Tension straightening, also known as drawing and straightening, is a machining method that applies longitudinal tension beyond the yield limit of materials to the workpiece to produce plastic extension and realize the correction of shape defects.
In the straightening process, the tensile stress in front and back of the titanium rod, titanium wire and titanium tube with wavy shape defects are applied beyond the yield limit of the material in the tension straightening machine. The tensile stress is superimposed with the original residual stress of the titanium bar, and part of the tensile stress is offset at the larger extension, so as to reduce the actual deformation stress and reduce the plastic extension when straightening; in the original small extension, the actual deformation stress increases due to the superposition of tensile stress, and the plastic extension increases during straightening. After the tension effect, the parts of the straightened workpiece are extended uniformly, and the wavy defects are thus eliminated.
Sinusoidal straightening method is widely used in the production of the simple section of bar and wire and tube. The straightening of titanium tube and titanium rod is carried out on the inclined roll straightening machine. The number of rollers of the straightener is greater than 4, and the working principle of the straightener is to reduce the variation range of the residual curvature of the workpiece step by step through the continuous and repeated three-point bending of the workpiece by each roll.
Sinusoidal straightening is usually used in conjunction with pressure straightening. Firstly, the workpiece with a large bending degree is straightened by a pressure straightening machine, and then the inclined roll straightening is carried out. The straightening effect mainly depends on the straightening machine pressure and roll inclination, and the pressure depends on the yield strength and bending degree of alloy material. If it is titanium alloy with high strength, the straightening pressure should be larger when the bending degree is larger, and smaller when the bending degree is larger. After straightening, the unqualified workpiece should be returned to be straightened again. The titanium pipe that cannot be straightened should be sent to the tension straightener for straightening.
The basic principles of roll straightening are as follows.
- Generally, the smaller the roll diameter and the more rolls, the higher the straightening accuracy; The smaller the roll spacing is, the better the workpiece bite and straightening process.
- The main function of roller straightening is to reduce the difference of residual curvature of the workpiece along the length direction, while the main function of roller straightening is to reduce the residual curvature which tends to be uniform.
- The quality of straightening mainly depends on the reasonable determination of the reverse bending rate of the workpiece under each roll. In the first several rollers (second and third rollers) choose a large reverse bending rate, the subsequent rollers on the reverse bending rate is exactly able to completely straighten the front adjacent rollers at the maximum residual curvature to determine.
- The larger the hardening coefficient is, the more difficult it is to straighten the material. At this time, a larger reverse bending rate and number of straightening rollers and a smaller diameter of rollers should be selected
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