What is the difference between a Straightener and a Leveler?
Misconception: Although there has been widespread use of Straighteners and Levelers for decades, there remains a great deal of confusion regarding the proper application and capabilities of each machine.
Clarification: Conventional Straighteners, sometimes referred to as Flatteners, incorporate a series of large diameter work rolls. Typically, between five and eleven rolls are used.
As the material passes through the rolls, it is alternately bent from the tangent of one roll to the tangent of the next. As a result of this bending process, coil set and crossbow is removed.
However, because this bending motion is restricted to one axis, i.e. up and down in the same horizontal plane, Straighteners cannot correct side to side strip length variations.
A similar machine used to remove coil set is the precision Straightener. The precision Straightener incorporates a series of relatively small diameter work rolls. Backups are used to maintain parallelism between the top and bottom rolls.
Because of their similarities, a precision Straightener can be mistaken for a roller type corrective Leveler. However, unlike the Leveler, the Straightener’s backups are fixed. As a result, a precision Straightener is also limited to the removal of coil set and crossbow.
Similar to the precision Straightener, a corrective Leveler incorporates a series of closely spaced relatively small work rolls. Along each roll are backups. However, the Leveler’s backups can be adjusted to intentionally deflect a portion of the corresponding roll.
Thus, if the material contains an edge wave, the rolls are deflected at their centers and the opposing edge. This stretches the center and opposing edge of the strip while leaving the wavy edge its original length. This stretching equalizes the strip dimensionally resulting in flat material.
Summary: While there are similarities between machines, there are evident differences between Straighteners and Levelers. Although a precision Straightener can work material more than a conventional Straightener due to the size and number of work rolls, the benefits of a precision Straightener over a conventional unit are marginal.
Both machines are limited to removing coil set and crossbow. In applications where the removal of coil set and crossbow is sufficient, either configuration will work satisfactory. Application that necessitates optimum flatness requires a corrective Leveler.
Conclusion: Although most misconceptions are based on assumptions and misinterpreted information, they are often perceived as being fact. However, by reviewing the surrounding information more closely, most can be explained.