1. Shrinkage marks and inner rib thickness: In actual production, it is found that the inner ribs are too thick compared to the outer wall, which is easy to cause shrinkage marks. The inner ribs exceed the outer wall thickness, the shrinkage marks are more obvious. On the contrary, the thinner the inner ribs, the less likely to produce shrinkage. mark. To be precise, when the thickness of the inner rib is less than 2/3 of the thickness of the outer wall, shrinkage marks are generally not produced. The analysis believes that this phenomenon is caused by uneven cooling shrinkage. When the shape is cooled, the intersection of the inner rib and the outer wall has a larger cooling heat dissipation than other wall thicknesses, and the temperature is higher, so there is a post-cooling shrinkage. The thicker the internal ribs, the greater the amount of heat stored, and the more serious the post-shrinkage.

2. Shrinkage marks and vacuum degree: the same mold, when the vacuum degree is small or the vacuum hole of the mold is blocked, it is easy to cause shrinkage marks. After careful observation, when the vacuum is low or the vacuum hole of the dry setting mold is blocked, the outer surface of the profile cannot be closely attached to the setting mold surface, so the cooling effect is reduced, and the cooling in the dry setting mold is not good, causing post-cooling shrinkage marks.

3. Shrinkage marks and barrel temperature: The same mold, under different process conditions, the degree of shrinkage marks on the surface of the T-shaped structure of the profile section is obviously different. In the production, it has been found that increasing the melt temperature will reduce the shrinkage marks. degree.

4. Shrinkage marks and mold runners: the internal ribs alone are not easy to produce shrinkage marks, and the T-shaped runner joints are prone to shrinkage marks. The degree of shrinkage is related to the width ratio of the T-shaped two junction runners, and the ratio is T-shaped The width of the cross flow channel is larger than the width of the vertical flow channel, and the greater the ratio, the less likely it is to produce shrinkage marks.