Hello,
I managed to run a small blown extrusion line, head diameter 70mm / screw 45mm.
The machine is to be used for extrusion of sleeves from 200 to 500mm wide. Unfortunately, I have a draw resonance problem. I cannot stabilize the balloon.
The head die has a cone that is designed to stabilize the balloon and the air ring characteristic for HDPE heads. (picture attached)
The machine temperatures are set to 140 degrees Celsius from the loading zone to the machine die head.
For the present moment I have only been able to stabilize the balloon for a 200mm wide sleeve, TUR was then 10.43. As soon as I try to blow the balloon to larger sizes the balloon begins to destabilize and there is a resonance phenomenon.
I don't understand what could be the cause of my problems, maybe the die that is designed for HDPE processing is not suitable for PLA?
Regards,
Michael
However is it possible to form a ø300 bubble with ø80 die head? It is not a problem while processing hdpe or ldpe, but the pla is way more stiffer.
Regards,
Michael
Do you have to use PLA? because, a different kind of biopolymer could be easier to process, something that has certain proportion of PBAT or something like that. PLA, as you mentioned, might be too stiff, and grades that are specifically designed for Blown Film Extrusion have to have something that lowers the stiffness of the polymer.
Miguel Angel Romano
Plastic processing specialist.
Chemical Engineer.
7 years as Blown Film Specialist and formulator.
Thank you very much for your answer. I've been working on a blend with PLA for over a year and a half and there are no problems with it.
My other machines have dies from 150-170mm and I am able to get sleeves from 390mm to 750mm. Unfortunately, the only problem has now emerged, with the fi80 head the maximum sleeve I can get is about 250mm. When I increase the size of the balloon, the whole baloon destabilizes.
During blowing, the air bubble is transported to the top, there it is squeezed by the pulling rollers and goes back down destabilizing the balloon even more.
In the next few days I will try to post a video showing my problem.
I don't know why do you want to use PLA as value biodegradable polymer with HDPE? I would prefer to select other polyolefin polymers such as LLDPE, LDPE.
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