Tension straightening is to apply longitudinal tension to the workpiece beyond the yield limit of the material, so that it produces plastic extension and realize the processing means of shape defect correction, also known as drawing straightening. During straightening, a tensile stress exceeding the yield limit of the material is applied to titanium rods, wires and tubes with wavy shape defects before and after the straightening in a tension straightening machine. The superposition of the tensile stress and the original residual stress of the titanium bar, in the extension of the larger, part of the tensile stress is offset, so that the actual deformation stress decreases, the plastic extension of the straightening of the small; and in the original extension of the small, due to the superposition of the tensile stress, the actual deformation stress increases, the plastic extension of the straightening of the increase, as a result of the action of the tension, the straightening of all parts of the workpiece extension of the uniformity of the wavy defects and therefore be eliminated.
Production of simple cross-section of the bar wire material, pipe widely used sine straightening method. Titanium tubes and rods are straightened on the inclined roller straightening machine. The number of rolls of the straightening machine is greater than 4 (usually 5~29 rolls), and its working principle is to continuously repeat the three-point bending of the workpiece through the rolls, so as to gradually reduce the range of changes in the residual curvature of the workpiece.
Sinusoidal straightening is usually used in conjunction with pressure straightening, whereby the workpiece with larger curvature is first straightened by the pressure straightening machine and then straightened by inclined rollers. The straightening effect depends mainly on the straightening machine pressure and the size of the roll inclination. The size of the pressure depends on the yield strength and bending degree of the alloy material. If the titanium alloy with high strength and large bending degree, the straightening pressure should be larger, and vice versa, smaller. The size of the roll inclination depends on the diameter of the workpiece,, the diameter of the workpiece should be larger than the small straightening inclination. Straightening should also be unqualified workpiece to return to re-straighten. Can not straighten the titanium tube should be sent to the tension straightening machine straightening.
The basic principles of roller straightening:
(1) Generally, the smaller the roll diameter, the more the number of rolls, the higher the straightening accuracy; roll distance value is small, it is conducive to the bite of the workpiece and the establishment of the straightening process.
(2) The main role of the first few rolls of roller straightening is to reduce the difference of residual curvature of the workpiece along the length direction, and the main role of the last few rolls is to reduce the residual curvature of the workpiece so that it tends to be uniform.
(3) The quality of straightening mainly depends on the reasonable determination of the workpiece under the rolls of the anti-curvature rate. In the first few rolls (second and third rolls) on the choice of a large anti-bending rate, the subsequent rolls on the anti-curvature rate is just completely straightened in front of the neighboring rolls at the maximum residual curvature to determine.
(4) hardening coefficient of 7 for the larger the material straightening is more difficult, this time to choose a larger anti-bending rate and more straightening rolls and smaller roll diameter.
