Abstract:
The
principal objective of this research was to produce a
series of extremely stiff and thermally stable porous
ceramic bearings, and to expand the performance envelope of
fluid film technology beyond that currently achievable with
conventional oil hydrostatic bearings. The driving force
for these developments came from recent advances in ultra-
precision and high speed machining, which have placed
severe demands on the accuracy and performance of spindle
and
guide-way bearing systems.
A critical part of this research was to develop a material
processing methodology, which enabled porous ceramic
bearing structures to be manufactured with consistent
permeability coefficients. Such control of the material
microstructure was necessary in order to produce a useful
and predetermined level of performance. The bearings were
fabricated using bimodal blends of alumina powder, and
vibratory packing into graphite tooling was used to achieve
uniform green densities. Following this, the tooling was
transferred directly to a hot isostatic press for capsule
free high pressure sintering. The influence of temperature
and pressure on sintering and permeability was studied, and
optimum processing conditions were established.
The operation of the water lubricated porous hydrostatic
bearing was investigated on a highly instrumented journal
test rig. This research has resulted in a bearing with
greater stiffness, higher operating speed and lower power
consumption than conventional oil hydrostatic technology
could achieve. Significant savings were also shown
regarding the energy required to drive the spindle
assembly, with a reduction in both rotating frictional
power and lubricant pumping power consumption.
