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Thin slab casting

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ISSN 1018-5593 £OÜJßSiV*'
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Commission of the European Communities
technical steel research
Thin slab casting r
Commission of the European Communities
Thin slab casting
D. P. Jackaman, H.S. Marr, T. Robertson
British Steel PLC
9 Albert Embankment
London SE1 7SN
United Kingdom
, Contract No 7215-CA/802
Final report
(1.4.1986-31.3.1990)
PARI EÖR0P. Biblioth.
Directorate-General N.C.
Science, Research and Development
CI FUR 13937 FN 1992 Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1992
ISBN 92-826-3496-5
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1992
Printed in Belgium THIN SLAB CASTING
British Steel Technical
ECSC Agreement No. 7215.CA/802
Final Summary Report
The report describes the work carried out in completing a project supported by the ECSC Steel
Research Pilot Plant and Demonstration Programme, under agreement number 7215.CA/802,
which ended in March 1990. The project utilised a pilot plant horizontal thin slab caster
constructed in the course of a previous ECSC supported project, and the aim was to find solutions
in various problem areas with a view to progressing to a detailed design for a prototype plant.
Attention was focused on the feed system which distributes the liquid metal onto the mould
surface, throughout the project duration. Major gains were made in achieving a smooth, low
turbulence presentation of the liquid metal as a result of the development of a low pressure system.
In consequence a number of product defects were eliminated, but others remained and so the
problems in this area could not be regarded as solved though substantial progress had been made.
The behaviour of the mould surface was also investigated in great detail, both as regards its
influence on product quality, and from the viewpoint of finding a practicable system as regards
maintenance and availability. From a number of points of view, the current mould train was
shown not to be viable, and following failure to find a suitable substrate material which could have
ameliorated the problems, attention was turned to belt systems. A series of computational
modelling exercises has shown how a belt system could be made to work, but the practical
problems associated with it are likely to be considerable and have not been investigated.
The product has been the subject of continuous surface assessment, and two series of small scale
rolling trials followed by metallographic and mechanical testing were undertaken. As already
indicated progress has been made in improving surface quality, but the situation where a need for
dressing could be eliminated has not been reached. The mechanical properties of the rolled
product were acceptable within a relatively narrow window of rolling reduction, and there is
confidence that this window could be widened by further processing.
Overall, a very detailed understanding of plant characteristics and their influence on product
properties has been obtained. In a number of areas problems have been overcome or ameliorated
with a significant improvement in plant operation or product properties being the result. However
sufficient areas of doubt have remained to make the step of moving to detailed design of a
prototype plant unrealistic. Accordingly the work has ended with the development of a new
conceptual design, and the identification of questions which remain to be answered before a move
to detailed design can be contemplated. CONTENTS
Page
1. INTRODUCTION 1
2. THE CASTING SURFACE 3
2.1 The Mould Assembly 3
2.2 Thed Material 4
2.3 The Use Of A Substrate 4
2.4 Special Moulds 5
6 2.5 Mould Distortion
2.6 Finite Element Analysis Of Mould Distortion 9
2.7 Measured Mould Strain 12
2.8 Review Of Casting Surface Work 12
TABLE 13
FIGURES 14
3. THE METAL FEED SYSTEM AND ITS INFLUENCE ON
LOWER SURFACE QUALITY 31
3.1 Existing Feed Arrangement
3.2 Electromagnetic Flow Control3
3.3 Hydraulic Feed Systems7
3.4 The Low Head Feedbox 4
3.5 Low Pressurex4
3.6 Lower Surface Quality8
3.7 Review Of Work On Metal Feed Systems 5
FIGURES 5
4. FURTHER INVESTIGATIONS DIRECTED TOWARDS THE
IMPROVEMENT OF THE AS-CAST PRODUCT 105
4.1 The Product Structure And Upper Surface
4.2 Unidirectional Solidification (UDS) 106
4.3 Enhanced Cooling Of The Slab Upper Surface 110
4.4 Review Of The Efforts Made Towards As-Cast Product Improvement 11
FIGURES 112
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5. FURTHER PROCESSING OF HORIZONTALLY CAST
THIN SLAB 133
5.1 Introduction
5.2 The Rolling Operation4
5.3 Assessment Of The As-Rolled Product
5.4 Review Of The Results Of The Rolling Trials 137
TABLES9
FIGURES 146
6. IMPLICATIONS OF THE PROGRAMME OF WORK 16
6.1 The Feed System 164
6.2 The Mould Design
6.3 Design Information Relevant To Upper Surface Quality 170
6.4 The Status Of Design Information 17
FIGURES1
7. CONCLUSIONS AND POSSIBLE FUTURE DEVELOPMENT 18
7.1 Conclusions 18
7.2 The Conceptual Design
7.3 Future Development5
FIGURE6
8. REFERENCE7
APPENDIX8
VI -LIST OF TABLES
2.1 Aim Specification for the Mould Castings
5.1(a) Mechanical Specification for E16 Steel
5.1(b) Aim and Cast Specifications for Rolling Trials
5.2 Rolling Schedule for Rolling Trial 1
5.3ge forg Trial 2
5.4 Metallographic Characteristics of Product Plates from Rolling Trial 1
5.5 Mechanicals of Product Plates from Rolling Trial 1
5.6cs of Product Plates from Rolling Trial 2
5.7l Characteristics of Product Plates from Rolling Trial 2
LIST OF FIGURES
2.1 Principal Dimensions of Mould Segments
2.2 View and Location of Thermocouple Plug
2.3 Early Unsuitable Method of Thermocouple Insertion
2.4 Positioning of Mild Steel Inserts into Mould Surface
2.5 Thermal Distortion of Mould During Casting (Quarter Segment)
2.6 Measured Inter-Mould Gap Formation
2.7(a) Effect of Mould Expansion on Mating Face
2.7(b) Gap Due to Distorted Mating Face
2.8 3D Finite Element Model for Temperature Prediction Showing Surfaces with Simulated
Heat Losses
2.9 Predicted and Measured Temperatures at Centre of Mould with 15 mm Thick Cast
2.10d andds ate ofd with 75 mm Thick Cast
2.11 500 mm x 650 mm Mould. Predicted Vertical Displacements of Mould Model with
15 mm Thick Cast
2.12 Predicted Vertical Displacement of Mould with 75 mm Thick Cast
2.13d Thermal Stresses at 120 Sec from Cast Start with 15 mm Thick Product
2.14dls at 120 Sec from Cast Start with 75 mm Thickt
2.15 Example of Fire Crazing on Mould Surface
2.16 Edge Dam Crack Found on One Mould
2.17 Strain Gauge Position and Results
3.1 Existing Feed System
3.2 Detached Feed Skull Using Weir Feed System Showing Metal Impact Zone
3.3g Feed System Modified to Use Impact Plate
3.4 Mechanism of Striker Plate Operation
3.5 Concept for E.M. Controlled Launder
3.6 Distribution of Electromagnetically Induced Body Forces at Lower End of 25 mm Duct
3.7 Plots of Magnetic Fluxes in 75 mm Duct at 50 Hz and 15 Hz
3.8 Scale Factors Used to Adjust Model to Required Flow Rate
3.9 Flow Regime in 25 mm Launder
3.10 Flow Regime in 75 mm Launder at 15 Hz
3.11 Edge Breakaway Effect, Unrestricted Duct, Flow 270 f/min
3.12 Side Elevation of Water Model Duct Showing Position of: 1. Ceramic Foam Restrictions;
2. Restriction of Inlet; 3. Reduction of Duct Section
3.13 Exploded View of Feed Chamber Below Tundish
3.14 Model 2 - Feed System (Feedbox 2)
3.15l 2 - Operating Characteristics for Square Edged Flow Controlling Orifices
VII -3.16 Model 3 - The Rectangular Shape of Feedbox 3
3.17 The Final Form of the Rectangular Shaped Feedbox 3
3.18 Equipment Used for Feedbox Flow Rate Calibration
3.19 Cumulative Weight of Steel Cast vs Time
3.20(a) Section Through the Graphite Seal on the Tray
3.20(b)nh Boron Nitride Seal on the Tray
3.21 Caster Modified and Fitted with Feedbox 3 Variant
3.22 Tundish/Feedbox Connecting Nozzle Assembly
3.23(a) Boron Nitride Sealing Strip
3.23(b) Sealing Strip Fixed onto the Feedbox
3.24 Roof Extension Variations
3.25 Schematic of Casting Box Used for Casts 70,71,72
3.26 Scale Drawing of the Water Model
3.27 Control and Instrumentation for the Water Model
3.28 Box to Mould Water Level Differences for the Water Model
3.29 Schematic of Casting Box to be Usedibr Cast 73
3.30 Late Feedbox Extension Design
3.31 Sectional View of Feedbox Exit Showing Sliding Seal Positions
3.32(a) Feedbox Seal Used in Cast 76
3.32(b)x Seal Used in Cast 77
3.33 Typical Feedbox and Manifold Pressures Obtained During Low Pressure Feedbox Casts
3.34 Cast 77 - Lower Surface Deposition Layers of Attached Feedbox Skull
3.35t 79 -re
3.36 Cast 44 - Lower Surface
3.37t 46 -re Detached Skull Showing Feed Impact Zone
3.38 Cast 71 - Lower Surface Showing Detail of Pinhole Defect
3.39 Underside of Slab 75g Distribution and Size of Air Penetration
3.40 Sections of Cast 75 Showing Severe Air Entrainment Effects
3.41 Possible Mechanism for Bubble Formation Resulting in Primary Bleed Defect
3.42 Cast 73 - Upper Surface Showing Detail of Entrapped Air Bubbles
3.41 Feedbox Used in Cast 78 (Half Section) (Ejector Not Shown)
3.44x Used in Cast 77 (Half)
3.-45 The Physical Model Showing Feedbox, Conveyor Water Supply and Ejector
3.46 Operation of the Physical Model Under Normal Simulated Casting Conditions
3.47 Cast 43 - Lower Surface Showing Details of Laps
3.48t 42 -regs of Laps in Proximity to a Detached Skull
3.49 Cast 80 - Lower Surface Showing Details of Gross Tear at a Mould Junction
3.50t 47 -reg Extended Skull and Acceptable Product
3.51 Cast 83 - Lower Surface Showing High Quality Surface Finish
4.1 Representation of Macrostructures Observed in Horizontally Cast Slabs by Designated
Type
4.2 Cast 48 - Upper Surface
4.3t 43 -re
4.4t 42 - Upper Surface
4.5 Cast 78 -re
4.6t 80 - Upper Surface
4.7 The Mechanism of Upper Surface Deformation
4.8 UDS Refractory Wool Insulation Operating Principle (Half Section)
4.9S Panel Operating Principle (Half Section)
4.10 Temperature of the UDS Panel Facing Product Surface
4.11(a) Energy Absorbed by Mould 4 (Non-UDS)
4.1 Kb)yd byd 12 (UDS)
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