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WORLD OF INDUSTRIES 6/2020

WORLD OF INDUSTRIES 6/2020

Protection-Highway to

Protection-Highway to machine efficiency Safety couplings prevent possible machine failures caused by overload. This will only work well, if users will have the chance to adopt them perfectly to their individual application. Torque limiters from KBK Antriebstechnik do allow a very precise adjustment of the disengagement torque and offer a unique range of different models. Author: Sven Karpstein, managing director, KBK Antriebstechnik, Klingenberg/Main, Germany MOTION AND DRIVES Having a huge choice of different types enables KBK to find the perfect matching overload coupling for many applications. The fundament for this flexibility is the modular system by KBK: it gives the opportunity of creating individual solutions based on standard components. Acting this way KBK is able to produce customized solutions easily and at competitive prices. “If we should not be able to find an ideal solution based on our modular system we also do develop and design completely new solutions”, says KBK managing director Sven Karpstein. The familyowned company based in the Bavarian village Klingenberg is very service oriented and offers custom solutions as well as an emergency service: “We are able to produce and ship almost all our servoinsert couplings or metal bellows couplings custom bored within 2 hours”, says Sven Karpstein. Safety couplings fit perfectly in test benches Safety couplings from KBK are used in applications where a high productivity needs to be ensured or whenever humans or expensive components have to be protected – for example in motor test benches, automation equipment, automatic drawer systems, machine tools or medical equipment. In such applications the torque limiters are used for disconnecting the drive and the driven parts mechanically as soon as the set torque is succeeded. In this way, overload cases and resulting damages can be avoided or at least minimized. The more precise the overload torque can be specified for an application, the better will the protection ensured by the coupling be. Furthermore, exact limitation of the torque will allow a more efficient usage of the drive, because it will disconnect very close to the point where damages can happen. 01 Overload clutches significantly reduce the risk of overload damage and associated machine breakdowns 20 WORLD OF INDUSTRIES 2020

Overload torque can be preset precisely The drive-component-specialists of KBK are using cup springs with degressive characteristics and steel-balls as blocking elements. This design allows an extremely precise adjustment of the overload torque and results in the torque transmission being cut-off within milliseconds after an overload occured. Degressive cup springs also cause a very low remaining torque after the couplings disengaged what dramatically increases the lifetime of the coupling. Torque limiters from KBK offer one more advantage to machine builders: due to the fact that they are adjusted so accurately, they are extremely reliable and other safety related mechanism can be reduced or eliminated, which helps to safe material and costs! Ball-detent principle used for backlash-free torque transmission KBK safety couplings are designed using the ball-detend system for having a backlash-free and repeatable transmission of torque. The couplings do have a flange with half-ball-shaved pits. The balls are positioned in those pits and are pushed out of them in case of an overload. Drive and driven side are disconnected and the torque transmission is interrupted. The overload torque is adjusted individually for each application. “We have to specify together with the customer what torque range will be needed. Depending on the torque range a certain number of cup springs are used”, says managing director Sven Karpstein. “As a next step we do lasermark the torque range on the coupling between minimum and maximum and test it. Finally, we exactly set the couplings to the desired disengagement torque.” This adjustment is realized by the pretension of the cup springs, which can be done by tightening a threaded adjusting ring. “We do test the torque several times and finally lasermark the set value on the coupling to enable our customers to re-adjust the coupling themselves, if necessary”, so Karpstein. Four product lines can be chosen to have the perfect solution KBK produces four different types of torque limiters in various sizes – two series for indirect drives and two series for direct drives. As one of very few producers, the company also manufactures miniature-safety couplings – the lowest possible torque can be set at 0.1Nm. Remarkable are also the torque limiters in split hub design, which are exclusively available at KBK. The execution with split hubs enables the user to perfectly align the shafts to each other before assembling the torque limiters and so to avoid failures due to misalignment. Each of the four series is available in four different function modes, where each of them has its specific characteristics. The synchronous or the multi-position mode are re-engaging automatically once the failure in the drive has been eliminated, so machine breakdown times are reduced to a minimum. On the other hand, those versions are wearing out faster compared to freewheeling versions. This is due to the fact that the balls will try to reengage one time per revolution for the synchronous version and 6 or 8 times for the multi-position types. If the failure is not removed at this point the balls will jump over it again and again and will create friction. “This friction is at a very low level but if the coupling is running at high speeds like 5000 rpm for a longer time it can happen that it will fail relatively fast”, so Karpstein. “That is why we always recommend to use a proximity switch in combination with our torque limiters, which cuts off the drive as soon as the coupling disengages.” Drive chain will be stressed less The wear on the free-wheeling safety couplings is remarkably lower, because drive and driven side are permanently disconnected in case of an overload. The re-engagement cannot be done before the drive stands still and has to be done manually – that reduces strains. “This coupling is perfectly used in applications like test benches, where long-term tests are running and where workers are not present permanently. If a crash happens here the couplings can run for a longer time at high speeds and will not be damaged.” Using the blocked coupling types, disengagement will not even happen – in case of an overload the coupling will only turn a few degrees and activate a switch, which cuts off the drive. Magnetic couplings do work completely non-wearing The new types of permant or hysteresis magnetic coupling by KBK are suited perfectly for torque limitation in bottle capping machines, pumps and also applications for testing or medical equipment. Due to their specific design they are non-wearing and cover a torque range from 0,1 to 60Nm. Permanent magnetic couplings cut off the torque transmission in a jerking movement, the hysteresis couplings show a sliding behavior – similar to a friction clutch. Cup springs and balls are superior to friction discs or electronics KBK torque limiters show numerous advantages compared to other systems like friction clutches or electronic torque observing systems. Friction type clutches do not give the chance to set the torque as precisely as it is possible with ball-detend KBK couplings. The reason is the design of the friction clutches: the function principle founds on friction discs with friction factors which can vary a lot. Therefore, it will never be possible to set the torque exactly at a certain point. KBK safety couplings do not have this problem because they are not in the need for friction discs – they are just using cup springs and steel balls as blocking devices. Also, safety systems using electronic observation and torque control do have disadvantages compared to the KBK couplings, which are simply working mechanically. They need three times more time until the drive is no longer transmitting torque. So, the drive components are overstressed for a way longer time compared to using KBK couplings. Photos: Lead AdobeStock/Microgen; others KBK 02 Activated or locked: The overload clutches are manufactured in four different switching types and numerous sizes www.kbk-antriebstechnik.de WORLD OF INDUSTRIES 2020 21

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