Electrofusion Welding Machine With Thermostic Controller For Connecting Polyethylene Pipes

According to Plastic Pipe Database Committee’s analysis of polyethylene pipe failure, except for excavator digging or piling, polyethylene (PE) pipe failure often occurred in the piping joints. With the widely use of PE pipe in gas and water distribution, as a key link for pipe connection, pipe connection technology has aroused more and more attentions.As a convenient and fast way for connecting, electrofusion welding is often used in PE pipe connection for its reliability and unsusceptible to outside interference. By way of electrifying the resistor buried in the pipeline, it will be heated to melt the pipe, thus followed by its expansion, the polyethylene pipeline will be connected with the connector. During the welding process, the change of voltage, heating time or cooling time will lead to cold welding or over welding, which often cause joint failure in PE pipeline system.According to the failure type and the corresponding failure reasons of PE electrofusion joints, this thesis conduct a comprehensive investigation of electrofusion welding machines from its works, welding process and functions. Besides, this thesis also makes an overall design to put the thermostatic control into the welding process. Main works are as follows:1) Design the whole system. Based on the inverter welder, closed-loop feedback is used in this paper to control the welding temperature, which keeps PE in its best molten state during the whole heating process, thus can improve the quality of electrofusion joints.2) Built the experimental platform. First, the main circuit, the isolation drive part and the data acquisition part are designed; second, the feasibility of these parts is verified through Matlab; finally, make circuit boards and set up the whole platform.3) Design a closed-loop feedback control program of temperature based on Mega16to complete the software design of the control system.4) Closed-loop experiments and open-loop experiments are carried out on this experimental platform. The open-loop experiment is set up to verify and improve the experimental platform and the control program. The closed-loop experiments prove that the whole experimental platform can achieve the thermostatic heating process, and make thermostatic welding feasible.The thermostatic welder not only has the advantages of small size, light weight and high work efficiency, but also used for different type of electric melting sleeves. Besides, with the PID control, it has high accurate output and fast response, and can control the temperature accuracy at±0.4℃. In addition, combined with a microcontroller, it can have a high flexibility and controllability.The thermostatic welder can avoid over welding and cold welding which are caused by the improper welding, ensures the quality of electrofusion joints and greatly improves the safety and reliability of PE pipes in gas and water distribution.We would like to acknowledge the financial support from the National Key Technology R&D Program of "Twelfth Five-Year Planning Program"(Project No:2011BAK06B01).