Filler feeding is separate storage for filler and the means for its controlled introduction into the pugmill should be provided. Measurement may be by weight or volume.
Filler is not passed through the dryer, as the flow of air to the dust extractor would carry most of the fine particles to the dust collector, and into the wet scrubber (if installed) or into the atmosphere.
Feeding of the filler is usually by mechanical means, which should be checked regularly to ensure that no obstructions have occurred to affect uniform feeding.
In batch plants the filler is proportioned by weight. In continuous mix plants the proportioning is achieved by varying the filler gate opening and interlocking the filler feed system with the aggregate feed system. The average proportions of filler in the mix can be checked by comparing the total quantity of filler used and the quantity of mix produced. Do you need to more details about filler feeding and see batch and continuous plants.