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Shaft Coupling Considerations

Backlash is an unwanted motion from connected parts that are not precisely aligned or fitted. Though couplings allow small amounts of backlash, it should be limited within the system‘s threshold. Excessive backlash causes a high level of misalignment, wear, mechanical stress, and even breakage. A backlash-free coupling is critical for motion control systems. In power transmission systems, backlash equates to power loss.

Backlash can be minimized by replacing worn-out, loosely-fitted, and defective components. Check the coupling inserts, gear teeth, splines, rubber bushing, springs, bolts, and other parts for wear or loose-fitting. The hub and the key must have no unnecessary clearances with the shaft. Backlash can also be controlled by keeping the torque at a consistent speed and direction. Generally, flexible couplings have more backlash than rigid couplings.

All shaft couplings have windup. Shaft coupling windup or torsional deflection occurs when the torque of one shaft is greater than that of the other, causing difference in angular displacement. This causes loss of motion, which leads to inaccurate positioning in motion control systems.

Shaft Coupling Selection and Maintenance
The factors to consider in selecting a shaft coupling are the torque transmission rating (horsepower), maximum speed (rpm), misalignments, stiffness, inertia, capability to absorb shock and dampen vibration, shaft mounting, environmental conditions, applications, cost, and more. These factors must be studied before acquiring a shaft coupling in order to prolong its service life, preserve its efficiency, and prevent failure.

Once the shaft coupling has been used, measures to minimize or eliminate backlash and windup must be taken. Excessive misalignments must be corrected. Lastly, shaft couplings must be lubricated regularly, and their internals must be free from contamination and dirt.
Higher Power Applications

Everything from kitchen food mixers to 600 MW steam turbines need flexible shafting. As the torque goes up, so

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