On the film thickness behaviour of polymer greases at low and high speeds

2015 ◽  
Vol 90 ◽  
pp. 435-444 ◽  
Author(s):  
David Gonçalves ◽  
Beatriz Graça ◽  
Armando V. Campos ◽  
J. Seabra ◽  
Johan Leckner ◽  
...  
Keyword(s):  
Film Thickness ◽  
High Speeds

Non-Newtonian behaviour in elastohydrodynamic lubrication

1974 ◽  
Vol 337 (1608) ◽  
pp. 101-121 ◽  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Film Thickness ◽  
Pressure Distribution ◽  
Critical Stress ◽  
Elastohydrodynamic Lubrication ◽  
Critical Factor ◽  
Molecular Size ◽  
High Speeds ◽  
Oil Films

The relation between shear stress and shear rate has been determined for elastohydrodynamic oil films. At low values the rate of shear is directly proportional to the shear stress, but at higher values the shear rate increases more rapidly than the stress. It is shown that the critical factor is the magnitude of the shear stress, not the shear rate, and that this critical magnitude depends upon the pressure and the molecular size. Above the critical stress, in the non-Newtonian region, the shape of the curve relating the stress to the rate of shear depends upon the distribution of the sizes of the molecules in the oil. It is shown that in elastohydrodynamic conditions the limits of Newtonian behaviour are frequently exceeded and that this is liable to influence the pressure distribution, the magnitude of the traction, the generation of heat, and, at high speeds, the value of the film thickness.

Film Thickness, Friction, and Scuffing Failure of Rib/Roller End Contacts in Cylindrical Roller Bearings

1992 ◽  
Vol 114 (2) ◽  
pp. 311-316 ◽  
Author(s):  
H. Aramaki ◽  
H. S. Cheng ◽  
D. Zhu
Keyword(s):  
Film Thickness ◽  
Critical Load ◽  
Strongly Correlated ◽  
Wear Process ◽  
Load Dependence ◽  
Roller Bearings ◽  
High Speeds ◽  
Lubrication Performance ◽  
Minimum Film Thickness ◽  
Cylindrical Roller

The lubrication performance of rib/roller end contacts of cylindrical roller bearings was studied both theoretically and experimentally for end-crowned rollers and inclined ribs. A partial EHL program was used to calculate the film thickness and the friction in the rib/roller end contact. Calculated minimum film thickness shows a strong load dependence although the central film thickness is still a weak function of the load. The influence of the contact position on the film thickness was also investigated for roller skewness and design tolerance. It was found that the contact location affects the minimum film thickness strongly in spite of a weak influence on the central film thickness. Friction and scuffing experiments were conducted on a special rig, which can achieve arbitrary slide/roll ratio to simulate the rib/roller end contacts. Good agreements were found between measured and calculated friction based on the assumption that the lubricant was Newtonian. In scuffing experiments, scuffing propagation was observed on the rib contact surface. The critical load for scuffing is strongly correlated with the sliding velocity. The critical load at high speeds is lower than that at low speeds although the friction at high speeds is lower. These data imply the importance of the contact location and the wear process for film breakdown.

Experimental Investigation of Film Thickness Behaviour at Very High Speeds

2008 ◽  
Author(s):  
Joslyn Hili ◽  
Andrew V. Olver ◽  
Simon Edwards ◽  
Leon Jacobs
Keyword(s):  
Experimental Investigation ◽  
Film Thickness ◽  
Viscous Dissipation ◽  
Frictional Heating ◽  
Magnetic Method ◽  
Regression Equations ◽  
High Speeds ◽  
Tractive Rolling ◽  
Shear Heating ◽  
Very High

At very high speeds, elastohydrodynamic (EHD) films may be considerably thinner than is predicted by classical isothermal regression equations such as that due to Hamrock and Dowson. This may arise because of viscous dissipation, frictional heating or starvation. In this paper, the contact between a steel ball and a glass disc was studied. The disc was driven at speeds of up to 20 ms−1, and the ball was driven by tractive rolling against the disc, its speed being determined using a magnetic method. It is shown that the results, which fall well below classical predictions, are consistent with inlet shear heating at the observed sliding speeds.

Experimental Investigation of Elastohydrodynamic (EHD) Film Thickness Behavior at High Speeds

2010 ◽  
Vol 53 (5) ◽  
pp. 658-666 ◽  
Author(s):  
Joslyn Hili ◽  
Andrew V. Olver ◽  
Simon Edwards ◽  
Leon Jacobs
Keyword(s):  
Experimental Investigation ◽  
Film Thickness ◽  
High Speeds

scholarly journals Grease Lubrication: Formulation Effects on Tribological Performance

2021 ◽  
Author(s):  
Tiago Cousseau
Keyword(s):  
Film Thickness ◽  
Film Formation ◽  
Physicochemical Interaction ◽  
Grease Lubrication ◽  
Term Operation ◽  
Lubrication Regimes ◽  
High Speeds ◽  
Lubrication Performance ◽  
State Of Art

Grease lubrication performance prediction is challenging. Only recently that empirical equations to predict grease film thickness for prevailing rolling conditions under fully flooded lubrication taking into account thickener properties and content for low, moderate, and high speeds were developed. At starved lubrication, although new insights about the supply and loss mechanisms that govern film formation have been published, contact replenishment and, consequently, film thickness predictions for long-term operation are still not available. Prediction of components efficiency requires film thickness values and properties, including film’s molecular structure, which makes it even more challenging. When it comes to prevailing sliding conditions, the literature is scarce and most of the knowledge developed for prevailing rolling conditions is not applicable. During the sliding of the contacting bodies, boundary and mixed lubrication regimes are expected. In this situation, the tribological response is primarily defined by grease thickener and additives physicochemical interaction with the surface. This complexity leads many researchers to seek simpler relationships between grease formulation and properties with its performance. This review aims to present the state-of-art on grease lubrication and update some of these relationships.

scholarly journals On the Relation between Friction Increase and Grease Thickener Entraining on a Border of Mixed EHL Lubrication

Lubricants ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 12
Author(s):  
Tomas Zapletal ◽  
Petr Sperka ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Contact Area ◽  
Stribeck Curve ◽  
Base Oil ◽  
High Speeds ◽  
Lubricant Flow ◽  
Direct Solid ◽  
Ehl Lubrication ◽  
Ball On Disc

This paper deals with an experimental study of film thickness and friction of commercial-grade grease and its base oil in a highly loaded contact. In-situ measurements were conducted for two surface textures on a ball-on-disc optical tribometer at the border of mixed lubrication. At high speeds, the film thickness and the friction of grease correspond with the base oil, while, the thickener enters the contact area and locally affects the film thickness and friction at low speeds. It was found out that the thickener starts to enter the contact area approximately at the same speed when the base oil friction increases on Stribeck curve but without direct solid to solid contact. It indicates that both effects can have the same origin. Change of lubricant flow in contact inlet area was discussed as a possible explanation.

Melt Friction and Pin-on-Disk Devices

1986 ◽  
Vol 108 (1) ◽  
pp. 105-108 ◽  
Author(s):  
A. Kent Stiffler
Keyword(s):  
Surface Roughness ◽  
Steady State ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Friction And Wear ◽  
Squeeze Film ◽  
High Speeds ◽  
Pin On Disk ◽  
Theory And Experiment ◽  
Good Agreement

A melt concept is proposed to explain the tribology of unlubricated metal pin-on-disk sliding at high speeds. A squeeze film model of the melt film is developed which depends on the continually forming melt to give steady-state load support. Expressions are derived for the film thickness, coefficient of friction, and wear. The theory is applied to pin-on-disk data available in the literature. There is good agreement between theory and experiment for the friction coefficient. The results for wear are inconclusive. A significant factor affecting the findings is surface roughness.

Surface Films on Zircaloy-2 Samples Cracked in Neutral Aqueous NaCl by Stress Corrosion

1973 ◽  
Vol 31 ◽  
pp. 46-47
Author(s):  
R.A. Ploc
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Film Thickness ◽  
Stress Corrosion ◽  
Zirconium Dioxide ◽  
Surface Film ◽  
Surface Films ◽  
Continuous Layer ◽  
Transmission Electron ◽  
Product Film

Samples of low-nickel Zircaloy-2 (material MLI-788-see(1)), when anodically polarized in neutral 5 wt% NaCl solutions, were found to be susceptible to pitting and stress corrosion cracking. The SEM revealed that pitting of stressed samples was occurring below a 2000Å thick surface film which behaved differently from normal zirconium dioxide in that it did not display interference colours. Since the initial film thickness was approximately 65Å, attempts were made to examine the product film by transmission electron microscopy to deduce composition and how the corrosion environment could penetrate the continuous layer.

(111) Monocrystalline Nickel Films

1972 ◽  
Vol 30 ◽  
pp. 512-513
Author(s):  
T.E. Pratt ◽  
R.W. Vook
Keyword(s):  
Film Thickness ◽  
Deposition Rate ◽  
Room Temperature ◽  
Narrow Range ◽  
High Vacuum ◽  
Residual Pressure ◽  
Temperature Dependent ◽  
Deposition Parameters ◽  
Transmission Electron ◽  
Substrate Temperatures

(111) oriented thin monocrystalline Ni films have been prepared by vacuum evaporation and examined by transmission electron microscopy and electron diffraction. In high vacuum, at room temperature, a layer of NaCl was first evaporated onto a freshly air-cleaved muscovite substrate clamped to a copper block with attached heater and thermocouple. Then, at various substrate temperatures, with other parameters held within a narrow range, Ni was evaporated from a tungsten filament. It had been shown previously that similar procedures would yield monocrystalline films of CU, Ag, and Au.For the films examined with respect to temperature dependent effects, typical deposition parameters were: Ni film thickness, 500-800 A; Ni deposition rate, 10 A/sec.; residual pressure, 10-6 torr; NaCl film thickness, 250 A; and NaCl deposition rate, 10 A/sec. Some additional evaporations involved higher deposition rates and lower film thicknesses.Monocrystalline films were obtained with substrate temperatures above 500° C. Below 450° C, the films were polycrystalline with a strong (111) preferred orientation.

The method of replication affects metal film granularity and resolution

1989 ◽  
Vol 47 ◽  
pp. 708-709
Author(s):  
George C. Ruben
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Film Thickness ◽  
Single Molecule ◽  
Metal Film ◽  
Vertical Surface ◽  
High Resolution Imaging ◽  
Controllable Factors ◽  
Resolution Imaging

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.

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