Analysis of Ohno continuous casting process using one-dimensional steady state heat transfer model

Abstract

The Ohno continuous casting process is being used regularly in the unidirectional crystallisation of high purity copper and silver wires for electronics applications. Many experimental investigations have been carried out on both fundamental and practical aspects of the process. This paper deals with the feasibility of a one-dimensional heat transfer approach for the analysis of the effect of the crucial processing parameters. The results on the effects of varying the parameters based on the calculation of the temperature profiles along the axis of the cast rod were in accord with the experimental results in the literature, indicating that the one-dimensional approach can be used as an analytical tool for the process.     

Experimental and numerical modelling of the flow field in a CuxSny direct chill caster

Abstract

To investigate the influence of the casting speed on the flow field and the shape of the solidification front in an industrial bronze caster, numerical calculations have been performed and experimental flow field measurements were used to validate the numerical model. Both numerical and experimental model represented 1:1 the real caster geometry of 820 × 250 × 800 mm³. A steady-state calculation, considering solidification and turbulent flow, was performed. Furthermore, a 1:1 water model of the industrial bronze caster has been built and combined with a Particle Image Velocity (PIV) setup to measure the apparent flow fields. Amongst other parameters, the numerical model provided information on the influence of the casting speed on the solidification front shape. The water model gave the experimentalist the facility to adjust the shape of the solidification front to the one predicted by the numerical model and compare the resulting flow field with the numerical prediction. This work presents a comparison of the results of both numerical and experimental models for different casting speeds with the same numerical parameters and boundary conditions.     

Measurements and modelling of air gap formation in Cu-based alloys

Abstract

The formation of an air gap has been experimentally studied during solidification of pure Cu, Cu–Te and Cu–6%Sn in a cylindrical mould. The displacements of the casting and the mould causing an air gap have been measured during solidification and cooling of the casting. The temperature distribution was measured simultaneously. Mathematical modelling has been performed to increase the understanding of the solidification process and the shrinkage of the casting leading to air gap formation. A model, which has been tested in earlier work showing good results for aluminium based alloys, has been applied here to describe air gap formation during solidification of copper based alloys. The model includes the effect of the formation and condensation of vacancies on the solidification process as well as on the material shrinkage resulting in air gap formation. The results from the modelling show a reasonable agreement with the experimental measurements.     

Enhanced cooling for solidification of aluminium alloys in permanent moulds using advanced heat pipe solutions

Abstract

In order to obtain sound cast components with good properties, a number of measures must be taken to make parts defect free. It is well recognised by the casting industry that it is essential to control cooling rates of permanent mould castings in order to speed up solidification and control the solidification pattern. Each of the traditional controlled cooling techniques (air or water cooling passages and chill inserts) presents certain disadvantages and none offers optimum thermal management. A new cooling method for permanent moulds is proposed. This new technique is based on heat pipe technology that was developed specifically for the cooling of permanent moulds in the casting of light metals where high heat fluxes are normally encountered. The influence of the conductivity of mould coatings on casting solidification and dendrite arm spacing with heat pipe cooling was investigated. Typical experimental results are also presented.     

Experimental and numerical investigations of NH4Cl solidification in a mould Part 2: numerical results

Abstract

This paper deals with the validation of a multiphase solidification model based on a benchmark experiment presented in Part 1. For the numerical modelling of NH₄Cl–H₂O solidification, the three different phases liquid, columnar dendrite trunks and equiaxed grains have been considered. The mass, momentum, energy conservation and species transport equations for each phase have been solved. The multiphase Eulerian-Eulerian model equations have been implemented in the Finite Volume Method based commercial software FLUENT-ANSYS using User-Defined Functions (UDF). The simulation of the NH₄Cl–H₂O solidification has been numerically investigated as a twodimensional unsteady process representing a cross-section of a 100 × 80 × 10 mm experimental benchmark. During the experiment both columnar and equiaxed growth of NH₄Cl were observed, therefore both phenomena were considered in the simulation. The predicted distribution of the solidification front has been compared with the measurements.     

Determination of the metal/die interfacial heat transfer coefficient and its application in evaluating the pressure distribution inside the casting during the high pressure die casting process

Abstract

High pressure die casting (HPDC) experiments were conducted on a 650 t cold chamber die casting machine to study the interfacial heat transfer behaviour between casting and die. A 'step shape' casting and two commercial alloys namely ADC12 and AM50 were used during the experiments. Temperature and pressure measurements were made inside the die and at the die surface. The metal/die interfacial heat transfer coefficient (IHTC) was successfully determined based on the measured temperature inside the die by solving the inverse heat transfer problem. The IHTC was then used as the boundary condition to determine the 3-D temperature field inside the casting. Based on the predicted temperature distribution, the pressure distribution inside the casting was evaluated by assuming that the transferred pressure from the plunger tip of the injection side to the casting is primarily influenced by the solid fraction of the casting. Reasonable agreement was found between the determined pressure values and the measured pressures at the die surface of the casting.     

A numerical analysis of fluid flow, heat transfer and solidification in the bending-type square billet continuous casting process

A numerical modeling system was developed which can simulate the transport phenomena of a bending type square billet continuous casting process. Fluid flow and heat transfer were analyzed with a 3-dimensional finite volume method (FVM) with the aid of an effective heat capacity algorithm for the solidification. For a complex geometry of the bending type billet caster, a body-fitted-coordinate (BFC) system was employed. The bent structure of the caster allows a recirculating flow to develop in the upper and outer-radius region and the main stream to shift toward inner radius. This causes the thinner solid shell in the inner radius region than in the outer one. Besides standard operation conditions, we have analyzed the results when casting speed, caster shape, and tundish superheat changes. Lower casting speed makes the solid shell thicker by reducing heat flux from the mold. In the vertical caster, solid shell thickness are more uniform than that in the bending-type in entire region. When superheat increases by 5°C, solid shell thickness at the mold exit becomes thinner by 1 mm.     

薄板坯连铸漏斗型结晶器内流动、传热和凝固行为的数值研究

针对薄板坯连铸漏斗型结晶器,建立了钢液流动与凝固传热的三维耦合模型,在不改变造型复杂的水口和漏斗型结晶器的尺寸和结构的前提下,计算分析了不同操作参数——拉坯速度和浇注温度对结晶器内流场、温度场和凝壳的影响,同时采用了第二类和第三类两种不同的热边界条件进行了流场和温度场的分析。计算结果表明,钢液凝固壳及糊状区对结晶器内钢液的流动有很大影响,采用第二类热边界条件能够更真实地反映出结晶器内流动对传热的影响。