Cause Analysis and Solution of Broken Strip in Plastic Granulation

Problem of broken strips

 

1. The reason of filter screen

Too large or a large number of mesh, will cause material transport resistance, resulting in broken strip. At this time, the main engine speed should be reduced or feed speed should be adjusted.

 

2. Impurities in material

External impurities: check the dead angle of the equipment for mixing and feeding, add filter screen to remove the impurities in the material.

Internal impurities: too high diehead pressure (including die clogging, too many filters, too low diehead temperature, etc.) will cause material reflux increase and increase material carbonation, extruder local overheating, and too strong screw shearing will also cause material carbonation resulting in broken strip.

 

3. Long service life of the machine

Long service life of the extruder, the gap of screw and barrel will increase because of wear and tear; vacuum or natural vent (including gasket and dead angle here) is not cleaned for a long time; diehead (including outlet and die angle) is not cleaned; Any of these factors which can cause material carbonization or cause material to stay for a long time will lead to strip breaking.

 

4. The interval between replacing the filter screen is too long

If the mesh is not replaced for too long, the material residue will be cooled and solidified to block the screen, which will also cause the broken strip.

 

5. Poor plasticization of materials

The extrusion temperature is too low or the screw shearing is too weak, the material and the low melting point assistant are not fully plasticized, the broken strip will also occur in the poor plasticizing material during extrusion granulation.

Reasons of the physical properties of raw materials

When the fluidity of the blend is different at the same temperature, the viscosity of the components is different, the broken strip will be caused, which can be solved by increasing the processing temperature and the speed of the main engine.

 

6. Exhaust obstruction

Bad natural exhaust or vacuum exhaust (including blockage, leakage, gasket too high, etc.), resulting in gas (or steam) trapped in the strip, under the action of traction, in the gas accumulation will cause broken strip.

Because of the complexity of the components of the recycled materials, there are also various auxiliaries in the products. In the process, sometimes there will be an auxiliary decomposition, and will release the gas. If these gases are not exhausted in time, and wrapped in the material, it is also prone to break the strip during extrusion.

If the water vapor is not exhausted in time, the vapor will be trapped in the strip, and the broken strip will be caused in granulation.

 

7. The material is rigid, the water is cooled or overwatered, the traction does not match

The material rigidity is too high, the water temperature is too low, the overwater is too much, when traction will cause the stress concentration, the material strip will break.

The material just coming out of the diehead is very soft, and for the rigid material, if putted in the cold water immediately, it will become very hard, and easy to cause broken strip. This phenomenon often occurs in the process of PBT or PET+ glass fiber, PC/PS/ABS+glass fiber, and other material that has high crystallization speed or has large rigidity, especially with small scale extruder machine. In this case, It can be solved by raising the water temperature, reducing the excess water, letting the strip into the granulator to maintain a moderate degree of softness.