[Science Stickers] Technical Processing Issues in the Production of Chlorinated Polyvinyl Chloride (PVC-C) Pipes

1. Formula

1. In order to become chlorinated polyvinyl chloride plastic (PVC-C) hot water pipes and electric power, cable buried pipes, why add chlorinated polyvinyl chloride (CPVC) in different parts? This is because chlorinated polyvinyl chloride ( There are certain standards for the physical and chemical indicators of CPVC. Among them, the chlorine content of 67.0±0.1% is very important for processing. The water content of CPVC in Japan (that is, volatile matter) is ≤0.1%. Set as the main 0.2%, and cannot remain unchanged for one year, only for three months. Therefore, using pure CPVC as a model to test its Vicat heat resistance index, the CPVC produced in Japan can reach 131°C, while the domestic CPVC can only reach 126°C. Adding additives other than plasticizers and other high polymers to the formula will reduce the Vicat temperature. In addition, the equipment, mold, process temperature and pressure, as well as the residence time of the screw, cooling traction, and flaring will be affected. As a result, the field test and product sampling test at the Institute of Zhongyuan Chemical Co., Ltd. in Japan from the end of February to the beginning of March 2001 were Vicat ≤116°C. Therefore, for international and domestic standard PVC-C hot water pipes, it was ≥11O. The index of ℃ means that there is a little margin. That is to say, use 100 parts of CPVC and various additives to cooperate, under certain process conditions, equipment, molds, etc., and careful operation will pass; as for the pipe fittings ≥103℃, you can add 10 parts of PVC or increase 0.1-0.2 lubricating and stabilizing agent is sufficient. Here again, it is recommended that the main raw material ratio of the power cable buried pipe is 55 parts of CPVC and 45 parts of PVC. I once asked the Central Laboratory of Beijing Research Institute of Chemical Industry of the Ministry of Chemical Industry to conduct a test of 50 CPVC vs. 50 PVC. The results did not improve, but decreased. Researchers in Beijing have been studying this mechanism. We recommend 55 CPVC to readers. 45 parts of PVC is quite reliable to reach the Japanese and domestic industry standards of Vicat ≥93℃. Of course, other additives should also be paid attention to. In addition, the Vicat of a thin tube with a thickness of 3mm should be within the range of 90℃±14℃.
2. Why add CPE after joining MBS?The strength is increased, but due to the excessive double bonds, the UV radiation will cause fracture, and the strength will decrease. This is when the pipe arrives at the construction site, if it is not buried in time, it only takes 5-7 days for the strength to drop by half. Therefore, the formula For example, adding 6-8 parts of MBS (it makes the Vicat temperature not drop much, which is another feature of MBS), and adding 3 parts of CPE can improve cold resistance and weather resistance. It has successively designed formulas for strong ultraviolet radiation in the cold season in the northwest and humid in the southwest to meet the protection of high-voltage and ultra-high-voltage cables in the power system.
3. Why should liquid paraffin (white oil) be added when adding CPE? According to a report from the United States at the 31st World Plastics Engineers Annual Conference, they tested in the cold, desert and high temperature of Arizona and New Jersey, and CPE has white oil. In the case of, its impact resistance can be improved and improved by several times, ten times and dozens of times. The improvement of several times, ten times, and dozens of times here refers to processing under the condition of the same formula. The influence of equipment, molds, and process conditions will vary. During production, put 3 parts of CPE in a plastic bucket, add 0.3 parts of white oil, and mix it. If it is the best sucked, the unsucked white oil will be used in the next pot of formula. This is also a way to test the quality of CPE, a thermoplastic elastomer. It is good if it is exhausted.

4. The impact resistance of CPE in PVC materials: The principle of white oil increasing the impact resistance of CPE: Since CPE particles contain a large number of linear CPE molecules, these molecules are entangled with each other, and it is difficult to evenly disperse into PVC during processing. In the middle, so the dispersion is poor, which affects the impact resistance of the material. Adding 10% white oil can stretch the linear molecules of CPE, which is convenient to move and disperse into the PVC molecular chain, thereby increasing the impact resistance of PVC materials.

5. Why is it not recommended to use calcium stearate in the production of chlorinated polyvinyl chloride and polyvinyl chloride products? This is because calcium stearate tends to cause white polyvinyl chloride when heated at a temperature higher than 160°C and for a long time. The plastic turns into reddish color. It can react with the decomposed HCL to form a very brittle calcium chloride compound, which is extremely unfavorable to the performance of the product when it is applied. Therefore, currently in the processing of polyhalogenated olefin plastic products, Generally, calcium stearate is not added, and only a small amount is added in view of pressure lubrication stability during injection molding. Of course, when there is titanium dioxide (titanium dioxide), it is advisable to add 0.06-0.12 parts of sodium carbonate Or 0.09-0.19 parts of sodium bicarbonate can avoid the disadvantages mentioned above.

2. Processing technology

Kneading point
A, heating sequence
CPVC or advanced kneading pot with PVC, followed by stabilizers, followed by various additives, and finally MBS and CPE with white oil to improve the impact strength of the system. What I want to introduce here is that polyhalogenated olefins require the entry of stabilizers to prevent the accelerated decomposition of hydrogen chloride (HCL) after being heated. The rest is added later to increase the chance of contact between stabilizers and polyhalogenated olefins. As for the final addition of MBS and CPE adding white oil makes the material characteristics of the entire batching system show, which is what the user requires.
B. Kneading temperature The
kneading temperature should be ≤105℃. At present, some production units reach ≥110℃, which is not good. Kneading only plays a role of mixing, and there is no requirement for plasticization. For example, excessively high kneading temperature and long time will bring thermal stress to the material. , It will bring problems to the future performance and installation and construction of the pipe.
C. The torque
of the twin-screw extruder during production. In view of the fact that it contains CPVC raw materials, its processing fluidity is poor. Therefore, in addition to considering this situation in the formula, we also set the torque at 35 to 60 to produce. Generally 40-55 is better. It needs to adjust the temperature and pressure, and even improve the formula finally, so that it can be produced. Only when the performance of the finished product can reach the standard required by the original imagination, it is considered a success.
D. Flaring requirements
PVC-C hot water pipes do not need to be flared, they are connected by pipe fittings, and power cable protection sleeves need to be flared. This has requirements for the equipment in terms of the shape and thickness of the pipe wall, and the focus is on adjustment The heating time and temperature of the pipe can make the pipe flaring area not deform. Generally, the flaring temperature is much higher than the extrusion temperature. The extrusion temperature should not exceed 195°C, and the flaring temperature should be around 250°C. Domestically produced instruments reflect more than 300°C. This requires attention.

3. Attention to the use of power cable protection sleeves buried in the ground

The wall thickness of the buried power cable protection sleeve is selected according to the different applications. Have done the steam 20 test and the cantilever beam pressure test. The specifications of the manufacturer can be used for road load, organic non-isolation zone, pedestrian green belt, in addition, there are shallow buried depths, and there is no water in the ground. The avoidance of frozen soil has become a consideration.

Fourth, the recommendation of materials

For PVC-C power pipes, you can use heavy calcium carbonate instead of light activated calcium carbonate. PVC-C hot water pipes use pure CPVC, so the amount of titanium dioxide is large, and calcium carbonate is not suitable. Add or add 0.5-1 part symbolically. Here to mention the red color of PVC-C power pipes. Generally, inorganic pigments are used. All organic pigments will decompose when exposed to high temperatures, which will make the color darker. Tests conducted in Japan's Zhongyuan Research have also confirmed this. Finally, to produce pipes that meet the standards, especially for users to be able to use it safely, there are still many issues that need to be paid attention to. Kaixin Pipeline Technology Co., Ltd. uses an imported KraussMaffei extrusion production line, which meets the production needs of all caliber products while ensuring the stability of product performance. Customers are welcome to come and order.

This article comes from the Internet, only for learning and communication, no commercial purpose.

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