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Sliding wear performance of polymer composites under abrasive and water lubricated conditions for pump applications
Wear 259 (2005) 693–696
Case study
Sliding wear performance of polymer composites under abrasive and water lubricated conditions for pump applications夽 R. Prehn ∗ , F. Haupert, K. Friedrich IVW GmbH, Kaiserslautern University of Technology, Germany Received 14 October 2004; received in revised form 31 January 2005; accepted 3 February 2005 Available online 10 May 2005
Abstract Bearings made of polymer-based composites are often used when corrosive environments prevent the application of other kinds of materials [N.N., Gleitlager mit Wasserschmierung, Materialwissenschaft und Werkstofftechnik 30 (1999) S243; N.G. Fontana, Corrosion Engineering, second ed., McGraw-Hill, New York, 1978; M. Pourbaix, Lectures on Electrochemical Corrosion, Plenum Press, New York, London, 1973, ISBN 0-306-30449-X]. This is due to the chemical resistance of the polymer matrix and the possibility to tailor the friction and wear properties of such bearings by the use of various types of fillers and fibre reinforcements [R. Prehn, F. Haupert, K. Friedrich, Entwicklung von polymeren Hochleistungsgleitlagerwerkstoffen, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S919–924]. The development of such a material for a journal bearing in pumps, transporting aggressive and abrasive fluids, is the content of this case study. Diverse material compositions were designed and investigated. One was composed of an epoxy resin matrix, highly filled, e.g. with ceramic particles (silicon carbide, i.e. SiC), to combine the ductile character of the polymer with the hardness of the ceramic. It showed an excellent wear behaviour under dry and water lubricated conditions, when operating against steel as the counterpart. Another one consisted of a polyetheretherketone (PEEK) matrix, reinforced with short carbon fibres for sealing applications. Here, an unexpected phenomenon was observed. When the experiments were carried out under water lubrication against a rotating stainless steel ring, the demineralized water strongly affected the wear behaviour of the carbon fibres. It is the purpose of the ongoing study to find out which effects, respectively wear mechanisms, take place in the contact area between both partners, and how the enhanced wear can be reduced under these severe conditions. © 2005 Elsevier B.V. All rights reserved. Keywords: Pump; Bearing; Wear; Polymer; Abrasive; Water; Lubrication
1. Introduction Regarding the chemical industry, where water, acids or any imaginable process media have to be dispatched, special pumps are required, that can sustain such environments. These media can be chemically aggressive as well as abrasive because of contained particles. For this reason the choice of materials that may get in contact with such media are 夽 Submitted to be published in the Proceedings of the 15th International Conference on Wear of Materials, 24–28th April 2005, San Diego, USA. ∗ Corresponding author. Tel.: +49 0631 2017 209; fax: +49 0631 2017 196. E-mail address: [email protected] (R. Prehn).
0043-1648/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2005.02.054
limited. State of the art are hermetical close polymer pumps with ceramic (silicon carbide, i.e. SiC) slide bearings [1–4]. This solution works out well under stable and lubricated conditions, but due to the brittle character of ceramic materials, these should not run dry or under boundary lubricated conditions [5]. Also fluid cavitation, thermal shocks and emptying of a reservoir are risks for such slide bearings, which may cause fatal damage to the whole pump. One way to solve this problem is to combine a ceramic material with a polymeric composite counterpart as a slide bearing [4]. The idea behind it is to make use of the hardness and wear resistance of the ceramic material and the ductile and stress tolerant character of a polymer. The later has to be modified with fibres and fillers to obtain a high wear
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R. Prehn et al. / Wear 259 (2005) 693–696
performance under dry sliding conditions as well as under abrasive lubrication. Within this case study, thermoset and thermoplastic composite materials are investigated to solve these problems.
2. Experimental 2.1. Samples and manufacturing In this case study thermoset as well as thermoplastic materials are used. In Table 1 a choice of the investigated composites with their filler and fibre contents is listed. The difference between SiC I and SiC II is the particle size. SiC I (9 m) is three times bigger than SiC II (3 m). The thermoset materials, based on epoxy (EP) resin, were manufactured with a laboratory scale dissolver. For the materials that are highly filled, the resin and hardener were mixed together and the fillers and fibres added thereafter. Frequent evacuation was applied to get out the air of the mixtures. Following, these were poured in quadratic casting moulds with a dimension of 100 mm × 100 mm × 15 mm. The mixtures were then gelatinised and cured at 140 ◦ C. The gelification process has to be fast, so that the fillers and fibres have no time to sediment. However, this cannot be avoided. Therefore, samples are always taken from the middle of the casted plates, to ensure a homogeneous filler distribution. The thermoplastic compounds are based on the commercial available polyetheretherketone (PEEK) 450 G from Victrex plc (UK), reinforced with short PAN-based carbon fibres. The materials were injection moulded in the shape of quadratic plates with the dimension of 80 mm × 80 mm × 5 mm. For the tribological experiments the geometry of the samples (block), which are cut from the thermoset and thermoplastic plates, is 4 mm × 5 mm × 10 mm. 2.2. Tribological experiments
Fig. 1. (a) Schematic of the block on ring testing method. (b) Picture of the tribological testing device for media.
operate under dry as well as under lubricated conditions. The latter is achieved by submerging the counterparts into small tanks as shown in Fig. 2. The standard counterpart is made of 100Cr6 with an outer diameter of 60 mm and a width of 25 mm. These were used for dry and water lubricated experiments with the EP composite materials. The testing parameters for tribological experiments are the surface pressure p, the sliding velocity v and the time t. The abrasive media lubricated investigations are conducted
The tribological experiments to determine the wear behaviour are conducted under dry and lubricated conditions. Therefore, a block on ring testing device is used. The principle of this testing method is shown in Fig. 1. This device can Table 1 Sample materials No.
Matrix
Fillers
1 2 3 4 5 6 7 8 9
EP EP EP EP EP EP EP PEEK PEEK
Neat resin 10 vol.% CF, 7 vol.% graphite, 4 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 8 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 12 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 4 vol.% SiC II (3 m) 10 vol.% CF, 7 vol.% graphite, 8 vol.% SiC II (3 m) 10 vol.% CF, 7 vol.% graphite, 12 vol.% SiC II (3 m) 10 wt.% CF 30 wt.% CF
Fig. 2. Results of modified epoxy resin composite materials under dry sliding conditions.
R. Prehn et al. / Wear 259 (2005) 693–696
in water, containing Wollastonit. This organic particle is abrasive and can be well dispersed in water. For the wear testing in tap water and demineralised water, the PEEK samples were used. But instead of 100Cr6 counterparts stainless steel (material no.: 1.4301) is utilised. For the calculation of the wear rate, the wear volume per sliding distance (volumetric wear rate) was normalized by the normal load applied, and it was designated here as the specific wear rate. This term is often found in the literature and it is equivalent to the so called wear factor or wear coefficient k, often used in technical brochures for the comparison of the wear performance of various materials under sliding wear testing conditions. The specific wear rate, ws (mm3 /Nm) was calculated by the following equation: ws =
Dm (LρFN )
where Dm is the mass loss in (g), L the sliding distance in (m), ρ the density of the composite in (g/cm3 ), and FN the normal load in (N).
695
Looking at the composite materials modified with SiC II particles, which are three times smaller compared to SiC I, the values for the 4 and 8 vol.% SiC content are one order of magnitude lower than the SiC I values. This indicates, that the smaller particles and the lower SiC contents enhance the wear performance significantly without being that abrasive. In contradiction, the material with the highest SiC II content shows almost the same value as the materials modified with SiC I. It can be concluded, that the abrasiveness increases significantly between 8 and 12 vol.% SiC II content. In Fig. 3 the results of the composite materials are also much lower than of the neat matrix. For the materials with SiC I particles a trend towards lower values with increasing SiC content can be seen. Especially the highest filled material reaches a very low specific wear rate. Concerning the results of the materials filled with SiC II Fig. 3 reveals that the 4 and 8 vol.% SiC containing grades are almost on the same level. Also in this case the highest filled material has the lowest specific wear rate. This value is about the same as the lowest filled material with SiC I. It can be concluded, that the wear resistance increases between 8 and 12 vol.% SiC II content.
3. Results 3.1. Results of the EP materials
3.2. Wear results of the PEEK materials under water lubrication
The calculated specific wear rates of the dry sliding experiments are given in Fig. 2 and for the abrasive media lubricated wear investigations in Fig. 3. According to Fig. 2, the values of the composite materials are much lower than that of the neat matrix. Regarding the materials reinforced with SiC I, the results are almost exactly on the same level. This could be explained with the particle size. The lowest content of SiC I has the same abrasive effect on the steel counterpart as the highest. This means that the surface of the steel ring is abraded by the SiC particles and getting rougher and then the rough surface is cutting into the composite material. This procedure seems to be stable over the variation of the filler content between 4 and 12 vol.%.
In Fig. 4, the results of the calculated specific wear rates of the sliding experiments under different aqueous conditions are given. The obtained values for the specific wear rate of these PEEK compounds are very different. Regarding the materials that were tested in tap water, the wear rates are very low and on the same level. It can be stated, that in the range between 10 and 30 vol.% carbon fibre content there is no significant influence on the wear behaviour. In contradiction the materials tested in demineralised water show high and unequal specific wear rates. Here, the influence of the carbon fibres is clearly visible. The material with the lower carbon fibre content shows the highest wear. Up to the present it is uncertain why there is such a difference concerning the wear behaviour of the same material
Fig. 3. Results of modified epoxy resin composite materials under abrasive media lubricated sliding conditions.
Fig. 4. Results of carbon fibre reinforced PEEK materials under water lubricated sliding conditions: tap water (left) and demineralised water (right).
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R. Prehn et al. / Wear 259 (2005) 693–696
in these two types of water. The investigation of this phenomenon will be continued. 4. Discussion The comparison of the wear results of the EP materials under dry and abrasive media lubricated conditions reveal: • The modification of the EP resin, either with SiC I or SiC II, has a very positive effect on the wear behaviour compared with the neat matrix. • The composites filled with SiC I show a little worse wear behaviour under dry conditions than the SiC II filled ones. However the SiC I materials exhibit the better values regarding the wear under abrasive lubricated conditions. This indicates, that the increasing particle size and content has a negative influence concerning the wear under dry sliding conditions but a positive effect under abrasive lubrication. • The variabilty of the obtained results under dry and lubricated conditions reveal from the difference between lubricated and unlubricated wear conditions. Under dry contact conditions the main wear mechanism is abrasive wear, which appears to be stable at a certain abrasiveness of the composite. Under lubricated contact conditons the main wear mechanism is erosive wear. With increasing filler content the composite materials show an increasing wear resistance because of the increasing hardness. • Developing a new composite material, which suits for dry and abrasive lubricated conditions constitutes a conflict of objectives. Until now, the obtained results characterise that a compromise has to be found to serve both aimed properties. In respect of the wear behaviour of the carbon fibre reinforced PEEK composites, the results are surprisingly: • The values for the materials tested in tap water are excellent and correspond to the commonly known data about PEEK, where as the tested PEEK composites in
demineralised water exhibit much higher values. The reason for this difference is yet unknown. • The materials tested in demineralised water show different results according to their carbon fibre content. This indicates, that an increasing fibre content has a positive effect on the wear behaviour. Thus it can be stated that the results for the EP materials are promising, but there is still some research work necessary to obtain the best compromise. For the PEEK materials the scientific investigations are going on to find out which phenomenon is responsible for this significant increase of the wear in demineralised water.
Acknowledgements The authors are grateful to the German Stiftung Industrieforschung (Project S 570) and the following German Companies, Comat GmbH, Lehmann und Voss und Co. and Munsch Chemie-Pumpen GmbH, for financing this research project and the fruitful cooperation.
References [1] Gleitlager mit Wasserschmierung, Materialwissenschaft und Werkstofftechnik 30 (1999) S243. [2] N.G. Fontana, Corrosion Engineering, second ed., McGraw-Hill, New York, 1978. [3] M. Pourbaix, Lectures on Electrochemical Corrosion, Plenum Press, New York, London, 1973, ISBN 0-306-30449-X. [4] R. Prehn, F. Haupert, K. Friedrich, Entwicklung von polymeren Hochleistungsgleitlagerwerkstoffen, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S919–924. [5] D. Klaffke, G. Steinborn, R. W¨asche, G. W¨otting, Tribologische Untersuchungen an SiC und Si3 N4 -basierten Keramiken, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S545– 550.
Case study
Sliding wear performance of polymer composites under abrasive and water lubricated conditions for pump applications夽 R. Prehn ∗ , F. Haupert, K. Friedrich IVW GmbH, Kaiserslautern University of Technology, Germany Received 14 October 2004; received in revised form 31 January 2005; accepted 3 February 2005 Available online 10 May 2005
Abstract Bearings made of polymer-based composites are often used when corrosive environments prevent the application of other kinds of materials [N.N., Gleitlager mit Wasserschmierung, Materialwissenschaft und Werkstofftechnik 30 (1999) S243; N.G. Fontana, Corrosion Engineering, second ed., McGraw-Hill, New York, 1978; M. Pourbaix, Lectures on Electrochemical Corrosion, Plenum Press, New York, London, 1973, ISBN 0-306-30449-X]. This is due to the chemical resistance of the polymer matrix and the possibility to tailor the friction and wear properties of such bearings by the use of various types of fillers and fibre reinforcements [R. Prehn, F. Haupert, K. Friedrich, Entwicklung von polymeren Hochleistungsgleitlagerwerkstoffen, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S919–924]. The development of such a material for a journal bearing in pumps, transporting aggressive and abrasive fluids, is the content of this case study. Diverse material compositions were designed and investigated. One was composed of an epoxy resin matrix, highly filled, e.g. with ceramic particles (silicon carbide, i.e. SiC), to combine the ductile character of the polymer with the hardness of the ceramic. It showed an excellent wear behaviour under dry and water lubricated conditions, when operating against steel as the counterpart. Another one consisted of a polyetheretherketone (PEEK) matrix, reinforced with short carbon fibres for sealing applications. Here, an unexpected phenomenon was observed. When the experiments were carried out under water lubrication against a rotating stainless steel ring, the demineralized water strongly affected the wear behaviour of the carbon fibres. It is the purpose of the ongoing study to find out which effects, respectively wear mechanisms, take place in the contact area between both partners, and how the enhanced wear can be reduced under these severe conditions. © 2005 Elsevier B.V. All rights reserved. Keywords: Pump; Bearing; Wear; Polymer; Abrasive; Water; Lubrication
1. Introduction Regarding the chemical industry, where water, acids or any imaginable process media have to be dispatched, special pumps are required, that can sustain such environments. These media can be chemically aggressive as well as abrasive because of contained particles. For this reason the choice of materials that may get in contact with such media are 夽 Submitted to be published in the Proceedings of the 15th International Conference on Wear of Materials, 24–28th April 2005, San Diego, USA. ∗ Corresponding author. Tel.: +49 0631 2017 209; fax: +49 0631 2017 196. E-mail address: [email protected] (R. Prehn).
0043-1648/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2005.02.054
limited. State of the art are hermetical close polymer pumps with ceramic (silicon carbide, i.e. SiC) slide bearings [1–4]. This solution works out well under stable and lubricated conditions, but due to the brittle character of ceramic materials, these should not run dry or under boundary lubricated conditions [5]. Also fluid cavitation, thermal shocks and emptying of a reservoir are risks for such slide bearings, which may cause fatal damage to the whole pump. One way to solve this problem is to combine a ceramic material with a polymeric composite counterpart as a slide bearing [4]. The idea behind it is to make use of the hardness and wear resistance of the ceramic material and the ductile and stress tolerant character of a polymer. The later has to be modified with fibres and fillers to obtain a high wear
694
R. Prehn et al. / Wear 259 (2005) 693–696
performance under dry sliding conditions as well as under abrasive lubrication. Within this case study, thermoset and thermoplastic composite materials are investigated to solve these problems.
2. Experimental 2.1. Samples and manufacturing In this case study thermoset as well as thermoplastic materials are used. In Table 1 a choice of the investigated composites with their filler and fibre contents is listed. The difference between SiC I and SiC II is the particle size. SiC I (9 m) is three times bigger than SiC II (3 m). The thermoset materials, based on epoxy (EP) resin, were manufactured with a laboratory scale dissolver. For the materials that are highly filled, the resin and hardener were mixed together and the fillers and fibres added thereafter. Frequent evacuation was applied to get out the air of the mixtures. Following, these were poured in quadratic casting moulds with a dimension of 100 mm × 100 mm × 15 mm. The mixtures were then gelatinised and cured at 140 ◦ C. The gelification process has to be fast, so that the fillers and fibres have no time to sediment. However, this cannot be avoided. Therefore, samples are always taken from the middle of the casted plates, to ensure a homogeneous filler distribution. The thermoplastic compounds are based on the commercial available polyetheretherketone (PEEK) 450 G from Victrex plc (UK), reinforced with short PAN-based carbon fibres. The materials were injection moulded in the shape of quadratic plates with the dimension of 80 mm × 80 mm × 5 mm. For the tribological experiments the geometry of the samples (block), which are cut from the thermoset and thermoplastic plates, is 4 mm × 5 mm × 10 mm. 2.2. Tribological experiments
Fig. 1. (a) Schematic of the block on ring testing method. (b) Picture of the tribological testing device for media.
operate under dry as well as under lubricated conditions. The latter is achieved by submerging the counterparts into small tanks as shown in Fig. 2. The standard counterpart is made of 100Cr6 with an outer diameter of 60 mm and a width of 25 mm. These were used for dry and water lubricated experiments with the EP composite materials. The testing parameters for tribological experiments are the surface pressure p, the sliding velocity v and the time t. The abrasive media lubricated investigations are conducted
The tribological experiments to determine the wear behaviour are conducted under dry and lubricated conditions. Therefore, a block on ring testing device is used. The principle of this testing method is shown in Fig. 1. This device can Table 1 Sample materials No.
Matrix
Fillers
1 2 3 4 5 6 7 8 9
EP EP EP EP EP EP EP PEEK PEEK
Neat resin 10 vol.% CF, 7 vol.% graphite, 4 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 8 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 12 vol.% SiC I (9 m) 10 vol.% CF, 7 vol.% graphite, 4 vol.% SiC II (3 m) 10 vol.% CF, 7 vol.% graphite, 8 vol.% SiC II (3 m) 10 vol.% CF, 7 vol.% graphite, 12 vol.% SiC II (3 m) 10 wt.% CF 30 wt.% CF
Fig. 2. Results of modified epoxy resin composite materials under dry sliding conditions.
R. Prehn et al. / Wear 259 (2005) 693–696
in water, containing Wollastonit. This organic particle is abrasive and can be well dispersed in water. For the wear testing in tap water and demineralised water, the PEEK samples were used. But instead of 100Cr6 counterparts stainless steel (material no.: 1.4301) is utilised. For the calculation of the wear rate, the wear volume per sliding distance (volumetric wear rate) was normalized by the normal load applied, and it was designated here as the specific wear rate. This term is often found in the literature and it is equivalent to the so called wear factor or wear coefficient k, often used in technical brochures for the comparison of the wear performance of various materials under sliding wear testing conditions. The specific wear rate, ws (mm3 /Nm) was calculated by the following equation: ws =
Dm (LρFN )
where Dm is the mass loss in (g), L the sliding distance in (m), ρ the density of the composite in (g/cm3 ), and FN the normal load in (N).
695
Looking at the composite materials modified with SiC II particles, which are three times smaller compared to SiC I, the values for the 4 and 8 vol.% SiC content are one order of magnitude lower than the SiC I values. This indicates, that the smaller particles and the lower SiC contents enhance the wear performance significantly without being that abrasive. In contradiction, the material with the highest SiC II content shows almost the same value as the materials modified with SiC I. It can be concluded, that the abrasiveness increases significantly between 8 and 12 vol.% SiC II content. In Fig. 3 the results of the composite materials are also much lower than of the neat matrix. For the materials with SiC I particles a trend towards lower values with increasing SiC content can be seen. Especially the highest filled material reaches a very low specific wear rate. Concerning the results of the materials filled with SiC II Fig. 3 reveals that the 4 and 8 vol.% SiC containing grades are almost on the same level. Also in this case the highest filled material has the lowest specific wear rate. This value is about the same as the lowest filled material with SiC I. It can be concluded, that the wear resistance increases between 8 and 12 vol.% SiC II content.
3. Results 3.1. Results of the EP materials
3.2. Wear results of the PEEK materials under water lubrication
The calculated specific wear rates of the dry sliding experiments are given in Fig. 2 and for the abrasive media lubricated wear investigations in Fig. 3. According to Fig. 2, the values of the composite materials are much lower than that of the neat matrix. Regarding the materials reinforced with SiC I, the results are almost exactly on the same level. This could be explained with the particle size. The lowest content of SiC I has the same abrasive effect on the steel counterpart as the highest. This means that the surface of the steel ring is abraded by the SiC particles and getting rougher and then the rough surface is cutting into the composite material. This procedure seems to be stable over the variation of the filler content between 4 and 12 vol.%.
In Fig. 4, the results of the calculated specific wear rates of the sliding experiments under different aqueous conditions are given. The obtained values for the specific wear rate of these PEEK compounds are very different. Regarding the materials that were tested in tap water, the wear rates are very low and on the same level. It can be stated, that in the range between 10 and 30 vol.% carbon fibre content there is no significant influence on the wear behaviour. In contradiction the materials tested in demineralised water show high and unequal specific wear rates. Here, the influence of the carbon fibres is clearly visible. The material with the lower carbon fibre content shows the highest wear. Up to the present it is uncertain why there is such a difference concerning the wear behaviour of the same material
Fig. 3. Results of modified epoxy resin composite materials under abrasive media lubricated sliding conditions.
Fig. 4. Results of carbon fibre reinforced PEEK materials under water lubricated sliding conditions: tap water (left) and demineralised water (right).
696
R. Prehn et al. / Wear 259 (2005) 693–696
in these two types of water. The investigation of this phenomenon will be continued. 4. Discussion The comparison of the wear results of the EP materials under dry and abrasive media lubricated conditions reveal: • The modification of the EP resin, either with SiC I or SiC II, has a very positive effect on the wear behaviour compared with the neat matrix. • The composites filled with SiC I show a little worse wear behaviour under dry conditions than the SiC II filled ones. However the SiC I materials exhibit the better values regarding the wear under abrasive lubricated conditions. This indicates, that the increasing particle size and content has a negative influence concerning the wear under dry sliding conditions but a positive effect under abrasive lubrication. • The variabilty of the obtained results under dry and lubricated conditions reveal from the difference between lubricated and unlubricated wear conditions. Under dry contact conditions the main wear mechanism is abrasive wear, which appears to be stable at a certain abrasiveness of the composite. Under lubricated contact conditons the main wear mechanism is erosive wear. With increasing filler content the composite materials show an increasing wear resistance because of the increasing hardness. • Developing a new composite material, which suits for dry and abrasive lubricated conditions constitutes a conflict of objectives. Until now, the obtained results characterise that a compromise has to be found to serve both aimed properties. In respect of the wear behaviour of the carbon fibre reinforced PEEK composites, the results are surprisingly: • The values for the materials tested in tap water are excellent and correspond to the commonly known data about PEEK, where as the tested PEEK composites in
demineralised water exhibit much higher values. The reason for this difference is yet unknown. • The materials tested in demineralised water show different results according to their carbon fibre content. This indicates, that an increasing fibre content has a positive effect on the wear behaviour. Thus it can be stated that the results for the EP materials are promising, but there is still some research work necessary to obtain the best compromise. For the PEEK materials the scientific investigations are going on to find out which phenomenon is responsible for this significant increase of the wear in demineralised water.
Acknowledgements The authors are grateful to the German Stiftung Industrieforschung (Project S 570) and the following German Companies, Comat GmbH, Lehmann und Voss und Co. and Munsch Chemie-Pumpen GmbH, for financing this research project and the fruitful cooperation.
References [1] Gleitlager mit Wasserschmierung, Materialwissenschaft und Werkstofftechnik 30 (1999) S243. [2] N.G. Fontana, Corrosion Engineering, second ed., McGraw-Hill, New York, 1978. [3] M. Pourbaix, Lectures on Electrochemical Corrosion, Plenum Press, New York, London, 1973, ISBN 0-306-30449-X. [4] R. Prehn, F. Haupert, K. Friedrich, Entwicklung von polymeren Hochleistungsgleitlagerwerkstoffen, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S919–924. [5] D. Klaffke, G. Steinborn, R. W¨asche, G. W¨otting, Tribologische Untersuchungen an SiC und Si3 N4 -basierten Keramiken, in: H.P. Degischer (Hrsg.), Tagungsbandbeitrag 14, Symposium Verbundwerkstoffe und Werkstoffverbunde, Wiley-VCH, Weinheim, 2003, pp. S545– 550.