Solving Static Problem in PET Plastic Thermoforming Application

PET plastic entering thermoforming machine to make cups

The image above shows a PET plastic sheet which is fed into a thermoforming machine. During thermoforming the plastic is made into drinking cups.  But, if the plastic enters the thermoforming machine with static present, the forming process cannot occur properly which results in defects.

The company in charge of thermoforming these cups reached out to the Application Engineering department at EXAIR in search of a solution to their problem. They had considered using Ion Bars, but were unsure if Ion Bars were the right solution.  So, we examined the process and the variables at play to determine the best path forward to remove this static.

The static in this application was present throughout the travel of the plastic sheet into the thermoforming machine. At EXAIR we always recommend to install any static eliminating solution at the last possible point before the static is causing a process disturbance, to ensure no static is regenerated.  Yes, a static charge has the potential to regenerate with friction, spearation or even simple contact with another surface. In the above example separation from the roll and friction upon the additional rollers could be a source of static. This meant finding a way to eliminate the static just prior to the sheet entering the thermoforming machine.

As it turns out, the thermoforming in this application can occur between 180-260°F, and this heat permeates from the machine to the area immediately outside of the plastic feed entrance. So, placing Ion Bars just outside of the machine, while potentially possible, would place them near temperatures at the high end of their operating temperature limits (maximum temperature for an EXAIR Ion Bar is 165°F).

However, just a couple of feet away from the machine this temperature dissipates significantly. So, if we could find a way to mount our solution 2-3 feet away and effectively eliminate static, we would have a viable solution.

That solution came in the form of Super Ion Air Knives. The Super Ion Air Knives provide the same static eliminating capabilities of an Ion Bar, but with an added benefit of transferring the static eliminating ions via a smooth and laminar air profile.  This allows for us to mount the Super Ion Air Knives a few feet away from the machine entrance, but to still effectively eliminate static.  At a distance of 12” away, the Super Ion Air Knife can eliminate a 5kV static charge in 0.18 seconds at an operating pressure of 80 PSIG, and in 0.60 seconds at an operating pressure of 5 PSIG.

Based on the width of 486mm, this customer opted for (2) 18” Super Ion Air Knives, model 111018, and (1) 230VAC power supply with (2) outlets, model 7907. By installing one Super Ion Air Knife on top of the plastic sheet, and one on the bottom, the static problem in this application is solved.

If you have an application in need of a static solution, contact an EXAIR Application Engineer. We’re here to help.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR.com

Cooling Efficiently

Last week, I had the opportunity to work with a customer who was trying to cool a thermoformed film from 85° C (185° F)  down to room temperature, 21° C (69.8° F) or low enough for the package to be handled by an operator. This container was 270 mm X 170 mm X 100 mm (10.63″ x 6.69″ x 3.94″)

 

In applications like this, the customer often calls in with the idea of using a Vortex Tube to produce the cold air.  There are two reasons to use a different product than a vortex tube in this application. First, a vortex tube is only going to cool a small area, so to cool anything this size would take several vortex tubes.  Second, the cold air is going to mix with the ambient air very quickly. When the ambient air mixes with the cold air from the vortex tube, the air will lose the cold temperature generated by the vortex tube. To counter act this mixing, we have had customers create an insulated container to hold cold air from a vortex tube close to a product, similar to a cooling tunnel. This works in some applications, but my customer had a continuously moving line. He did not have time to stop the line and install insulation around each product.  He also didn’t have the length of conveyor needed to put a cooling tunnel over the line.

Super Air Knife Promo

Instead of using the vortex tube, I suggested that he use a 12” (305 mm) Super Air Knife to cool the thermoformed container. The 12” Super Air Knife moves significantly more air than a vortex tube over the surface of the part. Thanks to the 40:1 amplification ration of the Super Air Knife, it creates more cooling to the product and use less compressed air than a series of Vortex Tubes.  By mixing a large volume of free ambient air, that is the same temperature he needs to cool the part to, and a small amount of compressed air over the product they can easily cool their part to close to ambient so the operator can handle the part. The best benefit for this customer was they would not need change their manufacturing line.  The air knife is the best choice when cooling a very hot, fairly flat, large surface part to a temperature close to ambient. If you need to cool a product to a temperature lower than room temperature, then a vortex tube would be a great product to do the job.

Dave Woerner
Application Engineer
DaveWoerner@EXAIR.com
@EXAIR_DW

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