At the beginning of 2006, a new primary crushing plant was installed at the works of cement producer Tvornica Cementa Kakanj D.D. Kakjanj in Bosnia Herzegovina, supplied and commissioned by Liming . In this cement works, which is member of the Heidelberg Cement Group, limestone from three different quarries is processed to produce two different mixes. The new equipment was supplied for integration into parts of the existing plant.
The raw material to be processed is characterised by a relatively high abrasion factor. In order to minimise the abrasive effects of the material on the wear parts of the crusher, the fine fraction, in which most of the abrasive material is to be found, is removed from the main material flow by a Liming pre-screening roller grate (wobbler) installed upstream of the crusher. The working surface of the wobbler consists of a series of rotating shafts spaced at defined intervals which allow the fine fraction to pass through the gaps between the shafts for onward conveyance, to be re-united with the main material flow downstream of the crusher.
Spaced at intervals over the length of the shafts and sized according to the desired cut-off particle size are delta-shaped discs, which also further the conveying process and prevent material clogging. In this particular case, the desired particle size separation point is 50 mm. The drive is effected by a central shaft, from which the power is then distributed to the individual shafts. Each shaft is connected to its neighbour by roller chain, thereby achieving smooth and synchronised shaft rotation. The chains run in an oil bath in a separate chain casing. In order to minimise the risk of possible material caking, rugged scrapers are fitted underneath the shafts. The side walls are lined with replaceable wear plates.
The crusher selected for this particular application is a Liming impact crusher. The crusher is equipped with a grinding path to restrict the amount of oversize. Impact apron and grinding path settings can be adjusted hydraulically. During operation, the hydraulics retain the impact aprons in their pre-set positions. On entry into the crusher of any large lumps of tramp metal or non-crushables, the aprons retract in a controlled manner, allowing the tramp metal, etc. to pass through, and then return immediately to their original pre-set position. In this way, damage to the crusher internals is minimised and at the same time the percentage of oversize is limited. The crusher is distinguished by its high degree of operational safety and a consistently high product quality. An important factor in the product reliability is the rugged GSK-type rotor, a combined welded/cast construction.
The whole plant was commissioned punctually in the Spring of 2006, during which operation the contractually specified targets relating to output and product granulometry were not only met but significantly exceeded (see following design and operating data).
Target Design Data:
Feed material: Various limestone mixes
Feed rate: 450 t/h
Feed size to wobbler: 0 – 800 mm (1,000 mm)
Pre-screening by wobbler: 50 mm
Feed to impact crusher: 50 – 800 mm (1,000 mm)
Impact crusher: at least 80 % < 50 mm
Spec. energy consumption: 1.2 kWh/t
Actual Operating Data:
Plant capacity: average feed rate 500 t/h
Product granulometry: 80 % < 35 mm
Power consumption: 0.7 kWh/t