Views:0 Author:Site Editor Publish Time: 2020-06-22 Origin:Site
1. The toxicity of UPVC pipes
UPVC pipes are used in water supply projects. People's first concern is the toxicity of the pipes. The toxicity of UPVC pipes is mainly reflected in two links in the manufacturing process. The first is based on polyvinyl chloride resin as the main raw material, containing vinyl chloride monomer (VCM), which is a carcinogenic substance recognized by the medical community. In some developed countries, the content of vinyl chloride monomer in food-grade UPVC resin must not exceed 5PPM, and its products must not exceed 1PPM, so that the products are harmless to humans. The second is the amount of heavy metal stabilizers required by the production industry, and the amount added directly affects the content of free heavy metal ions dialysis into the water on the pipe wall, thereby affecting the water quality sanitation index. In the 1980s, with the development of my country's food industry, plastic packaging placed strict requirements on resin hygiene. Resin production plants are suitable for development and improvement. The content of vinyl chloride monomer in UPVC resins produced in China can be stabilized at 5-10PPM. The Ministry of Health and the National Bureau of Standards have formulated national standards (GB4625-87), which stipulate the content standards and inspection methods of vinyl chloride monomers in PVC resins for food and their products. Since the 1980s, many manufacturers have successively introduced twin-screw extruders with the international advanced level from the United States and Germany. Their plasticizing effects are good, the stabilizers used are greatly reduced, and it is easy to ensure the hygienic requirements of VPC pipes. At the same time, the Ministry of Health made specific regulations with reference to the relevant regulations and testing methods in the international standard ISO.
2. UPVC pipe service life problem
When formulating international standards for UPVC pipes and fittings, China has integrated domestic and foreign technical levels, and determined that the rated worker's working pressure of pipes in the standard is 0.6MPa and 1.0MPa, and the selected hoop design stress value is 100kfg/cm2. From this, it is estimated that the wall thickness of various pipes and parts under different rated working pressures and their service life is 50 years.
3. Problems of brittleness and aging of UPVC pipes
To improve the impact resistance and aging resistance of UPVC pipes, the development of modern plastic industry and technology has been able to solve. Its technical measures are reflected in the formula design of plastic pipe fittings, which should be able to ensure the forming process and the physical properties of the pipe.