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Mobile paper shredders lose weight with planetary drives

12 May 2013

When Whitham Mills Engineering sought a drive for its latest mobile paper shredder, one of its key design criteria was the need to keep the drive as compact as possible in order to keep the weight of the product down and ultimately increase the shredding vehicle’s payload.

Whitham Mills Engineering is a UK based manufacturer of equipment for the recycling industry. Its products - paper shredding machines for the industrial disposal of confidential documents - includes vehicle mounted mobile shredders, which are able to shred paper on-site.

As with any mobile waste collection system, payload is key to profitability, so the hunt was on to find a more compact drive system for Whitham’s shredders.

The shredders require three separate gearboxes: two to drive the individual shredder shafts, and another to drive the auger screw, which compacts the paper and transfers it to a storage compartment at the back of the truck.

The original shredder shaft drives used two heavy, shaft-mounted, right angled bevel helical gearboxes, each driven by an electric motor. The units needed to be quite large to transfer the required torque output to the shredder and keep the blades turning while processing up to four tonnes of paper per hour. Whitham Mills Engineering’s Malcolm Moon takes up the story:

“We were looking for something that would allow us to reduce the weight of the shredding machinery and therefore increase the profitability of the shredding vehicle. The original gearboxes were not particularly efficient which meant that we also needed larger motors to drive them than was ideal. The decision was made to approach Brevini, which already supplies gearboxes for some of our static products, to see if it could engineer a lightweight solution.”

In the end, Brevini was able to supply Whitham Mills Engineering with a complete package, providing high efficiency planetary gearboxes in combination with hydraulic motors from sister company, Brevini Fluid Power. Each stage of Brevini’s gearbox uses three planetary gears which are located inside a toothed outer ring, ensuring that the load is spread among many contact points.

This not only leads to less internal pressure – contributing to the 98 percent efficiency per stage – but it also means that smaller units can transfer high torque without the risk of slipping. The overall result is that smaller gearboxes can be driven by smaller motors, which reduces the weight of an application and its overall footprint.

To replace the shredder shaft gearboxes Brevini specified two stage planetary gearboxes with a reduction ratio of 14.28:1 and a female splined output shaft to connect with the shredders. Each gearbox is connected to an individual shredder shaft - the first transmitting 5,306Nm at 27rpm and the second transmitting 4,621Nm at 28.5rpm.

A two stage planetary gearbox was also supplied to drive the auger screw with a 12.5:1 reduction ratio. Each gearbox is driven by a compact Brevini Fluid Power Samhydraulik hydraulic motor.

As Brevini’s Gonzalo Salvatierra recalls, the trucks were already to be equipped with a hydraulic power pack for the loading system, so all his team had to do was change the gearbox input adaptor to accept the Brevini Samhydraulik motors. This produced significant weight savings compared with the alternative approach using electric motors. Malcolm Moon again:

“Brevini’s solution met all of our requirements. The compact design and weight saving using planetary gearboxes with hydraulic motors means that we are able to offer customers a very reliable product, which allows them to carry more shredded paper and therefore achieve more profit.”




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