By Shell Polymers on Jan 15, 2021
From using polymer processing aids to upgrading to the latest multi-layer film equipment, unlocking a competitive advantage as a PE film producer can take a variety of forms.
These Polymer Pioneers are:
- Dan Falla, Senior Technical Service Engineer | Film
- Shaun Pirtle, Senior Technical Service Engineer & Competency Advisor
- Adam Mix, Senior Applications Technologist – Film
At a time when the need to improve competitiveness has never been greater, Shell Polymers is dedicated to providing high-value tips that can help converters unlock business improvements in PE blown film extrusion operations.
Blown Film Extrusion: 5 Expert Insights
1. Install Screen Packs to Improve Productivity
Installing screen packs has the potential to greatly improve productivity. Although some converters avoid them due to concerns that they can increase back pressure and cause gels, they help fulfill a number of important functions that can unlock major performance improvements.
Shaun Pirtle comments, “A screen pack has many functions in an extrusion line. First, it acts as a filter and prevents large gels and contaminants such as sand, dirt, and metal from entering the die, where they might scratch and damage the finely polished surfaces and likely become stuck. Second, the screen pack also functions to help in mixing the polymer melt and reducing the ΔT across the melt flow, which helps in thickness control.”
While screen packs provide multiple productivity-boosting benefits, operators should be aware that screen packs will build up back pressure slowly over time as contaminants collect on the screen. If the screen experiences an unexpected drop in back pressure (usually below the initial back pressure of the fresh screen pack), this is a sign that it has broken. Maintenance teams should immediately replace the screen pack, since it is no longer preventing the contaminants from getting into the die.
2. Start Up Slower to Avoid Screen Pack Breaks
As mentioned in the previous section, screen packs have the potential to help PE blown film extrusion producers increase productivity. But, they are also prone to breaking if they experience unexpected drops in pressure. According to Adam Mix, he’s seen this issue fairly often, which prompts him to conduct root cause analyses to understand what is happening.
He elaborates, “Screen pack breaks occur when there is high back pressure and happens most often when starting up a cool extruder before the resin has reached a high enough temperature to flow easily. In essence, screen pack breaks usually occur because the operators are too eager to get back online and start up production quicker than is best practice.”
He also recommends looking at how the screen packs are installed. Screen packs need to be supported from the breaker plate (downstream) side of the screen pack. Symmetrical screen packs that are welded together often provide the best performance.
3. Use Polymer Processing Aids to Enhance Product Quality
In general, converters may be reluctant to add a polymer processing aid (PPA) because they believe it will reduce their profitability. When in reality, PPAs have the potential to unlock value in a variety of ways and have a major impact on an extrusion line’s product quality and output and, therefore, its profits.
“PPAs bring a wide variety of benefits to an extrusion operation.” Dan Falla explains, “They can enhance product quality because they help prevent melt fracture, improving the film’s surface appearance. PPAs also enable narrow die gaps to be used, which result in films with increased physical strength.”
In addition to positively impacting product quality, PPAs also contribute to reduced die lip buildup, which means less time required for die cleaning, fewer surface imperfections, and less scrap. They can help increase output by reducing the back pressure and the motor-load drop, and increasing the extruder screw speed.
4. Identify The Optimum Speed For Your Line
According to Dan Falla, “Ideally, the line should be running at a speed at which you are able to control many different variables, including melt and extrusion temperatures, resin freeze point, clearance past screw flights, efficiency of the air ring, temperature of the cooling air, and the use of internal bubble cooling.
Once converters have identified the ideal parameters, Falla suggests that operators carefully document them. This helps to develop a recipe for that film product to ensure that they can get back to those conditions quickly next time they run that film.
5. Replace the Air Board with Carbon-Fiber Rollers
Based on his experience, Adam Mix recommends considering replacing the air board in the collapsing frame of a blown film line with carbon-fiber rolls.
“Air boards are probably the most expensive bubble-collapsing method and although they offer some important advantages, including enhanced cooling, they are prone to quality issues and are not easy to repair.” Adam continues, “Throughout my career, I’ve worked at facilities that used a lot of air boards and air holes would plug frequently, which would cause scratches in soft sealant blown films.”
When that happens, companies usually have to repair the whole board, which is not a quick process as it requires lifting the equipment out and lowering in a new one. Compare that with a bad roller, which could be identified and replaced quickly and with less spend.
There is a strong need for educational materials across the plastics sector. Especially as many highly skilled and experienced operators are preparing to retire and the next-generation of plastics professionals plays a more active role in the industry. To help ensure that the skill level of the workforce remains high, Shell Polymers is committed to creating a stream of informational resources across injection molding, blow molding, polyethylene film, pipe, and rotomolding to help transfer knowledge and best practices.