Extrusion of Fluoropolymers

Mr.Peter,

We are facing some problems in processing of Flouoro polymers like FEP,ETFE and ECTFE for insulation.

We hve 30mm Rosendahl extruder with SF 3 cross head specially for extrusion of Fluoro polymers. U know tht SF 3 is self centered cross head still we are not getting the proper centering and good surface finishing. For ETFE we are considering DDR as 50 and DRB as 1.

Can you tell me wht factors we hve to monitor to get good results.

Hello again Venkat;

We would first ask you to read the thread titled Problem on Self Centering submitted by Mr. R .G. Sahasrabudhe a few days ago. I believe he is one of your co-workers. That thread is here: www.wirenet.org/forum/viewmessages.cfm?Forum=8&Topic=358

The only difference is the crossheads as he states they are models SF3 & SF10 supplied by SWISSCAB. It is also more correct to refer to these crossheads as "fixed center" rather than "self-centering".

It is almost impossible to resolve your processing problems from the other side of the world because we don't know what you see of these problems and what you don't tell us because you believe it is obvious. That makes it really very hard for us.

For example, are these day 1 problems or are they problems that have surfaced recently?

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Day 1 Problems
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If these are day 1 problems then you should be discussing them with your machine suppliers; Rosendahl and Swisscab. This is because there is something fundamentally wrong that we cannot see from here.

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Recent Problems
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If these are recent problems and the supplied fluorocarbon polymers and color concentrates are not long out of date, then the first item I would look at in regards to surface finish is drying. This is because you are into the monsoon season and I imagine the relative humidity is nearing 100% as you are not that far from the equator. Your polymers and color concentrates must be dry and that doesn't mean running hot air through them in a closed loop. It means running the hot air through them in a closed loop with a properly maintained desiccant dryer so that the moisture in the air is actually removed.

Likewise look at the extruder carefully. Make sure ALL the heating zones on the extruder and crossheads are working properly. Moreover make sure there is no flow of air in the plant at or across the crosshead as that could cause improper cooling or differential cooling of the crosshead. (You would be amazed to see how a small airflow can create extrusion problems.) An easy check for this is to wrap the crosshead, including the neck, with fiberglass wool insulation. ( www.owenscorning.com/around/insulation/insulationhome.asp (Remove the paper backing first.) Wire the insulation in place and see if the surface finish and possibly centering improves. It doesn't matter if the crosshead looks messy for this experiment.

Finally look for any and all changes in the process and tooling if the problems are recent.

With regards to tubing the Tefzel (ETFE - Dupont HT 2185), I suggest you keep within Dupont's recommendations for the draw down ratio (DDR). If the problem has just recently surfaced, don't muddy the issues by introducing new die designs, including the bearing length.

Keep asking yourself this: "If it worked before, what has changed in the machinery, process or materials to give us these problems?"

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There is a chance I will be in your country and not too far away from you on other business in January should you wish to contact me privately. Possibly you and that other company could share our traveling costs.

Sincerely,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com