About the introduction of metal plastic composite pipe.

- Feb 10, 2019-

There are many metal-plastic composite pipes, such as steel-plastic pipes, copper-plastic pipes, aluminum-plastic pipes, and steel skeleton plastic pipes. The aluminum-plastic composite pipe is a new type of pipe tree that has developed rapidly in recent years. This article introduces the aluminum-plastic composite pipe.


1. Material properties and production process


The aluminum-plastic composite pipe is made of aluminum alloy, and the inner and outer layers of the aluminum pipe have a certain thickness of plastic pipe. There is a layer of glue (affinity layer) between the plastic tube and the aluminum tube, so that the aluminum and the plastic are integrated into one body and cannot be peeled off. At present, almost all plastics used for aluminum-plastic composite pipes are PE pipes, and PE pipes are divided into HDPE or PEX. HDPE or general-purpose aluminum-plastic composite pipe is suitable for water temperature stems at 40 °C; PEX is called internal diplomatic polyethylene-plastic composite pipe, suitable for water temperature of 75 °C.


The thickness of the polyethylene outside the aluminum-plastic composite pipe is not less than 0.4 mm, the inner layer of polyethylene is not less than 0.8 mm (two times the thickness of the outer layer), and the thickness of the aluminum strip is 0.2--0.25 mm. The adhesive (hot melt adhesive) used for the glue layer mainly uses copolymer modified polyethylene or chemical grafted polyethylene.


Aluminum-plastic composite pipes have good metal and non-metallic properties. There are two processes for the production of aluminum-plastic composite pipes: co-extruded composite and step-by-step fitting. The co-extruded composite type is one-time extrusion molding of inner and outer plastic (including hot melt adhesive) and aluminum tube, and is generally suitable for step-by-step composite type extrusion of inner tube with a diameter of less than 32 mm. Squeeze the inner rubber, wrap the aluminum tube, squeeze the outer rubber, and squeeze the outer plastic tube step by step.


2. Main features and uses of aluminum-plastic composite pipe


The composite pipe is based on metal pipe, and is formed by welding non-metallic materials such as polyethylene and cross-linked polyethylene inside and outside, and has the advantages of metal pipe and non-metal pipe. Most of the composite pipes are composed of a working layer (requires water corrosion resistance), a support layer, and a protective layer (requires corrosion resistance). It is characterized by light weight, smooth inner wall, low resistance and good corrosion resistance; composite pipe is the most ideal pipe for water supply and drainage pipe with pipe diameter ≥300mm or more. It combines the advantages of high strength, rigidity and corrosion resistance of non-metallic pipes.


The connection of the composite pipe should be cold-worked, and the hot-worked method is likely to cause expansion, deformation and even melting of the lining plastic. Generally, there are connections such as threads, ferrules, and clamps. Since the composite pipe is still a new type of pipe, there is no uniform design, construction and acceptance specification in China. Design and construction personnel often apply galvanized pipe technology for design and construction.


3, composite pipe classification and its characteristics and uses


At present, there are aluminum-plastic composite pipes, copper-plastic composite pipes, steel-plastic composite pipes, plastic-coated composite pipes, and steel-framed PE pipes.


1. Aluminum-plastic composite pipe (PAP):


The aluminum-plastic composite pipe is a new composite pipe manufactured by an extrusion molding process, which consists of a polyethylene layer (or cross-linked polyethylene) - an adhesive layer - an aluminum layer - an adhesive layer of polyethylene ( Or cross-linked polyethylene) consists of a five-layer structure. Among them, the aluminum layer is lap welded and butt welded. Since the aluminum-plastic composite pipe is a plastic/metal composite pipe with a metal pipe, the advantages of both the metal pipe and the plastic pipe are combined.


The inner and outer layers of PE have the characteristics of non-toxicity, corrosion resistance, light weight and low embrittlement temperature. After cross-linking of PE, the heat resistance and mechanical strength are significantly improved. In addition to strengthening the PE, the aluminum tube in the middle greatly improves the compressive strength of the pipe. It also has 100% oxygen barrier, completely eliminates penetration; good magnetic and antistatic properties; good plastic deformation ability, so that the pipe can Arbitrary deformation; strengthen the longitudinal heat dissipation capacity of the pipe, increase the flame retardant effect of the pipe; the coefficient of thermal expansion is lower than that of PE, which reduces the comprehensive thermal expansion coefficient of the composite pipe and improves the dimensional stability of the pipe.


Therefore, the aluminum-plastic composite pipe has unique characteristics and a wide range of applications:


1 high compressive strength, good temperature resistance (PAP pipe working temperature -40 ~ 60 ° C, XPAP pipe working temperature -40 ~ 95 ° C), hygienic non-toxic, long service life, can be applied to building hot and cold water pipes.


The 2 sets of rigid and flexible one can quickly eliminate the pressure shock in the pipeline system and will not generate water hammer noise.


3 It is easy to install by using the embedded clamping joint; the pipe can be bent freely, which can reduce the pipe joint and elbow. It can bend without rebounding, and can bypass the beam and column and other components according to the actual situation, reducing a large number of elbows, saving labor by 50% compared with galvanized steel pipes.


4 The coefficient of thermal expansion is 2.5 × 10? 6m / m. K, which is only 1 / 8 of the polyvinyl chloride tube.


5 flame retardant performance is far superior to PVC pipe, good corrosion resistance, can transport a variety of corrosive liquids, gases.


2. Steel-plastic composite pipe:


PVC lined steel pipe. This is a new type of water supply pipe developed in the foreign countries in the 1970s. Because of the weakness of the plastic pipes such as PVC and the insufficient pressure resistance, it is reluctant to apply in the harsh load. At this time, metal pipes are required. PVC-lined steel pipes have been developed based on this.


A thin-walled PVC pipe is inserted into the traditional water-conveying steel pipe so that the two are closely combined to become a PVC-lined steel pipe. It combines the advantages of plastic tubes and steel tubes to avoid their disadvantages. The connection method is also a pipe thread, which is completely compatible with the original galvanized pipe system and is extremely convenient to use. Therefore, it has developed greatly in Japan, the United States, and Europe, because its price is much lower than that of traditional copper and stainless steel pipes, especially in high-rise buildings.


PE powder resin lined steel pipe. This is a new pipe developed in the late 1970s and early 1980s. Its development goal is to have the same performance as PVC-lined steel pipes but with better economic performance. It is formed by melting a layer of PE powder resin on the inner wall of the water pipe. In recent years, developers in Shanghai, Sichuan, and Zhejiang have invested in such pipes at a price lower than that of aluminum-plastic composite pipes, which is very competitive. According to the characteristics of the lining steel pipe, it can be considered as a plastic piped steel pipe, that is, the lining steel pipe is a steel pipe having the advantages of a plastic pipe.


In addition, it is worth mentioning that recently Sichuan has developed a water-lined plastic pipe with its own intellectual property rights. It is a galvanized welded steel pipe with a convex mesh pattern on the inner wall and a non-toxic acrylic plastic pipe. Mechanical compounding. In addition to all the advantages of the steel-plastic composite pipe on the market, the inner-layer steel pipe has a convex mesh pattern processed by a special process, which greatly enhances the reliability of the composite and better solves the inner and outer layers. The problem of consistency of thermal expansion between different materials, and the use of snap-on quick-fit and then connect, easy installation, high reliability, unique in steel-plastic pipe.


3. Steel skeleton PE pipe: The steel skeleton PE pipe is made of high-quality low-carbon steel wire as the reinforcing phase and high-density polyethylene as the matrix. Through the wire-welding of the steel wire and the plastic extrusion and filling, the film is continuously pulled on the production line. New double-sided anti-corrosion pressure pipe for forming. The pipe diameter is Φ50~Φ500, and the flange is connected. It is mainly used in municipal, chemical and oilfield pipe networks, and the price is relatively expensive.


4. Plastic coated steel pipe: Plastic coated steel pipe is melted in the inner wall of steel pipe with a thickness of 0.5-1.0mm polyethylene (PE) resin, ethylene-acrylic acid copolymer (EAA), epoxy (EP) powder, non-toxic poly Steel-plastic composite pipe made of organic materials such as propylene (PP) or non-toxic polyvinyl chloride (PVC). It not only has the advantages of high strength, easy connection and water flow impact resistance of steel pipes, but also overcomes the corrosion of steel pipes. The design life expectancy is up to 50 years due to the disadvantages of pollution, scale and plastic tube strength, poor fire performance. The main disadvantage of the pipe is that it must not be bent during installation, hot working and electric welding cutting, etc., the cutting surface is applied by the manufacturer with non-toxic room temperature curing adhesive. The main specifications are Φ15-Φ100.