Deltran Clutches & Brakes Catalog 2009 - Thomson - #9

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www.thomsonlinear.com 7 THE GENUINE WRAP SPRING Clutches & Brakes The Genuine Wrap Spring clutch/brakes provide hundreds of simple motion processes that can be controlled through the three basic wrap spring clutch functions: overrunning, start-stop, and single revolution. Important Facts • The torque capacity of a spring clutch or brake is a direct function of the diameter of the hub and the tensile strength of the spring. • A spring clutch or brake will not slip. It will attempt to supply the torque demanded, up to the mechanical limitations of the spring. • When the spring is allowed to wrap down (or grip the hubs) the output hub will accelerate to the input RPM in .003 seconds, the output in .0015 seconds. • The dynamic torque of acceleration or deceleration is proportional to the RPM multiplied by the load inertia and divided by the acceleration time. This fact indicates that spring clutches and brakes are inertia sensitive—the more inertia, the higher the dynamic torque. • The torque demand of the spring clutch is equal to the system frictional torque of the load plus the dynamic torque of acceleration. • When coming to the stop position of the cycle, there must be enough energy in the rotating mass of the load to allow the spring to release its grip on the input hub. This means that if there is a large frictional load, or a torque demand such as coming up to the top of a cam, there must be sufficient energy in the rotating mass to open the spring. Failure to do so will result in possible input hub wear and/or noise. Egg Packaging When cartons of eggs are detected on the conveyor, the carton is pushed off onto the pallet. A CB-6 clutch/ brake is fitted to a crank assembly. The crank profile is designed to accelerate slowly to gently move the eggs and accelerate rapidly back to be in position for the next carton. Thus the inertia at start and stop is only the inertia of the crank. Start-Stop (Accurate Positioning) The Genuine Wrap Spring Clutches & Brakes Applications Single Revolution Riveter Through a wrap spring clutch, the motor drives a large flywheel and a large eccentric mass connected to the piston-like riveting ram. The wrap spring clutch-brake always stops at just past top dead center position ready for the next cycle.