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Lizhan Flat head self-drilling screws

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It is of great significance to improve the efficiency of bolts

the friction coefficient of chromate treatment with c2C is much larger than that of chromate treatment with c2D. (3) The use of chromate-treated c2D bolts can reduce the friction consumption of torque on the bolt support surface and thread friction consumption, and obtain greater axial pre-tightening force than c2C chromate-treated bolts, which is useful for saving energy. It is of great significance to improve the efficiency of bolts.

At a certain temperature, C and Cr in stainless steel will form compounds, especially near the grain boundaries, which will cause 'Cr-poor zones' in the grain boundaries, leading to grain boundary corrosion. ④Poor corrosion resistance to CI media (except A4 stainless steel). ⑤The price is higher (about 4 times that of Dacromet). 4.2 Changes in the heat treatment state Steel materials are mainly multi-phase structure (the second phase such as impurities, carbides, intermetallic compounds, etc.

usually exist in the steel as the cathode, and the Fe matrix as the anode). There is a potential difference between the phases in the multiphase structure, forming a corrosion microbattery. The second phase may be the anode-induced passivation phase or the cathode-dissolved phase, both of which will affect the corrosion resistance of the matrix.

For example, machine screw manufacturers must be very carefully welded and heat treated. After high temperature solution treatment, stainless steel is heated between 400C and 850C, and a large amount of CrsC is produced. And Cr, C; carbides will precipitate along the grain boundary, forming a Cr-poor zone near the grain boundary. Carbide is used as the cathode of the corrosion battery, and the Cr-poor area is used as the anode of the corrosion battery, which leads to grain boundary corrosion, and its corrosion resistance will be greatly reduced.

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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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