Having recently launched its new RDBK releasable backstop, Stieber Clutch has demonstrated its unique performance by developing an impressive test rig in partnership with Bauer Gear Motor.
This latest generation of Stieber backstop features a compact design with increased torque capacity compared to conventional designs. The RDBK allows for a full mechanical release, plus, In the event of a blockage, belt jam or overload, a controlled release when under load. Unlike many other designs that offer only limited reverse rotation after being engaged it is able to rotate backwards under tension, for maintenance and clearing work.
In most large conveying applications, backstops are installed onto the gearbox to prevent the conveyor from rolling backwards in the event of a breakdown. To satisfy customer demands many backstops now include load sharing / torque limiting and releasable functions which help to reduce downtime once the backstop has been engaged.
The RDBK is a centrifugal lift-off sprag type backstop with an internal limiter which is designed for use on the high speed or intermediate shaft of the driving unit in multi-drive systems, such as on large inclined belt conveyors, where two or more backstops share the reverse load. With a maximum torque capacity of 170,000Nm the unique, compact design gives it up to 3.5 times more torque capacity than conventional designs of a similar size; with up to 15 times more energy dissipation.
In order to demonstrate the performance of this new backstop, Stieber required a compact, efficient and reliable motor/gearbox combination onto which the RDBK backstop could be mounted. Fortunately Bauer Gear Motor, a sister company of Stieber under the Altra Industrial Motion umbrella, was able to supply a solution; the Bauer BK series of bevel geared motor, which is designed to operate using an onboard variable speed drive (VSD) and can be equipped with motors up to 75kW with the combination producing up to 18,500Nm of available torque.
Frank Villwock, the Design Engineer who built the demonstration platform comments: “Because the RDBK provides such a high capacity for controlled release, we needed to use a torque provider that could apply the right torque level from a relatively compact display plinth, but more importantly, be consistent at mimicking the reduced load as the clutch released the torque.
“The Bauer unit applies 5,000Nm of torque and then reduces this in stages as the RDBK allows for limited rotation under load. The Gearmotor had to be inverter driven, but also well protected as it as applying a large amount of torque and allowing very little rotation. Both products had to operate very precisely and deal with heat dissipation and load reliably, which they did extremely well.
“In fact you can watch the video from our virtual exhibition centre here www.altraex.com select the ‘Heavy Duty & Overrunning Clutches & Brakes’ segment, then chose ‘Stieber’, then ‘RDBK’, it is available to watch in English and German and is also on our YouTube Channel.”
The completed test rig includes a VSD and torque measurement indication to allow the spectator to see the applied torque increase beyond the setting for the RDBK backstop to engage. As the demonstration continues, the backstop then starts to slip in a controlled manner, preventing the virtual belt from running back due to the weight of the load on its top side, while also dissipating any additional belt tension until the torque figure drops below the pre-set value.
In the event of the RDBK backstop operating, it also incorporates a reverse rotational release capability with a simple hand operated hydraulic or mechanical disengagement feature. The release function allows the belt to be released through an internal hydraulic system, after the belt tension has been released under control. The release is performed using a simple hand pump to actuate the internal hydraulic cylinder; progressively releasing the backstop (a mechanical alternative is also available). When the oil pressure is released, the backstop is automatically re-set to the original slipping torque.
The operation can be controlled and halted at any time, helping to boost productivity. Where multiple backstops are employed, these can be linked and operated simultaneously from a centralised control location.
Unlike other releasable backstops which feature only limited reverse rotational abilities, the RDBK is capable of performing as many reverse rotations as may be required to completely unload the conveyor prior to maintenance work being carried out; within the limits of energy dissipation. This feature can significantly reduce downtime and ensure that loss of productivity is kept to a minimum. Being able to demonstrate the functionality using equipment from within the Altra Group serves to underline both the breadth and the quality of the Altra worldwide power transmission product portfolio and the skill of its engineers.
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