Applications needing extremely high torque ratings, such as mining equipment, however, still rely on shear-pin torque limiters.
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Plus the torque level at which ball-detent types actuate or trip tends to be more repeatable than that of shear pins. These shear-pin torque limiters have been largely replaced by ball-detent types because the latter are easier and quicker to reset, which boosts machine uptime. Ball-detent torque limiter image via Carlson-Dimond & Wright Ī simpler, manually resettable design shears a replaceable pin when overloaded. Pneumatic or hydraulically actuated units often incorporate sensors that detect an overload condition and cut pressure to decouple the load. Some units reset in multiple clock positions, while those used in timed mechanisms reset to the same clock position each time. Depending on the configuration, an overload trip may need that an operator manually reset the device, while other designs automatically reset when the overload condition clears.
Exceeding a set value overcomes spring force, which in turn dislodges the balls and uncouples the load. A typical design uses springs to push bearing balls into pockets (detents) on a drive flange that transmits torque.
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Ball-detent torque limitersīall-detent torque limiters may be automatic or manually resettable, while hybrid models combine both automatic and manual reset functions in a single unit.ĭetent-style torque limiters transmit nominal torque then fully disengage when they see excessive torque levels, and freewheel until reset. Some electromagnetic types also work without friction material but need external power to generate magnetic flux. In contrast, torque limiters employing permanent magnets that couple loads through magnetic flux have no friction material to wear or produce debris. Available sealed units contain the wear debris. Debris generated by friction material in open, dry designs make them unsuitable for certain environments such as in clean rooms.
Friction-style torque limiters, dry or wet, wear over time and may need maintenance or eventual replacement. Friction-plate torque limiter image via Bondioli & Pavesi Though torque limiters differ from clutches in that they can’t or shouldn’t continuously throttle mechanical transmission, some temporarily slipping limiters (especially those based on friction plates) are referred to as slip or overload clutches. Generally, higher-capacity units that dissipate more energy (or those designed to continuously slip) use oil cooling to maintain friction material at safe operating temperatures. Pneumatic and hydraulic actuated torque limiters may also use friction material to transmit torque but rely on pistons or diaphragms moved by air or fluid pressure to force friction surfaces together and adjust torque limits.įriction material may be dry or in an oil bath. Exceeding a set torque level causes the surfaces to slip relative to one another, limiting power transmission. A spring-actuated frictional torque limiter applies spring force to opposing friction surfaces on input and output hubs. Friction torque limitersįriction torque limiters slip in response to an overload event and fully engage other times. They come in three basic types: friction, ball detent, and shear pin. Torque limiters span a wide range of rated torque - from much less than 1 N-m to over 10,000 kN-m. Torque limiters are indispensable on bottle-capping machines. A machine that installs bottle caps, for example, must apply sufficient torque to tighten a cap but not break the bottle. They also serve in equipment needing specific torque levels. Torque limiters actuate on the order of milliseconds to prevent overload, shock, and torque spikes that could otherwise damage components or shorten operating life. Industrial robots, conveyors, wind turbines, machine tools, packaging machines and pumps are just some of the places you’ll find torque limiters.