Development of an air classifier for the classification of crushed aggregates
Aggregates play an important role in road construction as they are used to produce asphalt. To ensure asphalt quality the content of grains smaller than 63µm in crushed aggregates must be reduced. To separate these small grain sizes, air classifiers are used. Anyhow, none of the currently used classifiers offers a space-saving, energy-efficient option for the classification of greater mass flows. This paper presents a newly developed machine for the classification of crushed aggregates. This machine uses a dispersing unit, which acts as a radial fan as well as an impact bar. The impact bar exerts an impulse on the particles, which catapults coarser particles in the classifying chamber. On impact, finer particles are going in suspension with air. The flow caused by the dispersing unit as well as the flow caused by an exhaust fan at the end of the classifying chamber transports the air-filler-suspension through the exhaust fan, whereas coarse particles fall onto a belt conveyor. As the flow can be set for the exhaust fan and for the dispersing unit, a variable separation cut is possible. Laboratory experiments have shown that this method is suitable to reduce the filler content from particle collectives with a filler content of 20% to below 7% while achieving relatively high mass flows. Ongoing tests and optimizations target to develop a prototype suitable for an industrial application by the end of this year.