The plastic PVC has the merits of the plastics. The thermal stability is poor. When the temperature is too high or the shear stress of the screw is too big,PVC is easily decomposed as the thermosensitive property .For reason given above, the PVC material plasticizing temperature in the barrel is 165~190℃.The nozzle temperature should be between 170~180℃.Different diameter of the screws have the different screw speed .
Diameter <60mm,speed is 50-70rpm.
Diameter>70mm,speed is 20-50rpm.
All of these are the most suitable parameters to avoid the big shear stress ,and the PVC decomposing.The decomposed PVC will release corrosive acids HD,corroding the screw and the barrel's inwall .
The retention time should be limited to 5 minutes specially when the temperature is 2100℃.
The stress on the screw usually is 5bar,although the increased stress is helpful to the venting and color mixing,the stress is as small as possible .
What's more,The barrel's thoroughly cleaning is important,because of the lower thermal stability.Some plastic with the high thermal stability and no chemical bond with PVC,such as LDPE, PP ,PMMA.If the PVC is mixed with the U-PVC and POMT,there will be fierce chemical bond and the barrel will be damaged heavily.
SINO PIPE FITTING Co,LTD branch from SINO GROUP is specialized in design and manufacture various types of PVC,PPR,PP,PE fitting system moulds .There are four solutions.
Unscrewing ejection system solution
Collapsible core system solution with min,ø 32mm
Curve sliding core system solution
Insert interchangeable fitting system solution
Tailor -made irregular shape moulding solution
All these solutions are depended on the features of the plastic parts .If you have any questions ,please contact me , Miss MAY!
E-mail:sino1509@sinomould.com
MSN:sinomould -16@hotmail.com
