Quality of raw material itself is poor, and there are too many black spots;
Partial overheating of screw causes carbonization of material to increase, and carbonization is carried into material strip, resulting in excessive feeding points;
Partial shear of screw is too strong, which causes carbonization of material to be aggravated, and carbonization is carried into material strip, resulting in too many feed points;
Too much pressure on machine head (including clogging, too much filter screen, too low temperature of machine head, etc.), too much return material, carbonization of material aggravated, and carbonization is carried into material strip, causing too many points;
Service life of machine is too long, gap between screw and barrel increases, and adhesion of char on barrel wall increases. With passage of extrusion time, it is gradually brought into strip, resulting in too many points;
Natural exhaust port and vacuum exhaust port are not cleaned for a long time, accumulated carbon material increases, and continuous extrusion is carried into strip in subsequent period, resulting in too many points;
Other impurities are mixed in by external environment or man-made, causing more black spots;
Die (including discharge port and internal dead corners) is not cleaned up, causing too many black spots;
Discharge port is not smooth enough (for example, some shallow grooves and potholes, etc.), and material may accumulate for a long time. With passage of extrusion time, it will be gradually carbonized and then brought into strip, resulting in more black spots;
Part of original thread is damaged (dead corners, abrasion, etc.), resulting in increased carbonization of materials at blind corners, which are gradually taken out to strip during subsequent continuous extrusion process, resulting in more black spots;
Natural exhaust and vacuum exhaust are not smooth, causing material in screw to be carbonized and causing more black spots.

 

Increase number of filters or sheets;
Properly reduce host speed or increase feeding speed;
Appropriately lower extrusion processing temperature (head or other areas).

Check whether dead corners of equipment in each link of mixing and discharging are cleaned up, whether there are impurities mixed in;
Minimize addition of crushed material or manually screen crushed material to remove impurities;
Increase number of filter meshes and sheets;
Try to cover holes (solid cover or net cover) where debris may fall.

Head pressure is too high (including clogging of die, too much filter, too low temperature of head, etc.), resulting in increased reflux and aggravated carbonization, carbonized material is carried out into strip, which will cause strip to break under action of traction;
Local overheating of extruder causes aggravation of carbonization, and carbonization is carried out to strip, which causes strip to break under action of traction;
Partial shear of screw is too strong, which causes local carbonization of material to be aggravated, and carbonized material is carried out to material strip, which causes strip to break under action of traction;
Service life of machine is long, screw and barrel are worn, gap increases, backflow increases, and carbonized material adhered to barrel wall increases. With extension of extrusion time, carbonized material is gradually carried out to material strip, and traction force causes strip to break；
If vacuum or natural exhaust port (including gaskets and dead corners) is not cleaned for a long time, existing char is brought to material strip, which will cause strip to break under action of traction;
Die of machine head (including discharge port and dead corner inside machine head) is not cleaned up, and carbonized or impurities in die are brought to material strip, and strip is broken under action of traction;
Time interval for replacing filter is too long, filter is blocked, and material cannot come out, causing strip to break.

Extrusion temperature is too low or screw shear is too weak, material is not fully plasticized, and material lumps appear, which will cause strip to break under action of traction;
Low melting point additives in formulation system (including EBS or PETS, etc.), under premise of weak screw shear, increased gap between screw and barrel and weak shear, will cause poor plasticization and cause broken bars.

Fluidity of blended components at same temperature is too different. Because fluidity is not matched or not completely compatible (including physical entanglement and chemical reaction), theoretically this is called "phase separation". "Phase separation" generally does not occur in blending and extrusion, but often occurs in  , but if MFR difference is too large, under premise of relatively weak screw shear, broken bars may occur;
Viscosity change of blending components: For same material, if MFR decreases, hardness, rigidity and gap become larger, it is possible that molecular weight of batch is higher than before, resulting in higher viscosity. Under effect of original processing temperature and process, plasticization is not good. At this time, it can be solved by increasing extrusion temperature or reducing screw speed of main engine.

Processing temperature is too high, local shear of screw is too strong, screw is locally overheated, which causes decomposition of some flame retardants, other additives and releases gas. Vacuum does not extract gas in time, gas is trapped in the strip, causing strip to break under action of traction;
Material is seriously damp, processing water vapor is not discharged through natural exhaust and vacuum in time, vapor is trapped in material strip, and strip is broken under action of traction;
Natural exhaust or poor vacuum exhaust (including blockage, air leakage, too high gaskets, etc.), causing air (or steam) to be trapped in material strip, causing strip to break under action of traction.

Material is too rigid, water temperature is too low, and passing water is too much. Output of machine head is very soft, and passing water will immediately become very hard. Under action of traction mismatch, it will cause broken strip-this phenomenon often occurs in PBT or PET fiber addition, PC fiber addition, AS fiber addition, ABS fiber addition and other materials with very fast crystallization speed or very high rigidity, especially small machines are more serious for experiments. At this time, increase water temperature and reduce amount of water passing, so that material strip entering pelletizer can maintain a certain degree of softness, which can be solved.

This phenomenon often occurs when above-mentioned head pressure is insufficient, external impurities and internal impurities.

Poor exhaust (or steam): due to natural exhaust or poor vacuum exhaust (maybe material itself is too heavy in water vapor, or additives such as flame retardants may be decomposed, vacuum may be blocked, vacuum is too small, or air leakage, vacuum gasket is too high), resulting in presence of gas (vapor) in particles, forming a hollow.

Processing temperature is low, material is not completely plasticized, the lighter (small holes) will cause particles to be hollow, and the heavyer (large holes) will cause broken bars;
Too many low-melting additives (including EBS or PETS), under premise of weak screw shear (for example, production of ordinary ABS on line 2, EBS cannot be too much, too many "pores"), cause poor plasticization of material and form a hollow;
Too many low-melting additives (including EBS or PETS), under premise that gap between screw and barrel is increased or screw shear is weak (for example, line 1 produces ordinary ABS, sometimes EBS can not be too much, too many "pores"), it will cause poor plasticization and form a hollow.
Water temperature is too low: cooling water temperature is too low, and material shrinks in contact with water, causing shrinkage holes, such as PP products-this kind of phenomenon is mainly for crystalline plastics; in general, crystalline plastics (such as PP, PA, PBT, etc.) should use low water temperature, and non-crystalline plastics (such as ABS, PC/ABS, HIPS, etc.) should use high water temperature.

Feeding speed does not match speed of main engine, appropriately reduce feeding speed or increase speed of main engine;
Temperature from feeding section to area contained in natural exhaust port is too low, and material is not plasticized, causing raw material to be emitted under action of screw;
Temperature near natural exhaust port is too high, viscosity of material drops seriously, screw in this section is slipping, and material cannot be transported to front section in time, causing clinker to be emitted under effect of subsequent material flow extrusion;
Position of natural exhaust port of screw does not match position of natural exhaust port of barrel, resulting in material loss;
There is no reverse conveying element or reverse engagement block, which cannot reduce pressure of natural exhaust port screw groove, which will cause material to be off under action of subsequent material flow extrusion.

Vacuum pumping force is too large, and material is sucked into vacuum pipe, causing material to be exposed;
Screw vacuum position is not equipped with reverse conveying elements or reverse meshing blocks, which cannot reduce pressure of screw groove in vacuum section, which will cause material ejection under action of vacuum;
Temperature in vacuum section is too high, viscosity of material drops seriously, screw in this section is slippery, and material cannot be transported to front section in time, which will cause material loss under action of vacuum;
Extrusion processing temperature is too low, material is not plasticized or flame retardant and other additives are not fully dispersed in resin, which will cause material to be out of way under action of vacuum;
Under premise that screw combination is reasonable, position is also matched, temperature, main engine and feeding speed are also matched, vacuum gasket is low, which will cause material loss under action of material flow extrusion and vacuum suction;
Too much pressure on machine head (causes include clogging of die, too much filter, too low temperature of machine head, etc.), resulting in increased reflux and material ejection under action of vacuum.

Too many fillers, moisture absorption, agglomeration will increase friction between mixture and hopper wall. Adding "white oil" and other liquid external lubricants can reduce friction between mixture, hopper wall and mixture, which can be solved;
Mixture is agglomerated (including high-temperature agglomeration and agglomeration due to excessive addition of liquid additives), reduce drying temperature or high mixing time, reduce amount of liquid additives, add powdery resin or additives that can absorb "oily" substances that (such as high rubber powder, AS powder, PP powder, etc.) can be solved.

Mainly because melting point of some processing aids is too low, processing temperature in zone 1 and zone 2 is too high, material is softened in feeding silo and adheres to equipment wall, causing subsequent feeding difficulties, so appropriately lowering processing temperature in zone 1 and zone 2 can be solved.