How to Troubleshoot a Blown Film Extrusion

Blown film extrusion makes plastic shopping bags like this one.

The process of extrusion with plastics involves melting raw materials and then shaping it into the desired form. Some products that rely on extrusion include flexible tubing, PVC fencing, window frames and weatherstripping, among others. Blown film extrusion is the process for making such items as plastic shopping bags. When looking at the finished product, you may notice several telltale signs that your blown film extrusion process needs adjustments.

Instructions

1. Check the appearance of your product exterior. If it's bumpy or rough to the touch, you have a symptom called "orange peel" or "applesauce." This can indicate extrusion temperature that is either too high or too low in the die and/or the adapter. Adjust those temperatures accordingly. The extrusion rate may also be too high, so if temperature adjustments do not work, slow down the rate.

2. Look for ridges or lines in your finished product. These can be a sign of melt fracture, which can happen when the extrusion temperature is too low, or when production is happening too quickly. Elevate the temperature and, if that does not work, slow production until the problem disappears.

3. Watch out for a foggy finish on your product. This can also be a result of extrusion temperatures that are too high or low, so you'll want to adjust the temperature accordingly. If there are regular splits that form in your film after extrusion, the temperature can also be the culprit.

References

• BHTool: Optimize your Polymer Extrusion Process by Eliminating Instabilities
• Westlake: Blown Film Troubleshooting Guide
• ExxonMobil Chemical: Producing Quality Polyethylene Blown Film