With sand and gravel washing, around 300 000 t sand in the size 0 – 2 mm and gravel in the sizes 2 – 8 mm, 8 – 16 mm and 16 – 32 mm are produced. The product in the size 16 – 32 mm has developed into a problem in recent years. While a few years ago, the supplied concrete plants liked using it, the current trend is increasingly towards more slender structures in which more flowable concrete with a finer grade content is needed. Consequently, the material extracted and washed at some expense had to be stored intermediately on a stockpile and recrushed at regular intervals with hired mobile equipment. The annual quantity of the grade to be reprocessed amounted to around 40 000 t in peak years.
To make operations at the gravel plant more flexible, together with company Christophel, the company took the decision that the monetary expense incurred for hiring equipment would be sufficient to finance its own machine. Moreover, the problems that the hirers of special crushers have would be eliminated. Key arguments for the company were that its own crusher would be always be available when it was needed. The comminution tools can be adjusted precisely to the application. The company’s own people know the machine and can work more productively as a result.
As the special case on site was that “only” one washed gravel grade of 16 – 32 mm had to be crushed, the MC8 cone crusher from the Irish manufacturer Portafill was chosen. On the 22-t-heavy track-mounted machine, a 750-mm-large cone crusher is installed. With suitable tool configuration, it can be operated with a crushing gap under 10 mm. In theory, it is a practically ideal machine capable of producing a target product of 0 – 16 mm with minimized content of 0 – 2 mm crushed sand.
During a two-day trial run during which the company also tested whether the cone crusher could be combined in a circuit with an existing Chieftain 1400 screen from Powerscreen, a feed rate of 80 t/h proved possible without any problems. The sand content 0 – 2 mm was a maximum of 15 % and the oversize content of around 10 % could be easily handled. The combination with the Chieftain 1400 is easily possible. In future, the crushed material can be fed directly to the gravel washing with the other materials and the machine can, depending on demand, in “dry” production also be used in combination with the screen.
Other key data of the cone crusher are a 4.5-m³ feed bin from which a regulated discharge belt continuously feeds the crusher unit. The combination of filling of the crushing chamber and regulation of feed belt is achieved with a filling level sensor, which scans the crushing chamber and automatically activates the belt. The machine also includes as standard a metal detector that protects the crusher unit from the ingress of impurities that cannot be crushed. With four different crushing tools, it is possible to feed a maximum particle size of 160 mm. Crushing tool change in the MC8 is possible without sealant and can therefore be performed within one day. The machine is driven by a 180-hp diesel engine and delivers a maximum throughput rate of 165 t/h.
The compact size (10 500 x 2300 x 3000 mm) and the low service weight make the MC8 a balanced machine package that can be transported to the working site without the need for any special permission and is ready for action within minutes.