Research On Wear Mechanism And Wear-Resistant Coating Of Bump Foil Bearings

At the start and stop stages of bump foil bearing,the relative velocity between foil and journal is slow,and the gas film has not formed completely,which leads to dry friction on the two surfaces,makes the surface of foil worn seriously and reduces the service life and working reliability of the bearing.Through the numerical simulation of the friction process on the bearing during start-up and shut-down,the friction and wear law is discussed.It is found that under dry friction condition,the friction heat on the contact surface is intense and the temperature rise is too high,and the friction coefficient has the most significant effect on the heat.Therefore,the preparation of wear-resistant coatings with low friction coefficient on the foil surface has become the main measure to improve the performance of bearings.Finite element simulation of stress distribution within and between coatings shows that the failure of coatings is related to the shear stress and thermal stress inside coatings.MoS₂ and WS₂ coatings are prepared on stainless steel specimens by air spraying.The surface of the coatings is smooth without defects such as voids,gaps and cracks.The performance of the coatings is tested.Coating and matrix are mainly combined by mechanical and physical adsorption,and the bonding strength can be further improved by sandblasting phosphating treatment.The average friction coefficients of MoS₂ and WS₂ coatings are 0.25 and 0.2.Compared with stainless steel,the friction coefficients are significantly reduced.In order to reduce the friction coefficient of coatings,MoS₂ and WS₂ coatings are modified by PEEK.The friction coefficient of partially modified MoS₂and WS₂ coatings are further reduced.Modified coating reduces friction by forming transfer film.But the wear is aggravated by the adhesion and abrasive action between the surfaces.MoS₂,WS₂ and modified coatings are applied to the foil,and the friction and wear tests are carried out.It is found that modified coatings with 10%PEEK exhibited the best antifriction and wear resistance.In the performance test of bump foil bearing,modified coatings can significantly reduce the friction between foil and journal.But at the start-stop stage,due to the local high temperature between the foil and journal,the binder resin in the coating is decomposed,and the bonding strength of the coating is reduced,and the surface wear is aggravated.The modified coating has good antifriction property when applied to bearing foil,but the wear resistance decreases.