Appeal No. 1999-2131 Page 8
Application No. 08/971,504
Drake discloses a roller cutter type drill bit (column 4,
line 60) which, as shown in Fig. 1, has a bit body (11) and
legs (12) (column 5, lines 13-14). As shown in Fig. 2, leg
(12) has roller cutter (60) rotatably mounted on the main body
(spindle) portion (50) of bearing journal (20) and a flat
thrust washer (86) is in the space between bearing surface
(58) and bearing shoulder (74) with lubricant being supplied
to the bearings from reservoir (38) via channels (39 and 40)
and passages (42). The thrust washer (86) is disclosed as a
floating type bearing element, although, under certain
conditions, it may alternatively be press fit or fixed to
journal (20) or roller cutter (60) (column 7, lines 8-14). It
is stated that "[i]t is an object of this invention to provide
aluminide coated superalloy sliding bearing elements for
roller cutter drill bits" (column 4, lines 39-41). As
explained by Drake,
[m]aterials used in combination with the
hardened steel surfaces in bit journal bearings
have included precipitation hardened copper-
beryllium... and cobalt-based stellite alloys
(shown in U.S. Pat. No. 4,323,284). These
materials offer suitable ambient temperature
yield strengths for use as structural elements
or inlays, and acceptable anti-galling
properties against hardened steel. However, at
elevated PVs they can undergo a transition to
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