Bloom Casting Roll Combination for Soft Reduction of Center Porosity
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Solution Overview
Problem
In continuous steel casting, the surface of a casting slab solidifies before the inside, leading to uneven shrinkage and the formation of shrinkage cavities and porosity, which results in macro-segregation and deformation resistance issues, particularly exacerbated by the production of high-alloy steel.
Innovation Solution
A soft reduction method combining flat and convex rolls, where the convex rolls have protuberances of varying lengths, is used to control the reduction force and prevent folding defects, by implementing a combination of flat and convex rolls on a continuous casting line, with model data-driven positioning and reduction rates based on solidification heat transfer and volume shrinkage calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a convex roll is used to achieve more effective soft reduction of unsolidified parts, then the reduction of shrinkage cavity and porosity is improved, but the deformation resistance increases due to complete solidification of both sides of the slab shell
Solution Approach 1:
The patent applies different reduction forces to different regions of the slab by using a convex roll with specifically designed curvature. The convex roll concentrates reduction force on the center region where liquid steel and shrinkage cavities are located, while applying minimal force on the already solidified surface regions. This local differentiation of reduction intensity resolves the contradiction by targeting the problematic center area without excessively loading the solidified shell.
Solution Approach 2:
The patent performs soft reduction at an optimal position where the solid fraction is between 0.2 and 0.8, before complete solidification occurs. This preliminary action allows the reduction force to effectively collapse shrinkage cavities and porosity in the center while the slab is still sufficiently plastic. By timing the reduction operation before the shell completely solidifies, the method reduces deformation resistance while achieving the desired elimination of internal defects.
2Manufacturing precision
If heavy reduction is applied at the solidification end to eliminate shrinkage cavity, then the internal quality is improved, but folding defects occur in subsequent steel rolling processes
Solution Approach 1:
The patent precisely controls the solid fraction parameter to be between 0.2 and 0.8 during soft reduction, avoiding the solidification end where solid fraction approaches 1.0. This parameter control ensures the steel is sufficiently plastic for effective cavity elimination while maintaining enough ductility to prevent folding defects during subsequent rolling. The method changes the critical parameter of solid fraction to an optimal range that balances both requirements.
3Ease of operation
If exchangeability of tension levelers is maintained with identical flat rolls, then the ease of operation is improved, but the reduction force distribution becomes excessive at upstream and insufficient at downstream positions
Solution Approach 1:
The patent introduces a convex roll with specific curvature characteristics to create localized variation in reduction force distribution. The convex shape naturally concentrates force on the center region while reducing force on the edges, providing the needed differentiation in reduction intensity without changing the basic flat roll structure. This allows downstream tension levelers to apply appropriate reduction force even with identical roll designs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces center porosity, shrinkage cavities, and segregation, while minimizing the reduction force and withdrawal resistance, thereby improving the internal quality of the rolled product and preventing folding defects in subsequent steel rolling processes.
Implementation Method 1
soft reduction is equivalent to compression casting, wherein the reduction is used to compensate for the current shrinkage of molten steel and restrict the flow of molten steel rich in low-melting impurities between dendritic crystals to the center
Implementation Method 2
the surface of a casting slab solidifies earlier than the inside of the casting slab due to external cooling. As a result, the surface shrinks more than the inside. As the solidification and crystallization end
Data Source
AI summary
Disclosed is a light reduction method for continuous casting of a bloom plain-barrelled roll-roll combination. The method comprises: firstly obtaining three-dimensional temperature field profile, a two-phase region, solid-phase region thickness, and solid-phase fraction of a billet, determining positions of start and end rolls of the reduction, and setting a reduction amount of each tensioner roll according to the volume shrinkage of the billet; in an interval fs=0.9-1.0 of the solid-phase fraction of the billet, performing a heavy reduction working mode; and in an interval fs=0.25-0.80 of the solid-phase fraction of the billet, performing a light reduction working mode.