If you are a blown film manufacturer, you will understand the importance of maintaining the bubble on your production line. When doing a color or a resin changeover, processors do not like to lose the bubble- as it adds extra time on to production to get the bubble up and running again and it can be frustrating.
Historically, in blown film production it has always been a preference to go from one color to the next WITHOUT having to stop production, and therefore to just allow a color to run i.e. from black to red OR white to yellow, until you get to the desired product. Depending on the color you are trying to get out of, this can take anything from several minutes to several hours. Although the time taken for the color change is not ideal (and produces much resin waste and machine downtime), it is often seen as a better option than the alternative, of stopping and starting a continuous process, possibly several times a day to clean the machine.
We know the importance of reducing downtime on changeovers and we also understand the issues that a processor can face, especially when it comes to something as intricate as blown film manufacturing. Therefore we are able to offer the customer a purge compound that can do a color change on the fly. This allows blown film manufacturers to carry out their color changes without having to stop the production line, it greatly reduces changeover times AND decreases resin waste--for many processors it is like a dream come true.
I have a customer in Mississippi manufacturing plastic bin bags. As custom extruders, they can see anything between 5-10 color changes in a week. One line in particular was often going from Black bag production into Clear bag production. This changeover was typically taking the processor up to 4 hours. As the bags were Low Density Polyethylene, the PE-based blown film grade of purge compound was recommended, which has been known to hold the bubble extremely well in LD applications in particular. The purge was able to follow immediately behind the resin through the barrel, and with no need to change any processing conditions, we were able to transition into purge with the bubble still intact. After just 30 minutes we were able to see NO remaining color in the purge. We then let the clear LDPE follow the purge compound, again the bubble was maintained, and as soon as the clear resin exited the barrel the processor was able to begin collecting useable product. An almost impossible dream of a Black to Clear changeover WITHOUT losing the bubble within less than half an hour was achieved.
A Cost saving analysis was completed by the customer, this is where we calculate the machine running cost (and multiply this by the time taken to purge). We then calculate the cost of resin/purge used (resin/purge cost per pound x pounds of product used in a changeover) and add this to the amount of resin it takes to get to useable product. The total of each step is added to provide the Cost per purge. Below is an example of a CSA from a Blown film manufacturer that reduced changeover times from 4 hours to 0.5 hours.
Here, the total cost saving from using the purge compound came to 77%!
Although the cost of the purge compound is typically a lot higher than the resin cost (in this example almost 6x the cost)- it is extremely important to take into account the quantities being used and the most valuable thing of all to any processer: TIME.
In blown film, production machines are running hundreds of pounds of material per hour, leading to the processor losing thousands of pounds of resin on every changeover. Even if the resin cost is low, as shown above, this adds up to a vast amount, investing in a good purge will drastically reduce that waste, allowing you to not only cover the cost of the purge, but also increase your production capabilities and output.
I personally see this particular grade of purge compound as a huge break-through in blown film manufacturing and would like to see more processors trying it out.
Ready to reduce your production downtime to protect your profits? Learn more about how purging compounds and process efficiency work in tandem.
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