## 4 Conclusions  
In this study, CFRP bar pultrusion process conditions were improved using a closed impregnation device, and the void fraction, surface roughness, deflection characteristics, and bending strength of the produced CFRP bars were evaluated. CFRP bars were produced and evaluated under three processes of different resin impregnation temperatures (20 \({}^{\circ}\)C, 30 \({}^{\circ}\)C, and 40 \({}^{\circ}\)C), pultrusion speeds (400 and 600 mm/min), and with and without the fiber spreading process. The possibility of manufacturing CFRP bars at a higher pultrusion speed by increasing the impregnation temperature and spreading fibers was confirmed by comparing Processes #2 and #3 to Process #1. In addition, the effect of increasing the impregnation temperature, as analyzed in Section 3.1, was confirmed by comparing Processes #2 and #3. The evaluation results for each process are summarized in Table 7. \begin{table}
\begin{tabular}{c c c c} \hline
**No.** & **Process \#1 (MPa)** & **Process \#2 (MPa)** & **Process \#3 (MPa)** \\ \hline
1 & 15.5 & 20.1 & 32.2 \\
2 & 23.8 & 24.4 & 36.1 \\
3 & 18.7 & 25.2 & 24.2 \\
4 & 19.9 & 32.5 & 28.2 \\
5 & 16.8 & 23.2 & 40.0 \\ Average & 19.0 (3.2) & 25.1 (4.6) & 32.2 (6.2) \\ \hline \end{tabular}
\end{table} 
Table 6: Bending strength of the CFRP bar produced in each process case. Figure 10: Cantilever test results. The lower the void fraction, surface roughness, and deflection, and the higher the bending strength, the higher the quality of the CFRP bar with effective impregnation. Throughout the evaluations, processes #2 and #3 achieved effective resin impregnation in the fibers due to increased impregnation temperature and the effect of fiber spreading, and the resulting CFRP bars were of a higher quality compared to process #1. In particular, for the surface of CFRP bars to be even, not only does the resin have to be well impregnated in the fibers but also the deviation in thickness of the fed fibers must be small. Therefore, the noticeable improvement in processes #2 and #3 compared to process #1 in the surface roughness evaluation appears to be the result of the effect of fiber spreading in addition to the increased impregnation temperature. Furthermore, the comparison between processes #2 and #3 verified the effect of the impregnation temperature. Based on the initial analysis result, the viscosity of the mixed resin must be 368 mPa-s or less for complete impregnation at a pultrusion speed of 600 mm/min, but the viscosity of the mixed resin at 30 \({}^{\circ}\)C was higher at 466 mPa-s, which resulted in a CFRP bar with a relatively lower quality compared to the result at 40 \({}^{\circ}\)C. This indicates that the impregnation temperature is directly related to the degree of resin impregnation in pultrusion, greatly affecting the quality of the final product. Since the CFRP bars produced in this study are used as a component for supporting the display mother glass in cassettes, the deflection and bending strength of the bars are the most important values among the physical properties, meanwhile, the pultrusion speed is imperative for reducing production costs. As a result, CFRP bars with enhanced deflection and bending strength by up to 34.9% and 70%, respectively, were produced by improving the process variables, and at the same time, the pultrusion speed was increased by approximately 50% from the typical speed of 300-400 to 600 mm/min. Conceptualization, B.K. and C.L. ; methodology, B.K. ; validation, B.K., C.L. and H.-M.Y. ; formal analysis, S.-M.K. ; investigation, S.-M.K. and H.-M.Y. ; resources, H.-M.Y. ; data curation, B.K. ; writing--original draft preparation, B.K. ; writing--review and editing, B.K., S.-M.K. and H.-M.Y. ; visualization, B.K. ; supervision, S.-M.K. and H.-M.Y. ; project administration, S.-M.K. and H.-M.Y. ; funding acquisition, H.-M.Y. All authors have read and agreed to the published version of the manuscript.