How to Extend the Life of Die-Casting Tools

The paper explores some possibilities of extending the life of die-casting tools for non-ferrous metals, particu-larly aluminium, magnesium, and their alloys. In the first part of the paper is shown theoretical background of the problem. The major part treats the tools: tool life, tool manufacture, tool certificate, tool operation and repair of tools by welding. Welding is the only technology fit for repair of tools and thus to extend their service life. In the paper is shown some welding processes, which are suitable for repair welding of tools

Analysis of Lack of Fusion in Welds at Water Heaters

The paper treats a weld discontinuity called lack of fusion, which is frequently a cause of leakage of a water heater. The heater was produced by MAG welding using two wires (twin arc welding). The paper states some reasons for the occurrence of lack of fusion, i.e. the arc blow effect, an inappropriate gun position, uncontrolled movement of the weld pool, too low energy input, an improper joint preparation. The defect is illustrated in a macrograph of a weld produced at the water heater with twin wires in a shielding gas. Welding with twin wires is schematically represented with a circumferential welded joint between the end and shell of the water heater

Analysis of Lack of Fusion in Welds at Water Heaters

The paper treats a weld discontinuity called lack of fusion, which is frequently a cause of leakage of a water heater. The heater was produced by MAG welding using two wires (twin arc welding). The paper states some reasons for the occurrence of lack of fusion, i.e. the arc blow effect, an inappropriate gun position, uncontrolled movement of the weld pool, too low energy input, an improper joint preparation. The defect is illustrated in a macrograph of a weld produced at the water heater with twin wires in a shielding gas. Welding with twin wires is schematically represented with a circumferential welded joint between the end and shell of the water heater

Experimental determination of the residual stresses in a Kraft recovery boiler tube

Neutron diffraction was used to determine the residual stresses in a spiral weld overlay tube used in Kraft recovery boilers by the pulp and paper industry. The specimen was a 2.5 inches OD carbon steel tube covered with a layer of Inconel 625 weld overlay. Residual strains in the carbon steel and weld overlay layers were determined using the ferritic (211) and austenitic (311) reflections, respectively. Residual stresses in each material were derived from the measured strains using Hooke`s law and appropriate elastic constants. Tensile stress regions were found not only in the weld metal but also in the heat affected zone in the carbon steel. The maximum tensile stress was located in the weld overlay layer and was found to be 360 MPa, or about 75% of the yield strength of the weld metal. The experimental data were compared with a finite element analysis based on an uncoupled thermal-mechanical formulation. Overall, the modeling results were in satisfactory agreement with the experimental data, although the hoop strain (stress) appears to have been overestimated by the finite element model. Additional neutron diffraction measurements on an annealed tube confirmed that these welding residual stresses were eliminated after annealing at 900{degrees}C for 20 minutes. 18 refs., 7 figs

Residual stresses in weld overlay tubes: A finite element study

Residual stresses and strains in a tube with circumferential weld overlay were analyzed by the finite element (FE) method. The objective of this work was to develop and verify a FE model, to determine the magnitude and distribution of residual stresses in the weld overlay tube, and to evaluate the significance of two contributing factors to residual stress: (1) difference in material properties between tube and weld material, and (2) thermal gradients in the weld. An axisymmetric FE model was developed to simulate the circumferential two-layer welding process of alloy 625 overlay on SA210 tube. The first layer was modeled as a gas metal arc welding process with filler metal, whereas the autogenous gas tungsten arc welding process was modeled for the second layer. Neutron diffraction technique was used to experimentally determine residual elastic strains in the weld overlay tube. Comparison with the FE results shows overall good agreement. Both the experimental and FE results show high compressive stresses at the inside tube surface and high tensile stresses in the weld overlay. This suggests that weld overlay may be used to relieve tensile or produce compressive stresses at the inside tube surface, which is significant for applications where crack initiation is found at the root pass of the joining weld

A new method to determine the elastopalstic properties of ductile materials by conical indentation

Based on load-displacement curves, indentation is widely used to extract the elastoplastic properties of materials. It is generally believed that such a measure is non-unique and a full stress-strain curve cannot be obtained using plural sharp and deep spherical indenters. In this paper we show that by introducing an additional dimensionless function of DA / A (the ratio of residual area to the area of an indenter profile) in the reverse analysis, the elastoplastic properties of several unknown materials that exhibit visually indistinguishable load-displacement curves can be uniquely determined with a sharp indentation

Modeling of residual stresses by HY-100 weldments

Residual stress distribution in a HY-100 steel disk, induced by GTA spot welding, was analyzed by finite element (FE) formulations and measured by neutron diffraction (ND). Computations used temperature- dependent thermophysical and mechanical properties. FE model predictions are in good agreement with ND data in far heat affected zone (HAZ) and in base metal. Predicted residual stresses in fusion zone and near HAZ were higher than those measured by ND. This discrepancy was attributed to microstructural changes and associated material properties in the HAZ and fusion zone due to phase transformations during the weld thermal cycle