UNTIL recently Havering Aggregates – a joint venture between Brett Aggregates and CEMEX – were regularly losing several hours of production time a day due to pegging problems, but investment in the UK’s first Metso Minerals D10 modular screen media has finally resolved the issue.
The Havering site at Wennington in Essex screens and separates sand and aggregate from ballast excavated at South Hall Quarry in nearby Upminster.
‘We process 110 tonnes/h throughout a 10h-a-day operation,’ said site foreman David Proctor. ‘The problem we had was that we were regularly being faced with pegging. This meant that twice a day we would have to stop and clear the stones caught in the screen. This could take more than an hour each time.’
Havering opted for a more pliable screen but again this suffered from pegging. It was not until the Trellex modular screen media were installed that the problem was finally overcome. ‘We have now had the Metso screen in operation for more than six weeks and it hasn’t had a single pegging problem,’ said Mr Proctor.
The Metso Minerals Trellex modular screen media can be fitted to almost any installation in the world. Its modular components have been designed to upgrade systems currently using other manufacturers’ standard fittings, a factor that proved invaluable for Havering Aggregates, as the rest of their installation was working well.
‘We separate then wash and bag the products here,’ said Mr Proctor. ‘The rest of the washing plant was operating effectively. Now the top deck is really making a difference. Previously we were getting stones ‘pegged’ in the screen, which meant a number of smaller stones were being rejected.’
Having passed through the top mat, the –25mm material goes into a log-washer and is separated into 20mm and 10mm fractions. Meanwhile the sand is washed and separated into sharp and soft grades.
Both joint-venture partners use these products for their own projects, but Mr Proctor says there is a thriving business supplying materials to construction businesses and merchants in south-east England. The Wennington plant is 15 miles from central London and even less from the London Olympics site where demand for building materials is increasing.
‘We work 10h a day here and it is important to keep the plant working,’ commented welder-fitter Paul Edwards. ‘It was pretty frustrating having to stop work every four or five hours to clear the screen. Fitting the Trellex step has been a great success.’
The new system has been designed with many positive features, including lightweight rubber or polyurethane modules, easy snap-on connections and an emphasis on recycling. Another key benefit is that the Trellex range has an improved open area compared with other solutions on the market, thereby giving better performance.
In addition, the strips that the modules are fixed to are narrower than the ones traditionally used on existing modular installations. This means that there is a smaller blind area at the intersections between panels.
Trellex Modular Screening Solutions is the family name for a system that includes a full range of components. Existing successful products, such as stepped modules, remain an important part of the family but have been joined by new additions that allow Metso’s products to be directly compatible with the other standard sub-frames used around the globe.
The new range is easily retrofitted to existing systems with no need to weld or cut steel rails. A new profiled strip is simply fitted to the rail and it is then ready to take the Trellex modules.
Metso Minerals’ screening media product line manager, Claes Larsson, said: ‘Customers will even be able to opt for a special tapered strip to allow them to mimic our existing system by introducing a step to the deck. This is particularly recommended for applications with a lot of fines.’
The new Metso range is divided into three families depending on the spacing between fixings (300mm or 305mm) and whether they are snapped on transversely or longitudinally. There are many options including material, size and aperture arrangement. The range also includes optional fittings such as deflectors to steer the flow.
Havering Aggregates were also interested in the improved wear life offered by the Metso system, a factor that has encouraged customers elsewhere in the world to move from custom-made steel wear cloths to rubber or polyurethane modules.
‘In extreme cases a woven wire cloth might need to be changed every week, while the rubber equivalent could last eight months or more,’ said Mr Larsson. He added that there are also environmental benefits in using rubber or polyurethane products, as they can reduce noise. Moreover, sections can be rotated or replaced as they wear out, instead of discarding an entire steel cloth.