Effect Of Hot Oil Aging On Mechanical And Tribological Properties Of NBR

In the field of modern aircraft,nitrile rubber seals are widely used in the hydraulic,fuel and environmental control systems,such as sealing rings in the aircraft landing gear system,braking or steering system and engine seals,flight controller and actuator seals and so on.In the complex and changeable environment,nitrile rubber faces high temperature and high pressure,oxygen gas and corrosive medium containing factors influencing,which is prone to hardening,cracking,being soft,being sticky,discoloration and ageing.Thus their physicochemical properties change,mechanical properties become poor,which greatly influences the sealing performance and service life.This paper aimed at above conditions carries out experiment research.First of all,based on the actual working environment,rubber seals in aircraft hydraulic system are selected as object of study.Accelerated aging test of nitrile rubber immersed in 15#red oil at different temperature and time is carried out.Then a series of macroscopic properties of the aged NBR rubber is carried out,including swelling properties-mass change rate and volume change rate,hardness test and mechanical properties-stress and strain,tensile strength,elongation at break,tensile stress,tear strength etc.It reveals that nitrile rubber is prone to swelling,shore A hardness decreases first and then increases.mechanical properties such as tensile strength,tensile elongation and tear strength,rapidly decline,mainly relating to temperature and aging time,high temperature damaging effect is more obvious because of the oil aging.Finally,based on the empirical formula of aging residual properties,the storage life prediction is carried out by taking the change rate of tear strength as an evaluation index,The storage life of NBR at ambient temperature of 23 degrees under the condition of hydraulic oil was about 15 years.Subsequently,the surface and tensile profile analysis and element content analysis of NBR before and after aging were carried out by means of field emission scanning electron microscopy(FESEM).It is found that the rubber surface and stretch section are more smoother after aging.Then,the fourior transform infrared spectrometer and thermogravimetric analyzer are used to test the change of functional groups and heat stability of NBR.The aging induces molecular structure changing,oxidation occuring and chain fracture,thermal stability deterioration,low weight loss.The longer aging time and higher temperature,the worse thermal stability of NBR sample,but the lower weight loss.Finally,this paper carries out friction and wear test of nitrile rubber specimen after accelerated aging experiments under rich oil and dry friction and wear state,it reveals that under rich oil lubrication,the NBR specimen of deeper aging degree has a higher friction coefficient but dry friction state is on the contrary.More apparent comet shape and furrow wear can be observed at the surface of lighter aging degree rubber,and the wear surface is more rough,with the aging degree deepening,the surface of rubber specimens becomes harder,the worn surface becomes more smooth,the debris is relatively rare.The element content of NBR samples under two kinds of friction states is just the same,and no obvious increase of O is observed,indicating that no serious oxidation occurres during the friction and wear process.All above,the studies of nitrile rubber immersed in 15#red oil under different ageing temperature and time conditions are completed.The aging failure behavior,thermal stability and friction variation and wear characteristics of NBR under the immersion condition of hydraulic oil are obtained,which provides guidance for the design and application of the rubber seal.