What materials are PE pipes made of?
What materials are PE pipes made of?
PE pipes In China's municipal pipe market, plastic pipes are developing steadily. PE pipes, PP-R pipes, and UPVC pipes all have their place. Among them, the strong development momentum of PE pipes is the most eye-catching. PE pipes are widely used. Among them, water supply pipe and gas pipe are its two largest application markets.
PE resin is made from the polymerization of monomer ethylene. Due to different polymerization conditions such as pressure and temperature during polymerization, resins with different densities can be obtained, so there are high-density polyethylene, medium-density polyethylene and low-density polymer. Ethylene. When processing different types of PE pipes, according to different application conditions, different resin grades are selected, and the requirements for extruders and molds are also different.
The materials of polyethylene pipes are divided into five grades of PE32, PE40, PE63, PE80, and PE100 internationally, and the materials used for gas pipes and water supply pipes are mainly PE80 and PE100. There is no grading of special materials for polyethylene pipes in China, which makes it difficult for domestic manufacturers of polyethylene gas pipes and water supply pipes to choose raw materials, and also brings a lot of hidden dangers to the use of polyethylene pipes.
Therefore, the National Bureau of Standards made a large number of revisions in the new standard GB / T13663-2000, which stipulates that different levels of PE80 and PE100 of the water supply pipe correspond to different pressure strengths, and removes the tensile strength performance in the old standard, and increases the fracture Elongation (greater than 350%), which emphasizes basic toughness.
PE water supply pipe
PE pipes for water supply are the replacement products of traditional steel pipes and PVC drinking water pipes.
The water supply pipe must bear a certain pressure, usually PE resin with large molecular weight and good mechanical properties is selected, such as HDPE resin. LDPE resin has low tensile strength, poor pressure resistance, poor rigidity, poor dimensional stability during molding, and difficult connection. It is not suitable as a material for water supply pressure pipes. However, due to its high hygienic index, LDPE, especially LLDPE resin, has become a common material for the production of drinking water pipes. LDPE and LLDPE resins have low melt viscosity, good fluidity, and easy processing. Therefore, they have a wide choice of melt index, usually MI is between 0.3-3g / 10min.
A good pipeline should not only have good economy, but also have a series of advantages such as stable and reliable interfaces, impact resistance, cracking resistance, aging resistance, corrosion resistance, etc. Compared with traditional pipes, HDPE pipeline system has the following one Series advantages:
(1) Reliable connection: the polyethylene pipeline system is connected by electric heat fusion, and the strength of the joint is higher than the strength of the pipeline body.
⑵Good low-temperature impact resistance: The low-temperature embrittlement temperature of polyethylene is extremely low, and it can be safely used in the temperature range of -60-60 ℃. During winter construction, due to the good impact resistance of the material, brittle cracking of the pipe will not occur.
(3) Good resistance to stress cracking: HDPE has low notch sensitivity, high shear strength and excellent scratch resistance, and environmental stress cracking resistance is also very prominent.
⑷Good chemical resistance: HDPE pipelines can resist the corrosion of various chemical media, and the chemical substances present in the soil will not cause any degradation of the pipeline. Polyethylene is an electrical insulator, so it does not rot, rust or electrochemically corrode; it also does not promote the growth of algae, bacteria or fungi.
⑸Aging resistance and long service life: Polyethylene pipes containing 2-2.5% uniformly distributed carbon black can be stored outdoors or used for 50 years without being damaged by ultraviolet radiation.
⑹ Good wear resistance: The comparison test of the wear resistance of HDPE pipe and steel pipe shows that the wear resistance of HDPE pipe is 4 times that of steel pipe. In the field of mud transportation, HDPE pipes have better wear resistance than steel pipes, which means that HDPE pipes have a longer service life and better economy.
⑺ Good flexibility: The flexibility of HDPE pipeline makes it easy to bend. In engineering, it can bypass the obstacle by changing the direction of the pipeline. In many occasions, the flexibility of the pipeline can reduce the amount of pipe fittings and reduce the installation cost.
⑻Small flow resistance: HDPE pipeline has a smooth inner surface, and its Manning coefficient is 0.009. The smooth performance and non-adhesive properties ensure that HDPE pipes have a higher transport capacity than traditional pipes, while also reducing the pressure loss of pipelines and energy consumption for water delivery.
⑼ Convenient handling: HDPE pipes are lighter than concrete pipes, galvanized pipes and steel pipes. It is easy to handle and install. Lower manpower and equipment requirements mean that the installation cost of the project is greatly reduced.
⑽ A variety of new construction methods: HDPE pipelines have a variety of construction techniques. In addition to traditional excavation methods, a variety of new non-excavation techniques such as pipe jacking, directional drilling, liner, Split pipes and other methods are used for construction. This is the only choice for places where excavation is not allowed, so HDPE pipeline applications are more extensive.
1. Softness: Because PE-RT is relatively soft. Therefore, no special tools are needed during construction, so the construction cost is relatively low. 2. Thermal conductivity: The pipes used for floor heating need to have good thermal conductivity. The thermal conductivity of PE-RT is better, and its thermal conductivity is twice that of PP-R and PP-B pipes. Very suitable for floor heating. 3. High temperature resistance: PE-RT can reach 90 ℃, while PEX can only reach 65 ℃. 4. Low-temperature thermal shock resistance: PE-RT has better low-temperature impact resistance. During the winter construction, the pipe is not easy to be broken due to impact, which increases the flexibility of construction arrangements. 5. Environmental protection: PE-RT and PP-R can be recycled without polluting the environment. And PEX can not be recycled will produce secondary pollution; 6, processing performance stability: PEX has problems such as controlling the degree of crosslinking and crosslinking uniformity, processing is complicated and processing directly affects the performance of the pipe. The PE-RT and PP-R are easy to process, the performance of the pipe is basically determined by the raw materials, and the performance is relatively stable. PE-RT is the abbreviation of Polyethylene Raised Temperature. It is a copolymer of ethylene monomer and 1-octene monomer. It is a medium-density ethylene-octene copolymer specially designed for heating systems. It has a narrow molecular weight distribution. , The special molecular structure of octene evenly distributed on the polymer main chain, it not only retains the original hygienic performance and processing performance of PE, but also strengthens the high temperature durability of a new type of special pipe material. The pipes produced from this raw material are mainly used in the field of hot water / heating pipes in buildings. Their durability is the same as the life of the building, with a minimum of 50 years. At the same time, it has good recycling and high added value.
■ Good hygienic performance: PE pipe processing does not add heavy metal salt stabilizer, the material is non-toxic, no scale layer, does not breed bacteria, and it solves the secondary pollution of urban drinking water.
■ Excellent corrosion resistance: Except for a few strong oxidants, it is resistant to various chemical media; no electrochemical corrosion.
■ Long service life: PE pipes can be safely used for more than 50 years under rated temperature and pressure conditions.
■ Good impact resistance: PE pipe has good toughness and high impact resistance, and heavy objects directly press on the pipeline, which will not cause the pipeline to break.
■ Reliable connection performance: The strength of the PE pipe hot melt or electric fusion interface is higher than the pipe body, and the joint will not be broken due to the movement of the soil or the effect of live load.
■ Good construction performance: light pipe quality, simple welding process, convenient construction, and low overall project cost.
■ Electrothermal fusion: the special electrothermal fusion welding machine is used to connect the straight pipe and the straight pipe, and the straight pipe and the pipe fitting. Generally used for tubes below 160mm.
■ Hot-melt butt connection: use special butt welding machine pipes to connect, generally used for pipes above 160mm.
■ Steel-plastic connection: It can be connected by flange, screw thread and other methods.
■ To facilitate construction and ensure construction quality, corresponding tools should also be prepared.
Such as: rotary cutter to cut the pipe; rotary scraper-scrape the oxide scale on the surface of the pipe; wall scraper-scrape the surface of the large-diameter pipe surface; gas shut-off tool-to achieve on-site gas shut-off operation
1. Clamp and clean the port
2. Adjust and smooth the port
3. Port straight
4. Pressure welding
5. Pressure relief cooling
■ Urban water pipe network system.
■ Urban and rural drinking water pipelines.
■ Material and liquid transportation pipelines in chemical industry, chemical fiber, food, forestry, printing and dyeing, pharmaceutical, light industry, papermaking, metallurgy and other industries.
■ Agricultural irrigation pipes.
■ Post and telecommunication lines, power wire protection sleeves.
■ Mine mortar transportation pipeline.
■ Post and telecommunication lines, power wire protection sleeves.
Characteristics of PE pipe:
HDPE is a non-polar thermoplastic resin with high crystallinity. The appearance of the original HDPE is milky white, with a certain degree of translucency in the thin section. PE has excellent resistance to most household and industrial chemicals. Certain types of chemicals cause chemical corrosion, such as corrosive oxidants (concentrated nitric acid), aromatic hydrocarbons (xylene) and halogenated hydrocarbons (carbon tetrachloride). The polymer is not hygroscopic and has good water vapor resistance, and can be used for packaging purposes. HDPE has very good electrical properties, especially high dielectric strength, making it very suitable for wire and cable. Medium to high molecular weight grades have excellent impact resistance, even at room temperature or even at low temperatures of -40F. The unique characteristics of various grades of HDPE are an appropriate combination of four basic variables: density, molecular weight, molecular weight distribution, and additives. Different catalysts are used to produce customized special performance polymers. These variables are combined to produce HDPE grades for different purposes; the best balance is achieved in performance.
This is the main variable that determines the characteristics of HDPE, although the four variables mentioned do indeed affect each other. Ethylene is the main raw material of polyethylene. A few other comonomers, such as 1-butene, 1-hexene or 1-octene, are also often used to improve polymer properties. For HDPE, the content of the above few monomers is generally not more 1% -2%. The addition of comonomer slightly reduces the crystallinity of the polymer. This change is generally measured by the density, which has a linear relationship with the crystallization rate. The general classification in the United States is in accordance with ASTM D1248, and the density of HDPE is 0.940g /. Above C; The density range of medium density polyethylene (MDPE) is 0.926 ~ 0.940g / CC. Other classifications sometimes classify MDPE as HDPE or LLDPE. Homopolymers have the highest density, the highest rigidity, good permeability resistance and the highest melting point of e799bee5baa6e58685e5aeb931333262343162, but generally have very poor resistance to environmental stress cracking (ESCR). ESCR is the ability of PE to resist cracking caused by mechanical or chemical stress. Higher density generally improves mechanical strength, such as tensile strength, stiffness, and hardness; thermal properties such as softening point temperature and heat deformation temperature; and permeability resistance, such as breathability or water vapor permeability. Lower density improves its impact strength and E-SCR. Polymer density is mainly affected by the addition of comonomers, but to a lesser extent also by molecular weight. The high molecular weight percentage slightly reduces the density. For example, homopolymers have different densities within a wider molecular weight range.
【Production and Catalyst】
The most common production method of PE is through slurry or gas phase processing, and there are a few that are produced by solution phase processing. All these processes are exothermic reactions involving ethylene monomers, a-olefin monomers, catalyst systems (which may be more than one compound) and various types of hydrocarbon diluents. Hydrogen and some catalysts are used to control molecular weight. The slurry reactor is generally a stirred tank or a more commonly used large-scale loop reactor in which the slurry can be circulated and stirred. When ethylene and comonomer (as needed) come into contact with the catalyst, polyethylene particles are formed. After removing the diluent, the polyethylene particles or powder particles are dried and the additives are added in dosages to produce pellets. A modern production line with a large reactor with twin-screw extruder can produce more than 40,000 pounds of PE per hour. The development of new catalysts has contributed to improving the performance of new grades of HDPE. The two most commonly used catalyst types are Philips' chromium oxide-based catalysts and titanium compound-alkyl aluminum catalysts. The HDPE produced by the Philip type catalyst has a mid-width molecular weight distribution; the titanium-alkyl aluminum catalyst produces a narrow molecular weight distribution. The catalysts used to produce narrow MDW polymers in a double reactor can also be used to produce wide MDW grades. For example, two reactors in series that produce products of significantly different molecular weights can produce bimodal molecular weight polymers that have a full-range molecular weight distribution. PE fittings
Higher molecular weight leads to higher polymer viscosity, but the viscosity is also related to the temperature and shear rate used in the test. Rheological or molecular weight measurements are used to characterize the molecular weight of materials. HDPE grades generally have a molecular weight range of 40 000 to 300 000, and the weight average molecular weight roughly corresponds to the melt index range, ie from 100 to 0. 029 / 10min. Generally, higher MW (lower melt index MI) enhances melt strength, better toughness, and ESCR, but higher MW makes processing
The process is more difficult or requires higher pressure or temperature.
Molecular weight distribution (MWD): The WD of PE varies from narrow to wide depending on the catalyst used and the process.
The most commonly used MWD measurement index is the unevenness index (HI), which is equal to the weight average molecular weight (MW) divided by the number average molecular weight (Mn). The index range for all HDPE grades is 4-30. The narrow MWD provides low warpage and high impact during molding. Medium to wide MWD provides processability for most extrusion processes. Wide MWD can also improve melt strength and creep resistance.
The addition of antioxidants can prevent the polymer from degrading during processing and prevent the finished product from oxidizing during use. Antistatic additives are used in many packaging grades to reduce the adhesion of bottles or packaging to dust and dirt. Specific applications require special additive formulations, such as copper inhibitors related to wire and cable applications. Excellent weather resistance and anti-ultraviolet (or sunlight) can be added by adding anti-UV additives. PE without anti-ultraviolet or carbon black added, it is recommended not to continue to use it outdoors. High-grade carbon black pigments provide excellent UV resistance and can often be used outdoors, such as wires, cables, tank layers or pipes.
PE can be manufactured with a wide variety of processing methods. Using ethylene as the main raw material, propylene, 1-butene, and hexene as the interpolymer. Under the action of the catalyst, the slurry polymerization or gas phase polymerization process is used. The resulting polymer is flashed, separated, dried, and granulated Process, to obtain a finished product with uniform particles. Including such as sheet extrusion, film extrusion, pipe or profile extrusion, blow molding, injection molding and rotomolding.
▲ Extrusion: The grades used for extrusion production generally have a melt index of less than 1 and a medium to wide MWD. During processing, low MI can obtain suitable melt strength. Wider MWD grades are more suitable for extrusion, because they have higher production speeds, lower die pressure and reduced melt fracture tendency.
PE has many extrusion applications, such as wires, cables, hoses,
Tubes and profiles. Pipe applications range from small cross-section yellow tubes for natural gas to thick-wall black tubes with 48-in diameters for industrial and urban pipelines. Large-diameter hollow wall pipes are rapidly growing as replacements for rainwater drainage pipes and other sewer pipes made of concrete.
Sheets and thermoforming: The thermoforming lining of many large picnic refrigerators is made of PE, which is tough, lightweight and durable. Other sheet and thermoformed products include fenders, tank linings, tray guards, shipping boxes and tanks. A large number of rapidly growing sheet applications are mulch or Chidi Village, which is based on MDPE's toughness, chemical resistance and impermeability.
▲ Blow molding: Over 1/3 of HDPE sold in the United States is used for blow molding. These range from bottles containing bleach, motor oil, detergent, milk and distilled water to large refrigerators, automobile fuel tanks and canisters. The characteristics of blow molding grades, such as melt strength, ES-CR and toughness, are similar to those used in sheet and thermoforming applications, so similar grades can be used.
Injection-blow molding is commonly used to make smaller containers (less than 16oz) for packaging medicines, shampoos and cosmetics. One advantage of this process is that the bottles are automatically bevelled without the need for post-finishing steps like normal blow molding. Although some narrow MWD grades are used to improve surface finish, medium-wide to wide MWD grades are generally used.
▲ Injection molding: HDPE has countless applications ranging from reusable thin-walled beverage cups to 5-gsl cans, consuming 1/5 of domestically produced HDPE. Injection molding grades generally have a melt index of 5 to 10. There are grades with low toughness and high flowability with processability. Uses include daily necessities and food thin-wall packaging; tough and durable food and paint cans; high resistance to environmental stress cracking applications, such as small engine fuel tanks and 90-gal trash cans.
▲ Rotomolding: The material used in this processing method is generally crushed into powder, which is melted and flowed in the thermal cycle. Two types of PE are used for rotomolding: general purpose and crosslinkable. General grade MDPE / HDPE usually has a density range from 0.935 to 0.945g / CC, with a narrow MWD, making the product have high impact and minimum warpage, and its melt index range is generally 3-8. Higher MI grades are generally not suitable because they do not have the impact resistance and environmental stress crack resistance desired for rotomoulded products.
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High-performance rotomolding applications utilize the unique properties of their chemically crosslinkable grades. These grades have good fluidity in the first stage of the molding cycle and are then cross-linked to form their excellent resistance to environmental stress cracking and toughness. Wear resistance and weather resistance. Cross-linkable PE is only suitable for large containers ranging from 500-gal tanks for transporting various chemicals to 20,000-gal agricultural tanks.
▲ Film: PE film processing generally uses ordinary blown film processing or flat extrusion processing. Most PEs are used for films, and general purpose low density PE (LDPE) or linear low density PE (LLDPE) are available. HDPE film grades are generally used where superior stretchability and excellent impermeability are required. For example, HDPE film is commonly used in commodity bags, grocery bags and food packaging.
High-density polyethylene is non-toxic, odorless, odorless white particles, melting point is about 130 ℃, relative density is 0.941 ~ 0.960. It has good heat resistance and cold resistance, good chemical stability, high rigidity and toughness, and good mechanical strength. Dielectric properties and resistance to environmental stress cracking are also good.
【Packing, storage and transportation】
Keep away from fire and heat insulation during storage. Keep dry and tidy in the warehouse. It is strictly prohibited to mix in any impurities. Sun and rain are strictly prohibited. Transportation should be stored in a clean, dry covered car or ship cabin, without sharp objects such as nails. Mixed transportation with flammable aromatic hydrocarbons, halogenated hydrocarbons and other organic solvents is strictly prohibited.
【recycle and re-use】
HDPE is the fastest growing part of the plastic recycling market. This is mainly due to its ease of reprocessing, minimal degradation characteristics and its numerous applications in packaging. The main recycling is to use 25% of the recycled materials, such as post-consumer recycling (PCR), and pure HDPE after reprocessing to make bottles that are not in contact with food.