Severe Scuffing Research Articles

Power Loss and Damage Behavior of Gears Operating Under Loss of Lubrication

Abstract Geared turbofans need to withstand loss of lubrication due to inevitable off-design conditions. Additionally, the loss of lubrication specifications that have to be fulfilled are getting stricter. For a loss of lubrication event, today's geared turbofans are equipped with secondary oil supply systems. Their omission would reduce space and weight and, consequently, carbon emissions. However, this requires geared transmissions to withstand loss of lubrication events. In order to enable this, knowledge of the power loss and damage behavior of gears under loss of lubrication is required first. In this study, power loss and bulk temperature measurements of test gears under loss of lubrication on an FZG gear efficiency test rig are presented. Hertzian pressures in the pitch point up to 1723 N/mm2 and circumferential speeds up to 20 m/s were considered. The experimental results show the characteristics of increasing power loss and bulk temperatures under loss of lubrication depending on load and speed. At moderate operating conditions, no damage occurs within 20 s under loss of lubrication, whereas a load increase results in slight scuffing, and a speed increase results in severe scuffing. Oil centrifugation has a strong effect on the loss of lubrication performance. Additional experiments under reduced quantity lubrication demonstrate the impact of the remaining oil on the survivability of gears facing the loss of lubrication.

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

AbstractGeneral 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.

Dynamic pressure scuffing initiation of a grade 250 flake graphite cast iron

The dynamic contact pressures experienced at the ring-liner interface of an engine are difficult to replicate in laboratory based reciprocating tribometers utilising a sliding Hertzian line contact, not least due to wear of the mating surfaces. A grade 250 flake graphite cast iron flat plate test geometry was designed to allow dynamic contact pressures between 8 and 62 MPa experienced in a heavy-duty diesel engine liner to be achieved on a reciprocating tribometer during the compression and expansion stroke.A constant normal load of 311 N was applied by sliding at 25 mm stroke length in PAO4 at 15 Hz against a 52100 rectangular contact area (2 × 20 mm). The temperature was slowly increased at 4 °C/min to initiate scuffing between the mating surfaces. Severe scuffing initiated at 250.8 ± 2.6 °C for all specimens. The spatially resolved friction force and non-contact optical profilometry suggested scuffing did not always initiate in the region of the highest contact pressure, whilst electron microscopy revealed that subsequent to lubricant failure, a transient low friction iron oxide layer was formed prior to removal and catastrophic adhesive wear.

Variable pressure scuffing of a flake graphite cast iron diesel cylinder liner

A novel scuffing methodology was developed utilising variable specimen geometry to replicate numerically modelled top compression ring contact pressures (4–62 MPa) from a 12.8-litre heavy duty diesel engine as a function of stroke position. Scuffing of grade 250 cast iron was induced by reciprocating sliding (TE77) against a drip lubricated (PAO4) 52100 rectangular contact operating at 15 Hz and 311 N normal load by incrementing the temperature at 4°C per minute until a sharp rise in friction coefficient was observed. Scuffing initiation temperature was insensitive to dynamic contact pressure. Formation of an oxide ‘glaze’ layer resulted in friction coefficients as low as 0.03 prior to severe scuffing.

Microstructure, Microhardness and Tribological Properties of Bronze-Steel Bimetallic Composite Produced by Vacuum Diffusion Welding.

In this paper, a lead–bronze/steel bimetal composite was produced by vacuum diffusion welding technology. The microstructure, hardness and tribological properties under the dry sliding condition of the bimetal structured material were investigated and compared with two reference samples, i.e., lead–bronze and Mn/Si–brass. The wear mechanism of the three materials was also analyzed in detail. It was found that the bimetallic structure possessed the best wear resistance among the three samples. When paired with the ball bearing steel, the wear rates of the lead–bronze and Mn/Si–brass were 13 and 54 times higher than that of the bimetal composite. When paired with bearing steel, the wear rates of the two materials were 13 and 54 times higher than the bimetallic composite, respectively. This is because the steel layer served as a bearing layer to decrease the plastic deformation of the bronze layer. Furthermore, the lead can accelerate the formation of a dense hardened layer at the sliding interfaces to avoid subsequent wear of the bronze surface. Nevertheless, this hardened layer caused severe scuffing on the steel balls. Therefore, lead–bronze/steel structured material is recommended to match with hard counterface material, such as cemented carbide.

Investigation on the parameters optimization and sliding wear behaviors under starved lubrication of discrete laser surface hardened 25CrNi2MoV steel

The discrete laser surface hardening (DLSH) parameters of 25CrNi2MoV steel were synthetically optimized and employed to enhance the surface sliding wear resistance under starved lubrication. Results showed that the DLSH treatment changed the sample’s surface microstructures, local hardness and residual compressive stress. The proper surface quality and hardening depth can be obtained in the laser power range of 400–500 W. DLSH treatment delayed the occurrence time of severe scuffing failure and decreased the wear loss. The formed arc-shaped dimples in substrate zone between the hardened spots helped to reduce the coefficient of friction. Different matching strategies of laser power and irradiation time caused the differences of surface wear mechanism.

Effects of Jatropha lubricant thermo-oxidation on the tribological behaviour of engine cylinder liners as measured by a reciprocating friction test

Bio-lubricants have emerged as a potential and viable way to replace, totally or partially, mineral oils due to their effectiveness in the boundary lubrication regime for different applications, including, automotive engine operation. However, the effect of thermo-oxidation caused by the long-term use of the bio-lubricants on their tribological properties has been scarcely analysed. In this work, the effect of thermo-oxidation of Jatropha oil (JO), an engine mineral oil (EMO) and a blend made up of 80%vol. EMO and 20%vol. JO (B20) on the tribological behaviour of a simulated piston ring/engine cylinder liner interface was studied in reciprocating friction tests at 26 and 100 °C. The oils were thermally oxidized and characterized in terms of carbonyl compounds, depletion of ZDDP additives, changes in kinematic viscosity and viscosity index. Friction coefficients, wear rates and scar morphologies were assessed. Thermo-oxidation resulted in significant viscosity increases in JO compared to EMO and B20. Also, it generated increased friction coefficients for JO and B20. However, they were lower than those for fresh and aged EMO. EMO increased the wear rate after thermo-oxidation in contrast to JO. Smearing was generated using most oil samples while severe scuffing was only produced by using fresh JO at 100 °C.

Scuffing mechanisms of EN-GJS 400-15 spheroidal graphite cast iron against a 52100 bearing steel in a PAO lubricated reciprocating contact

Scuffing of the automotive piston ring on liner contact is likely to increase due to engine downsizing and the use of low viscosity engine oils to achieve greater fuel efficiency. This work investigated the scuffing mechanism of EN-GJS 400-15 spheroidal graphite cast iron caused by reciprocating sliding of a 52100 roller bearing element lubricated with PAO base oil.The contact was conditioned at 100N and 15Hz over a stroke of 25 mm at 180°C. Subsequently the load was incremented in 100N/min steps at 5min intervals until severe scuffing occurred, indicated by a rapid rise in the average friction coefficient. High speed friction was used to determine the onset of mild and severe scuffing. Stylus and 3D optical profilometery revealed that mild scuffing produced a smooth surface with small cracks compared to the severe scuffed surface which contained adhesive wear craters of 40µm in depth. Focused ion beam cross-sections of the mild scuffed surface and EDS analysis of the microstructure indicated that cracks were initiated by dross inclusions with a similar morphology to flake graphite. The transition to severe scuffing occurred at 700N when crack networks facilitated adhesive transfer of cast iron material to the counter-surface.

Effect of oil quality on electrostatic charge generation and transport

This paper presents an experimental investigation into the effect of lubricating oil quality on tribocharging. The work forms part of a larger investigation into the causes of electrostatic charging events detected prior to severe scuffing during base oil lubricated wear experiments. A variable speed spinning disc charger was used for measurements of tribocharging, whilst controlling the oil viscosity, temperature, ageing and disc surface roughness. The results are discussed with reference to interactions between the double layer and fluid boundary layers and shear stress which could lead to charge separation at the disc-oil interface. Viscosity and surface roughness have been shown to affect the tribocharging of a base oil in a direct relationship, while temperature effects indicate a maxima due to transportation-recombination competition. Ageing experiments indicate an increase in conductivity, which will eventually lead to an increase in charging ability. Charge sign inversion is discussed in relation to specific adsorption of charged species (additives) on the disc surface, the presence of oppositely charged impurities and the differential of adsorption and/or diffusion rates for the negatively and positively charged species within the oils.

COMPLICATIONS OF HIP ARTHROSCOPY

Complications associated with hip arthroscopy occur between 1.6% and 5%. Fortunately, with the greater understanding of the causes and advancements in techniques and equipment, the incidence is declining. Most of the complications were transient neuropraxias and fluid extravasations resulting in no permanent damage. Severe scuffing of two femoral heads and one case of avascular necrosis were considered serious and permanent, thereby resulting in a 0.5% rate in our series for significant complications.

Electrostatic monitoring of oil lubricated sliding point contacts for early detection of scuffing

Electrostatic sensors have been used to investigate scuffing events in oil lubricated sliding point contacts. A pin-on-disc and a reciprocating laboratory wear rig have been used for this investigation in a fixed ball-on-disc configuration. Electrostatic charging events have been detected up to 1200 s prior to severe scuffing and have been shown to coincide with microstructural changes in the contact and regions of increased wear. The experiments presented demonstrate that the electrostatic detection technology has the potential to be used as the basis of an on-line (real-time) machinery condition monitoring system.

Comparison of the wear behaviour of six bearing materials for a heavily loaded sliding system in seawater

A problem of severe wear occurred at the guidance system of a door of a sea-lock. The seawater immersed guidance was a linear system with aluminium bronze bearing material on stainless steel rail material. A satisfactory laboratory simulation of the wear behaviour of the guidance system was achieved by testing with large test specimens. Six bearing materials were tested. Nodular and lamellar cast iron suffered severe scuffing and cannot be used. Sintered graphite bronze shows a wear coefficient about six times smaller than the original aluminium bronze. Two plastics were tested: PETP and PA. PA has the best friction and wear characteristics and is suggested as bearing material for the sliding system.

Compositional changes in lubricated sliding metal surfaces related to seizure

AbstractThis paper presents an investigation into the mechanisms of failure in lubricated sliding metal contacts. Reciprocated sliding with cylinder‐on‐disc geometry was performed with three types of lubricants based on polyalphaolefin (PAO) oils and three sets of additives. The normal force and sliding speed were chosen to give partial scuffing or seizure within a few hours. The chemical surface films which form through reactions between additives in the lubricants and the metal surfaces were analysed by scanning electron microscopy and Auger electron spectroscopy, before and after the onset of seizure.It is concluded that all three oils formed a rigid surface film as a result of a combination of chemical and mechanical actions in the contact surface. Seizure was initiated by mechanical fatigue and disruption of the film which exposed the metal surfaces to severe scuffing. It Was Also Noticed that different additives gave different friction and wear properties to the contact system.

Experience With Piston and Piston-Rod Seals for High-Pressure Reciprocating Compressors Injecting Natural Gas on North Sea Production Platforms

Summary The need to restrict flaring of associated natural gas has emphasized the importance of reliability of high-pressure reinjection compressors installed on certain North Sea platforms. This paper reviews the contribution made by the development of piston and rod seals used on injection compressors, with reference to three important fields: Beryl, Statfjord, and Thistle. Early North Sea Reinjection Experience During 1977 the first associated natural gas was reinjected in the U.K. oil sector. This operation is performed by two-stage reciprocating compressors. Early experience with these compressors revealed that the piston and rod seals. which are subjected to pressures approaching 400 bar [40 MPa], were a major source of machine failures. These failures consisted of severe scuffing and wear between the bronze sealing elements (piston and packing rings) and the countersurface (liners and piston rods), causing erratic seal life, sometimes of only a few hours' duration, together with badly damaged liners and piston rods. The typical condition of used bronze piston rings is illustrated in Fig. 1, and the operating lives achieved with bronze seals are summarized in Table 1. The most serious consequence of this unreliability was its effect on continuity of oil production, and an immediate development program to eliminate such failures was begun by the platform operator in collaboration with the appointed seal manufacturer. Details of this development are presented, including an analysis of the causes of seal failures and measures taken to remedy them, with particular attention to seal material and design and to lubrication requirements. Field experience gained in the application of the modified seals is summarized in three case histories. details of which arc given in Tables 2 through 4, with comparative results listed in Table 5. Selection of Seal Material At the outset of this development program, a change to nonmetallic seal materials for both the piston rings and the rod packings was considered on the basis of a proprietary grade of filled polytetrafluoroethylene (PTFE), which had already been used successfully for packings and piston rings in various lubricated compressor installations, includingethylene primary compression to 350 bar [35 MPa],ammonia synthesis gas compression to 350 bar [35 MPa], andhydrogen compression in refinery service to 200 bar [20 MPa]. JPT P. 2294^

The Effect of Lubricants on Gear Tooth Surface Fatigue

This paper presents some of the results of a recent investigation on the effect of lubricants on gear tooth surface fatigue (pitting). The work described comprises the development of a laboratory test procedure for exploratory purposes, and the determination of the performance of a number of lubricants using this procedure. It was found that bulk lubricant viscosity, as measured by the conventional viscometric method, did not have a predominant effect on gear tooth surface fatigue. Examination of the development of scuffing and pitting on the gear teeth indicates that the initial incidence of scuffing and the initial incidence of pitting were unrelated. It was further noted that as pitting became advanced, severe scuffing of the pitted teeth would almost invariably result. On the other hand, there was no evidence that severe scuffing would lead to gear tooth pitting. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Toronto, Canada, October, 1957.