Measurement of surface tension of liquid metalsand alloys under arc welding conditions

Abstract

This paper deals with a new method for measuring the surface tension of liquid metals and alloys under arc welding conditions. The method is based on the oscillation behaviour of the weld pool and consists essentially of triggering a partially penetrated weld pool into oscillation and measuring the oscillation frequency and the diameter of the weld pool. The oscillation frequency is obtained from the arc voltage variations caused by the weld pool oscillation by means of Fourier analysis. The surface tension is determined from the measured values of the oscillation frequency and the weld pool diameter, using the relation that exists between the surface tension, the oscillation frequency, and the weld pool diameter. In order to determine the surface tension as a function of temperature, the temperature of the weld pool is varied by changing the arc current. The temperature of the weld pool is measured by means of an infrared radiation pyrometer. To check the feasibility of the method, measurements were carried out on technically pure iron, using argon, helium, and argon + 0.1 vol.-% oxygen shielding gases.