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critical requirement in the design of many machines is
the need to protect against damage and downtime that is often caused by machine overloads. Torque limiters address this challenge by behaving as 1:1 transmissions as long as torque is less than a specified value. When the torque surpasses the limit, torque limiters operate as a clutch to disconnect the drive from the driven system in a short period of time. By disconnecting the motor from the driven load, the torque limiter removes much of the inertial energy from the drive train, typically in a time period between a few milliseconds and tens of milliseconds. Typical applications for torque limiters include packaging machinery, conveyors, assembly lines, machine tools, woodworking machines, textile machinery, industrial robots, sheet metal processing equipment, printing and converting machines, and servo and dc motor drives. Simple torque limiter devices The simplest type of mechanical torque limiter is a shear pin that links two rotating bodies and is designed to break at a certain torque level to separate the drive system from the load. However, shear pins are rarely used when protecting missioncritical machinery because it can be difficult to accurately control the level of torque at which the shear pin will break. Thus, the potential exists for either nuisance failures if the shear pin breaks at too low of a torque or damage to the machine if the shear pin breaks at too high of a torque. Friction torque limiters operate in a similar manner to automotive brakes with a drive
component sandwiched between friction linings connected to a driven component that grips the drive component in normal operation. An overload causes the drive component to slip relative to the friction innings, protecting the machine from damage. Removal of the overload causes the drive to resume transmission of torque. The spring pressure of a friction torque limiter is adjusted to accurately change the level of torque that will cause the device to slip. Friction torque limiters offer simple and relatively low-cost overload protection so they are generally used in sprocket drives on conveyors and other similar applications. A
>> All of Nexen’s torque limiters feature a ball/detent interface. Mechanical torque limiters (MTLs) are available in ten model sizes with three to six
engagement spring selections up to 24,000 in.-lb of trip torque. MTLs are available in three interface designs—single-position, which automatically re-engages after a trip at a single position; multi-position, which automatically re-engages at multiple points; and the full disengagement MTL free wheels when an overload occurs. Re-engagement is not automatic; the spring must be manually moved into position after an overload occurs.
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