In order to reasonably develop the bolt tightening process and deepen the understanding of the bolt tightening process, it is necessary to conduct experimental research on the bolt tightening curve form. Test conditions The test bolts have 8 batches according to the strength level, section shape and surface treatment, for example. Among them, the bolt specifications of 5.6 and 8.8 grades are MIOxl.5, the bolts of grade 10.9 are M121.6 bolts directly formed by cold deformation, and the bolts of grade 8 are heat treated, and the surfaces are respectively galvanized, dry phosphatized or phosphatized; The 9-stage bolt is phosphatized by surface.
The bolt tightening test clamping method is in accordance with the "Test Method for Frictional Properties of Threaded Fasteners" (EQY-262-97). During the test, torque is applied to the bolt head, the bolt is rotated, the washer and the nut are fixed, and each bolt is provided with a set of washers and nuts. The accuracy of the bolts and nuts used is 6 steps. The test nuts are all white parts, and the strength levels are greater than or equal to the strength level of the corresponding bolts.
The test gasket is 40Cr, and the heat treatment hardness is about 50HRc. The torque, axial force and rotation angle during bolt tightening are automatically collected and generated by the computer data acquisition system. Wait for the thick rod and other thin rods. 4 and other thick rod white parts galvanized, dry phosphating, oil phosphating galvanizing, dry phosphating, oil phosphating oil phosphating 40. Test bolt tightening test results.
According to 1 and the data, the relevant parameters of the bolt drawing and tightening process can be obtained. The A and A data of all the test bolts are similar. During the tightening process of the bolts, the tightening torque of the elastic deformation stage and the axial force of the bolts keep increasing until the bolts yield.
However, during the bolt tightening process, the maximum torque point and the maximum axial force point are not necessarily reached at the same time. Bolts with small torque factor K (SDY, SXY), their on-, dynamic, and torque-axial force curves are in the form of (a); bolts with large K values ​​(8D Mao SDG, SXX, SXG, IODY and SDX) The strike is greater than or approximately equal to the buckling, and the torque-axial force curve is shaped as and (c), respectively.
In addition, some bolts have no obvious deformation strengthening process during the tightening process, that is, when the bolt starts to plastically deform, the tightening torque or the axial force does not increase with the increase of the tightening angle, but directly with the tightening angle. Increase and decrease.
The surface oil phosphating grade bolt has a low yield ratio when tightened except for a bolt with a small K value and no obvious deformation strengthening, and the yield ratio at the time of stretching is high. The high-strength bolts above the grade have higher resistance to tightening torque than the tensile overload resistance; and the 5.6-class bolts that have not been heat-treated have the anti-tightening overload capability lower than the tensile overload resistance. 3 There is no obvious deformation to strengthen the over-tightening of the tightening.
There is no obvious deformation between the torque and the n-nine V); the axial force has no obvious deformation strengthening (slave G), the yield torque is the maximum torque, and the torque has no obvious deformation strengthening process; while the surface dry phosphating K value is The yielding axial force of the large thin bolt (SXG) is the maximum axial force, and the axial force has no obvious deformation strengthening process. The data shows that the 5.6-stage bolts, which have been hardened by cold work and not strengthened by heat treatment, have a high yield ratio when tightened, and a low yield ratio at the time of stretching;
Conclusion (1) During the tightening process of the bolt, the tightening torque in the elastic deformation phase keeps increasing with the axial force of the bolt; after the bolt yields, the bolt with the smaller torque coefficient K reaches the maximum torque point first and then reaches the maximum axial force point, K value. The larger bolt first reaches the maximum axial force point and then reaches the maximum torque point. (2) After the partial bolts are tightened to yield, there is no obvious deformation strengthening process. The bolts with smaller K value are prone to torque without obvious deformation strengthening; while the thin bolts with larger K value are prone to axial force without obvious deformation strengthening. .
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