Precautions for Inspection and Maintenance of Electric Forklift Motors in Winter

The precautions for the inspection and maintenance of electric forklift motors in winter should be carried out around four core dimensions: low-temperature environment characteristics, protection of key motor components, safe operation specifications, and maintenance effect traceability. Combined with the failure mechanisms of motors under low temperatures (such as reduced insulation, lubrication failure, metal shrinkage, and condensation erosion), a practical and comprehensive precaution system is formed, as detailed below:

I. Environment Adaptation and Operation Condition Control

Temperature Control of Operating Environment

Avoid directly starting the motor in extreme low-temperature environments (≤-20℃). Preheat the motor before startup (e.g., turn on the forklift power supply for 3-5 minutes of preheating, or transfer it to the operating site after heat preservation indoors) to prevent cracks in the winding insulation due to instantaneous cold-heat shock.
Maintenance operations shall be performed indoors at ≥5℃. If emergency outdoor treatment is required, set up a temporary thermal insulation shed, and the operation time shall not exceed 30 minutes to avoid operational errors caused by hand frostbite and stiff tools (such as inaccurate torque control and insufficient tightening of terminal blocks).
Avoid open-air disassembling maintenance (e.g., opening junction boxes, disassembling bearings) in rainy, snowy, or foggy weather to prevent condensation from directly seeping into the motor and exacerbating insulation moisture.

Humidity and Condensation Protection

Check the sealing status of the motor housing and junction box before and after operation to ensure that waterproof gaskets and oil seals are free from aging and cracking, and that there are no gaps at the wire inlets. This prevents condensation from forming due to day-night temperature differences after ambient moisture enters.
If the ambient humidity exceeds 70%, additionally spray three-proof paint (IP65 grade) on the windings after maintenance, and extend the re-test time of insulation resistance (let it stand for 2 hours after cooling to room temperature before measurement to ensure stable values).
For forklifts parked for a long time, start the motor for 10-15 minutes of no-load operation every month to use the motor's own heat to dispel internal moisture and avoid long-term moisture-induced insulation failure.

II. Special Protection Precautions for Key Components

(1) Protection of Electrical Systems

Specifications for Insulation Resistance Measurement

Use a calibrated 500V megohmmeter to measure insulation resistance, and the motor must be cooled to room temperature (≤30℃). Avoid low readings caused by measurement at high temperatures (misjudging insulation failure) or reduced accuracy due to stiff windings at low temperatures.
If the insulation resistance is below the standard value (stator to housing <1MΩ, between three phases <2MΩ), adopt the "low-temperature hot air drying method" (40-50℃). Strictly prohibit high-temperature baking (>60℃) or open flame heating to prevent insulation aging and carbonization.
Apply conductive paste (thickness: 0.1mm) to terminal blocks after treatment, but do not overapply to avoid short circuits caused by moisture absorption of the conductive paste. Tighten the terminals according to the manufacturer's specified torque (6-10N・m) to prevent loosening due to metal shrinkage at low temperatures or damage to terminal threads due to excessive torque.

Taboos for Current and Temperature Monitoring

Avoid full-load operation at startup. First run the motor at no load for 5-10 minutes, and gradually apply load after the motor temperature rises above 40℃ and the current stabilizes. This prevents accelerated bearing wear due to insufficient lubrication at low temperatures or winding heating due to instantaneous overload.
Do not continue operation when the motor housing temperature exceeds 80℃. Stop the motor and cool it to below 40℃. Do not directly rinse the housing with cold water to cool it, as this may cause cracks due to excessive temperature difference between the housing and windings.

(2) Key Taboos for Lubrication Systems

Specifications for Grease Selection and Filling

Strictly prohibit the use of general-purpose summer grease (pour point ≥-10℃). Must use winter-specific low-temperature lithium-based grease (NLGI Grade 2, pour point ≤-35℃, dropping point ≥180℃). Otherwise, grease solidification at low temperatures will cause bearing jamming and excessive motor startup load.
Thoroughly remove old grease (residual amount ≤10%) before filling new grease. Do not mix old and new grease (different types of grease have poor compatibility and are prone to caking and failure). The filling volume should be 1/2-2/3 of the internal bearing space. Excessive filling will cause high-temperature carbon deposition during motor operation and block heat dissipation channels.
For motors with grease fittings, rotate the output shaft 3-5 times after greasing to ensure uniform coverage of balls and raceways with grease, avoiding local insufficient lubrication.

Precautions for Bearing Inspection and Replacement

Bearing clearance will decrease due to metal shrinkage at low temperatures. If the original clearance is close to the upper limit (radial clearance ≥0.08mm), replace the bearing in advance (standard radial clearance ≤0.1mm) to prevent jamming caused by excessively small clearance at low temperatures.
When replacing bearings, select deep groove ball bearings consistent with the original model (precision class ≥P6). Strictly prohibit mixing bearings of different precisions and materials. Avoid tapping the bearing inner ring during installation (use special pressing tools) to prevent ball damage.

(3) Mechanical Structure and Heat Dissipation Protection

Adaptation to Air Gap and Metal Shrinkage

Additionally check the air gap between the motor stator and rotor in winter to ensure that the average three-phase air gap complies with the manufacturer's specifications (0.2-0.5mm) with a maximum deviation of ≤0.1mm. Prevent uneven air gap caused by different shrinkage amounts of the stator and rotor at low temperatures, which may lead to "rubbing" (friction between the rotor and stator).
Check the fixing bolts of the motor housing and end covers. Metal shrinkage at low temperatures may cause bolt loosening. Retighten the bolts according to the manufacturer's torque standards to avoid increased vibration during operation and damage to bearings and winding ends.

Taboos for Heat Dissipation System Maintenance

Clean cooling fins with a soft brush or compressed air (pressure ≤0.4MPa). Strictly prohibit scraping with sharp tools to prevent fin deformation and blockage of heat dissipation channels. For ice and snow coverage, let it melt naturally or dry with low-temperature hot air (≤50℃). Do not directly pour hot water to avoid housing deformation.
If installing a motor insulation cover (for environments below -20℃), ensure that the cover does not block the cooling fan and fins, and use flame-retardant materials to prevent excessive temperature due to poor heat dissipation during motor operation.

III. Safe Operation Specifications

Power Off and Discharge Operation

Before all inspections and maintenance, disconnect the forklift's main power supply, pull out the motor wiring plug, wait for the capacitor to fully discharge (at least 5 minutes), and hang a "No Switching On" sign to prevent electric shock from residual current.
When disassembling terminal blocks, first mark the lines (such as phase marks and wiring position marks) to avoid reverse phase connection during reassembly, which may cause motor reversal or electronic control system failure.

Tool and Material Safety

Use explosion-proof lighting equipment (when combustible dust is present in the operating environment). Tools such as thermometers, megohmmeters, and torque wrenches must be calibrated (error ≤±2%) to ensure accurate measurement data (e.g., insufficient torque leading to terminal loosening, excessive torque leading to component damage).
Store materials such as grease, conductive paste, and three-proof paint away from open flames in a dry environment at 0-25℃. Strictly prohibit the use of expired or mismatched materials (e.g., replacing three-proof paint with ordinary paint, resulting in ineffective moisture protection).

Personnel Protection

Wear insulating gloves and non-slip gloves during operation to avoid direct contact with the low-temperature motor housing (which may cause skin frostbite at ≤-10℃) or chemical substances such as grease and three-proof paint.
Use special tools when disassembling bearings and end covers to avoid component splashing due to brute force operation or hand scratches from sharp edges.

IV. Maintenance Process and Effect Traceability

Taboos for Maintenance Sequence

Follow the sequence of "external inspection first, then internal inspection; electrical system first, then mechanical system; static inspection first, then dynamic inspection": first check the housing, seals, and terminal blocks (static), then measure insulation resistance and current (electrical), and finally check bearings and air gaps (mechanical). Avoid component contamination due to lack of protection after disassembly.
After maintenance, first perform a no-load test (30 minutes, stable temperature ≤60℃, noise ≤75dB), then a full-load test (current ≤110% of rated current). Confirm no abnormalities before putting into use. Prohibit direct operation without testing.

Data Recording and Traceability

Establish a special maintenance file to record key data of each inspection: insulation resistance value, bearing temperature, operating noise, current parameters, grease model and filling volume, and replaced component models (such as bearings and oil seals).
If the motor experiences three consecutive instances of insulation resistance decrease (each decrease ≥0.5MΩ) or excessive temperature (continuous operation >80℃), suspend use and conduct a comprehensive disassembly and inspection. Do not force operation to avoid expanding faults (such as winding burnout and bearing seizure).

Maintenance for Long-Term Parking

Before long-term parking in winter (more than 15 days), complete a comprehensive maintenance: replace with new low-temperature grease, measure and record insulation resistance, seal all wire inlets and vents, park the forklift in a dry and insulated indoor area, and start no-load operation for 10 minutes every month to maintain the internal lubrication and insulation state of the motor.

V. Common Misunderstanding Avoidance

Misunderstanding 1: Repeatedly starting the motor when it is difficult to start at low temperatures —— This easily causes winding overload and heating. Instead, first check the grease condition and power supply voltage, and start after preheating.
Misunderstanding 2: Directly replacing windings when insulation resistance is low —— Prioritize low-temperature drying treatment. Only consider replacement if the resistance remains substandard after drying to avoid excessive maintenance.
Misunderstanding 3: The more grease filled, the better —— Excessive grease leads to high-temperature carbon deposition during motor operation and blocks bearing gaps. Strictly control the filling volume to 1/2-2/3.
Misunderstanding 4: Cleaning ice and snow on the motor housing with hot water —— This easily causes housing deformation and internal condensation accumulation. Instead, use natural melting or low-temperature hot air treatment.

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