Straightening machine is a process which reduces the residual stresses of rolled, drawn or extruded material. It involves the material being alternately stretched and compressed between sets of straightener rollers which are adjustable to the required spacing and size of work area. This produces a flat and parallel surface on both the top and bottom of the sheet steel, and eliminates problems such as gnawing, correction marking and up and down bending which can occur during metal processing and transportation.
A good quality straightening machine will be capable of processing a wide range of materials, widths and thicknesses. Due to the potential variation in these variables, no single straightener will be suitable for all applications.
For this reason, the specification of a straightener requires a detailed understanding of all the factors which can affect the process. This is done to allow a machine to be specified which can deliver effective results for the application, whilst maintaining high production efficiencies and high quality finished product.
There are two main types of straightening machines; powered and non-powered. Power-driven machines are normally equipped with higher capacity drives and will produce a greater quantity of final straightened material than non-powered systems. Those which are powered may be either fully or partially driven by the feed strip, whereas those which are non-powered can only be operated by manually feeding the material.
The optimum depth of work roller penetration needed to achieve an acceptable level of final straightness will depend on the combination of the material thickness and type, the work roller diameters and centre distance spacing, and the support journal diameters. Once the optimum depth setting has been established for a particular material, it is critical that the work rollers are consistently returned to this position each time the straightener is started. For this reason most straighteners are supplied with a method of calibration to establish the ‘zero’ or ‘home’ position of the upper work rollers.
As the material moves through the straightener, the ‘zero’ or ‘home’ setting is moved along the entire length of the machine by means of an adjustment system. This system is usually a combination of a calibrated scale and pointer or a dial height indicator.
To allow a wider range of materials to be processed, some straighteners are provided with one or more rows of back-up rollers which can be placed across the width of the working rollers. This reduces the forces and stresses on the rollers when running narrower material, which would otherwise result in deflection of the work rollers and excessive wear to their bearing surfaces. The proper placement of these back-up rollers minimizes the effects of this variation. This is one of the key reasons why it is important to consider all the possible variables at the point of equipment specification.
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