29 March 2002

Buying a shredder?

Farmers and contractors

wishing to earn extra

income by composting

green waste have plenty of

choice when it comes to

buying a shredder. Here,

Mervyn Bailey runs through

the different types of

machine on offer

SHREDDING is the first operation in a process that can turn green waste into a saleable commodity. And it is a process that manufacturers have latched on to as one with big potential.

Machines range from small chipper-like units that can be towed by a 4×4 or operated by a tractor to vast industrial-scale models capable of producing 100t of processed material/hour.

The accompanying table covers the middle ground, with details of shredders giving outputs from 4cu m/hour to 60cu m/hour. There are three main types, characterised by the type of shredding system used and the way material is loaded.

A hammer mill, comprising a rotor with stubby swinging blades, is the most common shredding system, pulverising green material with a tearing, ripping action. Robust build and lack of sharp cutting edges means the hammer mill can tackle non-green waste, such as pallets and demolition timber, without too much risk of coming to harm.

Small trailed machines, which are best suited to handling green waste, are ideal for working on-site and would normally be loaded manually using a plain chute in most cases, although some of the larger machines in this category have a short intake conveyor to help things along. One or two rollers may be fitted to compress material as it feeds into the hammer mill.

Where the quantity of waste involved demands greater output and mechanical handling and loading, the choice comes down to top-loading tub grinders and conveyor-fed models.

The former have the advantage of relative simplicity; gravity is relied upon to feed material into the mill without the added complication of a conveyor. But conveyor-fed machines can generally take bigger loads of green waste from the telehandlers and wheeled loaders most commonly used for the handling side of the operation.

An alternative approach is to use a green waste processor. Derived from heavy-duty diet feeders, these machines have a large hopper with two augers, which carry blades around the edge of the auger flights. &#42

The Gannon range of shredders use a gravity-fed tub with the hammer mill in the base, with processed material discharged by a rear-mounted conveyor.