Investment in Metso Minerals' Trellex rubber screen media has helped Hanson overcome blinding in wet weather at its Forestwood quarry. Brian O'Sullivan reports
Wales in the UK is home to a large number of quarries and is renowned for many things - but dry weather is not one of them. This high rainfall causes problems for some quarry operations, especially fine screening of limestone using conventional steel wire mesh.
The problems caused by wet conditions were familiar at
It also meant that two or three times a day in bad weather the screen would have to be shut down and site engineers asked to climb into the screen and clear the blinding using rubber mallets. Taking up to an hour each time, this unpleasant job in a confined space also resulted in a significant loss of productivity, estimated to be between 20,000 and 30,000tonnes a year.
Since installing the new rubber screen media, quarry foreman Howell Bryant reports that he has only had to carry out the task twice, rather than upwards of twice a day. Specified and supplied by Metso's area manager Gareth Brooks, Trellex TFX works well in conditions of up to 7% moisture, thanks to its high flexibility, which help prevent the material from blinding over.
Forestwood Quarry was opened in the 1950s and acquired by Hanson in 2001. The quarry's plant was installed in the late 1990s by Unifloc and consists of a
Hanson production supervisor Richard Grey was the driving force for the quarry's switch from wire media to Trellex TFX rubber mats. "We were having a terrible problem with the Module 4 fine screen that produces 10mm, 6mm and dust," he said.
"It was constantly blinding up in wet weather. The Trellex TFX system was more expensive but as it needs almost no unclogging - and therefore no production stoppages - the payback in terms of increased efficiency was very rapid. The lifespan of the rubber is also considerably more than the metal wire - by up to five times.
"Other than checking the tension and pinching up the bolts once a month, they require almost no maintenance during their expected lifespan. This frees up our engineers for other duties, as they are not constantly being asked to clean the screens anymore." The Trellex TFX system is available in several thicknesses with molded and punched apertures. Installed on screens with longitudinal supports, they can be fitted on cross and longitudinally tensioned screening machines. Their effectiveness lies in the extreme flexibility of the rubber screen 'cloth', where constant movement inhibits the material from blinding or pegging. The mats are reinforced with integral cords that maintain tension and provide accurate separations. No deck modifications are needed to the screen and panels are fitted with wear strips to protect the panel from wear from the camber bars.
"Metso supplied two of its own engineers to fit the new deck and ensure it was installed properly," said Grey. "They also showed our fitters how to install and maintain them correctly. Since then the Trellex TFX mats have been largely trouble free. No screen can cope in extremely wet conditions, and even the Trellex TFX mats can blind over. But with the rubber system blinding is a rare exception - only twice in eight months - rather than a twice daily occurrence. This guarantees that the aggregates are clean and of the right size whatever the weather, and as they are so durable I'm not expecting to replace them for some time," concludes Grey. "In fact I'm considering using Trellex TFX for the top deck of the screen also."
