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Paper shredders benefit from planetary drives

Paper shredders benefit from planetary drives High torque capability of planetary drives enables smaller drives to be used in mobile paper shredders.

When Whitham Mills Engineering was looking for a drive solution for its latest mobile paper shredder it turned to Brevini Power Transmission for assistance. The company required a compact solution which would keep the weight of the product down thus increasing the shredding vehicle's payload. Fortunately Brevini was able to supply a complete solution using its high efficiency planetary gearboxes combined with hydraulic motors from its sister company, Brevini Fluid Power.

Whitham Mills Engineering is a UK manufacturer of equipment for the recycling industry whose products include paper shredding machines for the industrial disposal of confidential documents. The range includes mobile shredders which are fixed to a commercial vehicle and allow end users to shred paper on-site; giving their customers peace of mind that all documents have been properly disposed of. As with any mobile waste collection solution, payload is a key to profitability, so Whitham Mills recently made the decision to find a new drive solution with a more compact design.

The shredders require three separate gearboxes: two to drive the individual shredder shafts, and a further one which drives the auger screw to compact the paper and transfer it to the storage compartment at the back of the truck. The original drive solution for the shredder shafts used two heavy shaft mounted, right angled bevel helical gearboxes, which were 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 up to four tonnes of paper per hour was processed. The weight of the motors and the gearboxes combined meant that the overall payload of the shredding vehicle was reduced.

Malcolm Moon, Technical Sales Manager for Whitham Mills Engineering, comments: "We were looking for a solution which 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."

Fortunately Brevini was able to provide a solution using its range of high efficiency planetary gearboxes. Each stage of the gearbox uses three planetary gears which are located inside a toothed outer ring meaning that the load is spread among many contact points. This not only leads to less internal pressure - and thus up to 98% efficiency per stage - but also means that smaller units can transfer high torque levels 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 connected to an individual shredder shaft: the first transmitting 5306Nm at 27rpm and the second transmitting 4621Nm at 28.5rpm. A two stage planetary gearbox was also supplied to drive the auger screw with a 12.5:1 reduction ration. Each gearbox was driven by a compact Samhydraulik hydraulic motor which was supplied by sister company Brevini Fluid Power.

Gonzalo Salvatierra, Sales Application Manager for Brevini Power Transmission, says: "Thanks to the efficiency and high torque capacity of the planetary gear system we can use smaller drives for this application and still deliver the required results. The trucks were all ready to be equipped with a hydraulic power pack for the loading system so all we had to do was change the gearbox input adaptor to accept the Brevini Samhydraulik motors. This produced significant weight savings over using electric motors.

"The mobile shredder is in use for up to eight hours a day 350 days a year so reliability is key. Thanks to the planetary gearbox design, and Brevini's ability to produce detailed design life calculations, the correct drives were selected and have been proven to be very reliable."
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