Nondestructive testing of sliding bearings
Abstract
A validation of electro-physical probing method usage is given for a sliding bearings diagnostic at a boundary friction. Electric circuits and a way of sliding bearings diagnostic, where an analysis of a boundary lubricating layer (BLL) thickness control is carried out on contact resistance parameters indirectly. A sliding bearing lubricating state is defined on previously installed threshold values which achievement defines its running regime.
Keywords
Download Options
Introduction
A diagnosing task of a boundary lubricating sliding bearing mode, containing a shaft and an insert, in the internal-combustion engine (ICE), for example, of all-purpose power unit (APU) at its loading under operating conditions is actual. As a result of forced operations ICE increasing in operation modes, increased requirements are laying claim to engine oils operational properties, therefore creation of the way, allowing to control the state and properties of a boundary lubricating layer (BLL), is rather necessary and actual [1].
The service load and high-speed ICE parameters increasing especially in a high-forced mode (GOST 17479.1-2015) are laying increased requirements to nanometer lubricating layers thickness, i.e. to boundary lubricating layers (BLL). BLL state is a complex value defined by its structural changes and causing many measured tribotechnical parameters (strength, antifrictional, antiscuff, thermo-oxidative stability etc.) which are defined operational properties of lubricating material (LM) in aggregate.
In connection with a degradation of producing LM a problem of their quality assessment is actual. Moreover, before machinery producers is a nagging problem of import on domestic oils replacement with an optimum combination price and quality. On-stream, LMquality analysis is carryout on 15 physical and chemical parameters (GOST 8581-78), basic of which are kinematic viscosity, flash and chilling temperature, amass fraction of water and mechanical impurities, alkali neutralization number, sulfonate ash content etc. Operational LMproperties complex estimation is carried out at benchmark teston driving axles, different installations and internal-combustion engines and also field test [2]. Usually a LMuser is interesting in its quality, but not a viscosity class and operational properties which define necessary, but not sufficient service oil conditions in specific installation. Under sufficient conditions we understand not that it is declared in the certificate at LMproduction, but those real LMcharacteristics, which define a sliding bearing state at specific load and speed service modes, especially during the moment of ICE start and stop or the forced acceleration in real time.
The work purpose is an estimation of operational properties and thermooxidative oil stability for its replacement age definition, and sliding bearing diagnostic on a boundary lubricating layer state to raise control reliability and its operation modes management in real time.
The method based on registration of a point contact conductivity parameters, was successfully applied by Bowden, Tabor [3], W. H. Abbot [4, 5], M. Antler [6, 7], J. F. Archard [8] for frictional behavior of "dry" materials used in electric contacts to research. Anti-wear properties of noble metals: platinum, gold, silver and their alloys were studied generally. It is installed, that in the absence of lubricants and comparatively low contact pressures the electric current passing promotes wear rising, acceleration of adsorbed films formation and chemical reactions passage on a surface. The results gained by them had qualitative character in the main, without a quantitative estimation of thickness and boundary lubrication continuity.
Conclusion
Electro-physical probing methods using foundation is given for sliding bearings operation modes estimation on BLL state. A calculation dependence analysis of tunnel resistance (R) from BLL nanometric thickness and the real contact area shows, tthat at load increasing by two orders the real contact area changes by one order, and the contribution from a BLL thickness in design valueR increases by ten orders. The BLL thickness brings a basic contribution in the calculated value tunneling tresistance, instead of real contact area that allows to estimate mechanical and frictional properties of boundary lubricant layers (BLL) at elastic contact interacting of conjugate objects at their relative moving.
Electric circuits and methods, allowing estimating BLL operational properties, are developed. This method allows to test BLL formation and destruction kinetics in real sliding bearings direct at their operation.
On the experimental data analysis basis an antifrictional and antiscuff oils and plastic lubricants of a various functional purpose properties estimation (transmission, motor, hydraulic, geared), the recorded contact resistance value relatively to an initial metal surface resistance value or contraction resistance is developed the diagnostic estimation state criterion of metal interface, namely at BLL formation and its self-organizing R/R >> 1 at a dynamic equilibrium between BLL formation and c okdestruction R/R > 1, BLL destruction R /R ≈ 1, metal interface destruction R /R ≈ 1. The developed criteria are the basisc ok c ok c sfor creating phenomenological models for predicting the state of lubrication of the interface surface of conjugated bodies during rolling and sliding. These criteria are laid in the basis of algorithms for monitoring the state of the interface of conjugated metal bodies under the conditions of rolling and sliding bearings, which is important for the diagnosis and management of their operation modes.
Contact resistance threshold, on which values it is possible to estimate sliding bearings operation modes, connected with its lubrication state, namely, hydrodynamic regime R , boundary friction mode R with polymolecular BLL conservation, g tpreemergency operation with monomolecular BLL (R ) conservation, emergency operation mode (R ) with very thin (≈ 0.3 o cr nm) monomolecular BLL conservation, destruction mode (R) are counted. Recorded contact R value with theoreticallys ccounted threshold values (R , R, R , R , R) comparison characterizes conjugate objects lubrication state. The proposed way g t o crsallows to estimate by means of nondestructive testing sliding bearing lubrication state at boundary friction that gives a chance, depending on conjugate surfaces lubrication state to introduce amendments in its operation modes,to define oil replacement age and thus to provide reliability and durability of its work.
Thus, the electro-physical probing method using foundation for sliding bearings diagnostic on the boundary lubricant layer state is given. The way for the boundary sliding bearing lubricant control mode, for example, internal-combustion engine (ICE) crankshaft journal at its loading in operating conditions, and also for an incoming control or engine oils quality estimation is developed. The given diagnostic way allows to make an incoming quality oils inspection (hydraulic, turbine, motor), their antifrictional, antiscuff, and operational properties estimation at an early stage before critical, emergency sliding bearing running, to operate its work mode. The developed way has a big practical importance, as on its basis the device which in real time carries out a quality control of used engine oil in the internal-combustion engine. The given device using, for example, in fodder harvesters will allow to the machine operator to carryout not only a quality control of bought engine oil in the market, but also to do its replacement indue time, on the basis of its thermal-oxidative ability.
