Tension straightening is to apply a longitudinal tensile force that exceeds the yield limit of the material to make it plastically extend to achieve shape defect correction, also known as drawing straightening. When straightening, on the tension straightening machine, the titanium rod, titanium wire, and titanium tube that often have wave shape defects are subjected to tensile stress exceeding the yield limit of the material. This tensile stress is superimposed on the original residual stress of the titanium rod. At the residual stress (ie, the wave with a large extension), a part of the tensile stress is offset, which reduces the actual deformation stress and reduces the plastic extension when straightening. At the residual tensile stress (ie, where the extension is small), due to the superposition of tensile stress, the actual deformation stress increases, and the plastic extension during straightening is large. Results After tension straightening, all parts of the workpiece were evenly extended, and the wave-shaped defects were eliminated. The straightening of the titanium tube and titanium rod was performed on the inclined roller straightener. It is usually used in conjunction with pressure straightening. First, the workpiece with a greater degree of curvature is straightened by a pressure straightening machine, and then the oblique roller straightening is performed. Send the workpieces that need to be straightened to the corresponding straightening machine, and then straighten them in order after turning on, which is also straightening one by one. The straightening quality mainly depends on the pressure of the straightening machine and the size of the roll inclination. The amount of pressure depends on the type of alloy and the degree of curvature. If it is a high-strength titanium alloy, the straightening pressure should be greater when the curvature is large, and vice versa. The size of the inclination angle of the stick depends on the diameter of the workpiece. A workpiece with a large diameter should be larger than a small straightening inclination angle. After straightening, the unqualified parts should be returned to straighten again. Titanium tubes that cannot be straightened should be sent to a tension straightener for straightening.
Multiple roll straightening with more than 4 rolls (usually 5 ~ 29 rolls) is widely used for simple-section workpieces in production. Its working principle is to continuously repeat the three-point bending of the workpiece through each roller, thereby gradually reducing the variation range of the workpiece’s residual curvature.
The basic principles of roller straightening are:
(1) Generally, the smaller the roller diameter and the larger the number of rollers, the higher the straightening accuracy; the smaller value of the roller distance 5 is beneficial to the bite of the workpiece and the establishment of the straightening process.
(2) The main function of the first few rollers for roll straightening is to reduce the difference in the residual curvature of the workpiece along the length, and the main function of the latter rollers is to reduce the residual curvature that tends to be uniform.
(3) The quality of straightening quality mainly depends on the reasonable determination of the reverse bending rate of the workpiece under each roller. A large amount of reverse curvature is selected on the first few rolls (second and third rolls), and the reverse curvature on the subsequent rolls is determined according to the maximum residual curvature that can exactly straighten the adjacent rolls.
(4) The greater the hardening factor 7 is, the more difficult it is to straighten the material. In this case, a larger reverse bending rate, a larger number of straightening rolls, and a smaller roll diameter are required.