Production technology of polyethylene (PE) double-wall corrugated pipe worth collecting
Production technology of polyethylene (PE) double-wall corrugated pipe worth collecting1. Overview of PE double-wall corrugated pipe
1. Definition: The so-called PE double-walled wave tube is a kind of smooth and flat inner wall with trapezoidal or arc-shaped corrugated outer wall which is optimized for the section design of the pipe under the premise of saving raw materials without reducing the ring rigidity of the pipe The corrugated wall of the outer wall is hollow and made by extrusion molding process. Because its main raw material is polyethylene (PE), it is simply referred to as PE double-wall corrugated pipe.
2. The advantages of PE double-wall corrugated pipe:
① Save raw materials, when using the same raw materials to make pipes of the same outer diameter, bellows save more than 30% of raw materials than solid-walled pipes;
②Light weight, the specific gravity is less than 50% of cast iron pipe and cement pipe;
③Convenient installation and fast construction progress. Compared with traditional cement pipes, the use of PE bellows can increase the installation progress by more than 3 times.
④ PE double-wall corrugated pipe adopts flexible connection with good sealing performance;
⑤Low production cost and superior comprehensive economic performance.
3. Application fields of PE double-wall corrugated pipe:
①Municipal engineering, used for underground drainage pipes, sewage pipes, water pipes and ventilation pipes of buildings;
②Electrical and telecommunications engineering, as protective tubes for power cables, optical cables, and communication signal cables;
③In industry, due to the excellent acid resistance, alkali resistance and corrosion resistance of polyethylene materials, structural wall pipes can be used for water supply and drainage pipes in chemical, pharmaceutical, environmental protection and other industries;
④ Agriculture and garden projects, used for irrigation and drainage of farmland, orchards, tea gardens and forest belts, can save water by 70%, save electricity by 13.9%, and can also be used for rural irrigation
⑤ Road works can be used as infiltration and drainage pipes for railways, highways, golf courses, football fields, etc .;
⑥Mine field, used as mine ventilation, air supply pipe and drainage pipe.
2. Raw materials of PE double-wall corrugated pipe
1. Composition of raw materials: The raw materials of PE double-wall corrugated pipes are generally composed of polyethylene, enhanced functional masterbatch and pigments. If the raw materials are wet, in order to improve production efficiency, appropriate defoamers can be added.
2. Requirements for raw material performance: How to produce a low-cost, high-quality corrugated pipe depends largely on the choice of raw materials and the combination of formulas.
1) General requirements for the performance of polyethylene (PE) include melt flow rate (MFR), oxidation induction time (OIT) and density. The size of the melt flow rate reflects the size of the molecular weight. Generally speaking, a material with a higher melt flow rate is advantageous for processing and forming, and can improve production efficiency. However, it should not be too large, too large has a greater impact on the ring stiffness, it is appropriate to choose between 0.8-1.5g / 10min (190 ℃, 5kg). Oxidation induction time determines the time of oxidation damage. For bellows requiring 50 years of use, controlling the oxidation induction time of raw materials is the key to ensuring 50 years of service life. GB / T19472.1-2004 clearly stipulates that the oxidation induction time of the raw materials of bellows should be ≥20min (200 ℃). For medium and high density polyethylene, the performance can be adjusted by changing the density. Because we know that polyethylene with relatively low density can prolong its brittle failure time. As shown in Figure 1.
figure 1
2) The choice of functional masterbatch is also critical. At present, there is no national standard for special functional masterbatch for drainage pipes. The performance of products of various manufacturers is not consistent. When selecting functional masterbatch, the dispersibility, coupling and modification degree of polyethylene should be fully considered.
3) Whether the formula is reasonable also determines the quality of the product. In order to reduce costs, some manufacturers increase functional masterbatches without restriction. Such products cannot guarantee the quality of the products, but also lose the ability to develop in the long run and compete with the core. The typical reasonable formula is as follows:
Table 2
3. Forming principle
1. Forming machine: The bellows forming machine is the key equipment for producing bellows, which is related to the quality and output of the pipe. The forming methods of double-wall corrugated pipes are also various and different from other pipe forming equipment.
According to the module assembly method, it can be divided into two types: vertical and horizontal (horizontal). The vertical molding device can open and close the module up and down, and it occupies a small area and has a compact structure. Module replacement; horizontal (also known as horizontal) molding device can make the module open and close horizontally (usually only large-diameter molding equipment), occupying a large area, but replacing the module is more convenient than vertical. Moreover, a cooling water circulation channel is designed in the module, and water is used as a cooling medium, which greatly improves the production speed.
According to the shaping method, it can be divided into two types: pneumatic shaping and vacuum shaping. At present, some manufacturers use pneumatic shaping equipment, which is to pass compressed air through the ribs on the core support of the machine head and the screw plugs fixed on the core. To the inner cavity of the outer tube blank, the tube blank is closely attached to the module to form a wave crest. The products produced by this equipment can be of any cross-section, and can also improve the quality of the bellows, reduce the thickness error on the width of the uneven corrugation, and reduce waste products. It also greatly simplifies the structure of the cooling equipment and the head structure of the product. However, the fluctuation of compressed air makes the peaks of the pipes inconsistent, and the appearance of the product is difficult to control.
2. Forming module: The forming mold of the bellows is mainly a module, which determines the basic structure and size of the pipe. With the different molding methods and the different trajectory of the module, the structure of the module is also different. At present, most production lines suck the blank on the inner surface of the mold through the vacuum of the module, and there must be a channel for vacuum on the module. The structure of the forming module directly determines the ring stiffness of the pipe. The structure is shown in Figure 3:
image 3
4. Process flow chart
Figure 4 Flow chart of double-wall corrugated pipe production process
V. Precautions during startup
1. Before starting the extruder, it is necessary to check whether the temperature of each section is normal. If an abnormality is found, the extruder must be started after the treatment is completed, so as not to damage the screw and other parts or spray the material;
2. Start the host machine after each starting condition is met. When starting the host machine, the melt pressure must be controlled within a certain range to avoid the material temperature being too high and spraying material to hurt people;
3. Observe the current and pressure of the main machine when extruding. If the current and pressure are too large, you must first check and eliminate the fault before starting the machine, so as not to damage the equipment;
4. Monitor the temperature and sound of the main motor and gearbox at any time. If there is any abnormality, report to the equipment management personnel in time to determine whether to shut down;
5. The material of the water jacket is relatively soft, and it can't collide with metal objects when changing the specifications, and can't be polished with sandpaper under 800 mesh when dealing with the damaged parts;
6. When the molding machine is in normal operation, it is necessary to observe the integrity of all bearings and accessories at any time, and replace and handle it in a timely manner if it is damaged or abnormal;
7. The lubrication system of the molding machine must be guaranteed to run normally at any time, otherwise the molding machine must be stopped immediately;
8. The moving track of the molding machine should be kept clean;
9. It must be cleaned every time the module is replaced;
10. Every time you replace the module, you must check whether all the pins and positioning grooves are intact, and install them after handling them if there are abnormal conditions;
11. Extra care must be taken in the transfer, installation and disassembly of the module, and no damage to any part is strictly prohibited;
12. The upper and lower modules (horizontal type are left and right modules) can not be pressed too tight to prevent the module from being deformed or the main motor of the forming machine being overloaded;
13. The vacuum pump should regularly clean the scale in the filter and the pump cavity, so as not to affect the vacuum or damage the motor.
