Friction characteristics of piston rings in a reciprocating engine

The performance of a reciprocating engine can be improved by reducing the friction between piston rings and cylinder liner, which significantly contributes to the mechanical friction losses of an engine. The friction force of a piston ring pack is calculated, based on hydrodynamic lubrication theory, for the piston rings. Calculations were carried out for three sets of conditions. Oil starvation is taken into consideration in the calculation of oil-film behaviour for a ring pack. The friction characteristics of piston rings are evaluated using the frictional mean effective pressure. The friction force of a piston assembly is measured experimentally by an improved floating liner method. The effects of lubricant viscosity and engine speed on friction characteristics are investigated by both calculation and experiment.     

Friction and wear characteristics of steel on rock under water and oil based lubricated sliding conditions

Abstract

In recent years, drilling extended reach wells have become more and more common in the petroleum industry to optimise the oil and gas production. Extended reach wells are defined as wells that have two times more horizontal step out than true vertical depth. High friction (frictional torque) and drag are two of the mechanical limiting factors while drilling longer horizontal wellbores. There are numerous methods and tools developed to lower the drillstring friction. Drilling non-circular wellbores is a new concept with potential to minimise the mechanical friction by reducing drillstring and sidewalls contact area. However, this will cause an increase of contact pressure owing to the reduced contact area between drillstring and the formation. This article presents results obtained from an experimental study pertaining to the friction behaviour using a pin on disc set-up with steel pin and granite disc in the presence of water and oil based lubricants. These tests have been designed to represent frictional contact conditions between a rotating steel drillstring and the wellbore wall at different contact pressures. Test results show that the friction coefficient decreases with an increase of contact pressure in wet condition for both water and oil based lubricants. It is also observed that the friction factor increased by adding sand and phyllite particles to the water based lubricant. Considering the wear scars, the friction coefficient shows reduction with increased contact pressure in all tests with and without particles for both water and oil based lubricants.     

Wear of aluminium bronze in sliding contact with lubricated stainless steel sheet material

Aluminium bronze, well known for its good sliding properties, is frequently applied as tool material in sheet metal forming (SMF) of stainless steel, e.g. for the production of washing, refrigeration and cooking equipment. The limited hardness of the material makes it, however, sensitive to tool wear that is: volumetric wear of the tool due to sliding contact with the sheet material. Conventional wear tests like the rubber wheel abrasion test or the Taber abrader test cannot be used to simulate the interaction of the tooling with lubricated sheet material. Dedicated tribo tests are therefore conducted with the slider-on-sheet test. The aim of the research is to measure the specific wear rate of aluminium bronze at SMF-like conditions. Experimental results showed a pronounced influence of lubricant selection and sheet material selection. The measured specific wear rate varied from 10⁻⁸ mm³/N m for a smooth stainless steel sheet quality to 10⁻⁶ mm³/N m for a rough surface quality.     

Friction of lubricated soft surface layers

Elastohydrodynamic lubrication of solids covered by a thin layer of material of low elastic modulus is studied theoretically and experimentally. The pressure and film thickness lie between the limits set by rigid and bulk elastic solids. The sliding friction shows a marked difference from that of rigid solids.     

Effects of surface texturing on friction and vibration behaviors of sliding lubricated concentrated point contacts under linear reciprocating motion

Friction and vibration behaviors of lubricated concentrated point contacts with surface texturing have been experimentally investigated under reciprocating motions. Ground, lapped and textured lapped flat surfaces are tested against polished ball surfaces. Coefficient of friction, surface temperature, electrical resistance and vibrations at the lubricated contacts have been measured and analyzed. In the presence of surface texture, the coefficient of friction reduces by 30% in some of the cases. Surface temperature distributions on reciprocating tracks have also been measured and compared. Vibrations associated with lubricated point contacts formed between textured surfaces/balls reduce significantly at resonance frequency in comparison to polished surfaces/balls.     

Tribological behavior of reciprocating friction drive system under lubricated contact

The dynamic friction and wear behaviors are investigated in reciprocating friction drive system using a 0.45% carbon steel pair. The effects of various operating parameters on the traction force, stick and slip time, and friction modes are examined under the lubricated contacts. Moreover, the critical operating conditions in classifying three friction modes are also established. Results show that the fluid friction induced by the shearing of lubricant dominates the variation of traction force and produces the positive slope γ at the first period of slip in the traction force–relative sliding velocity curve. The γ value decreases at higher driver speed during stick-slip motion due to the thicker fluid film and shear thinning effect. The γ value increases due to the asperity interactions as the friction region is transferred from stick-slip to sticking with normal load from 196 to 980 N. Furthermore, it is also found that the static friction force is independent of stick time for the tangential loading rate ranged from 1.12 to 16.8 s⁻¹. The transition region produces the severest wear under the different driver speeds, but the wear is insensitive to the friction regions and the severe wear only occurs at higher normal load due to the action of Hertzian contact.     

Friction behavior of lubricated zinc phosphate coatings

The aim of the present work is to elucidate the influence of lubricants on the friction behavior of zinc phosphated coatings and provide an explanation for the results in terms of physical–chemical interactions between lubricant and phosphate. The friction behavior was studied through a sliding wear test, with a conventional ball-on-disc configuration. Discs, made of AISI 1006 low carbon steel, uncoated and coated with zinc phosphate, were tested against bearing steel balls. A stearate sodium soap, paraffinic oil and both soap and oil were used as lubricants. The sodium stearate soap was found to have the best seizure resistance. The nature of the interfacial forces between the lubricant and surface has an important role in determining the friction behavior.     

Friction and wear of CuZn alloys against stainless steel

The friction and wear of CuZn alloys containing 8–57% Zn against an 18% Cr stainless-steel disc were studied by electron microscopy and Auger electron spectroscopy. The behavior of Zn in the surface played an important role in controlling the wear and friction properties of the alloys. With increasing zinc oxide the coefficient of friction decreased but the wear rate increased.Information is given about the concentration changes of Zn in the α-,β- and γ-phases with frictional contact and the changes are discussed in relation to the diffusion rate of Zn in the matrix.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Patterns of wear in reciprocating motion

Many cases of wear that are important in practice involve the reciprocating motion of one body over another. It is a common finding that the depth of the wear track on the second body approaches a maximum near the extremes of the travel of the first body. A simple theory suggests that, other things being equal, the depth of wear is inversely proportional to the velocity of motion of the contact across the second body. This simple theory obviously breaks down towards the extremes of the travel where the velocity approaches zero, and other factors must then taken into account.In this paper we present a theoretical treatment of the problem and describe its application to a specific case — that of a rig which simulates the essential features of the contact between a cam and a finger follower. Theoretical and experimental results are compared and reveal discrepancies that cannot be fully explained.     

Friction and wear behaviour of an Al-Si alloy against steel lubricated with N- and O-containing organic compounds

The friction and wear properties of an Al-Si alloy against AISI 52100 steel were investigated with a block-on-ring wear tester lubricated with a liquid paraffin base oil containing organic additive compounds, such as ethylenediamine, ethyleneglycol, ethanolamine, and N,N-dibutylethanolamine. The boundary film formed on the rubbed surface of the Al-Si alloy was then examined using FT-IR microscopy and XPS. The friction and wear tests revealed that ethylenediamine, ethanolamine and N,N-dibutylethanolamine additives provide good lubrication in the Al-Si alloy-on-steel system, especially N,N-dibutylethanolamine. FT-IR microscopy and XPS revealed the possible formation of a chemically stable five-ring complex of aluminium or silicon with diamine and ethanolamine.     

A study of Bioloxdelta subject to water lubricated reciprocating wear

Biolox^®delta is the latest commercial ceramic material for artificial hip-joint replacements manufactured by CeramTec AG, Germany. This zirconia toughened alumina composite employs several toughening mechanisms and has been successfully implanted over the past 8 years. Although extensive in vitro testing has been carried out for ceramic-on-ceramic artificial joints, the wear mechanisms that occur in Biolox^®delta are not fully understood, in particular, the role of the zirconia. Reciprocating sliding wear tests were undertaken in ultra pure water according to ISO 6474 using a ball-on-flat configuration. Loads were varied in the range of 0.5-4 N and the reciprocating frequency was varied through 8.3-11.7 Hz over a stroke length of 10 mm in order to construct the Stribeck curve. The Stribeck curve indicated that there were two lubrication regimes for these test conditions, namely full fluid-film lubrication and mixed lubrication. The worn surfaces were characterised in detail using scanning electron microscopy (SEM), atomic force microscopy (AFM) and focused ion beam (FIB) cross-section milling. Damage, which comprised dislocation flow, inter- and transgranular fracture, was limited to one grain depth below the worn surface. The zirconia grains distributed in the alumina matrix near the worn surface had almost completely transformed to monoclinic symmetry. The observations of surface damage accumulation are discussed in relation to the current understanding of the wear mechanisms of alumina based ceramics.     

Cutting characteristics in the end milling of stainless steel

A method is proposed for calculating the cutting characteristics in the end milling of stainless steel workpieces. The calculation is based on analysis of the parameters for the chip-formation zone and takes account of softening of the material under the action of the cutting temperature. The calculated tool life and the torque are approximated by polynomial equations, which may be used to calculate the constraints on milling and to optimize the machining conditions.     

Friction and wear characteristics of lead and its compounds filled polytetrafluoroethylene composites under oil lubricated conditions

The friction and wear properties of Pb, PbO, Pb₃O₄, or PbS filled polytetrafluoroethylene (PTFE) composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15 bearing steel were then investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling Pb, PbO, Pb₃O₄ or PbS to PTFE can greatly reduce the wear of the PTFE composites, but the wear reducing action of Pb₃O₄ is the most effective. Meanwhile, PbS increases the friction coefficient of the PTFE composite, but Pb and Pb₃O₄ reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of lead or its compounds filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by one order of magnitude. Optical microscope investigation of transfer films shows that Pb, PbO, Pb₃O₄ and PbS enhance the adhesion of the transfer films to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites creates some cracks on the worn surfaces of the PTFE composites; the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites, and this leads to deterioration of the friction and wear properties of the PTFE composites filled with lead or its compounds under higher loads in liquid paraffin lubrication.     

Scuffing of steel under boundary lubricated conditions

This research was conducted to examine whether a relationship exists between the true elastic limit of steel and its scuffing load measured under boundary lubricated conditions. Scuffing tests were carried out on a pin-on-disc machine using steel components which were heat treated to give differeing yield points. Yield point was also altered by testing at elevated temperature. The true elastic limits of steels in the same conditions as for scuffing tests were measured by a highly sensitive technique. True yield points are reported for EN8 steel in both soft and hard condition at room temperature and at 201°C. A difference in scuffing load for soft and hard specimens was measured for certain operating conditions giving some validation of the elastic limit hypothesis. Scuffing testing at elevated temperatures produced some unexpected results which do not allow a thorough proof of the hypothesis. These findings are discussed     

Hot working characteristics of S32760 super duplex stainless steel

Journal of Mechanical Science and Technology - Hot deformation behavior of S32760 super austenitic stainless steel was studied in the temperature range of 950 ∼ 1250 °C and strain rate...     

Friction and wear studies of an internally lubricated polyetherimide composite

Polyetherimide (PEI) is one of the latest generic high-performance engineering thermoplastics. PEI (developed by General Electric (USA) under the trade name ULTEM) is an amber and amorphous polymer with a heat distortion temperature between those of polyarylate resin and thermally stable crystalline polymers such as polyether-ether ketone (PEEK) and polyamideimide (PAI). It has excellent thermal, mechanical and electrical properties along with easy processability. In the work reported here, a wear-resistant formulated composite supplied by GEC (ULTEM 4001) was selected for tribological investigations on a pin on disc machine under unlubricated conditions, against mild steel. Analysis of the composite revealed that this grade contained PTFE (13–15%), which is the most promising polymeric lubricant. A very low and stable frictional coefficient was observed against moderately finished surfaces. However, its specific wear resistance (⋍10⁻¹⁴ m³/Nm) was comparatively lower than that of fibre-reinforced thermoplastics. The wear mechanism was found to be significantly dominated by the presence of PTFE. The friction coefficient was in the range of 0.2 and reduced to a still lower value (0.1) as the apparent contactpressure increased. Scanning electron microscopy was used to investigate the underlying wear mechanism. Film transfer of PTFE was observed to be the principal factor responsible for reduced friction.