What Is a Straightening Machine?
Straightening machine is a piece of industrial equipment used to remove the wavy edges and centre buckles from a coil of metal, prior to it being used in manufacturing products. Straightening machines can eliminate a number of conditions in a coil that could cause problems for the production process, such as jamming or resulting in parts that are not up to specification. These conditions include kinks, side bending, up and down bending, torsion, gnawing, correction markings, and a variety of others. These conditions are often caused by a combination of factors, such as insufficient control means and procedures in steel rolling and cooling, unavoidable impact and extrusion during transportation, or simply the inherent stresses and distortions from the manufacturing process itself. The best way to avoid these issues is to run the coil through a straightener after it is removed from the furnace.
There are many different types of straighteners available, and the machine that is right for a particular application depends on the material, work width, and other variables. However, even the best straightener can only produce effective results if it is properly specified and set up. The combination of pinch roll pressures, drag brake strength, and work roller depth settings is critical to achieving the desired level of straightness.
The work roller depth setting (often referred to as ‘amount of penetration’) is based on the maximum material thickness and width that the straightener can comfortably handle. This value is typically determined by attempting to draw a straight line across the upper and lower ‘fixed’ bank of work rollers, when the machine is initially set up. As the material is processed through the straightener, the work rollers are progressively moved forward by the feed cylinders.
Depending on the specific requirements of a material type and width, the straightener may be equipped with ‘back-up’ rollers that are located in one or two places on each row of the work rolls. The purpose of these back-up rollers is to minimise the amount of back bending that can occur during the straightening process.
The two main categories of straighteners today are known as’straighteners’ and ‘precision levellers’. Straighteners are generally distinguished by their relatively large diameter, closely spaced work rollers that are backed up and do not flex. Precision levellers, on the other hand, have a much higher number of smaller diameter, tightly spaced and flexibly backed up work rollers. The use of this arrangement allows them to more effectively correct conditions such as camber, wavy edges and centre buckles in addition to the removal of trapped stresses within the material that cause wavy or rippled surface finishes. Consequently, levellers require drives with much higher power outputs than straighteners. This is primarily because they are doing more work on the material than straighteners.