| Rubber O-ring seal as a main seal style has been using in hydraulic system.The continuous operation of the hydraulic system led to the increase of the temperature of the hydraulic system.The rubber O-ring,long-term in a high temperature environment,can easily bring about the rubber themooxidative aging so that the wear resistance of the rubber will be decreased and the operation efficiency and service life of the hydraulic system are affected.At present,many scholars have been actively conducting research on aging properties of rubber for many years,but the related research is rarely reported about the chemical and mechanical property changes of rubber in high temperature before and after aging,the friction behaviors and wear mechanism of aged rubber.So this research will provides an important theoretical and technical support for the O-rubber ring material selection in aircraft hydraulic system.In addition,it will be enrich and develop the theory of rubber tribology and provide experimental data for engineering techniques.In the present study,accelerated thermal-oxidative aging oven was used to treat NBR rubber and then surface morphology,mechanical properties,molecular structure of aged specimens were measured.Test results showed that(1)the additives migrated from inner to surface of NBR samples in the process of accelerated aging.(2)with the increase of aging temperature and time,hardness for rubber increased,tensile strength increased slightly in the early stage of aging and then decline,100% tensile modulus increased,elastic modulus increased,elongation at break decreased.When temperature was no less than 105 degrees,mechanical properties of rubber which were mentioned earlier increased significantly.The tensile fracture morphology of rubber before and after aging includes two kinds: brittle fracture and delamination fracture.(3)the temperature is above 75 degree,methylene C-H fracture of nitrile rubber began breaking,which implied that rubber began free chain reaction and then the reaction of oxidation process has been started.In 105 degrees,rubber aged 7days began to produce oxidation products containing-C=O,such as ketones and esters.Rubber aged 21 days reacted the oxidation products increasing significantly.The law of energy dissipation in 105 degrees can be seen that migration rates of the molecular structureof rubber at this temperature increased.so that rubber oxidation products increased and make crosslink density too large,which resulted in the formation of cross point concentrated stress and then tensile strength of rubber decreased and hardness increased,elastic deformation resistance decreased,the elongation at break decreased.In present study,UMT-3 tribo-tester was used to study the tribological properties.Wear surface morphology was combined to analysis wear mechanism of rubber under different aging condition.Test results showed that(1)the stability of rubber friction process was different under different temperature due to change in rubber properties.The aging temperature is lower than 105 degree,the friction coefficient of rubber have big fluctuation range and the stability is bad.The temperature is 105 degree and above,the result is opposite.The higher the temperature,the shorter the time required for friction coefficient to be stable.(2)the temperatures and aging time had influence on the friction coefficient and wear rate of rubber.The higher the temperature,the smaller the friction coefficient and When temperature was no less than 105 degrees,the friction coefficient was changed obliviously with increasing the aging time.Friction coefficient and wear rate changed clearly before aging 3 days and the trend of change was relatively slow at 3days to 21 days.The effect of temperature on friction coefficient and wear rate was larger than aging time.(3)the wear mechanism of the rubber before aging was adhesive wear.With the increase of aging time,the wear mechanism of 60 degrees changed from adhesive wear to abrasive wear,wear mechanism of 75 degrees and 90 degrees changed from the adhesive and abrasive wear is abrasive wear.The wear mechanism of 105 degrees changed from abrasive wear to fatigue wear.The wear mechanism of 120 degrees always was fatigue wear.According to the change of friction coefficient and wear rate,friction coefficient and wear rate decreased quickly when wear mechanism change from adhesive wear to fatigue wear. |
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