often offer many of the services already mentioned, and are ultimately a benefit to the refurbished equipment. Also, as important as any warranty is the proper installation of a gearbox. Proper installation can assure years of trouble-free operation, provided that adequate preventive-maintenance procedures are performed.


While identifying the cause of equipment failure is only the first step in establishing an overall preventive-maintenance program, it is an important step. The information gathered will ultimately serve as the foundation for planning future preventive maintenance — a particular necessity when working with mission-critical equipment.


Luchetta is Director of Engineering for Philadelphia Gear Corp. (Tel: 610/265-3000)


Preventive Maintenance Checklist: Equipment Repair

  • Breakdowns
  • Scheduled Maintenance
  • Parts Reconditioning
  • Service Upgrades
  • Reverse Engineering
  • Alignment and Balancing
  • On- or Off-Site Services


Oil Analysis

  • In Service Condition Monitoring of Lubricant and Operating Equipment
  • Wear Particle Analysis
  • Monitor Mechanical Condition of Wearing Parts
  • Monitor Lubricant Viscosity
  • Measure Concentration of Contaminants


Vibration Analysis

  • On-Site Diagnostic Assistance
  • Phone Support
  • Preventive-Maintenance Program Support
  • Turnkey Preventive-Maintenance Services
  • System Design and Calculations



  • Engineering Assistance in the Identification, and Swift Resolution of Operational Problems
  • Analysis of operational problems including:
    • System
    • Component
    • Sound
    • Vibration
    • Failure


Vibration Analysis

  • Determine Root Cause of Gear and Bearing Failures
  • Evaluate Entire System
  • Identify Root Cause and Permanent Corrective Action
  • Operational Loads
  • Component Design
  • Maintenance Practices
  • Maintenance Practices


© 2003, PRIMEDIA Business Magazines & Media Inc. All rights reserved. This article is protected by United States copyright and other intellectual property laws and may not be reproduced, rewritten, distributed, redisseminated, transmitted, displayed, published or broadcast, directly or indirectly, in any medium without the prior written permission of PRIMEDIA Business Magazines & Media Inc.




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