Power Requirements of a Straightening Machine
Straightening machine are used to remove residual stress, up and down bending, side bending and torsion in any rolled, drawn or extruded product. They are also commonly used to eliminate gnawing, correction markings and other defects in the surface of the product. In order to achieve this, the work rollers must be positioned at an optimum depth setting which is determined by the combination of tube or bar diameter, material thickness, roller diameter and centre distance spacing. This set-up is then maintained consistently across the length of the product to ensure that effective results are obtained every time the machine is run.
Generally speaking, the most common method of calibration is through the use of a simple calibrated scale and pointer combination. Alternatively, other methods of positioning are used including mechanical indicators or dial height indicators. Ultimately, it is critical that the correct and consistent ‘zero’ position is established for each material type to be processed. It is from this point that the upper work rollers are able to back bend the material to an acceptable level of flatness.
Different metals have different yield strengths which imply that there is no one size fits all solution for the straightening of any particular product. Furthermore, the thickness of the material results in different power requirements as thinner materials can be processed with smaller diameter work rollers whereas thicker materials require larger diameter working rollers. The center distance spacing of the work rolls can also significantly impact the required power requirements.
As a result, it is not uncommon for an individual to demand a certain capacity of a straightener without considering the effect which this will have on the power requirement. The reason for this is that the maximum capacity of most straighteners is based on the assumption that the quality of the rolled material will remain constant throughout the length of the tube or bar. When this is not the case, as is often the case, the extra stress or load on the straightening machinery is concentrated at the head and tail of the material which can place significant strain on the end journals and bearings of the work rollers.
This extra strain will also require increased power to be applied by the drive motors to overcome this. A common mistake is to simply multiply the maximum capacity of a straightener by the maximum progression speed which is often misguided and short sighted as there are other factors which must be taken into consideration to correctly calculate the power requirement.
The use of back-up rollers is generally employed to alleviate this problem as they can effectively support the weight of the material and distribute it evenly across the width of the work rollers. Depending on the maximum width of the material to be processed and the specific machine, back-up rollers may be positioned at one, two or three places across the width of the work rollers. This will reduce the stress on the work rollers and will increase the ability of the straightener to acheive an acceptable level of flatness across the entire length of the product.