Plastic Injection Molding - Part Defects - Flash

Описание: In this #Short we look at the defect called Flash

Today’s defect is Flash. Flash, fundamentally occurs, when there is either tooling damage, or the plastic pressure exceeds the clamping force in that section of the tool. There can be many causes of flash, however, a good molding practice is to always check the surface of your tool and if running a multi gated mold, verify that all pins are moving and/or all drops are allowing plastic to flow. If you have stuck plastic or a gate not shooing, the flash will likely be impossible to correct and may even damage the tool.

On occasions, if you can reduce the viscosity of the plastic, you then also make other pressure reduction adjustments in conjunction to help reduce or eliminate a flash issue.

For example, if we raise the melt temp of the plastic to lower its viscosity, we could then see a reduction in the amount of pressure needed to hit the VPT setpoint, we would then lower the pressure during the packing and holding stages to approximately 50% of the recorded VPT pressure. If this was enough to eliminate screw bounce and achieve the part weight, it can often times, reduce or eliminate flash.

I could probably have a conversation about flash for an hour straight, but in keeping with the them of the channel, we are keeping it at 60 seconds!

The example I referred to was a PBT (Valox) main bezel that gets decorated. This material is prone to flashing that we referrer to as (Angel Hair Flash) due to its thin feather like appearance. We raised the barrel temps to raise the melt and lower the viscosity (from 460f to 510f). It took the transfer pressure down from 1700psi to 950psi (hydraulic) so we could pack it at 500psi instead of the 900psi we had been using.

This completely eliminated the flashing condition! We then read this across to other jobs running the same material with a similar flashing condition.

Happy Molding! May your water always be clean and your dryers keep drying!