These conditions are improved after tightening to the yield limit, which naturally improves the bolting resistance of the bolted joint. Although the torque method can reach the plastic zone, the torque method has the disadvantage that the plastic elongation of the bolt is uncontrollable. Tilt tightening method This is also a tightening method that can reach the plastic zone. The plastic domain cornering method requires the bolt to be tightened to the working condition just before the yield limit point, but it is an artificially determined point, if it can be measured according to the tightening process. The data derives the position of the yield point better. It is shown that the pre-tightening force varies with the rotation angle, and the inclination is also different. When the bolt tightening process is divided into three regions, the change of the rotation angle can be described as a torque gradient variation curve. The torque gradient is increasing in the starting zone, and the torque in the tightening zone is increasing, but the torque slope is no longer increasing or decreasing (the end of this zone is the bolt begins to yield). The torque in the yield zone rises slightly, and the torque slope drops significantly, eventually the bolt is damaged at the section shrinkage. When the bolt yields, the torque slope changes very rapidly, and the slope drops sharply from the maximum 70% 80% to 25% 30%, so the yield limit can be effectively measured by measuring the swing angle, that is, the slope curve. Bolt tightening of the tower crane standard section The tower crane is a large-scale mechanical equipment that is often used during construction. It is very important to connect the standard section of the tower crane during on-site construction. If the bolt connection fails, a major engineering accident will occur. According to the author's practice, the following points should be noted when bolting the standard section of the tower crane. Tower cranes are often disassembled and assembled, and the bolts used should have reusable functions. The amount of plastic elongation caused by each tightening should generally be screwed to the limit just after the yield. In order to obtain better reusability, the amount of deformation of the tightened part should not be too large when determining the corner. Therefore, not only the limit torque value and the corner error are small, but also the accuracy of the thread pair is improved.
OVERVIEW
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Bolt tightening method and analysis of tightening torque method This is a commonly used tightening method. It is a given bolt torque value to control the pre-tightening force of the connected parts, and the operation is simple and intuitive. The tightening torque when tightening the bolt is in the formula, Q0 is the pre-tightening force; K is the calculation coefficient; D is the nominal diameter of the bolt. The design bolts should be connected with sufficient preload to ensure the reliability of the bolt operation. The coefficient K usually varies between 0103, resulting in a large change in the preload force given a torque. The smoothness of the thread surface and the contact surface, the presence or absence of lubricating oil, the tightening speed, the tightening tool and the temperature change during repeated tightening all have an effect on the preload force, and the variation range is about 40%, so if the torque method is used to design the bolt The calculated load needs to be calculated according to 13 times the maximum working load. This must be achieved by increasing the bolt diameter, increasing the number of bolts or improving the mechanical properties of the bolt. This is disadvantageous for simplifying the mechanical structure, reducing costs, and reducing weight.