Tribological study of peroxide-cured EPDM rubber filled with electron beam irradiated PTFE powder

The aim of this work is the evaluation of the effects of electron beam modification of Polytetrafluoroethylene (PTFE) powder on the friction and wear properties of PTFE filled Ethylene-Propylene-Diene-Monomer (EPDM) rubber cured by a radical-initiated peroxide system. Friction and wear properties of EPDM vulcanizates were determined with the help of pin-on-disc tribometer in sliding contact with a steel-ball at room temperature without lubrication. PTFE powder was modified in atmospheric conditions with low (20 kGy) and high (500 kGy) irradiation doses using electron beam accelerator. The spectroscopic investigations reveal that the increasing concentration of reactive free radicals and functional groups with irradiation dose has a drastic influence on crosslinking efficiency due to their interference with peroxide radicals in curing process. As a result, non-irradiated and low-irradiated PTFE filled EPDM with higher crosslinking densities showed remarkably enhanced friction and wear properties. On the contrary, 500 kGy PTFE filled EPDM having significantly lower crosslinking density resulted in poor friction and wear characteristics. The apparent crosslinking density measured directly from the curing curves was found to be the most dominating parameter influencing friction, wear as well as the physical properties.     

Dry sliding wear behaviour of PTFE filled with glass and bronze particles

Abstract

The wear behaviour of polytetrafluroethylene (PTFE) filled with 25% glass and 40% bronze particles was studied on a pin on disc test rig. Solid lubricant composite materials were prepared by compression moulding technique. The wear parameters considered for the study were applied load, sliding speed and sliding distance. The experimental results indicate that the weight loss increases with increasing load, sliding speed and sliding distance, as expected. Sliding distance has more effect on weight loss followed by applied load. The 40% bronze+PTFE composite exhibits better wear resistance compared to other types. The dominant interactive wear mechanisms during sliding of PTFE and its composites are discussed in this paper.     

Friction and wear properties of metal powder filled PTFE composites under oil lubricated conditions

Four kinds of polytetrafluoroethylene (PTFE)-based composite, pure PTFE, PTFE+30vol.%Cu, PTFE+30vol.%Pb and PTFE+30vol.%Ni composite, were prepared. The friction and wear properties of these metal powder filled PTFE composites sliding against GCr15 bearing steel under both dry and lubricated conditions were studied using an MHK-500 ring-block wear tester. The worn surfaces of the PTFE composites and the transfer films formed on the surface of GCr15 bearing steel were examined using scanning electron microscopy (SEM) and optical microscopy respectively. Experimental results show that the friction and wear properties of the PTFE composites can be greatly improved by liquid paraffin lubrication. The wear of these PTFE composites can be decreased by at least 1 to 2 orders of magnitude compared with that under dry friction conditions, while the friction coefficients can be decreased by 1 order of magnitude, SEM and optical microscopy investigations of the rubbing surfaces show that metal fillers of Cu, Pb and Ni not only raise the load carrying capacity of the PTFE composites, but also promote transfer of the PTFE composites onto the counterfaces, so they greatly reduce the wear of the PTFE composites. However, the transfer of these PTFE composites onto the counterfaces can be greatly reduced by liquid paraffin lubrication, but transfer still takes place.     

Friction and wear of PTFE seal materials

Shaft seals made from polytetrafluoroethylene (PTFE) materials, called PTFE lip seals, have been successfully used for decades in the chemical industry. Owing to their chemical and thermal stability, PTFE lip seals are used instead of elastomeric lip seals in many automotive and hydraulic applications. This paper deals with the fundamental tribological properties and effects of filled PTFE materials employed in rotary shaft seals, mainly on the basis of experimental work done in the authors' laboratory. The tribological components of a sealing system and the main influences on the sealing function are briefly surveyed. The test methods and conditions used are also described. The experimental results show that the fillers used in the PTFE compounds, as well as the topography of the shaft, play a crucial role in fluid sealing.     

Friction and wear of PTFE composites at cryogenic temperatures

This paper presents investigations on the tribological behaviour of PTFE composites against steel at cryogenic temperatures. The results showed that the friction coefficient decreases with temperature down to 77 K, but did not follow a linear evolution further down to extreme low temperatures. It can be stated that the cryogenic environment has a significant influence on the tribological performance of the polymer composites. The effect of low temperatures was more clearly detected at low sliding speed, where friction heat is reduced. A change in wear mechanism from adhesive to abrasive was observed in this case. SEM and AFM analyses showed that the PTFE matrix composites investigated under these experimental conditions have transferred material onto the disc down to very low temperatures. Chemical analyses indicate the presence of iron fluorides.     

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.     

Friction and wear behavior of hybrid glass/PTFE fabric composite reinforced with surface modified nanometer ZnO

Nano-ZnO was successfully grafted with 2,4-toluenediisocyanate (TDI) and β-aminoethyltrimethoxylsilane (OB551) to avoid the agglomeration of nano-ZnO in composite. The hybrid glass/PTFE fabric composites reinforced with the untreated, OB551 and TDI modified nano-ZnO, respectively, were prepared by dip-coating of the hybrid fabric in a phenolic adhesive resin containing the nanoparticles to be incorporated and the successive curing. The friction and wear behaviors of various nano-ZnO reinforced hybrid glass/PTFE fabric composites sliding against AISI-1045 steel in a pin-on-disk configuration were evaluated on a Xuanwu-III high-temperature friction and wear tester, with the unfilled one as a reference. The morphologies of the worn surfaces of the composites and of the counterpart pins were analyzed using scanning electron microscopy. In addition, FTIR spectrum was taken to characterize the untreated and treated nano-ZnO. It is found that the untreated and treated nano-ZnO reinforced hybrid glass/PTFE fabric composites exhibit improved wear resistance and friction-reduction in comparison with the unfilled one. The TDI modified nano-ZnO reinforced composite can obtain the best friction and wear performance under different applied load; followed by the OB551 modified nano-ZnO reinforced one. Sliding conditions, such as environmental temperature and lubricating condition, significantly affect the tribo-performances of the unfilled and filled hybrid glass/PTFE fabric composites.     

Friction and dry sliding wear behaviour of cermets

The friction and wear behaviour of cermets/steel rubbing pairs were investigated. Friction and wear tests were carried out using three different crèmets on the base of tungsten, titanium and chromium carbides under dry sliding conditions against steel disk (0.45% C). Sliding wear tests were carried out using modified block-on-ring equipment at a sliding speed of 2.2 m/s and normal load 40 N.It is shown that wear resistance and coefficient of friction depend on the type and chemical composition of the cermets. The WC–Co cermets have the highest wear resistance. The wear rate of WC–Co and TiC–NiMo cermets increased with increasing binder content in the cermets. The wear of Cr₃C₂–Ni cermets is more complicated and depends on the composition of cermets. The wear of WC–Co cermets is caused mainly by preferential removal of the cobalt binder, followed by fracture of the intergranular boundaries and fragmentation of the carbide grains. The main wear mechanism in the TiC–NiMo cermets is polishing (micro-abrasion) and adhesion, resulting in a low wear rate. The main wear mechanism of Cr₃C₂–Ni cermets involves thermal cracking and fatigue-related crushing of large carbide grains and carbide framework and also adhesion.     

Sliding wear behaviour of PEEK‐PTFE blends

The role of PTFE in tailoring the tribological performance of PEEK is not clear from the literature, and conflicting evidence is reported about its ability to improve friction, wear, or both. Moreover, little has been reported on the optimum composition of such blends for the best possible combination of mechanical and tribological properties. Hence, in this work various blends of PEEK with PTFE have been injection moulded and characterised for their mechanical properties. Their friction and wear behaviour was evaluated using a pin‐on‐disc machine. It was observed that the inclusion of PTFE powder not only removed scuffing problems associated with the friction behaviour of PEEK, but also improved both friction and wear characteristics. A blend with 7.5 wt. % PTFE showed the best wear behaviour, while a blend with 30 wt.% PTFE exhibited the best friction performance. A concentration of 7.5 wt. % PTFE was thought to be the optimum amount for the best possible combination of mechanical and tribological properties.     

Friction and dry sliding wear of bismaleimide filled with carbon nanotubes

Three types of bismaleimide–carbon nanotubes (CNTs) nanocomposites were fabricated using two types of original multiwalled CNTs with different diameters and one amide functionalized CNTs. The influence of diameter, content and functionalization of CNTs on the flexural and dry sliding wear behaviour were measured with universal testing machine and pin-on-disc wear apparatus. The experimental results indicated that at 1.5 wt-%, the bismaleimide-functionalized MWCNTs exhibited highest flexural strength of 156 MPa which is increased by 164% as compared to the neat matrix, and lowest specific wear rate of 1.8 × 10^?4 mm³ N^?1 m^?1 which is decreased by 90% as compared to the neat matrix. This was attributed to the dispersion of CNTs in the matrix and the filler-matrix adhesion and internal strength of the composite.     

Friction and wear behaviour of pyramidal nanoscaled surface features

This study reports on the friction and wear behaviour of nanoscaled pyramidal surface features of chromium nitride thin films in relation to the dimensions of those features. The pyramidal features were created, and their size controlled, by PVD based in-process structuring. Microtribological tests analysed both the evolution of wear-induced surface alterations and the correlated evolution in the coefficient of friction as functions of normal load and duration of the loading. Results indicate that the severity of wear diminishes tremendously with increasing feature size when tested at the same normal load. So, wear-induced damage similar to that seen on surfaces with small-sized features was observed for the largest surface features tested only after a 100 times longer test duration. The less severe wear of the largest pyramids leads also to friction up to 75% lower compared to surfaces with the smallest features.     

Friction and wear behavior of self-lubricating and heavily loaded metal–PTFE composites

A new 16 MnNb steel–PTFE composite (A) containing 60% area proportion of PTFE composite was developed. Another type of common solid lubricant embedded C86300 bronze–PTFE composite (B) containing 35% area proportion of PTFE composite was also selected for a comparative investigation under similar testing conditions. Friction and wear experiments were performed in an oscillating sliding tribotester at an oscillating frequency of 0.13 Hz, contact mean pressures from 15 to 80 MPa and counterface roughness of 0.10 μm R_a. The composites A and B slid against a 38CrMoAlA steel shaft. Results showed that the composite A exhibited low coefficient of dry friction and long wear life as compared to that of the composite B. It was found that the surface of PTFE composite was higher than that of steel backing at the intervals of testing. This was because modulus of the elasticity of PTFE composite was much lower than that of 16 MnNb steel backing; under a same load condition the elastic deformation amount of PTFE composite was much bigger than that of steel backing. Thus, the composite A provided sufficient lubrication during the whole tests.     

Tribological behaviour of PTFE modified cotton polyester composites

Abstract

An attempt on modification of tribological behaviour of cotton polyester composite was done with polytetrafluoroethylene (PTFE). PTFE modified polyester–cotton composites were developed and studied for their friction and sliding wear behaviour at different applied loads. The sliding wear tests of composites were conducted against EN-31 steel counter face. The coefficient of friction μ as well as the sliding wear rate of cotton–polyester composites reduced significantly on addition of PTFE. The reduction in wear rate of PTFE modified polyester–cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction.     

Lubricated wear of PTFE and graphited PTFE

Tribological behaviour of PTFE and graphited PTFE have been evaluated under lubricated conditions and compared with dry wear. The stress selected is in the range of 0.44 to 1.64 MPa, and the data generated are relevant to conformal contacts. Mineral oil lubrication can reduce wear of PTFE by one to two orders of magnitude. With graphited PTFE the lubricant effect is lower in comparison to that observed with PTFE. Specific wear rates are plotted on a histogram.     

Friction and wear characteristics of ion-beam modified graphite coatings

Solid lubricated surfaces are now widely used in the tool industry, and the new concept of ‘soft tools’ recently introduced has emphasized low-friction surfaces. The present paper deals with a novel ‘burnishing’ process based on ionic bombardment of powder graphite coating/substrate systems. This process may influence both the coating and the coating/substrate interface, and it is effective for improving lubrication even at low doses of bombarding ions. The present study will discuss the friction and wear properties of graphite-powder coatings on a silicon wafer bombarded with 200 keV ion beams of argon, nitrogen and hydrogen ions, the last two as molecular ions. The coefficients of friction and wear rates of the coatings were found to be strongly dependent on the ion-bombarding species and ion dose. The argon ion bombardment increased the coefficient of friction and wear rate of the powder coating. However, at the interface of the silicon substrate, the ion-induced burnishing improved the tribological behaviour of the silicon material. Bombardment with nitrogen and hydrogen ions showed a marked improvement in the tribological properties of the graphite powder coating. Thus a reduction in wear rate by three orders of magnitude was observed in the case of nitrogen, and for both ions it was noted that ion-beam burnished graphite was lubricating in a dry environment, which has not been reported previously. The perspectives of ion bombardment as a burnishing process will be discussed and the observed effects will be qualitatively explained in the context of the theory for ionic penetration into solids.     

On the abrasive wear behaviour of mineral filled polypropylene

The effects of mineral fillers on the wear resistance of polypropylene (PP) have been investigated. A general purpose homopolymer grade was used as the matrix. The mineral fillers investigated were talc, CaCO₃, BaSO₄ and fly ash, representing a range of morphology, size and hardness. The wear behaviour was assessed by pin-on-paper abrasion tests. The wear surfaces were examined using scanning electron microscopy (SEM). The addition of mineral fillers to the polypropylene matrix decreases the wear resistance under severe abrasive conditions. Under mild abrasive conditions the shape and size of the reinforcing filler influence the wear performance. The tensile strength behaviour of each composite, together with the physical properties of the fillers and a microscopic investigation into the modes of material deformation and removal are used to interpret this observed wear behaviour.     

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.     

On dry sliding friction and wear behavior of PPESK filled with PTFE and graphite

Novel poly(phthalazinone ether sulfone ketone) (PPESK) resins have become of great interest in applications such as bearing and slider materials. In this paper, dry sliding wear of polytetrafluoroethylene (PTFE) and graphite-filled PPESK composites against polished steel counterparts were investigated on a block-on-ring apparatus at the same sliding velocities and different loads. The results indicated that the addition of 5–25 wt% PTFE and 5–30 wt% graphite contribute to an obvious improvement of tribological performance of PPESK at room temperature. Worn surfaces were investigated using a scanning electron microscope (SEM). As a result, the friction coefficient and wear rate of the PPESK composites decreased gradually with addition of fillers. A moderately low friction coefficient and specific wear rate were reached when the filler contents were above 20 wt%. The mechanical properties of PPESK composites were also investigated. The tensile and impact strength of PPESK composites decrease slightly as the addition of fillers contents were below 15 wt%.     

Friction and wear behaviour of hard coatings in vibrating contacts

The friction and wear behaviour of thin hard coatings, such as TiN and the promising class of C-based coatings (a-C, a-C:H, and diamond for example), are compared under oscillating and reciprocating sliding conditions. The typical effects of test parameters, such as stroke, frequency, normal force, relative humidity and test duration, are described as a basis for the proper selection of test conditions or, conversely, for the selection of suitable coatings for particular practical applications. Friction and wear data from over 1000 vibrating tests using thin hard coatings against 100Cr6 and against Al₂O₃ have been compiled in a database. This allows easy manipulation and comparison of test results. Using selection criteria and filter procedures (e. g., lifetime of coatings, friction limits, and critical wear rate), suitable coating systems for different test conditions can be chosen from the database. The effects of test parameters on friction and wear behaviour and changes have anyway to be known for meaningful tribotesting, as well as for the selection of coatings.     

Tribological behaviour of new chemically bonded PTFE polyamide compounds

Topic of the study is the formation of new PTFE polyamide materials by reactive extrusion. The new type of formed PTFE polyamide compound shows very good material properties. Recently it has been revealed that carboxylic acid groups exhibit a very high reactivity under polyamide melting conditions. PTFE micro powders functionalized by carboxylic acid groups are the base for the block copolymer formation in polyamide melts under defined process conditions. Such functionalized micro powders are formed from virgin PTFE by electron irradiation in the presence of oxygen. These new PTFE polyamide materials can be processed easily using commercial (common) process equipment like twin-screw extruders and injection molding. Many experimental investigations have been performed under dry sliding friction on PA 6, PA 6.6 and PA 12 compounds with PTFE weight portions between 3.3 and 50%. They show low coefficients of friction and low specific wear rates. The wear resistance of newly developed PTFE polyamide compounds is comparable with commercially available mechanically or physically produced PTFE and PEAK compounds.