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As a result of forming, the structure of the material is modified, the sheet becomes rigid and frail, therefore it is not applicable for further usage. However, this can be terminated by heat treatment. The process can be done in several ways, here in a bell furnace, so that several coils are piled, a protective cover is placed onto them, below which protective gas not containing oxygen is lead. A heating bell is placed onto this, where firing happens.
When the rolled coils cool down, the next step is skin pass rolling (finishing). This time the thickness of the base material is not changed, but a rolling of approximately 1 percent is carried out on the strip (by coarse roll). This ensures that the sheet can be processed well later. During finishing, the fine sheet is prepared according to the customer’s demand. Some require wide or slit coils, others sheets. These are packaged and then taken to the transporting and storage plant, from where it goes to the customers. |
Cold rolled fine sheet is produced by DWA DUNAFERR-Voest Alpine Hideghengermû Kft. (DWA DUNAFERR-Voest Alpine Cold Strip Mill Ltd.). Fine sheet has different sizes depending on what the customer uses it for. The base material is hot rolled steel strip, which has scale (iron-oxide) on its surface. To be able to produce a material with appropriate surface that meets the requirements, the non-deformable hard scale has to be removed. In the first phase of fine sheet production iron-oxide modifications are removed from the surface of hot rolled strip by scale breaking and pickling, so that the uncoiled strip goes through hot bathes containing muriatic acid. Then the acidic surface is washed down, oiled and then the strip is rolled to the required thickness on the reversing mill.
The coils are heated and the temperature is kept high until the structure of the material is changed.