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Coil Preparation Lines
The coil preparation line is used for side-trimming of the strips, as necesary, and also to provide the coils with leader strips, which can be reused, for optimization of the yield.
In former times, when processing small-sized coils, the coil preparation lines were also used for coil build-up, i.e. for the formation of double or triple coils. For this purpose, rollable welds are necessary. However, rolling of welds can be achieved successfully only when processing austenitic material qualities, with considerable restrictions when processing ferritic materials but absolutely impossible when processing martensitic materials.
The material used for the coil leader strips is normally austenite. The leader strips generally have a thickness ranging between 2 mm and 5 mm, and a maximum length of 8 m, with the length depending on the distance between the roll gap and the reversing coilers of the cold rolling mill.
Notes / Special Features
Almost all coil preparation lines will also be used for the production of hot rolled metal sheets. The incoming coil, which is normally annealed and pickled, is loaded on the uncoiler, pulled from the uncoiler by the pinch roll unit and straightened in the following 5-roll flattener.
The strip then passes through the crop shear, where the strip length is normally measured by a counter, and cut to length. The cut-to-length operation will of course take place in the start-stop mode. The sheets are stacked from the shear exit roller convey by the same vacuum hoist which is also used for loading the coil leader strips onto the roller conveyer.
At the welder entry and exit ends, side guides are located at an adequate distance to ensure that the coil leader strips are aligned parallel to centerline of line at the two strip ends.
Side trimming of the strip will be required only when processing strips with edge cracks. In most cases, the strip and the as-rolled edges will be finish-rolled, and side trimming and, as necessary, slitting, will take place only on the finished product.
The back tension roll unit ensures that the strip tail, having left the uncoiler and flattener, is wound with adequate back tension applied to the recoiler. Back tension is produced by deformation of the strip without drive motor. The upper rolls of the back tension unit will more or less mesh into the lower rolls as a function of the respective strip thickness.
Most customers use coil leader strips and side trimmers when processing unannealed and unpickled hot rolled strip, at least in case of austenite. When processing hot rolled strip, which is to be bell annealed, the bell anneal operation will be the first production step. Regarding austenitic strip, many customers think it is an advantage for the cutting edges, which are somewhat strain-hardened by the side trimming operation, to be re-annealed for removal of the strain-hardening effect, after having passed through the hot rolled strip annealing and pickling line. This, however, according to the customers, has the disadvantage that a higher wear of the side trimmer knives and the edge scrap shear is to be expected when side trimming hot rolled strip.
The welder is normally followed by a side notcher, which will perform a crescent-shaped cut between the strip and the coil leader strips so as to avoid strip breakage during mill operation, considering the high tensions applied to the strip.
The uncoiler on this type of line is normally provided with a paper winder, because, in some cases, the coil preparation line may also be used for rewinding of cold rolled strip.
The scrap removal carriage located downstream the crop shear or below the welder normally carries two or three scrap boxes for classification of the scrap according to the respective type of material. |
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