Conveyors: Afterthought or integral to operations?

The humble horizontal baler might not be the most exciting item of plant machinery, but it plays a key role in compacting loose and often bulky materials to facilitate economic handling, storage and transportation. What is less recognised is the importance of the conveyor, both to feed production line processes and for any baling and recycling required.

Design considerations

Conveyors that are overfilled and continually spilling material or even under filled, are typical. Inefficiencies and production issues will impact the overall effectiveness of the operation and poor design and inappropriate conveyor choice are often the reason. But belt speed, overloading issues, poor synchronisation with other machinery and maintenance issues all play their part. 

As the baler won’t deliver uniform, well compacted and consistent bales of material unless the feed conveyor is up to the job, it means you won’t achieve maximum payload weights for the bales produced. 

A smooth and consistent flow of material optimises the loading of the baler and minimises the number of compression strokes and therefore power and time required to achieve bale density and weight. Productivity depends in part on the effectiveness of this relationship.

Of course the conveyor needs to be robust enough for the environment and the weight of the materials to be handled. Reliability is crucial too. The last thing you want is constant shut downs as this inevitably brings other processes to a halt. Planning is crucial.

Bespoke unit

Middleton Engineering has installed a second bespoke conveyor at Biffa Polymers' food grade High Density Polyethylene (rHDPE) recycling plant, in Redcar. Designed and manufactured at Middleton’s facility, the conveyor forms part of a separate recycling line for mixed post-consumer rigid polypropylene (PP). This produces high quality mixed plastic flakes for onwards distribution and forms part of the continued expansion of production capacity at Biffa Polymers.

The new conveyor, which has an overall length of 9.3m, transfers material from a shredder, to the in-feed conveyor for a granulator. It has a 600mm wide cross-stabilised 3-ply rubber belt, with a rising section angled at 25° to carry material currently at a rate of 1.5t/h. Sprung castor wheels maintain belt tracking while 50mm high cleats across the belt together with valances to either side at 275mm high, prevents material from slipping back to ensure a consistent feed rate. 

A special feature to further improve waste stream purity and quality includes a magnetic head drum for separating ferrous contamination at the head of the belt or discharge end of the conveyor. This provides secondary metal protection with continuous separation, trapping metal debris as the drum rotates, while clean product is discharged. A stainless steel chute diverts the unwanted material into a collection bin below. 

Lock off emergency stop switches, safety pull gantries on the rising section and SCADA controls to fully integrate the conveyor with the other machine processes complete the installation.

Alan Edwards, project and improvement engineer for Biffa Polymers said: “Running the Poly Prop processing line 24/7, as with all our production processes, requires robust and reliable equipment. Selecting Middleton Engineering for this new conveyor was the obvious choice. The company takes the time to understand our requirements, is quick to resolve issues and support has been excellent.”

Options 

Understanding material volumes and throughput is important and there is a huge range of options. Slider-bed, steel slat, rubber or steel belt, chain driven, inclined, swan neck, fully enclosed, in-floor or on-floor designs. Generally a chain conveyor will be used where larger volumes of material are being handled. A slider-bed solution is more appropriate for lighter materials and smaller volumes and will generally cost less as it doesn’t need to be as rugged. Products like RDF which can be much denser in volume than card and plastics require higher specification parts for chains, belts, motors and gearboxes. The corrosive nature of the material can also mean higher wear and maintenance considerations.  

Achieving a continuous and even flow of material will also depend on factors like belt width, motor sizes - powerful enough to handle the weight of the material to be conveyed - and control systems used. 

The temptation to fit a low cost standard option might provide initial savings, but it’s unlikely to deliver the overall performance you expect and is more likely to result in frustration and downtime. Bespoke solutions designed and tuned for your specific environment are superior, and in the long run guaranteed to be more cost effective and safer to use.

Optimal speed

With the right design, a conveyor feeds material at the optimal rate for your process, and at a volume and speed that matches other machines or processes. Generally control systems and telemetry should link each piece of machinery so that they work smoothly and harmoniously as one. It is important, therefore, that your supplier is equally competent with both the mechanical and software aspects of your chosen solution. And check that commissioning, testing and training are all provided as part of the service.