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Frozen Layer,Gas Trap,

Edit: ABIS Mold Technology Co.,Ltd    Date: Apr 21, 2017
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Frozen Layer

During mold filling, as molten plastic comes in contact with the perimeter of any cooled channel (sprue, runner, gate and part forming cavity) a frozen layer will develop.  An initial frozen skin will develop nearly instantly and its thickness will dynamically change throughout the mold filling and packing portions of the molding cycle.  During mold filling, the thickness is significantly influenced by shear rate and will influence the filling pressure.

Fountain Flow

Gas Trap

Gas traps result when the air inside a part forming cavity has nowhere to escape as the molten polymer fills the cavity.  The trapped air can create both cosmetic and mechanical flaws in the molded part. Compression of the trapped air by the high pressure of the injection process can cause a significant temperature rise that can easily burn the surrounding polymer and even damage the mold steel.  Gas traps can generally be avoided by proper gate positioning, allowing the air to exist through vents along the parting line of the mold.  If venting along the normal parting line is not possible, vacuum venting or special internal cavity venting may be attempted.

 

gas trapgas trap




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