PVC-O, Chinese name biaxially oriented polyvinyl chloride, is the latest evolution of PVC plastic pipe. The plastic pipe manufactured by special orientation processing technology will be extruded axially by PVC-U plastic pipe produced by extrusion method. And radial stretching, so that the long-chain PVC molecules in the pipe are arranged in a biaxial direction to obtain a new PVC pipe with high strength, high toughness, high impact resistance and fatigue resistance.

Many high molecular polymers have their molecular alignment through orientation processing (or orientation), which can significantly improve their performance. In fact, many of the competitive advantages of plastic products in the market rely on the superior performance of oriented processing, such as fiber, biaxially stretched film, containers and so on. The orientation plus 212212 art can improve the performance of plastic pipes on the one hand, and reduce the consumption of materials on the other hand. It is a cutting-edge technology that conforms to the general direction of sustainable development. The biaxially oriented polyvinyl chloride (PVC-O) pipe is a plastic pipe manufactured by a special orientation processing process. The processing process is to axially stretch and radially pull the PVC-U plastic pipe produced by the extrusion method. Stretching, the long-chain PVC molecules in the pipe are arranged in a biaxial direction, and the new PVC plastic pipe with high strength, high toughness, high impact resistance and fatigue resistance is obtained, and the performance is far superior to ordinary PVC-U plastic pipe. Research and development of PVC-O plastic pipe can greatly save raw material resources, reduce costs, improve product performance, and have obvious economic and social benefits.

 Let's take a look at the difference between PVC-O and traditional water supply pipes.

PVC-O was first developed in the UK in 1970 by Yorkshire lmperial Plastics (Uponor). Later, Australian Vinidex (1986), American Upomor-ETI (1990), Dutch Polva and French Seperef were also produced. In the early days, the "off-line" process (two-step process) was used to expand the extruded and cooled PVC-U pipe sections (thick blanks) into the mold by heating and pressing. Size to achieve orientation. The experimental research and practical application prove that PVC-O has extraordinary performance, but the "offline" processing technology has low production speed and high equipment investment, which is difficult to promote. Later, it was developed to "in-line" the orientation during the extrusion process to continuously produce PVC-O. The production process is a one-step processing method, that is, in the pipe extrusion production line, the extruded PVC-U pipe (thick material embryo) is biaxially oriented by radial expansion and axial stretching, and then cooled and shaped. Become a PVC-O pipe. The “online” biaxial orientation production process greatly increases production efficiency, reduces manufacturing costs, and enhances the competitiveness of PVC-O and other tubing.

PVC-O pipes have been used in the United Kingdom, France, the Netherlands, Portugal, the United States, Australia, South Africa and Japan for many years. The United States, Australia and other countries have issued PVC-O product standards, and the International Standards Organization has also published the PVC-O standard - ISO/DIS 16422-2006. Table 2 lists some of the PVC-O pipes and manufacturing companies on the international market. There are already some research institutes and large enterprise groups in China that are exploring and developing.

So what is the production principle of PVC-O?

1. Tensile orientation mechanism of polymer materials

The stretching and orientation process of the polymer material is a process in which the molecules are arranged from disordered to ordered under the action of external force under the temperature condition between the glass transition temperature and the melting temperature (generally near the softening point). Due to the ordered arrangement of the polymer molecular chains, the material changes from isotropic to anisotropic, that is, the strength of the material in the direction of molecular orientation is greatly increased, and the strength perpendicular to the stretching direction is greatly reduced, that is, the material By stretching the orientation, the intensity perpendicular to the stretching direction is superimposed on the strength in the direction of the molecular orientation. Biaxial stretching is a process in which the strength of the stretched surface perpendicular to the biaxial stretching is superimposed on the strength of the direction of the stretched surface by biaxial stretching, thereby increasing the strength of the direction of the stretched surface of the material. The tensile orientation of the polymer material is determined between the glass transition temperature and the melting temperature. If it is lower than the glass transition temperature, the molecular chain is frozen. Stretching at this temperature will only cause the material to be forced. Stretched and destroyed. If it is higher than the melting temperature, the molecular chain can move freely, and the stretched molecular chain cannot achieve orientation. The most effective molecular orientation can be achieved and maintained only between the glass transition temperature and the melting temperature, preferably near the softening point of the material.

2, ratio and stretching rate

Stretching orientation, in plain language, straightens the curled molecular chains and aligns them in the direction of stretching. When the stretching ratio is appropriately increased, the degree of molecular orientation is increased, and the strength of the material is also increased. However, excessively increasing the stretching ratio leads to the destruction of the material. In plain language, the molecular chain of the material is broken and the material is destroyed. In addition, if the stretching temperature is too high and the stretching rate is too low, the molecular chain will be slack during the stretching process, that is, the molecular chain has sufficient time and ability to return to the original curl state during the stretching process, so that The degree of orientation is reduced. Therefore, in order to obtain a more ideal degree of orientation, a reasonable stretching temperature and a faster stretching rate should be established, and the temperature of the material after stretching should be lowered below the glass transition temperature in time.

3. Biaxial stretching of PVC-U pipe

PVC is an amorphous amorphous plastic. Since chlorine in the molecule has a large polarity, it is rigid, has a high glass transition temperature, and has no clear melting point. Plastic pipes of this type are more suitable for biaxial stretching orientation than other crystalline polyolefin pipes. PVC plastic pipes are easily uniaxially stretched during the forming process. PVC plastic pipe is easy to perform uniaxial stretching orientation during the molding process, that is, axial stretching orientation, and this orientation can be realized by increasing the ratio of pipe drawing and extrusion. However, this axial stretching orientation is meaningless to the performance of the pipe because it increases the strength of the pipe orientation by the tensile orientation, but reduces the radial (ie, circumferential) strength of the pipe. For plastic pipes, especially for water pipes, it is very harmful, because it will greatly reduce the hydraulic burst strength of the pipe, which is also the reason why the pipe quality standard should specify that the longitudinal retraction rate of the pipe must be less than or equal to 5%. . The desired stretch orientation should be bidirectional, i.e., biaxially oriented, by biaxially oriented orientation, which increases the axial strength of the tubing while also increasing the radial (i.e., hoop) strength of the tubing. That is to say, the overall performance of the pipe is improved by the biaxial stretching orientation. On the basis of greatly increasing the strength of the pipe material and the original hydraulic bursting strength of the pipe, the method of reducing the wall thickness saves the raw materials and reduces the cost of the product.

In foreign countries, PVC-O is mainly used in water supply pipelines, mine pipelines, non-excavation laying and repair pipelines, gas pipeline networks and other fields. In some countries, the application of PVC-O in the drinking water network has gradually expanded to become a substitute for PVC-U. According to the Wavin Group's survey, the Netherlands, France, Spain, North America, South America, Australia and other countries are using PVC in large quantities. O pipe. The Dutch drinking water network has already used PVC-O pipes 100%, and France and other countries will adopt them in the past one or two years. The mine environment is particularly harsh and the safety requirements are particularly strict. In a corrosive underground environment, PVC-O pipes with high strength, high toughness, impact resistance and non-corrosion are very competitive. The use of trenchless technology to lay new pipelines and repair old pipelines is a huge market, and DuralinerTM repair methods can significantly save money. PVC-O pipelines are used in gas pipeline networks in the Netherlands and other countries, providing good strength, stiffness and toughness, and materials and laying costs are much lower than competing materials.

The Wavin Group of the Netherlands has produced and used PVC-O pipes for many years. According to the Wavin Group, compared with PVC-U plastic pipes, the investment and expenditure of PVC-O pipes are as follows.

(1) The average saving of raw materials is 11.58%.

(2) PVC-O investment increased by 2.5-3 times (in European case).

(3) The yield is 300-650 kg/h, and the length is increased by 20%-40%.

(4) The scrap rate increases by 2%-4%.

(5) Energy consumption increased by 25%.

(6) Manpower running costs increase by 10%-15%.

(7) The length of the production line is increased by 25%.

Comprehensive calculation, 1 m pipe savings investment 33% -44%, the price can be increased by 10% -15%. It can be seen that PVC-O pipe is a one-time investment and lifetime income.

The changes and development of the international situation have provided an unprecedented historical opportunity for the development of PVC plastic pipe systems in China. The soaring oil prices have severely affected the polyalkylene piping systems that compete with PVC piping systems in many applications, while coal-based PVC has increased competitiveness by maintaining lower prices. PVC plastic pipe system has a history of nearly 70 years. Because of its high modulus, high strength and low price, it has been the most widely used plastic pipe system in the world. It has been obtained in many fields of modern society. A wide range of applications. China's plastic pipe industry has developed rapidly and has become one of the world's largest producers and suppliers of plastic pipes. China's PVC plastic pipe production capacity is above 2 million t / a, accounting for only about 50% of the total plastic pipe, while in developed countries, PVC plastic pipe consumption generally accounts for 70% -80% of the plastic pipe market.

Due to the extraordinary versatility of PVC, outstanding durability and economy, it will be the material of choice for pipes in the future. As a new type of rhyme tube, PVC-O has the advantages of good performance, low cost, light pipe quality, easy handling and laying, etc. Its superior performance makes it suitable for higher pressure and harsher environments. Reducing the cost of a product while improving its performance is a problem that people have been pursuing but not easy to achieve. The biaxially oriented PVC pipe not only provides an example for this subject, but also lays the foundation for the future development of a new product.

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