[0001] The invention relater to a rotating bit as set forth in the preamble of claim 1.
[0002] A bit of the kind referred to is known from US-A-4 098 363 including junk slots which
have a single profile throughout their longitudinal length.
[0003] What is needed is a bit having substantially improved hydraulic flow within its junk
slots.
[0004] To this end the invention provides a rotating bit as claimed in Claim 1. Further
embodiments are included in claims 2 - 4.
[0005] By reason of the junk slot design according to the invention reverse flow, turbulent
or unstable flows and eddies which have been observed in conventional junk slots,
can be avoided or at least substantially diminished.
[0006] The invention is more graphically depicted in the drawing illustrating a top plan
view of a mold from which a matrix bit incorporating the invention is fabricated.
[0007] What is shown in the drawing is a plan view of the settings of the large diamond
compact cutters on the face of a bit as seen looking into a mold in which such a diamond
bit would be made by matrix infiltration. Thus the bit, generally denoted by reference
numeral 10, is characterized by an exterior cylindrical surface or gage 12 terminated
on its lowermost portion by a bit face, generally denoted by reference numeral 14.
Defined within gage 12 is a plurality of junk slots 16 and 18. Junk slots 16 are distinguishable
from junk slots 18 in that junk slots 16 have uniform contour as opposed to a contoured
or compound surface within junk slots 18 as will be described below.
[0008] In the embodiment illustrated a 12 1/4 inch diameter bit is illustrated in which
nine large cutters 21-29 will be formed, each comprising a substrate 45, a slug 44
and a diamond table 46 as shown at cutter 24, which is brazed into a pocket 48 of
the mold at positions 1 - 9. For the sake of clarity of illustration each cutter is
shown in midline cross-sectional view with the diamond cutter in place. In actuality
the diamond slugs may be fixed or brazed into the bit in a later step, and would not
be seen in place in the mold as depicted in the drawings. See generally US-A-4 098
363 for background information concerning the casting of the bit body, cutter shapes
and materials, and various methods of attachment of the cutters. However for ease
of conceptualization, the drawings illustrates the diamond cutters in place as would
be seen looking downward through the diamond bit toward the rock formation. In reality
in a top plan view of a mold, only the pockets into which the diamond slugs were later
brazed would be seen.
[0009] Corresponding to each cutter is a nozzle 31-39 which provides a directed flow to
the cutter. Nozzle 31 thus provides directed flow for cutter 21, nozzle 32 for cutter
22 and so forth through nozzle 39 and cutter 29. In addition to cutters 21-29, a plurality
of gage cutters 40 are defined within the shoulder and gage of bit 10 which are also
illustrated in a sometimes overlying relationship. The depiction of gage cutters 40
appears to be overlying since the cutters, which may be vertically separated, are
superimposed in the diagrammatic view of the drawing.
[0010] In addition to junk slots 16 and 18, a plurality of collectors 42 are similarly provided
within gage 12. These are provided to enhance the cleaning and cooling of gage cutters
40. Gage defining cutters 40 are comprised of conventionally fabricated Stratapax
or Compax cutters and can, by virtue of their relative scale to cutters 21-29, provide
a relative feel for the sizes of cutters 21-29.
[0011] Generally, cutters 21-29 of the illustrated embodiment have a predetermined rake
angle of diamond table 46. In the illustration, however, each cutter 21-29 has been
shown only in a midline section for the sake of clarity. Therefore it must be kept
in mind that portions of the face of diamond table 46 actually extend both in front
of and behind the midsection line shown in the illustration for each cutter 21-29
by an amount depending on the rake angle of each cutter.
[0012] The cutter can have different shapes, e.g. triangular, hexagonal, square, or octagonal.
The cutter can be composed of thermally stable diamond or some other material such
as silicon carbide, tungsten carbide, or baron carbide. During manufacture of the
bit, the cutter can be furnaced with the bit body in order to attach it to the bit.
[0013] The junk slot 18 is characterized by having at least two distinct cross-sectional
profiles, namely a symmetric profile at its upper portion farthest from the bit face
and an asymmetric profile along its lower portion. The asymmetric and symmetric profiles
are connected by a surface providing a smooth hydrodynamic transition.
[0014] Consider specifically the contoured junk slots 18 as depicted in the drawing. Junk
slot 18 is a longitudinal cavity defined within gage 12 to facilitate removal of cut
material. In the lower portion of junk slot 18, nearest bit face 14, junk slot 18
is characterized by a first asymmetric profile shown in dotted outline as portion
80. The upper portion of junk slot 18, furthest away from the face 14, has a distinct
second profile 82 as depicted in solid outline. Thus, the lower section of junk slot
18 has a nonuniform asymmetric profile 80 while the upper section has a substantially
uniform symmetric profile 82. The transition between profiles 80 and 82 within the
middle region of junk slot 18 is smoothed so that cross sections (not shown) would
reflect a smooth hydrodynamic transition between the dramatically different profiles
80 and 82.
[0015] In the illustrated embodiment the first profile 80 has been shown with a wedge shaped
leading portion, which transitions to a full depth, following portion which is equivalent
to second profile 82. It is entirely within the scope of the invention that profile
80 may be reversed, namely having a full depth leading profile transitioning to a
wedged-shaped following portion. Furthermore, any junk slot profile known in the art,
in addition to illustrated profiles 80 and 82 may be used or variously combined with
each other as may be desired. Similarly, the longitudinal relationship of the portions
may be reversed if desired. For example, asymmetric profile 80 may characterize the
upper section of junk slot 18, while full portion 82 would characterize the lower
section nearest bit face 14.
1. In a rotating bit (10) having a bit face (14) and a gage (12), and at least one junk
slot (18) defined in and extending substantially longitudinally along said gage (12)
of said bit (10), the improvement characterized in that said junk slot (18) includes
a compound profile along its longitudinal extent, said compound profile including
at least two distinct substantially longitudinally superimposed regions (80;82) of
differing cross-sectional configuration connected by a hydrodynamically smooth transitional
region.
2. The improvement of Claim 1 wherein said at least two profiles of said junk slot (18)
comprise a symmetric profile (82) and an asymmetric profile (80).
3. The improvement of Claim 2 wherein said asymmetric profile (80) is longitudinally
defined within said junk slot (18) nearer said bit face (14) than said symmetric profile
(82).
4. The improvement of Claim 3 wherein at least one portion of said asymmetric profile
(80) is identical to said symmetric profile (82).
