The feed bins store and weight the aggregates (virgin mineral) individually by means of belts with variable, continuous, and automatic speed in the proportion indicated by the control system.
The aggregates that have been weighed are delivered to the dryer, which is a type of rotating cylinder with a burner on one end where the drying process is done in order to eliminate the water in the aggregates and heat is added in order to reach the correct mixing temperature with the binder (150°C to 190°C, variable according to the type of mix and binder).
The aggregated material is inserted in the dryer on the opposite end of the burner. The flow of aggregates is counterclockwise to the flow of hot gasses coming from the flame of the burner. This is the main characteristic of the process known as counter-flow with external mixture, which ensures better use of the energy generated in the burner, as well as more efficiency in the extraction of moisture. Once they are dry and heated, the aggregates go on to the external mixer.
Parallel to this, the particles (fine aggregates, dust) coming from the drying process are retained by 2 main components: the pre-collector of particulates®, which captures the fine aggregates that have a larger granule size (retained in the 200 screen) and the Bag Filter, which is responsible for retaining the fine aggregates with smaller granule size (through the 200 screen). These components deliver the particles to the mixer, preventing them from being released into the atmosphere and in this way, preserving the environment. It is not only an ecologically correct solution, it also brings economic advantages. When compared to traditional systems of other manufacturers, it decreases the need of weighing this material. Waste is zero in the counter-flow process: every material weighed is used and will be present in the final mixture composition.
At the same time, the PAC weighing system injects this binder directly into the mixer on top of the dry and hot aggregates, following the commands of the control system.
The arms of the mixer exert great energy on the mixture and the resulting product is a hot asphalt mix that is usually abbreviated as HMA (Hot Mix Asphalt).
This mix is taken by elevator to a storing silo from where it is unloaded into a truck that will transport it to the paving location (road).