Multi-stack Bell-type Annealing Furnaces (MBAF) for Silicon Steel Strip

In the production of grain-oriented electrical strip, the material is annealed at about 1,200 °C following decarburizing and coating to obtain defined grain growth and a specified surface layer on the electrical strip.

In contrast to their widespread use for carbon steel and stainless steel, single-stack bell-type annealing furnaces have not become as established solution for the annealing of grain-oriented electrical steel sheet. Most of the new plants constructed for these applications over the past 20 years have therefore been multi-stack bell-type annealing furnaces (MBAF).

Normally three or four individual charge stations are installed in a row under the heating hood. Small coils (usually ≤ 12 t) are often charged in two layers. In other words, two coils may be stacked on each other on self-supporting plates.

Larger coils (usually ≥ 12 t) are charged in one layer on a charge plate manufactured from a high-temperature-resistant alloy or positioned directly on the base.Throughout the world, it has become normal practice to install electrically heated MBAF-plants. Multi-stack plants for two-layer operation have already been constructed with gas firing system with significant lower operating costs.