| Most Marine diesel engines are under high temperature and high load,and the loss caused by friction and wear is incalculable.Adding additives into lubricating oil can greatly improve the antifriction and antiwear performance of lubricating oil and even achieve certain self-repair effect so as to effectively reduce the friction and wear of Marine diesel engine.In this paper,firstly,graphene and calcium borate were used as raw materials,oleic acid was used as modifier,and calcium borate/graphene lubrication additive(collectively referred to as 1~#lubrication additive)was prepared by plasma assisted ball milling.In order to further explore the process of preparing graphene-loaded borate composite powder by plasma-assisted ball milling,a second group of calcium borate/graphene lubrication additives(collectively referred to as 2~#lubrication additives)was prepared using expanded graphite instead of graphene as the raw material.The microstructure and surface characteristics of the two lubricating additives were analyzed by means of SEM,FT-IR,Raman,TEM,XRD,etc.The tribological properties of the two lubricating additives at different temperatures were tested by a friction and wear testing machine,and the mechanism of friction reduction and anti-wear was explored.The main research contents of this thesis include:(1)The formation mechanism of lubricating additives synthesized from two different raw materials was studied.The particle size of calcium borate in the two lubrication additives prepared by ball milling for 20 h is about 8nm-10 nm,and it is wrapped by 2-3 layers of graphene as a sphere.This shows that in the process of plasma assisted ball mill,the role of the mechanical grinding ball prompted the expanded graphite stripping for graphene,at the same time,the heating effect of the plasma calcium borate granular surface temperature rise rapidly and to produce"Heat Explosion Effect",boric acid calcium particles under high stress state heat explosion splash out,condensing deposition on the graphene and immediately was enshrouded is ball,The two gradually form a nanocomposite structure.(2)The dispersion of two lubricating additives in lubricating oil was tested.The results showed that the adding amount of 0.05 wt%20 h two ball mill powder composite oil,no obvious subsidence phenomenon let stand for 30 days,this is because the plasma auxiliary ball mill has realized the oleic acid of two kinds of surface modification of nanometer lubricating additive,oleic acid of nonpolar long chain alkyl adsorption on the surface of the two kinds of lubricant additives,and the space steric effect in base oil,The two lubricating additives have good dispersion in the base oil.(3)The tribological properties of the two lubricating additives at different temperatures were analysed.The results show that the friction coefficient of 1~#-PM20h composite oil is reduced by 28.6%and the wear quantity is reduced by 33.4%compared with the base oil at room temperature.Compared with the base oil,the friction coefficient of 2~#-PM20h composite oil is reduced by 26.4%and the wear amount is reduced by 32.5%.Compared with base oil,the friction coefficient of 1~#-PM20h composite oil decreases by 47.7%at high temperature,and the wear amount decreases by 46.1%.Compared with the base oil,the friction coefficient of 2~#-PM20h composite oil is reduced by 48.9%and the wear quantity is reduced by 48%.It can be seen that the tribological properties of the two lubrication additives prepared by ball milling with different raw materials for 20h are basically the same,which indicates that the plasma-assisted ball milling can effectively peel the expanded graphite and obtain higher quality graphene-based composite lubrication additive materials.(4)The tribological mechanism of the two lubricating additives was explored.The results show that the spherical nano-sized calcium borate particles can produce rolling friction on the surface of the friction pair during the friction process of the two lubricating additives,which can effectively reduce the friction on the surface of the friction pair.The nano-composite powder in the composite oil is filled and deposited into the pits and grooves of the wear surface,and the wear marks on the surface of the friction pair are repaired in situ.In addition,when the graphene sheet is broken during the friction process,nano calcium borate particles released will be deposited on the surface of the friction pair and further play the role of friction reduction and wear resistance.Especially under high temperature conditions,graphene and borate are easier to deposit and adsorb on the friction surface,and effectively repair the worn surface through synergistic effect,thus reducing the friction coefficient during the whole friction process. |
PDF Full Text Request