Wear of electric motor bearings is the most common cause of unscheduled shutdowns of industrial equipment. According to our service center statistics in Tashkent, up to 60% of calls for repairs are related to bearing units. The good news is that a bearing almost never fails suddenly. It gives clear signals weeks and even months before the final breakdown. This article contains 7 signs by which an experienced mechanic will accurately identify the problem, a table of sounds by type of defect and the service life of popular models 6303, 6306, 6309.
Why bearings wear out prematurely
A rolling bearing is a high-precision and capricious part. The design life of a high-quality 6306 at rated load is 20,000–30,000 hours, that is, 3–5 years of round-the-clock operation. In practice, in the dusty workshops of Tashkent and Chirchik, bearings often fail within 8–12 months. The main culprits: contamination of the lubricant with abrasive, overheating, shaft misalignment, rotor imbalance and electrical erosion from frequency converters.
Timely diagnostics of electric motors allows you to catch a defect at an early stage, when replacement costs several times less than a major overhaul.
7 signs of bearing wear
- Extraordinary noise. A healthy bearing operates almost silently - only a smooth rustle is heard. The appearance of a howl, hum, grinding or periodic clicking is the first and most reliable sign.
- Increased vibration. If previously the engine stood level on the frame, but now it shakes noticeably when touched by hand, it’s time to measure the vibration velocity. Exceeding 4.5 mm/s according to ISO 10816 is a reason to stop.
- Local heating of bearing shields. The housing temperature in the bearing area should not exceed +70…+80 °C. If the non-contact pyrometer shows +90 °C and above under normal load, the bearing is on the verge.
- Leaks and release of lubricant. A black oily track on the housing under the bearing cover indicates destruction of the separator or burnout of the lubricant due to overheating.
- Axial and radial play of the shaft. Rock the shaft by hand with the engine off. Any noticeable move is a reason for immediate disassembly.
- The smell of burning grease or burnt insulation. An overheated bearing heats the shaft and heats the winding again - this is a double accident.
- Drop in speed and current drawdown. A jammed bearing creates a parasitic torque, the rotor slows down, and the current in the phases jumps by 10–20%.
Table: bearing sound and type of defect
| Sound character | Probable cause | Urgency of repair |
|---|---|---|
| Even rustling | Normal | Scheduled maintenance |
| High-frequency howling, whistling | Dry running, lack of lubrication | 1–2 weeks |
| Hum, low frequency rumble | Wear of raceways | 2–4 weeks |
| Periodic clicking | Sink on outer ring | 1 week |
| Grinding, metallic crunch | Destruction of the separator, jamming of balls | Immediately |
| Knocking in time with the revolutions | Chip on the inner ring | 3–5 days |
| Howling hum with beating | Clip distortion, broken seat | Immediately |
When to change a bearing urgently
There are situations when the operation of the engine becomes downright dangerous - the rotor may jam, the shaft may break, or the winding may catch fire. Immediately turn off the engine and order urgent repair of electric motors if you observe:
- bearing shield temperature above +95 °C;
- grinding or metal hitting metal;
- visible smoke or droplets of melted grease;
- radial shaft play more than 0.2 mm;
- thermal current protection is triggered more than once per shift.
In our service in Tashkent, we carry out express diagnostics with a vibration meter and a thermal imager in 2-3 hours, after which a decision is made - replacement of bearings or complete disassembly with defect detection.
Service life of popular bearings
The design life depends on the load, speed, lubricant quality and environmental conditions. Below are guidelines for asynchronous motors AIR, 4A, 5AM when working in two shifts:
- 6303 (1.1-2.2 kW motors):25,000-35,000 hours, approximately 4-5 years.
- 6305 (3–5.5 kW motors): 22,000–30,000 hours, approximately 3.5–4 years.
- 6306 (7.5-11 kW motors):20,000-28,000 hours, 3-4 years.
- 6308 (motors 15–22 kW): 18,000–25,000 hours, 2.5–3.5 years.
- 6309 (30–45 kW motors):16,000–22,000 hours, 2–3 years.
- 6312 (engines 55–90 kW): 14,000–20,000 hours, 2–2.5 years.
In dusty production conditions - cement, brick, foundries - the actual resource is reduced by 30–50%. Therefore, in Tashkent, we recommend scheduled replacement of bearings every 18–24 months, without waiting for a breakdown.
Prevention: how to extend service life
The bearing lasts a long time if you follow simple operating rules:
- Add lubricant (Litol-24, CIATIM-221, Mobil Polyrex EM) every 2,000–4,000 operating hours.
- Do not overwork the assembly - excess lubricant heats up just as much as its lack. Fill the case 1/2–2/3 full.
- Control the alignment of the shafts during a coupling connection. A deviation of more than 0.1 mm kills the bearing within months.
- After any winding repair, carry out balancing the rotor - an imbalance over 6.3 mm/s kills the bearing 3-4 times faster.
- Use high-quality bearings SKF, FAG, NSK, ZKL. Cheap Asian analogues last 2–3 times less.
- Once a quarter, measure vibration and temperature - it takes 5 minutes, but saves you from accidents.
For critical drives of cranes, pumping stations and elevator equipment, prevention is especially critical - a breakdown stops the entire technological process. We carry out repair of crane electric motors with complete replacement of bearing units and load testing.
Need help with diagnostics?
If your electric motor in Tashkent starts to hum, heat up or vibrate, don’t wait for an accident. Elektromotors engineers will conduct vibration diagnostics, thermal imaging examination and accurately determine the remaining life of bearing units. Replacing bearings takes 1-2 business days, and all work comes with a 12-month guarantee. Contact us to make an appointment for diagnostics or call an engineer to the site.