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Get your sums right for bales

Bale

With a huge amount of recyclables shipped overseas for reprocessing, containerised transportation costs are a significant issue. Volatile prices for materials and often slim margins mean it is crucial that maximum payload weights and space are fully utilised, otherwise a business is simply transporting air and eating into profits.

Materials such as paper and card, plastics, cans or refuse-derived fuel are bulky and need to be compacted and baled to facili­tate economic handling and stor­age. The baling press therefore is an essential piece of kit, and most MRFs will have one or more as part of a waste processing line.

But it is rather more complex than throwing waste material in one end and squirting out nicely compacted, uniform and stable bales from the other. Achieving the optimum baled weight and density for the material you are working with can be problematic.

Appropriate bale dimensions to optimise container loading is still an issue, especially with older machines. Bales are not always a nice, easily stackable, shape. Contamination can be an issue, while poor compaction will often result in deformed bales that expand or sag.

For containerisation of baled waste there are three factors to get right: compaction, shape and size.

Compaction is governed by the density of the material and the press force of the baler. A channel baler or twin-ram machine with 80 or 100 tonnes press force is ideal, especially where multiple waste streams are handled. As a general rule, the greater the bale size, the harder it is to achieve bale density/weight required to make payloads.

Shape is all about the uniform­ity, stability and integrity of the bale. Poorly tied bales, insufficient ties or wire ties of the incorrect gauge and hardness can all cause problems. Bales that burst may need to be re-baled while de-formed bales will be harder to handle and difficult to load.

Size or the dimensions of the bale dictate how efficiently the container is loaded. There is wide variation across the industry.

The challenge for many operators is balancing throughput (the speed at which you can process material) with bale density (how much material you can crush into the same space). This is an impor­tant calculation to get right.

Material needs to be processed and baled at a rate that keeps up with the volume of material arriv­ing at the depot. But sacrificing density for speed is unlikely to make economic sense when onward transportation, storage and handling costs are taken into account.

For example, average bale weights for HDPE or PET should be around 600kg. But if a company is averaging only 300kg for the same volume, then transportation costs will increase. Machine choice will always be something of a compromise because most operators are work­ing with multiple waste streams and therefore switch from one material to another, each with dif­ferent properties.

While the horizontal channel baler or shear press is the industry stalwart, older machines will not necessarily deliver the compaction needed. A modern twin-ram machine, such as the Middleton ME2R80, which compresses material against a solid wall before ejecting it sideways, will produce significantly heavier bales, with fewer compression strokes and lower energy consumption. Operators can do a number of things to maximise production. Monitoring bale weight will give an immediate indication of what is going on. It is essential to ensure the pressure is properly adjusted for the material being processed and that the machine is regularly serviced. The addition of shred­ders, perforators and other pre-processing measures may help.

Making money from recycled waste remains challenging. With literally thousands of containers in transit, optimising payloads is essential because even a small per­centage improvement will go straight to the bottom line.

Mark Smith is engineering director at Middleton Engineering

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