Non-Grain-Oriented Electric Strip Recrystallisation Annealing
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Solution Overview
Problem
The production of non-grain-oriented electric strips in continuous annealing and coating lines is hindered by residual water and fluids on the strip surface, leading to condensate formation and uncontrolled heat induction, which impairs the quality and magnetic properties of the strips.
Innovation Solution
A method involving a two-stage heating process in a continuous annealing and coating line, where the strip is first heated to at least 300°C at a controlled rate to evaporate residues, followed by induction heating to suppress microstructure recovery and achieve a homogeneous grain size distribution, using a combination of continuous furnaces and inductors to manage temperature and heating rates effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If rapid heating is applied in the induction stage to achieve fine grain size, then magnetic properties are improved, but condensate formation occurs due to residual water and fluids on the strip surface
Solution Approach 1:
The patent applies preliminary action by introducing a pre-heating stage before the induction heating. The cold strip is first heated to 300-600°C in a continuous furnace to evaporate residual water and fluids from the rolling process. This preliminary heating eliminates the harmful condensate formation issue before the rapid induction heating occurs, allowing the strip to enter the induction stage clean and dry while still achieving the desired fine grain size and magnetic properties.
2Manufacturing precision
If heating rate is increased to suppress microstructure recovery, then magnetic flux density is improved, but temperature control becomes more difficult
Solution Approach 1:
The patent applies segmentation by dividing the heating process into two distinct stages: a first continuous furnace stage for preliminary heating to 300-600°C at a controlled rate of 10-50 K/s to evaporate residues, followed by an induction heating stage for rapid heating at 80-200 K/s to suppress microstructure recovery. This segmentation allows each stage to be optimized independently for its specific purpose, making overall temperature control more manageable while achieving high magnetic flux density.
3Object-affected harmful factors
If conventional heating is used to evaporate residues, then condensate formation is prevented, but heating time increases
Solution Approach 1:
The patent replaces conventional slow heating with induction heating for the second stage. After the preliminary continuous furnace heating to 300-600°C, the strip undergoes rapid induction heating at 80-200 K/s to reach the final temperature for suppressing microstructure recovery. This substitution of heating methods dramatically reduces the total heating time while still effectively evaporating residues and preventing condensate formation through the initial pre-heating stage.
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 prevents condensate formation, ensures a homogeneous fine-grained microstructure, and enhances magnetic properties by rapidly passing through the microstructure recovery temperature range, maintaining high magnetic flux density and crystallographic texture.
Implementation Method 1
the non-grain-oriented electric strip is initially heated before the induction furnace via a first continuous furnace to a temperature of at least 300° C. at a heating rate of at most 60 K/s. As a result, residues such as water, oils and other fluids that remain on the strip surface of the electric strip from the pre-process can be evaporated particularly gently and without leaving any residue.
Implementation Method 2
the then residue-free electric strip is heated to a temperature of at least 680° C. at a heating rate of at least 80 K/s, preferably at a heating rate of at least 100 K/s, more preferably at a heating rate of at least 150 K/s, even more preferably at a heating rate in the range from 150 to 250 K/s
Implementation Method 3
then in an optional second continuous furnace to a temperature of at least 820° C. at a heating rate of at most 20 K/s
Data Source
AI summary
A method for the recrystallisation annealing of a non-grain-oriented electric strip (2) in a continuous annealing and coating line (1) is presented. Therein, the electric strip (2) is heated in an induction furnace (5) to a temperature of at least 680° C. at a heating rate of at least 80 K/s and then, in an optional second continuous furnace (8), to a temperature of at least 820° C. at a heating rate of at most 20 K/s. The electric strip (2) is initially heated before the induction furnace (5) via a first continuous furnace (3) to a temperature of at least 300° C. at a heating rate of at most 60 K/s.