Tension straightening is to apply longitudinal tension to the workpiece beyond the yield limit of the material, so that it produces plastic extension to achieve shape defect correction, also known as drawing straightening. When straightening, the tensile stress exceeding the yield limit of the material is applied before and after the tension straightening machine to the titanium rods, wires and tubes which often have wavy shape defects. The tensile stress is superimposed on the original residual stress of the titanium bar, and at the residual stress (i.e. the original extension of the larger waves), part of the tensile stress is cancelled out, so that the actual deformation stress is reduced, and the plastic extension is small when straightening. In the residual tensile stress (i.e. the extension is small), due to the superposition of the tensile stress, the actual deformation stress increases, and the plastic extension is large when straightening. As a result, after tension straightening of the workpiece, all parts of the extension of the uniform, wavy defects are therefore eliminated titanium tube, titanium bar straightening is carried out in the inclined roll type straightening machine. Usually used in conjunction with pressure straightening, firstly the workpieces with large curvature are straightened by the pressure straightening machine, and then the inclined roll type straightening is carried out. The workpieces to be straightened are sent to the corresponding straightening machine and straightened accordingly in sequence after switching on the machine, also one after the other. The quality of straightening depends mainly on the pressure of the straightening machine and the size of the roll inclination angle. The size of the pressure depends on the type of alloy and the degree of bending. If the titanium alloy with high strength and large bending degree, the straightening pressure should be larger, and vice versa. The size of the stick tilt angle depends on the diameter of the workpiece, the diameter of the workpiece should be larger than the small straightening tilt angle. 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.
Production of simple cross-section of the workpiece is widely used in the number of rolls greater than 4 (usually 5 ~ 29 rolls) of the multi-roller straightening. Its working principle is through the rolls of the workpiece continuous repeated three-point bending, thus gradually reducing the range of changes in the residual curvature of the workpiece.
The basic principles of roller straightening are:
(1) The smaller the general roll diameter, the larger the number of rolls, the higher the straightening accuracy; roll distance 5 value is small is conducive to the bite of the workpiece and the establishment of the straightening process.
(2) The main role of the first few rolls 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 that 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 (the 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 neighbouring 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.
