1. The principle of electrofusion welding of polyethylene (PE) pipes
The principle of electrofusion welding of polyethylene pipe is to use an electrofusion welding machine to energize and heat the resistance wire embedded in the inner wall of the electrofusion pipe. The heating energy melts the connection interface of the pipe and the pipe. After the gaps at both ends of the pipe are closed, the melt in the melting zone of the interface will diffuse each other under the action of high temperature and pressure. When the depth of mutual diffusion on the interface reaches the size necessary for chain entanglement, the interface will become The necessary welding strength can be obtained to form a reliable welding connection of the pipe connection.
According to the principle of electrofusion welding and practical experience at home and abroad, it has been confirmed that whether a reliable welding connection can be formed is mainly based on the design of electrofusion pipe fittings, the temperature-resistance characteristics of resistance, the stability of the power supply voltage provided by the electrofusion welding machine, Material properties of pipe fittings and pipes, pretreatment conditions of pipe fittings and pipe connection interfaces, gap width and uniformity between pipe fittings and pipe connection interfaces, stable conditions of pipe fittings and pipes centering and clamping, welding process parameters (such as voltage, current) , Time, etc.), the ambient temperature during welding, the level of the operator and other factors. Therefore, the product standards, process parameters, operating specifications, quality inspection and test methods, etc., compiled based on the principles of electrofusion welding and the practical experience of the factors affecting welding quality and responsibility are the consensus of all parties in production, application and management in my country in the current development stage And guidelines.
2. Electrofusion pipe fittings
In the composition of the polyethylene piping system, electrofusion fittings are an indispensable part, and the electrofusion fittings selected must meet the corresponding product standards. The electric fusion pipe fittings used in the gas piping system must meet the standard of polyethylene pipe fittings for gas; the polyethylene electric fusion pipe fittings used for water supply must meet the standard of polyethylene pipe fittings for water supply.
1. The polyethylene blends used by manufacturers of fused pipe fittings must meet the requirements of their product standards for PE raw materials.
The performance of pe pipe manufacturer's mixed ingredients has a decisive influence on the long-term performance of electrofusion pipe fittings. Therefore, selecting special materials is the basis for ensuring the quality of polyethylene electrofusion pipe fittings. If the materials used by the electrofusion pipe fitting manufacturers do not meet the requirements of the product standards for raw materials, at the current level, no matter how good the equipment is and how advanced the technology is, it is impossible to produce qualified products.
The most basic factor for the difference in the performance of PE raw materials is the difference in molecular structure. Only advanced polymerization equipment and processes can produce PE pipe special materials with excellent performance. Therefore, it must be a certified material to be qualified. Special mixing ingredients.
2. The heating wire used for PE electric melting pipe fittings must meet the requirements of its product standards. The electrical performance of fused pipe products is mainly reflected in the product resistance. According to the requirements of the national standard "Buried Polyethylene Pipe Fittings (PE) Piping System Part Two: Pipe Fittings for Gas Use": At 230C, the resistance of the fused pipe fittings should be within the following range: Maximum value: nominal value X (1 +10%) +0.1Ω; minimum value: nominal value X (1-10%).
Therefore, it is required that the heating wire used must have a very stable resistance value per unit length in order to ensure that the product has stable electrical performance. The resistance wire distributed in the polyethylene electric fusion pipe is the main component of the electric fusion pipe. The diameter, length, and pitch distribution of the resistance wire determine the heat generation. Different requirements have different designs, and each specification must be determined through design and experiment.
