The common straightening methods of rod wire and titanium tube are tension straightening, sinusoidal straightening, pressure straightening, etc.
Tension straightening is a processing method that applies a longitudinal tensile force exceeding the yield limit of the material to the workpiece to cause the plastic extension to achieve shape defect correction, also known as drawing straightening. During straightening, tensile stress exceeding the yield limit of the material is applied to the titanium rod, titanium wire, and titanium tube with wave shape defects on the tension leveler. The tensile stress is superimposed with the original residual stress of the titanium bar. At the larger extension, a part of the tensile stress is offset, so that the actual deformation stress is reduced, and the plastic extension is small during straightening; while at the original extension, due to the tension of The superposition of stress, the actual deformation of stress increases, and the plastic extension increases during straightening. As a result, through the action of tension, all parts of the straightened workpiece extend evenly, and the wavy defect is therefore eliminated.
In production, the sine straightening method is widely used for rods, wires, and pipes with simple cross-sections. Titanium tubes and rods are made on an inclined roll straightening machine. The number of rolls of the straightening machine is more than 4 (usually 5~29 rolls), and its working principle is to continuously and repeatedly bend the workpiece through three-point bending of each roll, thereby gradually reducing the variation range of the residual curvature of the workpiece.
Sinusoidal straightening is usually used in conjunction with pressure straightening. First, the workpiece with large curvature is straightened by a pressure straightening machine, and then inclined roller straightening is performed. The straightening effect mainly depends on the pressure of the straightener and the inclination of the roll. The magnitude of the pressure depends on the yield strength and bending of the alloy material. If it is a high-strength titanium alloy when the curvature is large, the straightening pressure should be larger, and vice versa. The size of the roll inclination angle depends on the diameter of the workpiece, and the workpiece with a large diameter should be larger than the small straightening inclination angle. After straightening, the unqualified workpiece should also be returned for re-straightening. Titanium tubes that cannot be straightened should be sent to a tension straightener for straightening.
The basic principles of roller straightening are:
(1) Generally, the smaller the roll diameter and the greater the number of rolls, the higher the straightening accuracy; the smaller the roll distance value is, it is beneficial to the bite of the workpiece and the establishment of the straightening process.
(2) The main function of the first few rollers of roller straightening is to reduce the difference of the residual curvature of the workpiece along the length direction, and the main function of the latter rollers is to reduce the residual curvature to make it uniform.
(3) The pros and cons of the straightening quality mainly depend on the reasonable determination of the reverse curvature of the workpiece under each roller. On the first few rolls (the second and third rolls), a large reverse curvature is selected, and the reverse curvature on the subsequent rolls is determined according to the maximum residual curvature that can just completely straighten the adjacent rolls in front.
(4) The larger the hardening coefficient 7 is, the more difficult it is to straighten the material. At this time, it is necessary to choose a larger inverse curvature, more straightening rolls, and a smaller roll diameter.
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