T. W. Eagar

Distribution of the heat and current fluxes in gas tungsten arcs

The distribution of heat flux on a water-cooled copper anode as a function of welding process parameters has been determined experimentally following an experimental technique developed previously. The results indicate that arc length is the primary variable governing heat distribution and that the distribution is closely approximated by a gaussian function. The half width of the heat flux is defined by a distribution parameter, σ, which was determined from the experimental data and is expressed as a function of arc length, current, and electrode tip angle. The distribution parameter, σ, increases from 1.5 mm to 3.6 mm as the arc length increases from 2 mm to 9 mm for a 100 A arc. The experimental data also show that arc energy transfer efficiency is greater than 80 pct on the water-cooled anode which is much higher than has been measured in the presence of a molten metal pool. For this reason, it is believed that the distribution of the heat flux and not the magnitude is the most useful information obtained in this study. The effect of helium additions to the argon on the heat distribution is also reported.

Metal vaporization from weld pools

Experimental studies of alloy vaporization from aluminum and stainless steel weld pools have been made in order to test a vaporization model based on thermodynamic data and the kinetic theory of gases. It is shown that the model can correctly predict the dominant metal vapors that form but that the absolute rate of vaporization is not known due to insufficient knowledge of the surface temperature distribution and subsequent condensation of the vapor in the cooler regions of the metal. Values of the net evaporation rates for different alloys have been measured and are found to vary by two orders of magnitude. Estimated maximum weld pool temperatures based upon the model are in good agreement with previous experimental measurements of electron beam welds.

Multiwavelength pyrometry: an improved method

It is demonstrated that the temperature of a thermal radiator can be determined without prior knowledge of the emissivity of the source by curve-fit-ting techniques using multiple spectral radiance measurements. This new passive measurement technique assumes only that a smooth function exists between spectral emissivity and wavelength. The spectral radiance values are fitted to a Planck radiation law relation to yield the temperature of the source. Error analysis shows that relative errors in the temperature measurements are generally an order of magnitude less than in the spectral radiance measure-ments and in the simultaneously calculated spectral emissivity values. Computer simulations are included that show the effects of varying different parameters, such as the number of data pairs, the wavelength range, the spectral emissivity behavior, the source temperature, and the measurement noise, on the accuracy of the temperature determination. Experimental confirmation of this technique is presented, showing temperature measurements within 1% of the actual temperatures on a platinum surface within a temperature range of 1273 to 1724 K.

Slag Metal Reactions during Submerged Arc Welding of Alloy Steels

The transfer of Cr, Si, Mn, P, S, C, Ni, and Mo between the slag and the weld pool has been studied for submerged arc welds made with calcium silicate and manganese silicate fluxes. The results show a strong interaction between Cr and Si transfer but no interaction with Mn. The manganese silicate flux produces lower residual sulfur while the calcium silicate fluxes are more effective for removal of phosphorus. The effective oxygen reaction temperature lies between 1700 and 2000 °C for all elements studied. Evidence of Cr and Mn loss by metal vaporization is also presented.

The role of transient convection in the melting and solidification in arc weldpools

A mathematical formulation has been developed to describe the transient growth and collapse of axisymmetric weldpools in spot welding operations. In the statement of the problem allowance is made for both conductive and convective heat transfer. In describing convection, the driving forces included buoyancy, electromagnetic forces, and surface tension forces. In most cases it was found that convection played a major role in affecting the weldpool shape, and that this convection was often dominated by surface tension forces. The model also allowed us to represent the transient collapse of weldpools upon the cessation of the heat and current supply. It was found that the melt velocity was reduced as the weldpool shrank. Most of the solidification took place from a circulating weldpool. By calculating both the growth rate and the relevant temperature gradients, it was possible to estimate the dendrite arm spacing which was found to be of the order of tens of microns.

Prototype device for multiwavelength pyrometry

The Multichannel Infrared-Red Temperature Micro-Analyzer (MIRTMA) system is used to experimentally demonstrate the feasibility of a method of multiwavelength pyrometry using least-squares fitting analyses. The MIRTMA is a prototype instrument capable of monitoring temperatures above 1100 K with a spatial resolution of 100 um using spectral radiance measurements at approximately 200 wavelengths in a range of 0.6 to 0.8 um. Demonstrations of this equipment on a heated platinum strip source are described and discussed. The temperature measurements of these sources are generally within 5% of the actual temperature but can be within 1% using certain techniques. Capabilities and limitations of the method and the MIRTMA equipment are presented. The various calibrations used with the technique are also described, particularly with respect to corrections for the nonlinear response of the silicon intensified target (SIT) detector employed. Potential improvements to the instrument based on this work are presented, and it is concluded that the SIT detector should be replaced with a more suitable detector.

Comparison of theoretically predicted and experimentally determined submerged arc weld deposit compositions

Modele mathematique de la composition du metal depose par soudage sous flux: teneurs en Si et Mn, avec une electrode en acier Mn 1,2-Si 0,03-C 0,09 dans un flux SiO 2 -CaO-CaF 2 pouvant contenir MgO-Al 2 O 3 -Al 2 O 3 -TiO 2 -MnO