The common PVC pipes are milky white. Below we will use the water supply pipe as the representative to introduce the reason of the yellowing of PVC pipes. The yellowing of PVC pipes is mainly due to the dehydrochlorination reaction caused by the decomposition of PVC. This conjugated multi-olefin series is yellow, which causes the decomposition of PVC and the formulation, process and equipment of PVC. We will introduce the reasons for the yellowing of PVC pipe from these aspects.

Formulation problem
When a manufacturer replaces an additive, it will cause the produced product to become yellow. We need to adjust the formula according to the following aspects and according to the actual situation:
(1) increase the content of stabilizer
(2) To adjust the balance of internal and external lubricants
(3) Resolve yellowing by pigment color supplement or increase of fluorescent whitening agent ratio
2. Process problems
During the extrusion process, the PVC is heated and sheared by the screw and the barrel. If it is not handled properly, PVC may be decomposed to some extent.
(1) The annoying temperature of the barrel can be appropriately lowered to improve the yellowing phenomenon.
(2) In the appropriate range, it is necessary to reduce the rotation speed of the main machine, increase the proportion of feeding, reduce the shearing, and evenly mix the materials in the screw groove, so that the stabilizer can be fully exerted, and the yellowing of the PVC pipe can be alleviated.
3. Equipment problems
(1) It is necessary to regularly check whether the electric thermocouples in each area of the barrel are working normally, and whether the fan operation in each area is normal. If there is a problem with the thermocouple or the fan, the barrel will be partially overheated and the product will be yellow.
(2) Check whether the heat transfer oil of the screw is sufficient, whether the oil pump works normally, and whether the oil pipe is blocked. If the friction heat of the screw is not able to be effectively discharged, the screw may be overheated to cause the material to decompose and turn yellow.
(3) In the case of severe screw wear, the gap between the screw and the barrel also becomes larger, and the pushing ability of the screw to the material also deteriorates, which may cause the material to flow back in the barrel. The heating time will also become longer, resulting in yellowing.
(4) Regularly check the mixing device, whether the mixing time is normal, whether the cold water circulation and the cold water temperature are normal. If the mixing time is too long or the cold mixing cannot be cooled to the normal temperature, it may cause mixing or storage. The stabilizer will be consumed in the formulation, so that the effectiveness of the stabilizer will be reduced, resulting in yellowing of the PVC pipe during the production process.
The above is the reason for analyzing the yellowing of PVC pipes from the three aspects of formulation, process and equipment, hoping to help everyone.

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