Material not meeting AST'M A6 tolerances and material that may have become bent or distorted during shipment and handling or in the punching operation may require straightening before further fabrication is attempted. In addition members may become distorted when they are trimmed or, in the case of W, S and M shapes, when they are split into tees. The bend press, generally used for straightening beams, channels, angles and heavy bars, is known commonly as a bulldozer, gag press or cambering press. This machine has a horizontal plunger or ram (or a set of rams or plungers) that applies pressure at points along the bent member to bring it into alignment. Also, the press is used to form long-radius curves in various structural members.
Long plates, which are curved slightly or cambered out of alignment longitudinally, are frequently straightened by a roll straightener. The plates are passed between three rolls. The resulting bending increases the length of the concave side and brings the plates back to acceptable tolerances of straightness.
Misalignments in structural shapes are sometimes corrected by spot or pattern heating. When heat is applied to a small area, of steel, the larger unheated portion of the surrounding material prevents expansion, causing a thickening of the heated area. Upon cooling the subsequent shrinkage produces a shortening of the member, thus pulling it back into alignment. Commonly, this method is employed to remove buckles in girder webs between stiffeners and to straighten members. Heating must be controlled. A special crayon that changes color or melts at a predetermined temperature is often used as a temperature check.
A press brake is used to form angular bends in sheets and plates. Curved plates used in tanks and stacks are formed in a plate roll machine.
The foregoing operations can also be used to induce curvature, rather than remove it.