Voids. A void occurs during cooling while the part is inside or outside the mold, usually in thick sections. In thick sections of a part, the center cools slowly and the polymer shrinks more, pulling away from itself to form a bubble.31 mar 2015
What is mold void?
Vacuum voids and sinks are usually caused when there's not enough plastic in the mold, and as the plastic cools, it leaves empty spaces as the plastic shrinks. Where the plastic touches the mold, it cools first, meaning the bubble will not be as visible: this is a void.21 may 2019
How void occurred in extrusion process?
With regard to extrusion, entrapped air in the feed section of the screw and polymer degradation are the main culprits behind voids. In addition to the myriad of extrusion issues, extrusion laminations can have entrapped air bubbles which appear to be voids.3 ene 2012
How do you reduce voids in injection molding?
- Raise the injection pressure to force out trapped air pockets.
- Choose a grade of material with lower viscosity to limit the risk of air bubbles forming.
- Place gates close to the thickest parts of the mold to prevent premature cooling where the material is most vulnerable to voids.
What causes voids in plastic parts?
Causes: Vacuum voids are often caused by uneven solidification between the surface and the inner sections of the prototype. This can be aggravated when the holding pressure is insufficient to condense the molten plastic in the mold (and thereby force out air that would otherwise get trapped).12 jun 2015
How do you prevent air bubbles in injection molding?
Thin down the nominal wall. Core out the thick section, if possible. To solve voids or sinks, try slow fill rates, use of gas counterpressure, or increasing backpressure. Ensure the runner or gate is not freezing too early and that longer hold times will allow more packing during the second stage.31 mar 2015