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Author
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Topic: "Double-Batching" PVC Powder Blends
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2beeps
Junior Member
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posted 07-31-2001 10:27 AM
   
Many have used "double-batching" in PVC powder blending, where twice the additive levels are blended in a high intensity mixer,then dropped to the cooler which contains a second resin charge. I know it's done to increase compound production per unit time, but what if any are the drawbacks to this technique?? Any ideas??Skip  IP: Logged |
DAN CRAWFORD
Junior Member
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posted 08-01-2001 02:43 PM
Skip,
My understanding is that heating the batch, in particular the resin, is to expand the resin particle to trap plastcizer in the resin for melt. I have had straight resin hit my extruders in the past and all I have gotten out the head is something that resembles sand. It seem like this "double batching" would only suspend the non-plastizied resin in the plastistized melt flow. This would be like putting stone dust or other fillers in the batches. I don't see how this would be cost effective. Then again I am not familiar with this method of mixing I assume it is because we run flexable PVC compounds. 
Please feel free to educate me(except my spelling) 
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2beeps
Junior Member
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posted 08-01-2001 04:43 PM
Dan,Considering plasticized PVC blends, I think you are right---the second resin charge in the cooler would not have time-or temp- to absorb plasticizer, and the extra resin would be almost like a filler. I've seen this technique mainly with RIGID PVC compound blending---especially pipe compounds.I know it's a compromise to allow the blending operation to keep up with added extrusion capacity--but does product quality suffer?? That's my main question. Regards,
Skip IP: Logged |
DAN CRAWFORD
Junior Member
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posted 08-02-2001 08:48 AM
Skip,
You would be walking a fine line. To get the raw resin to disperse throughout the heavy mix would require more than one quick spin in the cooling mixer. I think someone is fooling themselves to think time is saved "if" it is being done right. To answer your question about quality: I would need to see the extrudate to be accurate but,,, my opinion would be that the mix would have two different densities of material and if these materials are allowed to free flow from the feed hopper to the feed box of the extruder, the physical tendencies is to seperate. This would cause pockets of raw resin to be encapsulated in the melt flow. The normal reason that fillers like stone dust are less adpt to show this is that there is a large difference in the fines or particle size. In this case(double batching) the particles would be realitively equal only the pasticized particles would be more dense.
That is my opinion but, then again everyone has one IP: Logged |
louis33
Junior Member
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posted 08-07-2001 07:18 PM
SkipI'm not up to speed on PVC Powder compounding, but I can tell you that that is a common practice when using intensive mixers when adding fillers and colors. Especially in the medical business. It adds one less heat history to the majority of the compound which helps to retain the physicals.
And a lot less running around to get the job done!
 I've used ratios as high as four to one and let the masterbatch down either at extrusion or a pelletizing stage. Powder and plasticiser - well thats another story  [This message has been edited by louis33 (edited 08-08-2001).] IP: Logged |
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