Measure And Influence Factors Of Friction Coefficient Of 42CrMo High Strength Bolts

Bolt connection are using in all walks of life with our daily lives. In order to improve the service life of bolts, as well as the applicability of environmental requirements, bolts always need be conducted surface treatment . In the installation of the bolts fastening process, the importantest influence factor is surface friction. The friction is a necessary condition for the anti-self-locking screw loose. At same time, it consumes a large amount of friction torque (energy) thus affecting the bolt axial force. Thus, the research to the friction coefficient of the bolt was of great practical significance. It is necessary to the research on the relationship between friction coefficient and surface treatment of bolts .In this paper, we studied and analysised the 42CrMo bolt's serviced five different surface treatment. It is studied the influence on friction coefficient of surface treatment, strength, diameter, and the load of bolts. The experimental results show that the type, surface treatment, strength, diameter, and the load of bolts have more significant impact on friction coefficient. Under the same condition of bolt's type, diameter, load and surface treatment, the thread friction coefficient increases with a increase of the strength of bolt; When the bolt type, size, load and strength level are the same level, the friction coefficient of the thin surface treatment layer with compact structure obtained by the plating, blackening, phosphating increases with a increase of the rise bolt's diameter; while for the thicker and softer coatings obtained by hot dip zinc and Dacromet, the friction coefficient are stable when the bolt size changed; When the bolt type, size, strength grade and surface treatment layer are in the same condition, before reaching the yield torque, the friction coefficient with increasing load rise first and drop later more slowly and thus tend to stabilize; When the bolt type, strength, load, and surface treatment layer are in the same condition, the friction coefficient increases with a increase of the bolt size. As well as the traditional friction theory of"the friction has nothing to do with the contact area"has been amended and supplemented; When the bolt surface treatment layer, diameter, load and strength are in the same condition, the friction coefficient changes with the bolt type (head type) .In these respects, this paper has made a good conclusion to the choice of automobile manufacturing and engineering properties of the optimal combination of corrosion and friction. Bolts friction is a complex system, many problems are still need to more further studies.