Bloom Soft Reduction Roll Layout to Limit Porosity and Folding
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Solution Overview
Problem
In continuous steel casting, the surface solidifies before the inside, leading to uneven shrinkage and porosity, which results in deformation resistance and quality defects like macro-segregation and folding defects during the rolling process, and existing soft reduction methods are inadequate for high-alloy steel production.
Innovation Solution
A soft reduction method combining flat rolls and convex rolls with protuberances of varying lengths is used, where flat rolls are employed upstream and convex rolls downstream, to control reduction force and prevent deformation, reducing porosity and segregation by dispersing the reduction force and widening the indentation profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single convex roll is used for heavy reduction at the solidification end, then shrinkage cavity and porosity are reduced, but folding defects occur in the subsequent rolling process
Solution Approach 1:
The patent divides the single heavy reduction operation into multiple sequential reduction operations using multiple tension levelers (first, second, and third tension levelers) with different reduction rates. This segmentation distributes the total reduction across multiple stages, preventing the concentration of excessive reduction force at one location that causes folding defects, while still achieving the overall goal of reducing shrinkage cavity and porosity.
Solution Approach 2:
The patent implements dynamic adjustment of reduction rates at different positions and stages. The reduction rate is controlled to be higher at earlier stages and progressively reduced in later stages, creating a dynamic reduction process that adapts to the changing mechanical properties of the slab during solidification. This dynamic approach prevents folding defects while maintaining effectiveness in eliminating internal defects.
2Reliability
If excessive reduction force is applied by upstream tension leveler, then shrinkage cavity is reduced, but deformation resistance increases and causes quality defects
Solution Approach 1:
The patent applies different reduction rates to different positions along the casting line and different locations on the slab surface. The first tension leveler applies higher reduction force where shrinkage cavity is most problematic, while subsequent tension levelers apply progressively lower reduction forces. This localized quality approach ensures effective shrinkage cavity elimination without uniformly increasing deformation resistance across the entire slab.
3Ease of operation
If a convex roll with protuberance is used, then soft reduction effectiveness is improved, but reduction force becomes concentrated causing folding defects
Solution Approach 1:
The patent segments the convex roll protuberance function across multiple tension levelers, each with smaller protuberances. Instead of one large protuberance concentrating all reduction force, multiple smaller protuberances distribute the reduction action across different locations and times, maintaining soft reduction effectiveness while preventing folding defects through force distribution.
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 effectively reduces the reduction force of the convex roll tension leveler, minimizes withdrawal resistance, and prevents folding defects in the subsequent steel rolling process, improving the internal quality of the rolled product by controlling center porosity and shrinkage cavity.
Implementation Method 1
soft reduction is equivalent to compression casting, it has the effect of eliminating shrinkage cavity, porosity and macro-segregation at the same time
Implementation Method 2
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
Data Source
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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.