Onset Of Scuffing Research Articles

A test for evaluating the scuffing performance of fully-formulated lubricants

This article presents the development and application of a test method to assess the scuffing resistance of fully-formulated lubricants using the Mini-Traction-Machine 2 tribometer. A barrel-on-disc contact in contra-rotation allows for high contact pressures along with high sliding velocities while maintaining low entrainment velocities. The test method is based on raising the sliding velocity in steps to increase the severity of contact conditions. These steps allow the effect of the lubricant composition on the scuffing performance to be studied. The results include an analysis of the maximum contact temperature and the frictional power intensity at the onset of scuffing.

In-Situ Observation of the Effect of the Tribofilm Growth on Scuffing in Rolling-Sliding Contact

General reductions in lubricant viscosities in many machine components mean that the role of lubricant additives in forming tribofilms has become increasingly important to provide adequate surface protection against scuffing. However, the relationship between scuffing and the formation and removal of tribofilms has not been systematically demonstrated. In this study, a step-sliding speed scuffing test based on contra-rotation using MTM-SLIM and ETM-SLIM has been employed to observe concurrently tribofilm thickness and the onset of scuffing. The initial sliding speed used was found to significantly affect scuffing performance since it determines the extent to which a tribofilm can form before critical sliding speed conditions are reached. In general, additives that formed thicker tribofilms, especially ZDDPs and triphenyl phosphate, gave effective protection against scuffing, though their protective tribofilms were progressively removed at higher sliding speeds, eventually resulting in scuffing.Graphical

Method for tribological experiment to study scuffing initiation on AISI 52100 steel and hard ceramic coatings

Though many models of wear have been proposed, the design of the lab-scale experimental procedures to reproduce and characterize a particular wear regime, scuffing, has been difficult to generalize and more limited in scope. In this study, we used a high-frequency reciprocating tribometer to determine a set of tribological experimental parameters that instigate material scuffing and yield reliable and repeatable results by varying grinding lay orientation, temperature, counter body material, substrate hardness, contact load, stroke length, and frequency. The onset of scuffing in through-hardened 52100 steel substrates lubricated with low viscosity fuels was most repeatable with a perpendicular grinding lay and alumina counterface, while no effect was observed with substrate temperature. The experimental method using a load progression from 1 N to 18 N was then used on several protective coatings to determine their effectiveness in inhibiting scuffing initiation.

Acoustic emissions from oil lubricated metal on metal sliding contacts

This study investigates the condition monitoring of oil lubricated metal on metal sliding contacts using various sensing techniques including acoustic emissions. The worn surfaces are examined and wear mechanisms are explored and linked with the on-line sensor signals. This study tackles the condition monitoring problems from the tribological point of view, ie at a micro-scale. Experimental work was carried out on a ball-on-disc tribometer using an En31 bearing steel ball and disc lubricated by a mineral base oil, Shell Vitrea 460. The base oil was used to eliminate the formation of possible additive films and to promote the onset of scuffing. The sliding speed was kept at 6 m/s under maximum Hertzian contact pressures of 3 GPa. An oil starvation strategy was also applied to promote adhesive failure. The tests generated multiple contact wear mechanisms and enabled correlations between AE signals and wear mechanisms to be identified. Tests were stopped at various stages to enable surface examination using scanning electron microscopy (SEM). The results show that AE gives an early indication of adhesive wear of the lubricated metal contacts using r.m.s signals. Snapshots of AE waveforms also show that burst signals changed to continuous signals when the contact changed from fully lubricated to starved conditions. AE energy shifts within the broad frequency band of 300 kHz and 1 MHz give early indications of scuffing.

Some Studies on Scuffing Performance of Surface Treated AISI 4340 Steels

Scuffing or scoring is an important form of damage leading to component replacements in lubricated mechanical systems such as power drives, gears, bearings, cams and followers, piston rings etc. Since scuffing necessarily involves localized welding of asperities, suitable surface modifications or coating can impart a good resistance to scuffing. A new class of low temperature salt bath nitriding process provides good resistance to scuffing. The current work is on evaluation of the scuffing resistance of AISI 4340 steels imparted with two such treatments. Experimental investigations were conducted on Sursulf and Arcor treated AISI 4340 steel specimen using a pin on ring test system under boundary lubrication condition. Continuous monitoring of friction records and (near surface) bulk temperature were done under step loading. Limiting loads and load velocity relations were evaluated and using the data generated and a thermo-mechanical wear model, performance is indexed. Off line studies on surface finish, hardness variations and surface transformations were also accomplished. Some salient aspects of the investigation and data generated are presented here. Onset of scuffing was observed to be far delayed with pin specimen imparted with these treatments compared to hardening.

Scuffing resistances of Al–Si alloys: effects of etching condition, surface roughness and particle morphology

Scuffing resistances of two eutectic Al–Si alloys with different second phase particle morphologies, were investigated using a block-on-ring wear machine under dry sliding conditions. The sample surfaces were modified by mechanical polishing and chemical etching to create different surface topographies. It was shown that at constant load (5 N) and speed (0.5 m s −1), the sliding distance to scuffing initially increased with etching time as the particles prevented the direct contact between the counterface and aluminum matrix. The onset of scuffing became less sensitive to surface conditions at longer etching times due to the weakening of particle/matrix interfaces. Polishing the surfaces to an optimum roughness ( R a=0.4 μm) prior to etching improved the resistance to scuffing. In the alloy containing second phase particles with small aspect ratios (more equiaxed particles), the onset of scuffing was delayed. Scratch tests showed that two types of fractures occurred in the hard phases during the sliding process: fracture from the root of the particles, and fracture of the edges of the particles. Both contributed to wear and scuffing, but the former process was more detrimental for scuffing of the alloy surfaces.

The effect of base oil oxidation on scuffing

In this work, the effect of base oil oxidation on scuffing was investigated. It was found that under mixed lubrication conditions there is a direct relationship between the level of base oil oxidation and the onset of scuffing, i.e., the greater the oxidation the lower the likelihood of scuffing. An oxidised base oil forms, among other products, carboxylic acids, which reduce scuffing failure in comparison with the parent oil. This was confirmed by the addition of a carboxylic acid directly to the base oil operating under the same mixed lubrication conditions. The removal of the carboxylic acids from the oxidised oil via column chromatography resulted in a scuffing failure performance equivalent to the parent oil.

Development of a Gear Oil Scuff Test (GOST) Procedure to Predict Adhesive Wear Resistance of Turbine Engine Lubricants

The Ryder gear test has been widely used to define the antiwear characteristics of lubricating oils intended for use in aviation gear boxes. However, an accelerated procedure is required, particularly for the screening and development of new lubricants, due to the cost and complexity of the Ryder test. The present study is a development of previous work that evaluated the suitability of a number of apparatus. Initial screening work indicated that a ball-on-rotating cylinder contact geometry had the potential to effectively predict the results of the Ryder gear test. The present work describes the development of the test procedure and confirms that similar wear mechanisms exist in both instances. Indeed, the calculated contact flash temperature in both the Ryder and ball-on-cylinder contacts was almost identical at the onset of scuffing. A simple model was developed to predict the effects of lubricant viscosity on the gear contact. Excellent correlation was observed between the model and the measured effects of hydro-dynamic lubrication in the full-scale Ryder gear test. As a result, the Gear Oil Scuff Test (GOST) procedure considers both chemical and physical lubricant characteristics. A correlation coefficient of 0.92 was obtained between the laboratory and full-scale test procedures for a matrix of 27 oils of widely varying quality. Presented at the 52nd Annual Meeting in Kansas City, Missouri May 18–22, 1997

Infrared and Visual Study of the Mechanisms of Scuffing

The development of a reliable model for predicting scuffing requires an understanding of the mechanism of scuffing initiation. This study examines the process of scuffing directly within a contact and thus tests some of the existing, proposed mechanisms. A lubricated steel ball is loaded and rotated against a sapphire flat and the load increased in stages until scuffing occurs. Two methods of observation are employed. In one, the temperature of the steel ball across the contact is mapped continuously using an infrared microscope. A novel, nodding mirror set-up enables temperature profiles to be taken many times a second. This work shows that scuffing does not occur at either a critical maximum or at a critical inlet temperature. In the second approach, a solid-slate TV camera and video recorder are used to monitor the contact visually up to and during scuffing. This work suggests that, for a range of different lubricants, the onset of scuffing is always immediately preceded by the buildup of fine wear deb...

5–Wear of gears

A discussion of the wear processes occurring in gears is followed by theoretical formulae for calculating the onset of scuffing and oil film thickness. Effects of materials on wear and of wear on performance are considered. Methods for preventing wear are given.