Dark spot
★ Poor quality of raw materials, more black spots;
★ Local overheating or shearing of the screw is too strong, resulting in increased carbonization of the material;
★ The head pressure is too large, the reflux material is too much, and the carbonization of the material is aggravated;
★ The service life of the machine is too long, the gap between the screw and the cylinder increases, and the adhesion of the cylinder wall increases;
★ Natural exhaust port and vacuum exhaust port are not cleaned for a long time, and the accumulation of carbonized matter increases;
★ Other impurities caused by external environment or man-made mixing;
★ Die cleaning is not clean;
★ The discharge port is not smooth enough, may accumulate materials for a long time, and be gradually carbonized;
★ Part of the thread is damaged, resulting in increased carbonization of the material at the dead corner
Broken bar
1. Causes of external impurities
★ Check whether the dead corners of the equipment in each link of mixing and discharging are cleaned up and whether there are impurities mixed;
★ Add as little crushing material as possible or manually screen the crushing material to remove impurities;
★ Increase the number of mesh and sheet;
★ Try to cover the holes that may have debris falling (solid cover or net cover)
2. Cause of internal impurities
Mainly the process or equipment caused by serious carbonization, carbonization is taken out to the material strip, under the action of traction, resulting in broken strips.
3. 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, resulting in poor plasticization, resulting in broken strips.
4. Material property difference or change
★ The fluidity of the blend components is too different at the same temperature, because the fluidity is not matched or not completely compatible (including physical entanglement and chemical reactions), in theory, this is called "phase separation". "Phase separation" generally does not appear in the blending extrusion, more in the injection process, but if the MFR difference is too large, under the premise of relatively weak screw shear, there may be a broken bar.
★ Blend component viscosity change: for the same material, if the MFR decreases, 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.
5. Poor exhaust
★ The processing temperature is too high or the local shear of the screw is too strong or the local overheating of the screw, 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 is trapped in the material strip, resulting in broken strips under the action of traction.
★ Material is seriously damp, processing water vapor is not timely through natural exhaust and vacuum removal, trapped in the material strip, resulting in broken strip 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, resulting in broken strips under the action of traction.
6. Material rigidity is too large, water is too cold or too much water, traction does not match
The material rigidity is too large, the water temperature is too low, the water is too much, the discharge of the machine head is very soft, and the water becomes very hard immediately, resulting in broken strips under the action of traction mismatch. This phenomenon often appears in PBT or PET fiber, PC fiber, AS fiber, ABS fiber and other materials with very fast crystallization speed or very large rigidity, especially when the small machine is doing the experiment, at this time, improve the water temperature, reduce the amount of water, so that the material entering the granulator to maintain a certain softness, can be solved.
hollow
1. Poor exhaust
The exhaust (or steam) is not smooth, because the natural exhaust or vacuum exhaust is not smooth (the material itself may be too heavy water vapor, it may also decompose the additives such as flame retardants, and it may be vacuum clog or the vacuum is too small or the vacuum gasket is too high), resulting in the existence 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 (small holes) cause hollow particles, and the heavy (large holes) cause broken strips.
★ Low melting point additives (including EBS or PETS) too much, in the screw and barrel gap increase, or screw shear weak premise, resulting in poor plasticization, hollow formation.
★ The water temperature is too low: the cooling water temperature is too low, the material is contracted by 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 feeding
★ Feed speed does not match the speed of the host, appropriately reduce the feed speed or increase the speed of the host;
★ The temperature of the area contained in the feeding section to the natural exhaust port is too low, and the material is not plasticized, which causes raw material to rise under the action of screw extrusion;
★ The temperature near the natural exhaust port is too high, the viscosity of the material is seriously decreased, this section of the screw slip, the material can not be transported to the front section in time, under the subsequent extrusion of the material flow, resulting in the 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 charging;
★ No reverse conveying element or reverse meshing
Block is set, 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 vacuuming;
★ The temperature of the vacuum section 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 bubbling under the action of vacuum pumping;
★ 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, causing rising under the action of vacuum pumping;
★ 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 under the action of the material flow extrusion and vacuum pumping force, resulting in charging;
★ The head pressure is too large (the reasons include: die blocking, too much filter, the head temperature is too low, etc.), resulting in increased reflux, resulting in rising under the action of vacuum pumping force.
bridging
1. Hopper bridge
★ 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;
★ 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 the "oil" substance with absorption effect of powder resin or additives (such AS high rubber powder, AS powder, PP powder, etc.), can be solved.
2. Cut material and build bridge
Mainly due to the melting point of some processing AIDS is too low, the processing temperature of the first and second zones is high, the material is softened in the feeding bin and adhered to the equipment wall, resulting in subsequent feeding difficulties, and the processing temperature of the first and second zones can be properly reduced.
