Design of a Micro-Mechanical Bearing

Solid Surfaces The shaft and bearing cage are constructed as an assembly by EFAB technology.15 Ra typical on horizontal surfaces..1 mm shaft.01 mm gap

Mechanical Contact A first attempt to describe the contact is made with Hertzian analysis. The rotor is subject to torque due to centrifugal loading at 4,000 rpm. Six design variations are analyzed.

Contact Stresses Design Max. Stress (Pa)Displacement (m) Hertzian (σ,  ) 46.4E6,108E6 Journal.252E6.116E-6 4-Lobe Channel.635E6.353E-6 4-Lobe Nozzle.618E6.348E-6 4-Lobe Diffuser.665E6.362E-6 6-Lobe Channel1.28E64.60E-6 6-Lobe Nozzle1.20E6.444E-6 6-Lobe Diffuser1.58E6.529E-6

Friction The two surfaces are Ni-Co alloy, either 30% Cobalt or 67% Cobalt Friction coefficient influenced by change in phase from FCC to HCP The two design variations seek to reduce the contact area

Wear Wear rate can be reduced by increasing Cobalt content With less than half Cobalt content, wear follows Archard’s Law. Greater than half Cobalt concentration result in inverse Archard’s Law.

Lubrication The gap between the shaft and bearing cage is lubricated with air. CFD will be used to study the shear and pressure distributions due to the rotation of the rotor.

Pressure Differential Bearing  P Nominal (Pa)  P Offset (Pa) Journal Lobe Channel Lobe Nozzle Lobe Diffuser Lobe Channel Lobe Nozzle Lobe Diffuser

Conclusions A reduction in clearance of 99E-6m will result in asperity contact Hertzian contact stresses are below the material yield stress Friction and Wear are dependent on Cobalt content. Lubrication is best for the journal design