Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Excavating tool
The present invention relates to a tool for breaking or ex-
cavating of hard material, such as asphal-t, comprising a tool
body and a cutting inser-t secured thereto, for instance by
brazing. The cutting insert is formed with a generally conical
-tip por-tion and provided with a shoulder which is intended to
res-t against a sllpporting surface on the tool body.
The purpose of the inven-tion is-to provide a tool of the above
type which requires a low cutting force at the same time as it
is ensured -that -the risk is low -that the cut-ting insert will
get loose even during working in wear resis-tan-t material.
This and other objects have been attained by giving the inven-
tion the characterizing features stated in the appending claims.
The inven-tion is described in de-tail in the following with re-
ference to the accompanying drawings, in which one embodiment
is shown by way of example. It is to be understood that -this
embodiment is only illustra-tive of the inven-tion and that va-
rious modifications thereof may be made within the scope of
the claims.
In the drawings, Fig. l shows a side view, part]y in sec-tion,
of a prior art -tool for breaking hard ma-terial.
Fig. 2 shows a side view, party in section, of another prior
art -tool.
Fig. 3 shows one embodimen-t of a tool according to the inven-
-tion.
Fig. L~ shows on an enlarged scale -the cutting insert in -the
tool shown in Fig. 3.
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Corresponding details in -the various figures have been given
the same reference numeral.
Tools of -the type in question are usually mounted rotatably in
a tool holder, which in its turn is at-tached to an excavating
machine, such as a road planing machine or a mining machine.
Due to its rotation the tool is self-sharpening. The machine
migh-t be of the -type disclosed in EP-A-25421.
F'or breaking or excavating of wear resistant material, for
instance for milling in poured asphalt (mastic), tools are used
of -the type shown in Fig. 1. This tool comprises a tool body 10
and a cutting insert 11 of hard metal. The cutting insert 11
is provided with a conical tip portion 12 and a shoulder 13,
which is in-tended to rest against a supporting surface 14 on
-the tool body 10. The rear contact surface 20 of the shoulder
13 is brazed to the supporting surface 14. The cutting insert
11 is provided with a conical intermediate por-tion 15 which is
located between the -tip portion 12 and the shoulder 13. The
portion 15 protects the portion of the -tool body 10 - the tool
body being made of s-teel - surrounding the cutting insert 11
from such wear that would cause -the cutting insert 11 to ge-t
loose. When wear resistant material is excavated, for instance
during milling in poured asphalt, -the tip portion 12 becomes
blunt-ended upon some wear of the cutting insert 11. This wear
increases the required cutting force.When milling in poured
asphalt the increase of the required cutting force might even
have the result -tha-t the road planing machine does not manage
-to rota-te -the cu-t-ter drum upon which the tools are mounted.
One way of decreasing the cutting force required for worn
tools would be -to use a tool of the type shown in Fig. 2. How-
ever, this should mean that the portion 16 of the tool body 10
surrounding -the cutting insert 11 rapidly would be abraded,
thereby causing -the cutting insert 11 to get loose. Thus,
cutting inser-ts of the type shown in Fig. 2 are suitable for
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use solely where the hard metal determines the life of the
-tool, for ins-tance at milling in concrete.
As shown in Figs. 3 and Ll the cutting insert 11 in a tool
according to the inven-tion is provided with an in-term~diate
portion 17 between the tip portion 12 and the shoulder 13;
said intermediate portion comprising a concave portion 171.
Due to -this i-t is achieved that -the required cutting force
is main-tained low even when the -tip portion 12 becomes worn.
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 protec-tion being provided by
the concave portion 17 and the shoulder 13.
According to a preferred embodiment the portion 17 comprises
a circular-cylindrical portion 1711 located adjacen-t to the
tip portion 12. Further in this embodiment the distance "a"
from -the transition 18 between the tip por-tion 12 and the
portion 17 to -the radially outermos-t portion 19 of the rear
contact surface 20 of the shoulder 13 is larger than the dis-
tance "b" from the transi-tion 18 to the axially forwardmost
portion of the tip portion 12; said rear contac-t surface being
intended to rest agains-t the supporting surface lLI of the -tool
body 10.
F'urther, in -the illustra-ted embodiment, the smallest diame-ter
"d" of the concave portion 17 is smaller -than the sum of the
above-defined dis-tances "a" and "b". The concave portion 171
is provided wi-th a constant radius of curvature, which is in -the
same order as half -the above-men-tioned smallest diameter "d",
preferably somewhat smaller -than said diameter.
The envelope surface of the cylindrical portion 17 extends
tangential to -the arc-sllaped portion 17 .
3~
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In the illustrated embodiment -the cutting insert is provided
with a rear portion projecting rearwardly from -the shoulder
13. The end surface of this portion is planar. It might,
however, be recessed, for instance half-sphericalor of the
general W-shape illustrated in Swedish Patent Application
No. 8400269-0. The bottom of -the recess might rest against
a correspondingly shaped protrusion on the tool body, or,
alternatively, the recess might provide a cavi-ty.
In a further modification -the cutting insert might be made
without a rear projection. The rear end surface of the
cutting insert, i.e. the end surface of the shoulder, and
the cooperating front surface of the -tool body might be
designed according -to any of the above alternatives.
