Pultrusion molding of continuous fiber reinforced thermoplastic composite pipe using partially-impregnated commingled yarns

Pultrusion molding is one of the high-cycle molding methods for continuous fiber-reinforced plastics using thermoplastic resin, and considering the expansion of industrial applications, shaped parts, such as pipes and L-shapes are more desirable. The following is an example of a product that can be used to achieve this goal. Braided fabrics are one of the most useful preforms for achieving pipe shapes. In this study, commingled yarns and partially impregnated commingled yarns were used as intermediate materials, because excellent impregnation properties and textile workability are required to the fabrication and pultrusion molding of the braided fabrics. However, when forming a pipe shape by pultrusion, the mandrel must be placed in the hollow of the molded product, which causes an increase in pull-out resistance due to shrinkage of the pipe diameter. To solve this problem and achieve high-speed molding of pipe-shaped products by pultrusion molding, this study examined the effects of different intermediate materials and molding conditions on the impregnation state and mechanical properties of molded products, as well as the optimization of the mandrel location. The first part of this study revealed that the impregnation time of partially impregnated commingled yarns is shorter than that of commingled yarns, and as a result, the decrease in void ratio and unimpregnated ratio is smaller, and the decrease in mechanical properties is smaller even if the molding speed is increased. The second part of this study, it was found that the mandrel tip should be positioned so that the temperature of the inner diameter side becomes lower than glass-transition temperature (T-g) during cooling to prevent separating. In addition, it was found that temperature history analysis based on heat conduction calculations is effective in predicting the optimum mandrel position, which varies depending on molding conditions. These results provide a guideline for high-speed pultrusion molding.