Preventative Maintenance: the Key to Minimizing Gearbox Equipment ...

Tag : gearbox

An important first step in any preventative maintenance program isidentifying the potential causes of equipment failure. By providingmanagers and service technicians with this knowledge, a cruciallink in the power transmission chain, they can establish aneffective preventative maintenance program that will ultimatelylengthen the lifecycle of gearboxes and help avoid excessiverepair/replacement costs.
Analyzing the Problem: Lubrication
Effective lubrication is extremely critical to all gearboxes andwill help prevent gear and bearing failures. The keys tomaintaining proper lubrication are using the appropriate lubricant,keeping oil clean and free of foreign materials, and maintaining asufficient oil flow. Lubricant selection is based on manyindependent factors including gear type, load type, speed,operating temperatures, input power and reduction ratio, and shouldbe left to a gear lubrication specialist. This is especiallyimportant due to the technical sophistication found in gearingtoday, along with increased speeds and loads, and the specializedlubricants and additives now available.
When lubrication problems do occur, they can cause failures likescoring and galling. Scoring and galling are generally caused byoil film breakdown, which results in metal-to-metal contact, andhigh temperatures, which cause tooth surface damage. If a gearcontinues to operate without adequate lubrication, the gear's toothprofiles will degrade to the point where replacement is the onlyremedy.
Maintenance professionals have several important tools at theirdisposal for diagnosing gearbox lubrication problems, the mostprevalent of which is oil analysis. By routinely analyzingparticulate content and concentration in the oil, engineers areable to monitor the condition of an operating gearbox andcircumvent damage that may be beyond repair. Further analysis ofthe oil can yield vital information about the condition of thelubricant used in the equipment, alerting engineers to possibleproblems within the lubrication system.
Lubrication problems can also be detected by examining wearpatterns on gears. Gear tooth "pitting" is characterized by a largenumber of very small pits, distributed evenly over the workingsurface of a gear. The appearance of such pitting is usually anindication of gear overload, but may also be symptomatic oflubrication problems caused either by some corrosive medium withinthe lubricant, or by improper lubricant additives.
Analyzing the Problem: Vibration
Vibration is another key indicator in the diagnosis of machinefaults. Each machine fault generates a specific vibration profile,and a single vibration measurement can provide informationconcerning multiple components.
By analyzing shaft vibration, engineers can determine whether thecause of the machine fault is imbalance, misalignment, generallooseness or wear, bearing defects, gear defects or some otherunforeseen problem.
Imbalance is the force created by a rotating body when its centerof mass is offset from its center of rotation. Imbalance can causeother faults to appear. Misalignment is the deviation from a commoncenterline during operation and can occur as offset (shafts meetingsquare, but not on a centerline), angular (shafts meeting at anangle from one another), or both. Gear damage caused bymisalignment often presents itself as a fracture originating at oneend of a gear tooth, occurring on a diagonal line. It is also acommon cause of broken teeth on helical and bevel gears. Wear isanother fault determinable by vibration analysis, and can cover abroader range of gear damage – from scoring and galling, toabrasive wear and plastic yielding. Left alone, any of thesemachine faults can cause enough damage to necessitate shutting downa process. The key is to analyze the vibration data on a routinebasis.
Establishing a preventative maintenance program
While identifying the cause of equipment failure can sometimes beas simple as looking closely at the damage, discovering the rootcause of such a problem can be considerably more difficult.Instrumenting the equipment solves only part of the problem. It ishaving the technical skill to interpret the data over time that hasthe biggest impact on reducing unplanned downtime. Unfortunately,many companies have reduced the number of in-house expertsavailable to review such data. Without these resources, how can apreventative maintenance program be established?
Outsourcing preventative maintenance functions is certainly anoption, and one that allows engineers to focus on their own corecompetencies, while letting experts, with access to both a strongknowledge base and a wide range of equipment, handle routinepreventative maintenance and repair duties.
When selecting a preventative maintenance provider, severalfundamental services should be evaluated as part of the program.Providers should be thoroughly skilled in performing gearboxfailure root cause analysis, as well as have the ability to reactto breakdowns, scheduled maintenance outages, parts reconditioning,service upgrades, reverse engineering, alignment and balancing andon- or off-site diagnostic services.
Troubleshooting is a significant component of a comprehensivepreventative maintenance program. Such duties include engineeringassistance in the identification and swift resolution ofoperational problems. Other important services include vibrationand oil analysis, which are paramount in identifying equipmentanomalies before they become a problem.
Any sound preventative maintenance contract should include a strongwarranty on all equipment serviced. Such warranties often covermany of the services already mentioned, and are ultimately avalue-add to the refurbished equipment.
The information gathered while analyzing the problem willultimately serve as the foundation for planning future preventativemaintenance – a particular necessity when working withcritical equipment. Although a preventive maintenance programrequires a sustained time and financial commitment, the investmentwill no doubt pay dividends if it ultimately averts a gearboxfailure that requires expensive repairs or, in some catastrophiccases, outright replacement of the equipment. Preventivemaintenance measures ensure that equipment will be kept running andthat equipment will be kept running at peak output levels duringcritical production cycles.

Jules DeBaecke is the Vice President of Engineering at Philadelphia Gear Corporation . For more information on developing a preventative maintenanceprogram please visit www.philagear.com/manuals_maintenance and receive a free copy of the company's whitepaper "PreventativeMaintenance: An Examination of the Root Causes of Gearbox Failure."