The innovation of the constructive solution is rather simple: it has been changed the shape of the storage bin of the hot aggregates coming from the dryer; the traditional hopper (more or less big) divided in more sectors, has been replaced by cylindrical elements, each one arranged to storage a single size-grading.

In every single silo the hot aggregate quantity in controlled by a continuos level measure.The storage bins and the weighing hoppers form a single group contained in an insulated panel and electrically heated shell, isolated toward the external environment.

With the method MET the weighing of the single size is done for deduction. Previously the weighing of each size was done discharging the materials from the hot bins into a weighing hopper: the operators know how much is the difficulty to set the queues and how poor is the precision of the dosing. We cannot deny that weighing for deduction as made by the MET is more reliable and exact. Furthermore this method allows the discharge of the various sizes into the mixer in different time.

We cannot deny that weighing for deduction as made by the MET is more reliable and exact. Furthermore this method allows the discharge of the various sizes into the mixer in different time.

That means the opening of the gates can be done both at the same time ( as it happens for the feeding of the weighing hoppers ) and Separately for every single size in different moments and ways in according to each mix-design.

With this system we can obtain the best spreading of the components in the mix in the shorter possible time

Another advantage concerns the output of the feeders and the possibility of their adjustment in feedback. Frequently some material already processed into the dryer is wasted owing to the low precision of the level signals. Now, the continous measure of the aggregates quantity in each storage bin will give a linear and constant signal of the level of the contents. In this way the extraction speed from the feeders will be controlled through the plant software in according to its needs.

Besides these important advantages, we can add that silo and weighing hoppers are enclosed in a heated single shell while the mechanical devices and the control instruments are placed outside duly protected. This involves that all dusts and steams produced during the screening of the aggregates and the mixing develop oniy inside this wide volumetric capacity shell.

In this way we get a very big reduction, even naught, of the typical “explosions” of steams that can arise when RAP is inlet into the mixer; we can so avoid the consequently sudden increase of pressure that causes dangerous escapes in the environment and we can ensure a more linear dusty air evacuation toward the filter.

it is interesting to specify that MET method can be use both in small production plants and in “hot stock type”. So we can have plants with a big deposit of hot material above a big capacity mixer or a small deposit above a mixer with discharge into a hot mix silos or even more solutions among the different possibilities.