B - IN THE EXTRUDER BARREL

 1.  High amps, material too fused at vent - generally results in a “hot”    
     extrusion with glossy and wavy I.D. caused by high melt viscosity,      
       or early fusion in barrel (in twin screw).

              (a) Formulation may need a higher external/internal lubricant ratio.
                  Decrease calcium stearate 0.2phr and/or increase wax 0.1-0.2phr.

              (b) Screw temperature may be too high.Screw temperature should be about
                  the same as the metering zone of the barrel for twins, and perhaps 100
                  degrees F lower than metering zone for single screw machines.

              (c) Rear barrel temperatures too high,reduce especially zones 1 & 2;
                  front barrel temperature may be too cold,increase zones 3 & 4.

              (d) Check barrel and screw temperature controllers for accuracy.
       
              (e) As an immediate answer in twins, reduce feed to starve screws,
                  while waiting for temperatures to cool.

2.  High back pressure caused by resistance of material being pushed
            through adapter, head and die.         

              (a) Check adapter,head and die heat zones and controllers:
                  May be too cold. Increase temperatures here by 10-20 degrees F.

              (b) Adapter orifice may be too small; use larger diameter orifice.

              (c) Formulation may be under lubricated, causing frictional drag in die.
                  Increase external lubricant 0.1-0.2phr (especially the polyethylene wax).

              (d) Melt may be too “stiff” coming from screws - increase metering zone
                  and screw temperature.  Check temperature controllers.

3.  Low amps, material too “powdery” at vent.           
             
               (a) Screw not full--increase feeder to flood-feed screws and
                   create more "work" in barrel.

               (b) Fusion occurring too far down the barrel - increase barrel and screw
                   temperatures with higher temperature settings in zone 1 and 2 to
                   cause fusion of powder earlier. 

               (c) Formulation over - lubricated on the external side. 
                   Increase calcium stearate and/or decrease Wax by 0.1-0.2 phr.

               (d) Add 0.8 phr process aid to promote fusion.

4.  Low back pressure.   
            
           
               (a)  Melt viscosity is too low--barrel and screw temperatures too high.
                    Reduce heats and check controllers.

               (b)  Formulation has too much externallubrication; 
                    reduce Wax level 0.1-0.2 phr.
       
               (c)  Orifice in adapter too large, use smaller diameter orifice.   


5.  Fluctuating amps and/or back pressure.           
           
               (a)  Frequent fluctuations indicate a non-homogeneous, non uniform powder
                    blend. Check blend room operation!!

               (b)  A sudden change to a new but steady amp and back pressure
                    level indicates a bulk density change in the powder blend.
                    Check blending and resin: bulk density, particle size,  percent volatility,
                    plasticizer absorption properties.

  6.  Vacuum at vent sucking powder. 
             
             
               (a)  Screws not full (no "seal" between vent and throat)--
                    Increase feed rate to flood screws.

               (b)  Rear barrel zones too cold,increase heat in zones 1 and 2.

               (c)  Formulation may have too much external lubricant, which delays
                    fusion.  Reduce wax 1.1-0.2 phr.
       
               (d)  Add process aid to promote fusion.

         7.  Powdered, or semi-fused material extruding out of vent, with flood feeding.           
             
             
               (a)  Generally a barrel temperature profile out of balance.
                    Rear zone (1&2) temperatures usually need an increase
                    for twin screws, but a decrease for single screws.

               (b)  Crammer RPM too high in single screw,forcing material into barrel
                    faster than it can exit through adapter; slow crammer RPM.