Lubricating Properties Of Castor Oil With Nano Hexagonal Boron Nitride And Its Application In Cutting

At present,most of lubricant oils are made from minernal oil,which is harmful to human health and environment.Castor oil,as a environment-friendly lubricating oil and cutting oil,has attracted more and more attention because of its good biodegradability,antioxidation and excellent lubricating properties.Beside,in the field of lubrication science,it has been found that some micro and nano particle additives can further reduce friction coefficient and improve wear resistance.Therefore,this paper studies the lubrication mechanism of the hBN(hexagonal boron nitride)nanofluid in different working conditions,and applies it to the machining of powder metallurgy parts.The modification of hBN nanoparticles was studied.The hBN nanoparticles were modified by A-151 silane coupling agent,and the modified hBN nanoparticles showed hydrophobicity and hydrophobicity.The mechanism of lipophilic property of modified hBN nanoparticles was analyzed by EDX.The modified hBN surface contained vinyl,thus its lipophilicity was enhanced.The stability of hBN nanoparticles before and after modification was studied.After modification,nanoparticles were more stable in castor oil.The viscosity characteristics of nanofluids at different concentrations were studied.The viscosity of 5 wt% and 8 wt% nanofluid was significantly higher than that of castor oil at low temperature,and the difference value gradually converged with the increase of temperature.The viscosity temperature equation and experimental value of ASTM were compared and analyzed.The viscosity temperature equation of ASTM could well predict the viscosity temperature relationship of nanofluids in this paper.Based on the method of least square method,the nanofluid viscosity-hBN concentration model was fitted at 30 ?.The fitting model could better predict the relationship between nanofluid's viscosity and hBN's concentration at each temperature point.The lubrication mechanisms of castor oil based nanofluids were studied under different working conditions.At the condition of high speed and low load,the lubrication was in mixed lubrication region.Because of the high viscosity,the friction coefficient of 5 wt% hBN nanofluids was higher,but the wear quantities was decreased by 55.05% because of a larger thickness of oil film.At the condition of low speed and high load,the lubrication is inboundary lubrication region.The friction coefficient of 1 wt% hBN nanofluids decreased by30.2% and the wear quantities decreased by 51.74%,which was result from the rolling effect of nanoparticles.At high speed and high load condition,the lubrication region changed from mixed lubrication to boundary lubrication.The effective lubrication time of 2 wt% was increased by 21.51%,which was due to the rolling action to avoid intense surface contact,thus reducing heat production and increasing the effective lubrication time.The surface quality and tool wear under the lubrication of castor oil nanofluids were studied.Compared to pure castor oil,the cutting force of 1 wt% nanofluid decreased significantly,and the surface roughness of workpiece decreased by 26.3%.The wear of tool was improved significantly.