Temperature Distribution and Scuffing of Tapered Roller Bearing

In the field of aerospace, high-speed trains and automobile, etc, analysis of temperature filed and scuffing failure of tapered roller bearings are more important than ever, and the scuffing failure of elements of such rolling bearings under heavy load and high speed still cannot be effectively predicted yet. A simplified model of tapered roller bearings consisted of one inner raceway, one outer raceway and a tapered roller was established, in which the interaction of several heat sources is ignored. The contact mechanics model, temperature model and model of scuffing failure are synthesized, and the corresponding computer programs are developed to analyze the effects of bearings parameters, different material and operational conditions on thermal performance of bearings, and temperature distribution and the possibility of surface scuffing are obtained. The results show that load, speed, thermal conductivity and tapered roller materials influence temperature rise and scuffing failure of bearings. Ceramic material of tapered roller results in the decrease of scuffing possibility of bearings to a high extent than the conventional rolling bearing steel. Compared with bulk temperature, flash temperature on the surfaces of bearing elements has a little influence on maximum temperature rise of bearing elements. For the rolling bearings operated under high speed and heavy load, this paper proposes a method which can accurately calculate the possibility of scuffing failure of rolling bearings.

Wear-resistance and anti-scuffing of multi-arc ion plating molybdenum films

The multi-arc ion plating technology was employed to prepare the molybdenum films with thickness of 3 μm on the AISI 1045 steel. The wear and scuffing tests were carried out on the ball-on-disc tester. AFM and SEM equipped with EDS were adopted to observe and analyze the morphologies and element compositions of surface,cross-section and worn scar of the Mo film. The phase structure was studied by XRD and the bonding strength between Mo film and substrate was measured by scratching tester. The tribological experiments show that the Mo film possesses a good wear-resistance and an excellent anti-scuffing property. The failure mechanism of Mo film under extreme condition is flaking off.

Influence of Surface Properties Modified with Fine Shot Peening on Scuffing

Recently, gears of high strength, reliability, and surface-damage-resistant under severe service conditions are required to achieve the weight saving and downsizing of a product. For the high-speed condition in particular, it is important to understand the influence of the surface properties on the scuffing resistance. If the effective surface profile to improve the lubrication property was found, the metal surfaces could be obtained with both surface strength and surface lubricity. Herein, the influence of surface properties modified with fine shot peening, which can form the arbitrary surface profile, on the scuffing resistance in the rolling-sliding contact machine element, was investigated. The scuffing test was performed using a two-cylinder rolling contact test machine. In a specific sliding, a faster roller of 60% and a sliding velocity of 1.75 m/s were utilized. The scuffing test results with shot-peened test rollers and those with non-shot-peened test roller were compared. The influence of the surface roughness of the shot-peened test roller was also discussed. We found that the shot-peened roller had a better scuffing resistance compared with the roller without the shot-peening process.

SCUFFING MODEL CONSIDERING INFLUEN OF HYDRODYNAMIC LUBRICATION

This paper attempted to solve the problem of scuffing mechanism on the basis of the-ories in three fields: Boundary lubrication , Hydrodynamic lubrication and Surface contact. forlineasr contacting, a simple solution has been obtained.

Scuffing failure analysis based on a multiphysics coupling model and experimental verification

General reductions in lubricant viscosities and increasing loads in machine components highlight the role of tribofilms in providing surface protection against scuffing.However,the relationship between the scuffing process and the growth and removal of tribofilm is not well understood.In this study,a multiphysics coupling model,which includes hydrodynamic lubrication,asperity contact,thermal effect,tribochemistry reaction,friction,and surface wear,was developed to capture the initiation of surface scuffing.Simulations and experiments for a piston ring and cylinder liner contact were conducted following a step-load sequence under different temperature conditions.The results show that high temperature and extreme load could induce the lubricant film collapse,which in turn triggers the breakdown of the tribofilm due to the significantly increased removal process.The failures of both lubricant film and tribofilm progress instantaneously in a coupling way,which finally leads to severe scuffing.

Experimental and theoretical studies of scuffing behavior in piston-pin/piston contacts

A bench rig was built and used to study the scuffing mechanisms and the effects of sur-face roughness, clearance, and groove on scuffing in piston-pin/bore contacts for dynamic loadsand an oscillatory rotation. The experimental results show that the deterioration of the surfaceshear strength by fatigue cracks appears to contribute to the final scuffing, and the effects of thebore surface roughness and groove on the scuffing behavior are more significant than the clear-ance. A macro-micro approached scuffing model and a criterion for scuffing failure were developedappearing to be justifiable for the practical design and analysis of piston pin/bore bearings.

Tribological performance and scuffing behaviors of several automobile piston rings mating with chrome-plated cylinder liner

The friction and wear properties,as well as the scuffing resistance,of different piston-ring coatings mating with a chrome-plated cylinder liner were investigated.Interrupted wear tests under the lubricant starvation condition were conducted to examine the wear behavior of Cr-diamond coating(GDC)and diamond-like coating(DLC).The results indicated that the DLC coating had outstanding tribological properties(small coefficient of friction and wear loss)at 150°C,while the GDC coating exhibited better performance at an elevated temperature(240°C).The DLC coating had a better scuffing resistance;no material adhesion occurred for 70 min under the unlubricated condition.The interrupted wear behaviors revealed that the scuffing process of the GDC coating involved the consumption of lubricant oil with relatively stable wear,a reduction in the friction force,and the occurrence of scuffing,in sequence.In contrast,although the friction force also increased after a short period of weak friction,no scuffing was observed.This is attributed to the formation of a mixed oxide and graphitic C tribolayer.

Thermal shock of subsurface material with plastic flow during scuffing

The thermal shock of subsurface material with shear instability and severe plastic flow during scuffing was investigated.The scuffing damage of M50 steel was tested using a high-speed rolling-sliding contact test rig,and the transient temperature during scuffing was calculated using the Fourier transform method considering the effects of both frictional heat and plastic work.The results show that a thermal shock with a rapid rise and subsequent rapid decrease in the contact temperature is generated in the subsurface layers.The frictional power intensity generates a high temperature rise,leading to the austenitization of the subsurface material.Consequently,the plastic flow is generated in the subsurface layer under the high shear stress,and the resulting plastic strain energy generates a further temperature increase.Subsequently,a rapid decrease in the contact temperature quenches the material,resulting in clear shear slip bands and retained austenite in the subsurface layers of the M50 steel.

Mechanism of scuffing——a dynamic system model

Scuffing, a major cause of failure in automobile engines, is considered as a dynamicprocess in this study. Local adhesions may occur randomly in lubricated contacts due to the exis-tence of asperity contact and breakdown of lubricating films. Scuffing would take place if the localevents develop rapidly into a large-scale plastic deformation and catastrophic failure. A systemdynamic established in the present paper allows one to predict dynamic behavior of a tribologicalsystem through numerical solutions of a group of differential equations. A simplified analysis basedon this model confirms that the system will develop into a state of instability if the friction force atthe interface increases with temperature.

EXPERIMENTAL INVESTIGATION ON PARTICLE EFFECT IN PISTON RING-CYLINDER LUBRICATION

To study the tribological properties of the piston ring-cylinder liner in liquid-solid lubrication, the experiment is carried out on a modified piston ring-cylinder liner tester. Two kinds of liquid-solid lubricants are used, one with ultra-dispersed diamond （UDD） nano-particles suspending in pure lubricant, the other with micro-sized MoS2 particles. The particle concentrations are 0%, 0.02% and 0.1% by weight. The experimental temperature is 30℃ and 75℃ respectively. The results show that with the presence of ultra-dispersed diamond particles, the load when scuffing failure occurs is increased. For the lubricant contains MoS2 particles, the scuffing load is decreased. The liquid-solid lubricant also affects the thermal behavior of piston ring-cylinder liner. The surface bulk temperatures of cylinder liner specimen are measured. It has been seen that liquid-solid lubricant used in this research tends to improve the thermal properties generally and the measured friction forces also decreases with the presence of UDD nano-particles. The surface bulk temperature when scuffing occurs is also measured. The results show that the size effect and environment temperature have obvious influence on scuffing load and scuffing temperature. With some new findings, this work is an important complement to the existing research on particle effect on lubrication, because the existing results only show one aspect of this problem.

改良缓慢连续超滤治疗肾病综合征水肿

目的探讨改良缓慢连续性超滤(SCUF)装置治疗肾病综合征水肿的临床疗效和安全性。方法106例肾病综合征重度水肿、利尿剂抵抗的患者，在病因治疗及对症支持治疗的同时，给予床旁SCUF治疗，观察治疗情况及相关不良反应。结果106例患者中2例出现上消化道出血退出治疗，余患者耐受性良好，水肿明显消退。SCUF进行时间(54．7±20．3)h，超滤率(150．0±33．5)ml／h，总超滤量(8375±2086)ml，净超滤量(8056±2335)ml。治疗过程中患者血压、心率无明显波动，内环境、肾功能稳定，未发生与改良SCUF装置相关的并发症。结论改良SCUF装置对利尿剂抵抗的肾病综合征水肿患者是一种安全有效的治疗方法，经济简便、易于掌握。

Calculation of flash temperature for hybrid ceramic ball bearing lubricated with solid

The scuffing behavior of hybrid ceramic bearing lubricated with solid is greatly affected by the contact flash temperature. Formulas are dedused using Lee’s asperity flash temperature method, to calculate the flash temperature of ball bearing lubricated with solid. The maximum flash temperature is calculated for hybrid ceramic ball bearings. The results show that under given conditions, the flash temperature of inner race is higher than that of outer race, the flash temperature of the hybrid ceramic bearing is sensitive to the load, rotational speed and race curvature. The flash temperature of inner race at 20 000 r/min is 66 9% more than that that at 11 000 r/min, and with the load changing from 1.1 kN to 2 kN, the flash temperature inner race goes up to 165 7%. Very common for high speed ball bearings, when curvature coefficients of both inner and outer race change from 0 515 to 0 56, the inner race flash temperature decreases from 421 446℃ to 56 2℃.

Applying ionic liquids as oil additives for gearboxes:Going beyond the state of the art by bridging the nano-scale and component level

Ionic liquids(ILs)have been used effectively in many applications for reducing problems related to friction and wear.In this work,the potential of ILs as an anti-wear and extreme pressure lubricant additive for high load-carrying gearbox applications such as helicopter transmissions has been studied.Two halide-free ILs:P_(8881)(BuO)_(2)PO_(2)^(-)(1)and P_(8881)(MeO)_(2)PO_(2)^(-)(2),which are blended at 5 wt%each into a standard non-additivated FVA2 base oil(BO)are examined.Their solid-liquid interface,friction and load-carrying capacity,and wear(scuffing)behavior are studied on the nano-,lab-,and component-scale,respectively,at a different range of temperature and loading conditions by using the atomic force microscopy(AFM),Schwing-Reib-Verschleiβ(SRV)friction tests,and Brugger tests,as well as forschungsstelle für zahnrader und getriebebau(FZG)back-to-back gear test rig.The AFM analysis shows nearly no change of adhesion over the full range of studied temperature for the IL blends compared to the BO.Similarly,IL blends demonstrate a very stable coefficient of friction(COF)of around 0.16,which even decreases with increasing test temperatures ranging from 40 to 120℃.A clear reduction in COF up to 25%is achieved by adding only 5 wt%of the investigated Ils in the BO,and the Brugger tests also show a pronounced enhancement of load-carrying capacity.Finally,on the component-scale,a significant improvement in gear scuffing performance has been observed for both used IL blends.A detailed characterization of the wear tracks from the SRV friction tests via the transmission electron microscopy(TEM)revealed the formation of a phosphate(P-O)-based amorphous tribo-chemical layer of about 20 nm thickness.Therefore,this work may present an approach for Ils to be used as an additive in conventional lubricants due to their ability to enhance the lubrication properties,making them an alternative lubricant solution for high load-carrying gearbox applications.