c

p





c

Improper wall thickness

a) Adjust annular gap in the distribution assly. b) Align take off equipment c) Adjust rpm of machine and take off equipment d) Avoid surging of melt in the extruder by balancing temp. profile and rpm of the screw. e) Check heaters on the die

Inside rough surface

a) Adjust temp. profile so as to melt polymer completely b) Avoid melt fracture by increasing die temperatures, lowering shear by reducing screw rpm c) Avoid moisture by pre-drying d) Avoid excessive frictional heat built-up on screw by cooling the screw

Outside rough surface

a) Increase temp. on barrel and die b) Cool the extrudate near die exit so as to avoid excessive swelling of Pipe before ing through sizer c) Avoid melt fracture by increasing die temperature.

Lack of gloss on outside

a) Increase die temperature. surface.

Lack of gloss on inside surface

a) Adjust temp. profile on barrel and die so as to melt the polymer completely

Porosity

a) Avoid moisture by pre-drying b) Avoid moisture and air entrapment by use of vented extruder or vacuum system c) Lower temp . of the rear zone so as to melt the polymer only near the head of the extruder





uurface defects

a) Avoid moisture and air entrapment

Indented pock marks

a) Avoid forced water spraying on the surface of PVC pipe during sizing

Discolored material

a) Lower temp. of barrel and die b) Avoid running at very high or at very low rpm. High rpm increases shear rate while low rpm increases residence time of melt in the extruder c) For larger pipes blow air through spider.

Lumpy surface

a) Extrudate is cold, check barrel temp. and adjust them so as to melt the polymer completely b) Increase rpm & temp. so as to give more shear to compound

Oval pipe

a) Cooling arrangement is not adequate, increase the effectiveness of cooling and sizing b) Reduce distance between Die exit and sizer c) Check alignment of the sizer

Brittle pipes

a) If failure is on weld line, avoid weld line by increasing the temperatures, and adjust rpm of screw (avoiding faster and cold extrusion.) b) Avoid excessive draw down of the pipe c) Avoid using excessive regrind material

Circumferential waviness

a) Avoid surging of melt by and ridge slowering rear zone temp. and adjusting rpm b) Avoid uneven take off speed