並走流ウェルドラインの表面V溝形状に関する形態学的研究

抄録

Weldlines occur wherever two or more melt fronts meet in injection moldings. The V-notch at the weldline causes a reduction in mechanical properties and visual defects. Flow weldlines that occur in actual injection moldings may have complicated V-notch shapes owing to variation of temperature and pressure during the process. In the present study, the depth and the cross-sectional shape of V-notches at weldlines behind an obstructive pin in injection-molded polystyrene were investigated. The main results obtained are summarized as follows;
(1) After the two flow fronts going around the pin collided at a point away from the pin, the impingement area expanded around the point in a short time. The V-notch depth was approximately uniform in this area and was dependent on the molding conditions.
(2) As the tip of the impingement zone reached the pin, the resin experienced higher pressures due to reduced flow. As a result, the V-notch depth decreased sharply toward the pin.
(3) Downstream from the collision point, the two impinging flow fronts formed a weldline with increasing impingement angle. The notch depth decreased gradually with increasing angle.
(4) When the impingement angle reached a critical value dependent on the molding conditions, the cross-sectional shape of the V-notch clearly changed.
(5) The trace of the V-notch finally disappeared after a gradual decrease of the depth due to the cooling effect of the mold.