# Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications
## 2 Materials and Methods
### Glass Fibre Production  
The fibres were produced using the down drawing process. A schematic representation of the drawing equipment can be seen in Figure 1.  
A platinum crucible with 8 nozzles with a diameter of 2.5 mm was used. The temperature near the tips and in the crucible was adjusted and monitored using two pyrometers. The fibre diameter was adjusted to between 15 and 17 um by the fine tuning crucible temperature and the winder speed. During the first drawing tests, the previously cast glass block was heated with the crucible, which led to increased crystallisation. To prevent this, the platinum crucible was heated up to the target temperature without glass, then the glass was added and melted.  
First, fibres were drawn from glass 18-06. The crucible temperature was 1200 degC and the temperature at the nozzles was 1110 degC. The desired fibre diameter of 14.9 um was achieved at a drawing speed of 1413 m/min. During the drawing of the fibres no drawing bulbs were formed, but drops from which the fibres were drawn. The formation of crystals during the drawing process was detected in these glass fibres. These crystals are formed by heterogeneous nucleation, reducing the tensile strength of the glass fibres and increasing the risk of fibre breakage. For glass 1-06, the crucible temperature was 1270 degC and the nozzle temperature was 1170 degC. At these temperatures, it was possible to draw fibres with 15.1 um at drawing speed of 1413 m/min without breakage. Surface crystallisation also  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & **Synthesis** & **Analysis** & **Synthesis** & **Analysis** & **Analysis** & **Synthesis** & **Analysis** \\  & **1-06** & **1-06** & **18-06** & **18-06** & **13-93** & **13-93** & **S53P4** & **S53P4** \\  & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **wt\%** & **wt\%** \\ \hline
**SiO\({}_{2}\)** & 50.0 & 52.63 & 65.0 & 66.87 & 53.0 & 52.25 & 53.0 & 53.22 \\
**P\({}_{2}\)O\({}_{5}\)** & 4.0 & 4.19 & 0 & 0.48 & 4.0 & 4.07 & 40 & 4.12 \\
**B\({}_{2}\)O\({}_{3}\)** & 0.2 & 0.20 & 1.5 & 1.50 & 0 & 0 & 0 & 0 \\
**Na\({}_{2}\)O** & 5.9 & 5.56 & 18.4 & 16.47 & 6.0 & 5.46 & 23.0 & 21.48 \\
**K\({}_{2}\)O** & 12.0 & 11.71 & 0 & 0.04 & 12.0 & 10.88 & 0 & 0.04 \\
**CaO** & 22.6 & 21.87 & 15.0 & 14.44 & 20.0 & 23.13 & 20.0 & 21.04 \\
**MgO** & 5.3 & 3.81 & 0.1 & 0.10 & 5.0 & 4.16 & 0 & 0.04 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Synthesis and analysis composition of the glasses.  
occurred in this glass. In addition, segregation of the fibres during the drawing process was observed. Many trials were required to produce fibres from glass 13-93, as this glass exhibited an increased tendency to crystallise. As a result, the fibres kept breaking off during the drawing process. At a crucible temperature of 1220 \({}^{\circ}\)C and a nozzle temperature of 1120 \({}^{\circ}\)C, fibres with a diameter of 15.5 \(\upmu\)m could be produced at a drawing speed of 848 m/min. There were many difficulties in producing fibres from the glass S53P4. Because of the very high tendency to crystallise, which was already observed during the production of the preform. Additionally, the narrow processing temperature ranged between 1050 and 1075 \({}^{\circ}\)C, lowering the drawability of the glass fibres, so the spinning tests were aborted. The drawing parameters and achieved fibre diameters are summarized in Table 4.