Virtually all shape defects in flat rolled strip are caused by non uniform dimensions and most can be corrected. When flat metal strip is really flat all the dimensions of the strip are equal. This means that thickness is uniform, the length of the strip is uniform from edge to edge and in line with the strip. If any of these dimensions are not uniform the strip tends to have bad shape.
Top side is longer than the bottom side in line with the length of the strip. Easy to correct.
Top or bottom side is longer than the other side. Length differential can be in line with the strip or from edge to edge. Relatively easy to correct.
Edges are longer than the center across the width and in line with the strip. More difficult to correct but can be corrected.
Center is longer than the edges across the width and in line with the strip. More difficult to correct but can be corrected.
From edge to edge the strip gradually gets longer, basically a large arc. Can be improved but very difficult to completely correct.
Thickness is greater in the center than the edges. Cannot be corrected with a leveler
Strip appears flat but apposing internal deformities are present and cancel each other out until released. Internal stress is a shape defect usually in the form of coil set, edge wave, or center buckle that is not apparent until the material is cut, punched, or processed later. Can be corrected but difficult to detect.
Shape Defect Measurement
In order to quantify a shape defect a unit of measurement is required. The most common industry standard for measuring shape is the "I Unit".
I UNIT = (H / 2L) * 100,000