Comprehensive guide to selecting the correct gear reducer for your application. Learn how to calculate required torque, verify thermal capacity, and match the right gearbox to your operating conditions.
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Torque is the rotational force that a gear reducer transmits from input to output. The gear reducer increases torque by reducing speed — the output torque equals input torque multiplied by the gear ratio (adjusted for efficiency).
For example, a 10:1 gear ratio with 95% efficiency multiplies input torque by 9.5. A 3kW motor at 1500 RPM producing 19 Nm torque with a 20:1 reducer outputs approximately 361 Nm at 75 RPM.
Understanding torque is fundamental to correct gear reducer selection. Under-sizing leads to premature failure. Over-sizing wastes capital and increases energy costs.
Step 1: Identify the load type — uniform, moderate shock, or heavy shock. Conveyor systems typically have moderate shock factors (1.5-2.0). Crushers and mixers may need 2.0-3.0.
Step 2: Calculate the actual working torque at the driven equipment. For conveyors: Torque = (Belt Tension × Pulley Radius). For mixers: Torque = Power / Angular Velocity.
Step 3: Apply the service factor based on duty cycle and load type. FEM duty class for cranes, ISO duty class for general machinery. Standard service factors: M3=1.25, M4=1.5, M5=1.75, M6=2.0, M7=2.5.
Step 4: Select a gear reducer with rated output torque exceeding the calculated torque × service factor. Always include a 10-15% margin above the calculated minimum.
Uniform load (1.0-1.25): Light duty, constant speed, no shock. Laboratory equipment, light conveyors.
Moderate shock (1.5-2.0): Standard industrial duty. Belt conveyors, mixers, packaging machines. Most common application.
Heavy shock (2.0-3.0+): Severe duty with frequent starts/stops and impact loads. Crushers, excavators, heavy conveyors with long start times.
The service factor accounts for operational conditions beyond the nominal load. Never skip this step — it is the primary reason gear reducers fail prematurely.
Overland Conveyor (2000 t/h, 500m): Input power 150kW at 1500 RPM. Required output torque approximately 955 Nm at 75 RPM. With 2.0 service factor for moderate shock: select helical gear reducer rated at 2000 Nm minimum output torque, ratio 20:1.
Underground Mining Conveyor (800 t/h, -30degC): Input power 45kW. Required output torque 2850 Nm. Cold-rated IP66 required. Select helical gear reducer with IP66 sealing, cold-rated lubricants, ATEX certification if in methane environment.
EOT Crane Hoist (5 ton, FEM M5): Input power 11kW at 1500 RPM. Required hoist torque 350 Nm at 15 RPM. With 1.75 service factor: select helical hoist gearbox rated at 700 Nm, integrated hold-back brake, FEM M5 duty class.
Cement Kiln Drive (500kW continuous): Input power 500kW at 1500 RPM. Required output torque 3183 Nm at 5 RPM. Continuous duty, high temperature. Select helical gear reducer with forced oil circulation, external cooler, FEM M7 duty class.
Calculating correct torque is only step one. You must also verify that the gear reducer can dissipate the generated heat during continuous operation.
Thermal capacity depends on: rated power, efficiency, cooling method (natural, forced air, oil circulation), ambient temperature, and duty cycle. A gear reducer sized for torque may still fail thermally.
BOYU BO provides free thermal analysis with every quotation. Our engineering team calculates heat generation, heat dissipation, and operating temperature for your specific application.