common problems and countermeasures in the granulation processing of modified plastics, how much do you know? Part 1
1. The original defect caused by the broken strip
Increase the mesh or number of filters;
Appropriately reduce the speed of the host or increase the speed of feeding;
Appropriately reduce the extrusion processing temperature (head or other areas).
2. External impurities
Check whether the dead corners of the mixing and unloading equipment are cleaned and whether impurities are mixed in;
Add as little crushed material as possible or manually screen the crushed material to remove impurities;
Increase the mesh and the number of filters;
Cover the holes (solid cover or mesh cover) where debris may fall.
3. Internal impurities
The pressure of the machine head is too high (including clogged die, too much filter screen, and the temperature of the machine head is too low, etc.), which causes an increase in backflow and leads to heavier carbonization. The carbonized material is taken out into the material strip, causing a broken strip under the action of traction;
The local overheating of the extruder caused the carbonization to increase, and the carbonized material was taken out to the material strip, which caused a broken strip under the action of traction;
The shearing of the screw is too strong, which causes the local carbonization of the material to increase, and the carbonized material is taken out to the strip, which causes a broken strip under the action of traction;
The machine has a long service life, the screw and barrel are worn, the gap is increased, the backflow is increased, and the carbonized material adhered to the barrel wall increases. With the extension of the extrusion time, the carbonized material is gradually taken out to the material strip, causing a broken strip under the action of traction ;
Vacuum or natural exhaust ports (including gaskets and dead corners) are not cleaned for a long time, and the existing carbonized materials are brought to the material strip, which causes broken strips under the action of traction;
The die of the machine head (here including the discharge port and the internal dead corner of the machine head) has not been cleaned up, and the carbur or impurities contained in the die are brought to the material bar, which causes a broken bar under the action of traction;
The time interval for replacing the filter screen is too long, the filter screen is blocked, and the material cannot come out, resulting in broken bars.
4. Poor plasticization of materials
The extrusion temperature is low or the screw shear is too weak, the material is not fully plasticized, and there are pimples, which will cause broken bars under the action of traction;
Low melting point additives (including EBS or PETS, etc.) in the formulation system cause poor plasticization and breakage under the premise that the screw shear is weak or the gap between the screw and the barrel is increased and the shear is weak.
5. Changes in raw material properties
Blended components at the same temperature, the fluidity is too different, because the fluidity does not match or is not completely compatible (including physical entanglement and chemical reaction), theoretically this is called "phase separation", "phase separation" Generally, it does not occur in blending extrusion, and it mostly occurs in the injection molding process. However, if the MFR difference is too large, broken bars may occur under the premise that the screw relative shear is weak;
Viscosity changes of blended components: For the same material, if the MFR decreases, the hardness, rigidity and notch become larger, it is possible that the molecular weight of the batch is larger than before, causing the viscosity to become larger at the original processing temperature Under the action of the process, it causes poor plasticization. At this time, it can be solved by increasing the extrusion temperature or reducing the screw speed of the host machine.
6. The strip is trapped in steam or exhaust is not smooth
The processing temperature is too high or the local shear of the screw is too strong or the screw is locally overheated, which causes the decomposition of certain additives such as flame retardants and releases the gas. The gas is not evacuated in time due to the vacuum, and the gas is trapped in the strip under the action of traction , Causing broken bars;
The material is seriously damp, the processed water vapor has not been exhausted by natural exhaust and vacuum in time, the vapor body is trapped in the material strip, and the strip is broken under the action of traction;
The natural exhaust or vacuum exhaust is not smooth (including blockage, air leakage, too high gasket, etc.), which causes gas (or steam) to be trapped in the material strip, and under the action of traction, it causes a broken strip.
7. The material has high rigidity, water cooling or excessive water, and the traction does not match
The rigidity of the material is too high, the water temperature is too low, too much water, the discharge of the machine head is very soft, and the water immediately becomes very hard. Under the effect of the mismatch of the traction force, it causes a broken strip-this phenomenon often occurs in PBT or PET plus fiber, PC plus fiber, AS plus fiber, ABS plus fiber and other materials with very fast crystallization speed or very high rigidity, especially the small machine is more serious to experiment, at this time increase the water temperature, reduce the amount of excess water, let the cut The pellet of the pellet machine can maintain a certain degree of softness, which can be solved.