Ningbo Fangli Technology Co., Ltd. is a mechanical equipment manufacturer with over 30 years’ experiences of plastic pipe extrusion equipment, new environmental protection and new materials equipment. Since its establishment Fangli has been developed based on user’s demands. Through continuous improvement, independent R&D on the core technology and digestion & absorption of advanced technology and other means, we have developed PVC pipe extrusion line, PP-R pipe extrusion line, PE water supply / gas pipe extrusion line, which was recommended by the Chinese Ministry of Construction to replace imported products. We have gained the title of “First-class Brand in Zhejiang Province”.
I. Analysis of Defects in PE Pipe Hot Melt Welding
1）Defects of weld joint forming
In general, the defects in the forming of welded junction mainly lie in the deviation of crimping geometry and structure, which cannot meet the relevant requirements.
First, if there is dirt or foreign matter on the welding end face, the thickness of the welding wall on both sides will be deviated. In the case of uneven heating, the circumferential direction of the welding interface will be asymmetric, and the size can not meet the relevant provisions, such as notch, flaw and other defects.
Second, if in the welding, the welding end is relatively wet, which will be impermeable and insecure; or if has water vapor, which will lead to welding quality problems and leakage channel.
Third, if the ovality of welded pipes does not meet the relevant provisions, the reliability of butt joint work cannot be guaranteed, and the problem of misalignment will occur.
Fourth, if the clamp stroke deviates, or when melting, the butt joint temperature and pressure are low, and the welding time is short, the quality of the welding interface will be reduced. If the speed of the clamp is fast, or the temperature and pressure are too high, the height of the welding interface is too high or too wide, and the water passing section is artificially reduced, reducing its design flow.
2）Micro defect problems
Micro defects refer to the internal quality problems of the welding interface during welding, such as cracks, cracks, poor penetration, etc.
First, if the quality of the hot melt used by the construction technicians is poor, or there is a deviation in the flow rate, the butt joint quality of the pipe will be reduced. For example, when the flow rate deviation is greater than about 0.6g/10min, the quality defects of the welding interface will occur. If the melting temperature is low or the welding environment is poor, problems such as welding interface cracks and cracks will also occur.
Second, in actual construction, the end faces of pipes are not parallel, or the end faces are not fully welded with heater plates, which leads to poor welding penetration.
3）Micro defect problem.
In the actual welding work, due to too high heating temperature or too long heating time, the pipe will be oxidized and damaged. In serious cases, carbonization will occur, and then material degradation will occur. As for welding defects, all kinds of problems are interrelated. If operators and technicians lack technical ability and sense of responsibility and cannot carry out relevant work according to equipment performance and welding requirements, the quality of welding engineering will gradually decrease.
II.Quality Control Points of PE Pipe Hot Melt Welding
In the process of hot melt welding of PE pipes, it is necessary to comprehensively control their quality, carry out management work for operators, mechanical equipment, welding materials, welding processes, etc., and rely on the test work to reduce welding cracks and cracks. At present, Chinese construction enterprises have started to use ultrasonic testing technology to carry out relevant testing work in hot melt welding, which can timely find the internal welding quality problems of PE pipes, take effective measures to carry out quality control before and during welding, and use inspection methods to control construction quality after welding.
1）Quality control measures before welding
Before welding, it is necessary to do a good job in quality control, which can improve the work quality. First of all, for welding operators, their professional quality and skills need to be strictly controlled, and they are required to have welding qualification certificates. At the same time, it is necessary to formulate a sound quality management planning scheme, build a high-quality talent team according to its actual development needs, so as to improve the construction quality. For welding raw materials, it is required to meet relevant national quality requirements. Secondly, in the process of selecting welding equipment, it is necessary to actively apply the fully automatic electric welding machine to enable it to have the functions of automatic compensation, automatic heating and pressurization, automatic display of welding data information, automatic inspection, automatic detection, automatic alarm, etc., so as to support the development of welding work. Thirdly, it is necessary to scientifically select the welding process and evaluate it. At the same time, it is necessary to ensure that the melt quality meets the relevant provisions and no quality problems can occur. Finally, for the welding process parameters, it is necessary to do a good job of evaluation, and control the temperature parameters within 230 ℃, so as to improve the work quality. At the same time, the quality of pipes and pipe fittings shall be comprehensively checked. After the quality meets the relevant requirements, the welding interface shall be prepared, the cleaning treatment shall be done well, and the oxide layer shall be scraped off.
2）Quality control measures during welding
In the actual welding work, it is necessary to do a good job in quality management, reduce misoperation and other phenomena, and gradually optimize its working system. First, the temperature of the welding machine needs to be controlled at about 210 ℃ to facilitate welding. In addition, in windy or rainy and snowy weather, it is not conducive to carrying out welding work to avoid the phenomenon of low temperature. Second, construction technicians need to operate in strict accordance with relevant regulations to ensure the accuracy of work data information. Third, the fixture stroke margin should be controlled above 21mm, and the operating speed and temperature should be controlled scientifically to avoid welding defects. Fourth, the welding seam shall be cooled (natural air cooling) under stable pressure, and it is not allowed to move or add pressure. Fifth, the surface of the heating plate shall be kept clean during welding.
3）Quality control measures after welding
After the completion of the welding work, the construction enterprise needs to conduct a full inspection of the appearance of the welding parts, and use the cutting inspection method (spot check of the incision is up to 5%) to find problems in the welding work in time. At the same time, technicians need to carry out pressure test, combine spot check with comprehensive inspection. For example, in the spot check of tensile capacity measurement, once quality problems are found, comprehensive inspection should be used to determine whether all welding parts have problems.
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