A Spatiotemporal Concept of the Viscously Deformable Zone in Continuous Basalt Fiber Drawing

This preprint introduces a spatiotemporal concept for describing the viscously deformable zone during continuous basalt fiber (CBF) drawing. The approach distinguishes the stages of shape formation, practical diameter fixation, and subsequent glass transition, and proposes two complementary parameters: the length of the viscously deformable zone, \(L_v\), and the corresponding residence time, \(\tau_v\). The concept is developed from published models of silicate and basalt fiber formation together with long-term laboratory and industrial observations. Particular attention is given to the distinction between a continuous radial temperature–viscosity field and the assumption of a mechanically distinct surface shell, as well as to the limitations of transferring single-nozzle laboratory models directly to industrial multi-hole bushings. The proposed framework extends the conventional temperature–viscosity forming window by introducing spatial and temporal measures of deformation sensitivity. A working hypothesis is formulated that a longer and longer-lived viscously deformable zone may, under otherwise comparable conditions, increase susceptibility to process disturbances and primary filament breakage. The proposed parameters are intended as measurable quantities for future experimental validation rather than as a fully verified universal model.