摘要 |
A liner (30) of polyethylene housing an SDR of (33) or less is pulled through a die (36) and through the pipe (10) and allowed to revert to the internal diameter of the pipe (10). The force of pulling is half the yield strength of the liner (30) or less. The die (36) has an entry (54); a throat (58) and an exit (59), the entry (54) decreasing in diameter towards the throat (58) and the exit (59) increasing in diameter away from the throat (58). The liner (30) has a maximum diameter before the die (36), a minimum diameter in the die (36) and intermediate diameter after the die (36). The liner (30) bending inwards before first contacting the die (36) at the entry (54), then continuously bending through its minimum diameter as it passes the throat (58) and then undergoing die (36) swell resulting in said intermediate diameter. The throat (58) is defined by the merger in a continuous curve of a radius joining the entry (54) and a radius joining the exit (59). |