C - OUT OF THE DIE

 1.  Material lumpy, low gloss (also “surging” in single screw). 
            Low impact, poor acetone test.        

                (a)  Material too cold--not fully fused.
                     Barrel and screw temperatures too low--increase heats in twin screw.

                (b)  Decrease screw temperature in single screw to provide more
                     friction and shear.

                (c)  Formulation may be over-lubricated.
                     Decrease external lubricant (Wax)0.1-0.2 phr.

                (d)  Add, or increase, process aid to promote fusion.
 

 2.  Wavy I.D. (with gloss in single screw, low gloss in twin screw).       
    Possible grey-brown “streaks”on O.D.           
             
             
                 (a)  Material flow unbalanced in twin screw extruders: screw and
                      metering zone barrel temps should be about the same.
                      Generally a little higher heat in both will help smooth out the I.D.

                 (b)  In single screw extruders, reduce heat in front barrel and screw which
                      should create more friction, work, and smoother flow.  Also higher
                      crammer RPM will create more shear.

                 (c)  Slight over lubrication - may require slight reduction in wax level.

 
        3.  Wavy, glossy I.D. in twin screw. 
             
                                   
          (a)  Material too hot entering die--reduce screw and metering zone
                      temperatures (possibly the entire barrel temperature profile
                      should be reduced).

  4.  Rough “orange peel” I.D. or O.D. sometimes starting at spider line -       
      leading to eventual burn.         

                  (a)  Reduce spider and cone heat zones (some heads have air-cooled spider legs).

                  (b)  Formulation may be under-lubricated - increase (.05-.10 phr) low
                       molecular weight polyethylene, the late working lubricant which
                       functions mainly in the head and die.                functions in the head and die.

            
 5.  Uniform yellowing, or discoloration of material.         

                  (a)  Overall temperatures too high--reduce heats and check controllers.

                  (b)  Discoloration combined with “orange peel” roughness and/or
                       high amps indicates under-lubrication. Increase external lubrication.

                  (c)  Check stabilizer use level, was it miss-weighed?

6.  Visible spider lines on I.D. with little or no gloss.         

                  (a)  Spider and die heat zones too cold. Increase heat carefully.

                  (b)  Possibly material too cold entering head and die -
                       increase barrel and screw heat.

 7.  Erratic flow out of die: smooth-to-rough-to-smooth again, with        
     some surging.            
            
            
           (a)  Too much cooling on barrel cooling zones, which cycle on and off,
                       resulting in "temperature shock".Decrease cooling water flow
                       to barrel cooling oil.   
 

        8.  Nonuniform wall thickness around pipe circumference.          

                  (a)  Bushing is not centered. Adjust die bolts for even flow out of die.

        9.  Increasing or decreasing wall thickness.         
             
               
                  (a)  Initially, adjust haul-off speed, then check for feed variations due to
                       bulk density changes, build-up of material on feed screw (static)
                       or bridging in the hopper. 

        Most of the above problems - and possible remedies - in the extruder are
 influenced by the quality of powder blend being fed to the extruder.  Blend
 consistency is MOST important.  Since PVC resin generally comprises 90-
 95% of the formulation, resin molecular weight, molecular weight distribu-
 tion, bulk density, particle size, percent volatility and plasticizer absorption
 properties must be correct for the application - and consistent.  Also, all
 additives - lubricants, stabilizers, etc., - must be of consistent quality. 
 Otherwise, many of the above described remedies will be of little use in
 overcoming these problems.