High-efficiency gearboxes from NORD Gear Corp. helped Ken Mills Engineering (KME) build the advanced processing machinery employed in a highly efficient new materials' recovery facility (MRF) operated by Nordic Recycling Ltd. in Tilbury, Essex, UK.
The new facility is Europe's largest single-line materials' recovery facility. The processing machinery was designed by KME and is believed to be the most advanced of its kind in the UK. It features a large number of automated screening stages to enable the extraction of different types of dry recyclable materials. The facility also incorporates a number of automatic balers, all linked together by a sophisticated feeding and materials' handling conveyor system with a total length of several hundred meters.
More than 50 gearboxes are used to drive the extensive materials' handling system. Helical bevel gears were selected for the application, to optimize performance, providing an efficiency of more than 95 percent and to minimize energy costs at the plant which typically operates 16 hours a day. This helical style of gear additionally runs very quietly, helping to reduce noise levels at the facility.
The MRF has a nominal capacity of 25 tons/hour and is expected to process at least 100,000 tons of mixed dry recyclable materials a year, which might otherwise go to landfill. About 50,000 tons of reclaimed paper is expected to be baled and shipped to Holmen Paper in Sweden for recycling into fresh newsprint.
The machinery in the facility is designed to have a very long life of some 25 years and part of KME's responsibility is to provide a 24/7 maintenance service. Consequently, when specifying the drive systems, reliability was a paramount concern.
“The demands of designing material recovery facilities means that wherever possible we employ very high-quality and field-proven automation components,” says Adam Moore, MRF project manager with Ken Mills Engineering Ltd.
NORD helped KME specify the gearboxes, choosing the sizes to provide a combination of economy and operating safety margins to assure reliability. The underlying performance margin built into the conveying system, and other elements of KME's processing machinery, has been demonstrated at similar facilities where the nominal capacity of 25 tons/hour is regularly exceeded — sometimes by as much as a third.
Helical bevel gearboxes from NORD's SK9000 family are used on the conveying system. These units provide the ideal right-angle connection to the conveying system. The helical bevel cut teeth provide a smooth, efficient and low noise meshing that is ideal for low-speed power transmission applications such as driving conveyors. They increase efficiency substantially compared with the more common style of worm gears used in this kind of application, in this instance providing about 25 percent greater efficiency, which equates to energy cost savings of many thousands of pounds a year.
To achieve a compact design, conveyors are often driven by right angle gearboxes, using either worm or helical-bevel gear stages. Worm gears are generally cheaper to purchase, but less efficient and providing higher operating costs. Worm gearboxes are known for mechanical robustness and silent operation. The downside of the worm's larger tooth contact area is greater losses and worm gears generally have an efficiency of only 50 to 80 percent (depending on the ratios required and other factors).
The helical-bevel gearboxes used in this application are much better suited for applications involving continuous operation, high and steady loads. This means worm gearboxes are suited for conveying applications involving non-continuous operation and possibly with high shock loads or overloads.
There is also a power rating consideration. Worm gears tend to be available to handle motor powers up to 22 kW. Beyond this, helical bevel stages take over as the optimal choice.
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