Starved Lubrication Conditions Research Articles

Journal bearing performance under starved lubrication

The hydrodynamic performance of a journal bearing under starved lubrication conditions is studied theoretically and experimentally. When lubricant is supplied to a journal bearing from an oil groove at an insufficient oil flow rate, the hydrodynamic oil film cannot cover the full width of the bearing at the inlet of the convergent bearing clearance, and the covered width increases gradually with the decrease in film thickness in the circumferential direction. This phenomenon affects the static and dynamic performance of the journal bearing. The oil film boundary in the bearing clearance is calculated numerically for a constant load and a constant speed under the assumption of laminar, iso-viscous lubrication. Measurements are in good agreement with predictions. Some more calculations of journal centre loci are given.

Scuffing behavior of 390 aluminum against steel under starved lubrication conditions

The scuffing characteristics of 390-T6 aluminum–silicon alloy sliding against 52100 steel are examined under starved lubrication conditions. The evaluation is based on a shoe-on-disc geometry which simulates the plate/shoe contacts in an automotive air conditioning swashplate compressor. Four shoe geometries (flat shoe, crowned shoe, crowned shoe with a dimple at the center and crowned shoe with a groove) are tested against 390-T6 aluminum discs. All tests are conducted in a high-pressure tribometer (HPT) under R134a (tetrafluoroethane) environment with a base polyalkylene glycol (PAG) lubricant. The effects of degree of lubricant starvation, sliding velocity, geometry of contact, surface topography, and a tin coating on scuffing are evaluated. It is hypothesized that scuffing of 390-T6 Al alloy under starved lubrication conditions is due to macroscopic adhesions leading to plastic shearing of the bulk material.

Scuffing of Area Contacts Under Starved Lubrication Conditions

The scuffing behavior of 390-T6 and DHT3 aluminum alloys, Si-Pb brass and gray cast iron, sliding against 1018 carburized steel, is experimentally studied under starved lubrication conditions. The major emphasis of the study is on the 390-T6 aluminum alloy. All tests are conducted in a high pressure tribometer (HPT) under RI34a (tetrafluoroethane) environment with polyalkylene glycol (PAG) and polyolester (POE) lubricants to simulate failures of critical tribocontacts in refrigerant compressors. An area contact, pin-on-disc geometry, is used to examine the effects of degree of lubricant starvation, sliding velocity, materials, and lubricant/refrigerant mixtures on scuffing. The scuffing transitions characteristics of 390-T6 aluminum as a function of lubricant supply rate are also examined. The processes leading to scuffing and failure mechanisms are studied by examination of scuffed surfaces and subsurfaces. Based on the experimental observations, it is hypothesized that bulk material failure during scuffing is due to plastic shearing or smearing. Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

Laser cladding of cast aluminum–silicon alloys for improved dry sliding wear resistance

AA333 specimens were hardfaced with mechanically mixed Mn–Al bronze powder by laser cladding to investigate its possible use in a boundary lubricated sliding application for better wear resistance. The coatings needed to be more seizure resistant than the AA333 currently in use. Like other cast aluminum alloys, AA333 possesses a hard, silicon rich secondary phase which helps impart good wear properties. However, in starved lubrication conditions, the relative softness and low melting point of the Al-rich matrix can result in its scuffing and even seizure. The laser used was a 6 kW cw CO2 laser, in an oscillating beam process. The experimental group of coatings consisted of a 3×3 matrix of three process parameters—laser power, traverse speed, and powder feed. The coatings were mechanically sound, relatively free of small cracks and porosities, with a strong, tough metallurgical bond. The coatings were 3 to 4 times harder than the AA333 substrate matrix which was about 90 Vhn. Many wear specimens were prepared from the coatings for comparison with AA333 properties, and for property versus process parameter correlations within the experimental matrix of coatings. The coating microstructure was primarily single phase, consisting of fcc columnar-type grains of varying size produced by rapid and directional solidification, with a homogeneous distribution of the alloying elements in solid solution (by wt %: 75 Cu, 12 Mn, 8 Al, 3 Fe, 2 Ni). Analysis of coating microstructures was carried out using optical and scanning electron microscopy, x-ray energy dispersive spectroscopy, and x-ray diffractometry. The interface microstructure was found to contain α-Al (fcc) in the remelt layer and θ-CuAl2 (tetragonal). Tribological tests showed that the seizure resistance of the coatings was superior to AA333 in dry sliding tribological tests, though the wear rates of the coatings show some dependence on the process parameters. The coatings exhibited up to 1/3 the wear rate of the AA333 substrate under the same dry wear test conditions of 4.5 kg normal load at 600 rpm, 30.3 mm radius of sliding, simulating actual component operation. However, the major benefit of the coating is increased resistance to an abrupt, work-stopping failure by seizure. Necessary repair and replacement of parts as a result of seizure can be very costly. The wear mechanisms of coatings and substrate are discussed, as are the coating properties versus process parameters.

A disc‐on‐flat wear test under starved lubrication

AbstractThe ‘disc‐on‐flat’ system has been used for testing wear under starved lubrication conditions. The rotating discs were made of a carbon steel, the surface finish of the discs being ground. Some of the discs were treated by ‘vibrogrooving’, to form regular microrelief. The flat counterface was made of a ground copper alloy. An industrial oil was used as a lubricant in a one‐drop test procedure. Microreliefs of a non‐touching design with a relative groove area of 34% caused less wear than microreliefs of a touching type with a relative groove area of 50%, whereas the wear caused by the ground disc was high, with seizure after 200–250 m of sliding distance. A one‐drop disc‐on‐cylinder test also showed that the wear caused by discs with regular microrelief was considerably less than that caused by discs treated by conventional finishing (grinding, polishing).

Elastohydrodynamic Lubrication of Grease-Lubricated Rolling Bearings

The lubricant film thickness of grease-lubricated, cylindrical roller thrust bearings was measured, using a capacitance type displacement probe. For comparison, the same tests were also performed with the bearings lubricated with mineral oils. The film thickness and friction torque as a function of rotational speed were determined both under fully flooded and starved lubrication conditions. The test results show that the lubricant film thickness in grease-lubricated bearings is influenced by the base oil, and the thickener.

Elastohydrodynamic Lubrication of Elliptical Contacts for Materials of Low Elastic Modulus: II—Starved Conjunction

By using the theory and numerical procedure developed by the authors in earlier publications, the influence of lubricant starvation upon minimum film thickness in starved elliptical elastohydrodynamic conjunctions for low-elastic-modulus materials has been investigated. Lubricant starvation was studied simply by moving the inlet boundary closer to the center of the conjunction. The results show that the location of the dimensionless inlet boundary m* between the fully flooded and starved conditions can be expressed simply as m* = 1 + 1.07 [(Rx/b)2Hmin,F]0.16, where Rx is the effective radius of curvature in the rolling direction, b is the semiminor axis of the contact ellipse, and Hmin,F is the dimensionless mimimum film thickness for the fully flooded condition. That is, for a dimension-less inlet distance m less than m*, starvation occurs; and for m ≥ m*, a fully flooded condition exists. Furthermore, it has been possible to express the minimum film thickness for a starved condition as Hmin,S = Hmin,F [(m − 1)/(m* − 1)]0.22. Contour plots of the pressure and film thickness in and around the contact are presented for both the fully flooded and starved lubrication conditions. It is evident from the contour plots that the inlet pressure contours become less circular and that the film thickness decreases substantially as the severity of starvation increases. The results presented in this report, when combined with the findings previously reported, enable the essential features of starved, elliptical, elastohydrodynamic conjunctions for materials of low elastic modulus to be ascertained.