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Author
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Topic: PE end cut problem
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kbroderick
Senior Member Posts: 5
From:
Registered: Oct 2005
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posted October 08, 2005 01:25 PM
  
My company extrudes medical grade tubing. The issue that we are currently experiencing is clean end cuts on our HDPE and LDPE tubing. The defect is classified as hairs or flashing on the I.D. of the tube and we have tried a multitude of things to eliminate the problem. Has anyone else experienced this and more importantly does anyone know how to eliminate it? I would really appreciate the help.IP: Logged |
Tom C
Moderator Posts: 674
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted October 08, 2005 06:44 PM
More than likely this is due to a residual amount of a prior incompatible resin in the die. The residual resin slowly extrudes out onto the surface of the part. When cut, the thin skim layer or strings of contamination will not cut clean with the base material.Being that you are medical manufacturer I would hope you use better manufacturing practices as I don't want stray peices of plastic breaking off inside my body! Even using a purge resin in the extruder can give you this effect. In the medical extrusions I have been involved in we have always cleaned to bare metal and started from there.
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Best Regards, Tom Cunningham Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
kbroderick
Senior Member Posts: 5
From:
Registered: Oct 2005
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posted October 10, 2005 11:56 AM
quote:
Originally posted by Tom C:
More than likely this is due to a residual amount of a prior incompatible resin in the die. The residual resin slowly extrudes out onto the surface of the part. When cut, the thin skim layer or strings of contamination will not cut clean with the base material.Being that you are medical manufacturer I would hope you use better manufacturing practices as I don't want stray peices of plastic breaking off inside my body! Even using a purge resin in the extruder can give you this effect. In the medical extrusions I have been involved in we have always cleaned to bare metal and started from there.
Tom, thanks for the response. we do complete cleanouts (down to bare metal) prior to each change over. If the material is the exact same and only a tool change is required a clean and polished die and mandrel is built out on the machine. Therefore I don't think that a residual compound in the machine is the problem. We are currently looking at blade thickness on our cutters and blade speed. I personally think it is the base PE resin that is creating this problem. We have spoken to a rep from RDN and he informed us that this problem is common in PE bottle manufacturing processes. If you have any further thoughts please let me know. Thanks again for the response.
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louis33
Senior Member Posts: 142
From:Allentown, PA - USA
Registered: Jun 2001
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posted October 10, 2005 12:12 PM
Try a lubricnt on the blade - Alcohol works. RDN should help you with that as they make a drip divice to bolt on the cutter. Sharp blades and higher blade speeds.louis IP: Logged |
kbroderick
Senior Member Posts: 5
From:
Registered: Oct 2005
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posted October 10, 2005 12:37 PM
quote:
Originally posted by louis33:
Try a lubricnt on the blade - Alcohol works. RDN should help you with that as they make a drip divice to bolt on the cutter. Sharp blades and higher blade speeds.louis
We use alcohol on all PE product we manufacture. But for some reason on these particular part families it doesn't help. Thats the main reason I am thinking base PE resin. One thought that I had was our banbury process. Anyone think that heat settings during babury may change the material to cause this problem? IP: Logged |
Tom C
Moderator Posts: 674
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted October 10, 2005 03:22 PM
Are you blending th base resin with something?
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kbroderick
Senior Member Posts: 5
From:
Registered: Oct 2005
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posted October 14, 2005 02:59 PM
quote:
Originally posted by Tom C:
Are you blending th base resin with something?
Yes Primarily a 20% R/O filler and colorant. But we blend this formula with other base PE resins with no effect on end cuts. IP: Logged |
Tom C
Moderator Posts: 674
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted October 14, 2005 04:42 PM
I read your posts again. I was thinking OD, but you said ID.If you are using compressed air piped through the die to hold open the tube, that air might be cooling the die ID enough to cause flow problems in the tube ID. In filled materials the flow problems might cause seperation of the base resin and the filler. This would cause resin rich areas that might be more difficult to cut, and not well connected to the matrix. Look closely at the tube ID to see if it has a nice surface. Try to see if you can increase the temperature along the die ID wall. That may be easier to say than to do. You can try to lower the air volume. Raising the melt temperature may also help. What type of die is it? Can you relate the strings to features of the die?
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Best Regards,
Tom Cunningham Extrusion Technical Services
www.ExtrusionTechnicalServices.com [This message has been edited by Tom C (edited October 14, 2005).] IP: Logged |
mademan5284
Senior Member Posts: 25
From:Easton, Pa U.S.A.
Registered: Aug 2005
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posted October 20, 2005 04:37 AM
Have you tried a heated cutter bushing, or heating the guide just after the tubing enters cutter. Also what is the the thickness of your wall, I can give you exact thickness of blade and or type to use. Smalleast amount of space without the blade touching cutter bushings is a must. Blade speed of 200 rpm is good for solid profile and upwards from there until around 1000rpm is good for all but the thinnest walls for example .003 or less. Blade changing is also needed. [This message has been edited by mademan5284 (edited October 20, 2005).] IP: Logged |
kbroderick
Senior Member Posts: 5
From:
Registered: Oct 2005
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posted October 29, 2005 09:15 AM
In response to Tom. The "hairs are not in coalition to the die and the air pressure is almost non existant through the mandrel. I did chec the ID of the product and it is smooth.Mademan, the wall of this product family ranges from 0.010 to 0.040 giving the same result on all parts with wall thickness in between. we have thought of a heated blade but not the cutterguides themselfs. As far as the RPM's fo the cutter blades that is what we are going to try next. We recently purchased a new Harrell cutter that allows adjustment in blade speed. All our other cutters are not equipped with that option. Again guys, thanks for the help. Any other ideas let me know.
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Tom C
Moderator Posts: 674
From:Brodheadsville, PA USA
Registered: Jun 2001
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posted October 29, 2005 09:47 AM
This certainly is a brain teaser. I would take a picture of the problem under high magnification to see what shows up. Perhaps you could post pictures at samll and high magnification. Sometimes these types of pictures offer suprising views into the problem. If you need help psoting pictures, email them to my address.
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Best Regards, Tom Cunningham Extrusion Technical Services www.ExtrusionTechnicalServices.com IP: Logged |
alpertl
Senior Member Posts: 46
From:Fremont, CA USA
Registered: May 2002
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posted January 13, 2006 12:48 PM
quote:
Originally posted by kbroderick:
My company extrudes medical grade tubing. The issue that we are currently experiencing is clean end cuts on our HDPE and LDPE tubing. The defect is classified as hairs or flashing on the I.D. of the tube and we have tried a multitude of things to eliminate the problem. Has anyone else experienced this and more importantly does anyone know how to eliminate it? I would really appreciate the help.
This is an old thread, and I hope you have found the root cause of your issue by now. Just in case, I'll throuw in my $.02.... You may want to look at your blade type. Size, thickness, material and surface finish as well as the blade speed of your cutter and your line speed. The blade speed can be either too slow or too fast, depending on the blade configuration used.
If you blade is rather large (or wide)with a low speed and your line speed is high, the cut end on the puller side may be creating pressure on the blade as it pushes it against the exit bushing. IP: Logged |
