In the most basic of terms, an electric motor is a simple device that converts electrical energy into rotary motion that, when transmitted to a driven load, will perform mechanical work. If applied correctly, the motor will run effortlessly. If set up correctly, the motor will perform reliably at minimal cost.
The motor will have a long service life if maintained regularly and correctly. This is so much so that, for most motors, only 2% of their total lifetime cost will be attributed to the original purchase price, with the remainder to energy costs.
Although the world is witnessing a renaissance of the electric motor with the advent and continued proliferation of e–motor vehicles, their fundamental design and purpose remain the same. Similarly, application, setup, and maintenance will continue to influence the performance, reliability, and life cycle of the e-motor.
Application, setup, and regular maintenance are all cornerstone elements of precision maintenance, providing a simple, effective, and straightforward approach to ensuring your motors work efficiently for a long time.
Application
A new machine pretty much guarantees the motor has been sized correctly to its intended load. Application problems arise when the maintenance department changes a defective or failed motor with one that’s not “like for like.” Motor application mismatching can also occur when the production team modifies operating conditions by:
- Changing the line or machine speed beyond its original design range.
- Changing the raw material that’s being worked.
- The machine was re-purposed for a different use than the one for which it was initially designed.
An oversized motor for the load condition can provide adequate performance. Still, light loading will often be inefficient and consume excess energy under regular operation, increasing the unit’s energy footprint.
Conversely, an undersized or too-light motor will, at best, stall or trip under load, may fail to operate, and could cause motor damage. In a worst-case scenario, the motor continues to run and overheats, causing a fire.
In particular, in applications when a heavy startup load is expected to reduce significantly once the equipment is running at operational speed, i.e., in a loaded conveyor drive system, there are two options: We can use reduced-horsepower motors that 1) are governed mechanically by a fluid coupling that allows the drive to come up to speed slowly without tripping the motor; or 2) are governed electrically through use of a Variable Frequency Drive (VFD).
If a motor size is suspect, ensuring the unit is sized correctly requires reviewing the original manufacturer’s literature (design specification, Bill of Material, spare parts list, etc.). If no literature is available and you are unsure if the replacement motor is the same size as the original unit or if you wish to change to a high-efficiency model, confer with your local motor supplier’s engineering department for assistance.
Setup: Balancing
Purchasing a new, reputable, name-brand electric motor should provide some assurance that the unit’s main shaft is balanced. When it comes to new, inexpensive, offshore “no-name” motors, operations should err on caution and have the balance checked and certified by a reputable motor shop. Rebuilt motors should have a balance certificate if purchased from a reputable rebuilder.
Unbalanced motor shafts are noisier, vibrate more than usual, require significantly more energy (and money) to operate over time, and often fail prematurely.
Always check a new or rebuilt motor’s balance using your vibration-analyzing equipment, or have it certified independently by a reputable local motor shop, and do so before you place the unit in operational use.
Setup: Alignment
The correct alignment between the drive and driven shaft is arguably the most essential part of any motor setup.
Misalignment comes in two forms: 1) Angular, in which the shafts line up center-to-center but not in a straight line, and 2) Offset, in which the shafts do not line up center-to-center. Both conditions can occur simultaneously. Both will place tremendous stress on the driver and driven bearings and couplings, assuring rapid wear, premature failure, and a considerable increase in motor energy consumption.
Remember: Poor alignment will rapidly wear out shaft bearings, sprockets and chains, belts, and sheave pulleys.
Setup: Soft-Foot Check
A soft-foot condition check should always be included in the alignment process. Aligning with a laser-type alignment system is easy, as virtually all laser alignment systems feature a soft-foot check feature.
Soft foot occurs when one or more motor base feet are not as flat as the others (think of a table with a short leg). Soft foot can also occur when the motor base grout is not flat or square. Both situations are easily remedied with precision shims and correct tie-down-bolt torquing.
If the soft foot persists, excess vibration will eventually loosen the bolts and cause the motor to vibrate more, which will transfer across the drive train and its components. Again, the result will be premature wear and failure, combined with excessive energy consumption.
Regular Maintenance: Lubrication
The reality is that most electric motors are grossly overlubricated. Incorrectly lubricated motors prematurely fail due to the simple act of neglecting to undo the grease drain plug.
This forces any excess grease to build up pressure that eventually ruptures the shaft seal. In that event, grease is free to purge into the motor winding, causing massive overheating, premature failure, and, once again, excessive energy consumption.
Some sub-fractional motors come equipped with grease nipples, even though they contain lifetime lubricated bearings and no drain port to allow excess grease entry to escape.
All motors should be assessed to understand their lubrication requirements and placed on an engineered lubrication program.
Regular Maintenance: Cleanliness
The simple act of keeping a motor dirt—and oil-free will combat the buildup of a debris/dirt-based thermal blanket, allowing the unit to cool as designed and, just as important, use no more energy than designed.
Regular Maintenance: Maintaining the Driven System
Simple maintenance of the driven systems can significantly reduce motor loads and increase energy use efficiency. Among other things:
- Ensure drive belts and chains are tensioned regularly and correctly.
- Use matched drive belts on multiple belt systems.
- Always replace sprockets while the worn chains are being replaced.
- Lubricate drive chains regularly.
- If the motor is coupled to a gearbox, ensure the lubricant has the correct viscosity.
- Ensure the driven component is balanced and lubricated regularly.
- When aligning with direct coupling, use the least-expensive non-flex style that’s required and enforce accurate alignment techniques.
- Check driven-system air filters or fluid-system filters regularly.
What’s the payback from following the steps described here? Remember: With a precision-maintenance approach, an electric motor will virtually always outlast its driven system.
First published in The RAM Review
