Kinds of Entrances
Spherical Pin Point Entrances are widely utilized for automated molding due to the simplicity of demolding. The entrance should have sharpened edges at the runner and flared at the components to encourage separation at the runner/gate interface, rather than affecting the components’ top layer. Most plastic molds used for PE employ this style of entrance.
Sprue or Straight Entrances are used with single impression molds, typically for large-sized, thick-walled components. Here, tension management is not required, and the entrance can be enlarged to ensure ease of filling and packing to prevent sinking.
Entrances are also referred to by their position within the mold, such as:
- Side Gating: Occurs at the wall of the components. It is generally used with components that are manually finished.
- Tab Gating: This type is used where it is desirable to remove entrance flaws from the components. The entrance is located on a tab connected to the component, which is removed during polishing.
- Submarine (Tunnel) Gating: This is particularly suited for automated demolding, as the components automatically delegate while being ejected from the plastic mold.
- Ring and Diaphragm Entrances: These are used to create round components with excellent concentricity and no knit lines. With a ring entrance, the punch can be fastened in each mold half, preventing shifting.
- Burr Entrances: These are used to create thin, flat components with minimal built-in stresses and warping. They combine rapid fill and quick entrance seal time.
Entrance Measurements
Small entrances will lead to higher injection melt temperatures and pressures. Large entrances will increase the time needed to seal the entrance region, extending cycle time, and can invite non-uniform filling in multi-cavity molds.
As a general guideline, the entrance area should not be less than 1.26 mm, and the maximum diameter or size of the entrance should not exceed half the thickness of the component at the entrance point. Entrance lands are usually about half of the entrance diameter. For a circular entrance, it should be about 0.76 – 1.1 mm in the case of a square gate.