Straightening machine is a mechanical apparatus which is used to straighten and smooth the surface of metal strips. It is usually a part of a rolling mill. It can also be known as a straightening or corrective leveler. These machines use a series of rollers that are set at different heights to bend and stretch the coil of steel and re-flatten it. Straightening machines eliminate residual stress, up and down bending, gnawing, torsional stresses, correction markings and a host of other problems in rolled and cast products. They also prevent re-twisting, distortion and corrosion. They are designed by highly skilled engineers and constructed with top grade raw materials to meet the industry requirements and global standards.
Most manufacturers of straighteners offer machines that can process a variety of material widths and thicknesses. To do so, they typically incorporate a number of ‘back-up’ rollers in the lower ‘fixed’ bank of work rollers. Depending on the maximum width of the material, and the machine type, these back-up rollers may be positioned in one, two or three places across the width of the work rollers. The purpose of these is to reduce the forces and stresses that the work rollers experience as they bend or back bend the sheet of metal during the straightening process.
During the initial setup and calibration of a straightener for a particular material, it is necessary to determine the exact position at which the upper work roller is tangent to the lower fixed work roller. This point is referred to as the ‘zero’ or ‘home’ work roller depth setting. Once this is established, it is critical to ensure that the work rollers are consistently returned to this ‘zero’ position each time the material is run through the straightener. To do so, most straighteners are provided with some method of calibration for the work roller depth settings – usually a combination of a calibrated scale and a pointer or LED readout.
Another important factor in determining the power requirements for a straightening machine is the maximum yield strength of the material which will be processed. This is important because higher yield strength materials require more power to straighten to an acceptable level of flatness than milder, lower yield strength materials. The combination of work roller diameter, centre distance spacing and material yield strength can drastically change the power requirement for a straightening machine.
Finally, the type of feed system which is utilized in a straightening machine will also influence its power requirements. Most modern straighteners employ a feeder which is separate from the straightening machinery. There are also all-in-one straightener/feeder models available which can produce acceptable results for many applications, but it is vital to consider the inertia associated with these pull-through systems when estimating power requirements. Excessive inertia can lead to poor straightening accuracy and effectiveness, marked or damaged materials as they pass through the machine, and slipping of the work rollers during starts and stops. The result can be wasted power and in severe cases even machine damage.