With an average compressive strength of around 180Mega-Pascals (MPa), granite is one of the hardest rocks on earth. The granite found in the Boda Quarry near Vrigstad, a small town in southern Sweden, even yields values of more than 300MPa in some cases. This imposes particularly high demands when it comes to processing the material.
TJ Gräv, a provider of crushing services from Brandstorp, was contracted to process 40,000tonnes of the material, and being already familiar with German manufacturer
“We bought our first crusher in 2007 after seeing the machines at work during a visit to Germany. In my opinion, they are durable and exceedingly robust,” says Tomas Johansson, proprietor of TJ Gräv.
Johansson chose a combination comprising a mobile jaw crusher and a mobile cone crusher with integrated triple-deck screening unit.
The granite is first loaded by an excavator onto the Mobicat 120 Z jaw crusher with separate pre-screening unit.
The preliminary crusher reduces the original material with an edge length of up to 1,000mm to a size of not more than 200mm and then transfers it downstream directly to the secondary crushing unit, a Mobicone MCO 11 S, the mobile cone crusher which produces three end products of different grain sizes in a single pass. In this case, a relatively large amount of material is being circulated through the system, which of course has an effect on the overall discharge rate of the plant.
With its three screening decks, measuring 2,050mm x 5,000mm (lower deck is 4,800mm), this has the challenging task of producing final grain sizes of 0-8mm, 8-14mm and 14-22mm.
As a result, the MCO 11 S cannot achieve its normal maximum total output of 280tonnes/hour but despite this, the mobile plant combination produces more than 1,000tonnes of crushed stone aggregate per day.
Tomas Johansson considers the Kleemann plants to be particularly suitable for the job in Boda.
“Both units have a diesel-electric drive, which is very good as regards the fuel consumption, in spite of the high load,” he says
Other plant features are also important for Johansson.
“We sometimes have operations in rock where prescreening is especially important. There are times when the end product has to be almost completely free of organic particles and this can only be achieved if the cone crusher is equipped with an independent pre-screening unit.”
Sweden has a lot of quarries often with little out-take each year.
The country has good rock everywhere, and often with large distances between customers transport costs from quarry to customer must be minimised.
The quarry at Boda, opened in 2006, covers an area of 1km² and some 50,000tonnes of granite are quarried each year, the material being used for whatever the market nearby requires: 0-18mm/0-40mm/0-90mm for road base; 16-22mm/16-32mm for drainage; 2-5mm slip stop and some years asphalt and concrete fractions are produced.
TJ Gräv will use the Boda site once or twice a year, crushing whatever is required using the Kleemann machines. Some material is later screened by the quarry owner’s Maskinmekano screen.
Contractors such as TJ Gräv, with two jaw crushers, two cone crushers and a number of screens, excavators and wheeled loaders, cover some ten and 15 different quarries and building sites each year.
