High Crusher Bearing Temperature: 8 Check Points and Three Root Causes

High bearing temperature is one of the most commonly mistreated crusher faults. In more than 40 years of field service since the 1980s, the most frequent scene we see is this: the temperature rises, grease is added, and it gets hotter still. In reality bearing heat has only three root causes — friction heat, externally transmitted heat and poor heat dissipation — and investigation should follow lubrication first, fitting second, load last. This guide covers the eight check points.

图：大美智造破碎机配件实物——轴承温升常与配件装配质量、配合精度直接相关

I. The Eight Check Points, In Investigation Order

Check point 1: correct grease or oil grade

• Base oil viscosity and thickener type determine the speed and temperature range a grease can serve. The wrong grade — especially mixing different thickener types — can harden the grease or cause oil bleed and loss of lubrication;
• Key point: keep one grade per bearing long term; when changing grades, purge the old grease completely.

Check point 2: grease fill quantity (most overlooked)

• Overfilling: rolling elements churn the grease, generating churning heat; the grease softens and bleeds, creating a vicious circle — the direct cause of "the more you add, the hotter it gets";
• Underfilling: insufficient film, metal-to-metal contact, wear and heat;
• Reference range: typically 1/3 to 1/2 of the bearing cavity; less at higher speeds, more for slow heavy-duty duty. Always follow the equipment manual and bearing maker recommendation.

Check point 3: grease degradation or contamination

• Emulsification: water ingress turns the grease white and destroys lubricity — common where dust is heavy and washdown frequent;
• Particle contamination: dust forms an abrasive paste that accelerates wear and heat;
• Hardening or oil bleed: dry caked grease or heavy oil separation both mean the grease has failed.

Check point 4: re-greasing interval and method

• Too short an interval causes the overfilling above; too long means starvation;
• Method: grease while running or immediately after stopping so fresh grease distributes and purges the old; greasing a long-idle machine tends to create local packing;
• Purge path: confirm the relief or return passage is clear; blockage prevents old grease escaping and raises cavity pressure.

Check point 5: bearing fitting quality (clearance and preload)

• Too little clearance or excessive preload: contact stress between rolling elements and races rises and friction heat climbs — the most common fitting-related cause;
• Too much clearance: impact during running also generates heat and vibration;
• The hammer-fitting trap: striking a bearing directly with a hammer causes raceway brinelling, leading to local stress concentration and heat that is hard to see; use proper tooling or heat fitting.

Check point 6: shaft and housing interference (creeping)

• Insufficient inner-ring interference: inner ring creep generates friction heat at the fit and wears the shaft journal;
• Insufficient outer-ring interference: outer ring creep does the same to the housing bore;
• Field indicator: circumferential bright marks, discolouration or a wear step on the journal or bore are classic creep evidence.

Check point 7: load and feed condition

• Prolonged overload or choking: loads beyond design keep bearing temperature high;
• Feed segregation: material striking one side loads the bearing unevenly;
• Oversized feed: higher impact loads indirectly raise bearing temperature;
• Method: compare no-load versus loaded temperature. High even at no load points to the bearing itself; normal at no load but rising under load points to load or feed.

Check point 8: cooling conditions and external heat sources

• High ambient temperature: summer or enclosed buildings compress the available temperature rise;
• Blocked dissipation: material accumulation around the housing, poor ventilation, blocked water cooling where fitted;
• External heat: hot material, steam or adjacent heat sources conducting through the shaft;
• Seal friction: over-tight or dry-running seals add extra heat.

II. A Field Lesson: The More Grease, The Hotter It Got

A cement plant crusher bearing ran hot and tripped alarms. The response was to add grease at every alarm — and the more often it was greased, the hotter it ran, until noise appeared and the machine had to stop.

We worked through the eight check points:

• Point 1 (grade): the grade matched the manual, no issue;
• Point 2 (fill): opening the housing showed the cavity almost completely packed with grease, far beyond the correct fill — rolling elements churning the grease generated continuous churning heat;
• Point 4 (purge path): the relief port was blocked with a mixture of old grease and dust, so old grease could not escape and every greasing simply added pressure;
• Point 5 (fitting): clearance measurement showed clearance on the tight side from excessive preload at assembly, the second contributor.

The root cause was overfilling plus a blocked relief port, aggravated by tight clearance. The fix: remove excess grease to the correct fill, clear the relief port, re-set clearance to specification and add "relief port clear" to the inspection list. Temperature returned to normal and the noise disappeared.

The rule recorded: high temperature does not mean low grease — confirm quantity and purge path before adding any. Blind greasing may itself be the problem.

图：红外测温点检——固定测点并记录温升，才能形成可横向对比的趋势数据

III. Eight Check Points Quick Reference (Save This)

Key discriminator: no-load versus loaded comparison

Bearing temperature and vibration feed each other — sustained vibration changes preload and load distribution, see crusher vibration diagnosis; lubrication starvation also leaves a characteristic appearance on teardown, see wear part failure modes.

IV. Insider Gotchas

• "Hot means add grease": the most common error. Excess grease raises temperature through churning, so adding more makes it worse. Check quantity and purge path first;
• Recording absolute temperature only: ambient varies widely (tens of degrees between winter and summer), so absolute readings are not comparable. Record temperature rise and compare;
• Overlooking a blocked relief port: a blocked purge turns greasing into pressurised packing, a hidden and common cause;
• Hammer-fitting bearings: causes raceway brinelling that shows up later as heat and is hard to detect; use proper tooling or heat fitting;
• Inconsistent measurement points: readings from the cap, housing and end cover differ widely. Fix the measurement point and record it so trends are comparable.

V. When NOT to Handle It Yourself

• Temperature rising fast or with clear noise: the bearing may be degrading rapidly; continuing to run risks seizure or journal damage;
• Journal or bore already worn or discoloured: a fit-surface problem that grease cannot solve; needs professional assessment and dimension restoration;
• Equipment under warranty: unauthorised dismantling may void it; contact the manufacturer or supplier first;
• No temperature instrument: hand feel varies and cannot be quantified; use an infrared thermometer and build a data-based record.

Three actions: 1. Fix the measurement point and record temperature rise, not absolute temperature, to build a trend; 2. Check grease quantity and the purge path first (lowest cost, highest hit rate); 3. Run a no-load versus loaded comparison to decide whether it is the bearing or the load.

FAQ

• Q: Does high bearing temperature mean low grease? A: Not necessarily, and that is the most common misjudgement. Too much grease also raises temperature through churning — that is how "the more you add, the hotter it gets" happens. Check quantity and the purge path before adding any.
• Q: How much grease should be used? A: Typically 1/3 to 1/2 of the bearing cavity, less at higher speeds and more for slow heavy-duty duty. Follow the equipment manual and bearing maker recommendation, and confirm the relief port is clear.
• Q: How do we tell a bearing problem from a load problem? A: Compare no load with loaded. High at no load indicates the bearing itself (lubrication, fitting, interference); normal at no load with a clear rise under load points to load or feed.
• Q: What bearing temperature is normal? A: Allowable values differ by equipment and bearing type; follow the manual. A practical approach is to record temperature rise (bearing minus ambient) and build a trend — whether it keeps climbing matters more than any single number.
• Q: Does Grand Heavy support bearings and related parts? A: Grand Heavy supplies crusher parts and technical support and can help investigate fitting and interference causes of bearing temperature rise. See also cone crusher lubrication troubleshooting and crusher vibration diagnosis.

VI. Final Verdict

The order is always: check lubrication first (quantity, purge path, condition), then fitting and interference (clearance, creep), and load and cooling last. And remember the counter-intuitive rule: high temperature does not mean low grease — too much generates heat as well. Record temperature rise rather than absolute temperature and build trend data to turn alarm response into predictive maintenance. Foshan Grand Heavy Trading Co., Ltd. has built mining equipment and wear casting expertise for 40+ years, holds 20+ patents, partners with Central South University and Guangdong University of Technology, and is certified as a National High-Tech Enterprise [To be added: certificate number]. We serve CNBM, Conch Cement and clients across 6 overseas markets with 24-hour response from Guangzhou, Foshan and Changsha.

Grand Heavy — Hot does not mean dry, check the fill before greasing!