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Predictive Maintenance 99

CHAPTER 12

PREDICTIVE

MAINTENANCE

redictive maintenance is more of an art than ascience. It requires extensive training and yearsof experience to become an expert. Predictivemaintenance is part of proactive maintenance.

It means locating deficiencies or small problems in

equipment and correcting them before they can becomemajor problems.

VIBRATION ANALYSIS

Vibration analysis is one type of predictive mainte-nance. It utilizes specialized equipment to take signaturesof the vibrations of rotating machinery. The signaturesmay be likened to the electrocardiogram (ECG) of apersons heart. The heart specialist analyzes the ECG sig-natures and determines the problem in the heart. The vi-

bration analyst analyzes the vibration signatures of themachine and determines the cause of the excess vibration.All machines have an inherent vibration but only the ex-

P

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cess vibration is analyzed.The excess vibration may be caused by a bad bearing,

an unbalanced condition, misalignment of motor and

machine shafts, misalignment of gears and numerousother causes. After the analyst has determined the cause ofthe excess vibration, the maintenance personnel can cor-rect the problem. More vibration signatures should betaken after the problem has been corrected to assure thatthe problem has been corrected.

If the excess vibration is minor, the analyst may rec-

ommend that nothing be done at that time but that itshould be checked periodically. A chart of successiveanalysis signatures is made. The chart will probably showa gradual increase in vibration levels. This will allow themaintenance supervisor to predict when the componentwill fail and schedule the repair before a breakdown canoccur. This is predictive maintenance.

Vibration analysts, with the requisite years of experi-ence, can take the examinations for Certified VibrationAnalyst I, II, or III.

THERMOGRAPHY

Thermography is the inspection of electrical equip-ment with an infrared camera. The service is performed ontransformers, switches, motor control centers, motors andother electrical equipment. The analyst studies the photosand compares the item with a like item at normal tempera-ture or the items temperature rise above the ambient tem-perature. If the items temperature is too high, the analystwill recommend replacing the item.

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If the temperature of the item is only slightly abovenormal, the analyst may recommend inspecting it periodi-cally. The temperature readings can be charted. This will

probably show a gradual increase in temperature. Themaintenance supervisor can schedule the replacement ofthe item prior to its failure and avoid a fire or poweroutage.

Thermographers, with the requisite years of experi-ence, can take the examinations for CertifiedThermographer I or II.

LUBRICATION

Lubrication is an important part of proactive mainte-nance. Equipment must be lubricated or it wont work.But which lubricant should be used in each machine?

There are specialized lubricants for various types of equip-ment and usage, for example, turbine bearings, aircraft,automobiles, etc. Lubricants used in the manufacturingindustry cannot be used in food processing equipment.Hundreds of thousands of bearings have been ruined byimproper lubrication at a cost of many millions of dollars.

The maintenance department should consult with themanufacturers of the equipment and the lubricant suppli-ers for the correct lubricants to use in the various items ofequipment. Over-greasing can sometimes be more damag-ing than under-greasing. The maintenance departmentshould obtain formal training for all lube personnel toassure that the equipment is properly lubricated.

Lubricant analysis will show the true condition of thelubricant, e.g., water in the oil, metal-wear particles,

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breakdown of the additives, acidity, etc. Also, when thelubricants should be changed. Some plants that havechanged oil on a scheduled basis without knowing the

condition of the oil have learned, when they used oilanalysis services, that they had been throwing away goodoil. With oil analysis, the period between oil changes wasgreatly extended.

Copyright 2002 by The Fairmont Press.