Behavior And Mechanism Of Action Of Emulsion Used In Process Of Rolling

Emulsion has been widely used in machinery and metal processing with its excellent lubrication and cooling performances.Lubrication technology in rolling process can reduce rolling force and friction as well as improve surface quality,meeting with the development direction of cleaner production,energy-saving and cost-reducing in metallurgical industries.Oil-in-water(O/W)emulsion is usually used as the lubricant media in metal rolling process,and oil plays the role of lubrication by adsorb on metal surface while water acts as coolant.Although the lubrication and heat transfer mainly occur in the work zone referring to the interfacial lubricantion and heat transfer,a few questions for the operation maintenance and management of lubrication system and plate-out behavior are also related to the lubrication and cooling properities,involving the emulsion stability and the adsorption of oil droplets on metal surface as well as the film formation.Thus,the lubrication and cooling effects are influenced by the composition of emulsion as well as the technological parameter in rolling process.It is meaningful to study the behavior and mechanism of action of emulsion in rolling process,and the results would provide guidance for the designing and controlling of lubrication system,rolling technology and formulation optimization of emulsion.Taking O/W emulsion prepared with nonionic surfactants as subject,the paper concentates on studying the behavior and mechanism of action of emulsion at molecular scale combining with the methods of experiment,simulation and model calculation.The research route is based on the transmitting procedure of emulsion in rolling process,taking the properties of stability,plate-out,lubrication and interfacial heart transfer into account.It could provide scientific support for the optimization designs of lubricating system and emulsion formulation in rolling process.(1)With the stewing experiment and dissipative particle dynamics technique,the effects of emulsifier HLB,concentration,stirring intensity and stirring time on the stability of emulsion can be obtained.The relation between interfacial film characteristics and emulsion stability is also analyzed.The most stable emulsion appears when HLB is 13 and concentration is 1.6%.The interfacial film thickness increases with the values of HLB and interfacial tension is the minimum when HLB is 13.The stability of emulsion has non-linear relationship with the intensity of interfacial film,while the emulsion is the most stable at HLB=13.Oil droplet size increases with the HLB value,resulting from the molecular structure and volume ratio of hydrophilic group and lipophilic group of emulsifier.The emulsion stability is mainly decided by the interfacial film intensity and interfacial tension when the preparation technology is the same.(2)To flexible control the plate-out property of emulsion,a new method is proposed in this study by adding propanetriol,1,2-propanediol,ethylene glycol and n-propanol in the emulsions.Adsorption model of additive and multilayer adsorption of plate-out film are constructed by molecular dynamic(MD)simulation.Also,the mechanism of action of additive molecules on the plate-out film formation is investigated based on the MD simulations.The amount of plate-out oil film of O/W emulsions prepared with the different additives follows the order of propanetriol < 1,2-propanediol < ethylene glycol < n-propanol,while there is no obvious difference among the adsorption energies and particle size distributions of oil droplets.It can be observed from the MD simulation of plate-out film that the changes of plate-out film is affected by the influence of additive on the re-adsorption of oil droplets on the formed oil film.It can also be explained by the calculation results of mean square displacement(MSD)and cohesive energy.(3)An analysis of the effects of rolling conditions on mixed lubrication characteristics has been carried out based on the theoretical model,which is developed from average volume flow model and asperity flattening model.The real contact area decreases with the increasing surface roughness,and more lubricant is brought into the contact interface at the same time.Asperity would share the main pressure when the RMS surface roughness exceeds 2 um.The hydrodynamic pressure and total pressure are conspicuously influenced by the rolling reduction,while the total pressures are almost unchanged with different surface roughness,rolling speed and lubricant viscosity.Increasing lubricant viscosity is benefit to increase the film thickness and decrease the real contact area.(4)The behavior of lubricant molecules and their effects on the normal load,friction and friction coefficient are analyzed based on the confined shear model.The main findings can be summarized: the increasing pressure between confined walls is helpful to transfer momentum from walls to central area of lubricant film.Although the friction increases with the lubricant pressure,friction coefficient can be well reduced.Stable layered adsorption structure usually appears within 3 nm nearby the walls and translates into liquid phase when oil film exceeds 6 nm.There exists a critical film thickness ?(8 in the variation of friction coefficient,friction coefficient starts to decrease only when the actual thickness ? > ?(8.Normal load increases with the shearing velocity,resulting in the decrease of friction coefficient.The rising of temperature can increasing the normal load and reduce the degree of solidification,leading to the decreases of shear force and friction coefficient.In the lubrication of oil and water mixtures,oil tends to adsorb on the wall surfaces while water aggregates in the central zone.The friction coefficient reaches the minimum when the volume ratio of oil and water is 1:1.(5)A theoretical research combining heat transfer theory and mixed-film lubrication model has been developed for interfacial heat transfer in the work zone of rolling process.The changes of contact conditions(contact pressure,film thickness and the real contact area)along the roll-strip interface are taken into account to investigate the heat transfer at different positions within the work zone.There are double peaks on the distribution of interfacial heat transfer coefficient(IHTC)conducted by contact asperities.One appears at the inlet and the other appears at the neutral point.The closer to the outlet,the higher the value of IHTC in the lubricant.The IHTC decreases by orders of magnitude when the thermal resistance of oxide layers on the metal surface is taken into account.The distribution of IHTC can be divided into three stages,and the actual variation of the IHTC is closely related to the changes of contact conditions and rolling technology.