Cast Shop Technology: DC Casting and Macrosegregation
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: David Gildemeister, Arconic Technology Center
Wednesday 8:30 AM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Samuel Wagstaff, MIT
8:30 AM Introductory Comments
A Study on DC Casting Trough/ Launder Design and Material Selection: Bin Zhang1; 1Wagstaff Inc
For successful and consistent casting on ingot DC casting systems, metal heat loss has to be reduced. Metal heat loss is directly influenced by casting trough/launder design and material selection. To assist in developing solutions to reduce metal heat loss from furnace to casting table, Wagstaff« developed a CFD modeling program for heat loss analysis from furnace spout to casting station. The influence of the degasser, CFF units, and automated metal level controls are all included in the program to improve accuracy. Case studies at Wagstaff« R&D facility (DC #1 and DC #6) are reported to reveal the influence of refractory geometry and material selection on metal heat loss.
Critical Role of Thermal Management during Cast Start-up of DC Casting Process: AndrÚ Larouche1; Sabrina Guy1; JosÚe Colbert1; 1Rio Tinto Aluminium
In the past, numerical modeling and measurements in the field have provided insight into direct chill casting of sheet ingot and helped identify critical parameters to achieve successful cast start-ups. The control of these critical parameters is of key importance to maximise performance and throughput of the cast house as well as to meet stringent client requirements. Among these key parameters, management of liquid metal temperature, at start of cast, is critical in regard to casting performance. This paper presents several process variables influencing direct chill casting performance such as ingot recovery, false start and ingot quality.
Modelling and Analysis of a Horizontal Direct Chill Casting Process: Garar Gararsson1; Ůr÷stur Gumundsson2; Magnus Jonsson3; Halldor Palsson3; 1Alcoa Fjaraßl; 2Reykjavik University; 3University of Iceland
The objective of this study is to analyse bleed-outs in Horizontal Direct Chill (HDC) casting process by using a finite element model (FEM). HDC casting machines for aluminium are made for continuous casting with typical duration from 3 to 20 days according to the equipment manufacturer. Reduced duration due to technical difficulties affects capacity, productivity and cost. In order to improve understanding of the operation and the effect of alternative casting parameters an FEM model was developed for a 36 bar HDC machine installed in the Alcoa Fjardaal casthouse. Simulations were done for alternative inlet metal temperatures, cooling water temperatures, cooling water flow rate and casting speed with the focus on extracting information about potential bleed out conditions of a cast bar. Physical measurements were done on the HDC under real casting conditions and compared with the results of the numerical simulation showing good agreement with the measured results.
9:50 AM Cancelled
Casting of Sound, Large Diameter 7050 Billets: Kjerstin Ellingsen1; Mohammed M'Hamdi1; 1SINTEF
Large diameter billets of 7000 series alloys are used for transport applications. The alloys are difficult to cast as they are prone to both hot and cold-cracking due to the large solidifcation interval and low thermal conductivity. When thermally induced stresses overcome the deformation limit of the alloy, cracks are generated either during solidification (hot tears) or during cooling (cold cracks). The difficulty to cast sound billets increase with billet diameter due to large thermal gradients in the billet and associated stress build-up in the center. Fully coupled heat transfer, flow and mechanical simulations for casting of large diameter billets have been performed performed. The simulations provide semi-quantitative predictions of hot tearing and cold cracking susceptibility. The importance the bottom block to avoid start-up hot-cracks using casting simulations is demonstrated. Furthermore, the effect of introducing a wiper on the cold-cracking susceptibility is analysed.
10:15 AM Break
Circulation of Grains during Ingot Casting: Carolyn Joseph1; Samuel Wagstaff1; Antoine Allanore1; 1Massachusetts Institute of Technology
We have recently proposed a novel method to minimize the degree of centerline segregation in a Direct-Chill (DC) cast aluminum ingot through the use of a turbulent jet . We theorize the functionality of this method relies on the ability of the jet to re-suspend solute poor grains which have settled to the bottom of the molten pool. To date, the presence of these grains has only been acknowledged by theory and post-mortem observations. We have performed a series of experiments in order to sample the re-circulating grains and analyze their shape and chemical composition. By varying the jet power we have also investigated whether the circulating behavior has an influence on the degree of high temperature diffusion of solute elements into individual grains.  S.R. Wagstaff and A. Allanore: Metall Mater Trans B, 2016, vol. 47, pp 1-7.
Minimization of Macrosegregation through Jet Erosion of a Continuously Cast Ingot: Samuel Wagstaff1; Antoine Allanore1; 1Massachusetts Institute of Technology
Recent investigations have suggested important benefits in using a turbulent mixing jet impinging into the molten pool of a continuously cast Al4.5Cu ingot . It was for example demonstrated that such jet can significantly modify the macrosegregation patterns found in large castings. One possible reason put forth for this modification is the ability of the jet to suspend previously sedimented grains from the ingot centerline. In this study, we propose a model to optimize the re-suspension of grains through the use of an engineered jet. A series of full scale experiments are reported using a variety of jet powers. The results of this study indicate the potential to not only reduce the degree of centerline segregation, but also optimize the jet performance for a variety of casting practices and alloys. S.R. Wagstaff, and A. Allanore: Light Metals, TMS, 2016, pp. 715-720.
Full Size Measurement and Simple Prediction on Macro Segregation of Aluminum Alloys Elements in Industrial DC Casting Slab: Tatsuya Yamada1; Nobuhito Ishikawa1; Takashi Kubo1; Koichi Takahashi1; 1UACJ Corporation
In direct chill casting of aluminum alloys, macro segregation can occur at the center of the slab. It is very important to investigate the mechanism because it influences the mechanical and chemical properties of the wrought products. The authors have performed a two-dimensional measurement of the macro segregation by optical emission spectroscopy, and important characteristics of this phenomenon were observed. They are explained qualitatively and quantitatively by our proposed hypothesis, the partially swept solute model. The model assumes that the sump flow penetrating into the mushy zone will sweep out the enriched or diluted liquid solute until the critical solid fraction fs* is reached, when the dendrite arms begin to sufficiently entangle with each other, making it difficult for the sump flow to penetrate into the mushy zone. Then, the ordinary solidification process continues.
Ultrasonic Assisted Reduction of Hot-tearing during High-speed DC Casting of 6000 Series Aluminum Alloys: Sergey Komarov1; Yasuo Ishiwata2; Yoshihiro Takeda2; 1Tohoku University; 2Nippon Light Metal Co.ltd
This work presents results of preliminary investigations concerning the effect of ultrasonic vibrations on the solidification structure and hot-tearing susceptibility of 6000 series aluminum alloys in high-speed direct chill casting process. A pilot DC caster was used to produce billets of 82~97 mm in diameter. Ultrasonic vibrations were introduced directly into the caster mold through a high-amplitude ceramic sonotrode, the tip of which was positioned at different distances from the melt crystallization front. Then, the cast billets were investigated for the microstructure and hot tearing susceptibility. The results revealed that the ultrasonic treatment leads to a significant reduction of hot tearing susceptibility although the ultrasonic effect is dependent on the vibration amplitude and sonotrode tip position. It is suggested that ultrasonically improved fluidity of the melt in the mushy zone and uniformity of solidification structure are the major contributor to the reduction in hot tearing susceptibility.