Weldlines
“In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to "knit" together, or "weld", during the molding process. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part. Knit lines are considered molding defects, and occur when the mold or/and material temperatures are set too low: thus the materials will be cold when they meet, so that they do not bond perfectly.” (Wikipedia, Weld Lines, 11/11/2011)
Recent Journal Articles
Effects of filler contents and processing parameters on the weldline strength of compression molded natural rubber
(2353–2359)Polymer Engineering & Science 51 #12 (2011)|
Patcharaphun et al of Kasetsart University and the Rubber Research Institute, Thailand, studied the effects of curing systems on the aging properties of NR vulcanizates on weld lines. The results show that an increased amount of calcium carbonate does not affect the weldline strength. However, the difference in tensile strength between weldline and nonweldline specimens becomes larger with the high loading of silica and carbon black. In addition, for the factors selected in the experiments, clamping pressure, and curing system were found to be the principal factors affecting the weldline property of vulcanizates. (RDC 11/10/2011)