Welding process and characteristics of fine K-type thermocouple: non-contact discharge welding for fine metal wires

Abstract

K-type thermocouples are fabricated using a chromel wire and an alumel wire of 50 m by the non-contact discharge welding method. The welding is carried out at six different butt angles. The size of the hot junction tends to decrease with an increase in butt angle, when the butt angle is larger than 1.4 rad. The response rate is measured and it is almost proportional to the reciprocal of the size of the hot junction. It is shown that the size of the hot junction is an important factor for the response rate. Wire diameter is another important factor for temperature measurement of small objects. When temperature is measured at the same point by a thermocouple under the conditions that only the hot junction and its vicinity are heated, the output of electromotive force, i.e. indicated temperature, will depend on the wire diameter. As the metal wire is a good thermal conductor and the rate of heat transport is proportional to the area of the wire cross section, deviation from the true value increases with an increase in wire diameter. Our experiments showed that the indicated temperature decreased linearly with the wire diameter. Furthermore, we measured the discharge voltage and current at various setting currents and discharge gaps.