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| Author | Topic: why different barrel temp. |
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slkoli Senior Member Posts: 12 |
posted November 02, 2007 06:33 AM
  
why there is different barrel temperature for producing pvc sheets & pvc pipes i.e for producing pvc sheets we keep rear barrel temp. lower than the front barrel whereas in producing pvc pipes we keep rear barrel temp. higher than the front barrel? IP: Logged |
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2beeps Moderator Posts: 121 |
posted November 06, 2007 04:34 PM
The formulations for rigid PVC sheet and PVC pipe are quite different: Pipe formulations are usually based on a med.-hi mol wgt. K-65-67 PVC resin, with a lean additive package that might contain only 0.4phr tin stabilizer,1,2phr wax,0.4phr Ca stearate,1.0phrTiO2,4.0PHR CaCO3. This formulation does not fuse(melt) quickly, and higher rear zone heats help to partially fuse (cheesy state at vent) mateial at high output rates. Sheet formulations (especially clears) are usually based on lower K-value--K-58-60--PVC resins, and also contain acrylic process aids and impact modifying resins, and are faster fusing(melting) formulations--hence do not need the higher rear zone heats to acheive proper degree of fusion at the vent. Oftentimes, the screw designs for sheet will tend to promote a lttle more shear than pipe screws-- IP: Logged |
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