Why does PVC pipe appear sink marks

Why does PVC pipe appear sink marks?

       The shrinkage marks on the surface of the PVC pipe will directly affect the appearance of the PVC profile, and even affect the cleanness of the corners, so it will leave regrets for the high-quality PVC pipes. So why does the PVC water pipe have sink marks?

        Causes of sink marks on PVC pipes

      1. Shrinkage marks and vacuum degree.

       The same set of molds are prone to shrinkage marks when the vacuum degree is low or the mold vacuum holes are blocked. After careful inspection, when the vacuum degree is low or the vacuum hole of the dry setting mold is blocked, the outer surface of the PVC profile cannot be closely attached to the setting film surface, so the cooling effect is reduced, and the cooling in the dry setting mold is not complete. This will cause signs of cooling shrinkage.

   2. Shrinkage marks and mold runners.

  Inner ribs alone are not easy to produce shrinkage marks, and T-shaped flow channels are easy to produce shrinkage marks. The degree of production is related to the width ratio of the two T-shaped junction flow channels. The ratio is the width of the T-shaped cross-flow channel to the width of the vertical flow channel. The larger the ratio, the less likely it is to produce shrinkage marks.

       3. Shrinkage marks and thickness of inner ribs.

  In actual production, it was found that the inner rib was too thick compared to the outer wall, which easily caused shrinkage marks. If the inner rib exceeded the outer wall thickness, the shrinkage marks were more obvious. On the contrary, the thinner the inner rib, the less likely it is to produce shrinkage marks. To be precise, when the thickness of the inner rib is less than 2/3 of the thickness of the outer wall, there is generally no shrinkage mark.

  According to relevant analysis, it is believed that this phenomenon is caused by cooling and shrinking. After the customized cooling of the PVC pipe, the intersection of the inner rib and the outer wall was compared with other wall thickness positions, and it was found that the cooling heat dissipation capacity was large and the temperature was high. Therefore, there is post-cooling shrinkage, the thicker the inner rib, the greater the stored heat, and the more serious the post-shrinkage.

        I hope that major PVC pipe manufacturers can pay attention to this problem when they reproduce PVC pipes and accessories, and avoid producing defective products.


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