A study of the combined socket and butt welding of plastic pipes using through transmission infrared welding.

摘要

Welding of polyethylene (PE) pipes of different diameters is critical for the infrastructure of natural gas transmission as well as for numerous industrial applications. A relatively new method of combined socket and butt through transmission infrared (TTIr) welding for polyethylene pipe was developed. It involves radiant heating of an absorbing element that is placed at the weld interface with air cooling of the exterior of the socket. The absorber element is a 0.1 mm thick PE film with a small amount of carbon black (0.5% by weight).; A prototype infrared welding system using tungsten halogen lamps was constructed and it was used to evaluate the effects of welding parameters on the combined socket and butt welding of 60-mm outer diameter medium density PE gas pipes. In addition, the effects of coupling thickness on power transmission of the infrared radiation and the effects of coupling thickness and width on weld strength were evaluated. For some welding conditions it was possible to create very strong welds without deformation of the coupling, no discontinuities in the butt joint, and with minimum inner bead. The size and shape of the inner bead was also found to be a good indicator of weld quality and it may be useful for inspection of completed welds.; For successful welds it is important to minimize deformation of the socket while providing sufficient heat input to form the butt weld in addition to the socket weld. To better understand the heat flow that occurs, finite element and analytical models for the heat transfer were developed. The model predictions were found to be in good agreement with experimental measurements of the temperature history in selected locations in the pipe. These models can be used to analyze and optimize the heating dynamics in the weld zone under different welding conditions.; The combined TTIr socket and butt welding method was also applied to polyvinylidene fluoride (PVDF) pipes for high purity water applications where the inner bead must be eliminated to avoid contamination. Using this method, it was possible to make strong joints without inner weld bead by inflating a silicon balloon with air pressure of 0.1724MPa (25psi) on the inside of the pipe at the weld area.; A feasibility study using a Nd:YAG laser source instead of lamps showed that it was possible to produce a spot weld between the PE coupling and pipes as well as a partial butt weld. It was proposed that by increasing the laser power and the spot size along with getting a more uniform power density distribution, laser sources could also be used to produce high quality welds.