Rock bit cone retention system

Details Rock bit cone retention system Rock bit cone retention system

1999-07-01

2001-01-09

Neuder, William (Department: 3672)

Boring or penetrating the earth

Bit or bit element

Rolling cutter bit or rolling cutter bit element

C384S096000, C175S371000

Reexamination Certificate

active

06170582

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates generally to roller cone drill bits. More particularly, the invention relates to a system for retaining a roller cone on a bearing journal of the drill bit.
2. Background Art
Roller cone drill bits are generally made of a plurality of legs that are welded together to form a unitary structure.
FIG. 1
shows an example of a drill bit leg
2
which defines a shirttail portion
4
and a cantilevered journal
6
. The journal
6
forms a main bearing surface
8
for a roller cone
10
. The roller cone
10
has cutting elements
12
which are adapted to deform earth formation as the drill bit leg
2
is rotated within a borehole. The roller cone
10
is retained on the journal
6
by a ball lock system which includes balls
16
that are retained between ball races
18
and
20
on the journal
6
and the roller cone
10
, respectively. To assemble and lock the roller cone
10
to the journal
6
, the balls
16
are inserted between the journal
6
and the roller cone
10
through a ball hole
22
which is drilled through the shirttail portion
4
and the journal
6
. The ball hole
22
intersects the top dead center
24
of the ball race
18
. The balls
16
are retained between the journal
6
and the roller cone
10
by welding a ball plug
25
in the shirttail side of the ball hole
22
.
The drill bit leg thus described retains a roller cone on a journal using a ball lock system. However, there are other methods of retaining a roller cone on a journal, for example, segmented cone retention rings disposed in a slot on the journal and subsequently threadedly locked to the roller cone using a hole to gain access to a device which prevents rotation of the rings. Generally, any cone retention system that includes a hole penetrating a ball race or other slot on the journal will induce localized stresses in the ball race or slot. In particular, when the hole intersects a high stress region on the ball race, localized stresses which develop around the intersection of the ball race with the ball hole during operation of the drill bit may be sufficient to initiate cracks in the ball race and, possibly, break the journal. It would, however, be desirable to access the ball race or other slot on the journal without initiating cracks in the journal.
SUMMARY OF THE INVENTION
A roller cone drill bit comprises a bit body adapted to be rotated about a longitudinal axis. The bit body has at least one leg depending from it. A journal is cantilevered from the leg. A roller cone is rotatably mounted on the journal. A cone retention member is disposed between a first slot in the journal and a corresponding second slot in the roller cone. An access hole runs through the journal to the first slot. The access hole intersects the first slot at a location away from the top dead center of the first slot.
Other aspects and advantages of the invention will be apparent from the following description and the appended claims.


REFERENCES:
patent: 4646620 (1987-03-01), Buchl
patent: 4646858 (1987-03-01), Strickland
patent: 4722615 (1988-02-01), Bailey et al.
patent: 4825655 (1989-05-01), Buchl et al.
patent: 4991671 (1991-02-01), Pearce et al.
patent: 5427182 (1995-06-01), Winter
patent: 5669452 (1997-09-01), Wright et al.

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