Decarburizing and Coating Line (DCL) for Silicon Steel Strip
Cold rolled GO Si steel strip is annealed in a continuous process line for primary recrystallization and decarburization. After the steel strip has passed through the DCL furnace, it is coated with magnesium oxide and then dried.
Overview
Tenova, with its over 40 years of experience, is the only company with the competence and knowledge, of the entire multi-stage thermal process chain, which is required for the production of grain-oriented electrical steel strip.
The final cold rolled GO silicon steel strip needs to be annealed in a continuous process line for primary recrystallization and decarburization to a level below 30 ppm. The decarburization of the silicon steel strip is necessary to make the steel ageing-resistant, so that the magnetic properties are stable even after long term operation as transformer core material. Besides the high requirement on accurate and reliable temperature profiles during annealing, soaking and cooling the atmosphere control in the DCL is essential.The atmosphere control, mixing and humidification system is the part with the highest degree of complexity in this annealing furnace.
The Cleaning Section is a key process component to remove the residual Rolling oil and Iron Fines. This helps in minimizing the Furnace roll contamination and thus the frequency of pitting defect on the strip surface
The Tenova cleaning section is equipped with the special high efficiency electrolytic cleaning unit (HTMCD) properly combined with spray alkaline cleaning, high efficiency-quick maintenance brushing units ( brush to brush type) to enhance the strip cleanliness and allowing to reduce of 20-25% the electrical consumption.
The annealed strip coming from the Furnace is coated with a MgO slurry layer that is dried in a dedicated oven (generally a gas infrared type is used) and cooled before recoiling on Tension reel. This heat resistant MgO layer is will avoid coil wrap sticking in the following step of production cycle in batch annealing and also it will contribute to the formation of the insulation glass film on strip surface.
Innovation
Key technology for the processing of silicon steel:
- Highest process accuracy and repeatability guarantees stable magnetic properties
- Lower operational costs (electricity); lower investment and maintenance costs
- Top level coating uniformity with high cooling uniformity preventing material tensioning
- High-turbulence high-efficiency Medium Current Density (HTMCD) electrolytic cleaning tank
- High efficiency quick maintenance brushing unit (brush-to-brush type)
- BCO (Brush Consumption Optimization)
- Camber improving special steering rolls at Furnace exit
- Strip cooling sections before MgO slurry coating with multi-channels cooling rolls design for even strip temperature.
- Coater design with upper applicator rolls allowing opening at joint passage avoiding slurry recirculation stop.
- Coater design lower applicator roll provided with hydrodynamic tray to spread uniformly the slurry on the roll face allowing to keep empty the coater drainage pan
- Lower roll with independent servo-actuator on each support for ‘in force’ and ‘in position’ control for top level coating uniformity across width and trouble-free weld joint passage management
- Slurry mixing and preparation system with temperature control and improved mixing and recirculation features, to assure optimal hydration and to avoid slurry aging phenomena, provided with automatic rinsing cycle, self-draining geometry to avoid particles agglomeration
- Special design of drying and exit section with minimum strip to roll contact for better MgO coating quality
- Flying shear in exit section to minimize coating speed transients for improved MgO coating quality constancy
Automation
Fully automated control system
Various software modules for process optimization
Improved strip camber and tracking along the line
Environment
Modern heating technology
High Efficiency HTMCD Electrolytic cleaning
Heat and energy recovery
Digital
Fully automated control system
Various software modules for process optimization
Improved strip camber and tracking along the line
Related Solutions
Europe
Wolfgang Eggert
General Manager Sales Heat Treatment of Steel Strip, Tenova LOI Thermprocess
Modernization, Service & Spare Parts
Marc Reynaert
Head of Revamp & Modernization, Tenova LOI Thermprocess
