Papers by Keyword: Cooling Curve

Abstract: The application of high strength steels in welded structures relies on easy to use quality assurance concepts for the welding process. For ferritic steels, one of the most common methods for estimating the mechanical properties of welded joints is the cooling time concept t8/5. Even without experimental determination, the calculation of cooling time with previously introduced formulas based on the welding parameters leads to good results. Because high strength structural steels and weld metals with a yield strength of 960 MPa contain higher quantities of alloying elements, the transformation start temperature Ar3 is found to be outside of the range of 800 °C to 500 °C. This leads to inadequate estimation results, as the thermal arrest caused by the microstructural transformation in this case is not considered. In this work the usage of the well-proven cooling time concept t8/5 is analyzed using high strength fine grained structural steels and suitable welding filler wires during gas metal arc and submerged arc welding processes. The results are discussed taking into account the microstructure and the transformation behavior. Based on the experimental work, an improved concept is presented.

Abstract: Thermal analysis is worldwide used in foundry for control of structure and properties of cast irons. In this paper is presented the experimental study realized to control the inoculation effect by thermal analysis method of inoculated grey cast irons. For this purpose was conducted an in ladle inoculation process with 0.5wt. % inoculant from LaCaAlFeSi and BaCaAlFeSi alloy systems. The main goals of this experimental research work are: to determine the particular characteristics of the registered cooling curves, to notice the solidification parameters that present sensibility as against inoculant addition in treated cast iron and eventually to improve thermal analysis technique of cast irons.

Abstract: For a number of methods used in the cooling heat treatment technique, are required quenching media with cooling rate lower than that of water and larger than that of oil. This can be achieved in industrial practice by using the synthetic quenching type media like gels or emulsions. The synthetic quenching coolants offer advantages such as non-flammability, safety of use and low cost price. The cooling medium to be tested is emulsifiable oil dissolved in water at various concentrations and the testing temperature is 50°C. In the paper were measured cooling curves for specified synthetic media and calculated for the same media the cooling rate variation and heat transfer coefficient on intervals. The experimental data were compared with those obtained from traditional media: water and heat treatment oil TT 50.

Abstract: In this paper, paraffin/polyurea (PU) phase change microencapsules were prepared through an interfacial polymerization method using composite paraffin with solid/liquid mass ratio 3:7 as core materials, 2,4 toluene diisocyanate (TDI) and ethylenediamine (EDA) as monomers, NP-10 as an emulsifier. It was explored the effect of the monomer mass ratio m_EDA: m_TDI on the yield of hollow PU microcapsules, and the effect of core/shell ratio on the particle size and coating efficiency and storage-energy performance of paraffin/PU phase change microencapsules. The experimental results showed the PU yield is increasing with the increasing of EDA:TDI mass ratio until 0.5:1,then keeps the constant. Paraffin/PU phase change microencapsules prepared with the core-shell ratio of 2:1 have better performance: the melting point of 28.1°C, the enthalpy of 58.4KJ/Kg, encapsulation efficiency of 87.5%, the average particle size of 4.32μm, and the uniform particle size distribution.

Abstract: In this paper, Microencapsulated paraffin/polyurea (PU) phase change materials were prepared through an interfacial polymerization method using composite paraffin with solid/liquid mass ratio 3:7 as core materials, 2,4 toluene diisocyanate and ethylenediamine as monomers, NP-10 as an emulsifier. It was investigated the effects of emulsion speed, the amount of emulsifier and polymerization temperature on the particle size and coating efficiency and storage-energy performance of microencapsulated paraffin / PU phase change materials. The results showed when the emulsion speed is 2000r/min and the amount of emulsifier to core material is 6% and the polymerization temperature is 70°C, Microencapsulated paraffin / PU phase change materials have better performance: the melting point of 28.1°C, the enthalpy of 58.4KJ/Kg, coating efficiency of 87.5%, the average particle size of 3~4μm, and the uniform particle size distribution.

Abstract: A baseline method to determine directly the solid fraction using the cooling curve was proposed for solidification of undercooled melts. To construct the baselines, a sudden function ξα(x) is introduced. In terms of present method, the solid fractions during solidification of Zr metal and Al-7wt.%Si alloy were predicted. The predictions coincide with the results of the available methods.

Abstract: Ni-3.3wt.%B alloy solidified at different undercooling by glass fluxing has been studied. The as-solidified structure is mainly controlled by the undercooling for eutectic solidification, ΔT₂, instead of ΔT₁, the undercooling for primary solidification. For ∆T₂2 ≥145±5K, three recalescence peaks appear in cooling curves. If ∆T₂2≥145±5 K, two kinds of dot phases occur. Further analysis declares that, the regularly distributed dot phases with larger size come from the transformation L→Ni₂₃B₆+Ni, whereas, the irregularly distributed ones with smaller size come from Ni₂₃B₆→Ni₃B+Ni. Both of them have a contribution to strengthen the mechanical property.

Abstract: The kinematics of the wetting front, i.e., the history of the locus of the boundary between the vapor blanket and the nucleate boiling area is of outmost importance in quenching operations. In this investigation, the effect of water temperature on the wetting front kinematics was studied in forced convective quenching experiments of conical-end cylindrical probes. Three values of water temperature (30, 45 and 60 °C) were studied for a free-stream water velocity of 0.2 m/s. The wetting front kinematics was characterized from: 1) the measured thermal response at three longitudinal positions inside the probe, near the probe surface, and 2) high-speed video-recordings of the events that took place at the probe surface upon quenching. From the video-recordings, the position of the wetting front as a function of time was determined to estimate the wetting front velocity from a linear regression. The wetting front velocity was constant for a given experiment and increased as the water temperature decreased. The bubble size decreased and the frequency of bubble formation increased as the water temperature decreased. Using the measured thermal responses, the surface heat flux history was estimated, solving the corresponding inverse heat conduction problem. A regression analysis was applied to relate the maximum (critical) surface heat flux and the water temperature as a first step towards modeling the surface heat flux history as a function of water temperature.

Abstract: In this paper, the effects of electric pulse on solidified structure and graining process of near eutectic Al-5%Cu alloy have been investigated during solidified process. It was treated with different pulse voltages at 740°C in this experiment, and established the cooling curve. The results show that the improvement of alloy casting macro-segregation and solidification structure refinement by electric pulse discharging; The change of the solidified casting structure has a preferable coincidence relation with the change of the cooling curve, and analysis of the cooling curve shows that the best granular effect has a maximal supercooling on the curve.

Abstract: The quality of compaction is important to Hot Mixed Asphalt (HMA) pavement. Most premature failures of asphalt pavement are concerned with poor compaction. Characteristics of cooling curve of asphalt mixture were studied in this paper. Through on site measurement, it was found that air temperature, solar radiation, wind velocity and layer thickness had great influence on cooling time. Then, with ABAQUS finite element software, the rule of HMA mixture cooling curves during paving was simulated. A simple multi-factors regression equation was given which can be used to estimate the effective compactible time.