⑶ Selection and quality control of hot-melt connection […]
⑶ Selection and quality control of hot-melt connection method
The selection of the hot-melt connection method mainly depends on the material grade and density of the plastic pipe. The connection method of plastic pipes should also be based on the buried "Polyethylene Water Supply Pipe Engineering Technical Regulations" (GJJ101-2004) and other relevant regulations. Most polyethylene pipes can be joined together by two hot-melt methods. However, some high-density polyethylene pipes cannot be connected by the method of undertaking.
When used in buried heat exchangers, polybutene is generally a socket connection. Both connection methods can be used to obtain a strong joint. Both connection methods are used properly to obtain strong joints, which are stronger than the strength of the pipe itself.
It should be noted that due to different melting points and service life, different plastics or different grades of plastic should not be welded together.
During construction, visual inspection and "back bend" test methods are mainly used to check the welding quality.
Visual inspection-observe with your eyes. The flanging should be solid and smooth with a wide root. If the root is narrow and curled in the middle, it may be caused by excessive pressure or short heat absorption time. The "back bend" test method is to press the outside of the flange with your fingers and bend the flange outward. During the bending process, observe whether there are micro-slit-like defects, if there is, it may indicate that there is slight contamination on the heating plate: if possible, an ultrasonic inspection system of polyethylene hot-melt butt joints can be used. According to the characteristics of the inspection and the use of mechanical tests, Correlate analysis results to make judgments on welding quality.
⑷Electrofusion connection process
① Preparations and precautions. The butt joints should be of the same material, and the same factory supporting materials should be used as much as possible. The outer diameter and wall thickness of the butt joints should be the same, and the tolerance is within the allowable range. Butt joints should have good processing and welding performances that match the welding machine. Protective measures should be taken when welding in cold climates and windy conditions; the surface to be welded must be scraped and cleaned before welding; the fused pipe is not unpacked when not in use. Welding is performed at time values; during the cooling process and after the welding is completed, the connection parts must not be moved or any external force applied.
② Operation points of electric fusion connection. Clean the dirt on the connection surface of the pipe, mark the depth of insertion, and scrape its skin; the pipe is fixed on the frame, and the fused pipe is placed on the pipe; cool down. When connecting, the selection of voltage and heating time during power-on heating should be in accordance with the regulations of the manufacturers of electric welding equipment and pipe manufacturers. During the cooling of the fused connection, do not move the connection or apply any external force on the connection.