Distribution of the heat and current fluxes in gas tungsten arcs
- PDF / 544,963 Bytes
- 6 Pages / 614.28 x 794.28 pts Page_size
- 53 Downloads / 147 Views
I.
INTRODUCTION
A L T H O U G H the traditional Rosenthal model of a traveling heat source provides useful predictions of cooling rates in weldments, the idealized point heat source does not provide quantitative information about the size or the shape of the weld pool. ~ Recently a number of revised theories have been presented which allow for a more realistic distributed heat source; 2'3'4 however, all of these require some estimate of the heat distribution on the surface, In several cases the heat distribution is used as an adjustable parameter which permits the theory to match the experimental pool shape. 2.3 Although these theories vary in complexity and hence in ease of solution, the results of one recent theory can be described through three simple parameters: the heat input magnitude, the equivalent gaussian width of the heat source, and the welding traveling speed. 4 The purpose of this paper is to relate the engineering parameters, viz., current, arc length, electrode tip angle, and shielding gas composition to scientific parameters, viz., heat input magnitude and heat source distribution. This enables one to compare the theoretical predictions of each of the models with experimental measurements of the penetration, the size, and the shape of a weld. Nestors and Schoeck 6 previously made a limited set of measurements of heat and current distributions on watercooled copper anodes of gas tungsten arcs; unfortunately, their results were not extensive enough to provide input to these new models of heat flow in weldments. In the present work, these measurements have been extended to include a wide range of welding process variables.
sten arcs. The method consists of splitting a water cooled copper anode, and measuring the heat flux to one of the sections as a function of arc position relative to the splitting plane. The radial heat distribution can then be derived by an Abel transformation of the heat flux measurements,
F"(x) dx f(r) = 771 fr" (X 2 __ r2)1 2
[1]
The split anode used in this work consists of two 7.5 cm diameter copper Dees which are separated by a gap of 0.2 mm, as shown schematically in Figure 1. Cooling water impinges on the bottom surface of the copper anode preventing melting and serving as the calorimetric fluid for measuring the heat flux to each Dee. To prevent localized melting, the inlet of the water is located exactly below the arc. The flowrates of the cooling water were measured by turbine flowmeters, and differential thermistors were used to sense the temperature rise of the water. The arc voltage. arc current to each Dee, water flowrates, and temperature rise of the water were monitored by a PDP 11/23 minicomputer using analog to digital convertors and preamplifiers. For each experiment, the computer recorded 256 values of each of the above eight quantities as the arc traversed the split anodes.
.•F'I
e ct rode
~Jfff~ ,~.~/~,.~Jfy node II.
EXPERIMENTAL PROCEDURES
The experimental method developed by Nestor was used to determine the heat and current distributions of gas t
Data Loading...
