There are too many black spots
(1) The quality of the raw material itself is poor, and there are more black spots;
(2) local overheating or local shearing of the screw is too strong, resulting in increased carbonization of the material, and the carbonized material is brought to the material strip, resulting in more black spots;
(3) the head pressure is too large (including clogging, too much filter, too low head temperature, etc.), there is too much reflux material, the carbonization of the material is aggravated, and the carbonized material is brought to the material strip, resulting in more black spots;
(4) The service life of the machine is longer, the gap between the screw and the cylinder increases, and the carbonized material adhering to the wall of the cylinder increases, which is gradually brought to the material strip with the passage of extrusion time, resulting in more black spots;
(5) The natural exhaust port and vacuum exhaust port are not cleaned for a long time, the accumulated carbonized matter increases, and the subsequent continuous extrusion is taken to the material strip, resulting in more black spots;
(6) The external environment or artificially caused by other impurities mixed, resulting in more black spots;
(7) The mouth die (including the discharge port and internal dead Angle) is not clean, resulting in more black spots;
(8) The discharge port is not smooth enough (such as some shallow grooves and potholes, etc.), which may accumulate materials for a long time, and be gradually carbonized with the extrusion time, and then taken to the material strip, resulting in more black spots;
(9) Part of the threaded components are damaged (missing corners, wear, etc., forming dead corners), resulting in increased carbonization of the material at the dead corners, which is gradually taken out to the material strip in the subsequent continuous extrusion process, resulting in more black spots;
(10) Natural exhaust and vacuum exhaust is not smooth, resulting in carbonization of materials in the screw, resulting in more black spots.
Broken bar
(1) Carbonization of the material strip
The pressure of the head is too high (including clogging of the die, too much filter, too low temperature of the head, etc.), resulting in increased backflow and aggravated carbonization, and the carbonized matter is taken out to the material strip, resulting in broken strip under the action of traction;
Extruder local overheating, resulting in increased carbonization, carbonization is taken out to the strip, under the action of traction, resulting in broken strips;
The screw shear is too strong in part, which causes the local carbonization of the material to increase, and the carbonized material is taken out to the material strip, and the strip is broken under the action of traction.
The service life of the machine is long, the screw and barrel wear, the gap increases, the backflow increases, and the carbonized material adhering to the wall of the cylinder increases. With the extension of the extrusion time, the carbonized material is gradually taken out to the material strip, resulting in the breaking of the strip under the action of traction;
Vacuum or natural exhaust port (here including gasket and dead Angle) is not cleaned for a long time, the presence of carbonized matter is brought to the material strip, under the action of traction, resulting in broken strip;
The die of the head (including the discharge port and the dead Angle inside the head) is not cleaned, and the carbonized matter or impurities contained in the die are brought to the material strip, causing the broken strip under the action of traction;
The time interval for replacing the filter screen is too long, the filter screen is blocked, and the material cannot come out, resulting in broken strips.
(2) poor plasticization of materials
The extrusion temperature is low or the screw shear is too weak, the material is not sufficiently plasticized, and the material bumps appear, resulting in broken strips under the action of traction;
Low melting point additives (including EBS or PETS, etc.) in the formula system, under the premise of weak screw shear or the gap between the screw and the barrel increases and the shear is weak, the plasticization is poor, resulting in broken strips.
(3) Changes in physical properties of raw materials
Blend components at the same temperature, there is too much difference in fluidity, due to fluidity mismatch or not fully compatible (including physical entanglement and chemical reactions), theoretically this is called "phase separation", "phase separation" generally does not appear in the blend extrusion, more appear in the injection process, but if the melt flow rate (MFR) difference is too large, On the premise that the relative shear of the screw is weak, it may break the bar.
For the same material, if the MFR decreases, the hardness, rigidity and gap become larger, it is possible that the molecular weight of the batch of material is larger than before, resulting in greater viscosity, under the original processing temperature and process, resulting in poor plasticization, at this time to increase the extrusion temperature or reduce the host screw speed can be solved.
(4) The strip is trapped or the exhaust is not smooth
The processing temperature is too high or the screw local shear is too strong or the screw local overheating, resulting in the decomposition of some additives such as flame retardants, the release of gas, the vacuum is not timely to extract the gas, the gas trapped in the material strip, under the action of traction, resulting in broken strips;
The material is seriously damp, and the processing water vapor is not discharged by natural exhaust and vacuum in time, and the water vapor is trapped in the material strip, and the strip is broken under the action of traction.
Natural exhaust or vacuum exhaust is not smooth (including blockage, leakage, gasket is too high), resulting in gas (or steam) trapped in the material strip, under the action of traction, resulting in broken strips.
(5) Material rigidity is too large, water is too cold or too much water, traction does not match
Material rigidity is too large, the water temperature is too low, too much water, the discharge of the head is very soft, the water immediately becomes very hard, under the action of traction mismatch, resulting in broken bars - this phenomenon often appears in PBT or PET fiber, PC fiber, AS fiber, ABS fiber and other crystallization speed is very fast or very rigid material, especially the small machine to do the experiment is more serious, At this time, increase the water temperature, reduce the excess water, so that the material entering the granulator to maintain a certain softness, can be solved.
(6) The number of mesh filters is too low or the number of sheets is not enough
This phenomenon often occurs when the above head pressure is insufficient and contains external impurities and internal impurities.
hollow
(1) Poor exhaust
Due to the natural exhaust or vacuum exhaust is not smooth (the material itself may be too heavy water vapor, it may also decompose additives such as flame retardants; There may also be vacuum clogging or vacuum is too small or air leakage or vacuum gasket is too high), resulting in the presence of gas (steam) body in the particles, forming a hollow.
(2) Poor plasticization
The processing temperature is low, the material is not fully plasticized, the light one (small hole) causes hollow particles, and the heavy one (large hole) causes broken strips;
Too many melting point auxiliaries (including EBS or PETS) will cause poor plasticization and hollow formation under the premise of increased clearance between screw and barrel or weak screw shear;
The cooling water temperature is too low, the material shrinks in water, resulting in shrinkage holes, such as
PP Products - this phenomenon is mainly for crystalline plastics; Under normal circumstances, 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.
spreader
(1) Natural discharge port charging
The feed speed does not match the main engine speed, and the feed speed should be appropriately reduced or the main engine speed should be increased;
The temperature of the area from the feeding section to the natural exhaust port is too low, the material is not plasticized, and the raw material is generated under the action of screw extrusion.
The temperature near the natural exhaust port is too high, the viscosity of the material is seriously decreased, and the screw in this section is slipping, and the material can not be transported to the front section in time, resulting in the clinker under the subsequent extrusion of the material flow;
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 charging;
There is no reverse conveying element or reverse meshing
Block set here, which can not reduce the pressure of the natural exhaust port spiral groove, resulting in charging under the action of subsequent material flow extrusion.
(2) Vacuum charging
The vacuum pumping force is too large, the material is sucked into the vacuum pipe, resulting in charging;
There is no reverse conveying element or reverse meshing block in the vacuum position of the screw, which can not reduce the pressure of the screw groove in the vacuum section, resulting in charging under the action of vacuum-pumping;
The temperature of the vacuum section is too high, the viscosity of the material is seriously decreased, and the screw in this section slides, and the material can not be transported to the front section in time, resulting in bubbling under the action of vacuum pumping force.
The extrusion processing temperature is too low, the material is not plasticized or the additives such as flame retardants are not fully dispersed in the resin, resulting in rising material under the action of vacuum pumping force;
The screw combination is also reasonable, the position is also matched, the temperature and the host and the feeding speed are also matched, the vacuum gasket is low, and the charging is caused by the extrusion of the material flow and the vacuum pumping force.
The head pressure is too large (the reasons include: die blockage, too much filter, the head temperature is too low, etc.), resulting in increased reflux, resulting in rising material under the action of vacuum pumping force.
Hopper bridge
(1) too much filler, moisture absorption, agglomeration, resulting in increased friction between the mixture and the hopper wall, adding liquid external lubricants such as "white oil" to reduce the friction between the mixture and the hopper wall and the mixture, which can be solved;
(2) The mixture caking (including high temperature caking and liquid additives added too much caking), reduce the drying temperature or high mixing time, reduce the amount of liquid additives added, add powder resin or additives that have absorption effect on "oil" (such AS, high rubber powder, AS powder, PP powder, etc.), can be solved.
Cut the material and build the bridge
The main reason is that the melting point of some processing AIDS is too low, the processing temperature in the first and second zones is high, and the materials soften in the feeding bin and adhere to the equipment wall, resulting in subsequent feeding difficulties. It can be solved by properly reducing the processing temperature of zone 1 and zone 2.
