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By L. S. Almeida, U. A. Courbassier, C. T. Guimãaraes, M. N. Souza, V. L. Silva, H. P. Dias, G. A. Bicalho, B. S. Rocha, P. N. Rodrigues, A. Carnevale

During primary aluminum production the anode changing is a very important task. So improvements on it will be essential to avoid disturbance and have a better operational control. After anode changing a good current distribution will be guaranteed using a cavity cleaner and precise anode setting. Albras switching a manually anode setting to an automatic one solved the setting problems. In this paper it will be shown some pot line results and the improvements on workers ergonomic and safety conditions. The device was developed in a partnership between Albras and Pesto.

Jan 1, 2006

By Z. Farhat

In spite of advances in cutting tool technology, the understanding of the basic wear behavior and failure mechanisms needs further study. Tool wear is the main factor contributing to geometrical error and thermal damage in machined components. Manifested as a reduction in tool life, it also affects the workpiece surface finish, increases cutting forces and induces residual stresses. Furthermore, the emergence of high and ultra-high speed machining processes necessitates the investigation of tool wear under these severe working conditions. Tungsten carbide-cobalt composite material has been used traditionally as wear resistant materials for many years. One main application of this material is in cutting tools. WC-Co tools consist of hard WC particles imbedded in a tough Co matrix, which functions as a binder phase. More recently, Cubic boron nitride (CBN) tool material have attracted special attention due to its high hardness and excellent wear resistance. Boron nitride in its cubic form is known to be the hardest material next only to diamond. In this paper microstructural and tribological properties of commercial grade WC-Co and CBN cutting tool materials are investigated under high speed cutting conditions. The CBN cutting tools were found to be superior to tungsten carbide (WC) tools. Four-fold increase in productivity and significant reduction in chipping and cratering was achieved for CBN as compared to WC. Wear mechanisms are proposed and are related to the observed wear characteristics in the cutting zone.

Jan 1, 2006

By F. H. Samuel, H. Tahiri, S. Valtierra, H. W. Doty, A. M. Samuel

L'affinage des grains dans les alliages d'aluminium consiste à augmenter le nombre de sites de cristallisation de la phase a-Al afin d'obtenir une structure fine. Les alliages mères de type Al-Ti-B sont largement utilisés comme raffineurs des grains. Cette étude a pour but d'établir des mécanismes convenables d'affinage des grains dans l'alliage A356 en utilisant cinq alliages mères et deux températures de coulée (750°C et 950°C). Les résultats montrent que la phase a-Al prend une forme selon l'alliage mère ajoute; les échantillons coules a haute température montrent une taille de grain plus grosse; les températures de germination et de croissance augmentent avec I' augmentation du Ti ou du B et la taille des grains diminue. L'alliage mère Al-4%B montre une puissance remarquable en comparaison d'autres alliages mères. Pour cet alliage mère, le titane résiduel dans l'alliage A356 réagit avec le bore pour former TiB2 qui, par la suite, agit comme un germe actif pour la phase a-Al.

Jan 1, 2006

By E. Demedde

Carbon anodes in aluminium reduction cells are continuously consumed during electrolysis. In prebake cells the anodes are replaced at regular intervals. The spent anodes, called butts, are often allowed to cool in air while emitting fluorides into the building from the hot alumina cover and the adhering bath. In modem smelters spent anodes are placed inside enclosures and fluoride emissions during cooling are effectively reduced. Fluoride emissions from spent anodes were estimated by considering the kinetics of fluoride formation, a heat transfer analysis of the cooling anode butt and the ventilation flow from a cavity. Fluoride emissions from large anode butts cooling inside enclosures were compared with those cooling in air. Good agreement with published experimental values was obtained for enclosures having different leakage opemngs, when a hydrofluorination reaction of the spent anodes was included.

Jan 1, 2006

By J. A. Finch

Solvent-coated air bubbles in the Air-Assisted Solvent Extraction (AASX) process achieve the dual role of high solvent specific surface area and ease of phase separation. The thickness of the solvent film is of fundamental interest but difficult to measure directly in the process itself. As an approach interferometry (in the UV-vis region) was used to measure the time dependent thickness of a film formed by blowing an air bubble in kerosene-based solvents. The film was stabilized by the presence of 1.5 ppm silicone oil, as employed in AASX. The film appears to comprise two layers; an outer "free" layer of almost constant thickness and an inner "bound" layer which decreased in thickness with time. The bound layer is considered relevant to AASX. For a 20 mm diameter bubble blown in LIX/kerosene solvent the initial thickness was ~ 3 um which decreased over 10 minutes to a final rupture thickness of 500 nm. The bound layer thickness and time to rupture decreased with decreasing bubble size. Correspondence to prior indirect estimates of solvent layer thickness is examined.

Jan 1, 2006

By M. Aljarrah

The phase equilibria in the Mg-Al-Ca system was investigated experimentally by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques similarly the Mg-Al-Sr system has been studied using DSC and XRD as well as scanning electron microscopy/energy dispersive spectrometer (SEM/EDS) and quantitative electron probe micro-analysis (EPMA). A new ternary solid solution MgxAl4,xSr was confirmed in Mg-Al-Sr system, which is a substitutional solid solution of Mg atoms in Al4Sr. Maximum solubilities of 21.3 at.% Al in Mg17Sr2 and 11.4 at.% Al in Mg were observed. It was also noticed that Mg38Sr9 dissolved 12.5 at.% Al. In the Mg-Al-Ca ternary system, one of the invariant transformations predicted by thermodynamic modeling was verified experimentally and found to occur at 512°C with composition close to 10.8 at.% Ca, 79.5 at.% Mg and 9.7 at.% Al. A ternary solid solution (Mg,Al)2Ca was confirmed where large solid solubility of Al in Mg2Ca was observed.

Jan 1, 2006

By L Mariani, G. Mendoza-Suarez

In this investigation, TiH2 powders were coated with copper and nickel by electroless plating to delay hydrogen evolution. Copper-coated samples were found to have a mixed acicular (2D growth) and cauliflower (3D growth) morphology whereas the nickel-coated samples had a cauliflower morphology. Examinations of the coated powder cross-sections revealed that the coating thickness ranges from 0.2 µm to 4 µm. Uncoated areas on the powder surface and coating flakes unattached to TiH2 particles suggest poor adhesion between the coating and the substrate. The phase transformation undergone by the TiH2 during dehydrogenation was studied in samples taken at intermediary points in the heating cycles and examined by XRD. The findings reveal that as the powder is heated from room temperature to 800°C, it changes from TiH1.971 to Tiu and to aTi. Differential Thermal Analysis (DTA) was performed to study the effects of the coatings on the temperature of hydrogen release. It was found that increasing the number of plating iterations, and therefore the thickness of the coating, creates a significant shift in the temperature of gas release.

Jan 1, 2006

By G. Barrasso

REACH was proposed by the EU Commission in October 2003 and stands for the Registration Evaluation, Authorisation and Restriction of Chemicals. It requires that all substances identified as persistent, bio-accumulative and toxic, whether the risk of those chemicals being released is real or perceived, require registration prior to them being allowed to be imported into the European Union. An internal investigation by the metals industry indicates that almost all primary raw materials streams would be classified as hazardous due to the potential health or environmental hazard properties of one or more of their ingredients. REACH uses a wide definition for chemicals and metals and as such its implications greatly impact the entire supply chain of the metals industry. The process of registration would require the producer/ importer to produce a dossier. Initiatives along the same lines as the EU REACH are also coming up in other parts of the world. REACH requires registration of at least four substances manufactured by the aluminium industry: aluminium metal, including powder, aluminium oxide, and aluminium hydroxide. The proposed legislation permits the affected companies to band together to form a consortium to develop certain aspects of the registration application. The aluminium industry has established a consortium and testing is currently underway.

Jan 1, 2006

By M. H. Colebrook

Nickel laterites contain about 70% of all continental or terrestrial nickel resources; therefore the recovery of nickel from lateritic ores has large economic significance. The processing of lateritic ores involves the preparation and movement of concentrated aqueous suspensions. However due to complex characteristics and non-Newtonian properties, ranging from shear-thinning to shear-thickening and from thixotropic to rheopectic, a basic understanding of the flow behaviour must be developed. This understanding will assist in the development of new plants and the operation of existing plants. The work in this paper involves the characterization of three ore types from the Vermelho ore deposit to categorize them as rheologically simple to complex. Rheological testing was also conducted on pure mineral samples that represent the main minerals in these samples. The results show that the rheological properties of the ore types can be related to the surface properties and physical characteristics of the main mineral constituents.

Jan 1, 2006

By F. Chiesa

The permanent mould process, which is a favoured process for producing premium quality aluminium casting, is rarely used to produce magnesium alloy parts. This may be attributed different factors such as: the reservation with which the automotive industry considers using magnesium in structural castings; also the relative hot shortness of most magnesium alloys when compared to aluminium A356/357 is another factor. A third reason stems from the fact that the "heat content" of magnesium is much less than that of aluminium, resulting in the difficulty, for a relatively slow process such as permanent mould (versus pressure die casting), to reach a mould dynamic equilibrium temperature sufficiently high to avoid premature freezing and misruns. The present work will address this problem by carrying out controlled cycling of a laboratory mould, poured with aluminium and magnesium alloys. The influence of insulation of the mould and artificial electric heating on the run-in mould temperature will be determined experimentally. A thermal model will be sought for these thermal devices that will allow to predict the thermal behaviour of moulds of different geometry before a single casting is poured. The model will be tested on an industrial casting in a workshop environment.

Jan 1, 2006

By E. Krause

The oxidation of Fe(II) with S(IV) and oxygen can be used advantageously in leaching systems requiring both Fe(III) and sulfuric acid; e.g., heap leaching of sulfide-containing ores or concentrates. The oxidation of Fe(II) with SO2/air is several orders of magnitude faster than with air alone; rates of up to ?20 g/L'h were observed at 25°C. The reaction proceeds via an intermediate orange-red mixed-valence Fe(II)/Fe(III) sulfite complex, which is present at an essentially constant concentration throughout most of the oxidation process. The oxidation rate of Fe(II) is approximated by the formula -d[Fe(II)]/dt = k [S(IV)] [02]0'3. The concentration of the mixed-valence complex, and thus the iron oxidation rate, decreases with increasing acidity. Certain impurities, such as SCN- and thiourea, negatively affect the rate. The oxidation reaction 2Fe2 + SO2 + 02 4 2Fe3+ + S042- is accompanied by the side reaction H20 + SO2 + 1/202 4 H2SO4. The side reaction becomes particularly important at low temperatures and whenever the oxygen mass transfer is insufficient with respect to the rate of addition of S(IV). Thus, effective oxygen mass transfer is essential for achieving high oxidation rates with minimal acid formation. The activation energy was estimated as 141 kJ/mol over the temperature range 10-35°C.

Jan 1, 2006

By K. Kawagishi, J. Ang, A. Sato, H. Harada

"We have recently proposed a new ""EQ Coating"" bond coat system to solve the problem of secondary reaction zone (SRZ) formation caused by bond coats applied on the hot section components of modem jet engines. A viable EQ coating alloy was previously found for a representative znd generation superalloy, TMS-82+. It would be ideal if the same could be done for a representative 5th generation superalloy, TMS-173. In this paper, we will show that the coating with the best oxidation resistance in the EQ system of TMS-173, although possessing considerably better resistance than TMS-173, did not have sufficient oxidation resistance. In order to improve the oxidation resistance of the EQ coating for TMS-173, we have ventured into ""Pseudo-EQ coatings"". A diffusion couple between the Pseudo-EQ coating and TMS-173, after 300hrs at 1100°C, had a 0-15µm IDZ, but no SRZ. A diffusion couple between a conventional coating and TMS-173 formed a 80-150 µm SRZ. After a 1 hr oxidation test at 1100°C, the PseudoEQ coating formed a thinner oxide layer than the EQ coating, but still contained NiO and spinel. Aerospace"

Jan 1, 2006

By P. Wanjara, M. Xiao

During fusion welding of aluminium alloys, the avoidance of defects (such as porosity, oxides, hot cracking, undercutting) as well as the ability to optimize the microstructure-property characteristics in the assembly are critical for the stringent manufacturing specifications in the aerospace industry. In this work, aluminium alloy (AA) 2024 was electron beam welded autogenously as part of a study to determine the influence of parametric conditions on the characteristics of the heat affected and fusion zones to obtain optimal welding conditions. In particular the evolution in the weld geometry, microstructure and mechanical properties were examined as function of the processing conditions, including beam current, beam focus, beam oscillation, linear heat input and welding speed. For optimized parametric conditions, microstructural examination of the joints revealed narrow fusion and heat-affected zones comprising of dendritic structures without the occurrence of defects that enabled a maximized joint efficiency.

Jan 1, 2006

By H. Attia, S. Engin

This paper presents a practical approach for determining the optimal spindle speed and the depth of cut in a milling operation within the ever-increasing economic and technical constrains. Analytical modeling and experimental work has been carried out to predict chatter in such operations. The stability lobes determined from this analysis were then used as a constraint in the optimization of the cutting process. The optimal cutting conditions are determined for two different objectives: maximum metal removal rate and minimum cost per unit. It is demonstrated that this approach can be generalized to impose multi-level constrains, e.g., surface integrity and machining accuracy. The approach presented in this work was examined and validated on three NC milling machines. The productivity improvement, cost reduction, while respecting part quality requirements, is demonstrated.

Jan 1, 2006

By M. Dupuis, V. Bojarevics

It is well known that horizontal current density in the metal pad contributes greatly to the generation of MHD driven bath-metal interface wave. It is possible to compute very accurately the metal pad current density using a very detailed finite element model [1], but a MHD model must be compatible to this level of mesh refinement and to recalculate the current distribution at each time step, including the full busbar supply system. The accuracy of the instability prediction of the cell depends on the accuracy of the metal pad current density calculation. This study presents the comparison of the metal pad current density calculation of the detailed finite element model and the MHD-Valdis model for different metal pad heights and ledge thickness. It also presents the corresponding cell MHD stability predictions.

Jan 1, 2006

By S. A. Vazhnov, A. G. Kalimov, A. A. Potienko

In this paper we describe a mathematical model of the magnetic field and magnetohydrodynamic processes simulation in aluminum reduction cells developed in St. Petersburg State Polytechnic University, Russia. The model includes: (a) calculation of the currents in the busbar system and inside the aluminum cell construction elements including cathode and anode structures, aluminum and electrolyte layers; (b) magnetic field simulation using the integral equation method; ( c) investigation of the magnetohydrodynamic characteristics on the basis of a shallow-water approach. The developed model was used to investigate operational characteristics of the different industrial aluminum cells. Calculated magnetic field distributions and MHD stability parameters were compared with the available experimental information; the comparison demonstrated a reasonably good agreement.

Jan 1, 2006

By G. Song

This paper reports the anodizing voltage, gas evolution and sparking behaviors of an anodized coating formed on AZ91D in a silicate containing solution. According to their responses to an anodizing current, a four-stage anodizing mechanism is proposed. At the same time, the formed coating is characterized in terms of its microstructure, composition, thickness and corrosion performance. It was found that deposition of MgSiO3, Mg(OH)2 and MgO as well as dehydration of Mg(OH)2 are involved in the anodising process; the vigorous gas evolution accompanied by intensive sparking and the corresponding negative anodising efficiency in the later stage of the anodising process are closely associated with thermal decomposition of water due to the high temperature resulting from the intense sparking on the surface of the anodized alloy; the thickness, porosity, and composition of the anodised coating on a magnesium alloy depend on the final anodising cell voltage; and the corrosion resistance of a thick but porous coating containing more silicates appears to be more corrosion resistant than a thin but compact coating containing less silicates.

Jan 1, 2006

By H. Vendette, N. R. Dando, A. Moras

The thorough analysis of results obtained from different testing campaigns performed on an alumina dry-scrubber pilot installation treating aluminum potline offgases, suggests a clear relationship between the emissions of gaseous fluoride and the fluoride saturation level of the alumina. The integration of this relationship into the development of a new generation of alumina dry scrubber represents an intriguing challenge regarding the design of more efficient air pollution control equipment. An innovative scheme challenging conventional industry practices was proposed. From theoretical simulations, the reduction in fluoride emissions can potentially be reduced by as much as 50% in the summer season. To validate this innovative approach, Solios in partnership with Alcoa Primary Metals, modified one of the Aluminerie de Deschambault's systems by adding new temporary equipment on the operating units and subjecting it to several test campaigns. This article presents the first results obtained in testing this new and innovative approach on alumina dry scrubbers used to capture fluoride emissions coming from aluminum electrolysis potlines.

Jan 1, 2006

By G. K. Mann

Fragmentation analysis of blast or crushed rock material is a time-consuming and costly process. During the last two decades, the mining industry has been investigating image-based analysis systems as an alternative to generate fragmentation results. Many image-based techniques and commercial products have emerged during the last few years, and the mining industry has recently begun using these tools for real-time estimation of size distributions. Some existing systems require manual image editing to add or delete edges (or net) before executing the fragmentation analysis routine. This manual procedure may take hours of time for each image analyzed. Reliable and robust image segmentation should be able to handle a wide range of rock textures and sizes under a variety of lighting conditions. This paper describes a novel software application, which has the capability to autonomously capture images and analyze them to generate the particle size distribution. The system can also process a batch of images captured during a fixed duration of time and produce the overall particle size distribution. The new method has different layers of segmentation modules, which allows the system to operate under a wide range of rock textures and lighting conditions. A new grey-level slicing technique is developed which can perform under a range of illuminating conditions. The Canny-based edge detection technique is used to segment rocks appearing in dark regions.

Jan 1, 2006

In the present work, the effect of pH, non-ionic polyacrylamide flocculant and anionic polyphosphate on rheology and settling behaviour of colloidal TiO2 suspensions (15 ? 50 wt% solid) is investigated. Maximum particle aggregation, reflecting in the highest suspension settling rate and maximum shear yield stress was achieved at pH 7.2, the isoelectric point (iep), consistent with DLVO expectation. However, the maximum aggregation condition at the iep also resulted in the poorest suspension consolidation behaviour. Significantly enhanced consolidation was achieved for a more dispersed suspension at pH values away from the iep but at reduced settling rate. Thus, when pH alone is used to control conditions which facilitate strong interparticle attraction, a high settling behaviour which is not conducive to compact consolidation results. Improved suspension consolidation may be achieved at the iep via anionic polyphosphate addition which leads to attenuation of the strongly attractive van der Waals forces and emergence of "soft" repulsion due to weak inter-particle electro-steric forces. The weak repulsion act to lubricate particles involved in the hydrodynamic interactions which controls the compressibility of the sediment bed, allowing a compact consolidation of solids to be obtained. Alternatively, non-ionic polyacrylamide homo-polymer (Magnafloc 333) was fairly effective in flocculating titanium dioxide suspensions leading to high settling rate and acceptable pulp consolidation at the iep.

Jan 1, 2006