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Blog: Mark Smith on plastic baling density

Date: 12/11/2013 | Author: Mark Smith

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Middleton Engineering's Mark Smith, who is its engineering director, shares his thoughts on the challenges of increased plastics recycling and how best to bale it


Figures vary but here in the UK we currently produce some 5 million tonnes of waste plastics every year, and it’s growing. About 2.4 million tonnes of this relates to packaging waste. We’re already doing a reasonable job at recycling plastic bottles and the percentage of waste plastics collected, recycled and sent on to reprocessing plants is growing. But we still have a long way to go to meet European environmental targets. Countries like Germany need a lot of chasing to catch up.

But we’re faced with a bit of an issue. Sorting different plastic waste might present headaches. However, as the volume of recycled plastics increases, so does the transportation bill. This presents the bigger issue, and it’s made worse by a relentless rise in fuel and utility costs. It’s not surprising, given the fact that most of this goes overseas, the top destination China which is over eight thousand miles away. Why we export so much of what is a valuable resource is a subject for another time, as you would think that there is more profit to be had if we processed it here.

Of course, waste plastics are bulky materials, they need to be compacted and baled to be handled conveniently and economically. The baler, therefore, is an essential piece of kit, and you’ll find one working away in most MRF facilities. But it’s a trifle more complex than throwing plastic waste in one end and squirting nicely compacted and uniform bales out the other.

The challenge for many operators is balancing throughput - the speed at which you can process a given volume of material - with bale density, how much stuff you can crush into the same space. This is an important calculation to get right. You need to process and bale material at a rate that keeps up with the volume of material arriving from kerbside collections. But sacrificing bale density for speed may not make economic sense when you take into account transportation, storage and handling costs.

For example, when baling hard plastics, it’s perfectly possible to achieve consistent 700kg bales, or even heavier. If you are only averaging 300kg for the same volume, and we see plenty of examples of this, your transportation costs will increase.

Machine choice will always be a bit of a compromise because most operators are working with multiple waste streams and switching from one material to another, each with different properties. While the horizontal channel baler or shear press is the industry stalwart, older machines won’t necessarily deliver the compaction needed. A modern twin ram machine which compresses material against a solid wall before ejecting it sideways, will produce significantly heavier bales, with fewer compression strokes and lower energy consumption. Our record with a 150 tonne twin ram machine is an 850kg bale of hard plastics.

There are a number of things you can do as an operator to maximise production. Monitoring bale weight will give an immediate indication of what’s going on. It’s essential to ensure the pressure is properly adjusted for the material you are processing and that the machine is regularly serviced. The addition of shredders, perforators and other pre-processing measures may help.

How the baler is fed is also key. A smooth and consistent flow of material is essential to produce uniform well compacted bales. Conveyor systems, hopper size and operator training all contribute. If bale weight is down these are some the first things we look at.

Bale size is also very important especially if you use road and sea containers. It’s really quite surprising that it’s only now that the industry has started to optimise bale size to maximise available container space. Bales measuring 1050 x 1050 x 1400mm are perfect for this.  An existing machine may give you the flexibility to adjust size to fit but if you are buying new this should be a key factor.

Making money from recycled plastics remains challenging. With fluctuating prices for raw waste product getting your strategy right is crucial, and as the emphasis moves to a wider range of plastic waste streams further flexibility will be required to control costs.  Planning ahead and talking to your supplier will help optimise your baler operation for the future.


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