During drying, the water still contained in the shards must be removed without causing damage. Due to the small pores, considerable drying stresses can occur. Too rapid or uneven drying leads to cracks or warping. Here, the local drying rates are strongly dependent on the relative humidity, the temperature and the air flow.
Fraunhofer-Center HTL has a device with which cullet can be weighed under controlled humidity, temperature and gas flow during drying. In this way, the drying rate during the different drying stages can be determined.
In the critical stages, the drying rate can be lowered in a targeted manner. The distortion of the cullet due to uneven drying is simulated in FE models in which the air flow and the local moisture gradient are taken into account. Moisture and flow measurements in the industrial drying units are taken into account during optimisation.