The constant-speed screw feeder has a volumetric capacity calculated by the volume of material in the section of one complete spiral and the diameter of the screw, so the dosage varies with the number of spirals.
With most dosers on the market the margin of error is around 4%. The variables are mainly from the filling of the hopper, technically known as the fill factor.
The agitator reel located up-line from the dosing screw feed, as well as breaking up clumps and crusts formed in the silo, makes the material more fluid, resulting in even pressure and weight on the spiral screw.
The variation in weight for our dosers is around 2%, representing a significant factor in the quality and continuity of dosing.
The dosing capacity also varies with the physical and chemical properties of the product: materials which are identical from a chemical point of view may show variations in weight and dosage capacity if they are not equivalent in granulation or other physical parameters, and thus cause variation in dosed quantity with the same rotation speed.