John Grandfield

Optimisation of ingot casting wheel design using SPH simulations

Performance improvements of a new filling system for aluminium ingot casting resulting from a combination of Smoothed Particle Hydrodynamic (SPH) modelling and pilot scale testing are reported in this paper. The SPH modelling was used as the primary design tool, passing through several design iterations to understand the flow fundamentals and to progressively improve performance. The best concept from the simulation design stage was then refined through a detailed programme of pilot scale testing and a final round of SPH simulation. The results of this development programme will be described, with the new wheel design now able to operate at 50% higher throughput with an expected reduction in the oxide content by about 53% compared to that of the original design.

Control and Removal of Impurities from Al Melts: A Review

Control of impurity elements in Al-based alloys is of increasing technological importance, both in primary and secondary alloy production. In primary alloy production, Ni and V concentrations in the coke are rising and this is increasing the level of impurities in the final products to the extent that they are out of specification. Impurity control is also of concern in recycling due to the pickup of elements such as Fe from contaminants in the scrap, which can detrimentally affect the alloy properties. Dissolved elemental impurities can be removed by a number of different processes including boron treatment for some of the transition metals. Other processes in the cast shop for removing impurities and inclusions from Al melts include fluxing, floatation, and filtration. Gas purging, vacuum treatment, filtration, the use of salts, and combinations of these presently find commercial applications. Ultra purity Al and its alloys can be obtained using zone refining and three-layer electrolysis methods. The demand for higher purity Al has been largely met by additional electrolytic refining processes. This paper reviews the tools that are currently available to the casthouse for removing impurities and inclusions from Al melts and suggests approaches that may be useful to meet future challenges.

The Use of Electromagnetic Fields for the Detection of Inclusions in Aluminium

Management of inclusions is an important part of quality control within the aluminium cast house. Inclusions have a detrimental effect on many aluminium cast products. The ability to reliably detect inclusions in a timely fashion is an essential part of this process. There are a number of tools available for inclusion measurement based on different principles. Techniques for inclusion detection such as metallurgical analysis, K-Mold, Podfa, Lais, Prefil all have a delay before detailed results are available. Ultrasound provides a possible technique for an online sensor, however has not as yet managed sufficient sensitivity. LiMCA, based on the Electrical Sensing Zone, has provided the most sensitive online detection to date, but other electromagnetic techniques such as a multiple voltage array sensor offer promise of a sensor which can be built for lower cost and can sample a larger portion of the melt.

3D Thermo-Mechanical Modelling of Wheel and Belt Continuous Casting

Wire rod is produced by hot-rolling a bar of metal coming from a wheel/belt continuous casting process. This kind of process, e.g. Properzi, is an elaborate process in which the molten metal is poured in a cooled rotating mould formed by the groove of a wheel and closed by a belt. In order to better understand the heat transfer phenomenon and solidified bar characteristics, depending on process parameters a three dimensional thermo-mechanical model has been developed. The model, based on the finite-element method, calculates the heat transfer coefficient of the air gap at the metal-mould interface as a function of the size of the gap determined by the bar contraction and wheel and belt thermal deformations. The air gap formation due to metal shrinkage and mould deformation is the main factor which determines the heat extraction. Wheel temperature measurements with thermocouple and belt temperature measurements with an infrared system were carried out to verify model results. Attempts were also made to measure a liquid pool profile using doping with copper rich alloy. The model shows the effect of the casting temperature and the rotation speed on the air gap formation and resulting temperature and stress fields. The model can be applied to issues such as maximising wheel and belt life and minimising solidification defects.

An Initial Assessment of the Effects of Increased Ni and V Content in A356 and AA6063 Alloys

Changes in calcined coke composition associated with different crude oil sources have caused nickel (Ni) and vanadium (V) levels in aluminum to rise. To ensure cast product quality is not compromised an understanding of the effects of these changes is needed. An initial investigation has been conducted for two commonly used alloys, A356 and AA6060/6063. Castings were produced with low typical levels of Ni-V and with high Ni-V levels approaching the maximum P1020 specification of 300ppm each. Micro structural changes were assessed using optical and scanning electron microscopy and tensile properties and corrosion resistance were measured. For as-cast A356 alloy, there was no significant difference in corrosion performance, but adding Ni and V had a small effect on tensile properties. For AA6060/6063 alloy there was no significant difference in the tensile properties of extrusions with low and high Ni-V levels but a small drop in corrosion performance was measured at high Ni-V levels.

Safety Enhancement in Ingot Casting at Tomago Aluminium

Tomago Aluminium experienced problems with the boiling of cooling water in ingot casting machines, where water splashed onto molten aluminium after mould filling. The boiling problem was particularly severe when new standard moulds were installed. This paper describes the experiments and modelling employed to analyse and identify the cause of the problem and based on the results, modifications to mould geometry were suggested. Subsequent testing in lab and field trials showed that the boiling was suppressed. The first set of modified moulds in service at Tomago Aluminium showed mould life was improved as predicted. Other issues with the modified mould design, which arose in service, are also discussed.

The Problem of Cavities in Open Mold Conveyor Remelt Ingots

Open mold conveyor casting machines for 8–25kg ingot produce millions of tonnes of remelt ingot every year. However, these ingots suffer from cavity formation. These cavities represent a safety risk during remelting of the ingots due to the possibility of water molten metal explosions if the cavities contain water. The formation mechanisms of these cavities and the effect of alloy, machine design and operational parameters are reviewed. Alternative means of controlling cavities are examined and assessed. The need for a new approach to the problem is highlighted.

Implementation of CASTfill Low-Dross Pouring System for Ingot Casting

Producing low-dross ingots has been a long-term goal in aluminium cast houses. The patented CASTfill technology [1] is a low-dross and high-productivity pouring system developed to fulfil this demand. This paper describes the research methods used during the development of CASTfill; now in service at Boyne Smelters Limited (BSL) since August 2009. The importance of combining scientific modelling and testing procedures with process operability, maintainability and durability to ensure the success of new technology in a production facility is also highlighted. Ingot assessments showed that the latest CASTfill design greatly reduced dross generated during mould filling. Improved ingot packaging and reduced variation of ingot weights were also observed as the results of a more tranquil flow of molten aluminium through CASTfill and its uniquely modular design.