5 years ago

MDA Technologies 4/2015

MDA Technologies 4/2015


SUCCESS STORY Company name: R+W Antriebselemente GmbH Headquarters: Klingenberg, Germany Employees: approx. 200 Products: precision couplings, industrial couplings, line shafts, safety couplings 04 The couplings of ST-series with feather key connection, conical clamp connection, elastic coupling and flexible tooth coupling (from top left to bottom right) offset-compensating shaft-to-shaft connection. Nevertheless, R+W decided to use a low-backlash tooth coupling instead of an elastic bolt coupling. This had the advantage of being able to transmit higher torques with a reduced size. In this way, open installation space was gained for the operating area of the safety coupling. Due to the low rotational speed of not even 20 rpm, it was possible to eliminate an elastic damping element. However, there was yet a further challenge: At which level of torque is the coupling to cut out? A machine that has been in use this long, on which already generations have provided proof of their technical capabilities in day-to-day operation simply does not have the required documentation to permit exact calculations. Based on rough calculations and empirical values, a value of 42 000 Nm was settled upon. Then, as soon as such a torque was present in the drive unit, the coupling disconnected the flow of driving force within the span of a few milliseconds. Indeed, already at the initial startup with a filled pan, the coupling released to the surprise of everyone involved. The reason: The startup torque under full load was evidently substantially greater than everyone assumed. The simple and advantageous handling of the ST series revealed itself here. With a face wrench and a few moves of the hand, it was possible to adjust the pre-set disengagement torque. With steps in the 1 kNm range, it was ultimately possible to precisely approach the required target mark. Today, the coupling is set to a disengagement torque of 57 000 Nm and switches only in the event of genuine crash. Once this happens, an employee corrects the fault in the travel path or manually clears the gear of its coating of slag. Then, he just has to re-engage the coupling and already production can resume. Here, an additional advantage of the ST model series from the R+W house becomes clear. No special tools at all are required for the restoration of operation. Unlike as it was with the shearing pin couplings that were standard in the past, no special replacement parts have to be additionally stockpiled. The coupling operates according to the backlash-free ball-detent principle, which has proven itself over the years. The two halves of the ST coupling are connected to each other in a positive-lock arrangement by a defined number of switching elements. In the interior of each switching element, a ball is axially pre-tensioned via disk spring assembly. One half of the ball shows from the element and sits on the second coupling half in a form-fitting detent. The torque is backlash-free and reliably transmitted via this force/form fitting. As soon as the tangential force generated by the applied torque and acting on the balls is great enough that the spring assemblies can no longer pretension the balls, the ball slips completely back into the interior of the switching element within the span of milliseconds. The ball is guided inside the switching element by a bolt that is correspondingly moved axially during the switching operation. To place the coupling back in operation, the two coupling halves just need to be turned into the correct position, and with the force of a soft-faced mallet on the bolt of each element, the ball is then pressed back into its detent recess in order to restore the flow of force. However, R+W had a few more advantageous features for the customer in the described scenario for the steel trolley. For easier turning of the coupling halves after a switching operation, the customer can also insert a lever into radially placed holes that are provided for this purpose. In addition, a re-engagement groove was placed on the hub of the coupling half with the switching elements. This is because, due to the scarce installation space because of the shortened hub on the safety coupling side, re-engagement using the soft-faced mallet is not possible. However, with the aid of the groove, the customer can insert a mounting iron there and push back the ball using the lever force created with it. According to the testimony of the employees in the steel mill, the coupling has already reliably switched multiple times. Since then, there have not been any failures as described at the outset. Accordingly, the coupling has already paid for itself several times over. Photographs: R+W Antriebselemente 58 MDA Technologies 4/2015

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