Study on the loss efficiency requirements of standard body parts
The torque factor is an empirical parameter that depends not only on the friction coefficient of the friction surface, but also on the geometry of the threaded coupling pair. The actual threaded coupling pair inevitably has manufacturing tolerances, and sometimes there are defects such as iron filings, thread bumps, thread clasping interference, etc. At this time, even if the friction coefficient of a batch of bolts (nuts) is kept constant, the torque coefficient will be Inevitably, there is a certain dispersion, and it is not a certain constant corresponding to the friction coefficient. The torque coefficient must be measured by the test in combination with the specific coupling conditions, and cannot be simply calculated based on the friction coefficient.
In general, the K value may vary from 0.1 to 0.4 or even wider depending on the thread joining method, the surface friction condition, and the thread manufacturing quality. (should) the ratio of force to monotonic stretch allowable strength. Relationship with the torque coefficient K. It is intuitively shown that the larger the torque coefficient is, the smaller the allowable axial force is after the bolt strength is selected.
Take the K=0.2 generation type to obtain the equivalent stress of ordinary coarse thread 1.28. That is, the allowable strength of the bolt when tightening is about 78% of its monotonic tensile allowable strength (guaranteed stress or yield strength), of course. This proportional relationship will change as the thread's secondary friction conditions change.
When tightened with torque control, threaded fasteners are usually required to meet certain friction performance requirements. The utility model can obtain the allowable axial mass performance of the bolt when tightening, and the surface of the threaded fastener is required to be coated with a water-dispersible synthetic polymer slip agent (the slip agent is not allowed to contain silicon, such as M company's To-sal). After drying, a waxy sliding film is produced. Volkswagen measured the torque factor of the two bolts.
The above analysis shows that the international automotive industry generally requires threaded fasteners to meet certain friction performance requirements. A common measure is to apply a friction performance stabilizer to the surface of the bolt. In recent years, with the introduction and digestion of China's automotive products and related process technologies, people's understanding of threaded fastening has gradually deepened, and new requirements for thread fastener quality and tightening torque control are constantly put forward.
In order to finally have a place in the world automobile industry, China's automobile complete vehicles and engines, axles and other host companies must improve the quality and reliability of their products, which will inevitably promote and deepen the assembly torque control. Friction performance requirements for threaded fasteners.
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