Continuous Casting. B.G. Thomas Mechanical & Industrial Engineering University of Illinois at Urbana-Champaign

Similar documents
Continuous Casting of Steel

Demand for high profits and low costs. Short Communication Development of a large ingot continuous caster. & Technology. Metallurgical Research

Introduction. 1 Method for making work rolls for cold rolling and characteristics required for rolls

Steel Making. Modern Long Product Manufacturing. Process Flow Chart

Metal Forming Process. Prof.A.Chandrashekhar

Manufacture of Iron & Steel. Prepared By: John Cawley

With a crude steel production capacity of more than

Speed limit! Producing high-grade steel is more. Direct control of electromagnetic braking for faster thick-slab casting.

Fluid Flow in the Mold

The formation of oscillation marks in continuous casting of steel

Research Background: Transient Surface Flow Problems

Outline CASTING PROCESS - 2. The Mold in Casting. Sand Casting Mold Terms. Assoc Prof Zainal Abidin Ahmad Universiti Teknologi Malaysia

Embedded Mold Temperature Sensor

Steel Forgings: Design, Production, Selection, Testing, and Application. Edward G. Nisbett. ASTM Stock No. MNL53

Chapter 11: Applications and Processing of Metal Alloys

Modeling of Fluid Flow, Mixing and Inclusion Motion in Bottom Gas- Stirred Molten Steel Vessel

MEASUREMENT OF MOLTEN STEEL SURFACE VELOCITY WITH SVC AND NAIL DIPPING DURING CONTINUOUS CASTING PROCESS

Special Bar Quality Steel:

Boosting Productivity and Quality in Slab Casting with ABB s Electromagnetic Systems

Bulk Deformation Processes

LAMINAR BARRIER INERTING FOR SPECIALTY STEELMAKING

Engineered Isostatic Ceramics. Specializing in products for the continuous casting of steel

Brian G. Thomas, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana- Champaign, Urbana, Ill.

CCC Annual Report Quantitative Measurement of Molten Steel Surface Velocity with Nail Boards and SVC Sensor in CC Molds

COMPUTATIONAL STUDY OF A TRAILBLAZER MULTI REACTOR TUNDISH (MRT) FOR IMPROVING YIELD AND QUALITY OF STEEL DURING CONTINUOUS CASTING

Utilization of CON1D at ArcelorMittal Dofasco s No. 2 Continuous Caster for Crater End Determination

The global market for flat products with highly

Principals of Billet Making

Electromagnetic Casting Technique for Slab Casting

The six-strand circular-arc continuous caster S0 at

Lecture 14 Modern trends in BOF steelmaking

Veranstaltungsgesellschaft mbh Stockumer Kirchstraße 61

The Production of Titanium and Titanium Alloys Using Electron Beam Cold Hearth Single Melt

Metal Casting. Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian Schmid 2008, Pearson Education ISBN No.

Module 4 Design for Assembly

Development of CaO-Al 2 O 3 Based Mold Flux System for High Aluminum TRIP Casting

CONTINUOUS CASTING - Special Products. The world s leading technology for long products

2

Liquid-Solid Phase Change Modeling Using Fluent. Anirudh and Joseph Lam 2002 Fluent Users Group Meeting

Induction Skull Melting Furnaces

Vacuum Arc Remelting (VAR)

EML 2322L -- MAE Design and Manufacturing Laboratory. Welding

High Performance Stainless Steel Long Products & Production Process of Daido Steel. ISSF-8 Seoul, Korea

Advances in Strip Surface Quality from Thin Slab Casters

Melting and casting technologies for the production of tool steels Dr. Harald Holzgruber, CEO DI Alexander Scheriau, CSO

EXPERIMENTAL INVESTIGATION ON COOLING RATE FOR CENTRIFUGAL CASTING Kirti Kanaujiya, Yugesh Mani Tiwari Department of Mechanical Engineering

Bulk Deformation Forming - Rolling

The World s Most Advanced Specialty Metals Manufacturing Facility Athens Operations

Chapter 15 Extrusion and Drawing of Metals

HOOK CRACK IN ELECTRIC RESISTANCE WELDED LINE PIPE STEEL

Furnace Monitoring and Billet Cutting System

Electroslag Remelting (ESR)

OF ALLOY 718 DURING VACUUM ARC REMELTING WITH HELIUM GAS COOLING BETWEEN INGOT AND CRUCIBLE. L. G. Hosamani, W. E. Wood* and J. H.

Metal Powder - the Raw Material of Future Production

EAF Steelmaking in North America An Overview

CFD MODELLING OF MACRO-SEGREGATION AND SHRINKAGE IN LARGE DIAMETER STEEL ROLL CASTINGS: A COMPARISON ON SEN AND DLP TECHNIQUES

Ingot oscillation in a steel mill. ThyssenKrupp Steel AG

Mould fluxes for steelmaking - composition design and characterisation of properties. Research Institute, Stockholm

Three-dimensional Simulation of Heat Transfer and Stresses in a Steel Slab Caster

Lecture 26 Degassing Practice

RAPID PATTERN BASED POWDER SINTERING TECHNIQUE AND RELATED SHRINKAGE CONTROL

15 years HYDRIS a revolutionary method to control hydrogen has become mature

Forging. Types of forging process. 1. Open Die Forgings or Hand forgings. Lecture Notes on Manufacturing Process

SIMULATION OF SHRINKAGE AND STRESS IN SOLIDIFYING STEEL SHELLS OF DIFFERENT GRADES

JIM / TMS Solidification Science and Processing Conference, Honolulu, HI, Dec , pp

Transient Fluid-Flow Phenomena in the Continuous Steel-Slab Casting Mold and Defect Formation

AEROSPACE MATERIAL SPECIFICATION

EDDY-CURRENT TECHNIQUE FOR SUB-SURFACE TEMPERATURE MEASUREMENT. BHP Melbourne Research Laboratories P.O. Box 264 Clayton, Victoria 3168 Australia

FEM Analysis of Bulging between Rolls in Continuous Casting

4 Shielded Metal Arc Welding*

Mechanism Of Hook And Oscillation Mark Formation In Ultra-Low Carbon Steel

TOTAL WATER MANAGEMENT IN THE STEEL INDUSTRY. By N. Ramachandran, Ion Exchange (India) Ltd

Improvement of Surface Quality of Austenitic Stainless Steel

Simulation of High Pressure Die Casting (HPDC) via STAR-Cast

Casting. Forming. Sheet metal processing. Powder- and Ceramics Processing. Plastics processing. Cutting. Joining.

GAS METAL ARC WELDING (GMAW)

Materials engineering. Iron and steel making

Casting Process Part 2

following investigation that examined the mold powder related POWDER RELATED STARTUP PROBLEMS

1.32 Mty greenfield turn-key plant for High Quality Steel Grades at Interpipe

MANUFACTURING PROCESSES

Solidification and Crystallisation 5. Formation of and control of granular structure

WELDING Topic and Contents Hours Marks

Current Refractory Technology and Practices in the Steel Industry

Temperature evolution in the spray zones: Plant measurements and CON1D predictions

Chapter 12. Flux Cored Arc Welding Equipment, Setup, and Operation Delmar, Cengage Learning

Modification In Weld Overlay for Productivity and Corrosion Resistance

9. Welding Defects 109

Module 3 Selection of Manufacturing Processes. IIT Bombay

Introduction. Online course on Analysis and Modelling of Welding. G. Phanikumar Dept. of MME, IIT Madras

1. METALS 2. FERRIC METALS 3. NON-FERRIC METALS 4. WORKING WITH METALS 5. METAL FORMING TECHNIQUES 6. ENVIRONMENTAL IMPACT OF METAL EXTRACTION

Copyright 1999 Society of Manufacturing Engineers FUNDAMENTAL MANUFACTURING PROCESSES Welding NARRATION (VO):

Joining. 10. Tool Design for Joining. Joining. Joining. Physical Joining. Physical Joining

Materials & Processes in Manufacturing

D.1 High Integrity Magnesium Automotive Castings (HI-MAC)

ATI 718 ATI 718. Technical Data Sheet. Nickel-Base Superalloy INTRODUCTION FORMS AND CONDITIONS AVAILABLE SPECIFICATIONS. (UNS Designation N07718)

Lecture 13 Submerged Arc Welding 13.1 Introduction 13.2 Components of SAW System

ME 4563 ME 4563 ME Introduction to Manufacturing Processes. College of Engineering Arkansas State University.

Transcription:

1 Continuous Casting B.G. Thomas Mechanical & Industrial Engineering University of Illinois at Urbana-Champaign bgthomas@uiuc.edu Continuous casting transforms molten metal into solid on a continuous basis and includes a variety of important commercial processes. These processes are the most efficient way to solidify large volumes of metal into simple shapes for subsequent processing. Most basic metals are mass-produced using a continuous casting process, including over 500 million tons of steel, 20 million tons of aluminum, and 1 million tons of copper, nickel, and other metals in the world each year. Continuous casting is distinguished from other solidification processes by its steady state nature, relative to an outside observer in a laboratory frame of reference. The molten metal solidifies against the mold walls while it is simultaneously withdrawn from the bottom of the mold at a rate which maintains the solid / liquid interface at a constant position with time. The process works best when all of its aspects operate in this steady-state manner. Relative to other casting processes, continuous casting generally has a higher capital cost, but lower operating cost. It is the most cost- and energy- efficient method to mass-produce semifinished metal products with consistent quality in a variety of sizes and shapes. Cross-sections can be rectangular, for subsequent rolling into plate or sheet, square or circular for long products, and even dog-bone shapes, for rolling into I or H beams. Many different types of continuous casting processes exist. Figure 1 pictures a few of the most important ones. Vertical machines are used to cast aluminum and a few other metals for special applications. Curved machines are used for the majority of steel casting and require bending and / or unbending of the solidifying strand. Horizontal casting features a shorter building and is used occasionally for both nonferrous alloys and steel. Finally, thin strip casting is being pioneered for steel and other metals in low-production markets in order to minimize the amount of rolling required. 1. Steel Continuous Casting Continuous casting is a relatively new process in historical terms. Although the continuous strip casting process was conceived by Bessemer in 1858, the continuous casting of steel did not gain widespread use until the 1960s. Earlier attempts suffered from technical difficulties such as breakouts, where the solidifying steel shell sticks to the mold, tears, and allows molten steel to pour out over the bottom of the machine. This problem was overcome by Junghans in 1934 by vertically oscillating the mold, utilizing the concept of negative strip where the mold travels downward faster than the steel shell during some portion of the oscillation cycle to dislodge any sticking. [1] Many other developments and innovations have transformed the continuous casting process into the sophisticated process currently used to produce over 90% of steel in the world today, including plain carbon, alloy and stainless steel grades. [1]

2 The continuous casting process for steel is shown in Figure 1 (second frame) and the close-up of the upper mold region in Figure 2. In this process, molten steel flows from a ladle, through a tundish into the mold. The tundish holds enough metal to provide a continuous flow to the mold, even during an exchange of ladles, which are supplied periodically from the steelmaking process. The tundish can also serve as a refining vessel to float out detrimental inclusions into the slag layer. If solid inclusion particles are allowed to remain in the product, then surface defects such as slivers may form during subsequent rolling operations, or they may cause local internal stress concentration, which lowers the fatigue life. To produce higher quality product, the liquid steel must be protected from exposure to air by a slag cover over the liquid surface in each vessel and by using ceramic nozzles between vessels. If not, then oxygen in the air will react to form detrimental oxide inclusions in the steel. Once in the mold, the molten steel freezes against the water-cooled walls of a bottomless copper mold to form a solid shell. The mold is oscillated vertically in order to discourage sticking of the shell to the mold walls. Drive rolls lower in the machine continuously withdraw the shell from the mold at a rate or casting speed that matches the flow of incoming metal, so the process ideally runs in steady state. The liquid flow rate is controlled by restricting the opening in the nozzle according to the signal fed back from a level sensor in the mold. The most critical part of the process is the initial solidification at the meniscus, found at the junction where the top of the shell meets the mold, and the liquid surface. This is where the surface of the final product is created, and defects such as surface cracks can form, if problems such as level fluctuations occur. To avoid this, oil or mold slag is added to the steel meniscus, which flows into the gap between the mold and shell. In addition to lubricating the contact, a mold slag layer protects the steel from air, provides thermal insulation, and absorbs inclusions. Below mold exit, the thin solidified shell (6-20 mm thick) acts as a container to support the remaining liquid, which makes up the interior of the strand. Water or air mist sprays cool the surface of the strand between the support rolls. The spray flow rates are adjusted to control the strand surface temperature with minimal reheating until the molten core is solid. After the center is completely solid (at the metallurgical length of the caster, which is 10-40m) the strand is cut with oxyacetylene torches into slabs or billets of any desired length. Different continuous casting processes exist to produce cross sections of different shapes and sizes. Heavy, four-piece plate molds with rigid backing plates are used to cast large, rectangular slabs, (50-250 mm thick and 0.5 2.2 m wide), which are rolled into plate or sheet. Similar molds are used for casting relatively square blooms, which range up to 400 x 600 mm in cross section. Single-piece tube molds are used to cast small, square billets (100-200 mm thick) which are rolled into long products, such as bars, angles, rails, nails, and axles. The new strip casting process is being developed using large rotating rolls as the mold walls to solidify 1-3mm thick steel sheet. When casting large cross sections, such as slabs, a series of rolls must support the soft steel shell between mold exit and the metallurgical length, in order to minimize bulging due to the internal liquid pressure. Extra rolls are needed to force the strand to unbend through the transition from the curved to the straight portion of the path shown in Fig. 1. If the roll support and alignment are not sufficient, internal cracks and segregation may result. These defects will

3 persist in the final product, even after many rolling and other operations, so it is important to control the casting process. The process is started by plugging the bottom of the mold with a dummy bar. After enough metal has solidified like a conventional casting onto its head, the dummy bar is then slowly withdrawn down through the continuous casting machine and steady state conditions evolve. The process then operates continuously for a period of one hour to several weeks, when the molten steel supply is stopped and the process must be restarted. The maximum casting speed of 1-8 m/min is governed by the allowable length of the liquid core, and to avoid quality problems, which are generally worse at higher speeds. After the steel leaves the caster, it is reheated to a uniform temperature and rolled into sheet, bars, rails, and other shapes. Modern steel plants position the rolling operations close to the caster to save on reheating energy. Further information on the continuous casting of steel can be found elsewhere. [1-6]. The application of computational models to understand and improve this process is discussed in Model_Chap. 2. Semi-Continuous Casting of Aluminum Over 90% of commercial aluminum alloys are cast by semi-continuous vertical casting machines, typically as 0.05-0.5m diameter round sections. This process is similar to steel continuous casting, with the significant difference that it must be stopped periodically when the bottom of the cast ingot reaches the floor of the casting pit. Other differences are the slower casting speed, (0.03 0.1 m/min.) which is required to avoid internal cracks, and the shorter metallurgical length (0.1-1.0 m). The two most popular types of aluminum continuous casting are the direct-chill (DC) and electromagnetic (EM) processes, which are distinguished by the method for supporting the liquid at the meniscus. The DC process uses water-cooled mold walls, similar to steel casting, while the EM process induces horizontal electromagnetic forces to suspend the metal from ever touching the mold walls. In both processes, the solid skin shrinks away from the mold walls shortly below the meniscus, whereupon the surface is cooled with spray water. Further [7, 8] information on aluminum continuous casting is available elsewhere. 3. Other Continuous Casting Processes Copper is often continuous cast using a vertical or horizontal process to produce round billets for subsequent extrusion, forging or wire drawing. [9] A wide variety of other continuous casting processes exist for special applications. Electroslag remelting (ESR) and vacuum arc remelting (VAR) are two forms of vertical continuous casting used for nonferrous metals, superalloys and specialty alloy sections up to 1.5m diameter. [10] Heat is supplied from an electrode above the melt and the top surface is protected with a thick slag layer (ESR) or a vacuum (VAR). These processes avoid oxide inclusions and remove impurities such as sulfur to produce highly refined metal with less segregation and fewer other defects than found in conventional continuous casting. Their products are more costly, but are needed for critical parts such as found in the aerospace industry.

Molten Aluminum Ladle Tundish Molten Steel Holding Furnace Submerged Entry Nozzle Molten Copper Mold Solid Billet Secondary Cooling Horizontal Mold Liquid Pool Spray Cooling Strand Meniscus Support roll Solidifying Shell Metallurgical Length Torch Cutoff Point Solid Steel Slab Molten Steel Twin Rolls Solid Thin Strip Vertical Curved Strip Casting Figure 1. Various continuous casting processes B.G. Thomas, 2000.

Protective Slag Layer Liquid Steel Tundish Copper Mold Refractory Brick Slide Gate (flow control) Solid Mold Powder Liquid Mold Flux Tundish Well (SEN Inlet) Submerged Entry Nozzle (SEN) Meniscus Steel Tundish Wall Molten Steel Jet Port Angle Nozzle Bore Liquid Steel Pool Submergence Depth Port Height Port Thickness Solidifying Steel Shell Continuous Withdrawal B.G. Thomas, 2000. Figure 2. Schematic of mold region of continuous casting process for steel slabs

6 4. References 1. M.M. Wolf, "History of Continuous Casting," in Steelmaking Conference Proceedings, 75, (Iron & Steel Society, Warrendale, PA, 1992), 83-137. 2. H.F. Schrewe, Continuous Casting of Steel, Fundamental Principles and Practice, (Stahl und Eisen, Dusseldorf, Germany, 1991), 194. 3. W.R. Irving, Continuous Casting of Steel, (London, UK: Inst. of Materials, 1 Carlton House Terrace, 1993), 1-206. 4. "Continuous Casting," in The Making, Shaping, and Treating of Steel, 2,A.Cramb,ed. (Pittsburgh, PA: Assoc. of Iron & Steel Engineers, 2001). 5. Mold Operation for Quality and Productivity, A. Cramb, ed., (Iron and Steel Society, 186 Thorn Hill Road, Warrendale, PA 15086-7512, 1991). 6. Continuous Casting, 1-9, (Iron and Steel Society, 186 Thorn Hill Road, Warrendale, PA 15086-7512, 1979-1997). 7. D.G. Altenpohl, Aluminum: Technology, Applications, and Environment, 6 ed., (Aluminum Association, Inc., Washington, D.C.). 8. "Cast Shop Technology," in Light Metals Conference Proceedings, (Minerals,Metals, and Materials Society, 186 Thorn Hill Road, Warrendale, PA 15086-7512, 1997), 647-1095. 9. R. Wilson, A practical approach to Continuous Casting of Copper Alloys and Precious Metals, (London, UK: Inst. of Materials, 1 Carlton House Terrace, 1999), #B0725, 1-300. 10. Proceedings of the 1997 International Symposium on Liquid Metal Processing and Casting, A. Mitchell and P. Auburtin, eds., (Santa Fe, NM:, 1997).