Patent ID: 9383052
Filing Date: 2016-07-05
CPC Classification: B29C,B29L,F16L,G01K,G05D

Claim Text:
1. A method of welding a pipe of a weldable polymer material to a muff of a weldable polymer material, where the pipe has ends, where the method comprises: placing the muff with an overlap over the ends of the pipes; welding the muff to the ends of the pipes through placement of an electrically conducting band that is permeable to molten plastic between the pipe and the muff; connecting a power supply to the band through feed cables; measuring the initial ambient temperature of the weld; calculating the initial resistance of the band, wherein the initial resistance of the band is calculated as a ratio of voltage across the band and current supplied to the band before the band is heated; supplying an electrical current in order to heat the band and the surrounding polymer material such that they melt together around the band in order to form a weld, wherein the current is supplied such that the temperature of the band is caused to reach a first target value of temperature during a heating phase, wherein the temperature of the band is caused to reach a second target value of temperature during an equilibrium phase, and wherein the first target value of temperature is higher than the second target value of temperature; measuring a voltage across the band; measuring the electrical current supplied to the band; causing the electrical current supplied to the band to increase; calculating the resistance of the band based on the voltage and the measured current; calculating the change in resistance as a difference between the resistance of the band and the initial resistance of the band; calculating the increase in temperature of the band based on the change in resistance based on the change in resistance and a material-specific conversion factor; calculating the temperature of the weld through adding the initial ambient temperature of the weld and the increase in temperature of the band; and terminating supply of current to the band based on the calculated temperature of the weld, wherein the calculated temperature of the weld is compared with a pre-determined final temperature of the weld, and wherein the supply of current to the band is terminated when the temperature of the weld has reached the pre-determined final temperature of the weld.