PVC calendering transparent sheet is one of the main varieties of hard PVC. It is usually produced by conical twin-screw extruder. The problems encountered in the process of production are: bubbles,crystal spots, yellow color of sheet material and so on. I according to the practical operation experience of the company's machine debugging technician, summed up a little information, hope it's helpful for other peer companies, if inappropriate, please also generous with your criticism.
1. Yellow color problem
The causes and solutions are:
First,PVC itself is stable. If it is the new PVC resin manufacturers, may be PVC itself stability is poor, you can change, change PVC try. However, even the used brand PVC is likely to be caused by the PVC resin itself, because even the PVC produced by the same manufacturer may vary in quality in different batches.
Second,Lack of stabilizers
Third,Temperature controller problems,the show temperature is lower than the actual temperature and the high temperature will cause PVC decomposition, yellow. At this point, you need to re check the thermostat. The method is simple, using a mercury thermometer. In actual production, the temperature of the temperature controller shows a difference between the temperature and the actual temperature due to the
looseness of the thermocouple and the sticking ofmaterial.Another suggestion,
temperature controller using high-quality, often foreign brands are RKC, Omron,Yatai( chinese brand).
2. Small bubble sheet
First,PVC material with too much moisture, as in summer's rainy days,moisture in the raw material can not be fully discharged in the barrel, then thermal expansion and bubble formation in a sheet.
Second,the additives may also have much moisture.
To sum up, solutions can be adopted: appropriately extend the mixing time of the mixer and use the cooling mixer,it will effectively remove the moisture in the raw materials.
Third, sheet MICROTEK points exceeded the standard, also known as "fish eye."
The common causes of crystal point formation are: some PVC resin particles are not plasticized or not plasticized well. The reasons are as follows: PVC resin with poor quality itself. Under the condition that the PVC resin is not changed, the measures for solving the problem are:
1) prolong mixing time and improve the mixing temperature, promoting the absorption of additives. And use the high quality hybrid units, mixing units on the pre-plasticizing effect of materials is irreplaceable.
Second, mixed material can be placed for half a day or a day, let it cure, and then use it.
Third, improving the setting temperature of barrel, increasing the screw speed, increasing the die pressure, it can further improve the plasticizing property.
Fourth, formulation, we must select the appropriate additives carefully, and the amount of additive,and the additive market is confusion at the moment, differences in product quality, need to be chose carefully and find a good balance between price and
Overview, we need to consider all above reasons, choosing the optimal solution. Some solutions are contradictory, such as raising the temperature may lead to yellowing of the sheet, and more stabilizers may cause rising costs and so on. Only by groping forward in practice.
Tongxiang long Cheng Plastic Co., Ltd. has nearly 20 years experience on PVC granule
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