Gear Coupling Selection Guide — Sizing & Service Factor
Selecting a gear coupling involves calculating design torque (rated torque × service factor), identifying misalignment type and magnitude, choosing the coupling type, sizing the bore to the shaft, and accounting for environment. SMI provides free coupling sizing — share your power, RPM, shaft diameter, and application for a recommendation.
Key Facts
- Design torque = (9550 × kW ÷ RPM) × service factor.
- Service factor ≈1.0 uniform, 1.5 conveyors/mixers, 2.0–2.5 crushers/mills.
- Match bore to shaft diameter; confirm RPM limit and misalignment type.
- Free sizing from SMI engineers — share kW, RPM and shaft sizes.
Frequently Asked Questions
How do I select the right gear coupling size?
Calculate design torque = (9550 × kW ÷ RPM) × service factor, then choose a coupling whose rated torque exceeds it. Confirm the bore fits your shaft and the coupling tolerates your misalignment type.
What is a service factor in gear coupling selection?
A service factor multiplies rated torque to account for application severity — e.g. ~1.0 for uniform loads, 1.5–2.0+ for shock or reversing duty like crushers and rolling mills — ensuring the coupling isn't undersized.
What information do I need to size a gear coupling?
Provide motor power (kW or HP), speed (RPM), driver and driven shaft diameters, the application/duty type and any known misalignment — SMI then calculates design torque and recommends a size free of charge.
How do I measure shaft size for the coupling bore?
Measure the shaft outside diameter with a vernier caliper and note the keyway width and depth; SMI machines the coupling bore to an H7 fit (or your specified tolerance) on those dimensions.
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