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Article
Publication date: 1 April 1980

P.K. ROHATGI and C.C. PAI

Seizure resistance of the cast graphite particle‐aluminium composite alloys, containing graphite particles of varying sizes has been studied using a Hohman wear tester…

Abstract

Seizure resistance of the cast graphite particle‐aluminium composite alloys, containing graphite particles of varying sizes has been studied using a Hohman wear tester. The size of the spheroidal graphite particles was varied from 30 µm to 400 µm, and in one case 80 µm size flake graphite was used to observe the effect of shape of graphite. When the graphite content of graphitic aluminium alloys is more than 2 per cent, these alloys can be self‐mated under condition of boundary lubrication without seizing. The size and shape of the graphite particles had no significant effect on the seizure resistance of these alloys, in the range of conditions investigated in this study. This is attributed to the extensive deformation and fragmentation of graphite due to the low yield strength of the aluminium matrix and the low flow stress of the graphite particles. During wear, the deforming aluminium matrix accentuates the deformation and fragmentation of subsurface graphite particles and causes them to come to the mating surface, thus providing continuous lubrication and preventing seizure. Even after a short run‐in period, a continuous layer of graphite is observed on the mating surfaces of graphite particle‐aluminium composite alloys. This layer persists even after extensive wear deformation.

Details

Industrial Lubrication and Tribology, vol. 32 no. 4
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 13 March 2007

C. Gomez‐Garcia, M.E. Rodríguez, V.M. Castaño and A. Herrera

The purpose of this paper is to know the effect of graphite particles distribution on wear behavior of ingots of an aluminium‐graphite, Al‐Gr(p), composite.

Abstract

Purpose

The purpose of this paper is to know the effect of graphite particles distribution on wear behavior of ingots of an aluminium‐graphite, Al‐Gr(p), composite.

Design/methodology/approach

By SEM and optical microscope, it was observed that the graphite particles were entrapped and placed at different regions of the aluminium ingots as they were cooled under three different cooling rate during solidification, mantaining 4.5 wt% of graphite content. Size of particles entrapped, were measured at three different region of the ingots.

Findings

Smaller size of graphite particles distribution were found in regions where the cooling rate was higher, while bigger size were located in regions where the cooling rate was lower, this phenomenon could improve the wear resistant performance found in ingots containing smaller graphite particles.

Research limitations/implications

A suitable dispersion of small graphite particles entrapped into a fine structure of the aluminium‐graphite composite as a result of high cooling rate while casting, could be extended to another processes for future researches.

Practical implications

This material could be used in sliding mechanical pieces improved by a uniform dispersion of small particles inside.

Originality/value

The improvement of wear behavior could be succeeded by dispersion of smaller graphite particles into the ingots, influenced by a higher cooling rate, and maintaining the weight fraction content of reinforcement.

Details

Industrial Lubrication and Tribology, vol. 59 no. 2
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 20 September 2021

Jared Allison, John Pearce, Joseph Beaman and Carolyn Seepersad

Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The…

Abstract

Purpose

Additive manufacturing (AM) of thermoplastic polymers for powder bed fusion processes typically requires each layer to be fused before the next can be deposited. The purpose of this paper is to present a volumetric AM method in the form of deeply penetrating radio frequency (RF) radiation to improve the speed of the process and the mechanical properties of the polymer parts.

Design/methodology/approach

The focus of this study was to demonstrate the volumetric fusion of composite mixtures containing polyamide (nylon) 12 and graphite powders using RF radiation as the sole energy source to establish the feasibility of a volumetric AM process for thermoplastic polymers. Impedance spectroscopy was used to measure the dielectric properties of the mixtures as a function of increasing graphite content and identify the percolation limit. The mixtures were then tested in a parallel plate electrode chamber connected to an RF generator to measure the heating effectiveness of different graphite concentrations. During the experiments, the surface temperature of the doped mixtures was monitored.

Findings

Nylon 12 mixtures containing between 10% and 60% graphite by weight were created, and the loss tangent reached a maximum of 35%. Selective RF heating was shown through the formation of fused composite parts within the powder beds.

Originality/value

The feasibility of a novel volumetric AM process for thermoplastic polymers was demonstrated in this study, in which RF radiation was used to achieve fusion in graphite-doped nylon powders.

Details

Rapid Prototyping Journal, vol. ahead-of-print no. ahead-of-print
Type: Research Article
ISSN: 1355-2546

Keywords

Content available
Article
Publication date: 16 July 2020

Tomasz Matusiak, Arkadiusz Dabrowski and Leszek Golonka

The purpose of this paper is to present the properties of thick-film resistors made of novel pastes prepared from glass and graphite.

Abstract

Purpose

The purpose of this paper is to present the properties of thick-film resistors made of novel pastes prepared from glass and graphite.

Design/methodology/approach

Graphite-based resistors were made of thick-film pastes with different graphite-to-glass mass fraction were prepared and examined. Sheet resistance, temperature coefficient of resistance, impact of humidity and short-term overload were investigated. The properties of the layers fired in atmospheres of air at 550°C and nitrogen at 875°C were compared.

Findings

Graphite-based resistors with various graphite-to-glass ratios made possible to obtain a wide range of sheet resistance from single O/square to few kO/square. These values were dependent on firing atmosphere, paste composition and the number of screen-printed layers. The samples made of paste with 1:1 graphite-to-glass ratio exhibited the temperature coefficient of resistance of about −1,000 ppm/°C, almost independently on the firing atmosphere and presence of a top coating. The resistors fired in the air after coating with overglaze, exhibited significantly lower sheet resistance, reduced impact of humidity and improved power capabilities.

Originality/value

In this paper, graphite-based resistors for applications in typical high-temperature cermet thick-film circuits were presented, whereas typical graphite-based resistors were fabricated in polymer thick-film technology. Owing to very low cost of the graphite, the material is suitable for low-power passive circuits, where components are not subjected into high temperature, above the typical temperature of operation of standard electronic components.

Details

Circuit World, vol. 47 no. 2
Type: Research Article
ISSN: 0305-6120

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Article
Publication date: 5 August 2014

B.K. Prasad

The purpose of the paper is to assess the influence of the volume fraction solid lubricants like talc lead and graphite in oil separately and in combination towards…

Abstract

Purpose

The purpose of the paper is to assess the influence of the volume fraction solid lubricants like talc lead and graphite in oil separately and in combination towards controlling the sliding wear behaviour of a grey cast iron and understand the factors controlling the response of the material in a given set of experimental conditions.

Design/methodology/approach

The composition of the lubricating medium (oil) has been changed by dispersing 5 per cent graphite, talc and lead particles separately and in combination. Sliding wear tests were conducted on grey cast iron samples over a range of applied pressures. Parameters determined were wear rate and frictional heating. The wear behaviour of the samples was further substantiated through the features of wear surfaces, subsurface regions and debris particles. Material removal mechanisms and factors responsible for a specific response of the samples have also been analysed.

Findings

The wear rate increased with increasing applied pressure. Addition of graphite and lead to the oil separately or in combination brought about a reduction in the wear rate of the samples; talc and talc + lead produced a reverse trend. Temperature near the specimen surface increased with test duration and applied pressure. The test environment influenced the frictional heating in a manner similar to that of the wear rate. Adhesion and abrasion were observed to be the operating material removal mechanisms. Smearing of the solid lubricating phase and delamination resulting from cracking tendency also controlled the wear response.

Research limitations/implications

Oil is a very popular lubricant used in engineering applications involving friction and wear. Solid lubricants are used along with the oil. The nature, characteristics and content of the solid lubricants very much control the performance. Limited information is available pertaining to assessing the influence of the type and fraction of solid lubricants in the oil towards controlling the wear behaviour of cast irons (popularly known tribomaterials). The present study enables to understand the effectiveness of talc, lead and graphite in oil towards governing the wear characteristics of cast iron and analyse wear mechanisms and controlling parameters.

Practical implications

Graphite and talc are available in nature in abundance. Graphite is a popularly known solid lubricant, while talc is less explored. Lead is also well-known as a solid lubricant but poses health hazard in practice due to its toxic nature. The present study explores the lubricating capability of talc when mixed with oil separately or in combination with lead and graphite towards controlling the wear response of a grey cast iron. It enables to understand the factors responsible for the specific response of talc.

Social implications

Assessment of the lubricating potential of talc as a possible substitute to lead is important in view of the toxic nature of the latter. If successful, the exercise could enable to replace lead with talc.

Originality/value

The present manuscript is an original piece of the author's research work.

Details

Industrial Lubrication and Tribology, vol. 66 no. 5
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 1 August 2003

R. Fuentes, E. Rubio, C. Gómez, A. Herrera and V.M. Castaño

The wear behavior of a novel composite aluminum‐graphite composite prepared by simple powder metallurgy techniques is reported. Graphite powders were surface‐treated with…

Abstract

The wear behavior of a novel composite aluminum‐graphite composite prepared by simple powder metallurgy techniques is reported. Graphite powders were surface‐treated with copper to activate the powder surface and to improve the wettability of the graphite surface. The mixed Al‐C (7 percent, 5 percent, 3 percent, 1 percent y 0.5 percent C weight content) powders <100 μm were pressed at room conditions and then heat‐treated at 600°C. The tests showed improvements in wear resistance as the graphite content decreases, achieving the optimal behavior at 1 percent content.

Details

Industrial Lubrication and Tribology, vol. 55 no. 4
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 1 September 1966

The mechanical properties of carbon and graphite as structural materials have been improved considerably since the 1940s, and graphite equipment is widely used in chemical…

Abstract

The mechanical properties of carbon and graphite as structural materials have been improved considerably since the 1940s, and graphite equipment is widely used in chemical and other plant. Here is part of a talk given at the recent British industrial exhibition in Moscow by Dennis Hills, sales director of Powell Duffryn Chemical Engineering Ltd., who have specialised in carbon/graphite equipment under the trade name Delanium.

Details

Anti-Corrosion Methods and Materials, vol. 13 no. 9
Type: Research Article
ISSN: 0003-5599

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Article
Publication date: 4 February 2014

Aleksandar Vencl, Ilija Bobic and Blaza Stojanovic

Aluminium alloys are frequently applied in automotive and other industries, since they provide mass reduction. Besides positive effects, aluminium alloys have their…

Abstract

Purpose

Aluminium alloys are frequently applied in automotive and other industries, since they provide mass reduction. Besides positive effects, aluminium alloys have their shortcomings reflected, first of all, in inappropriate tribological properties of these materials. The aim of this research was to enable the production of cheap aluminium alloy matrix composite with favourable combination of structural, mechanical and tribological properties, focusing on the tribological behaviour.

Design/methodology/approach

The A356 Al-Si alloy was used as a matrix for producing metal matrix composites in compocasting process. Three different materials, in form of particles, were added to the matrix (Al2O3, SiC and graphite). Hardness and tribological properties (wear, friction and wear mechanism) of heat-treated (T6) samples were examined and compared. Tribological tests were carried out on ball-on-block tribometer under dry sliding conditions. Sliding was linear (reciprocating). Counter body was alumina ball. Average velocity was 0.038 m/s (max. 0.06 m/s), sliding distance was 500 m and normal load was 1 N.

Findings

The effect of two different ceramic particles and graphite particles on tribological properties of obtained composites was evaluated. Wear resistance of composites reinforced with SiC particles was higher and coefficient of friction was lower compared to the composite reinforced with Al2O3 particles. A dual hybrid composite (with SiC and graphite particles) showed the lowest value of wear rate and friction coefficient. Dominant wear mechanism for all tested material was adhesion.

Research limitations/implications

It seems useful to continue the work on developing hybrid composites containing soft graphite particles with A356 Al-Si alloy as matrix. The major task should be to improve particles distribution (especially with higher graphite content) and to explore tribological behaviour in diverse working conditions.

Originality/value

Particulate composites with A356 aluminium alloy as a matrix produced in compocasting process using ceramic particles (Al2O3, SiC) were investigated in many researches, but there are only few detailed analyses of dual composites (with the addition of ceramic and graphite particles). In some previous studies, it was shown that compocasting process, as relatively cheap technology, can obtain good structural and mechanical characteristics of composites. In this study, it was shown that even a low graphite content, under specified conditions, can improve tribological properties.

Details

Industrial Lubrication and Tribology, vol. 66 no. 1
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 16 September 2013

S. Venkat Prasat and R. Subramanian

The purpose of this paper is to explore the use of fly ash and graphite particles as low cost reinforcing materials for improved wear resistance, enhanced mechanical…

Abstract

Purpose

The purpose of this paper is to explore the use of fly ash and graphite particles as low cost reinforcing materials for improved wear resistance, enhanced mechanical properties and reduction in density of hybrid composites.

Design/methodology/approach

The AlSi10Mg/fly ash/graphite (Al/FA/Gr) hybrid composite was synthesised by stir casting method. The dry sliding wear and friction behaviour of hybrid composites were studied using pin-on-disc machine by varying parameters like load and weight fraction of fly ash, and compared with the base metal alloy and aluminium-graphite composite. The tests were conducted with a constant sliding speed of 2 m/s and sliding distance of 2,400 m.

Findings

The hybrid composites exhibit higher hardness, higher tensile strength and lower density when compared to unreinforced alloy and aluminium-graphite composite. The incorporation of fly ash and graphite particles as reinforcements caused a reduction in the wear rate and coefficient of friction (COF) of the hybrid composites. The improvement in the tribological characteristics occured due to the load carrying capacity of hard fly ash particles and the formation of a lubricating film of graphite between the sliding interfaces. The wear rates and COF of unreinforced aluminium alloy and composites increase with an increase in the applied normal load. The wear rates and COF of hybrid composites decrease with an increase in the fly ash content. 9 wt.% fly ash and 3 wt.% graphite reinforced hybrid composite exhibited the highest wear resistance and lowest COF at all applied loads. Abrasive wear and delamination were dominant in the mild wear regime of aluminium alloy and composites. Due to subsurface deformation and crack propagation, plate-like wear debris were generated during delamination wear. In the severe wear regime, the dominant wear mechanism was adhesive wear with formation of transfer layers.

Practical implications

It is expected that these findings will contribute towards the development of lightweight and low cost aluminium products with improved tribological and mechanical properties.

Originality/value

The wear and friction data have been made available in this article for the use of Al/FA/Gr hybrid composites in tribological applications.

Details

Industrial Lubrication and Tribology, vol. 65 no. 6
Type: Research Article
ISSN: 0036-8792

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Article
Publication date: 1 May 2009

B.K. Prasad

The purpose of this paper is to understand the sliding wear response of a cast iron as influenced by applied load and changing concentration of solid lubricant (graphite

Abstract

Purpose

The purpose of this paper is to understand the sliding wear response of a cast iron as influenced by applied load and changing concentration of solid lubricant (graphite) particles in oil lubricant, and operating material removal mechanisms in different sets of experimental conditions.

Design/methodology/approach

The sliding wear response of a grey cast iron has been examined as a function of test environment and load. Properties evaluated were wear rate, friction coefficient and frictional heating. The wear behaviour of the samples has been substantiated through the characteristics of their wear surfaces, subsurface regions and debris particles.

Findings

The wear rate and frictional heating increased with load while friction coefficient was affected in an opposite manner. The presence of oil lubricant led to a substantial improvement in wear response (in terms of decreasing wear rate, friction coefficient and frictional heating) while the presence of graphite particles in the oil lubricant proved to be still better. A critical content of graphite in the oil lubricant becomes most effective towards improving the wear response of the samples. Formation of dark patches on the wear surface, substantial subsurface deformation and fine debris led to improved wear response.

Research limitations/implications

The study enables one to understand the wear behaviour of a cast iron as influenced by the changing concentration of solid lubricant (graphite) particles in the oil lubricant. It also enables one to understand the operating material removal mechanisms responsible for the observed wear characteristics of the samples under varying test conditions. The investigation helps one to see that only a critical concentration of the solid lubricant particles in oil can lead to the best wear performance of materials.

Originality/value

From a practical standpoint, the observations made here gain importance from the fact that solid lubricants are added frequently in oil in engineering applications but it becomes imperative to understand that only a critical concentration can lead to the best wear behaviour of materials.

Details

Industrial Lubrication and Tribology, vol. 61 no. 3
Type: Research Article
ISSN: 0036-8792

Keywords

1 – 10 of over 2000