Design And Characteristic Analysis Of Liquid Lubrication Bearing Of 850 Hot Strip Mills

At present,around 50% of the world's crude steel output is from China,which has become the world's largest steel producer country.However,the high value-added plate and strip products share a relatively low proportion,and some products still need to be imported.With the transformation and upgrading of the domestic manufacturing,the demand for high quality plate and strip products is increasing with each passing day,and the contradiction between supply and demand is formed with the low strip manufacturing capability.The domestic strip mill equipment is backward,with serious pollution,high cost,serious product homogeneity and market competition.After the year 2000,some large domestic steel enterprises have been built and advanced equipment has been installed,with the new equipment,the environmental impact is smaller,the cost is lower,the product performance is better,the market prospects are wider,but the amount of investment in the early stage is bigger.After fully communicating with steel enterprises and rolling mill designers,medium or narrow strip mills equip liquid lubrication bearing instead of roller bearing system is a viable option.Same with the wide strip mill,using liquid lubrication bearing in the medium or narrow strip mill,in line with the national energy saving industry policy.One of 750 stainless steel hot strip mill,which is designed and manufactured by Tianjin Zhongzhong Company,because of the large rolling force,the burning loss of the bearing is large,and even the accident of the roller broken is occurred.In 2013,Tianjin Zhongzhong Company and TZ had discussed to replace the liquid lubrication bearing for the backup roll of the finishing mill to solve the above problems.After calculation,the liquid lubrication bearing rolling system can reduce the burning loss of the bearing by about 55%.In 2014,Tianjin Zhongzhong Company had recommended using the liquid lubrication bearing in the rolling system as the optimum scheme for users in the design of the 850 hot strip mill in Ningbo,so as to improve the technical level of the rolling system and reduce the loss of the bearing.First,the loss of four row cylindrical rollers are large,which are widely used in medium or narrow strip mills;the influence factors of four row cylindrical roller bearing life are analyzed.Then,aiming at the shortage of roller bearing,the assumption that liquid lubrication bearing instead of roller bearing is derived,and its feasibility and superiority are expounded from the aspects of theory(lubrication theory and bearing capacity),mechanical structure design,lubrication system design and characteristic analysis.The operation mechanism of hydrodynamic liquid lubrication bearing is based on the dynamic pressure convergence oil wedge effect.The main theoretical basis of calculating dynamic liquid lubrication bearing is the Reynolds lubrication equation.Hydro-static dynamical liquid lubrication bearing improve the low speed performance of hydrodynamic liquid lubrication bearing through increasing the hydro-static oil chamber at working area.The main theoretical basis of calculating dynamic liquid lubrication bearing is the Reynolds lubrication equation,flow continuity equation and boundary equation.Bearing calculation of hydrodynamic liquid lubrication bearing includes two aspects;the first side is the relationship between speed and bearing capacity when the oil film thickness reaches the critical minimum oil film thickness;the second side is the relationship between speed and bearing capacity based on the heat balance equation of the bearing when the average working oil temperature is 75?.Finally,the bearing capacity is limited by drawing the bearing safety working curve.It is feasible using liquid lubrication bearing to bear the rolling force considering the technical and cost advantages in 850 Hot Strip Mills system.However,medium or narrow strip mills steel enterprises have limited understanding of liquid lubrication bearing,and the actual recognition degree of customers is the key factor for final decision.