A shut-off angle in plastic part design refers to the angle between two mold surfaces that come together to block or "shut off" the flow of molten plastic during the injection molding process. These surfaces meet without leaving any gaps, ensuring no plastic leaks into unintended areas.
Shut-off angles are typically used in features such as holes, undercuts, or areas where two mold halves must create a seal without the use of additional components like slides or lifters.
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Uses of Shut-Off Angle in Plastic Parts:
1. Sealing Two Mold Surfaces:
The shut-off angle ensures that the two mold surfaces come together tightly to prevent molten plastic from seeping into undesired areas.
2. Creating Undercuts or Side Features:
Shut-off angles allow for the formation of sidewalls, undercuts, or openings without requiring complex mold mechanisms.
3. Minimizing Flash:
Proper shut-off angles help eliminate or reduce flash (excess plastic) around parting lines, resulting in a cleaner final part.
4. Simplifying Mold Design:
By designing with effective shut-off angles, the need for secondary operations like machining or trimming is minimized, reducing production complexity and cost.
5. Improving Mold Life:
Correct shut-off angles reduce wear on the mold, as there’s a clean seal between surfaces, avoiding unnecessary stress or deformation during ejection.
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Typical Shut-Off Angle Values:
A shut-off angle is typically 3° to 5° to ensure proper sealing and easy part ejection. Smaller angles may lead to poor sealing, while larger angles may not be practical for tight design tolerances.
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Example Applications:
1. Snap-Fit Features:
Shut-off angles are used to create interlocking features in plastic parts like snap-fits.
2. Holes or Slots:
When forming holes or openings in the side walls of a part, shut-off angles allow the mold halves to meet precisely and seal.
In summary, shut-off angles are crucial for ensuring the quality and precision of plastic parts while optimizing mold functionality.
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