The aim of this investigation was to examine several types of commercially available polymers for potential application in machine elements that are exposed to abrasion. Selected materials were evaluated on a rubber and steel wheel abrasion test rig according to the standard ASTM G65, using as abrasive quartz sand (SiO2) as abrasive, with a particle grain size in the range of 0.8 – 1.6 mm. Tests were performed under dry conditions and at room temperature. Applied load was 50 N, within testing times of 1½, 3, 4½, and 6 hours respectively. Results of testing revealed influence on wear behavior of polymer hardness as well as influence of abrasive particle embedment

Franek, F

Jisa, R

Pejaković, V

English

Journal.fi

V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials21TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015ABRASION RESISTANCE OF SELECTED COMMERCIALLYAVAILABLE POLYMER MATERIALSV. Pejakovi *, R. Jisa , F. FranekAC²T research GmbH, Wiener Neustadt, AustriaABSTRACTThe aim of this investigation was to examine several types of commercially available polymers for potentialapplication in machine elements that are exposed to abrasion. Selected materials were evaluated on a rubberand steel wheel abrasion test rig according to the standard ASTM G65, using as abrasive quartz sand (SiO2)as abrasive, with a particle grain size in the range of 0.8 – 1.6 mm. Tests were performed under dryconditions and at room temperature. Applied load was 50 N, within testing times of 1½, 3, 4½, and 6 hoursrespectively. Results of testing revealed influence on wear behavior of polymer hardness as well as influenceof abrasive particle embedment.Keywords: ASTM G 65 abrasive tester, quartz sand, three body abrasion, polymer*Corresponding author: Vladimir Pejakovi ; AC²T research GmbH; Viktor Kaplan Straße 2; 2700 WienerNeustadt; Austria. E-mail: pejakovic@ac2t.at; Telephone: +43(0)2622 81600-144INTRODUCTIONIn recent years, due to the trend in designing ofmachines and machine elements, polymers havetaken a significant role as materials for partslike cams and gears, as a substitution forconventional materials [1]. Additionally,polymers are extensively used as materials formanufacturing of parts for mining equipment,conveyor lines, rotary valves, etc. [2]. In allthese applications, polymers are exposed toabrasive wear.Abrasive wear is a wear mechanism generatedby the sliding of a hard material over a softermaterial under load, while surface asperities ofthe harder material tend to remove the softermaterial [3]. In general, abrasive wear can bedivided into two major groups due to themechanisms of generation: two body abrasion,and three body abrasion [3]. Two body abrasionoccurs in direct contact of two counter surfaceswhen one is significantly softer than the otherone, while three body abrasion occurs whenhard particles get trapped between two slidingsurfaces. Some estimation say that abrasivewear contributes up to 60% of total costs causedby wear [4].Since polymers became important technicalmaterials in modern engineering, numerouspapers referred to these in the last decades.The first article in history summarizing resultsof polymer abrasion was published in 1969[5]. The following years brought a widevariety of experiments related to abrasivewear of polymers [6-13]. Furthermore, a widevariety of experiments has been performed onpolymer composites, reinforced polymers andepoxy resins [14-16]. Most of theseexperiments have been performed onconventional pin-on-disc testing setups withsand paper as counterbody to the polymerpins  (two  body  abrasion),  as  well  as  on  theASTM  G65  abrasion  tester  with  differenttesting setups (steel or rubber wheel, Threebody abrasion). Attempts to investigateabrasion resistance of polymer materials onmicro scale have also been done [17]. Most ofthese studies can be seen as a summary inseveral review articles [5; 18].V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials22TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015In this work we investigate polymer materialspossibly replacing metals for dosing wheels inrotary feeders, especially for those withsmaller geometry, where entire parts have tobe made from bulk polymer and where theimplementation of reinforcing fibers in thepolymer structure is not possible. Theselected polymer materials are commerciallyavailable.EXPERIMENTALTesting samplesFour different commercially availabletechnical polymers, one polyethylene andthree polyurethanes, named Polymer A, B, Cand D, have been examined in order todetermine their abrasion resistance. Thematerials were supposed to exhibit beneficialperformance under abrasive conditions eitherby providing pronounced abrasion resistanceor by general mechanical properties allowingproper function of the system, e. g. lowtendency for wear attack on the counterbody.The size of the specimens used in the ASTMG65 abrasion test rig was10 mm × 25 mm × 75 mm. The selectedtesting materials, and their properties can beseen in Table 1.Table 1. Abbreviations, chemical structuresand mechanical properties of selectedpolymers.SampledesignationChemicalstructureShorehardn.(HS)Elong.%Density(g/cm³)Polymer A polyethylene 60 - 0.96Polymer B polyurethane 72 800 1.24Polymer C polyurethane 85 410 1.20Polymer D polyurethane 92 490 1.11As reference materials with high abrasionresistance, two steels intended for quenchingand tempering have been selected, Table 2.Table 2. Reference steel materials34CrNiMo6, and 42CrMo4.Alloying elements 34CrNiMo6 42CrMo4C 0.30-0.38 0.38-0.45Si Max. 0.40 Max. 0.40Mn 0.50-0.80 0.60-0.90Cr 1.30-1.70 0.90-1.20Ni 1.30-1.70 0.15-0.30Mo 0.15-0.30 Max. 0.035Hardness [HB]248 255EN 10083-3Hot rolled Hot rolledAbrasiveAs abrasive material, quartz sand (SiO2) with agrain  size  of  0.8  -  1.6  mm  was  selected.  Thechoice of this specific abrasive followed theapplication requirements. For each test a newstock of sand was used, in order to maintainthe grain shape conditions and grain sizedistribution as a constant parameter.Figure 1. Abrasive particles used in theexperiments (Image of abrasive particlesbefore experiment).Experimental procedureFor the selected specimens, the tests wereperformed using the ASTM G65 abrasiontester [19]. The decision was based on alreadyavailable experiences, not only from literature(chapter  1)  but  as  well  from  our  ownexperimental work. Nevertheless, adjustmentsof the test system according to the applicationdemands  could  be  done  easily  to  the  ASTMG65 apparatus. Adjustment of the systemV. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials23TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015consisted of retrofitting of the test rig with thenew nozzle which was capable to maintainthe sand flow within the limits defined byapplication. A schematic of the test rig can beseen in Figure 2. The tested samples werefixed to the sample holder lever, which waspositioned in the tangential direction inrelation  to  the  rubber  or  steel  wheel.  Thesample holder lever is connected to the loadlever having the same pivot. The load wasapplied by positioning a calibrated deadweight at the end of the load lever. Duringtesting, the examined samples were exposedto the influence of the abrasive. The abrasivewas stored in the sand tank and fed into thecontact zone through an appropriate nozzle[19]. After leaving the nozzle the abrasivewas entrapped in and moved through thecontact zone due to the relative motion of thewheel,  which was rotating in direction of thesand flow (clockwise in the schematic).Figure 2. Schematic diagram of the ASTMG65 abrasion test rig.Tests were carried out at modified conditionswith  a  load  of  50  N,  a  rotational  velocity  ofthe wheel of 200 min-1,  a  sand flow rate of 3litres/minute and testing times 1.5, 3, 4.5, and6 hours,  respectively.  Both test  setups – withrubber  wheel  and  with  a  steel  wheel  –  wereused. Before and after testing, each testsample was cleaned in ethanol and dried.Mass loss was determined by weighing thesamples  before  and  after  the  tests  with  ananalytical balance (RADWAG XA 210/X,0.01 mg to 210 g, RADWAG Balances &Scales, Radom, Poland). Each test wasrepeated at least two times, and forcomparison the volume loss for each selectedtesting sample was calculated. Wear tracks onthe wheel surfaces were measured by aconfocal microscope (Leica DCM 3D, ErnstLeitz Wetzlar, GmbH, Germany) for non-contacting assessment of the microscaletopography. The size of the scanned area was0.96 mm × 1.3 mm.RESULTSASTM G65 abrasive test resultsThe 1.5 hour experimentsAverage volume loss (mm³) as a function ofthe polymer hardness (HS), for theexperiments of 1.5 hour lenght is presented inFigure 3. In general, for both test setups(rubber and steel wheel) the highest volumeloss was detected for the Polymer A, whichpossess the lowest hardness. Nevertheless, itshould be noticed that for the steel wheel testsetup, the polymer A exhibits lower wearvolume  (by  65  %)  when  compared  to  therubber wheel setup.A similar trend was detected for Polymer B,with approximately 22 % volume lossobtained in the tests with the steel wheel setupas compared to those with  rubber wheel one.However, it can be noticed that this trendchanged after an increase in hardness onShore scale over 85 HS. Polymer C exhibited48% lower, and Polymer D 35% lowervolume losses in the tests with the rubberwheel setup in comparison to the tests withthe steel one. Moreover, the lowest wearvolume  in  the  tests  with  two  setups  wasobtained with Polymer C.V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials24TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015Figure 3. Average volume loss for theselected polymer materials in the 1.5 hrexperiments: a) ASTM G65 rubber wheelsetup; b) ASTM G65 steel wheel setupFigure 4 presents the comparison chartsbetween Polymer C and D, which were the bestperforming polymers, and the reference steels.It can be clearly seen there was no difference inwear resistance between Polymer C and thereference steels in the tests with the ASTM G65rubber wheel setup (Figure 4 a). Only PolymerD  exhibited  a  worse  performance  than  thereference steels, when tested in the rubberwheel setup. Furthermore, the differencebetween the four materials when tested in theASTM G65 steel wheel setup was even morepronounced; 35% less wear was detected forPolymer C, and 20% less wear for Polymer D.Figure 4: Average volume loss of best performingpolymers and selected steel materials.3 – 6 hour experimentsThe two best performing polymers, PolymerC and Polymer D were selected for the longerterm experiments. The average volume loss(in mm³) as a function of time is presented atFigure 5. It can be seen that, by increasing thetesting time, the difference between PolymerC  and  Polymer  D  became  obvious.  In  therubber wheel test setup (Figure 5 a), PolymerC exhibited a mild increase in wearcomparing to the 1.5 hour test results,reaching a wear loss volume of about 750mm³ at the volume loss at the end of the test.On the other hand, Polymer D was completelyworn off after 4.5 hours of testing. Thisdifference was even more pronounced in thetests with the steel wheel test setup, seeFigure  5  b,  in  which  Polymer  D  wascompletely  worn  off  after  2  hours  of  testing.A negatiive trend in the wear behavior wasdetected for Polymer C in the time sequencebetween 4.5 and 6 hours; for all testedsamples, the detected mass loss was lowerafter  6  hours  of  testing  than  after  4.5  hours.a)b)a)b)V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials25TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015Figure 5. Average volume loss for selectedpolymer materials after the 6 hr experiments:a) ASTM G65 rubber wheel setup; b) ASTMG65 steel wheel setup.Surface analysisImages of 3D surface topography results fromthe measurements inside the wear scars arepresented in the Figures 6 and 7. The scannedareas were 0.96 mm × 1.3 mm in size. As itcan be seen for all selected polymers in theFigures 6 and 7, the abrasion grooves wereparallel to the main direction of motion of thewheel of the test setup and the abrasive sand.The only exception was Polymer A, for whichno grooves were detected.Figure 6. 3D surface topography within thewear scar generated during the tests with therubber wheel for: a) Polymer A; b) PolymerB; c) Polymer C; d) Polymer DNote: Arrows indicates sliding directions!Figure 7. 3D surface topography within thewear scar generated during the tests with thesteel wheel for:a) Polymer A; b) Polymer B; c) Polymer C;d) Polymer DNote: Arrows indicates sliding directions!DISCUSSIONAs known from the literature, hardness playsa significant role in abrasive resistance [20]. Itis a common rule that harder materialspossess higher anti abrasion resistance [21]. Itshould be taken into account that throughoutthe entire experiment, different contactconditions were present. For instance,depending on the surface material of thea)b)a) b)c) d)a) b)c) d)V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials26TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015testing  wheel  of  the  ASTM  G65  equipment,the conditions in contact could be either asoft-soft or soft-hard combination, and thisaffects the abrasive behaviour dramatically.As  it  can  be  noticed  from  Figure  3,  for  bothtesting setups, Polymers A, B and C behavessimilar to the steels and ceramics in the termsof the abrasive resistance (lower wear lossvolume for materials with higher hardness).For Polymer D which possesses the highesthardness, abrasive behaviour changescomparing to Polymer A, B, and C.Additionally, it should be mentioned that thehardness is not the only parameter that affectsthe present tribosystems. For instance, for allpolyurethanes (Polymer B, C, and D), theelongation is the lowest for the Polymer C,which exhibits the best performance. Amongthe polyurethanes, Polymer C is the stiffestone, which from a design standpoint can playa significant role considering the necessity formaintaining the geometry of the designedmachine component within prescribedtolerances during the operation. Apparently,Polymer C with the lowest elongation-to-hardness ratio exhibits the highest resistanceagainst abrasive wear. Relatively low wear incomparison with that of the reference steels(Figure 4) can be attributed to the elasticity ofPolymer C, which is high enough to allowdeformation of the surface of the test sample,in  order  to  allow  the  passage  of  sharp  sandparticles  without  significant  damage  of  thesurface,  and  still  not  high  enough  to  allowextensive wear of the surface. In the lasttesting sequence of Polymer D in steel wheelsetup (Figure 5 b), a diverging trend wasobserved; while for the rubber wheel setup,the  amount  of  wear  was  progressive  withcontinuous increase in the wear volume withtime, the progress of wear was rather unlinearin the steel wheel test setup. The reason for adecrease in the volumetric wear rate after 4.5hours  of  testing  was  sand  particles  that  hadbecome embedded in the sliding surface ofPolymer C, protecting the surface from wearand adding to the mass of the test sample.Figure 8 presents the wear scar topographygenerated on Polymer C after 6 hours ofexperiments. In this case the entrapment ofthe particles occurs on the inlet side, whensand particles enter into the contact zone, andget embedded to the high contact pressure.Due to the elasticity, which is not highenough to allow displacement of particles outof the bulk polymer material, the sandparticles remained in the contact area.Figure 8. 3D surface topography of PolymerC wear scar from a 6 hours experiment (Thearrow shows the direction of motion of thewheel surface, and the main direction of theabrasive sand).Additionally, it is noteworthy that the surfacetopographies of the other selected specimenstested under steel and rubber wheel setup(Figure 6 and 7) revealed a similar behaviorof polymer samples as reported previously inthe literature [5]. All selected polyurethanehad topography with grooves parallel to thesliding direction. The groove formation is theconsequence of delaminating of surfacepolymer layers due to the abrasion.CONCLUSIONSSeveral conclusions can be derived:Among the present materials studied, thepolyethylene-based samples exhibited thelowest resistance against abrasion.For the polyurethane-based samples, theabrasion resistance depended on bothhardness and elongation before breakAt high contact pressures, the entrapmentof sand particles, and hence, lower wearare possible.V. Pejakovi  et al.: Abrasion resistance of selected commercially available polymer materials27TRIBOLOGIA - Finnish Journal of Tribology 1 vol 33/2015ACKNOWLEDGEMENTS:This work was funded by the AustrianCOMET-Programme (Project K2XTribology, no. 824187) and carried out atthe Excellence Centre of Tribology.REFERENCES1. Friedrich K., 1986, ‘‘Composite materialsseries 1’’, Amsterdam: Elsevier; [Chapter8].2. Budinski KG., 1997, ‘‘Abrasionresistance of plastics’’, Wear; 203 (204)302–9.3. Mang T., Dresel W., 2007, ‘‘Lubricantsand Lubrication’’, WILEY – VCH VerlagGmbH & Co.4. Neale MJ., Gee M., 2001, ‘‘Guide to wearproblems and testing for industry’’, NewYork, USA: William Andrew Publishing.5. Lancaster  JK.,  1969,   ‘‘Abrasive  wear  ofpolymers; Wear’’, Elsevier6. Hailing J., 1983, ‘‘Toward a mechanicalwear equation’’ ASME, J. Lubr. Tech.;105:212-219.7. Bolvari AE., Gleen SB., 1996, ‘‘Abrasivewear of polymer composites’’, Eng.Plast.; 9:205–215.8. Friedrich K., Reinicke P., 1998, ‘‘Frictionand wear of polymer-basedcomposites’’,Mech. Compos. Mater.;34;5: 503–514.9. Rabinowicz E., 1981, ‘‘The wearcoefficient-Magnitude, Scatter, Uses’’,ASME, J. Lubr. Tech.; 103:188-193.10. Bijwe J., Tewari US., Vasudevan P.,1989,  ‘‘Friction  and  wear  studies  of  ashort glass-fibre-reinforcedpolyetherimide composite’’,Wear;132:247–264.11. Fang L., Zhou QD., Li YJ., 1991, ‘‘Anexplanation of the relation between wearand material hardness in three-bodyabrasion’’, Wear; 151:313–321.12. Trizona RI., Hutchings IM., 1999,‘‘Three-body abrasive wear testing of softmaterials’’, Wear; 233–235:209–221.13. Budinski KG., 1997, ‘‘Resistance toparticle abrasion of selected plastics’’,Wear 203-204; 302-30914. Suresha B., Chandramohan G.,Siddaramaiah, Kunigal N. Shivakumar,Mohammed Ismail, 2008,  ‘‘Mechanicaland three-body abrasive wear behaviourof three-dimensional glass fabricreinforced vinyl ester composite’’,Materials Science and Engineering A480; 573–57915. Cenna A.A., Doyle J., Page N.W., BeehagA., Dastoor P., 2000,  ‘‘Wear mechanismsin polymer matrix composites abraded bybulk solids’’, Wear 240; 207–21416. Harsha A.P., Tewari U.S., VenkatramanB.,  2003,   ‘‘Three-body  abrasive  wearbehaviour of polyaryletherketonecomposites’’, Wear 254; 680–69217. Shipway PH., Ngao NK., 2003,‘‘Microscale abrasive wear of polymericmaterials’’. Wear;255:742–750.18. Evans D.C., Lancaster J.K., 1979,‘‘Treatise on Materials Science andTechnology’’, 13. New York, USA: 85–139.19. ASTM G65-04(2010), Standard TestMethod for Measuring Abrasion Usingthe Dry Sand/Rubber Wheel Apparatus,ASTM International, WestConshohocken, PA, 2010, www.astm.org20.  Stachoviak G., Batchelor A., 2005,Engineering tribology-Third edition,Butterworth Heinemann21. Wirojanupatump S., Shipway P.H., 2000,‘‘Abrasion  of  mild  steel  in  wet  and  dryconditions with the rubber and steel wheelabrasion apparatus’’, Wear 239; 91–101The paper was presented at NORDTRIB2014,Aarhus, Denmark.

Abrasion resistance of selected commercially available polymer materials

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Abrasion resistance of selected commercially available polymer materials

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