WEAR TESTING AND MEASUREMENT TECHNIQUES FOR POLYMER COMPOSITE GEARS

Transcription

1 WEAR TESTING AND MEASUREMENT TECHNIQUES FOR POLYMER COMPOSITE GEARS N. A. Wright and S. N. Kukureka Wear, 250, 1567, (2001) Presented at 13 th International Wear of Materials Conference, Vancouver, 2001.

2 INTRODUCTION

3 Introduction Polymers and composites widely used for machine elements including gears, cams and pulleys Polymers used for power transmission and motion transmission Small components often highly stressed Typical applications Automated teller machines (ATM) Computer printers, photocopiers Small drives and gear mechanisms

4 Introduction Advantages of polymer gears low mass and inertia cost reduction if moulded design freedom no lubrication corrosion resistance noise reduction

5 Introduction Disadvantages temperature effects Polymer metal contact better heat dissipation Polymer polymer contact cheaper if complex geometry Typically conformal contacts polymers against steel Non-conformal contacts polymers against polymers

6 Introduction Gear geometry Gear contact is concentrated and nonconformal throughout Gears have an involute profile and a constant velocity ratio The sliding velocity, contact radius, and contact load all vary over the tooth face Motion is a combination of rolling and sliding

7 Introduction Rolling and sliding in gears

8 Introduction Gear action Initial contact tip of driven gear near root of driver Between initial contact and pitch point a mixture of rolling and sliding Rolling always same direction on both teeth Contact length less on driving than on driven gear flank since pitch point nearer to root than tip Therefore gear teeth must also slide to move contact to pitch point

9 Introduction Rolling and sliding in gears

10 Introduction At the pitch point pure rolling momentarily Direction of friction force now changes on both teeth On driving gear direction of friction is always away from pitch line On driven gear direction of friction is always towards the pitch line Therefore friction and rolling are - opposed for half the action - in the same direction for half the action Sliding motion greatest at start and end of tooth engagement

11 Introduction Rolling and sliding in gears

12 TEST METHODS FOR GEARS

13 Test methods for gears Direct gear testing Electronic measurement Weight loss Co-ordinate measurement Gear contact simulation Twin-disc test

14 Test methods for gears Gear test rig

15 Test methods for gears Electronic measurement solely at pitch line combines wear viscoelasticity hub movement moisture absorption thermal expansion

16 Test methods for gears Weight loss moisture loss at running temperatures differences in absorbed water for filled polymers dry weighing tedious Alternative - control gears

17 Test methods for gears Co-ordinate measurement tooth profiles measured qualitative information individual teeth scanned compared with involute profiles at various roll angles

18 Test methods for gears Datum axes for co-ordinate measurement

19 Test methods for gears Orientation of co-ordinate measuring scan

20 Test methods for gears Orientation of the tangential co-ordinate measuring scan

21 Test methods for gears Wear measurement by co-ordinate measuring data

22 Test methods Gear contact simulation by twin-disc testing

23 Test methods Twin-disc machine

24 Test methods Twin-disc tests separate rolling from sliding two discs loaded and run together if discs at same velocity then pure rolling velocity difference allows controlled rolling and sliding slip ratio = (Sliding velocity) / (Average rolling velocity)

25 Test methods Discs run at varying normal loads, speeds and slip ratios Wear and coefficient of friction measured continuously Wear measured by on-line displacement monitoring weighing samples Heat dissipation conduction (40%), convection (40%), radiation (20%) superimposed local flash temperatures

26 MATERIALS

27 Materials Materials Polyamide % short glass fibres + 30% short glass fibres + 30% short carbon fibres + 15% PTFE + 30% short carbon fibres + 15% PTFE + 30% long glass fibres

28 SPECIMENS

29 Specimens MATERIALS INJECTION MOULDING MACHINE GEARS DISCS

30 Specimens Specifications of gear specimens Standard involute profile Teeth 30 Pitch circle diameter 17 Module 2 Addendum height 2 Face width 17 mm mm mm mm

31 Specimens Geometry of disc specimens

32 EXPERIMENTAL METHODS

33 Experimental methods Testing parameters for gear specimens Torque 10 Nm Speed 1000 rpm

34 RESULTS AND DISCUSSION

35 Results and discussion Corrected weight loss against cycles

36 Results and discussion Weight rates compared with pin-on-disc tests

37 Results and discussion Glass Fibre Reinforced Gear Teeth after Testing

38 Results and discussion Geometric change by co-ordinate measurement great differences in worn profiles load sharing complicates load changes wear rates for carbon fibre polyamide change with roll angle and change tooth profile changing tooth profiles poor for gear performance

39 Results and discussion Overall wear from co-ordinate measurement (Average measured wear rate over all roll angles) x (length of involute in contact) x (tooth face width) = (total wear volume / tooth) Hence total wear for all teeth More accurate since measured over range of roll angles

40 Results and discussion Weight loss and co-ordinate measuring methods

41 Results and discussion Co-ordinate measuring and twin-disc methods

42 CONCLUSIONS

43 Conclusions Conclusions 1. Measuring wear of polymer gears is difficult 2. Recording displacement at the pitch line and weight loss measurements both have problems 3. Co-ordinate measurement provide data on wear rates as a function of roll angle, and hence load, sliding speed and slip ratio 4. Geometry can be separated from materials effects by twin-disc tests 5. No correlation with pin-on-disc tests in simple sliding 6. Some correlation between twin-disc tests and gears 7. Materials effects important including fibres and matrix crystallinity