Gray Cast Iron Disc Research Articles

Water suspended nanosized particles released from nonairborne brake wear debris

The paper addresses characterization of nanosized particles which may be potentially mobilized from nonairborne brake wear debris when being suspended in the water environment. Wear particles were generated in a fullscale automotive brake dynamometer simulation using a model low metallic friction composite and a gray cast iron disc. The three types of samples were analyzed: (a) nontreated wear debris, (b) wear debris particles dissolved in water and (c) filtered suspension of dissolved wear debris particles. Samples were subjected to a combination of analyses (XRD, TEM, SEM with EDS, Raman microspectroscopy and vibration magnetometry). Raman microspectroscopy revealed the presence of Fe2O3, Fe3O4, BaSO4, CaCO3, MoS2, graphite and amorphous carbon in the wear debris samples. The TEM analysis of particles in water suspension proved that the nanosized particles are released into water. Barite particles were detected in the water suspension by Raman microanalysis most often. The prepared filtered suspension exhibited magnetic character which is probably related to the presence of magnetic forms of iron and iron oxides.

Layered structure of friction films revealed by the comparison between multi-energy X-ray microanalysis and Monte Carlo simulations

Multi-energy X-ray spectra were acquired on friction films formed on semi-metallic brake pads rubbed against grey cast iron discs in friction tests at low and high speed, performed in a full scale bench dynamometer. The amount of X-rays generated with electrons in the same energy range as in the experimental measurements was calculated with Monte Carlo simulations performed with CASINO software, on structures of multi-layered and mixed phase films. The comparison of the qualitative behavior of the experimental peaks with results from the simulations enabled conclusions on layering, mixing, and thickness of the measured structure and revealed a layered structure on some friction films.

Tribological Properties of Gray Cast Iron/ AISI 52100 Steel Contacts when Lubricated with Fluorosilicone Oils as Additives

Abstract. Two fluorosilicone oils as additives were evaluated using an Optimol SRV reciprocating friction and wear tester by gray cast iron disc against AISI 52100 steel ball at 20 N and sliding speed of 0.20 m/s, respectively. The morphologies of worn surface of the disc were examined using a scanning electron microscope (SEM). In addition, the elemental compositions and chemical states of several typical elements on the worn surfaces of the gray cast iron discs were examined by means of X-ray photoelectron spectroscopy (XPS). Results indicate that PAO(Poly-alpha-olefin)+F-Si-E exhibite excellent tribological properties. This is partly attributed to material properties and tribological reaction between the lubricant and the sliding surface.

A Pin-on-Disc Study Focusing on How Different Load Levels Affect the Concentration and Size Distribution of Airborne Wear Particles from the Disc Brake Materials

Airborne wear particles originating from disc brakes are one important contributor to the concentration of airborne particles in urban environments. It is therefore of interest to improve the knowledge of these particles. The purpose of this article is to investigate the concentration and size distribution of the airborne wear particles generated from the contact between a low-metallic pad material and a grey cast iron disc at different load levels. This is done on model level with a pin-on-disc machine that allows the cleanliness of the air surrounding the test specimens to be controlled, and thus the airborne portion of the wear particles to be studied separately. The concentration and size of airborne wear particles were measured online during testing with four particle instruments. In addition, airborne wear particles were collected on filters during the tests and afterward analysed using SEM. Trimodal size distributions with peaks around 280, 350 and 550 nm were registered during running-in for all load levels. After running-in bimodal size distributions with peaks around 350 and 550 nm were registered for all load levels with the exception of the highest load level where multimodal size distributions were registered. At the two highest load levels the concentration of ultrafine/fine particles showed an increase up to a factor hundred indicating a change in wear mechanism. SEM images show ultrafine, fine and coarse airborne wear particles.

Tribological properties of grey cast iron lubricated using organic compounds containing Mo and ZnDTP additives

ABSTRACTThe lubricating effectiveness of organic compounds containing Mo and ZnDTP in different ratios in poly‐alpha‐olefin (PAO) was investigated using an Optimol SRV‐IV (Optimol Instruments, Munich, Germany) reciprocating friction and wear tester. The morphologies of the worn surfaces were observed using a scanning electron microscope with energy‐dispersive X‐ray spectroscopy. The chemical states of several typical elements on the worn surfaces of grey cast iron discs were examined by means of X‐ray photoelectron spectroscopy (XPS). The results indicated that the grey cast iron discs exhibited different friction‐reducing and wear‐resistance capabilities when lubricated with PAO containing MoDTP and ZnDTP additives in different ratios. The lowest frication coefficient is only 0.072. XPS analyses indicated that ZnDTP + MoDTP and ZnDTP + MoDTC formed different chemical products. Copyright © 2012 John Wiley & Sons, Ltd.

Investigation of the dynamic response in a dry friction process using a rotating stick–slip tester

In this paper, the friction stability of brake materials is investigated by means of a rotating stick–slip tester. Experimental results are compared with a computational model implemented in Simulink. The main goal of this work is to find out how vibrations induced by friction are related to mechanical system parameters such as inertia (mass), stiffness, damping and sliding speed. At the same time, a computational model is developed in order to analyse the dynamic response of a dry friction process at different conditions. A friction sample with nominal contact area of 254 mm2 was subjected to sliding against a gray cast iron disk. The sliding speed was varied between 0.28 and 10 mm/s, while the normal load was kept constant (400 N, equivalent nominal pressure 1.57 MPa). Moreover, tests were carried out in three different damping values and two different stiffnesses. Experimental results show typical stick–slip behaviour for the lowest speeds while for the highest speeds stick–slip disappears and smooth sliding prevails. The computational model can be used to evaluate the dynamic response in dry friction process, as far as static/dynamic coefficient of friction of the mating materials are known as well as the mechanical characteristics of the system.

Uniform Design of Optimizing Formulation of Friction Materials with Composite Mineral Fiber (CMF) and Their Friction and Wear Behavior

In this work, the uniform design method was applied to arrange the experimental scheme for optimizing formulation of friction materials. The friction and wear of the friction materials based on the optimized formulation was carried out on a constant speed friction tester (JF150D-II), using pad-on-disc contact mode against gray cast iron disc. The worn surfaces of the friction materials were examined by scanning electron microscopy (JSM5310) and the friction mechanism was discussed. The results showed that the uniform design method was appropriate for finding the optimum formulation of the friction materials with better properties. Compared with two conventional friction materials, the friction materials based on the optimized formulation possessed higher and stable friction coefficient and higher wear resistance, even at the disc temperature of 350°C. The adhesion, strain fatigue and abrasive wear were the main wear mechanisms of the friction materials. Tribo-chemical phenomenon and plastic deformation existed on the worn surface layer.

Tribological properties of Fe7Mo6-based-alloy lubricated with poly-alpha-olefin containing PN additive

Tribological properties of Fe–Mo type disk specimens were investigated against ASTM 52100 steel balls under the lubrication of poly-alpha-olefin (PAO) and PAO containing 1.5mass% alkyl-phosphonic acid-triazole-methanamine (PN additive). Both the Fe7Mo6-based alloy and Mo disk specimens exhibited lower friction and lower wear rates than the Fe and gray cast iron disk specimens under the lubrication of PAO. The friction coefficients of the Fe7Mo6-based alloy disk specimens were reduced to 0.07 by adding 1.5mass% PN additive to PAO. No wear volume loss was observed on the Fe7Mo6-based alloy disk specimens when they were lubricated with PAO containing 1.5mass% PN additive.

Tribological performance of PTFE-based coatings for air-conditioning compressors

Research on coatings in environments simulating compressor conditions, especially in a carbon dioxide (CO 2) environment, has been limited. In this study, polymeric, PTFE-based coatings were investigated for use in air-conditioning compressors. Tribological experiments were performed to simulate piston-type compressors as well as swash plate compressors. Specifically, the tribological contact at the connecting “rod-wrist” pin interface of a piston-type compressor and the “shoe-disk” interface of a swash plate compressor were simulated. Machined 52100 steel wrist pins from a piston-type compressor and 52100 rounded steel pins, referred to as shoes, from a swash plate compressor were used. In both cases the counterparts were gray cast iron disks coated with three commercially available PTFE-based coatings, namely, DuPont® 958-303, DuPont® 958-414 and Whitford Xylan® 1052. These coatings were tested in CO 2 environment, while testing was also performed in ambient air, and R410a, a common hydrofluorocarbon refrigerant, and the results were compared with a diamond-like-carbon (DLC) coating. The PTFE-based coatings showed low friction characteristics and high load carrying capacity and it was found that unlike the DLC coating they were not greatly affected by the testing environment. There was a significant increase in wear of the coatings under high contact pressures, however, it was shown that the wear debris generated acted as a third-body lubricant with a beneficial role in the overall wear performance. Due to their excellent tribological behavior under a range of experimental conditions, the coatings tested in this work could find use in compressor systems and other engineering applications.

A new family of low wear, low coefficient of friction polymer blend based on polytetrafluoroethylene and an aromatic thermosetting polyester

AbstractTo improve the wear resistance of polytetrafluoroethylene (PTFE), a crosslinked aromatic thermosetting polyester (ATSP) has been blended directly with PTFE. Cured ATSP powder which was directly synthesized as a cured powder form was used for this application. Because of the similar processing temperature range of cured ATSP and PTFE, composites within the entire composition range were successfully prepared by blending these two powders using a hot press. Tribological pin‐on‐disk tests (composite pins sliding against gray cast iron disks) showed improvement on friction coefficient of all composites and much less wear than pure PTFE. The composites survived at contact pressures of 7 MPa, which is higher than either pure PTFE or pure ATSP could sustain. With an increase in the amount of ATSP in the composites, storage modulus, and glass transition temperature were higher, and the wear resistance was enhanced. SEM images helped provide explanations for the unusually low mean wear rates that were observed for these composite samples. Copyright © 2008 John Wiley & Sons, Ltd.

Tribological Properties of MoS<sub>2</sub>-Coated Gray Cast Irons with Some Different Matrix Phases under the Boundary Lubricating Conditions

In this study, Fe-2.0Si-4.6C (mass%) gray cast iron disk specimens with three different matrix phases were coated with MoS2 using pressure spraying, and the friction and wear properties of the specimens were investigated against AISI52100 steel and polytetrafluoroethylene balls under the lubrication of oil using an Optimol SRV friction tester. When AISI52100 steel balls were used as the paired material, all of the MoS2-coated gray cast iron specimens showed lower friction coefficients and higher wear resistance than the non-coated disk specimens. On the other hand, MoS2-coated gray cast iron specimens exhibited higher friction coefficients than non-coated disk specimens for the most part, when polytetrafluoroethylene balls were used as the paired material.

The effect of Al 2O 3 on the friction performance of automotive brake friction materials

This study consists of two stages. In the first stage, bronze-based break linings were produced and friction-wear properties of them were investigated. In the second stage, 0.5%, 1%, 2% and 4% alumina (Al 2O 3) powders were added to the bronze-based powders and Al 2O 3 reinforced bronze-based break linings were produced. Friction–wear properties of the Al 2O 3 reinforced samples were aslo investigated and compared to those of plain bronze-based ones. For this purpose, friction coefficient and wear behaviour of the samples were tested on the grey cast iron disc. The hardness and density of the samples were also determined. Microstructures of the samples before and after the sintering and the worn surfaces of the wear specimens were examined using a scanning electron microscope (SEM). The sample compacted at 350 MPa and sintered at 820 °C exhibited the optimum friction–wear behaviour. With increase in friction surface temperature, a reduction in the friction coefficient of the samples was observed. The lowest reduction in the friction coefficient with increasing temperature was for the 2% and 4% Al 2O 3 reinforced samples. The SEM images of the sample indicated that increase in Al 2O 3 content resulted in adhesive wear. With increase in Al 2O 3 content, a reduction in mass loss of the samples was also observed. Overall, the samples reinforced with 2% and 4% Al 2O 3 exhibited the best results.

Wear behaviour of A356/25SiC p aluminium matrix composites sliding against automobile friction material

In the present paper, the wear behaviour of aluminium metal matrix composite (Al MMC) sliding against automobile friction material has been compared with the conventional grey cast iron. The wear tests have been carried out on a pin on disc machine, using pin as brake shoe lining material and discs as A356/25SiC p Al MMC and grey cast iron materials. Pins of 10 mm diameter have been machined from a brake shoe lining of a commercial passenger car. The grey cast iron disc has been machined from a brake drum of a commercial passenger car. The Al MMC disc has been manufactured by stir casting technique using A356 aluminium alloy and 25% silicon carbide particles and machined to the required size. The friction and the wear behaviour of Al MMC, grey cast iron and the semi-metallic brake shoe lining have been investigated at different sliding velocities, loads and sliding distances. The worn surfaces and sub-surface regions of MMC, the cast iron and the lining have been analysed using optical micrographs. The present investigation shows that the MMCs have considerable higher wear resistance than conventional grey cast iron while sliding against automobile friction material under identical conditions. A gradual reduction of friction coefficient with increase of applied load is observed for both cast iron and Al MMC materials. However, in all the tests it is observed that the friction coefficient of Al MMC is 25% more than the cast iron while sliding under identical conditions. The wear of the lining material has been observed more when sliding against MMC disc because of the ploughing of the lining material by the silicon carbide particles. The wear grooves formed on the lining material while sliding against MMC and cast iron have been analysed using optical micrographs.

Experimental device for the observation of rubbing surfaces during braking tests

AbstractThis paper introduces an experimental device, developed at the Laboratoire de Mécanique de Lille, specially designed for application in braking tests. The purpose of this device is to monitor the course of events on the rubbing surfaces during simulated braked stops and, in particular, the life and the dynamics of the third body. The usefulness of the device is demonstrated by the results of braking experiments performed on a grey cast iron disc for two different energies. These first experimental results show that the technique provides efficient and exploitable observations of tribological phenomena occurring on the wear‐track scale as well as on the microscopic scale. Copyright © 2006 John Wile & Sons, Ltd.

The mechanism of changes in the surface layer of grey cast iron automotive brake disc

The aim of the study was to create a model, describing the run of tribological processes in the surface layer of grey cast iron automotive brake discs. Grey cast iron discs mating with non-asbestos organic brake pads were chosen for the investigations, as the most widely used materials in car brakes. Samples for surface analysis were prepared from disc operating in stand and road conditions. Stand tests were pin-on-disc kind. Operating parameters for the stand tests were chosen on the basis of results of our earlier research. Topography of brake disc surface was evaluated by surface roughness measurements. The surface layer was examined with use of metallography and scanning electron microscopy. In order to differentiate structures of grey cast iron brake discs SE and BSE modes were used in scanning electron microscopy. Chemical investigations of samples were done by X-ray analysis linked with SEM. Studies showed influence of grey cast iron structures on tribological processes taking place in a brake friction pair. The surface layer of grey cast iron discs was described and features and functions of separated structures were presented. On the basis of the obtained results a physical model of friction mechanism was created. Special attention was paid to the influence of graphite on the run of tribological processes and mechanism of compaction and removal of wear debris.

Interface pressure distributions and thermal contact resistance of a bolted joint

The paper studies interface pressure distributions and thermal contact resistance (TCR) of a large automotive bolted joint. The research was initiated by the need to determine accurately conductive heat dissipation from a commercial vehicle disc brake. The main area of interest was the conduction between the grey cast iron disc and the spheroidal graphite cast iron wheel carrier. The bolt clamp forces and interface pressure distributions were investigated theoretically and experimentally. Finite-element analyses and pressure-sensitive paper experiments provided very similar interface pressure distributions. TCR change with interface pressure was studied experimentally, by conducting numerous temperature measurements. The derived linear relationship is of generic nature, enabling the calculation of the TCR for a variety of engineering bolted joints, over a wide range of interface pressures.

Scuffing of cast iron and Al390-T6 materials used in compressor applications

Scuffing can lead to catastrophic failure in engineering components, but the surface mechanism that leads to scuffing is not well understood. In this experimental study, the surface and subsurface changes on gray cast iron and Al390-T6 were investigated under starved lubrication (a mixture of R410A refrigerant combined with a polyolester lubricant) and pure sliding. Controlled tribological experiments were conducted using a high-pressure tribometer to simulate the contact conditions found in typical air conditioning compressors. Tribological tests were conducted on several sets of tribo-pairs consisting of gray cast iron disks and gray cast iron pins, for periods of 25, 50, and 75% of the time-to-scuff in order to investigate the progression of surface and subsurface changes leading to scuffing. The evolution of the chemical composition in the topmost surface layer of the disks was investigated as the disk/pin tribo-pairs progressed towards scuffing. Important changes in chemical composition were observed on the disks that had scuffed. Specifically, a marked decrease in manganese compounds was measured, which indicates a significant loss of the protective coating that was applied to the disks. Vickers microhardness tests were also performed on the disks at all stages, and showed a reduction in the means of hardness measurements as the disk neared the scuffed stage, in agreement with other studies. Similar scuffing experiments were also performed with tribo-pairs of Al390-T6/52100 steel; surface and subsurface changes were also characterized using chemical analysis and cross-section scanning electron microscope (SEM). In this case, depletion of silicon, which is embedded in the aluminum matrix to increase the hardness of the alloy compounds, was observed at scuffing. This observed reduction in hardness not only agrees with the cast iron hardness study, but also was consistent with the chemical analysis of the cast iron where a chemical component associated with hardening is depleted at the instance of scuffing.

The effect of metal fibers on the friction performance of automotive brake friction materials

This study investigates the effect of different metallic fibers upon friction and wear performance of various brake friction couples. Based on a simple experimental formulation, friction materials with different metal fibers (Cu, steel, or Al) were fabricated and then evaluated using a small-scale friction tester. Two different counter disks (gray cast iron and aluminum metal matrix composite (Al-MMC)) were employed for friction tests. The friction tests were carried out at two different temperature ranges: ambient and elevated temperatures. Results from ambient temperature tests revealed that the friction materials with Cu fibers showed a pronounced negative μ– ν (friction coefficient versus sliding velocity) relation when the friction material was rubbed against gray cast iron disks, implying that stick–slip may occur at low speeds. The negative μ– ν relation was not observed when the friction material with Cu fibers was rubbed against the Al-MMC counter surface. On the other hand, elevated temperature tests showed that the friction material with Cu fibers exhibited better fade resistance than the others. The test results also showed that the friction material with steel fibers was not compatible with Al-MMC disks due to severe material transfer and erratic friction behavior during sliding at elevated temperatures.

Characteristics of wear particles produced during friction tests of conventional and unconventional disc brake materials

Recent attention to the improvement of line-haul truck brake effectiveness, to compensate for lowered aerodynamic drag and to increase road safety, has prompted the US Department of Energy to support several projects aimed at the development of lightweight, high-performance friction materials. Using a specially designed, sub-scale disc brake testing system, a series of experiments was conducted to study the friction, wear, and frictional heating characteristics of both conventional and unconventional candidate disc brake materials. The selected sliding speed (11.0 m/s) was comparable to that experienced by a commercial disc brake surface on a truck travelling 60 miles/h (96.6 km/h). Material combinations included a commercial friction material on a gray cast iron disc, a commercial friction material on an aluminum metal matrix composite disc, a commercial friction material on a cast iron aluminide (Fe 3Al) alloy disc, and a carbon/silicon carbide material pad on a disc of similar composition. An adhesive extraction method was used to remove the loose wear particles from the surfaces of the test discs. The characteristics of brake material wear particles differed significantly between the four sliding material combinations studied and are correlated with both surface roughness changes and wear modes.

The role of friction film in friction, wear and noise of automotive brakes

A brake system must provide high and stable friction, low wear and noise- and vibration-free performance for reasons of safety, comfort and durability. These performance characteristics can be influenced by the friction film (glaze) formed on the sliding surfaces of the brake rotor and pads. This investigation was undertaken to study friction film formation and destruction between a semimetallic friction material formulation and a gray cast iron disk, and its influence on passenger car disk brake behavior. Brake rotor surface roughness, the ease or difficulty of friction film formation, its formation mechanism, its effect on friction and wear, and brake squeal are discussed.