What Quality Problems for the Common Plastic Pipe (PVC, PP and PE pipe)
Extrusion in the Production?
1, Big tolerance in the wall thickness dimensions of the pipe circumferential cross-section.


Poor concentricity accuracy of the mouth die and mandrel assembly in the forming die, so
that the melt flow gap between the two parts is not uniform.
for this case, you should
adjust the concentricity accuracy of the two parts.
Pipe extrusion production work for a period of time after the appearance of the
circumferential cross-sectional wall thickness error exceeds the poor phenomenon. This is
because The adjusting screw was loose for adjusting the gap between the die and the
mandrel, you should tighten the screws.
2, There is a big wall thickness dimension tolerance in the longitudinal cross-section of the pipe.


The running traction speed of the pipe billet is unstable, the transmission system of tractor
should be checked to ensure it is smooth operation.
The barrel process temperature fluctuates is big, resulting in materials melt unstability , the
screw rod speed is unstable also makes the extrusion materials melt can’t keep same, at last,
the longitudinal wall thickness of the pipe is uneven. Process temperature fluctuations is the
impact of temperature control heating system, screw speed instability is the impact of power
supply and transmission system, it should be overhauled.
3, The pipe is brittle.





The quality of raw material plasticization does not meet the process requirements (including
uneven plasticization of raw materials), and the melt temperature after plasticization of raw
materials is low. Should be appropriate to improve the plasticizing temperature of raw
materials (i.e. to improve the barrel temperature), if necessary, should replace the screw.
There is too much moisture or volatiles in the raw material, the raw material should be dried
before production.
The molding compression ratio is small, should be appropriate to improve the mold
compression ratio of the melt molding.
The size of the flat section between the mouth mold and the mandrel is too small so that the
pipe billet is formed with a more obvious longitudinal melt fusion line, this reduced the
strength of the pipe, and the tooling should be modified again.
The amount of filler material in the raw material is too high, this is a reason for making the
pipe brittle, should change the raw material formula.
4, The outer surface of the pipe is rough and lustreless.


The temperature control of the die part in the forming mold is unreasonable, and the process
temperature is too high or too low will affect the outer surface quality of the tube. The
temperature of the tooling should be adjusted properly.
The inner surface of the mold is rough or has residual material. The mold should be
disassembled in time and the working face of the die should be polished.
5, The inner surface of the tube is rough.





The length of the straight part of the mandrel in the forming mold is insufficient or the
temperature is on the low side. The structure of the die should be improved and the size of
the flat section should be extended.
The temperature of the screw is too high, so it should be cooled down properly.. When
extruding PVC material, the temperature of the screw cooling with heat-conducting oil
should be controlled at about 90°C.
The compression ratio of the die is relatively small, so that the inner surface of the pipe has a
longitudinal melt bonding line. The die structure should be improved and the compression
ratio should be increased.
The mandrel temperature of the large size die should be controlled at about 150°C (when
using PVC raw material), which can improve the forming quality of the inner surface of the
pipe.
It should be noted that the high content of moisture or volatile matter in the raw materials
will also affect the inner surface quality of the pipe. The raw materials should be dried if
necessary.
6, Small black or white dots and fish eyes on the surface of the tube.



There are too many Impurities in the raw material. A strainer should be added in front of the
machine barrel. If a strainer is fitted, it is possible that the strainer is damaged and should be
replaced.
There is a stagnant material area in the forming mold, a small amount of raw material
decomposition. Should repair the mould, remove the residual material.
There are fisheyes or small amounts of low molecular weight compounds in the raw material
that cannot be easily plasticised. The raw material should be replaced if necessary.
7, There are streaks or scratches on the surface of the pipe.


Scratches or hanging material on the surface of the mouth mould in the forming mould. The
working surface of the mouth mould should be repaired and the residual material removed.
The small round holes of the vacuum sizing sleeve are not reasonably distributed or the
aperture specifications are not uniform, and tiny streaks appear, the arrangement of the
vacuum holes of the sizing sleeve should be improved.
Page:of 7
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