Tag Archive for: Air vents defects

Burn marks

How to avoid the Air Traps Defects

As plastic fills the mold cavity, it compresses the air that is in the cavity. The pressure of the air pocket increases until the required pressure is achieved to push air out of the mold vents. If the areas where the air is trapped do not have a vent, the pressure of the air pocket will approach the pressure of the injection pressure causing several quality issues. The high pressure air pocket could cause a short shot and/or a poor weld line, and/or  burn marks or small black spots on the part.

Because air traps defects are seldom thought of in the design process, it is almost routine for plastic molds to have venting put in after the mold is initially sampled!  However, mold flow analysis can be used to pin point the air vents issues in the design phase of the project.  In fact, it can also be used to move air traps that are in an area that is difficult to vent by changing the gate location!  This is one of the benefits of our mold Gate location Optimization Analysis.  Never underestimate the fact that mold venting is crucial to successful molding.

The image below is an air traps defects plot. Notice how the air traps issues (light blue bubbles) correspond to the areas where flow fronts reach the end of fill or where a weld line forms. As you can see in the fill time animation (see below), there are three major weld lines formed.  The first is at the center between the two gates, the second is formed as the flow moves around the hole at the end of the part, the third is formed at the hole on the other end (see Weld Lines defects for image). Notice the collection of air traps in those areas.  You can also see three main end of flow areas.  The first occurs when the flow enters into the circular depressions, the second is at the eight bosses, and the third is at the ribs on the ends of the part.

air trap issues

Short shot issue

With an air trap  plot  from our Part design Analysis, a part designer can specify the venting locations on the part print assuring that his mold will not suffer from quality issues due to air traps.  The plots from the part Gate location Optimization Analysis can also be used to discuss different gating / venting options with your mold manufacturer.

At here. Sincere Tech will offer part design analysis, mold-flow analysis and make completely DFM report for your project, to minimize any possible issue before mold manufacturing, after mold trial we will fix all of mold issue for you as well.

Air trap