Views: 0 Author: Site Editor Publish Time: 2023-02-10 Origin: Site
The water and electricity lines in home decoration are like the blood vessels of the human body. Once blocked or leaked, the consequences can be known. We suggest not only choosing high-quality products, but also professional construction and installation to ensure the normal use of various piping systems. How to ensure the welding quality of PP-R pipes? Here are a few things to keep in mind:
PP-R hot melt welding temperature: 260±10℃. If the temperature is lower than 255°C, the pipes and fittings are only melted on a thin surface layer. Once they are welded, the strength of the weld cannot be guaranteed. This is what we usually call virtual welding; on the contrary , if the temperature is higher than 270 ° C, the surface molecules of the pipe and pipe fittings are damaged by the high temperature, making PP-R form a thin liquid and form interface stacking, which will make the inner diameter of the pipe smaller after connection, and more importantly, the connection part Embrittlement can occur, especially when water pressurization is done after the piping system is fully completed, which is a common problem.
The length of the constant temperature time is one of the important signs of the performance of the hot melt welding equipment. After the hot melt equipment is heated up to the set temperature, there is still a problem of heat consumption, especially in winter, the heat consumption at the tuyere is very large even in the non-working interval, and once it is in operation, the pipes and fittings They are all consuming heat energy respectively, which requires the hot melt equipment to have a strong heat energy storage capacity, high sensitivity temperature sensing ability and secondary heating ability.
Qualified welding sleeves are designed with full consideration of the cross-sectional structure and welding depth of the pipe after welding, as well as the non-stick surface and smooth surface. At present, there are hundreds of domestic manufacturers that weld PP-R, PB, PE and other water supply pipes by hot-melt method. Due to the different raw materials used in the pipes produced by various manufacturers, different environmental conditions, and different equipment selections, the sizes of pipes and fittings produced by each manufacturer are also different. Therefore, each pipe manufacturer and user must choose a welding sleeve suitable for their own pipe diameter. For the operator, after the last welding, the surface of the welding sleeve should be cleaned necessary to avoid impurities such as sticky materials in the welding part.
When welding pipes with a caliber of 40mm or more, due to the large caliber, it is beyond the reach of personal strength, and mechanical equipment must be used to ensure the depth and straightness of the pipe entering the fitting. We found that on many construction sites, five to six workers are used to weld a 110mm caliber interface, and it takes a lot of effort to ensure the straightness and insertion depth of the pipe. The entire pipeline is tortuous and stressful situations.
It should be said that the piping system that is constructed and operated in strict accordance with the requirements of the welding process and welding technology will not have any problems when used under normal temperature and pressure. However, in our daily construction, we often find that bursts or sand holes occur at the joints of pipes and fittings.
(1) The temperature of the fusion welding machine is incorrect, too high or too low, which changes the properties of polypropylene;
(2) There is dirt on the surface of the welding sleeve, or the surface coating falls off, causing sand holes in the contact part with the pipe;
(3) The size of the welding sleeve is wrong and the design is wrong, which makes the melting depth and welding structure of the pipe inappropriate;
(4) The welding surface of the pipe is not cleaned before welding;
(5) The welded pipe and fittings are not kept concentric or straight.
(1) Use detergent (or alcohol) and towels to clean the surface of the welded part of the pipe and fittings;
(2) When the pre-assembled parts are welded, mark the required positions of the pipes and fittings before connecting;
(3) The welding of pipes with a diameter of 40mm or more must use plane and vertical pipe welding machines;
(4) After the pipes are welded, wipe the welding sleeve with a dry cloth or dry paper to ensure that the welding sleeve is clean.
(1) After inserting the pipe and fitting into the heating jacket and heating head respectively, do not rotate or move too fast (enough time for the material to melt).
(2) After heating, remove the tube and fittings from the heating element, do not rotate the heating part.
(3) Immediately after heating, press the pipe and fitting together along the axis without turning. Strictly adhere to the hold time and cool down time of the hot melt welding standard.
(4) In order to ensure the welding quality of the pipeline, please choose the configuration hot-melt machine provided by ERA Company.
There is a mantra in the pipeline industry "Three points depend on quality, seven points depend on safety.
It can be seen that whether the design and installation are standardized plays an important role in the later use of the pipeline. The pressure test process after the installation is completed is an important way to test the quality of the pipeline installation.
(1) The pressure test pressure of the pipeline shall not be less than 1.0Mpa; the hydraulic test shall be carried out 24 hours after the connection is completed. Before the test, the piping shall be fixed and the joints shall be exposed.
(2) The pipe is filled with water, and the air is exhausted first. The boost time shall not be less than 10 minutes; the pressure shall be maintained for 2 hours, and the test pressure drop shall not exceed 0.06Mpa.
(3) Pressure testing is required before and after the pipe is buried, and other accessories should be opened, and stop valves, faucets, etc. should not be used as plugs.
(1) There is no pressure test before the pipeline is buried, and there is a big risk in the later use.
(2) The pressure test pressure is low and the time is short. If there is a hidden danger of "false welding" at the joint position, it is not exposed in time, and there will be a hidden danger of water leakage in the later stage.
(3) Effective protective measures are not taken after the pipeline pressure test. For example, during the later construction process, the pipeline is damaged by external force rolling, impact, etc., and there is no secondary pressure test after the pipeline is buried, there will be hidden dangers of water leakage.
(4) The pressure test is mainly to check whether the pipes and pipe fittings are damaged during transportation, handling and installation. Because the pressure test pressure is low and the pressure holding time is not long, the problem of "false welding" of pipe jointscannot be completely eliminated. It is recommended to install and pressure test by a professional plumber.
Polypropylene random copolymer [1] is also a type of polypropylene. The basic structure of its polymer chain is modified by adding different types of monomer molecules. Ethylene is the most commonly used monomer that causes changes in the physical properties of polypropylene. Compared with PP homopolymers, random copolymers have improved optical properties (increased transparency and reduced haze), improved impact resistance, increased flexibility, lower melting temperatures, and thus lower thermal welding temperatures. ;Also essentially identical to homopolymers in terms of chemical stability, water vapor barrier properties and organoleptic properties (low odor and taste). It is used in the fields of blow molding, injection molding, extrusion, film and sheet extrusion processing, household water pipes, food packaging materials, pharmaceutical packaging materials and daily consumer goods.
chemical structure
PP random copolymer [2] generally contains 1-7% (weight) ethylene molecules and 99-93% (weight) propylene molecules. In the polymer chain, ethylene molecules are randomly inserted between propylene molecules. In this random or statistical copolymer, most (usually 75%) of the ethylene is incorporated as single-molecule insertions, called X3 groups (three consecutive ethylenes [CH2] arranged in sequence On the main chain), this can also be seen as an ethylene molecule inserted between two propylene molecules.
Another 25% of ethylene is incorporated into the main chain through multi-molecule insertion, also called the X5 group, because there are 5 consecutive methylene groups (two ethylene molecules are inserted between two propylene molecules) . It is difficult to distinguish between X5 and higher groups such as X7, X9, etc. In view of this, the ethylene content of XS and higher groups is calculated as >X3%.
The randomness ratio X3/X5 can be measured. When the percentage of groups above X3 is large, the crystallinity of the copolymer will be significantly reduced, which has a great impact on the ultimate properties of the random copolymer. Very high levels of ethylene in the copolymer have an effect on polymer crystallinity similar to that seen at high atactic polypropylene levels.
Random PP copolymers differ from homopolymers in that the ethylene molecules randomly inserted into the polymer backbone hinder the crystalline arrangement of the polymer molecules. The reduction in the crystallinity of the copolymer causes changes in the physical properties: compared with the PP homopolymer, the stiffness of the random copolymer is reduced, the impact resistance is improved, and the transparency is better. Ethylene copolymers also have lower melting temperatures, which can be an advantage in some applications.
Random copolymers contain more extractables and random PP, as well as polymer chains with a much higher ethylene content. This higher extractable content is present in all commercial copolymer materials to varying degrees depending on the polymerization process and creates difficulties in meeting Federal Food Administration (FDA) food contact regulations.
Manufacturing method
Ethylene/propylene random copolymer is produced by the simultaneous polymerization of ethylene molecules and propylene molecules. The reactor used is the same as that used to produce PP homopolymer. Ethylene molecules are smaller than propylene molecules and react faster (about ten times more reactive) than propylene. This weakens the stereospecificity of the catalyst and increases its activity, resulting in an increase in the amount of random polypropylene. In order to reduce the generation of this random substance, it is necessary to lower the reaction temperature, thereby reducing the activity of the catalyst and reducing the content of random isomers in the final product to obtain a product with more balanced properties.
Random copolymers with high ethylene content (>3%) are difficult to handle during the production process and are difficult to polymerize in hexane diluent due to the secondary by-products of the reaction (random polypropylene and ethylene content). Very high copolymer) soluble in hexane. This is also true for bulk polymerization of liquid propylene, albeit with lower solubility. The hexane dilution process produces a large number of by-products that must be separated in the hexane recirculation stage, which increases the overall production cost, but results in a cleaner polymer with a small amount of soluble components. In bulk polymerization processes, these impurities can remain in the polymer and cause problems when processing flake materials. Moreover, the final copolymer product contains more soluble impurities. Using organic solvents for secondary cleaning can remove most impurities, but it will increase the total production cost of the copolymer. Generally, when the by-product content is high, the flaky random copolymer will become sticky. This problem is more prominent when the ethylene content is higher than 3.5% (weight).
The melting point decrease of the copolymer is directly related to the ethylene content. At 7% ethylene content, the copolymer has been reported to have a melting point as low as 152°F. The X3 content has a greater impact on the melting point of the copolymer than does X3 and higher gene content. It also depends on the catalyst itself and its ability to bind ethylene with the X3 group instead of the X5 group.
Material properties
Physical properties: Generally speaking, random PP copolymers have better flexibility and lower rigidity than PP homopolymers. They maintain moderate impact strength when temperatures drop to 32°F, but are of limited usefulness when temperatures drop to -4°F. The flexural modulus of the copolymer (secant modulus at 1% strain) ranges from 483 to 1034MPa, while that of the homopolymer ranges from 1034 to 1379MPa. Effect of molecular weight of PP copolymer material on rigidity
Not as big as PP homopolymer. Notched Izod impact strength is generally in the range of 0.8 to 1.4 ft·lb/in.
Chemical resistance: Random PP copolymer is resistant to acids. Highly resistant to the effects of alkalis, alcohols, low boiling hydrocarbon solvents and many organic chemicals. At room temperature, PP copolymer is basically insoluble in most organic solvents. Also, when exposed to soap, soap lye. They are not subject to environmental stress cracking damage like many other polymers when exposed to aqueous reagents and alcohols. When in contact with certain chemicals, especially liquid hydrocarbons. Chlorinated organic compounds and strong oxidants can cause surface cracks or swelling. Non-polar compounds are generally more readily absorbed by polypropylene than polar compounds.
Barrier properties: PP copolymers and homopolymers have very low water vapor permeability (0.5 g/ml/100 square inches/24 hours). These properties can be improved through orientation. Stretch blow molded polypropylene bottles have improved water vapor permeability resistance to 0.3 and oxygen permeability to 2500.
Electrical properties: In general, polypropylene has good electrical properties, including: high dielectric strength, low dielectric constant and low dissipation factor; however, homopolymers are generally chosen for power applications.
