As the industry increasingly focuses on decarbonisation activities, sustainable and effective action is needed to address climate change. As a solution for the automotive industry, there is a shift towards electric mobility or electric vehicles to reduce the impact on the environment. With lightweight design and greenhouse gas reduction, electric vehicles will have a positive impact on the vehicle's carbon footprint throughout their life cycle. However, changes in the automotive industry have placed a direct demand on the steel industry to produce thin specification, high permeability, oriented and
non-oriented electrical steel products. In practical applications, these high-grade electrical steel products will improve the energy efficiency of motors, transformers and high-performance generators. However, steel producers must increase production and maintain stable operating conditions to ensure high-quality end products to meet the growing demand for high-strength materials and excellent magnetic materials.
Due to the increase in demand for electrical steel in the automotive industry, electrical products have also begun to use more electrical steel. In addition, the industry has also put forward a new requirement: the development of ultra-thin electrical steel products with a thickness of 0.25mm and below. Although the current production of electrical steel only accounts for 1% of global steel production, the electrical steel market size is expected to grow by 7.5% in the next few years. With the increasing demand for high-quality electrical steel grades in the industry, electrical steel producers have encountered some difficulties. Although processing ultra-thin specifications of high-strength steel is not a problem, existing equipment is not able to rapidly increase product production.
However, while the industry is focusing on expanding production capacity, the risks and challenges of high-silicon electrical steel production are also increasing. Due to the high brittleness of high-silicon electrical steel, this means that edge cracks can start and spread, ultimately leading to strip breakage, equipment damage and production delays. In addition, with the quality target thickness has been reduced to 0.2mm, it has also put forward higher requirements for manufacturers to produce cold-rolled electrical steel products. Fortunately, the latest cold rolling technology has made it possible to produce high-quality electrical steel products that meet the challenges in terms of thickness, flatness and surface quality.
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In order to produce electrical steel efficiently, it is necessary to consider the current situation of work roll diameter of traditional cold rolling units. By increasing the pressure to produce a thinner product, the pressure may cause the elastic deformation of the work roll, but reducing the diameter of the work roll reduces the rolling force required to achieve a specific thickness. With the growing demand for thin gauge steels with higher silicon content, it is critical to obtain standard thickness with less rolling force. Another major challenge in rolling hard electrical steel is the reduction of strip edge thickness, a phenomenon known as "edge thinning". Edge thinning occurs due to roll bending and work roll flattening. It is crucial to control this, because smaller side thinning results in a motor with a higher sandwich coefficient and lower iron loss. Edge thinning control is typically applied to conical work rolls, which use hydraulic cylinders to move the rolls accordingly and apply uniform pressure, called "work roll crossed-roll UC-Mill" or UCMW.
As mentioned earlier, the brittleness of high-silicon electrical steels (i.e., Si≥2.5%) at normal cold rolling temperatures also increases the risk of strip breakage. Increased rolling loads, i.e. strip tension, contact pressure, and shear stress in roll occlusion, can increase edge cracks and delay production. One way to reduce brittleness is to reheat it before cold rolling.
In general, cold rolling steels with high silicon and aluminum content at room temperature (20-30 ° C) may result in reduced flexibility and formability during cold rolling. In order to reduce the brittleness of high-silicon electrical steel, induction heating devices can be installed to increase the temperature by 60-160 ° C, creating conditions for the first "warm rolling" of the first continuous rolling stand or reversible mill. By reducing the risk of strip breakage during hot rolling, producers can increase the mill speed or deformation rate, which means increased production and productivity of high-silicon electrical steel.
