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| Author | Topic: custom sheet extrusion |
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zuelly Member Posts: 2 |
posted September 28, 2003 03:54 AM
   
I work for a plastic extrusion company and we are having a few problems with the extusion process. For one, it is the pits in the sheet that appears in the sheet. What is this caused from. Second, drying time of materials and distance from actual production line. Third,heat profile for the barrel temperatures. Material being processed is an acrylic material co-extrude over ABS. I would appreciate any help. Thanks IP: Logged |
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Steve H Moderator Posts: 265 |
posted September 28, 2003 04:21 AM
What drying are you applying to the material? could be slightly too damp still. Are you blending regrind? dust etc on reclaim can cause the kind of pitting you appear to be talking about. Another posibility is the colorant being added to your sheet, carbon black can suck in moisture and cause pitting in sheet. What L/D is your extruder, what screw speed, barrel/adaptor/die temps are you setting, what melt temp are you getting? Steve H IP: Logged |
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zuelly Member Posts: 2 |
posted September 28, 2003 06:39 AM
We are drying our ABS material @180 degrees for at least 4 hrs at original start-up, Yes we are blending a small percentage of regrind material(10%). Color is being added in base layer and cap layer also. Cap layer which is an acrylic material, we are drying @ 180 degrees for at least 4 hrs at original start-up. IP: Logged |
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Steve H Moderator Posts: 265 |
posted September 28, 2003 05:35 PM
The problem could be caused by inadequet drying of the PC layer,or the PC/ABS regrind. Try drying the regrind at 212F(100C). Is your machine hopper heated? and how long is the residence time of the material in the hopper- if it is longer than an hour, you might need to consider purging the top of the machine hopper with Nitrogen (dry and inert) or heating the machine hopper. Steve H IP: Logged |
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Steve H Moderator Posts: 265 |
posted September 28, 2003 05:37 PM
The problem could be caused by inadequet drying of the PC layer,or the PC/ABS regrind. Try drying the regrind at 212F(100C). Is your machine hopper heated? and how long is the residence time of the material in the hopper- if it is longer than an hour, you might need to consider purging the top of the machine hopper with Nitrogen (dry and inert) or heating the machine hopper. Steve H IP: Logged |
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garyproform Member Posts: 2 |
posted November 11, 2003 06:20 PM
hi i have coextruded acrylic over abs 1: are you using a vented barrel 2: the pits could be from your roll temp profile ( i had the same problem ) 3: r u using a up stack or down stack? IP: Logged |
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Steve H Moderator Posts: 265 |
posted November 12, 2003 10:17 PM
G'day Gary Welcome to the single screw extrusion forum, great to see another kiwi here If the chill roll temps are the cause of these marks, the sheet between die lip and the first nip will be unblemished and the dimpling will only appear after the sheet contacts the rolls Steve H IP: Logged |
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garyproform Member Posts: 2 |
posted November 13, 2003 02:39 PM
Hi there steve tony is great and the company doing very well also.thanks for the welcome. the pitting problem i was having was due to moisture. but we have overcome this. we don`t dry our abs or acrylic instead we use a vacume unit that pulls around 25 mercs this draws all the moisture and contaminents out through the vented barrel.have you tryed this methed before? IP: Logged |
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Steve H Moderator Posts: 265 |
posted November 15, 2003 03:11 PM
Tried it on ABS and had major problems with vent bleed (27LD extruder, with major balance problems between the first and second stages). Using venting on a suitably designed machine for ABS should work fine, I've never played with Acrylic, I don't like the the idea for Apet. Steve IP: Logged |
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