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Lizhan Flat head self-drilling screws

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The disadvantage is that it needs to use an automatic tightening

Yield point method multi-function electric drill set yield point method, also known as the torque slope method, is a method of tightening the threaded part to the yield point by monitoring the slope of the torque change curve with the angle during the tightening process. During the tightening process, the tightening curve changes from the elastic zone to the plastic zone, the linear relationship between torque and angle changes, and the slope also changes. When the slope change reaches a certain range,

it is considered to have reached the yield point, as shown in Figure 5. Figure 5 Yield point method The tightening quality (pre-tightening force dispersion) of the yield point method is only related to the yield strength of the bolt, and is not affected by the friction coefficient and the starting point of the coer, which can improve the assembly accuracy; because the bolt is tightened to its yield point , Can maximize the ability of bolts.

The disadvantage is that it needs to use an automatic tightening machine with arithmetic function, the control system is complicated, the price is high, and the material, structure and heat treatment of the bolt are very demanding, and it is generally used in the assembly parts with higher requirements. 4

. The elongation methodThe elongation method uses a micrometer or ultrasonic method to measure the elongation length of the bolt during the tightening process or after the tightening is completed, and the relationship between the pre-tightening force and the change in the length of the bolt is used to control the axial direction. A method of pretension. Within the range of elastic deformation, the axial pre-tightening force is related to the cross-sectional area, elongation and strength of the bolt, namely: where: δb: elongation, F: axial pre-tightening force, Cb: bolt stiffness , le: bolt effective length,

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