Scandinavia is known for its hard rock deposits. In the south of Sweden, or the Boda quarry near the small town of Vrigstad to be precise, a particularly hard granite can be found. TJ Gräv AB from Brandstorp has the task of processing 40 000 t of this material.
The feeding material is very hard rock with a compressive strength of over 300 MPa in places. It is charged at a size of up to 1000 mm edge length to the primary crusher, which is a Mobicat MC 120 Z type mobile jaw crusher (Fig. 1). The MC 120 Z crushes the material to approx. 0-200 mm and transfers it directly to the downstream crushing system, a Mobicone MCO 11 S type mobile cone crusher. With its three screening decks, measuring 2050 mm x 5000 mm (lower deck: 4800 mm), this has the challenging task of producing final grain sizes of 0-8 mm, 8-14 mm and 14-22 mm in one process. 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. Even though the MCO 11 S system’s maximum output capacity of approx. 280 t/h cannot be utilised as a result, it is still possible for 1000 t of these stone chips to be produced every day.
Tomas Johansson, owner of TJ Gräv AB, considers the Klee-mann plant systems to be particularly well suited for this purpose (Fig. 2): “Both plant units have a diesel-electric drive system, which has a very favourable effect on fuel consumption. Not only that, they are built very sturdily.” But other features of the plant system are also important to 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 prescreening unit.” Moreover, as a quarrying contractor, it is important to him that the plant systems are relatively easy to transport and can be made ready for operation quickly on-site. In addition, the highest level of equipment availability is always of extreme importance. Here also, Johansson can count on the familiar good service of the company.