How do manufacturers prevent sink marks in thick polyethylene castings?

Sink marks are common defects in thick polyethylene castings, caused by uneven cooling and material shrinkage. Manufacturers employ several strategies to prevent them:

1. Optimized Cooling Rates: Ensuring uniform cooling by designing efficient cooling channels in molds reduces temperature differentials, minimizing sink marks.

2. Material Selection: Using high-quality polyethylene with consistent flow properties helps maintain structural integrity during solidification.

3. Adjusting Injection Parameters: Slower injection speeds and higher holding pressures allow the material to fill cavities evenly, reducing shrinkage.

4. Mold Design: Incorporating ribs or coring in thick sections distributes material more evenly, preventing localized shrinkage.

5. Post-Molding Treatments: Controlled cooling or annealing processes can further mitigate sink marks in finished castings.

By combining these techniques, manufacturers produce defect-free polyethylene castings with smooth surfaces and consistent dimensions.