The dry wear of steels II. Interpretation and special features

1965 ◽  
Vol 257 (1077) ◽  
pp. 51-70 ◽  
Keyword(s):  
Oxide Film ◽  
Phase Change ◽  
Strain Hardening ◽  
Frictional Heating ◽  
Combined Effects ◽  
Phase Hardening ◽  
Special Effects ◽  
Severe Wear ◽  
Wear Rates ◽  
Mild Wear

The pattern of wear outlined in part I is interpreted in the light of further experiments which reveal that the change from severe wear to mild is governed by the hardness and state of oxidation of the surfaces. At light loads (< T 1) severe wear is inhibited by the combined effects of strain hardening and oxidation. At higher loads (> T 2) mild wear recurs primarily as a consequence of a change of phase induced by frictional heating. The hardness accompanying the phase change is great enough, initially, to suppress severe wear without the intervention of an oxide film. At loads immediately above T 2, however, the hardness tends to fall if rubbing is prolonged and oxidation is again essential to preserve the mild wear state. Sustained phase-hardening does not occur until a higher load, roughly coinciding with the T 3 transition, is attained and this finding has an important bearing on the influence of inert atmospheres. The onset of permanent hardening is not responsible for the divergent pin and ring wear rates at T 3, though the phenomena may be linked by the magnitude of the temperatures required to cause phase-hardening; the T 3 transition and the trend at higher loads have been identified as special effects associated with the thermal asymmetry of the rubbing system.

Predicting Bearing Performance of Filled Teflon TFE Resins

1967 ◽  
Vol 89 (1) ◽  
pp. 182-186 ◽  
Author(s):  
R. B. Lewis
Keyword(s):  
Surface Temperature ◽  
Bearing Surface ◽  
Temperature Dependent ◽  
Wear Factor ◽  
Severe Wear ◽  
Wear Rates ◽  
Surface Temperatures ◽  
Mild Wear ◽  
New Evidence

The wear rates of filled compositions of Teflon can be reliably predicted using an experimentally determined wear factor if the bearing pressure, velocity, temperature, and geometry are known. New evidence confirms the wear rates are directly proportional to pressure and velocity in both the mild wear regime and the severe wear regime, although the wear factors are much higher in the severe regime. The transition from mild to severe wear is pressure and surface temperature dependent and coincides with (but is not adequately described by) PV limit. An application factor is proposed to relate bearing surface temperatures to PV and geometry.

Paper 17: Basic Mechanisms of Wear

1967 ◽  
Vol 182 (1) ◽  
pp. 281-292 ◽  
Author(s):  
W. Hirst
Keyword(s):  
Severe Wear ◽  
Wear Rates ◽  
Mild Wear ◽  
Dry Conditions

This review deals with the wear of conforming and non-conforming surfaces, both lubricated and dry. It covers the scuffing, pitting and mild wear of lubricated surfaces, the range of wear rates in dry conditions, the patterns of wear and the main causes of severe wear.

Transition of Mild Wear to Severe Wear in Oxidative Wear of H21 Steel

2008 ◽  
Vol 32 (2) ◽  
pp. 67-72 ◽  
Author(s):  
S. Q. Wang ◽  
M. X. Wei ◽  
F. Wang ◽  
X. H. Cui ◽  
C. Dong
Keyword(s):  
Oxidative Wear ◽  
Severe Wear ◽  
Mild Wear

Model of Effect of Hot Gas Ingress on Temperatures of Turbine Disks

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
J. Michael Owen ◽  
Hui Tang ◽  
Gary D. Lock
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Flow Rate ◽  
Frictional Heating ◽  
Practical Importance ◽  
Combined Effects ◽  
Buffer Effect ◽  
Cooling Flow ◽  
Hot Gas ◽  
Radial Outflow

Ingress is the leakage of hot mainstream gas through the rim-seal clearance into the wheel-space between the rotating turbine disk (the rotor) and the adjacent stationary casing (the stator). The high-pressure rotor is purged by a radial outflow of air from the high-pressure compressor, and this cooling air is also used to reduce the ingress. The engine designer needs to predict the stator and rotor temperatures as a function of cooling-flow rate. The sealing effectiveness determines how much air is needed to reduce or prevent ingress; although there are numerous theoretical and experimental papers on the effectiveness of different seal geometries, there are few papers on the effect of ingress on the temperature of the rotating disk. This is an unsolved problem of great practical importance: under high stress, a small increase in metal temperature can significantly reduce operating life. In this paper, conservation equations and control volumes are used to develop theoretical equations for the exchange of mass, concentration and enthalpy in an adiabatic rotor–stator system when ingress occurs. It is assumed that there are boundary layers on the rotor and stator, separated by an inviscid rotating core, and the fluid entrained from the core into the boundary layer on the rotor is recirculated into that on the stator. The superposed cooling flow protects the rotor surface from the adverse effects of hot-gas ingress, which increases the temperature of the fluid entrained into the rotor boundary layer. A theoretical model has been developed to predict the relationship between the sealing effectiveness on the stator and the adiabatic effectiveness on the rotor, including the effects of both ingress and frictional heating. The model involves the use of a nondimensional buffer parameter, Ψ, which is related to the relative amount of fluid entrained into the rotor boundary layer. The analysis shows that the cooling flow acts as a buffer, which attenuates the effect of hot gas ingress on the rotor, but frictional heating reduces the buffer effect. The theoretical effectiveness curves are in good agreement with experimental data obtained from a rotor–stator heat-transfer rig, and the results confirm that the buffer effect increases as the sealing effectiveness of the rim seals decreases. The analysis quantifies the increase in the adiabatic rotor temperature due to direct frictional heating, which is separate from the increase due to the combined effects of the ingress and the indirect frictional heating of the entrained fluid. These combined effects are reduced as Ψ increases, and Ψ = 1 at a critical flow rate above which there is no entrained fluid and consequently no indirect heating of the rotor. The model also challenges the conventional physical interpretation of ingress as, in general, not all the hot gas that enters the rim-seal clearance can penetrate into the wheel-space. The ingress manifests itself through a mixing of enthalpy, which can be exchanged even if no ingested fluid enters the wheel-space.

The Fundamentals of Sliding Contact Melting and Friction

1989 ◽  
Vol 111 (1) ◽  
pp. 13-20 ◽  
Author(s):  
A. Bejan
Keyword(s):  
Phase Change ◽  
Friction Factor ◽  
Phase Change Material ◽  
Relative Motion ◽  
Temperature Difference ◽  
Normal Force ◽  
Frictional Heating ◽  
Contact Melting ◽  
Sliding Contact ◽  
Change Material

This paper focuses on the phenomenon of melting and lubrication by the sliding contact between a phase-change material and a smooth flat slider. The first part of the study considers the limit in which the melting is due primarily to “direct heating,” that is, to the temperature difference between the solid slider and the melting point of the phase-change material. It is shown that in this limit the relative motion gap has a uniform thickness and that the friction factor decreases as both the normal force and the temperature difference increase. The second part considers the limit where the melting is caused mainly by the frictional heating of the liquid formed in the relative motion gap. This gap turns out to have a converging-diverging shape that varies with the parameters of the problem. As the normal force increases, a larger fraction of the melt is pushed out through the upstream opening of the relative motion gap. Means for calculating the melting speed, the friction factor, and the temperature rise along the slider surface are developed.

TRIBOLOGICAL PROPERTIES OF THE CARBON AND NITROGEN-BASED HARD FILMS SLIDING AGAINST THE NICKEL-BASED SUPERALLOY

2020 ◽  
Vol 27 (08) ◽  
pp. 1950197
Author(s):  
X. L. LEI ◽  
B. X. YANG ◽  
Y. HE ◽  
F. H. SUN
Keyword(s):  
Tribological Properties ◽  
Cutting Tools ◽  
High Hardness ◽  
Wear Rates ◽  
Nickel Based Superalloy ◽  
Dlc Coating ◽  
Nano Crystalline ◽  
Debris Particles ◽  
Mild Wear ◽  
Super Alloy

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy. Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining.

An Experimental Examination of the Effect of Interface Cooling on Thermal Wear Mechanisms in Carbon Graphite

2005 ◽  
Author(s):  
Daryl S. Schneider ◽  
Lyndon S. Stephens
Keyword(s):  
Heat Sink ◽  
Elevated Temperatures ◽  
Frictional Heating ◽  
Operating Conditions ◽  
Stable Operation ◽  
Mechanical Seal ◽  
Premature Failure ◽  
Thermally Induced ◽  
Wear Rates ◽  
The Impact

Premature failure of mechanical seal components is often a result of the elevated temperatures at the sealing interface that arise due to frictional heating. The Heat Sink Mechanical Seal (HSS) is a new approach to interface cooling in which a micro heat sink is constructed within millimeters of the sealing interface. Coolant circulated through the highly structured pin fin region carries away the generated heat. This work investigates the impact of interface cooling on carbon wear rates for a tungsten carbide (WC) and carbon graphite material pair. Experiments are performed using a thrust washer rotary tribometer to simulate a mechanical seal operating in dry running conditions within and in excess of the PV limit for the material pair (17.5 MPa*m/s or 500,000 psi*ft/min). Results show stable operation of sealing components in harsh operating conditions as well as the potential to reduce the occurrence of thermally induced wear and failure.

Tribological behaviour of hypereutectic Al-Si automotive cylinder liner material under dry sliding wear condition in severe wear regime

2020 ◽  
pp. 135065012096461
Author(s):  
Ajith Kurian Baby ◽  
M Priyaranjan ◽  
K Deepak Lawrence ◽  
PK Rajendrakumar
Keyword(s):  
Surface Morphology ◽  
Wear Behaviour ◽  
Dry Sliding Wear ◽  
Dry Sliding ◽  
Liner Material ◽  
Severe Wear ◽  
Mild Wear ◽  
The Matrix ◽  
Pin On Disk ◽  
Silicon Particles

Hypereutectic Al-Si alloys are used as material for the engine block and cylinder liners in automobiles. Wear behaviour of hypereutectic Al-Si alloy system changes significantly with applied normal load in both mild wear and severe wear regime. Significant improvement in wear resistance can be obtained by exposing silicon particles through the chemical etching process. For Al-25% Si alloys, most studies are reported in mild and ultra-mild wear regime. In the present work, the wear of exposed silicon particles with varying load and speed in severe wear regime was investigated under the unidirectional sliding condition and bi-directional sliding condition using a pin-on-disk tribometer (POD) and a linear reciprocating tribometer (LRT), respectively. Rapidly solidified and T6 heat-treated Al-25Si alloy was polished and etched using 5% NaOH solution to expose the silicon particles. Experiments were carried out with normal loads varying from 40 N to 120 N in dry sliding conditions. Sliding speeds of 0.8 m/s and 1.5 m/s were applied for each load in case of a pin on disk tribometer whereas, in an LRT, the sliding velocities were 0.2 m/s and 0.45 m/s respectively for each set of the load. The surface topography was measured by means of a 3-D optical profilometer, and surface morphology was analyzed using SEM images. It was observed that at higher loads, larger Si particles were fractured and pushed into the matrix. Fractured silicon particles, along with smaller particles, were embedded into the matrix, thereby increasing the silicon concentration in the wear region. The comparison of the experimental results of unidirectional and bi-directional sliding that reveal the change in surface morphology of silicon particles, the friction characteristics at the interface, variation of surface 3-D roughness parameters, the wear rate and wear mechanisms of Al-25% Si alloys are analyzed and reported in the study.

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