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Mold Material 38 MoldMaking Technology August 2015 A venting issue in the mold caused a burn in this automotive center console and increased scrap rate. cavity, or short shots. Enhanced venting materi- als can decrease the required injection pressure by reducing back pressure, and can also help to vent blind holes and eliminate gas traps by reducing fill time. Pulling a vacuum during injec- tion will also reduce back pressure and fill time, while reverse blowing during ejection breaks any vacuum and eases the ejection. In some cases, it also is possible to reduce resin temperatures but maintain good fill. Despite these advantages offered by enhanced venting materials, the revolution I expected 20 years ago never came. Why not? I pulled out a few plastic mold design and engineering handbooks to find references to venting. Each one said basically the same thing: Proper venting is crucial, and lack of proper vent- ing can cause short shots, burns, poor weld lines, splay, internal stress in parts and inefficient cycle times. All of these problems can be solved with enhanced venting materials. Consider these real- world examples: • The mold for an automobile door panel wasn't FIGURE 3 A retroft of the mold with an enhanced venting material resolved the venting issue and cost around $3,000.