10.3 Mechanical Drive and Alignment Indicators
Key Takeaways
- Belt drives show thermal clues from friction at sheaves, belt surfaces, and loaded bearings; mismatch between driver and driven sheave temperatures can indicate tension, alignment, or overload problems
- Gearboxes radiate mesh and bearing heat through the case and inspection covers; oil level, cooler performance, and load strongly affect case temperature patterns
- Shaft misalignment and coupling problems often heat near-coupling bearings and coupling regions; patterns should be interpreted with guard limitations and multi-tech confirmation
- Vibration analysis and infrared are complementary: vibration is often more sensitive to early bearing defects; IR quantifies thermal severity, lubrication heat, and system-level friction losses
- Level II recommends combined PdM approaches for critical machines and never removes belt or coupling guards on operating equipment to improve an image
Mechanical power moves through belts, chains, gears, shafts, and couplings. Each interface can waste energy as heat when alignment, tension, lubrication, or loading is wrong. Section 10.1 covered bearing housings and end shields; this section focuses on drive trains—belt systems, gearboxes, misalignment thermal patterns, coupling heating, and the professional decision to pair vibration + IR (and related tools) on critical assets.
Belt Drives: What Heat Is Telling You
V-belts, synchronous (timing) belts, and banded belts transmit torque through friction or tooth engagement. Abnormal heat sources include:
- Belt slip on V-belts (under-tension, overload, worn sheaves)
- Misaligned sheaves causing edge wear and sidewall friction
- Over-tension loading bearings (bearing heat may dominate even if belt looks normal)
- Worn or damaged belts running hot on one rib or strand
- Idlers and tensioners with failed bearings
Typical IR observations
| Observation | Possible causes |
|---|---|
| Belt spans unusually hot vs sister drive | Slip, overload, wrong belt, severe misalignment |
| One sheave much hotter than the other | Slip at that sheave, lagging damage, belt mismatch |
| Hot idler bearing housing | Idler bearing failure or over-tension |
| Driver motor DE hot + belt heat | High belt pull / tension / misalignment load |
| Only edge of belt hot (if safely visible) | Angular sheave misalignment |
Safety and access: Belt guards exist for a reason. Image through designed openings when provided; do not remove guards on a running drive. Shiny sheaves and polished guards are low-ε—use housing temperatures, painted surfaces, or high-ε references when quantitative claims matter.
Tension logic (exam-relevant)
| Condition | Belt thermal tendency | Bearing thermal tendency |
|---|---|---|
| Too loose (V-belt) | Slip heat on belt/sheaves | May be lower mechanical load |
| Too tight | Belt may be moderate | Elevated shaft bearings |
| Misaligned | Localized belt/sheave heat | Elevated loaded bearings |
| Correct | Stable modest temperatures under load | Comparable to baseline |
Level II should not “tighten until the belt stops squealing” based only on IR. Use OEM tension methods; IR flags the thermal cost of a bad setup.
Synchronous belts slip less but still show heat from misalignment, overload, damaged teeth, or failing idlers. Do not assume “timing belt = no thermal issues.”
Gearboxes and Enclosed Drives
Gear reducers convert speed and torque; mesh friction and bearing losses heat the oil and case.
Thermal mapping on gearboxes
Useful comparative points:
- Input end bearing region
- Output end bearing region
- Case mid-section near mesh (when accessible)
- Oil sump region / sight glass area (external)
- Cooler lines and heat exchanger (if forced lubrication/cooling)
| Pattern | Interpretation lean |
|---|---|
| Whole case much hotter than sister unit at same load | Overload, wrong oil, low oil, cooler failure, severe internal friction |
| Input end hot, output cooler | Input bearing or high-speed mesh issues |
| Output end hot | Output bearing, high torque stage, overhung load |
| Hot cooler inlet, cool outlet (or reverse of design) | Cooler effectiveness check |
| Localized hot bolt pattern on cover | Possible internal rub or external heat source—confirm |
Oil level and type dominate gearbox temperature. A “hot gearbox” after an oil change to the wrong viscosity is a classic plant story. IR trends before/after oil work are valuable. Low oil may eventually reduce churning heat then spike wear heat—correlate with oil analysis and vibration, not IR alone.
Painted gearbox cases are radiometrically friendly. Bare aluminum housings need ε care. Sight glasses and shiny tags are poor absolute targets.
Worm gears and high-ratio drives
Some worm reducers run intrinsically hot by design. Comparative sister units and OEM temperature guidance matter more than a universal “green” temperature from an electrical NETA table. Do not apply electrical connection ΔT criteria blindly to gear cases.
Shaft Misalignment Thermal Patterns
Misalignment (parallel offset, angular, or combined) increases reaction forces at bearings and stresses couplings.
Thermal indicators:
- Elevated temperatures at near-coupling bearings on one or both machines
- Coupling region heat (direct view or via guard heating)
- Sometimes asymmetric housing temperatures
- Worsening after piping installation (soft foot / pipe strain) or foundation work
| Alignment-related clue | Supporting non-IR evidence |
|---|---|
| Both near-coupling bearings hot | High 1×/2× vibration; coupling wear |
| Temperature drop after laser alignment | Confirms thermal was load-related |
| Hot after piping hookup | Soft foot / strain check |
| Only one machine’s far bearing hot | Less classic for pure coupling misalignment—consider other faults |
Misalignment heat is a severity signal. Precision alignment still uses dial indicators or laser tools under LOTO. IR prioritizes which trains need alignment resources.
Coupling Heating
Couplings (elastomeric, gear, disk, grid, rigid) dissipate heat when:
- Misaligned beyond capability
- Improperly lubricated (gear/grid types)
- Inserts worn or failed
- Operating at extreme torque/speed for the element
- Guards restrict cooling (secondary effect)
| Coupling type notes | IR practicality |
|---|---|
| Elastomeric element degradation | May show heat; often diagnosed by inspection at stop |
| Gear coupling lubrication loss | Can run hot; lubrication program + IR screening |
| Disc packs | Misalignment fatigue; heat may be subtle early |
| Rigid couplings | Transmit misalignment forces to bearings (bearing heat) |
Again: guards block view. Report “elevated temperature at coupling guard / near-coupling bearings—recommend alignment and coupling inspection at next safe outage” rather than inventing a coupling hub temperature from a reflective cover.
Chains, Clutches, and Brakes (Brief)
- Chain drives: hot sprockets or idlers from poor lubrication, misalignment, or overload
- Clutches/brakes: intentionally dissipate energy as heat during slip; abnormal continuous slip shows sustained high temperature—coordinate with process (is it supposed to be slipping?)
- Fluid couplings / torque converters: case temperature tracks load and oil condition
Distinguish designed slip heat from fault heat using operating mode knowledge.
When Vibration + IR Is the Right Multi-Tech Approach
No single technology sees every failure mode at every stage.
| Technology | Relative strengths | Relative limits |
|---|---|---|
| Infrared | Fast route screening; thermal severity; lubrication film heat; alignment thermal cost; electrical + mechanical in one tour | Later for some subsurface spalls; surface ε issues; needs load |
| Vibration | Early bearing race defects; unbalance; misalignment signatures; gear mesh frequencies | Needs sensors/mounting skill; less direct on pure thermal insulation of steam |
| Ultrasound | Leak detection; some bearing friction; trap testing | Point coverage; training |
| Oil analysis | Wear metals, contamination, chemistry | Sampling lag; not spatial |
| Motor current / electrical | Electrical faults, some load issues | Not a full mechanical map |
Decision guidance for Level II
Lead with IR when:
- Many machines must be screened quickly
- Heat itself is the risk (lubrication, brakes, couplings, steam, electrical)
- Comparing sister units thermally under load
- Quantifying severity for maintenance prioritization after a known defect class
Lead with vibration when:
- Critical high-speed bearings need earliest warning of spalling
- Diagnosing unbalance vs misalignment vs looseness with spectra
- OEM or ISO vibration severity programs are the plant standard
Use both when:
- IR shows elevated bearing or gearbox heat on a critical asset
- Vibration alarm exists and IR can show thermal consequence / other machines on the train
- Root cause is unclear (is it electrical motor heat, belt pull, or bearing?)
- Post-repair verification: alignment done → vibration down and bearing ΔT down
| Scenario | Multi-tech plan |
|---|---|
| Motor DE + pump DE hot near coupling | IR document + vibration + schedule laser alignment |
| Gearbox case rising over months | IR trend + oil analysis + vibration on input/output |
| Belt drive motor bearing hot | IR + tension check + sheave alignment + vibration |
| Subtle bearing defect, little housing ΔT | Vibration/ultrasound may lead; IR still baselines |
| Steam trap route | IR + ultrasound (Section 10.2)—not vibration |
Exam takeaway: Saying “IR replaces vibration” is wrong. Saying “vibration replaces IR” is also wrong for thermal severity, lubrication heat, and multi-machine routes. Level II selects complementary tools.
Inspection Discipline for Drive Trains
- Identify driver, driven, ratio, belt/coupling type, and guards.
- Confirm representative load and speed.
- Measure motor DE/NDE, driven bearings, gearbox points, and accessible sheave/guard patterns with correct ε.
- Compare to baseline/sister equipment.
- Note recent maintenance (belt change, alignment, oil change).
- Classify findings and recommend the next diagnostic (not only “monitor”).
- Respect LOTO for any guard removal, belt tensioning, or coupling work.
Documentation fields that matter
| Field | Why |
|---|---|
| Machine train diagram (even a sketch) | Shows where heat sits relative to coupling/belts |
| Load / product rate | Severity context |
| Belt or coupling type | Interprets expected heat |
| Guard on/off status | Explains limited view |
| Companion vibration work order # | Multi-tech trail |
| ε and measurement points | Repeatability |
Common Traps
| Trap | Correct Level II view |
|---|---|
| Removing belt guard while running for IR | Never |
| Using NETA electrical ΔT tables for all gearboxes | Use mechanical program/OEM context |
| Ignoring over-tension when only belts were inspected | Bearings carry tension load |
| Declaring alignment perfect because vibration tech is “scheduled someday” | Still report thermal risk and priority |
| Trusting shiny sheave absolute temperatures | Fix ε or use comparative patterns |
| Claiming multi-tech is optional on critical hot findings | Critical assets deserve confirmation |
Summary for Recall
Drive-train thermography reads friction and load paths: belt slip and sheave heat, gearbox case and bearing patterns, misalignment-driven near-coupling heating, and coupling stress—always through safe access and correct emissivity practice. Vibration and IR complement each other: vibration often catches early defect dynamics; IR maps thermal severity and system friction. Level II documents the whole train, compares under load, and recommends alignment, tension, lubrication, or multi-tech tests without compromising guards or LOTO.
A V-belt driven fan shows unusually hot belt spans and a hot driver sheave, while bearings are only mildly warm. Which cause is most consistent with that pattern?
Why is a multi-technique approach (for example vibration + IR) preferred on a critical pump train with elevated near-coupling bearing temperatures?
Compared with a sister gearbox under the same load, a unit’s entire case is much hotter after an oil change. What should Level II consider early?