What rules can be summarized about the hardening speed of glass?

① For glass with fast hardening speed, the viscosity changes significantly with temperature.
② When there is no coloring oxide (except manganese oxide), the hardening speed of glass also depends on the thermal conductivity and heat capacity of glass. Glass with different compositions will have different thermal conductivity and heat capacity, but when the glass composition fluctuates slightly during production, the change in thermal conductivity and heat capacity is very small.
③ When adding coloring oxides such as FeO, CoO, CuO, Cr2O3, etc. that can absorb infrared rays (1~5μm wavelength), the hardening speed of the outer layer of glass will be greatly increased while the hardening speed of the inner layer will be reduced. In addition to the factors directly affected by the glass composition, the hardening speed of glass is also affected by the mass of the cooled glass, the ratio of surface area to mass, and the temperature and flow rate of the cooling medium (such as air). When glass fiber is formed, the ratio of surface area to mass is very large, so the hardening speed is faster. Generally, after the glass composition is determined, the temperature-viscosity curve is not easy to change, and the heat capacity and thermal conductivity rarely change. However, iron oxide in glass is inevitable, and a small fluctuation in the FeO content has a significant effect on the hardening speed. Therefore, with the improvement of wire drawing technology, it is now required that the iron oxide content in the glass should be controlled within a certain range, generally around 0.4%. If the hardening speed of the glass changes, the flow rate flowing through the nozzle will change accordingly. In addition, for fiberg lass drafting deformation, it also affects the tension on the fiberglass and the change in fiberglass diameter.