Ian F. Bainbridge

The Surface Tension of Pure Aluminum and Aluminum Alloys

The surface tension of high purity and commercial purity aluminum in vacuo was determined using the sessile drop method and the results were found to compare favorably with published data. The effects of holding atmosphere, substrate, and “surface fracture” of the sessile drop on the measured surface tension values were investigated together with the effects of different solute elements commonly present in commercial aluminum alloys. The results obtained suggest that the nature of the surface oxide film formed on the droplets (affected by alloy composition and atmosphere) and the rupture of this film are the dominant factors influencing the surface tension values obtained. Changes in surface tension values of up to 60 pct were observed. The possible effect of this variable surface tension on practical casting processes, such as direct chill casting, is suggested.

Creating a green supply chain: a simulation and modelling approach

This paper presents a case study of a supply chain which is concerned with the distribution of aluminium metal, starting from raw material from a Metal Supplier to a Casting Plant, billets from the Casting Plant to the Component Producer, and finally, die-cast components from the Component Producer to the Market. The paper creates a green supply chain by integrating the concerns of transport pollution, marketing costs, time to market, recycling of scrap metal and energy conservation. Simulation and modelling tools are introduced to aid in the decision making process of distance selections and choices of transportation in the case study. Based on a series of user input selections, the simulation results are used to determine a range of optimal plant locations that will balance economical benefits (highest scrap values, least total costs, etc.) as well as environmental stewardship (least pollution).

Experimental Determination of Heat Transfer Across the Metal/Mold Gap in a Direct Chill (DC) Casting Mold—Part I: Effect of Gap Size and Mold Gas Type

An experimental apparatus to determine the heat-transfer coefficient in the gap formed between the cast metal and the mold wall of a vertical direct chill (DC) casting mold is described. The apparatus simulates the conditions existing within the confines of the DC casting mold and measures the heat flux within the gap. Measurements were made under steady-state conditions, simulating the steady-state regime of the DC casting process. A range of casting parameters that may affect the heat transfer was tested using this apparatus. In the current article, the operation of the apparatus is described along with the results for the effect of gas type within the mold, and the size of the metal-mold gap formed during casting. The results show that the gas type and the gap size significantly affect the heat transfer within a DC casting mold. The measured heat fluxes for all the conditions tested were expressed as a linear correlation between the heat-transfer coefficient and the metal-mold gap size, and the fluxes can be used to estimate the heat transfer between the metal and the mold at any gap size. These results are compared to values reported in the literature and recommendations are made for the future reporting of the metal/mold heat-transfer coefficient for DC casting. The results for the effect of the other parameters tested are described in Part II of the article.

Minimizing total setup cost for a metal casting company

The optimizing sequence of production for a set of customer orders - in order to minimize machine set-up time and costs - is one of the typical problems found in many manufacturing systems. In this paper, we develop a simulation model to capture a practical system of a metal casting company in Queensland, Australia, and optimize the production sequence for a set of customer orders. The method addressed in the paper can be applied to ether optimization problems in manufacturing industry.

The Measurement of Heat Flow Within a DC Casting Mould

The heat flow between the molten metal and the mould-wall in DC casting is often assumed to be negligible compared to that due to the sub-mould water cooling. Furthermore, the entire DC casting process is often descnbed based on this assumption. However, the assumption of negligible heat transfer in the metalmould region, as oompared to the sub-mould region, and its subsequent minimal influence on cast product quality remains unproven. The focus of the present paper is therefore on understanding the heat transfer in the metal/mould wall region. To this end a method for the laboratory measurement of the flow of heat from the metal being cast to the wall of a DC casting mould has been developed. The equipment and methodology are briefly described together with some of the initial results obtained. The implications of this work for use in simulation models and for the design and operation of OC casting moulds are disct1ssed.

Modelling of the Metal/Mould Interactions in the DC Casting Process for Aluminium and Magnesium

The process of direct chill (DC) casting of aluminium and magnesium alloys is regarded as a mature technology. The thrust of more recent work to understand and upgrade the technology has been centred on developing models of the process, the most advanced of which (e.g., Alsim and Calcasoft) have been used to examine what may be considered macro-features of the process (macro-segregation, hot cracking, etc.). These models, being macroscopic, rarely elaborate on the role of mould-wall heat transfer in the DC casting process. As part of the work on DC casting being conducted at CAST, for the investigation of small scale features of the process (e.g. heat extraction through the mould wall), a 2D finite Difference model of the process near the mould-wall region has been developed. The basic features of the model are described and initial results outlined.In particular, the effect of mould-wall heat transfer on the solid shell formed during the steady state regime of DC casting will be presented.

Improved VDC Casting of Aluminium Alloys through an Understanding of the Surface Properties of the Molten Metal

Vertical direct chill (VDC) casting of aluminium alloys is a mature process that has evolved over many decades through gradual change to both equipment design and casting practice. Today, air-pressurised, continuous lubrication, hot top mould systems with advanced station automation are selected as the process of choice for producing extrusion billet. Specific sets of operating parameters are employed on these stations for each alloy and size combination to produce optimal billet quality. The designs and parameters are largely derived from past experience and accumulated know-how. Recent experimental work at the University of Queensland has concentrated on understanding the way in which the surface properties of liquid aluminium alloys, e.g., surface tension, wetting angle and oxide skin strength, influence the size and shape of the naturally-stable meniscus for a given alloy, temperature and atmosphere. The wide range of alloyand condition-dependent values measured has led to the consideration of how these properties impact the stability of the enforced molten metal meniscus within the hot top mould cavity. The actual shape and position of the enforced meniscus is controlled by parameters such as the upstream conduction distance (UCD) from sub-mould cooling and the molten metal head. The degree of deviation of this actual meniscus from the predicted stable meniscus is considered to be a key driver in surface defect formation. This paper reports on liquid alloy property results and proposes how this knowledge might be used to better design VDC mould systems and casting practices.

Surface Formation on VDC Casting

A range of surface defects commonly formed on vertical direct chill (VDC) cast products have been examined by various metallographic techniques. Whilst the presently accepted model for the formation of cold folds on the cast surface can be reconciled to the details observed in these examined samples, the suggested explanations for the formation of other common surface defects could not. This paper describes current research efforts aimed at measuring the strength of the molten aluminium alloy oxide skin under various conditions. This data is used as the basis for understanding the behaviour of the melt surface in the meniscus region of a VDC mould during casting. The results obtained from the surface skin strength tests and the metallographic examination of the cast samples are discussed and a framework of possible factors responsible for the formation of various surface defects is proposed.