A shaft to hub lock is critical in the design of a mechanical transmission as an unsuitable choice could cause serious damage to the machine or system and result in economic loss. Shaft-hub coupling designs must take several parameters into account: » Assessing application loads: torque, bending moment, axial force, radial force. Stresses that may occur simultaneously; » Alternating loads, sudden starts and stops, very rapid acceleration; » Fatigue limits of the coupling components; » Suitable material use; » Frequent installation and removal requirements; » Fretting corrosion. As mentioned, coupling breakages could cause high economic damages due to: » Downtime and subsequent production loss; » Damage to other parts of the system; » Material damage to persons or property. Traditional shaft-hub locking systems include: » Feather keys » Key » Spline coupling » Interference coupling: forced We assess the features of traditional systems: Feather Keys Feather key couplings are the most commonly used. Assessing the disadvantages: » High concentration of stress on the shaft and hub due to the high pressure generated on the keyway sides. » Micro-movements caused by the lack of even contact can cause fretting corrosion making it difficult to remove. » Not recommended for alternating loads. Over time, the pressure generated on the keyway sides can widen it and cause the shaft or hub to break. Not recommended in damp environments. » The lack of contact over the shaft-hub surface may lead to oxidation, making it difficult to remove. » Cannot accept axial loads. » Not recommended for transmissions that require zero backlash. » Significant decrease in shaft strength due to the keyway. » Difficult axial and angular positioning. Keys Keyed shaft-hub couplings have the same disadvantages as feather key couplings and also cause significant hub-to-shaft concentricity error. Splined Profile This coupling has the following disadvantages: » Fretting corrosion from the lack of contact making it difficult to remove. » Significant decrease in shaft strength. » Increased cost as it is difficult to make. » Play between shaft and hub. » Difficult angular and axial positioning. » Not recommended in damp or dusty environments. » Lack of contact may impair removal. D Eccentricity Mt P P P P Key Hub Advantages compared to conventional systems ® SIT-LOCK Keyless Locking Elements 2 www.jbj.co.uk/couplings.html #DriveLineHarmony T d T Shaft Mt Shaft on feather key action Hub on feather key action Hub rotary shaft Feather Keys Keys Splined Profile
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