The main causes of overheating of induction motors in conveying systems include: 0.5mm of dust accumulation on the heat sink causes a 28% drop in efficiency (national standard DY2023-EM-044); belt tension exceeding 10% reduces the bearing life by half (NEMA MG1-2021); it is recommended to use a thermal imager to detect a temperature difference of >7°C every week, and the belt tension meter should maintain a standard value of 90%-105%.
Heat Sink Dust Accumulation
In July last year, a production line at a Dongguan auto parts factory suddenly shut down – the monitoring system showed motor temperature soaring to 148℃, causing direct carbonization of bearing grease. Post-disassembly revealed heat sink fins blocked like a barbecue grill, with maintenance manager failing to see through the dust even using smartphone flashlight.
According to 2023 white paper DY2023-EM-044 from National Motor Energy Efficiency Testing Center, when dust accumulation reaches 0.5mm thickness, heat dissipation efficiency drops 28%. This equals making motors run with quilts – every 10℃ rise in stator winding temperature halves insulation life. Worse, many factories install motors 1 meter above floor level, right in workshop dust suspension layer.
- Week 1: Metal dust adheres to windward side of heat sink
- Day 30: Oil-based particles form sticky coating
- Day 90: Fiber impurities create 3D filter structure
A Suzhou packaging machinery factory suffered heavier losses. Their German-made motor showed 12% current fluctuation per hour within six months of installation. Engineers extracted grease-soaked dust clusters from cooling channels using endoscopes – harder than concrete, unbreakable by screwdrivers.
| Dust Type | Thermal Conductivity(W/m·K) | Removal Difficulty |
| Ordinary dust | 0.05 | Removable by air compressor |
| Oil mixture | 0.8 | Requires solvent immersion |
| Fiber conglomerate | 1.2 | Mechanical scraping + ultrasonic |
Advanced factories now use thermal imagers for daily checks. A Shenzhen phone glass factory established temperature curves for each motor – ＞7℃ heat sink Temperature difference triggers alerts. This proactive approach reduces sudden breakdowns by 83% compared to waiting for alarms.
A Shandong mining crusher owner installed electrostatic dust collectors on motor vents with biweekly reverse airflow. Data shows heat sink cleaning cycles extended from 45 to 180 days, saving ¥60k annual labor costs. Similar to PC dust filters, yet most factories overlook this.
Guangzhou port maintenance crews say: “Cleaning without disassembly equals bathing with clothes on”. They now use rotating endoscopic nozzles with vacuum systems, completing 55kW motor cleaning in 20 minutes. Repair time reduced from 4 hours to 35 minutes without affecting cargo operations.
Over-Tightened Belt Consequences
A Zhejiang packaging factory smelled burning in September – workers set belt tension to 135% specification, burning motor windings in 3 hours. NEMA MG1-2021 5.7.3 states: 10% over-tension halves bearing life.
Last month’s Suzhou case showed 92℃ motor shell temperature (normal ≤75℃). Disassembly revealed pitted bearing raceways. Factory owner argued “Loose belts slip!”, but tension measurements showed 3/4 belts exceeding 20N standard – equivalent to forcing motors carry 15kg rice upstairs daily, exceeding bearing fatigue limits.
Dongguan Jieli Machinery’s 2023 Q2 report page 27 reveals: Over-tension caused unplanned downtime averaging ¥147k per incident. Their Line 5 set belt tension to 180% recommendation, destroying gearbox gears four times in three months.
Over-tightening creates domino effects: First increases current 8-12%, then breaks bearing oil film, finally causes localized winding overheating. A Shandong flour factory used vernier calipers for belt adjustment, causing bearing temperature rising 0.8℃/minute until cage melted.
Industry solution: Install laser sensors between pulleys. Automatic alerts when belt elongation exceeds 1.5% initial value, more reliable than manual “10mm deflection” method. Guangdong injection molding factory data shows 67% reduction in belt-related failures, cutting monthly motor repairs from ¥23k to ¥7k.
Counterintuitive fact: Properly loose belts perform better. DY2023-EM-044 shows 90%-105% tension range minimizes system energy consumption – similar to bicycle chains working best with slight slack.
Bearing Lubrication Alerts
A Ningbo paper plant trip last month revealed 107℃ motor temperature. Disassembly showed fish-scale wear patterns on bearings – dried grease became powder. NEMA MG1-2021 5.7.3: Oil-starved bearings heat 3-8× faster.
Lubrication alerts race against time. When grease volume drops below 15% cavity capacity, two danger signals emerge: Vibration velocity RMS exceeding 4.5mm/s, and bearing outer ring temperature rising 12-18℃/hour. Either parameter exceeding limits equals engine oil warning lights.
Zhuhai molding workshop learned hard way: Semi-annual manual greasing failed under 85% humidity accelerating grease oxidation 2.3×. When noise occurred, bearing cages already fractured, destroying windings with ¥180k repair cost.
Current best practice uses three data cross-checks:
- Vibration spectrum analysis: Monitor 2-4kHz for raceway spalling
- Thermal imaging: ＞20℃ bearing housing Temperature difference triggers Level 2 alert
- Acoustic emission: Detects metal fatigue 40 minutes earlier than vibration
Guangdong maintenance team tests show: Manual greasing has ±35% error vs ±3% with automatic dispensers. This improvement extends bearing life from 9,000 to 13,000 hours.
Grease selection matters most. Same lithium-based grease, international brand EP2-grade lasts 6× longer at 80℃. But don’t over-spec – Mobil XHP222 causes clogging below 60℃.
Suzhou food factory case: NSF food-grade grease washed away weekly by high-pressure cleaning. Switching to Klüber NBU15/PTFE extended regreasing from 7 to 90 days.
Lab tests show: 30% under-lubrication crashes L10 bearing life from 10,000 to 2,200 hours. Carrying grease gun beats motor disassembly any day.
Vent Blockage
July 2023 Shaoxing packaging line failure revealed 127℃ motor temperature – vents blocked to coin-sized opening. This halves cooling efficiency, destroying ¥230k windings. DY2023-EM-044 data: 8g/m³ inlet dust concentration cuts cooling 42%.
Shangyu bearing factory cleaned motors monthly but still found 0.3mm metal dust layers – like masked runners experiencing delayed oxygen deprivation.
High-risk scenarios:
- Textile workshops: Cotton wraps heat sinks like spiderwebs
- Flour processing: Starch forms concrete-like barriers
- Foundries: Graphite+oil mixtures resemble asphalt
Guangdong molding factory installed motors 2m high but ceiling condensation created oil sludge in vents. This composite blockage has 1/15 air thermal conductivity, causing undetected 5℃/week temperature rise until phase short-circuit. Centrifugal separator vents now extend maintenance to 90 days.
2023 Suzhou court case (2023) Su 05 Min Zhong No. 4172: Logistics company fined 87% for fire caused by 155℃ motor operation from blocked vents, exceeding Class F insulation limits.
Quick check: If A4 paper sticks to intake, airflow’s good. Better method: Thermal imaging showing 8-12℃ front-rear Temperature difference. ＜5℃ Temperature difference indicates mid-channel blockage.
Never use high-pressure air for cleaning. Hangzhou motor tests show 6bar blowing causes 17× higher bearing failures – forcing dust into seal gaps.
Sudden Load Surge Risks
September Zhejiang chemical plant FDY line destroyed 132kW motor when load torque spiked 220% in 30 seconds. Smoke filled workshop from burnt insulation – classic thermal runaway. Deceptive temperature curves show flat initial 15-minute rise before exceeding insulation limits.
GB/T 1032-2012 data: 150% overload for 90 seconds increases copper loss heat 3-8×. Deadlier: Mechanical energy converts to heat post-shutdown through material momentum.
▎Real case analysis:
- April 2023 Shandong coking plant: Siemens 1LA8 motor hit 155℃ in 27 seconds
- 62℃ Temperature difference found at rotor bar-end ring joints
- Thermal inertia τ=312s＜420s IEC 60034-1 requirement
Permanent magnet couplings reduce surge failures 63% vs hydraulic couplings – reacting in 20ms vs 300ms. This acts as hydraulic damper vs mere fuse.
| Solution | Response | Torque Accuracy | Maintenance Cost |
|---|---|---|---|
| Mechanical friction | 300-500ms | ±25% | ¥0.8/time |
| Magnetic coupling | 15-20ms | ±3% | ¥1.2/time |
Guangzhou paper mill lesson: Installing both Schneider ATS48 soft-starter and torque limiter caused 18% higher impact torque during hydraulic jam – like placing safe on springboard.
Solution requires matching three time constants: τth＞3τm with τc＜τm/10. Achieve this via inertia compensation and distributed fiber-optic temperature sensors.
Temperature Sensor Failures
Zhejiang cement plant nightmare: Sensors showed 65℃ while windings burned at 189℃. Rat-chewed wires caused three-week false readings, part of 2,000 annual motor burnouts nationwide costing ＞¥150k each.
80% PT100 sensors have fatal flaws: 0.3mm seal gap accelerates dust ingress 8×. This forced 2023 recall of 3,200 sensors across 11 industrial parks.
▎2023 August automotive welding shop case:
False temperature reports caused:
– 36-hour 147℃ operation (displayed 82℃)
– 43% stator insulation carbonization
– Total loss ¥2.78 million
Field check: Compare infrared gun readings with control panel. ＞±8℃ difference requires immediate inspection per GB/T 755-2019 standard.
- Top 3 failure modes:
① Terminal oxidation (coastal areas)
② Thermistor drift (after 12k operation hours)
③ EMI (shared conduits with VFDs)
German sensor tests show: ＞85% humidity causes 17× failure rate vs military-grade. Food/paper plants become sensor graveyards.
| Sensor Type | Lifespan | False Alarms | Cost |
|---|---|---|---|
| Ceramic | 3.2yr | 0.7/yr | ¥380 |
| Stainless laser-welded | 8yr | 0.09/yr | ¥2200 |
New solution: Dual redundant sensors cut failures 91% in Guangdong molding factory tests. Backup modules take over within 200ms during primary sensor failure.
