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Chemically Assisted Surface Engineering, or CASE sm,
is a two-stage process developed by Metal Improvement
Company to extend a component's surface fatigue life
beyond that provided by shot peening alone. CASE consists
of shot peening followed by isotropic finishing. The
isotropic finishing step of the CASE process improves
traditional vibratory honing techniques by the addition
of mild chemicals, which removes the asperities left
from shot peening and retains shallow micro-indentations
for lubricant retention.
CASE is ideal for surfaces that require both excellent
fatigue strength and surface finish due to contact loading.
CASE has proven effective in improving resistance to
pitting and micro pitting of gear teeth flanks, failure
mechanisms that limit the performance of many gear designs.
For example, transmission gears utilized in aerospace,
automotive racing and off-highway applications are required
to run for many years under high root bending loads
and tooth flank contact loads. CASE has proven successful
for use in all these industries.
Surface finishes of 10 micro-inches (Ra) or better are
attainable with CASE on carburized gears. The figure
below shows a typical roughness profile of a carburized
gear after shot peening and also after the isotropic
finishing portion of CASE.
Click
image to enlarge |
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The "peak to valley" of the shot peened finish is
~ 2.9 microns. After isotropic finishing, performed
as part of CASE, this improves to ~ 0.6 microns.
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