Wrijving en slijtage van kunststofproducten

Transcription

1 Society of Plastics Engineers Europe Wrijving en slijtage van kunststofproducten Jan Spoormaker Spoormaker-Consultancy in Reliability and Liability of Plastic Products Tribologie/polymeren

2 Friction Dictaat Hfdst. 3 tekst Friction and wear of plastic products Friction is a force that resist relative movements between two surfaces in contact. Wear Wear is a process in which interaction of surface(s) or bounding face(s) of a solid with the working environment results in the dimensional loss of the solid, with loss of material. Friction and wear are system properties Tribology Science about friction, lubrication and wear Tribotechnology Engineering application of tribology

3 Tribological System according to Czichos Loads & environment Loads & environment Tribological quantities Relative movement Gliding, rolling Load F n Velocity v Ambient temperature 1. Body 2. Body 3. Substance 4. Environment Friction force F w Friction coefficient f, μ Wear h Friction temperature Noise Dictaat Hfdst. 3 Fig. 3.1 Surface parameters Roughness Macro geometry

4 Polymeren Plastics are fantastic, they can fail in many unexpected ways - polymerisatie - ketenopbouw en ketenlengte - fysische eigenschappen - kristallisatie IO

5 Polymeriseren en ketenlengte additiepolymerisatie IO

6 Polymeriseren van etheen C 2 H 4 PE IO

7 Polymeriseren van etheen C 2 H 4 PE onvertakt IO vertakt

8 Ketenlengte Dictaat Hfdst. 3 Fig. 3.1

9 Ketenlengte Dictaat Hfdst. 3 Fig. 3.1

10 Ketenlengte van PE Paraffine (500 g/mol ) lijmtube (10 5 g/mol) UHMW-PE ( g/mol) IO

11 Molecuulmassa - sterkte en viscositeit IO

12 Amorf en semi-kristallijn tie-molecule IO

13 Kristallisatiesnelheid IO parison

14 Pwrijving en slijtage bij kunststoffen wrijving slijtage contactoppervlak vervorming cohesie en adhesie IO

15 Normal force, drag force and friction force Dictaat Hfdst. 3 Fig. 3.3 Material combination PA6 - PA PA6 POM PA6 PTFE POM POM μ, f (no lubrication) (no lubrication) 0.60 (no lubrication) 0.10 (no lubrication) 0.55

16 Wear h k p v t Material combination wear factor k POM steel (Ra = 0.1 μm) m 2 /N POM steel (Ra = 0.6 μm) m 2 /N Dictaat Hfdst. 3 Fig. 3.4

17 Micro contact surface Dictaat Hfdst. 3 Fig. 3.5

18 Deformation Dictaat Hfdst. 3 Fig. 3.6

19 Physical processes cohesion and adhesion Bonding forces Cohesion Adhesion Dictaat Hfdst. 3 Fig. 3.9

20 Wrijving bij kunststoffen ruwheid snelheid stick-slip effect IO

21 Friction coeeficient as a function of roughness High yield strength Low yield strength Surface roughness Surface roughness Dictaat Hfdst. 3 Fig. 3.10

22 Friction coefficient as a function of roughness for POM and HDPE Roughness Ra (μm) Roughness Ra (μm) Dictaat Hfdst. 3 Fig. 3.11

23 Friction coefficient as a function of speed Speed Dictaat Hfdst. 3 Fig. 3.12

24 Mass-spring model Dictaat Hfdst. 3 Fig. 3.13

25 Stick-slip effect time Dictaat Hfdst. 3 Fig. 3.14

26 slijtage bij kunststoffen deformatie adhesieve slijtage abrasieve slijtage pitting IO

27 Boundary and deformation zone Hard roughness asperity top Boundary zone Deformation zone Dictaat Hfdst. 3 Fig. 3.15

28 Adhesive wear Dictaat Hfdst. 3 Fig. 3.16

29 Abrasive wear Dictaat Hfdst. 3 Fig. 3.17

30 Shear stress for rolling contact Dictaat Hfdst. 3 Fig. 3.18

31 Pitching as a result of fatigue Fatigue cracks Pitting Dictaat Hfdst. 3 Fig. 3.19

32 Knieprothese

33 Knieprothese

34 Putvorming in UHMPE

35 Lagers slijtage ruwheid meten van slijtage vlaktedruk pv waarde warmte-ontwikkeling PTFE Hardheid IO

36 Wear as a function of roughness for POM and HDPE Dictaat Hfdst. 3 Fig. 3.20

37 Wear as a function of roughness and pressure for PA6.6 Dictaat Hfdst. 3 Fig. 3.21

38 Wear as a function of pressure Dictaat Hfdst. 3 Fig. 3.22

39 Different wear tests Dictaat Hfdst. 3 Fig. 3.23

40 Pin on disk Dictaat Hfdst. 3 Fig. 3.24

41 Calculation of average bearing pressure and wear p F T D p 43MPa h k p v t Extra

42 Heat flux and Average Bearing Pressure f p v h 2 (W/m ) - heat flux f friction coeficient p average bearing presure v - velocity Dictaat Hfdst. 3 tekst

43 Critical pv-values Dictaat Hfdst. 3 Fig. 3.25

44 Prediction of wear h k p v t k wear factor p average bearing presure v velocity t - time Dictaat Hfdst. 3 tekst

45 Coefficients of friction and wear rates h1 k1 p v t h2 k2 p v t Extra

46 Effect of PTFE content on wear Extra

47 PTFE & silicone to reduce friction and wear Extra LNP Lubricomp

48 Effect of hardness on wear Extra LNP Lubricomp

49 Effect of shaft finish on wear (micro-inches!) Extra LNP Lubricomp

50 Tandwielen warmte-ontwikkeling vermoeiing IO

51 Failure analysis Extra

52 Failure analysis Extra

53 Guidelines for plastic bearings Metal bearing surfaces must be smooth (< 1 μm), hard and corrosion resistant. Wear particles must be collected in grooves. Bearing clearance must account for high thermal expansion and absorption of water (PA) The average bearing pressure should preferably be not higher than 1 N/mm 2 and at most 5 N/mm 2. The out-of-roundness of bearings should be as small as possible and film gates are preferred. Bearing plastics with PTFE are preferred especially for applications without lubrication. Boundary lubrication is must better than running dry. Grease or oil can affect plastic bearings (swelling & ESC) Dictaat Hfdst. 3 tekst