There are two main goals behind the science of leveling metal strips. One is to make the surface flat, and ripple-free. The second is to eliminate any hidden internal stresses that can cause the strips to twist and bow during subsequent operations, such as stamping.
When choosing the right corrective leveler, there are some important factors to consider – the roll diameter, the roller pitch and the number of work rolls. A leveler is the best choice to a straightener as the leveler will remove more than cross bow or coil set.
There are three stages in the leveling process:
Stage 1 – Leveling is achieved by accurately bending the metal strip back and forth as it passes through a series of small-diameter offset rolls. The gap between the rolls are set independently on a leveler's entry and exit. The entry rolls should be deeply nested, as this forces the material through extreme angles to erase memory caused by trapped internal stresses. This is also known as ‘plunge', a technique for removing strip memory.
Stage 2 – A corrective leveler uses adjustable pressure points called flights, under the rolls to raise and lower them to an exact position.
By adjusting a work roll's shape, the material's path length can be altered through the leveler. A longer path length allows the material to be stretched more because more work is being performed on it as it passes through the rolls.
In rewind slitting (recoiling) the web is unwound and run through the machine, passing through knives or lasers, before being rewound (recoiled) on one or more shafts to form narrower rolls. The multiple narrower strips of material may be known as mults (short for multiple) or pancakes if their diameter is much more than their width. For rewind slitting (recoiling) the machine used is called a slitter rewinder (recoiler), a slitter or a slitting machine – these names are used interchangeably for the same machines. For particularly narrow and thin products, the pancakes become unstable, and then the rewind (recoiling process) may be onto a bobbin-wound reel: the rewind (recoiling) bobbins are much wider than the slit width and the web oscillates across the reel as it is rewound (recoiled). Apart from the stability benefit it is also then possible to put very long lengths, (frequently many tens of kilometres), onto one bobbin.
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