Influence of Lubricating States and Pre-Clamping Force on the Anti-Loosening and Corrosion Resistance of Dacromet Plated Fasteners

The loosening of fasteners has an important impact on the safety of subway and other rail transit.Aiming at the anti-loosening performance of GB/T 5782，M16×80，10.9 class Dacromet plated hexagon fastening bolts，the effects of lubrication state of fasteners on anti-loosening performance， wear behavior and corrosion resistance were investigated through lateral vibration anti-loosening test and neutral salt spray test.Results showed that when the preload force was set to 76 kN， the residual preload force of non-lubricated fasteners was more than 95%of the initial preload force for 1 500 vibration times，and the anti-loosening performance was excellent.Meanwhile，the anti-loosening performance of dacromet plated fasteners would be greatly attenuated by applying lubricants.When the preload force was set to 76，93，110 kN， the remaining preload force after 1500 vibration of the lubricated fasteners was less than 8%of the initial preload force.When the preloading force was set to 110 kN， the average residual preloading force after 200 times of vibration of the lubricated fasteners was 76.19%of the initial preloading force， which was higher that at 76 kN and 93 kN， but the residual preloading force of the late surface was not much different.In the process of vibration， the solid friction of the thread surface was transformed into solid liquid friction， and the relative friction was greatly reduced.When there was no lubrication， the fasteners were not loose， and the coating damage was light.Furthermore， the coating could protect the substrate from salt spray corrosion by sacrificial anode method of zinc ion， while the lubricant would loosen the bolts and produce a large relative movement between nuts and threads.The friction could destroy the surface coating and expose the carbon steel substrate of the fastener， causing corrosion under the condition of salt spray.