Weld Line

(weld mark, flow line) A flaw on a molded plastic article marking the meeting of two flow fronts within the mold. Because the two fronts may have cooled and skinned over before meeting, or had too little time in the molten state for interdiffusion of molecular segments across the interface, the weld may be imperfect and weak. (2) In extrusion of pipe, tubing, and some profiles from end-fed dies in which the cores are supported by spiders, a line parallel to the product axis where the flow front was split by a spider leg and subsequently reunited downstream. Weakness at such weld lines can depress the hoop strength of the pipe or tubing. (Whittington's Dictionary of Plastics, Carley, James F., ed., Technomic Publishing Co., Inc., 1993; Engineering Plastics and Composites, Pittance, J. C., ed., SAM International, Materials Park, OH, 1990)