Couplings in roll forming mills

Roll forming mills further process flat steel sheets into profiled sheets. For this purpose, the sheets are guided over rollers driven by geared motors. Robust couplings from R+W provide the connection between the drive and the roller.

Roll forming creates profiles from strips or sheets. Many industries make use of these profiled sheets, for example vehicle and furniture construction, the construction industry and general mechanical engineering. Typical products and applications include structural rails, guard rails, steel shelving or drawer runners.

Compared with other forming processes, roll forming is characterized by particularly high flexibility and economy. Due to production speeds of up to 200 meters per minute, this process is particularly suitable for large-scale production. The sheet thickness remains almost constant during processing, which distinguishes the process from classic rolling. However, both machining methods have the basic arrangement of the tools in common. Rotating pairs of rollers successively reshape the sheet in several work steps. Similar to a conventional rolling mill, the flat sheet is drawn through rotating tools and shaped into the desired profile form with the aid of profile rolling rolls – in a correspondingly large number of bending processes.

To ensure consistent production quality and increasingly important process stability, high operational reliability and repeatability of the drive components used are essential. The Klingenberg-based coupling manufacturer R+W has many years of experience with applications in the steel industry as well as a wide range of coupling series that meet the high requirements there.

Rolling stands specify installation space

A special challenge came from a large profile rolling mill in Asia: Here, a roll forming line for two bending processes was projected. Precision couplings were required at each roller station to connect the rollers on the assembly stands to the series-connected gearmotors. The possible dimensions of the couplings were based on the conditions in the rolling stand: they could not be longer than 145 millimeters with an outside diameter of 200 millimeters. At the same time, however, for all their compactness, they should transmit a rated torque of 2000 newton meters and have sufficient safety reserves. Thus, the couplings had to be designed for a maximum acceleration torque of 3100 newton meters and peak torques of up to 5500 newton meters.

The engineers at R+W found a solution to these requirements. With a special design based on the proven BK8/1500 metal bellows coupling, it has been possible to provide a coupling solution that combines the required characteristics. Thanks to a stainless steel metal bellows specially designed for this purpose, the coupling was able to practically triple its power density. With a length of 144 millimeters and an outer diameter of 190 millimeters, the coupling could be perfectly integrated into the application. Metal bellows couplings such as the BK8 series are backlash-free, torsionally stiff couplings designed for direct connection to gearboxes. The compact series was originally developed for connection to robot gearboxes. It enables the torsionally stiff but misalignment-compensating connection between input and output. Their metal bellows compensate for lateral, axial and angular shaft misalignment with low restoring forces. For connection to the gearbox, they have a suitable intermediate flange. The series operates wear-free and with a long service life and ensures reliable torque transmission even at high speeds.

Many types of couplings in use

Depending on the requirements, many different types of couplings are used in steel processing. Under other conditions, for example, a special version of the ST1 industrial safety coupling was the right choice for the experts at R+W. Compact and torsionally stiff torque limiting clutches were required that could safely limit the torque at 1500 Newton meters in the event of an overload and also compensate for lateral, axial and angular shaft misalignments. The couplings used in a roll stand should be designed with an assembly-friendly clamping hub for connection to the gear shaft. In addition, the torque limiting clutches should offer a certain adjustment range so that the preset torque can be adapted to the conditions if necessary.

The modularly designed ST1 model series in Series 5 provided the best prerequisites for these requirements. Although these are designed for indirect drives as standard, they can easily be combined with other misalignment-compensating coupling components. Thanks to the intelligent modular system, a torsionally stiff metal bellows coupling with clamping hub could therefore be flange-mounted in the specific application. This enabled direct connection to the gearboxes and the required shaft misalignment compensation could be ensured due to the metal bellows. The Series 5 is available, among other things, with an adjustment range of 1200-4000 newton meters, which made the required disengagement torque/shutdown torque of 1500 newton meters possible without any problems. With this adaptation, an ideal solution was found here as well.

ST couplings are in high demand in industrial applications anyway, because their safety function offers users decisive advantages: In the event of a collision, the robust torque limiters protect the drive train from expensive damage and also minimize any downtimes. Like all safety couplings from R+W, the models in the ST series operate as spring-loaded form-fit couplings. The respective transmittable torques are largely determined by the number and pitch circle diameter of the shift segments. In the event of an overload, the balls, which are preloaded within the switching segments, move axially out of the spherical caps and cause a permanent load separation of the input and output sides within milliseconds. Re-engagement is achieved simply by applying axial pressure to the shift plungers. If required, the preset disengagement torque can be adjusted subsequently and in just a few steps.

R+W safety couplings of the ST model series are available in various designs – depending on the requirements. Depending on the model and series, the couplings can be obtained, for example, with keyway, flange or cone clamp connection as torsionally stiff or vibration-damping shaft-shaft connection for direct drives as well as for indirect drives as standard up to 250,000 Newton meters. Special designs and designs for even higher torque ranges are also available on request.

The two examples from steel processing show how many different influencing factors must be taken into account when selecting couplings or developing them. In order to provide users with the right coupling solution in terms of function, process reliability and cost efficiency, industry and application know-how play a decisive role alongside flexibility and technological expertise in the field of couplings. R+W Antriebselemente GmbH is in close dialog with designers and engineers from a wide range of sectors and industries. As a result, the wide product range of the manufacturer and developer of precision and industrial couplings therefore includes many other coupling models, such as flexible gear couplings, torsionally stiff multi-plate couplings or vibration-damping elastomer couplings, which are suitable for a wide variety of applications and uses, depending on requirements.