BACKGROUND OF THE INVENTION
a) Field of the Invention
The present invention relates to a boring bit which is mounted
on boring machines such as auger boring machines, all casing boring
machines or multiaxial boring machines and in particular to a
boring bit and a boring casing using the same for boring mainly
hard rock such as large gravel, cobble stone to achieve extension
of service life as well as enhancement of the boring efficiency.
b) Description of the Related Art
Various methods of boring have recently been developed to meet
the requirements of reduced noise and vibration on foundation
working for civil or building structures. Among them, auger and
all casing methods are expected to be feasible. The auger methods
are mainly classified into earth auger method in which boring is
conducted by rotating in a given direction an auger screw 50 (shown
in Fig. 5) on which bits 51 made of cemented carbide are mounted at
its tip end; a donut auger method in which a casing 52 on which
bits 53 are mounted on its tip end is disposed around the auger
screw 50 as shown in Fig. 6 and the auger screw 50 and casing 52
are rotated in opposite directions for penetrating into the ground
for boring; and a separate auger method in which the above-mentioned
auger screw 50 and the casing 52 are independently
rotated depending upon the kind of ground formation.
However, it is difficult for these methods to bore hard rock
layers including large gravel and cobble stone. Accordingly, the
above-mentioned all casing method has been developed for boring in
particular had rock layers. In this method, soil is discharged
with a hummer grab 54 simultaneously with boring with the casing as
shown in Fig.7. Currently, this method is dominantly conducted in
civil and construction working in urban areas.
The boring bit 55 which is mounted on the auger screw 50 and
casing 52 at the tip end thereof comprises a chip 57 which is
buried in a shank 56 as shown in Fig. 8. The bits 55 are mounted
on the auger screw 50 or casing 52 at the tip end thereof by means
of welding or bolts.
Development of chips for boring bit 55 having an excellent
boring efficiency, a high wear resistance and an extended service
life has been made for many years. However, bits which overcome
the problems encountered in boring of hard rock layers including
large gravel and cobble stone have not yet been put into market as
products. The wear of chips is still so high that the chip may
have to be exchanged within one or two days. Since development of
chips having a remarkably long life can not be currently expected,
various shapes of bits such as saddle shape, insertion type or
cylindrical shape as shown in Figs. 9(A) to (C) ( quoted from
brochure of Toshiba Tungalloy K.K.) for ease of exchange.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a boring
bit and a boring bit using the same which has a high wear
resistance, extended period of life and increased boring efficiency
even if they are used for boring hard rock layer including large
gravel and cobble stone.
In order to achieve the above mentioned object, the present
Invention provides a boring bit mounted on a ground boring machine,
comprising a cutter which is brought into contact with the face of
the ground to be bored for substantially conducting crushing of the
groun d and a shank for holding said cutter, said cutter being held
at the distal end of said shank so that it is rotatable around its
rotation axis.
In this case, said cutter may be preferably provided within
the shank in such a manner that only its boring blade projects
outwardly beyond the distal end of the shank.
Said cutter may preferably comprise a disc-shaped cutter main
body and journals which are integrally formed with the opposite
sides of the cutter main body.
The boring bit may further include a blade having a wedge-shaped
section, which is integral with the outer periphery of said
disc shaped cutter main body.
The boring blade of said cutter may comprise a plurality of
buried blades which are buried in the outer periphery of said disk
shaped cutter main body at a given space. Since in the this case,
only the blade which is buried in the cutter main body is required
to replace if the blade is worn, working efficiency can be
enhanced.
The range in which the present invention can be applied is not
particularly limited. Since line cutting is carried out along the
cutter locus, the present invention is most preferably applied to
a boring casing in which cutting is carried along the circular
contour of the tube wall.
The boring bits which are mounted on ground boring machine
such as auger, all casing and multiaxial boring machines always
comprise chips which are buried in the tip end of a billet type
shank. In the present invention, the cutter at the tip end of a
shank in this type of boring bit comprises a rotary blade to
provide an extended life time of the bit. In the prior art chip
fixed bit, wear of the bit is very high since high shearing forces,
bending moments and/or frictional forces are always applied to the
chip. In contrast to prior art, the blade is contact with the face
of ground to be bored while being rotated due to the fact that the
blade is rotatable. Therefore, the wear is remarkably reduced,
achieving the enhancement in boring efficiency.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view showing a manner of boring which is
conducted by a full rotation all casing method;
Fig. 2 is a longitudinal sectional view showing a bit of the
present invention;
Fig. 3 is an enlarged view showing a blade tip of a rotary
cutter 24;
Fig. 4 is an enlarged view showing a blade tip of another
rotary cutter 24;
Fig. 5 is a view showing a manner of boring which is conducted
by a prior art earth auger method;
Fig. 6 is a view showing a manner of boring which is conducted
by a prior art donut auger method;
Fig. 7 is a view showing a manner boring which is conducted by
a prior art all casing method;
Fig. 8 is an elevational view showing a prior art boring bit;
and
Figs. 9(A) to 9(c) are views showing the manner in which prior
art bits are mounted.
BEST MODE FOR EMBODYING THE INVENTION
Referring now to Fig. 1, there is shown a manner of boring
which is conducted by a peripheral full rotation all casing method.
In the entire peripheral rotation all casing method, a casing
1 in which a multiplicity of boring bits 2 (hereinafter referred to
as "bit") spaced at given spaces along the periphery of a tube are
mounted on the tip end of the tube having an outer diameter
corresponding to the inner diameter of a bore to be bored is
penetrated into the ground while it is rotated around its central
longitudinal axis in a given direction by means of a casing driver
(not shown) on the ground and the sand and mud within the tube is
discharged by a hummer grab 3 which is suspended by a crane while
achieving protection of the bore wall as shown in Fig. 1. The
present invention may be preferably applied to the bit 2.
As shown in Fig. 2, each of the bits 2 mainly comprises a
rotary cutter 24 which is in contact with the boring face for
substantially crushing it and a shank 20 which is a member for
rotatably holding the rotary cutter 24 and for mounting the cutter
24 on the casing 1.
The shank 20 has a slit groove 21 extending in its
longitudinal direction on the base side thereof, which is defined
between two opposing bracket pieces 22A and 22B. A bolt hole 22a
is formed through two bracket pieces 22A, 22B. The bracket pieces
22A, 22B are fitted into notches 1a which are formed on the inner
and outer sides of the tip end portion of the casing 1. Then, the
shank 20 is firmly secured to the casing 1 by fastening a bolt (not
shown) which is inserted into the bolt hole 22a. Alternatively, the
bits 2 may be secured to the tip end of the casing 1 by welding and
the like.
The bit 2 is formed on the distal end side thereof with an
opening 23e through which a blade 24a of a rotary cutter 24 extends
outwardly. The bit 2 is further formed on more inner side thereof
with a bearing space 23 which is in communication with the opening
23c and is also formed in more inner position thereof with a blade
space 23b which is in communication with the space 23. The bearing
space 23 enables the rotary cutter 24 to be rotatably born.
The rotary cutter 24 is provided within the shank 20 in such
a manner that the boring blade 24a projects externally beyond the
distal end of the shank 2. The rotary cutter 24 comprises a cutter
main body 24A which is in the form of disc and journals 24B which
are formed on and integrally with the both sides of the cutter main
body 24A.
The bearing which defines the bearing space 23 is formed on
the inner surface thereof with convex ribs 23a having a semi-circular
section extending in a peripheral direction. The journals
are formed with recesses 24b having a semi-circular section.
Mating of the ribs 23a into the recesses 24b enables the rotary
cutter 2 to be rotatably born on the bearing at a less rotational
friction. Suitable lubricants such as solid or liquid lubricant
may be used.
The blade structure of the cutter main body 24A of the rotary
cutter 24 may include a peripherally extending tip 25 having a
wedge-shaped section, which is integrally buried in the outer
periphery of the cutter main body 24A as shown in Fig. 3 or may
include buried blades 26 having their base portions in holes 24
which are spacedly formed along the outer periphery of the cutter
main body 24A as shown in Fig. 4. The chip shape of the buried
blade 26 may be semi-spherical as shown in the drawing, chisel-shaped,
bulletin-shaped, or double cone-shaped. These chips are
changed depending upon the rocks to be bored.
Although only an embodiment in which one disk shaped cutter
main body 24A is provided, that is single type cutter is
illustrated, it is to be understood that other cutter structures
such as a structure in which two cutter main bodies 24A are
provided, that is, a double disk type cutter structure or a
structure having two or more cutter blades may be used. Although
only one embodiment which is used for the casing 1 for all casing
method has been described, it is to be understood that the present
invention may be applied to tip bits of an auger screw of auger
boring machines, multiaxial boring machines or rod tip bit of a
large diameter boring machines.
As mentioned above in detail, the boring bit of the present
invention has a high wear resistance of the chip in comparison with
the prior art and achieves the extension of the service life of the
bit even if it is used for boring of hard rock layer including
large gravel and cobble stone, resulting in an enhanced boring
efficiency.