When it comes to forming metal into the shapes that are used in the manufacture of a wide range of products, straightening is one of the most critical processes. The ability to properly straighten coil material, even after decoiling, allows for the elimination of most flatness defects and the minimization of residual stresses.
The straightening process is based on elastoplastic flexing of the sheet upon passing between powered rollers arranged in a roll stand in two staggered rows. The number of work rollers and the diameters and center distance spacing significantly affect straightening precision.
In most cases, the optimum straightener design is a result of careful attention to all potential variables for a given application. This includes defining the maximum thickness, width and yield strength of the material being processed; the specific work roller depth settings required; and the maximum line speed for the application.
For most applications, powered straighteners are preferred over manual pull-through machines. Manual machines are typically less expensive than their powered counterparts, but can be subject to a wide variety of problems that negatively impact straightener accuracy and efficiency. These include inertia caused by the power that is used to straighten the coil (as it starts and stops); roller bending as the material is passed through the machine; and marked or scratched materials from contact with the rolling surfaces.
During the straightening process, the pressure exerted on each work roller is measured as a function of the roller depth setting. It is also necessary to define the optimum level of overlapping between each pair of straightening rollers. This level of overlapping can be varied to allow the machine to accommodate material with different thicknesses and widths.
There are a number of other variables that need to be addressed when designing a straightening machine. The most significant is the amount of power required to operate the machine. This is commonly misunderstood, as the power requirement for a machine is often based on its ability to straighten mild steel with a yield strength of 35 tons/square centimeter. The fact is that there are many other factors which can dramatically affect the power requirement of a given straightening machine, such as the maximum width and thickness of the material being processed.
There are some all-in-one straightener/feeders that combine these functions, but the issues still apply. In particular, these machines tend to have a relatively large number of small work rollers that can be difficult to control. As a result, they can be subject to uneven bending as the material is fed through the machine and can be subject to a wide variety of other problems such as inaccurate and inefficient straightening and marked or scratched materials. In addition, these types of machines typically have a much lower capacity drive than their powered counterparts. This can lead to a loss of production due to slow or incomplete straightening. Therefore, the best option for most applications is a standard powered straightener that is designed with the correct configuration to suit the specific needs of the application.