Rotary straightening of curved shape near both ends of seamless pipe

A new straightening method is proposed for the curved shape near both ends of seamless pipe by using a rotary forming process with three rollers. A helical rolling mill with three rollers was used in the experiment. The prebend aluminum seamless pipes were straightened under various working conditions. It was found that the pitch and the nominal reduction in radius can determine an attainable straightening ratio of the product, and there exists a minimum length of rollers to guarantee the selected straightening ratio of the product. The curved shape of pipe specimen can be straightened up to 90% under optimum working conditions. It was also found that there exists a maximum pitch to guarantee a certain straitening ratio of the product, and the axial feed rate can be selected arbitrarily in practice.