10.1 Bearing and Rotating Equipment Signatures

Mechanical thermography turns friction, inefficiency, and heat flow into spatial temperature maps. Unlike a single-point contact probe on one grease fitting, infrared shows where heat is generated and how it spreads through housings, end shields, couplings, and connected machines. Level II work on bearings and rotating equipment is quantitative when emissivity and setup allow, but always comparative: the same machine over time, identical sister trains, drive end versus non-drive end, or motor versus driven load under documented operating conditions.

This section focuses on thermal signatures of bearings and rotating assemblies, end-shield ΔT practice, lubrication-related heat, misalignment patterns, coupling and guard interpretation, motor-versus-driven logic, and the role of ISO 18434 concepts in a Level II mechanical program.

Why Mechanical IR Works

Friction at rolling elements, inadequate or contaminated lubricant films, misaligned shafts, overloaded belts, and binding seals all convert mechanical energy into heat. That heat conducts into bearing housings, end bells, and frames and then radiates (and convects) to the environment. A thermal imager maps surface temperature. With correct parameters, you can:

• Detect abnormal heat before catastrophic failure
• Rank severity using ΔT against baselines or similar components
• Support trending (Chapter 12) when inspections repeat under similar load
• Direct vibration, ultrasound, or oil analysis to the right machine

IR does not replace vibration analysis for early bearing race defect diagnosis. High-frequency vibration and ultrasound often detect subsurface defects earlier than bulk housing temperature. IR excels at thermal severity, lubrication film problems that generate heat, alignment/coupling stress, and rapid route-based screening of many machines.

ISO 18434 Context (Rotating Machinery Thermography)

ISO 18434 (Condition monitoring and diagnostics of machines — Thermography) is the international standard series that frames how thermography is used in machine condition monitoring. Level II candidates should know the role of the standard even when a specific plant procedure cites a corporate version or vendor guide:

Exam items may reference ISO 18434-1 style zones or severity thinking for rotating equipment (relative temperature rise classes used in condition monitoring programs). Your site’s severity chapter (Chapter 8) covers formal zone tables in detail; here the operational rule is: use an adopted program criterion consistently, record load and ambient, and never invent a one-off ΔT rule after the fact to force a priority.

Common program patterns (illustrative—always follow client/OEM standard):

Exact numeric bins belong to the written program (and Chapter 8). Level II owns consistent measurement and honest uncertainty, not memorizing a single global number for every bearing in every industry.

End-Shield and Housing Measurement Practice

Drive end (DE) and non-drive end (NDE)

Motors and many pumps/fans present end shields (end bells) that enclose bearings. A standard route measurement records temperature (or ΔT to ambient or to a reference point on the frame) at:

• DE bearing housing / end shield — often higher duty when shaft load, coupling, or belt pull is present
• NDE bearing housing / end shield — compares symmetry; NDE may show different loading or cooling
• Motor frame / stator body — helps separate winding/electrical heat from pure bearing friction
• Driven equipment bearings (pump, fan, gearbox) — may be hotter or cooler than the motor depending on process load

How to take a defensible reading

1. Identify the machine (tag, photo, nameplate) and note running state: speed, load estimate, product temperature if process-connected, hours since start.
2. Emissivity — Painted cast iron/aluminum housings are typically high-ε (often ~0.90–0.95). Set ε accordingly. Bare shiny shafts and chrome are not reliable absolute targets without tape/paint.
3. RAT — Set reflected apparent temperature correctly outdoors or near hot process equipment; reflected heat from steam lines or furnaces can fake hot spots on shiny guards.
4. Geometry — Fill the measurement area; avoid grazing angles on curved end bells when quantitative ΔT is claimed.
5. Compare — Same point type on sister units, or DE vs NDE, or today’s reading vs baseline under similar load.
6. Document ambient air temperature, wind (outdoor), and any temporary covers or insulation.

ΔT definitions matter. “20 °C above ambient” is not the same as “20 °C above the sister motor DE” or “20 °C above this machine’s baseline at 80% load.” Report the reference explicitly.

Lubrication-Related Thermal Signatures

Lubricant forms a film that separates rolling elements and races. Thermal clues include:

Important Level II nuance: A hot bearing after greasing is not automatically “good lubrication.” Over-greasing can increase temperature. Trend before/after lubrication under similar load; coordinate with the lubrication technician’s procedure rather than greasing solely because IR looked warm.

Grease fittings and purge paths may show local warm grease expulsion—useful qualitative clues, not always quantitative targets if fittings are shiny metal.

Misalignment, Soft Foot, and Coupling-Related Heat

Shaft misalignment and soft foot increase bearing loads and coupling stress. Thermal patterns may include:

• Elevated temperature at both machines’ near-coupling bearings
• Hot coupling region (when visible) or hot coupling guard surfaces heated by convection/radiation from the coupling
• Asymmetric heating around a bearing housing (one side of the end shield warmer)
• Combined IR + high vibration at 1× or 2× running speed (vibration confirms; IR shows thermal cost)

Coupling guards are safety covers. They often block direct view of the coupling. A warm guard indicates heat generation nearby but is a poor emissivity surface if polished. Treat guard temperature as a screening indicator, then plan a controlled inspection (lockout, guard removal per safety rules) or use other CM methods. Never remove guards on running equipment for a better IR shot.

Motors Versus Driven Equipment

A frequent exam and field trap is blaming the motor for heat that originates in the driven machine, or the reverse.

Motor-centric heat

• Elevated stator/frame with relatively modest bearing ΔT → electrical load, cooling fan, dirty fins, voltage imbalance (also check electrical IR on connections when safe)
• DE hotter than NDE with coupling load → mechanical load from drive train
• Both bearings hot after long stop-start in high ambient → check ventilation and duty cycle

Driven-equipment-centric heat

• Pump stuffing box / seal area hot → seal friction, flush issues, process temperature
• Fan bearing hot with cool motor → fan bearing, belt, or wheel issues
• Gearbox case hot → gear mesh load, oil level, cooler effectiveness (Section 10.3)

Always record process fluid temperature for pumps and heat exchangers. A “hot” pump housing may simply track hot product.

Emissivity and Target Selection on Rotating Machines

For trending programs, mark permanent high-ε spots (paint dots or approved tape locations) so every tech measures the same point.

Inspection Conditions and Safety

• Survey under representative load. Idle machines hide friction heat.
• Allow thermal equilibrium after start-up when the program requires steady state (many bearings need tens of minutes to hours depending on size).
• Respect rotating equipment hazards: coupling guards, belts, shafts, loose clothing, and arc-flash rules if electrical panels are opened in the same tour.
• Outdoor machines: sun load can heat housings nonuniformly—note solar condition or survey in shade/evening when absolute comparisons matter.
• Do not interpret a single hot pixel on a bolt head without context; use area tools on the housing mass.

Multi-Technique Confirmation

Level II reports gain credibility when thermal severity triggers the right next method:

If vibration is normal and IR is high, still investigate lubrication, process heat, and measurement error before dismissing either technology.

Common Traps

Summary for Recall

Bearing and rotating-equipment thermography is comparative heat mapping under known load, guided by program criteria and ISO 18434-style condition-monitoring practice. Measure DE/NDE end shields and housings with correct ε/RAT; interpret lubrication, misalignment, and coupling-guard patterns carefully; separate motor electrical heat from driven mechanical heat; and confirm critical findings with vibration, oil, or ultrasound. Pretty color images without load context, emissivity discipline, and a defined reference are not Level II mechanical analysis.