Mining or in situ disintegration of hard material – Cutter tooth or tooth head – Rolling or rotatable bit
Reexamination Certificate
1999-10-22
2001-08-07
Bagnell, David (Department: 3673)
Mining or in situ disintegration of hard material
Cutter tooth or tooth head
Rolling or rotatable bit
Reexamination Certificate
active
06270165
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to cutting tools used on mining and construction machines to break hard natural materials such as rock and minerals (e.g., coal) and also man-made materials such as concrete and asphalt.
Known in the industry is a prior art cutting tool of that type which comprises a hard alloy cap having a base mounted on a metal shank (e.g., see U.S. Pat. No. 4,938,538). The base of the hard alloy cap is shaped in such a way as to provide the tool with sufficient strength and durability for its intended operating conditions. Also known in the industry is the fact that caps have a better geometric shape than inserts, which improves the cutting efficiency of the tool by reducing the cutting forces needed to break the material. Further known is the fact that caps increase the operating life of prior art tools by better protecting the metal shank from the material being cut.
However, the geometric form of the cap is not optimal for the operating life of the tool. A prior art tool depicted in
FIGS. 1 and 2
comprises a steel tool body
10
and a cap
11
of hard metal. The cap
11
has a conical tip
12
, and a base
13
intended to rest against a supporting surface
14
on the tool body
10
, to protect the portion of the steel tool body
10
surrounding the cutting cap
11
from such wear as would cause the cap
11
to become loose. The rear contact surface
20
of the base
13
is brazed to the supporting surface
14
. The cap
11
is provided with an intermediate portion
15
located between the tip
12
and the base
13
.
The intermediate portion
15
comprises a cylindrical intermediate surface portion
17
″, and a concave portion
17
′. Due to the elongated intermediate surface portion
17
″ the required cutting force is maintained low even when the tip portion
12
becomes worn since the tip size remains generally the same as the tip wears down along the elongated intermediate surface portion
17
″. Due to this design it is also ensured that the steel in the tool body
10
surrounding the cutting insert is protected against premature abrasion; this protection being provided by the concave portion
17
′ and the base
13
. The base
13
has a diameter D, and the intermediate surface portion
17
″ has a diameter d. A distance H extends from the front of the tip portion
12
to a rear end of the base
13
. A ratio of H/D is less than 1.0, and a ratio of d/D is less than 0.7.
Despite the successful performance of that cap
11
, room for improvement remains. Often times the cap wears down to a shape that increases the cutting forces so much that the tool becomes unusable. Larger caps can increase the life of the tool, but since the hard alloy material is usually an expensive tungsten-cobalt material, the cost of the tool also increases.
An object of the invention is to provide a cap geometry which reduces the cost of the tool by using less tungsten-cobalt material while increasing the life of the tool by maintaining lower cutting forces longer, and at the same time protecting the metal shank from the material being cut.
SUMMARY OF THE INVENTION
The invention relates to a rotatable tool for breaking hard material.
The tool comprises an elongated tool body, and a cutting cap formed of hard metal and defining a longitudinal axis. The cutting cap includes a generally conical front tip, a rear base portion, and an intermediate portion. The tip has a maximum first diameter (d). The base portion has an outer peripheral surface defining a maximum second diameter (D), and a rearwardly facing surface bonded to a front end of the tool body. The intermediate portion extends from the tip to the base and defines an abrupt transition from the tip. At least part of the intermediate portion has a concave outer peripheral surface. A longitudinal extent (H) of the cap extends from a front end of the tip to a rear end of the outer peripheral surface of the base. The ratio of d to D is equal to or greater than 0.7. The ratio of H to D is equal to or greater than 1.0.
The invention also relates to the cutting cap per se.
REFERENCES:
patent: 4893875 (1990-01-01), Lonn et al.
patent: 4938538 (1990-07-01), Larsson et al.
patent: 5112165 (1992-05-01), Hedlund et al.
patent: 5219209 (1993-06-01), Prizzi et al.
patent: 5503463 (1996-04-01), Ojanen
patent: 5702160 (1997-12-01), Levankovskii et al.
Bagnell David
Burns Doane , Swecker, Mathis LLP
Kreck John
Sandvik Rock Tools, Inc.
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