Preventative Maintenance: Averting Gearbox Failures

Posted by  Sarah Evans 16-Dec-2014 10:36:00

Marketing Communications Manager with over 20 years experience and a keen interest in new product and service innovation.

eriks-gearbox-repairs

When equipment fails, often the biggest concern is how to get it running again. However, equally as important is discovering the root cause and how it can be prevented in the future.  Often, managers and their employees are ill equipped to identify the root cause failure mode, ultimately leading to recurrence of the failure and or other issues surrounding the drive.

Preventive maintenance is defined as the regular performance of equipment maintenance practices in order to avoid future equipment problems.  An important first step in any preventive maintenance program is learning to identify the causes of equipment failure.

By providing managers and service technicians with the knowledge to identify causes of gearbox failure (a crucial link in the power transmission chain), they can establish an effective preventative maintenance program to support their plant / site operations.

 

Analysing Problems

Lubrication

Effective lubrication is extremely critical to all gearboxes and will help prevent gear and bearing failures. Many internal gear and bearing failures result from insufficient or interrupted lubrication to the drive train.

Maintaining a proper lubrication to any gearbox includes using the appropriate lubricant, keeping oil clean and free of foreign materials, and maintaining a sufficient supply of lubricant to all of the internal operating components.

Since selecting a lubricant is based on many independent factors including gear type and style, load type, speed, operating temperatures, input power and reduction ratio – choosing a lubricant should be left up to a gear lubrication specialist or the Original Equipment Manufacturers to advise and provide guidance. This is especially true considering the technical sophistication found in gearing today, along with increased speeds and loads, and the specialized lubricants and additives now available in the market place.

When lubrication problems occur they can cause several gearing issues. Failures, like scoring and        spalling, are generally caused by oil film breakdown resulting in metal-to-metal contact, and high temperatures resulting in tooth surface damage and wear. If a gear continues to operate without adequate lubrication, damage will progress until the gear’s tooth profiles are degraded to the point where replacement is the only option available.

Additional, foreign materials present in the lubricant can cause abrasive wear throughout the gearbox.  Specialist maintenance companies like ERIKS have several important tools at their disposal for diagnosing gearbox problems, including but not exhaustive lists in condition monitoring like oil, vibration and thermal analysis or even endoscope inspections.

By analysing particulate content and concentration in the oil, ERIKS engineers are able to monitor the condition of an operating gearbox.  Further analysis of the oil harvests vital information about the condition of the lubricant used in the equipment.   Analysis of this oil used for lubrication could alert engineers to possible problems within the lubrication system.

Lubrication problems can also be detected by examining wear patterns on gears. Gear tooth “pitting” is characterised by a large number of very small pits, distributed evenly over the working surface of a gear. The appearance of such “pitting” is usually an indication of gear overload, but may also be indicative of lubrication problems caused either by some corrosive medium within a lubricant, or by improper lubricant additives and, or grades.

Vibration

Vibration – the motion of a body about a reference point caused by an undesirable mechanical force – is another key indicator in the diagnosis of machine / gearbox / equipment faults.  Each fault generates a specific vibration profile, and a single vibration measurement provides information concerning multiple components. The frequency of the vibration is determined by the machine geometry and operating speed.

By analysing vibration, ERIKS engineers are able to determine whether the cause of the machine fault is an imbalance, misalignment, general loss of interference fits or wear, bearing defects, gear defects, or some other unforeseen problem.

Imbalance is the force created by a rotating body when its centre of mass is offset from its centre of rotation. Imbalance can cause other faults to appear within the gearbox assembly.

Misalignment is the deviation from a common centerline during operation and can occur as offset        (shafts are meeting square, but not on a centerline), angular (shafts are meeting at an angle from one another), or both.

Gear damage caused by misalignment is visible as a fracture originating at one end of a gear tooth, occurring on a diagonal line.

Misalignment is also a common cause of broken teeth on helical and bevel gears.  Wear is another fault determinable by vibration analysis, and can cover a broader range of gear damage – from scoring and spalling, to abrasive wear and ultimately gear failure.

Left alone, any of these gearbox faults can do enough damage to necessitate shutting down a piece of process equipment making vibration analysis even more important.

 

Working With a Preventive Maintenance Specialist

While identifying the cause of gearbox failure can sometimes be as simple as looking closely at the damage, discovering the root cause of such a problem is often considerably more difficult.

Not all companies have the sophisticated equipment needed to identify vibration anomalies or analyse oil samples for foreign materials. Without these resources, how then can they establish a preventive maintenance program?

Outsourcing preventive maintenance functions to an outside service provider such as ERIKS is certainly an option.  Outsourcing these duties allows companies to focus on their own core competencies, letting specialist like ERIKS, with access to both a strong knowledge base and a wide range of necessary equipment, handle maintenance and repair duties.

ERIKS as a specialist preventive maintenance service provider, have many key services included in our portfolio along with product sourcing and supply.  Agreements and contracts can cover breakdowns, scheduled maintenance, parts reconditioning, service upgrades, reverse engineering, alignment and balancing, and on- or off-site diagnostic services.  ERIKS have thoroughly skilled and trained engineers in performing gearbox root cause failure mode analysis covering simple diagnostics to more comprehensive investigations and assessments.

Troubleshooting is another necessary service, as part of a comprehensive preventive maintenance program. Such troubleshooting duties include engineering assistance in the identification, and prompt resolution of gearbox operational problems.

Other important services that ERIKS offer include vibration, thermographic and oil analysis to name but a few. These monitoring techniques are paramount in identifying equipment anomalies before they become a problem.

Any good preventive maintenance contract should include a quality repair/overhaul with dependable warranty on all gearboxes serviced and, or repaired. ERIKS can also support warranties with the offering of many of the additional services already mentioned, and are ultimately a benefit to the refurbished gearbox. As important to any warranty is the proper installation and setup of a gearbox, which can promise years of trouble-free operation, if adequate preventive maintenance procedures are performed.

 

In Summary

While identifying the cause of gearbox 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 programmes - a particular necessity when working with critical equipment.

Such information will also help service technicians avoid making the same mistakes after initial gearbox repairs.

For more information, or for additional support please contact your local ERIKS Service Centre on 0845 006 6000.

 

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Topics: Best Practice, Power Transmission, Flow Control, Preventative Maintenance, Gearboxes

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