I. Black spot problem

The black spot problem is the most common problem in the production of recycled materials, for light-colored products, because of the existence of black spots, affecting its use. Raw material itself black spot problem we do not discuss, in addition to the raw material itself, generally cause the product black spot more reasons are as follows.

1、Screw localized overheating, shear too strong

Screw local overheating and shear too strong will cause the local temperature of the material is too high, resulting in serious carbonization of the material, carbide is brought to the material strip, the formation of black spots.

2, the head pressure is too large (including clogging, screen more, low head temperature, etc.)

Head pressure is high, it will cause the head material reflux aggravation, serious cases will lead to head material carbonization, the formation of black spots.

3, the machine is old, screw and sleeve clearance increases

With the machine used for a long time, the gap between the screw and the sleeve will increase, a large amount of material will remain in the gap for a long time, carbonization occurs, the formation of black spots.

4、Natural exhaust port and vacuum exhaust port not cleaned for a long time

In the production process, the exhaust port gradually form a pile of materials, the pile of materials will be slowly carbonized, in the subsequent extrusion pelletizing is brought to the material strip, the formation of black spots.

5、Mouth mold (including the discharge port and internal dead space) cleaning is not clean

If the discharge port is not smooth enough, there are shallow grooves and pits, etc., as well as part of the threaded original damage (lack of corners, wear and tear to form a dead end) will cause the accumulation of materials and then carbonized, forming black spots.

6, the external environment or man-made impurities mixed.

To pay attention to the production environment and operating procedures to avoid foreign impurities mixed into the raw materials and finished products.

Second, the problem of broken bars

1, the reason for the screen

The mesh size of the screen is too large or the number is too large, which will trigger the resistance of material transportation, resulting in broken bars. At this time should be appropriate to reduce the host speed or adjust the feeding speed.

2、Materials containing impurities

External impurities: Check whether there are impurities mixed in the dead center of the equipment in each link of mixing and discharging, and increase the screen to remove the impurities mixed in the material.

Internal impurities: head pressure is too high (including the mouth of the mold clogging, too much screen, head temperature is too low, etc.), will cause the material to increase the reflux and aggravate the carbonization of the material, the extruder is locally overheated, the screw shear is too strong will cause carbonization of the material resulting in the occurrence of broken strips.

3, long service life of the machine

Extruder service life, screw and barrel will be due to wear and tear and increased clearance; vacuum or natural exhaust port (including gaskets and dead space) long time not cleaned up; the head mouth mold (including the discharge port and the dead space inside the head) is not cleaned up; these factors that can cause the material carbonization or carbonization of the material for a long time will cause the occurrence of pelleting broken bars.

4, replace the time interval of the screen is too long

If the replacement of the screen, too long, the material residue is cooled and cured blocking the screen, will also cause broken bars.

5, poor material plasticization

Extrusion temperature is low or screw shear is too weak, the material and low melting point additives are not fully plasticized, in the extrusion granulation will also occur in the poor plasticization of the material at the broken bar.

6, the physical properties of raw materials

Mixed components at the same temperature, there are large differences in mobility, in the extrusion back due to the viscosity of the two components are different, resulting in broken bars, which can be resolved by raising the processing temperature and increase the host speed.

7, the material strip trapped steam or exhaust is not smooth

Natural exhaust or vacuum exhaust is not smooth (including clogging, leakage, gaskets too high), resulting in gas (or steam) trapped in the material strip, under the action of traction, in the gas gathered at the strip will cause breakage.

Recycled materials because of the complexity of the components, there will be a variety of additives in the product, in the processing, sometimes there will be additives decomposition, and often there will be additives decomposition degradation explanation of the release of gas, if these gases are not discharged in a timely manner, in the extrusion of the wrapped in the material is also prone to cause breakage of the strip.

Material moisture is serious, processing, if the water vapor can not be discharged in a timely manner, the vapor trapped in the material strip, pelleting will also cause broken strip.

8、 Material rigidity, water-cooled or overwater, traction mismatch

Material rigidity is too large, the water temperature is too low, too much water, traction will be due to stress concentration, the material strip breakage.

Just out of the head of the material material is very soft, for rigid materials, water is immediately become very hard, the material from soft to hard process if the traction is not appropriate, will cause the broken strip - this phenomenon often occurs in the PBT or PET plus fiberglass, PC, PS, AS plus fiberglass, ABS plus fiberglass, etc., the crystallization speed is very fast or very large rigidity of the material processing time. Very large material processing time, especially the small machine to do experiments more serious, at this time to improve the water temperature, reduce the amount of water, so that the material into the granulator to maintain a moderate degree of softness, can be resolved.