www.jbj.co.uk/couplings.html #DriveLineHarmony ® SIT-LOCK locking devices for applications with high bending moments Bending moment The bending moment in a shaft-hub coupling is a crucial factor to consider during the design phase. The diagram shows an application for clamping a conveyor belt pulley. A typical application that requires simultaneous torque transmission and bending moment. The bending moment changes the pressure the locking device generates on the shaft and hub contact surfaces. An excessive bending moment could cause an additional load on the locking device clamping screws causing them to break if the load is excessive. The pressure generated by the bending moment causes an increase and decrease in the pressure generated by the SIT-LOCK® locking device and may significantly affect the transmissible torque. The sum of the static pressure generated by the locking device and the pressure generated by the bending moment, generates a minimum and maximum value. This occurs on both the shaft and hub contact surfaces. Checking these pressures is crucial as they affect the choice of shaft diameter and correct hub sizing. For proper use, the minimum pressure generated on the surfaces must be at least 30 N/mm² to avoid oxidation. Lower values may cause difficulty when removing the coupling. Transmissible torque moment ® A shaft-hub coupling using SIT-LOCK frictional locking devices can simultaneously allow a torque Mt, an axial force Fax and a radial force (a force that results in a bending moment Mb). To determine the final resultant force, these values must be added together in a vector-based way. ® SIT-LOCK screw tightening torque The screw tightening torque values are calculated taking into account a friction coefficient between the threads equal to 0.14 (oiled screws and threads). If necessary, the tightening torque Ms in the table can be reduced. As a result, the M, F , P and P values will vary proportionally. For further information, t ax w n please contact our Technical Department. Tolerances and surface finish The values shown in the tables are valid when the correct tolerances and surface finishes are used. Tolerances greater than those indicated can have a significant effect on the transmittable torque. These are the recommended values: ® SIT-LOCK 1 shaft h9 - hub H9 ® ® SIT-LOCK 7 and SIT-LOCK 4 COMPACT shaft h8 - hub H8 Surface finish of shaft and hub Ra. Surface finish of shaft and hub. 70
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