I-SUP 2008 April Evaluating self-lubricating materials for large scale bearings functioning under seawater conditions

Transcription

1 I-SUP 2008 April Evaluating self-lubricating materials for large scale bearings functioning under seawater conditions Van Autrève S., Ost W., Van Wittenberghe J. and De Baets P. 1

2 Application Civil engineering : moving parts Ships & deck applications Locks, gates, drawbridges Mooring systems Hydropower What makes these applications special Water lubricated Small amplitude Small velocity Corrosive/ underwater Permanent loading 2

3 Typical materials Bulk polymer materials - Cheap - Low strength - Low PV value Bronze materials - Base material + solid lubricant - High strength - Friction µ Use of lead (lead bronze / lubricant) - Adhesive wear / fretting wear Composite materials - Fibres : increased strength - Solid lubricant PTFE - Friction µ 0,1 - PV limit 3

4 Large scale testing SCALE DEPENDENT: Distribution of solid lubricant Contact pressure & distribution Edge effect Non-uniform pressure Behaviour of wear particles Effect of (small) stroke Typical application Ø 300 mm Typical small scale test Ø8 mm 4

5 Test setup Radially loaded bearing Load introduced by carriage (8 wheels) Shaft of bearing: oscillating movement Side flanges + seals: water lubrication Measured signals Friction torque Bulk temperature countersurface Vertical displacement of bearing (wear) Controlled Drive piston displacement Radial load 5

6 Test setup Max radial load: 1350 kn Max transferable torque: 100 knm Radial load Max bearing size Max rotation Max torque Configuration 1350 kn Ø 400 mm, Length 300 mm +/ knm Moving shaft Moving bearing 6

7 Test setup 7

8 Specimens Bearing material Back-up ring Countersurface Temperature sensor 8

9 Hydraulic piston Calculation of the COF Sliding Loadcell F P Contact line at θ = a µ = F F F N sin α = 1 = tanα = 1 R R L B F P F L + F L sin 2 α 1 1 µ = = tan α 2 2 R b FP + F L 1 R L F L Loadcell F L R L, R b : known geometrical values 9

10 θ: position contact line Oscillating movement At velocity reversal: ROLLING b=0 φ = θ y = x = ( R R ) s R s b ( R R ) ( 1 cosθ) b ( R R ) sin θ b Bearing clearance s s Shaft rotation during rolling: Sliding θ = ± α Rolling -α < θ <α ( R R ) s b clearance ϕ2 α = 2α = 2α R diameter s 10

11 Materials and test conditions Normal load: Contact Pressure: Velocity bearing: Sliding stroke: Friction material: Counterspecimen: Bearing clearance: 100 kn (compression) 2.8 MPa 10 mm/s 10 mm Filament wound composite material Polyester fibres Phenolic resin and PTFE (solid lubricant) 300 mm x 120 mm Steel S355J2G3 surface roughness: 0.2 µm < R a < 0.3 µm 1.1 mm 11

12 Normal force F N Test results Drive piston displacement Friction force F F 12

13 Measured horizontal displacement Calculated horizontal displacement Force on loadarm F L Test results Elastic deformation Drive piston displacement 13

14 Test results Coefficient of friction µ stat 0.14 Drive piston displacement µ dyn

15 Test results Coefficient of friction shaft rotation Clearance in loadcell connection 15

16 Conclusions Test apparatus developed for Large scale testing(heavy loading conditions) Evaluation of friction and wear behaviour of journal bearings Dry and wet (seawater) operating conditions First tests show COF can be calculated from the measured F P and F L Measured values of COF correspond to manufacturers values Elastic deformation should be taken into account for the calculation of the rolling angle 16