The Butt Fusion Jointing Process - Fundamental Aspects [PE]

This paper reports a study of the burr fusion process as used for medium density polyethylene gas and water pipe. Investigations of the process mechanisms, the response of the material being welded and mechanical rest data are discussed. 

Polyethylene pipe is widely used for low pressure gas and water distribution systems and is of increasing importance in industrial plant. Pipes of sizes in the range 16-1600mm are used. The pipe lengrhs are joined on sire by a number of welding techniques. A common technique is hot plate butt fusion welding. The pipe ends are held in clamps which press them onto a plate heated to about 200'C. When sufficient time has elapsed for a semi-molten lager to form at rhc pipe end (hear eoak time). the pipes are pulled back, the tool is withdrawn and the pipe ends are pressed together to farm a veld. Molten material is extruded around the joint to produce an external and internal "bead". Pressure is mainrained while rhe weld cools. 

In ho~ place welding the most imparrant parameters are: the rrnperarure of ihe tool, the heating cime, the heating pressure, :he relding time and the welding pressure. Workpiece prepararion far welding is also important: the parts to be joined must be flat and square to the heating tool and must be cleaned immediately prior to welding.