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Sheet PVC black masterbatches have pockmarks how should we solve?

Time: 2021-05-28 15:07:57

Author: Dongguan Tereal Plastics Factory

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When pitting appears in the sheet PVC black masterbatch, we should first think about whether the mold is rusty or not. If there is no rust in the checking mold, quite bright, no mark, we should increa...

When pitting appears in the sheet PVC black masterbatch, we should first think about whether the mold is rusty or not. If there is no rust in the checking mold, quite bright, no mark, we should increase the melting temperature and back pressure and other methods to improve the quality of melting, although the situation may be a little better, but still can not be completely removed from the pockmarks. When this happens, we should consider whether the color powder is not completely melted. Because the surface of the mold is too smooth and bright, the tiny end-melted color powder particles left on the surface of the injection molded parts will be faithfully reflected in the cause.


Therefore, with the color species to match the color, the numbness automatically disappeared, the surface of the injection molded parts and as bright as a mirror. In actual production, we find that the proportion of black injection molded parts appear this situation is more. Therefore, the surface of the bright parts in the emergence of pitting problem, may wish to consider the problem of color powder.


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Black spot defect analysis and troubleshooting methods


Melt temperature is too high


Material temperature is too high will make the melt overheating decomposition, the formation of carbide, in order to avoid melt overheating decomposition, for PVC and other heat-sensitive thermoplastic materials, must be strictly controlled barrel tail temperature is not too high. When black spots and streaks are found on the surface of the plastic parts, the temperature controller of the barrel should be checked immediately to see if it is out of control, and the temperature of the barrel and mold should be lowered appropriately. However, it is worth noting that if the barrel and mold temperatures are too low, the surface of the molded part will also produce bright streaks.


Cylinder gap is too large


If the wear gap between the screw and the barrel is too large, the melt will be retained in the barrel, resulting in localized overheating of the retained melt and decomposition of the black spots and streaks. In this regard, you can first slightly reduce the barrel temperature, observe whether the fault can be eliminated. Secondly, should check the barrel, nozzle and mold there is no dead space in the storage material and grinding smooth.


After taking the above measures, if the failure is still not eliminated, should be timely maintenance equipment, adjust the gap between the screw and the cylinder.


Melt and mold wall friction overheating


If the injection speed is too fast, the injection pressure is too high, the relative movement speed of the melt and the cavity wall is too high, it is easy to produce friction overheating, so that the melt decomposition produces black spots and know lines. In this regard, the injection speed and injection pressure should be appropriately reduced.


Barrel and mold exhaust bad


If the barrel or mold exhaust is poor, the residual gas in the melt will cause combustion due to adiabatic compression, causing the melt to decompose overheating and produce black spots and stripes. In this regard, the injection speed can be appropriately reduced, under the conditions of appropriate particle size and uniformity of raw materials, improve the barrel exhaust port structure.


For the bad exhaust of the mold part, it should be checked whether the location of the gate and the location of the exhaust hole are correct, and whether the selection of the type of gate is appropriate; remove the adhering antirust agent and other volatile substances in the mold; and reduce the amount of mold release agent. Under the premise of not generating overflow flying edge, the mold closing force can be appropriately reduced and the exhaust clearance increased. In addition, the barrel and thimble should be checked for oil seepage faults.


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