To eliminate air traps, you can modify the filling pattern by reducing the injection speed, enlarging venting, or placing proper venting in the cavity. In the figure below, an air trap results from race-tracking in a part with a large thickness ratio. Remedies Alter the part design Reduce the thickness ratio. This will minimize the race-tracking effect of polymer melt. Alter the mold design Pay close attention to the proper placement of your vents.
Place vents in the areas that fill last.
Vents are typically positioned at discontinuities of mold material, such as at parting surfaces, between the insert and mold wall, at ejector pins, and at mold slides. Re-design the gate and delivery system. Make sure the vent is large enough so that the air present in the cavity can escape during injection. Be careful, however, that the vent is not so large that it causes flash at the edge of the molding. Reduce the injection speed.