Title

SPEED INCREASING AT CM2 THROUGH THE ELIMINATION OF CBS SCRATCH GOUGE

SPEED INCREASING AT CM2 THROUGH THE ELIMINATION OF CBS SCRATCH GOUGE

Authorship

Junior, Francisco José Henrique de Carvalho; Ferreira, Adriano Manuel Póvoa; Ramos., Paulo

Junior, Francisco José Henrique de Carvalho

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Ferreira, Adriano Manuel Póvoa

I am this author

Ramos., Paulo

I am this author

DOI

10.5151/2594-5297-22611

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Abstract

Anticipating market demands for fiscal year 2011/12 an extra 10 kt per year output in the Cold Rolling area was one of the main targets for "Novelis do Brasil". From the cold rolling perspective this was a quite challenging number considering the speed constraints at CM2 (Cold Mill #2), main process route for canning finishing passes, where average rolling speed was limited to 930 mpm due to a severe surface defect and secondary bearing issues. Historically CM2 had three main speed constraints(1): "Scratch gouge" (surface defect); work roll axial thrusting; work roll chocks overheating. The most severe one was the scratch gouge defect, because its incidence was a day-to-day routine and the average monthly rejection was 187 t. This defect is a more pronounced manifestation of wear and is formed during coiling when each new layer of aluminum lands on the already coiled metal. Due to the dynamics of coiling, some air is unavoidably wrapped into the coil. This air gap between the sheets is expected to persist for several laps into the coil and when this occurs the coiling stress is supported only by the highest asperities of the metal surface(2). Thus any transverse or longitudinal vibrations may cause wear at high stress points. This project outlined the mechanical initiation of the defect and confirmed its mechanism. Discussions of the proposed solutions are highlighted in this presentation.

Anticipating market demands for fiscal year 2011/12 an extra 10 kt per year output in the Cold Rolling area was one of the main targets for "Novelis do Brasil". From the cold rolling perspective this was a quite challenging number considering the speed constraints at CM2 (Cold Mill #2), main process route for canning finishing passes, where average rolling speed was limited to 930 mpm due to a severe surface defect and secondary bearing issues. Historically CM2 had three main speed constraints(1): "Scratch gouge" (surface defect); work roll axial thrusting; work roll chocks overheating. The most severe one was the scratch gouge defect, because its incidence was a day-to-day routine and the average monthly rejection was 187 t. This defect is a more pronounced manifestation of wear and is formed during coiling when each new layer of aluminum lands on the already coiled metal. Due to the dynamics of coiling, some air is unavoidably wrapped into the coil. This air gap between the sheets is expected to persist for several laps into the coil and when this occurs the coiling stress is supported only by the highest asperities of the metal surface(2). Thus any transverse or longitudinal vibrations may cause wear at high stress points. This project outlined the mechanical initiation of the defect and confirmed its mechanism. Discussions of the proposed solutions are highlighted in this presentation.

Keywords

Cold rolling; Surface defect; Aluminum flat rolling.

Cold rolling; Surface defect; Aluminum flat rolling.