First, the cause of the black spot is too much
The quality of the raw material itself is poor, and the black spot is much more.
The local overheating of the screw causes the carbonization of the material to aggravate, and the carbonization is brought into the material bar, resulting in more feeding points.
The local shearing of the screw is too strong, which causes the carbonization of the material to be aggravated, and the carbonization is brought into the material bar, resulting in more feeding points.
The pressure of the head is too large (including clogging, too much filter net, too low head temperature), too much reflow material, heavier material carbonization, and carbonized material being brought into the strip, resulting in a large number of points.
The longer service life of the machine, the increase of the gap between the screw and the cylinder, the increase in the adhesion of the wall to the wall of the cylinder, and gradually brought to the strip with the time of the extrusion.
Natural exhaust and vacuum exhaust are not clear for a long time, the accumulation of carbide increases, and subsequent continuous extrusion is carried to the bar, resulting in more feeding points.
External environment or artificial cause other impurities to mix in, resulting in more black spots;
Mould (including outlet and internal dead angle) cleaning is not clean, resulting in more black spots;
If the outlet is not smooth enough (for example, some shallow grooves and potholes), the material can be accumulated for a long time. With the time of extrusion, it is gradually carbonized and then taken to the strip, causing more black spots.
The damage of the parts of the part of the thread (angle, wear and so on form the dead angle), resulting in the aggravation of the material carbonization at the dead angle. In the subsequent continuous extrusion process, the material is gradually brought out to the material, resulting in more black spots.
Natural exhaust and vacuum exhaust are not smooth, resulting in carbonization of materials in the screw, resulting in more black spots.
Two. Analysis of the processing of finished products
The broken bar produces the original deficiency:
Increase the number of mesh or number of filters.
Lower the speed of the host or the feed speed of the feed.
Reduce the extrusion temperature (die or other areas) appropriately.
Check whether the dead corners of mixing and discharging equipment are cleaned up and whether impurities are mixed in.
As far as possible to add less crushed materials or manual screening of crushed materials to remove impurities;
Increase the number of mesh and number of filters.
Try to cover holes (solid or mesh) where debris may fall.
The pressure of the head is too high (including the blockage of the die, too much filter net and the low temperature of the head), which causes the increase of the reflux and lead to the aggravation of the carbonization. The carbonized material is taken out into the strip and causes the broken bar under the action of the traction force.
The local overheating of the extruder causes carbonization to aggravate, and the carbide is taken out of the bars, resulting in broken bars under the action of traction.
The screw shearing part is too strong, resulting in the local carbonization of the material is aggravated, the carbide is taken out of the bars, under the action of traction, resulting in broken bars.
The long service life of the machine, the wear of the screw and the cylinder, the increase of the gap, the increase of the reflux, the increase of the charcoal adhesion to the wall of the machine, the carbonized material is gradually taken out to the strip with the extrusion time, and the broken strip is caused by the effect of the traction force.
Vacuum or natural vents (gaskets and dead corners included here) are not clear for a long time, and the existing carbides are brought to the bars, resulting in broken bars under the action of traction.
The die of the head of the machine (including the outlet and the dead angle of the head of the machine) has not been cleaned up. The inside of the die contains carbon or impurities which are brought to the strip, and the broken bar is caused by the action of the traction force.
The time interval for replacing the filter screen is too long, the filter screen is blocked, the material can not come out, resulting in broken bars.
Poor material plasticization:
The extrusion temperature is too low or the screw shearing is too weak, the material is not fully plasticized, and the material is lumpy, resulting in broken bars under the action of traction.
The low melting point additives (including EBS or PETS, etc.) in the formulation system, in the condition of the poor shearing of the screw or the gap between the screw and the cylinder and the shear weak, cause the plasticization and the broken bar.
Changes in material properties:
The fluidity of the blend components at the same temperature is very different. Due to the flow mismatch or incomplete compatibility (including physical entanglement and chemical reaction), the "phase separation" is called "phase separation" and "phase separation" generally does not appear in the blend extrusion, but it appears more in the injection process, but if the difference of MFR is too large, in the screw On the premise of relatively weak shear, the broken bar may occur.
The viscosity change of the blend component: for the same material, if the MFR decreases, the hardness, rigidity, and the notch are larger, it is possible that the molecular weight of the batch is larger than that before, resulting in a larger viscosity, resulting in poor plasticization under the original processing temperature and process. At this time, the extrusion temperature can be increased or the screw speed of the host can be reduced. Solve.
A strip of steam or exhaust is not smooth.
The processing temperature is too high or the screw local shear is too strong or the screw local overheating, causing the decomposition of some flame retardant and other additives, releasing gas, the vacuum is not pumped out in time, the gas is trapped inside the strip, and the broken bar is caused by the traction force.
The material is seriously damped, the processing water vapor does not pass through the natural exhaust and the vacuum elimination in time, the steam body is trapped in the material strip, under the action of the traction force, causes the broken strip;
Natural exhaust or vacuum exhaust is not smooth (including clogging, leakage, gasket too high), resulting in gas (or steam) trapped in the strip, resulting in a broken bar under the action of traction.
Material too rigid, too cold water or too much water, traction mismatch:
Material rigidity is too large, water temperature is too low, too much water, too much water, the head of the material is very soft, the water is very hard immediately, in the effect of mismatch in traction, cause broken bars - this phenomenon often appears in the PBT or PET adding fiber, PC fiber, AS adding fiber, ABS and fiber, the crystallization rate is not very fast or very large rigid material, especially small The machine does the experiment seriously, at this time raises the water temperature, reduces the excessive water quantity, lets enter the material sliver of the granulator to maintain certain softness, may solve.
The filter mesh is too low or the number is not enough.
This phenomenon often occurs when the head pressure is insufficient, external impurities and internal impurities.
Three. Granulation hollow
Exhaust (or vapour) is not smooth: because natural exhaust or vacuum exhaust is not smooth (possibly the material itself is too heavy water vapor, can also be decomposed by flame retardant and other auxiliaries, there may be vacuum clogging or vacuum too small or air leakage or vacuum gasket too high), resulting in the existence of gas (steam) body in the particles, forming hollow.
Processing temperature is low, the material is not completely plasticized, light (small holes) caused by hollow particles, heavy (large holes) caused by broken bars;
Low melting point auxiliaries (including EBS or PETS) are too much, and the material plasticization is bad, so that the material plasticized and hollow is formed under the condition that the shearing of the screw is weak (for example, the ordinary ABS is produced on line 2, the EBS can not be too much and too many "blowholes").
Low melting point auxiliaries (including EBS or PETS) are too large in the gap between the screw and the cylinder (for example, line 1 produces common ABS, sometimes EBS can not be too much, too many "holes") or screw shear weak, resulting in poor plasticization and hollow.
The water temperature is too low: the cooling water temperature is too low, the materials shrink in the water, causing shrinkage holes, such as PP products - such phenomena are mainly for crystalline plastics; in general, crystalline plastics (such as PP, PA, PBT, etc.) should use low water temperature, non crystalline plastics (such as ABS, PC/ ABS, HIPS and so on) use high water temperature.
Four. Natural vent, vacuum riser
Natural exhaust vent:
If the feeding speed does not match the main engine speed, the feeding speed can be reduced or the main engine speed can be increased appropriately.
The temperature from the feeding section to the natural exhaust port is too low, and the material is not plasticized. Under the action of the screw extrusion, the raw material is produced.
The temperature of the natural exhaust port is too high, the viscosity of the material drops seriously, and the screw slips, the material can not be transported to the front section in time, and the clinker is caused by the subsequent extrusion of 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, which results in the discharge.
There is no reverse conveying element or reverse meshing block set here, which can not reduce the pressure of natural exhaust outlet groove, resulting in outflow under the action of subsequent material flow extrusion.
Vacuum pumping force is too large, sucking materials into the vacuum pipe, resulting in the outflow;
The screw vacuum position has no reverse conveying element or reverse meshing block, which can not reduce the pressure of the screw groove in the vacuum section, resulting in the outflow under the action of vacuum pumping.
The temperature of vacuum section is too high, and the viscosity of material is seriously decreased. The screw of this section slips, and the material can not be transported to the front section in time. Under the action of vacuum pumping force, the material will rise.
The extrusion temperature is too low, the materials are not plasticized or flame retardants and other additives are not fully dispersed in the resin, resulting in the blanking under the action of vacuum pumping.
The screw combination is also reasonable, the position is also matched, the temperature and the host and feed speed also match the premise, the vacuum gasket is low, in the material flow extrusion and vacuum pumping force, cause the material;
The pressure of the head is too large (due to the blockage of the die, too much filter net, too low head temperature), which causes the reflux to increase, and the material is caused by the vacuum pumping force.
Five. A hopper to bridge the bridge
There are too many fillers, moisture absorption and agglomeration, resulting in the increase of the friction between the mixture and the wall of the hopper, and the addition of liquid lubricants such as "white oil" to reduce the friction between the mixture and the wall of the hopper and the mixture.
The mixture caking (including high temperature caking and liquid additive adding too much and caking), reducing the drying temperature or mixing time, reducing the amount of liquid additives and adding the powder resin or auxiliary (such as high glue powder, AS powder, PP powder, etc.) to the "oil" material (such as high rubber powder, powder material, and so on) can be solved.
Six, laying off the bridge
It is mainly because the melting point of some processing aids is too low, the processing temperature in one area and two area is high, the material is softened in the feeding silo and adheres to the equipment wall, which causes the subsequent material difficulty, and the processing temperature of one area and two areas can be properly reduced, and the solution can be solved.
Related Industry Knowledge
- In the face of low-cost competition...
- How to remove the pungent taste of ...
- What is the food grade PVC?
- What types of PVC waterproofing mem...
- PVC material! Market development pr...
- The demand of PVC products market w...
- What should we pay attention to whe...
- How to choose a good quality PVC bu...
- Brief Introduction to the Developme...
- Why do you choose PVC trim?
- Injection molding of thermosetting ...
- How to solve the mold release diffi...
- Features of commonly used film pack...
- Three development trends of plastic...
- How to control the ;’fish eye' phen...
- Rational understanding of the curre...
- What are the key technical paramete...
- Technical requirements for four par...
- What should we do if the product is...
- How to solve the problem of poor gl...