Raw material and additive dosing

Dosing refers to the continuous flow of product between two steps of the process. Dosing can be of two types: volumetric or gravimetric. Volumetric dosing involves the constant transfer of product without weight control, while gravimetric dosing utilizes weighing systems, either at the starting or ending point, allowing for more accurate dosing. This stage of the process is of great importance, and the gravimetric type is the most widely used. The recipe preparation typically occurs in balance tanks where the products are dosed. In the case of gravimetric dosing, there are several dosers, based on the components of the recipe, that feed the balance one by one, referred to as “sum” weighing. Once the weighing sequence is completed, the batch is transferred to the next step. In other cases, “loss-in-weight” technology is used, allowing the tank to be loaded from multiple dosers simultaneously, with each doser positioned on load cells.

Dosing is usually divided into “macro” components and “micro” components (usually additives) based on the percentage in the recipe, to achieve the best accuracy in weighing, as the precision of weighing systems is a function of their full-scale range. For precise dosing, it is necessary to use continuous conveying systems, typically screws or micro screw dosers, and not discrete systems such as rotary valves, bucket elevators, or chain conveyors.

In the gravimetric dosing phase, to achieve the best precision, motors are typically controlled by inverters, which vary the frequency to slow down the dosing in its final part.

It is also possible for dosing/weighing to occur at the end of pneumatic conveying, where the balance is positioned downstream of the conveying, and by managing the dosing device at the starting point, various components of the recipe can be weighed to feed the processing machine.

In all dosing cases, software plays a crucial role, capable of managing each phase effectively and providing important data such as consumption, inventory, and production batches.