（17） Air traps Injection Molding Process Defect Handling Manual (65 types)

Air traps refer to the process of covering the air in the mold cavity before melting the adhesive, which occurs when the air converges from different directions before melting the adhesive, or when air cannot escape from the exhaust hole or the gap of the embedded part. Wind wrap usually occurs in the final filled areas. If the exhaust holes in these areas are too small or do not have exhaust holes, it can cause wind wrap, causing voids or bubbles, short shots, or surface defects within the plastic. In addition, when there is a large difference in the thickness of plastic parts, the molten glue tends to flow towards the thick zone, resulting in a race tracking effect, which is also the main reason for wind blowing,
To eliminate air pockets, the injection speed can be reduced to change the filling mode; Or change the position of the exhaust hole and increase the size of the exhaust hole. "The windage caused by the racing flow effect can be improved by changing the thickness of the plastic part or changing the position of the exhaust hole.". The improvement methods for air bag are described as follows:
(1) Changing the design of plastic parts: Reducing the proportion of meat thickness can reduce the competitive flow effect of melt adhesive.
(2) The mold design should be changed: setting the vent hole in the appropriate position can improve the exhaust. The vent hole is usually located in the final filled area, such as the mold to mold interface, the parting surface, between the embedded parts and the mold wall, the location of the ejector pin, and the mold slider. Redesigning the gate and melt transfer system can change the filling mode so that the final filling area falls at the appropriate vent location.
In addition, it should be ensured that there are sufficiently large exhaust holes to allow air to escape during filling; However, it is also important to be careful that the vent hole is not too large to cause burrs. The recommended vent size is 0.025 cm (0.001 inch) for crystalline plastic and 0.038 cm (0.0015 inch) for amorphous plastic.
(3) Adjust the forming conditions: High ejection velocity can lead to jet flow, resulting in wind wrap. Using a lower ejection velocity allows sufficient time for the air to escape.