Abstract
Glass fiber veil is produced with a wet forming process, after which the veil is dried in a wire-type cross-flow dryer. The wet nonwoven web structure of glass fibers and binder undergoes the drying process under specific conditions as air velocity, air temperature and air humidity, each of which can be controlled separately. Drying is an important process step, which highly defines the end product properties of the glass fiber veil.
A simulation model is presented that give the opportunity for a better understanding of the cross-flow drying process in relation to product and process properties, and also a better controllability and a better energy management of the drying process. Thermocouples placed beneath the supporting transport wire and air humidity sensors in the dryer sections are the key for evaluation of important non-measurable drying air and glass web properties. The model has been validated using correction factors for heat and mass transfer and assuming leaking air flows between the dryer sections.
The impact of the underlying work goes further in the direction of understanding some related product and process problems: (1) There is an explicit binder migration process from the wet glass web to the wet upper surface of the supporting transport wire, while flash-drying of the wet web proceeds on the dry and hot wire surface. (2) The drying process of wet glass fibers and wet binder gels proceeds at a specific temperature under which a solid binder film forming process occurs. Control of the temperature and time for solid film forming in the whole fiber web structure can be effectuated in this way.
The relevance of the simulation model may be proved by continuous inline measurements at the production line.