The most important rheological parameter for lubricants is viscosity as it also affects the tribological properties like friction between interacting surfaces and wear. This research intends to study the relationship between viscosity and temperature at different shear rates for multiple grades of three different categories of lubricants used for different applications viz. L1: MG20W50 (engine oil), L2: SAE20W50 (engine oil), L3: MC20W50 (mineral engine oil), L4: EP90 (gear oil), and L5: DXTIII (steering fluid). Constant high dynamic viscosity, shear stress, and low compressibility at different temperatures in multigrade as well as single grade industrial oil will help to maintain the surface film over the period of time and hence the reduction in wear. The dynamic viscosity of these chosen samples has been measured experimentally in temperature range of 20 to 50°C. The measurements have been extended to observe the dependence of shear rate, time, and temperature on the dynamic viscosity. All the samples are observed to behave like Newtonian fluids in the entire temperature range of study. Further, all samples seem to obey the Arrhenius relationship with temperature. Shear stress shows linear variation with shear rate exhibiting uniform viscosity which is substantiated by almost no variation in dynamic viscosity with shear rate for value above 5 per second.

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Study of Rheological Properties of Industrial Lubricants

Current researches show that mechanical deformation of seal ring face makes fluid film clearance decrease at high pressure side, thus a divergent clearance is formed and face wear occurs more seriously at the high pressure side than that on the low pressure side. However, there is still lack of published experimental works enough to prove the theoretical results. In this paper, a spiral groove dry gas seal at high pressures is experimentally investigated so as to prove the face wear happened at the high pressure side of seal faces due to the face mechanical deformation, and the wear behavior affected by seal ring structure is also studied. The experimental results show that face wear would occur at the high pressure side of seal faces due to the deformation, thus the leakage and face temperature increase, which all satisfies the theoretical predictions. When sealed pressure is not less than 5 MPa, the pressure can provide enough opening force to separate the seal faces. The seal ring sizes have obvious influence on face wear. Face wear, leakage and face temperature of a dry gas seal with the smaller cross sectional area of seal ring are less than that of a dry gas seal with bigger one, and the difference of leakage rate between these two sizes of seal face width is in the range of 24%–25%. Compared with the effect of seal ring sizes, the effect of secondary O-ring seal position on face deformation and face wear is less. The differences between these two types of dry gas seals with different secondary O-ring seal positions are less than 5.9% when the rotational speed varies from 0 to 600 r/min. By linking face wear and sealing performance changes to the shift in mechanical deformation of seal ring, this research presents an important experimental method to study face deformation of a dry gas seal at high pressures.

Experiment on wear behavior of high pressure gas seal faces

Frictional characteristics of impregnated graphite with different graphitization degree versus chromium stainless steel under varying PV values

As the expectations for modern machinery’s tribological and thermal performances continue to rise, the retention of lubricant on the contact surfaces of their sliding components becomes an increasingly important issue. Friction and wear cause heat-related failures which lead to catastrophic damage to machinery. Evaporation of a lubricant’s volatile constituents as well as lubricant migration leads not only to a reduction in lubricant quantity but also in its quality, thus facilitating component failures. In order to enhance component reliability, the surface should incorporate features that actively retain lubricants. The unique properties of nano-porous topographies such as their high surface area-to-volume ratio indicate they hold great potential to address these lubrication issues. Thermodynamics-based numerical models of smooth and nano-porous Si-Cu composite topographies were developed to predict the trends of lubricant retention. Photolithographic processes as well as physical etching and thin film deposition tools were utilized to fabricate smooth and patterned Si-Cu composite sample types. The nano-porous topographies incorporated various nano-pore geometries for determination of the optimum conditions for lubricant retention. Amorphous Si film was deposited on the samples using chemical vapor deposition which served as a surface chemistry modification to examine the film’s potential to enhance lubricant retention. Lubricant retention tests were performed using a custom-fabricated apparatus for evaporating lubricant from the sample types. Finally, the model’s predictions of lubricant retention trends were compared to actual testing results to examine the validity of those predictions. The predictions of the models were supported by the evaporation testing data obtained from the samples. It was found that surface nano-pores having the proper geometry, in combination with the dehydrogenated amorphous Si surface chemistry, could significantly enhance retention above the one micrometer fluid film thickness typically formed between interacting surfaces of machine components undergoing relative motion. The surface features show potential to prevent many types of mechanical failures, reduce maintenance costs, and achieve higher energy efficiency.

Characterization of Nano-Porous Si-Cu Composites to Enhance Lubricant Retention Impacting the Tribological Properties of Sliding Surfaces

11 - Simulation of Wear and Friction Experiments and Presentation of Tribological Data

Blisters that are observed on carbon-graphite seal faces are created by a fracture process that derives from viscous friction forces present at the instant that relative rotation begins between seal faces. High speed data acquisition of shaft torque and shaft rotation data was used in this study to measure breakaway torque for different types of oils that were present between seal faces at startup. Synthetic polyalphaolefin oils create higher traction forces and a larger number of blisters than do mineral oils of comparable viscosity.

The effect of oil type on blister formation in carbon-graphite mechanical seals©

Blisters that develop on carbon-graphite mechanical seal faces are irregularities in surface topography that result in poor sealing performance and a high incidence of catastrophic failure. On first inspection, a blister is a burnished area that is slightly elevated above the surrounding seal surface. In this study, the topography of several hundred blisters was examined with interference microscopy. The shape of the burnished area is typically elliptical or cylindrical. The leading edge against the direction of rotation of the mating seal ring extends abruptly upward from the surrounding seal surface. The trailing surface gradually merges into the parent seal face. Most blisters have a maximum height of 0.25 μm to 0.75 μm (10 μ-in to 30 μ-in). Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

The Detection and Characterization of Blisters On Carbon-Graphite Mechanical Seal Faces

Mechanical seals can wear differentially in a radial direction across their faces when initially flat faces are distorted by fluid pressure and thermal gradients. In this study, differential wear on carbon graphite seal faces was determined by comparing local wear measurements that were made with a novel measurement method. A minute scratch was made on the seal face surface with a toolmaker's riffler file and then the depth was measured using a vertical interference microscope. A second image of the same scratch was taken after a wear test was complete to yield a measure of the absolute wear of the face at one location. Because the scratches are small, differential wear across the face can be measured by placing several scratches at different radial positions. The wear data of this study validate and analytical model of thermoelastic seal face deflections. The data also show that wear rates decrease with test time.

Experimental verification of thermoelastic mechanical seal face deflection by Local Wear Measurements

Blister formation on carbon-graphite mechanical seal faces most commonly occurs in oil and hydrocarbon service, with higher viscosity oils, and with stop-start cycling. Blisters form unexpectedly, often with catastrophic results. In this study, an experimental apparatus that closely simlates field conditions was used to form blisters onfive different grades of carbon-graphite seal faces. The tests showed that blisters form at the instant of initial shaft rotation. Significantly more blisters form as the viscosity of the oil between the seal faces increases when chilled. The blisters are located randomly around the seal face and not in regular patterns. The authors conclude that blister formation is a mechanical process through which a shallow subsurface crack is formed by shear forces acting at the carbon-graphite seal face.

Deborah A. Wilde

Papers

The effect of oil type on blister formation in carbon-graphite mechanical seals©

The Detection and Characterization of Blisters On Carbon-Graphite Mechanical Seal Faces

Experimental verification of thermoelastic mechanical seal face deflection by Local Wear Measurements

The mechanism of blister formation on carbon-graphite mechanical seal faces