In March 2012 HAZEMAG Group received an order from Hammerfall Dolomitt A/S in Røsvik/Norway (Fig. 1), for the delivery and setting up of a processing plant with a feeding capacity of 600 t/h. Because of the site of operation which is situated approx. 80 km to the north of the polar circle the plant was designed for extreme operating temperatures of -40 °C. Top priority is given the minimization of the fines’ content resulting during the crushing procedure. A final grain size as cubic as possible is being achieved from an initial material with a maximum grain size.
The order was successfully finalized in only 8 months. The commissioning took place in November 2012. As ordered, HAZEMAG supplied the complete plant components, the steel construction, the engineering for the foundations and the setting-up and commissioning of the equipment. The processing plant includes the field-tested HAZEMAG chain conveyor KF 1500 as feeding unit for the primary crusher, the HAZEMAG center sizer HCS 1020, a HAZEMAG threestage roller screen and the HAZEMAG center sizer HCS 0820 as secondary crusher. In addition a stockpile belt conveyor with belt weigher and a dedusting plant are part of the scope of supply.
The dolomite stone which is extracted underground by means of blasting has cubical feed sizes of up to 1200 mm and partially even larger ones, and is conveyed by truck to the 30 m³ feed hopper. The chain conveyor KF 1500 with a length of 24.5 m conveys the material to the primary crusher HCS 1020 (Fig. 2). The crushed fraction with maximum sizes of 250 mm is transported via 2 belt conveyors to the secondary crushing plant. For the protection against metallic foreign bodies the second conveyor has permanent magnets and a metal detector.
The HAZEMAG roller screen is in front of the secondary crusher. The first and second screening stage seperates the < 12 mm fraction from the material flow. This fraction gets to a reversing belt conveyor which permits the material to be conveyed to a stockpile during the winter months or – in summer – to the end product. The flowability of the material during winter is being assures in a downstream silo.
The opening width of the third screening stage is 70 mm. Due to the prescreening the feed quantity and the size of the secondary sizer are reduced. In addition an unnecessary crushing is prevented, in order to minimize the share of fines of the end product by a further crushing. The oversize (70...250 mm) is crushed to the target fraction (< 70 mm) by the secondary sizer and is conveyed to the downstream finishing process (Fig. 3).