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Author
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Topic: foam-core pipes
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Ariana
Member Posts: 4
From:Portugal
Registered: Jan 2006
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posted January 26, 2006 12:38 PM
   
Hi, I'm working on a foam core pipe, with 140 mm diameter. Outer layers in rigid PVC and middle in PVC foam using a blowing agent. My problem is on how mutch to use and how does that effect the density of the foam in the end. I´m using a k57 resin, one pack, CaCO3 and a processing aid.
I know the effect of screw rpm´s on melt temperature and foam density. So my main question is the blowing agent. How mutch will it effect on the density is I put more or less.
Anyone have an idea?
ThanksIP: Logged |
2beeps
Moderator Posts: 104
From:Silver City, NM, USA
Registered: Jun 2001
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posted January 28, 2006 10:55 AM
Ariana,For more detailed info and help, contact Reedy International --specialists in blowing agents. Most common blowing agent-for rigid PVC- is azodicarbonamide, which emits about 225cc's gas per gram at STP conditions(standard temp/pressure), and decomposition is around 400F, with some versions activated to blow in the 385-390F range of a PVC pipe melt via twin screw extrusion. Therefore a typical 1-2phr level,if changed by 0.5 phr or so can have a significant effect on foam density,plus or minus.
One question----isn't a K-57 resin a little on the low side?? Most PVC pipe --even foam core--uses K65 or so,for end use strength properties. Cheers, Skip IP: Logged |
Ariana
Member Posts: 4
From:Portugal
Registered: Jan 2006
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posted February 01, 2006 03:56 AM
Well from what I know and have read, with k57 you can get a lower density compared to others. Of course I´m talking about the foam core of the pipe. For rigid (compact) PVC the resin usually has 67/68. The strength of the pipe is given by the inner and outer layer in compact pvc, mostly the inner layer. The main objective is to achieve a final density of 1000 g/dm3, cause at this point you are having a material saving of aproximately 30% compared to compact. Costs savings can be further increased by incorporating regrind in the foam layer.
With k65 that is not possible, the density will be singnificantly higher.
But I guess it also depends on the final use of the pipe. Allthough in general I think everyone is using it to replace the convencional compact sewer pipes.
With the 200 and 160 pipe diamters I was using aproximately 0.25 - 0.35 and got excelent results. But with the 140 I'm still not satisfied with the final density. But considering I've made some modifications on the compound, being the most significant one the adding of more regrind, I guess I'll just have to run more tests and perfect the compound.
Anyway thanks for help  IP: Logged |
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