Common Problems and Countermeasures of Plastic Granulation Modification Processing(2)

2.The analysis of the finished product processing process

 

Broken strand:

Increase the mesh number or number of screens;

Properly reduce the host speed or increase the feed speed;

Properly reduce the extrusion processing temperature (diehead or other areas).

 

External impurities:

Check whether the equipment corners of mixing and discharging are clean and have impurity mixed;

As far as possible to add less crushing material or artificial crushing material for the initial screening, remove impurities;

Increase mesh number and number of meshes;

Cover as much as possible the hole (cover or net cover) where debris may fall.

 

Internal impurities:

The diehead pressure is too high (including die plug, too much mesh, too low head temperature), resulting in increased reflow, carbonization is brought out into the material strip, under the traction effect, resulting in broken bar;

Extruder partical overheating, resulting in heavier carbonization, carbonized material was brought out to the material strip, under the traction effect, resulting in broken strip;

Screw shearing partical too strong, resulting in material carbonization aggravating, carbonized material was brought out to the material strip, under the traction effect, resulting in broken strip;

Long life of the machine, screw and barrel wear, gap increased, reflux increased, the barrel wall adhesion of the carbonized material increased, with the extrusion time extended, the carbonization is gradually brought out to the material strip, under the traction effect, resulting in broken strip;

Vacuum or natural vent (here including gaskets and dead ends) for a long time do not clean, the carbonized material is brought to the material strip, under the traction effect, resulting in broken strip;

Diehead (here includes the dead corner of the outlet and inlet) is not clean, the carbonized or impurities in the mold were brought to the material strip, under the traction effect, resulting in broken strip;

The time interval of replacing the filter screen is too long, the screen is blocked, the material cannot come out, causing the broken strip.

 

Poor plasticizing of Materials:

The extrusion temperature is low or the screw shearing is too weak, causing the material cannot fully plasticizing, the material lump appears, and under the traction force, the broken strip is caused;

The low melting point additive in the formula system (including EBS or pets, etc.), under the condition of weak screw shearing, causes the poor plasticization, resulting in broken strips.

 

 

Material Physical Changes:

At the same temperature, the fluidity of the blending component exists large difference. because the fluidity does not match or is not completely compatible (including the physical entanglement and the chemical reaction), theoretically speaking, this is called "Phase separation". "Phase separation" in general blending extrusion will not appear, more appear in the injection process, but if the MFR difference is too large, in the screw relative shear weaker premise, may appear broken strip;

Viscosity change of blending components: for the same material, if the MFR is reduced, hardness, rigidity and gap become larger, it is possible that this batch of material molecular weight is larger than before, resulting in a large viscosity; in the original processing temperature and process, resulting in poor plasticizing. At this time, it can be resolved by increasing the extrusion temperature or reduce the host screw speed.

 

The steam or exhaust of the material section is not smooth:

The processing temperature is too high or the screw partical shear is too strong or overheating, resulting in the decomposition of additives, such as some flame retardants. The gas did not timely extracted by the vacuum, and trapped in the material, under the traction effect, resulting in broken strip;

Material moisture is serious, the water steam was not extracted in time through natural exhaust and vacuum exclusion, the vapor trapped in the material, under the traction effect, resulting in broken strip;

Natural exhaust or vacuum exhaust (including plugging, leakage, gasket too high) is not smooth, resulting in air (or gas) trapped in the material strip, under the traction effect, resulting in broken bars.

 

High rigidity material, too cold or too much water, mismatch traction:

While the material rigidity too big, water temperature too low, too much water, the soft material out the diehead and into the water will immediately become very hard, under the effect of traction mismatch, causing broken strip-this phenomenon often appears in PBT or PET compounds fiber, PC compounds fiber, ABS compounds fiber, and other materials that of very fast crystallization or high rigidity. It is more serious especially do experiments with small machines. At this time to improve water temperature, reduce the amount of water, and keep a certain degree of softness of the material that into the granulator can be useful.

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