The reason for the black spot is more

(1) The quality of raw material itself is poor, and the black point is on the high side;
(2) The screw is locally overheated, resulting in aggravated carbonization of the material, and the carbide is brought into the material strip, resulting in a biased give point;
(3) Screw local shear is too strong, resulting in aggravation of material carbonization, carbide is brought to the material strip, resulting in giving more points;
(4) The pressure of the head is too big (including clogging, too many filters, too low temperature of the head, etc.), too much reflux material, the material carbonization is aggravated, and the carbide is brought into the material strip, resulting in giving more points;
(5) The machine is used for a long time, the gap between screw and barrel increases, the barrel wall adheres to the carbonized material more, and with the extrusion time, it is gradually brought to the material strip, resulting in giving more points;
(6) The natural exhaust port and vacuum exhaust port are not cleaned for a long time, and the accumulated carbide increases, which is then brought into the material strip in the subsequent period of continuous extrusion, resulting in more give points;
(7) The external environment or man-made other impurities mixed in, resulting in more black spots;
(8) The mouth mold (including the discharge port and internal dead space) is not clean, resulting in more black spots;
(9) The discharge port is not smooth enough (e.g., some shallow grooves and pits, etc.), the material may accumulate for a long time, and with the extrusion time, it is gradually carbonized and then brought to the material strip, resulting in more black spots;
(10) Some of the original threads are damaged (lack of corners, wear and tear, etc. to form a dead end), resulting in increased carbonization of the material at the dead end, which is gradually taken out to the material bar during the subsequent continuous extrusion process, resulting in a high number of black spots;
(11) The natural exhaust and vacuum exhaust are not smooth, resulting in carbonization of the material in the screw, causing the black spot to be on the high side.
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Finished product processing process problem analysis

(1) Broken bars produce original insufficiency:
Increase the number of mesh or sheets of the screen;
Appropriately lower the host speed or adjust the feed speed;
Appropriately reduce the extrusion processing temperature (head or other zones).
(2) External impurities:
Check whether the dead ends of the equipment in each link of mixing and discharging are cleaned up and whether there are impurities mixed in;
Try to add as little as possible to the crushed material or manual primary screening of crushed material to remove impurities;
Increase the mesh and number of screens;
Try to cover the holes where impurities may fall (solid cover or mesh cover).
(3) Internal impurities:
Head pressure is too high (including clogging of the mouth mold, too many screens, too low head temperature, etc.), resulting in increased reflux leading to aggravated carbonization, the carbonized material is taken out into the bar, which causes the bar to break under the action of the traction force;
The extruder is locally overheated, resulting in aggravation of carbonization, and the carbide is taken out into the material strip, which, under the action of traction force, results in broken strips;
The screw shear is too strong locally, causing the material to be carbonized locally, and the carbide is taken out to the material strip, which causes the strip to be broken under the action of traction force;
The machine is used for a long time, the screw and barrel are worn out, the gap increases, the reflux increases, the carbonized material adhering to the barrel wall increases, with the extension of the extrusion time, the carbonized material is gradually taken out to the material strip, and under the action of the traction force, it causes the broken strip;
Vacuum or natural exhaust port (including gaskets and dead space) is not cleaned for a long time, and the carbonized material is brought to the bar, which will cause broken bars under the action of traction force;
The mouth mold of the machine head (here including the discharge port and the dead space inside the machine head) is not cleaned up, and the carbide or impurity contained in the mouth mold is brought to the material strip, which causes the strip to break under the action of the traction force;
Replacement of the screen interval is too long, the screen is blocked, the material can not come out, resulting in broken bars.
(4) Poor plasticization of materials:
Extrusion temperature is low or the screw shear is too weak, the material is not fully plasticized, the material lumps, under the action of traction, resulting in broken bars;
Formulation system of low melting point additives (including EBS or PETS, etc.), in the screw shear weak or screw and barrel clearance increases and shear under the premise of weak, resulting in poor plasticization, resulting in broken bars.
(5) Physical properties of raw materials change:
Mixed components at the same temperature, there are too many differences in mobility, due to mobility mismatch or not fully compatible (including physical entanglement and chemical reactions), theoretically speaking, this is called “phase separation”, “phase separation” generally in the mixing and extrusion will not appear, more often appear in the injection molding process, but if the screw shear is weak or screw and barrel gap increases and shear bias weak premise, resulting in poor plasticizing broken bars. In the injection molding process, but if the MFR difference is too large, under the premise of the relative shear of the screw is weak, there may be broken bars;
Co-mingled component viscosity changes: for the same material, if the MFR decreases, hardness, rigidity and notch, it is possible that the molecular weight of the batch of material is larger than before, resulting in viscosity, in the original processing temperature and process, resulting in poor plasticization, at this time to improve the extrusion temperature or reduce the host screw speed can be resolved.
(6) The material strip is trapped in the vapor or poor exhaust:
Processing temperature is too high or screw local shear is too strong or screw local overheating, resulting in the decomposition of certain flame retardants and other additives, the release of gas, the vacuum is not timely gas pumping, the gas is trapped in the material inside the strip, under the action of traction, resulting in the broken strip;
The material is seriously affected by moisture, the processing water vapor is not timely eliminated by natural exhaust and vacuum, the vapor is trapped in the material strip, under the action of traction, resulting in broken strips;
Natural exhaust or vacuum exhaust is not smooth (including blockage, leakage, gaskets too high), resulting in gas (or vapor) trapped in the material strip, under the action of traction, resulting in broken bars.
(7) material rigidity is too large, the water is too cold or too much water, traction mismatch:
Material rigidity is too large, the water temperature is too low, too much water, the head of the material is very soft, over the water immediately becomes very hard, under the action of traction mismatch, resulting in broken bars - this phenomenon often occurs in the PBT or PET fiber, PC fiber, AS fiber, ABS fiber, etc. crystallization speed is very fast or rigidity of the material is very large, especially the small machine to do experiments more serious. Is a small machine to do experiments more serious, this time to improve the water temperature, reduce the amount of water, so that the material into the granulator to maintain a certain degree of softness, can be resolved.
(8) filter mesh is too low or insufficient number of sheets:
This phenomenon often occurs in the above head pressure is insufficient, containing external impurities and internal impurities.

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Pelleting hollow problem analysis

(1) Poor exhaust:
Poor exhaust (or vapor): due to natural exhaust or vacuum exhaust is not good (may be the material itself is too heavy water vapor, but also may be flame retardants and other additives decomposition;
There may also be a vacuum blockage or vacuum is too small or leakage or vacuum gasket pad too high and other reasons), resulting in the existence of gas (vapor) in the particles, the formation of hollow.
(2) poor plasticization:
Processing temperature is low, the material is not fully plasticized, light (small holes) resulting in hollow particles, heavy (large holes) resulting in broken bars;
Low melting point additives (including EBS or PETS) is too much, in the screw shear weak (for example, 2 line production of ordinary ABS, EBS can not be too much, too much “air holes”) under the premise of causing poor plasticization of the material, the formation of hollow;
Low melting point additives (including EBS or PETS) is too much, in the screw and barrel gap increases (for example, line 1 production of ordinary ABS, sometimes EBS can not be too much, too much “air holes”) or the premise of the screw shear weak, resulting in poor plasticization, the formation of hollow.
Water temperature is too low: cooling water temperature is too low, the material shrinkage in water, resulting in shrinkage holes, such as doing PP products - such phenomena are mainly for crystalline plastics; in general, crystalline plastics (such as PP, PA, PBT, etc.) should be used in low water temperature, non-crystalline plastics (such as ABS, PC / ABS, HIPS, etc.) Adopt high water temperature.
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Natural exhaust port, vacuum port bubbling

(1) Natural exhaust port bubbling:

The feeding speed is not matched with the host speed, reduce the feeding speed or increase the host speed appropriately;

The temperature of the area from the feeding section to the natural exhaust port is too low, the material is not plasticized, and under the extrusion of the screw, the raw material is bubbled;

The temperature near the natural exhaust port is too high, the viscosity of the material is seriously reduced, the screw slips in this section, the material can not be transported to the front section in time, under the subsequent extrusion of the material flow, resulting in the emergence of clinker;

The position of the natural exhaust port of the screw does not match the position of the natural exhaust port of the barrel, resulting in bubbling material;

This is not set reverse conveying elements or reverse engagement block, can not reduce the natural exhaust port screw groove pressure, in the subsequent material flow extrusion, resulting in risen material.

(2) vacuum bubbling material:

Vacuum pumping force is too large, the material is sucked into the vacuum pipe, resulting in material bubbling;

Screw vacuum position is not set reverse conveying elements or reverse engagement block, can not reduce the vacuum section of the screw groove pressure, under the action of vacuum, resulting in bubbling material;

The temperature of the vacuum section is too high, the viscosity of the material decreases seriously, the screw slips in this section, and the material can not be transported to the front section in time, which causes bubbling under the action of vacuum pumping force;

Extrusion processing temperature is too low, the material is not plasticized or flame retardants and other additives are not fully dispersed in the resin, under the action of vacuum pumping force, resulting in bubbling material;

Under the premise that the screw combination is also reasonable, the position is also matched, the temperature as well as the host and feeding speed are also matched, the vacuum gasket is on the low side, and under the action of material flow extrusion and vacuum pumping force, it causes material bubbling;

Head pressure is too large (reasons include: mouth mold clogging, too many filters, head temperature is too low, etc.), resulting in increased reflux, under the action of vacuum pumping force, resulting in bubbling material.

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Hopper bridging

(1) too much filler, moisture absorption, agglomeration, resulting in increased friction between the mixture and the hopper wall, add “white oil” and other liquid external lubricants to reduce the mixture and the hopper wall as well as the friction between the mixture, can be resolved;

(2) mixed material caking (including high-temperature caking and liquid additives to add too much caking), reduce the drying temperature or high mixing time, reduce the amount of liquid additives to add to the “oily” material has the effect of absorption of powdered resins or additives (such as, high gum powder, AS powder, PP powder, etc.), can be solved.

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Material bridging

Mainly due to some processing aids melting point is too low, a zone, two processing temperature is high, the material in the feed bin softening, adhesion in the wall of the equipment, resulting in subsequent feeding difficulties.
Appropriately reduce the processing temperature of one area, two areas, can be resolved.