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Fitting a torque limiter: why bother?

Fitting a torque limiter: why bother?

Whether you're designing a new machine or you're responsible for the operation and maintenance of a plant or piece of equipment, keeping costs down is always at the forefront of your mind. To be competitive you must always try to save money or perhaps more specifically you must aim to spend your money in the wisest way possible.

Spending money on things that are designed to protect us in the unlikely event of an accident or failure can sometimes be seen as an unnecessary expense or one that can be minimised, but how many of us would now be happy to buy a new car without seat belts or airbags, or ride a motorbike without a crash helmet? For those that would this article is not for you and I wish you luck.

Insuring ourselves against loss or damage is something we're all familiar with. Most of us will pay for car or home insurance and whilst we may begrudge the initial outlay, when something does go wrong we're suddenly very glad that we made the investment.

Fitting a torque limiting device into a piece of equipment is no different. Yes you can run a machine without one - many people do - but if, or should I say when, something goes wrong there is no seatbelt or crash helmet to save the day, and whether or not damage (or extended downtime) is incurred is purely down to luck. Is riding your luck really the best way to operate?

We have heard machine designers say that their customer "can't afford to fit a torque limiter, they haven't got the budget." We ask if they can really afford not to fit one and do they have the budget to repair or replace the equipment when it gets destroyed? Accidents do happen, machines do go wrong and people sometimes do press the wrong buttons. In times like these torque limiters can save you a small fortune.

A torque limiter connected to a sprocket or drive pulley, or fitted between two shafts will continue to transmit torque up until its pre-set limit is reached at which point it will slip or disengage the drive. Once the load torque has dropped below the setting of the limiter, the drive will be ready to operate again without having incurred any damage.

Friction type limiters can be used where load holding is required and backlash free ball indent type units can offer protection to high precision drive systems or systems where total disconnection is required in the event of an overload.

By limiting the torques to a maximum permitted value, machines and systems with torque limiting clutches can be optimally dimensioned, and constructional safety factors can be reduced. In problem-free operation, high-quality torque limiting clutches transmit the transmission power from a motor backlash-free onto an output-side element, for example onto a sprocket or a toothed belt pulley, or onto a second shaft.

It is true that there are options for electronic monitoring of the machine control, but this cannot replace a torque limiting clutch. Modern machines work at consistently-increasing production speeds. At the same time, increasingly high precision is being demanded. However, this can only be achieved via highly rigid machine constructions. High speeds and high rigidity lead to hard collisions when machines malfunction. If, in case of overload, there is a sudden increase in torque, only mechanical torque limiting clutches which disengage immediately can prevent expensive subsequent damages.

Not all clutches on the market fulfil the require-ments for quality and reliability. It is therefore important to consider the optimum characteristics with regard to backlash-free function, service lifetime, torque progre-ssions in case of overload, installation, operating and adjustment convenience. With trip torque settings ranging from 0.1Nm to hundreds of thousands of Newton metres, and a wide variety of standard and application specific product designs, there will be a torque limiter to suit your need - all you have to decide is can you really afford not to fit one?

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