U.S. patent number RE35,271 [Application Number 08/001,050] was granted by the patent office on 1996-06-11 for pipe bursting and replacement apparatus.
This patent grant is currently assigned to Consolidated Edison Company of New York, Inc.. Invention is credited to Allan T. Fisk, David I. Freed, Thomas H. Mann.
United States Patent |
RE35,271 |
Fisk , et al. |
June 11, 1996 |
Pipe bursting and replacement apparatus
Abstract
Tool for slitting and laterally expanding underground steel gas
mains and inserting replacement plastic piping into the spread
apart pipeline has a forward end cylindrical portion mounting a
single, rearwardly angled blade to make only one line of cut, and a
conical pipe spreader portion at its rearward end. The conical
spreader portion is eccentrically disposed with respect to the
forward end cylindrical portion. A single roller type pipe slitter
aligned with the fixed blade may be mounted on a removable
extension of the forward end cylindrical portion, to initially
groove and weaken the pipe along the intended line of cut. A
pneumatically operated impact ram is attached to the rearward end
of the tool, as is the leading end of the replacement piping. A
wire cable pulls the tool through the underground pipe, thereby
grooving, slitting and laterally expanding the pipe. The spacing of
the roller slitter in advance of the fixed knife blade is
dimensionally related to the length of any coupling or clamp as may
be anticipated along the line of cut, and the spacing distance of
the fixed knife blade forwardly of the conical spreader portion is
related to the cone angle of the latter to increase hoop tension
immediately in front of the fixed blade as the cutting
proceeds.
Inventors: |
Fisk; Allan T. (Needham,
MA), Freed; David I. (Sudbury, MA), Mann; Thomas H.
(Littleton, MA) |
Assignee: |
Consolidated Edison Company of New
York, Inc. (New York, NY)
|
Family
ID: |
24088333 |
Appl.
No.: |
08/001,050 |
Filed: |
January 6, 1993 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
524231 |
May 15, 1990 |
04983071 |
Jan 8, 1991 |
|
|
Current U.S.
Class: |
405/184.3;
30/92.5; 166/55.2; 166/55.7; 138/97 |
Current CPC
Class: |
E21B
29/00 (20130101); F16L 55/1658 (20130101); E21B
7/205 (20130101); E21B 7/30 (20130101) |
Current International
Class: |
E21B
7/20 (20060101); E21B 7/00 (20060101); E21B
29/00 (20060101); E21B 7/30 (20060101); F16L
001/00 (); F16L 055/18 () |
Field of
Search: |
;405/154,156,184
;30/92.5 ;166/55.2,55.3,55.7 ;138/97 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
94694 |
|
Nov 1983 |
|
EP |
|
3800869 |
|
Jan 1989 |
|
DE |
|
266185 |
|
Oct 1990 |
|
JP |
|
2139938 |
|
Nov 1984 |
|
GB |
|
Primary Examiner: Taylor; Dennis L.
Attorney, Agent or Firm: Brooks Haidt Haffner &
Delahunty
Claims
What is claimed is:
1. A pipe bursting tool for longitudinally slitting and laterally
expanding a length of steel pipe, said tool having a forward end
and a rearward end, comprising a substantially cylindrical portion
including said forward end and whose diameter is smaller than the
inner diameter of said pipe so as to be received therein, a
truncated substantially conical spreader portion for laterally
expanding said pipe and having a truncated apex end conjoining with
said cylindrical portion and a base end adjacent to said rearward
end of said tool which is substantially larger than said inner
diameter of said pipe, said spreader portion having a conical
surface-generating side element aligned with and forming a rearward
extension of a cylindrical surface-generating side element of said
cylindrical portion and together providing a straight side surface
of said tool, said conical spreader portion thereby being
eccentrically disposed with respect to the longitudinal axis of
said cylindrical portion, and a fixed blade member mounted on and
projecting outwardly from a second surface of said tool which is
opposite to its said straight side surface, said blade member
having an angularly rearward extending and forwardly facing cutting
edge.
2. A tool according to claim 1, wherein said blade member is
mounted on said cylindrical portion at a location whereby its said
cutting edge at a point adjacent to said second surface is spaced a
distance forwardly away from the location of said conjoining
between said cylindrical portion and said apex end of said conical
spreader portion.
3. A tool according to claim 2, wherein said conical spreader
portion has a predetermined included cone angle, and said distance
is determined with respect to said included cone angle whereby,
when said spreader laterally expands said pipe, said conical
spreader portion exerts tearing action on said pipe at a location
immediately forward of said point on said cutting edge.
4. A tool according to claim 2, wherein said distance is within the
range of from substantially one and one-half times to substantially
twice the diameter of said underground pipe.
5. A tool recording to claim 4, wherein said conical spreader
portion has an included cone angle which is within the range of
from substantially ten degrees (10.degree.) to substantially twenty
degrees (20.degree.).
6. A tool according to claim 5, wherein said distance is
substantially one and one-half times said diameter, and said
included cone angle is substantially fifteen degrees
(15.degree.).
7. A tool according to claim 2, which further comprises a rotary
pipe slitter mounted on and projecting outwardly from said
cylindrical portion in longitudinal alignment with said blade
member along said second surface and spaced a second distance
forwardly away from said point on said blade member cutting
edge.
8. A tool according to claim 7, wherein said second distance is
greater than substantially one and one-half times the diameter of
said underground pipe.
9. A tool according to claim 7, wherein said tool cylindrical
portion comprises a fixed portion extending forwardly from said
conjoining location, said blade member being mounted on said fixed
portion, a removable portion extending forwardly of said fixed
portion, said rotary slitter being mounted on said removable
portion, and connection means removably connecting said removable
portion to said fixed portion.
10. A tool according to claim 1, wherein said blade member cutting
edge extends rearwardly at an angle which is within the range of
from substantially twenty degrees (20.degree.) to substantially
thirty degrees (30.degree.) with respect to said second surface of
said tool.
11. A tool according to claim 10, wherein said angle is
substantially twenty-five degrees (25.degree.).
12. A tool according to claim 1, wherein said conical spreader
portion has an included cone angle of substantially fifteen degrees
(15.degree.), said blade member cutting edge extends rearwardly at
an angle of substantially twenty-five degrees (25.degree.), said
blade member is mounted on said cylindrical portion at a location
whereby its said cutting edge at a point adjacent to said second
surface is spaced a distance of substantially one and one-half
times the diameter of said underground pipe forwardly away from the
location of said conjoining between said cylindrical portion and
said apex end of said conical spreader portion, and which further
comprises a rotary pipe slitter mounted on said cylindrical portion
in longitudinal alignment with said blade member along said second
surface and spaced a distance which is greater than substantially
one and one-half times the diameter of said underground pipe
forwardly away from said point on said blade member cutting
edge.
13. A tool according to claim 1, which further comprises means
defining a plurality of circumferentially spaced apart,
longitudinally disposed junk slots extending along the length of
said cylindrical portion from its said forward end and continuing
at least a substantial distance along the length of said spreader
portion.
14. A tool according to claim 1, which further comprises a rearward
end cylindrical portion conjoining at its forward end with, and
having diameter substantially equal to the diameter of said base
end of said conical spreader portion, the longitudinal axis of said
rearward end cylindrical portion being parallel with the
longitudinal axis of the first said cylindrical portion, and said
rearward end cylindrical portion having a cylindrical
surface-generating, side element aligned with and forming a
rearward extension of said spreader portion conical
surface-generating element.
15. Apparatus for longitudinally slitting and laterally expanding a
length of underground steel pipe, comprising an elongated pipe
bursting tool having a forward end and a rearward end, an elongated
pneumatically actuated impact ramming tool connected to and
extending in tandem relation rearwardly of said pipe bursting tool,
said ramming tool having a longitudinal axis which is parallel to
the longitudinal axis of said pipe bursting tool, and connection
means on said forward end of said pipe bursting tool for connecting
a wire pulling rope thereto, said pipe bursting tool comprising a
cylindrical portion including said forward end and whose diameter
is smaller than the interior diameter of said pipe so as to be
received therein, a truncated substantially conical spreader
portion having a truncated apex end conjoining with said
cylindrical portion and a base end adjacent to said rearward end of
said tool which is substantially larger than said inner diameter of
said pipe, said conical portion being eccentrically disposed with
respect to said cylindrical portion, and pipe slitting means
mounted on and projecting outwardly from said pipe bursting
tool.
16. Apparatus according to claim 15, wherein said pipe
.[.splitting.]. .Iadd.slitting .Iaddend.means comprises a fixed
blade member mounted on and projecting outwardly from said
cylindrical portion and having an angularly rearward extending and
forwardly facing cutting edge, said cutting edge being spaced a
distance forwardly away from the location of said conjoining
between said cylindrical portion and said apex end of said conical
spreader portion.
17. Apparatus according to claim 16, wherein said pipe has
externally attached pipe coupling or clamping means having length
extending along a portion thereof, and said pipe .[.splitting.].
.Iadd.slitting .Iaddend.means further comprises a rotary pipe
slitter mounted on and projecting outwardly from said cylindrical
portion in longitudinal alignment with said blade member along said
second surface and spaced a distance greater than said length of
said pipe coupling or clamping means forwardly away from a point on
said blade member cutting edge adjacent to said second surface.
.Iadd.
18. A tool for longitudinally slitting and laterally expanding a
length of steel pipe, said tool having a forward end and a rearward
end and comprising a longitudinally extending cutter portion
including said forward end of said tool and having opposite
longitudinal sides and transverse dimensions smaller than the inner
diameter of said pipe so as to be received therein, a pipe cutter
mounted on and having a forwardly facing cutting edge projecting
outwardly from said cutter portion on one of said sides thereof for
slitting said pipe along one line of cut and means on the other of
said sides thereof for engaging the interior surface of said pipe,
and a spreader portion adjacent to said rearward end of said tool
and having a narrow forward end adjacent to said cutter portion, a
wider rearward end, and a substantially longitudinal side extending
rearwardly between its said forward and rearward ends with respect
to said other side of said cutter portion, said spreader portion
being disposed eccentrically with respect to the longitudinal axis
of said cutter portion in the direction of said one side of said
cutter portion with its said narrow forward end disposed whereby,
at least adjacent to said forward end it will enter said one line
of cut and with its said wider rearward end disposed to follow its
said forward end within said line of cut to progressively spread
said slit pipe substantially laterally along said one line of cut
as said tool is moved in the direction of its said forward end
through said slit pipe..Iaddend. .Iadd.19. A tool according to
claim 18, wherein said means on the other of said sides of said
cutter portion comprises at least one skid plate attached to said
cutter portion..Iaddend. .Iadd.20. A tool according to claim 18,
wherein said means on the other of said sides of said cutter
portion comprises at least one rolling idler element mounted on
said cutter portion..Iaddend.
.Iadd. . A tool for longitudinally slitting and laterally expanding
a length of pipe, said tool having a forward end and a rearward end
and comprising a cutter portion adjacent to said forward end and
whose transverse dimensions are smaller than the inner diameter of
said pipe so as to be received therein, a pipe cutter mounted on
and projecting outward from said cutter portion on one side thereof
for slitting said pipe when said tool is moved therethrough in a
forward direction, said cutter portion having an opposite
longitudinal side, and a spreader portion for laterally expanding
said slit pipe and having a forward end connected to said cutter
portion which is smaller than the diameter of said pipe to be
received therein and a rearward end which is wider than said
forward end, said rearward end of said spreader portion being
eccentrically disposed with respect to the longitudinal axis of
said cutter portion towards said one side thereof, said spreader
portion having an opposite side which extends substantially
longitudinally and rearwardly between its said forward and rearward
ends with respect to said opposite longitudinal side of said cutter
portion, and said spreader portion widening in lateral direction
between its said forward and rearward ends to engage and spread
apart opposite sides of said slit pipe as said tool is moved
therethrough in said forward direction..Iaddend.
Description
FIELD OF THE INVENTION
This invention relates to techniques for removal and replacement of
underground pipelines, such as gas mains, service lines and the
like. More particularly, the invention relates to apparatus and
methods for bursting open and thereby effectively removing such
existing but deteriorated underground steel pipelines, while
concurrently feeding replacement piping into the pipe tunnel
thereby created.
BACKGROUND OF THE INVENTION AND THE PRIOR ART
Although the invention may have other uses such as in the
replacement of underground steel conduits of different size and
having a variety of uses, the invention was made and will therefore
be described in connection with devising an effective manner of
removal of steel gaslines extending under paved roads and streets,
particularly 4" diameter natural gas mains, and replacing of the
gasline with plastic piping.
As such underground steel gaslines age, they deteriorate and begin
to leak. Apart from inherent safety considerations, the repair and
eventual replacement of such deteriorated lines is expensive and
disruptive of normal street activity taking place thereabove.
Expense can be significantly reduced by replacing the steel gas
main with plastic pipe of the same size but, still, the steel pipe
must first be effectively removed. In the past, street excavation
and trenching along the length of the deteriorated steel piping has
been necessary. It is intended by the present invention to avoid
such trenching and extensive excavation when removing the old
pipe.
A successful alternative to such trenching and excavating has been
devised in connection with the removal of cast iron pipelines, this
technique being known as "pipe bursting". The underground pipe is
broken apart in situ using a pipe bursting tool pulled or pushed
therethrough, the tool also incorporating a spreader which pushes
the fragmented pipe remains radially outward into the surrounding
soil so that the pipe is effectively, though not actually removed
to make way for the replacement pipe. The replacement plastic pipe
or, alternatively, a larger diameter plastic pipe liner within
which the replacement pipe will be received, is usually attached to
the pipe bursting tool so that it is pulled into place as the old
pipe is removed. For example, see the impact ram boring tools of
U.S. Pat. No. 4,505,302 (Streatfield et al.) and U.S. Pat. No.
4,732,222 (Schmidt) which employ pneumatically actuated, so-called
"impact moles" of larger diameter than the cast iron pipe to be
broken and having radially projecting angular blades which
initially impact and cut into, and break the pipe as the mole is
pulled and hammered therethrough. Similar disclosures are found in
U.S. Pat. Nos. 4,720,211 (Streatfield et al), 4,738,565 (Strutfield
et al), and 4,674,914 (Wayman et al).
However, these conventional percussive pipe breaker devices, though
successful in replacing cast iron mains, have thus far not been
successfully adapted for similar removal of steel gas mains,
especially those which have all or some of their pipe sections
joined using conventional, so-called Dresser couplings. The reason
is that steel pipe has greater hoop strength than does cast iron,
is more ductile, and therefore does not shatter and fragment as
does cast iron. Even the chain of alternately upward and downward
projecting pipe cutter wheels followed by a concentric conical
spreader for cutting and separating the pipe into two halves as
described in U.S. Pat. No. 3,181,302 (Lindsay) will not remove
steel pipe in an entirely satisfactory manner, especially where
local reinforcement is provided at the pipe joints by the very
formidable Dresser couplings. Other possible techniques are known,
such as downhole motors, sawblades, plasma cutters and lasers.
However, in addition to their inabilities to satisfactorily perform
the desired bursting function in steel pipe as aforesaid, all
appear to be unduly complicated in construction, or expensive, or
require very high power, or are difficult to operate or maintain.
Thus, the task of cutting longitudinally all the way through such
steel pipe would be extremely difficult using currently known
hardware and methods.
BRIEF DESCRIPTION OF THE INVENTION
Although it may have other uses, the present invention provides a
steel pipeline bursting and plastic liner insertion system for
replacing gas mains without the high cost of excavation and
disruption of street activity, and which avoids the aforementioned
difficulties of previous systems if attempted to be used for such
purpose. The apparatus and tooling employed is intended to utilize
much existing technology to avoid radical experimentation, but to
require less power yet operate more effectively than other systems
of its type. It must also be easy to use by utility workers who
will normally replace such pipelines.
A guiding concept of the presently proposed technique is the belief
that the best way to burst a steel pipeline is to split the pipe on
only one line of cut along its length, and to then expand the pipe
by spreading it apart along the line of cut, pushing the pipe wall
laterally outwardly into the surrounding soil. Preferably, the line
of cut will be made along the bottom of the length of pipe. The
advantages of this approach include:
(1) The split pipe will remain as a single, arch-shaped piece and
will resist soil rebound better than if it were split into more
than one piece;
(2) The remaining one-piece, laterally spread apart steel pipe will
provide a low-faction surface along which the replacement plastic
liner pipe or gas pipeline can slide, thus permitting longer
distances between the excavations for the necessary launching and
receiving pits at either end of the pipe run; and
(3) Slitting the pipe along only one line of cut requires less
effort, and consequently less energy than slitting it along
multiple lines of cut, or otherwise bursting the pipe to be
removed.
In addition, the apparatus utilized in so slitting the pipe must be
effective to similarly slit through commonly used exterior repair
clamps and pipe couplings mounted on the pipe at spaced intervals,
as may be encountered along the intended line of cut. Particularly,
the method and apparatus must be effective to routinely split apart
the somewhat massive Dresser type couplings as will probably be
encountered one or more times along any given length of steel
gasline to be replaced, even along those in which the pipe sections
are more usually welded together. Further, and recognizing that the
conventional cone-shaped spreader mounted on the rearward end of
the bursting tool is a viable way to spread apart the split pipe
and even the Dresser couplings, an object of the invention is to
devise a means for overcoming the pitching or nosing-over action of
the elongated tool as is found to occur when an elongated bursting
tool having a concentrically mounted spreader cone is passed
through longer lengths of pipe, which causes its nose to jam
against the wall of the pipe and requires increased force to pull
the tool on through due to unproductive bending of the pipe wall
about a transverse axis.
Further, recognizing that a fixed blade is the least complicated
manner of cutting through an object such as a length of steel pipe,
but also recognizing that blade shape, blade angle, blade size and
its disposition will greatly affect the ease with which the object
can be cut, it is intended by the present invention to provide a
fixed blade cutter employing the optimum of these aspects of blade
technology, as applied to the intended purpose, and to consider the
use of cooperating ancillary devices and mounting relationships as
will enhance blade action.
Briefly and generally describing the invention in its preferred
embodiment, when a length of underground steel gas main piping is
to be replaced, a so-called "launching" pit for introducing the
pipe bursting apparatus is excavated at one end of the pipe length
to be removed, and a "receiving" pit is excavated at the other end
of the length to be removed. Since the pipeline probably runs
continuously through each of these pits, the sectional length of
the pipe within each pit is cut out and removed, thereby providing
an open, entrance end of the pipe within the launching pit, and an
open, exit end thereof within the receiving pit.
A conventional, hydraulically operated reciprocating wire rope
puller is positioned adjacent to the receiving pit, and a wire
pulling rope is fed therefrom into the receiving pit and thence
into the exit end and all the way through to the entrance end of
the pipe length to be removed. The thus fed free end of the wire
rope has a connector thereon which is then attached to the forward
end of the elongated pipe bursting and spreading tool provided by
the invention, so that the latter may be pulled into and through
the pipeline using pulling force exerted by the wire rope puller at
the receiving pit. A conventional, pneumatically or hydraulically
operated impact ram or "mole" is attached to the other or rearward
end of the tool, as is the leading end of the plastic liner or
replacement pipe which is to be inserted into and fed through the
area of the removed pipe as the bursting tool proceeds
therethrough. Pulling force of from five to twenty tons is applied
by the wire rope puller to pull the bursting and spreading tool
through the pipe length to be removed. A fixed blade mounted on the
body of the tool thereby slits the pipe length along only a single
line of cut, and an eccentrically disposed conically shaped
spreader portion at the rearward end of the tool causes an outward
spreading apart of the slit pipe as the work proceeds. The curing
action is preferably enhanced by the action of a single roller type
pipe slitter mounted in fixed position on the forward end of the
tool in longitudinal alignment with the fixed blade, which slits
partly through and thereby grooves and weakens the pipe thickness
in advance of the fixed blade cutting action. As one or more
Dresser couplings or clamps are encountered at locations along the
length of pipe being removed, the impact mole is actuated to
augment the wire rope pulling action, and force the fixed blade
therethrough. The impact mole may also be actuated while only the
pipe wall is being slit, if necessary.
The roller slitter on the bursting tool is preferably spaced a
sufficient distance in advance of the fixed blade such that the
roller slitter will have performed its function of grooving and
thereby weakening all of that portion of the pipe length passing
through, and reinforced by the Dresser coupling by the time when
the fixed blade first encounters the Dresser coupling to cut
therethrough. Because it will require very little power to force
the fixed blade through the weakened pipe length beneath the
Dresser coupling, virtually all of the power exerted by the fixed
blade, due to its being pulled and rammed, will be utilized in
forcing it through the structure of the Dresser coupling itself,
thus reducing total peak power requirements for this purpose.
In addition, the eccentrically disposed conical spreader is spaced
a distance behind the fixed knife blade such that, considering its
cone angle and the amount of lateral spreading apart which it will
thereby induce in the slit pipe, the spreader will also
significantly assist the cutting action of the knife blade by
generating increased hoop tension immediately in front of the blade
cutting edge.
Moreover, the manner in which the eccentricity of the conical
spreader portion of the pipe bursting tool is preferably
established with respect to the forwardly extending cylindrical
body portion on which the fixed knife blade and roller slitter are
mounted, is such as to provide a flat or straight longitudinal edge
all along the length of the tool which is circumferentially
opposite to the blade and slitter, including that beneath the
conical spreader itself, which avoids the referred to nosing over
or pitching of the tool and consequent transverse bending of the
pipe wall as is found to occur when using concentrically arranged
conical spreaders.
The preferred fixed blade is comparatively thin and is disposed at
an angle of between twenty degrees (20.degree.) and thirty degrees
(30.degree.), preferably twenty-five degrees (25.degree.), from the
longitudinal axis in the rearward direction of the bursting tool.
The included angle of the conical spreader portion of the tool is
from ten to twenty degrees (10.degree. to 20.degree.), preferably
fifteen degrees (15.degree.). The narrow end of the cone faces
forwardly, and one of its conical surface generating side elements
is aligned with, and forms a straight continuation of one of the
cylindrical surface generating side elements of the forward end
portion of the tool on the side thereof which is circumferentially
opposite that on which the fixed blade and roller slitter are
mounted.
These and other objects, features and advantages will be more fully
understood from the following detailed description of the
invention, when taken with reference to the accompanying drawings
in which:
FIG. 1 is a diagrammatic and fragmentary sectional side view
illustrating the use of the apparatus and the method of the
invention;
FIG. 2 is a fragmentary sectional side view of the pipe bursting
tool and other apparatus of the invention as are connected
thereto;
FIG. 3 is a top plan view of the apparatus shown in FIG. 2;
FIG. 4 is a view of the forward end of the apparatus as seen from
lines 4--4 in either of FIGS. 2 or 3;
FIG. 5 is a view, partially in section, of the rearward end of the
apparatus as seen from lines 5--5 in either of FIGS. 2 or 3;
FIG. 6 is a perspective view, to an enlarged scale, of a preferred
blade member which is mounted on the pipe bursting tool illustrated
in FIGS. 2-5;
FIG. 7 is a similar perspective view of an alternative blade member
as might be mounted on the pipe bursting tool;
FIG. 8 is an end view in cross-section of a pipe bursting tool
incorporating the alternative blade of FIG. 7, and showing its
operation in bursting a pipe;
FIG. 9 is an exploded view in perspective, to a similarly enlarged
scale, of the rotary pipe slitter which is mounted on the pipe
bursting tool illustrated in FIGS. 2-5;
FIG. 10 is a fragmentary perspective view of the apparatus
illustrated in FIGS. 2-5, showing its operation in slitting and
expanding a length of underground pipe; .[.and.].
FIG. 11 is a transverse sectional view, as seen from lines 11--11
in FIG. 10, showing in detail the operation of the roller pipe
slitter on the pipe bursting tool.[...]. .Iadd.; and .Iaddend.
.Iadd.FIG. 12 is a fragmentary sectional side view similar to FIG.
2, to illustrate a modification of the invention..Iaddend.
Referring to FIG. 1, a pipe bursting and replacement apparatus in
accordance with a preferred embodiment of the invention is
generally indicated by reference numeral 20 and includes a pipe
bursting tool, generally indicated by reference numeral 21, and an
impact boring ram 22 (sometimes referred to in the trade as an
"impact mole") removably connected to the rearward end 21a of the
tool 21 and driven pneumatically by the compressed air supply 23
via the pneumatic air line 24. A wire rope pulling line 25 is
removably connected via a coupling 26 to the forward end 21b of the
tool 21 for pulling the pipe bursting tool 21 through the length of
underground pipe 27 which is to be effectively, though not actually
removed in situ, in the manner to be described. Typically the
length of pipe 27 to be removed will be several hundred feet long,
depending upon factors not relevant to this disclosure. Pulling
force on the order of from 5 to 40 tons is exerted on the pulling
line 25 by a conventional type of wire rope puller, such as the
reciprocating cable puller 28 which, in the preferred embodiment,
is actually a modified rod pusher made by Powerram Corp. The puller
28 is hydraulically driven by the hydraulic pump 29 via the
hydraulic fluid lines 30. As the wire rope 25 is progressively
drawn through the puller 28 its emerging portion 25a, which is no
longer under tension, is wound on to the drum 31.
An alternative method for pulling the tool 21 through the pipe 27
could utilize a standard rod pusher such as the aforementioned unit
by Powerram Corp., or its equivalent. In this instance the rod
pusher would be located co-linearly with the pipe 27 and the wire
rope 25 would be supplanted by solid or hollow steel rods which are
standard with such rod pushers. Of course, the reciprocating rod
pusher would operate in the pushing, rather than the pulling mode,
utilizing the reversible feature found on most such units.
In the embodiment of the invention being described the pipe 27 to
be removed is a horizontally extending 4" diameter steel pipeline
which is buried beneath the ground level 32, usually under a street
or roadway (not shown), which is used as a gas main for supplying
natural gas from a public utility to homes, factories or other
distribution points. The wall thickness of such typical 4" steel
pipe is 0.237". Either when initially laid or during a previous
repair, the 20' long or 40' long steel pipe sections 27a, 27b (only
two of which are illustrated) which make up its length may have
been joined using a conventional, exterior mounted pipe joint or
coupling 33 which, in the illustrated embodiment, is a standard
Dresser pipe coupling. As is well known, the Dresser type pipe
coupling includes a closely fitting sleeve or cylindrical ring 33a
which peripherally surrounds the loosely abutted ends of the pipe
section 27a, 27b, with a plain or armored gasket material (not
shown) being disposed at each end of the ring 33a and forming seals
between the ring ends and the respective exterior surfaces of the
pipe sections 27a, 27b. The gasket material is compressed and held
in place by the pair of end rings 33b at either end of the coupling
33, these being drawn together by a plurality of peripherally
disposed bolts 33c, all as is well known. For a typical, nominally
4" diameter steel pipe whose actual outside diameter is 4.5", the
length of the middle ting 33a is typically 5" or 7" and its
thickness is 0.188". The diameters of the respective end rings 33b,
which are also made of mild steel, is 83/4", and their greatest
ring thickness adjacent the gasket material is about 3/8". These
Dresser couplings are available in various sizes for use on steel
pipe sizes of 2" through 12" diameter, and their lengths and other
dimensions are correspondingly greater or less for larger or
smaller pipe. Thus, these exteriorly mounted pipe couplings present
formidable obstacles to the intended bursting apart of the entire
length of the pipe 27, because the couplings 33 must be similarly
split apart by the pipe bursting tool as it moves therethrough.
Similarly, where previous repairs to the pipe 27 have been made, it
may be anticipated that elongated pipe clamps 34, each having been
installed for sealing a pipe leak or for strengthening an otherwise
weakened point, may be found at various locations along the pipe
length 27. As is well known, each pipe clamp 34 is formed
peripherally around the pipe using a peripherally extending rubber
gasket, a stainless steel bridge strap, and a stainless steel outer
peripherally extending band 34a whose ends are drawn together as a
hoop by a plurality of longitudinally disposed rails and
transversely extending bolts 34b. These, too, present formidable
obstacles to the passage of the pipe bursting tool along the entire
length of the pipe 27, as is intended.
When a gas main such as the length of steel pipe 27 has
deteriorated in general condition over the years to an extent where
it must be replaced, it is unnecessary to trench and excavate the
ground 32 along its length to reach and actually remove all of the
pipe length 27 from the ground and replace it. Rather, it is only
necessary to split or burst the pipe length 27 apart and expand it
radially to press its severed parts into the surrounding soil so as
to create a pipe tunnel of enlarged diameter (not illustrated) into
which replacement piping, of the same or larger diameter as that of
the removed piping, may be inserted and connected. In general, such
manner of pipe replacement is known as "pipe bursting and
insertion".
To remove and replace the length of pipe 27 in this manner requires
excavation to reach and expose the pipe at each end of the length
to be replaced. Thus, with reference to FIG. 1, a launching pit 32a
is excavated to expose an entrance end 27c of the pipe 27, and a
receiving pit 32b is excavated to expose the other, exit end 27d of
the pipe length 27 to be replaced. The launching pit is made long
enough, say about 10' feet long, to accomodate the connected
lengths of the bursting tool 21 (about 2' long) and its connected
impact ram 22 (about 5' long) which will be pulled into the
entrance end 27c of the pipe 27. The receiving pit 32b is made as
small as is convenient for working to disassemble and remove the
bursting tool 21 and impact ram 22 as they emerge from the exit end
27d of the pipe length 27. Although the wire rope puller 28 might
be set within the receiving pit 32b in alignment with the pipe 27
to exert direct pull on the wire rope 15, in the illustrated
preferred embodiment a metal support frame 40 is erected within the
receiving pit 32b, having wire rope pulleys 41, 42 mounted thereon
as shown, to guide the wire rope 25 out from the receiving pit 32b
and into the wire rope puller 28 which is mounted atop the
framework 40.
Of course, as will be understood, when the launching pit 32a and
receiving pit 32b are formed, an exposed section of the pipe 27
(not shown) as would otherwise extend through each of them must be
cut out from the pipe 27 and removed, to form the exposed entrance
and exit ends 27c, 27d of the pipe within the respective pits.
Thus, severed continuations 27e and 27f of the pipe 27 are
illustrated as exposed at the opposite ends of the respective pits
32a, 32b.
Referring now to FIGS. 2-5, the pipe bursting tool 21 of the
invention is a tool for longitudinally and laterally expanding the
length of underground pipe 27 which is thus to be effectively
removed. The leading end 77a of the plastic replacement pipe 77 is
connected to the rearward end 21b of the tool so as to be thereby
pulled into the split and enlarged pipe 27, so that the pipe 27
will be replaced in situ. The tool 21 has a cylindrical portion 45,
formed by the fixed cylindrical portion 45a and the cylindrical
portion 45b. The portion 45b may be integrally formed with the
portion 45a or, preferably, is removably connected, as shown, in
tandem alignment with the fixed cylindrical portion 45a. In the
embodiment shown the connection is made using the end of the
portion 45a, generally indicated by reference numeral 46.
The diameter of the cylindrical portion 45 is slightly smaller than
the inside diameter of the pipe 27 within which it will be
received. For example, the inside diameter of a typical 4" steel
pipe presently being described is 4.026" and, therefore, the
outside diameter of the cylindrical portion 45 would be made about
3.75". In this regard, it should be noted that a 1/8" thick
hardened steel skid plate 47, welded on to the underside of the
tool 21, including a portion 47a along the removable cylindrical
portion 45b, locally increases the effective diameter of the
forwardly projecting cylindrical portion 45, as will be
understood.
The forward end of the removable cylindrical portion 45b has a
threaded end 48 to which the correspondingly threaded wire
terminator 26 is coupled by cylindrical connector 49 for removable
attachment of the wire pull rope 25, as shown. The threaded end 48
is preferably sized and threaded identically to the size and
threading of the threaded end 46 so that, when the cylindrical
portion 45b is unscrewed and removed from the threaded end 46, the
wire rope connector 49 may be threadedly connected to the end 46,
for reasons which will be explained.
Extending toward the rearward end 21b of the tool 21 from its
welded, conjoining attachment along line 50a to the fixed
cylindrical portion 45a as seen in FIG. 3 is an eccentrically
disposed, conically shaped spreader portion 50 of the tool 21, for
laterally spreading apart and thereby expanding the burst pipe 27
as will be described. In the preferred embodiment being described,
the portion 50 has right circular truncated conical shape, its
narrower, truncated apex end 50a conjoining with and being welded
to, or formed with (if cast or fully machined) the rearward end of
the fixed cylindrical portion 45a, and its base end 50b being
attached as by welding, or otherwise formed in conjoining relation
with a short-length cylindrical rearward end portion 51 which
extends to the rearward end 21b of the tool 21. The diameter of the
enlarged cylindrical portion 51 in the presently described
embodiment for 4" pipe is 6.[.].]..Iadd.1/2.Iaddend.". The
conically shaped spreader portion 50 has an included cone angle A
of from ten degrees (10.degree.) to twenty degrees (20.degree.),
preferably fifteen degrees (15.degree.) as shown in FIG. 2 or FIG.
3. One of its conical, surface-generating side elements 50c (FIG.
2) is longitudinally aligned with, and forms a rearward extension
of a cylindrical surface-generating side element 45c (also FIG. 2)
of the fixed cylindrical portion 45a on one side of the tool 21 as
shown, so that that side of the tool, to which the skid 47 is
attached, is continuously straight therealong. Thus, on the
opposite .Iadd.side .Iaddend.of the tool as seen in FIG. 2, the
conical surface-generating side element of the spreader portion 50
is disposed at an angle, with respect to the longitudinally
extending cylindrical portion 45, which is equal to the included
cone angle A, since the shape of the conical spreader portion 50 is
that of a right circular cone.
In a like manner, one of the cylindrical surface-generating side
elements 51c of portion 51 is also longitudinally aligned with, and
also forms a rearward extension of the aforementioned cylindrical
surface-generating side element 45c of the portion 45a. The effect
of this continued longitudinal alignment is that the longitudinal
axes of fixed cylindrical portions 45a and 51 are parallel to each
other but offset, or eccentric, by a distance equal to one half of
the difference between the respective diameters of cylindrical
portions 45a and 51. The angular disposition of the axis of right
circular conical spreader portion 50 provides a smooth transition
between body portions 45a and 51, and provides for the alignment of
the three respective surface-generating side elements 45c, 50c, and
51c.
It will be appreciated that there are numerous ways in which to
configure the conical spreader portion 50 in addition to the right
circular conical shape described for the preferred embodiment of
FIGS. 2 and 3. It is sufficient that spreader portion 50 form a
generally conical transition between the round crossections of
fixed cylindrical portions 45a and 51, and that the axes of
cylindrical portions 45a and 51 be parallel, and that longitudinal
alignment exist along surface-generating side elements as described
above.
A longitudinally extending blade slot 55 (FIG. 2) is formed on the
same, opposite side of the tool 21 for receiving a fixed knife
blade member 56, which is wedged and held in place by a blade
back-up piece 57. The blade member 56 has a forwardly facing and
rearwardly angled cutting edge 56a for slitting the pipe 27, as
will be described. As perhaps best seen in FIG. 6, the rearward
angle of the blade member cutting edge 56a with respect to the side
surface of the tool 21 from which it projects (FIG. 2) is the angle
B, which is from about twenty degrees (20.degree.) to about thirty
degrees (30.degree.). In the preferred embodiment being described,
the angle B is twenty-five degrees (25.degree.). Although the width
W (FIG. 6) of the base portion 56b and of the blade slot 55 (FIGS.
2 and 3) is 1/2 in the preferred embodiment, the blade thickness T
is comparatively thin, e.g. 1/4" in the preferred embodiment. The
blade height H projects 2" radially outwardly from its associated
side surface on the cylindrical portion 45a of the tool 21, and the
preferred included angle I (FIG. 6) of the cutting edge 56a itself
is forty degrees (40.degree.).
As seen in FIGS. 2 and 3 the fixed blade cutting edge 56a is spaced
a distance forwardly away from the conical spreader portion 50.
This distance is somewhat critical in that it will determine
whether or not, during the action of the spreader portion 50 on the
split pipe as will be described, the spreader portion will generate
or establish increased hoop tension in the pipe 27 at a location
immediately in front of the cutting edge 56a as the latter slits
the pipe 27 longitudinally. Such will facilitate the cutting
action, as will be explained. For this purpose, it has been found
that the distance between the point P on the cutting edge 56a which
will initially "bite" or contact the pipe 27 and the location in
longitudinal alignment therewith along the line 50a (FIG. 3) of
conjoining between the cylindrical portion 45a and the conical
portion 50 should be varied depending upon the cone angle of the
eccentric spreader. In the preferred embodiment being described
wherein the cone angle of spreader portion 50 is fifteen degrees
(15.degree.) that distance will be from about one and one-half
times to substantially twice the diameter of the pipe 27 to be cut,
preferably one and one-half times the pipe diameter.
An alternative flat top blade 59 as might be similarly mounted in
fixed position on the tool 21 is illustrated in FIG. 7. Its flat
surface 59a has thickness equal to the full width W of the blade
member base 56b, preferably 1/2" as shown, and its blade angle B is
the same as that of the previously described embodiment, i.e, from
about twenty degrees (20.degree.) to about thirty degrees
(30.degree.), preferably twenty-five degrees (25.degree.). Although
its cutting action as will be described is somewhat different from
that of the thinner, sharpened blade 56a of the previously
described embodiment, the flat top blade 59 has advantages of
strength, and the fact that it does not dull easily and therefore
need not be replaced or sharpened often. Accordingly, it is
relatively inexpensive.
Referring again to FIGS. 2 and 3, and also to FIG. 9, the removable
cylindrical portion 45b of the tool 21 has a rotary type pipe
slitter 60 mounted therein, between respective bearing blocks 61
which are received in the opening 62 formed in the cylindrical
portion 45b. The opening 62 is appropriately longitudinally
slotted, as at 63, to receive the slitter wheel 60, as best seen in
FIG. 9. The rotary pipe slitter 60 is longitudinally aligned with
the fixed blade cutting edge 56a when the removable cylindrical
portion 45b is secured to the fixed cylindrical portion 45a, as
seen in FIG. 3. It projects outwardly from the surface of the
cylindrical portion a distance substantially equal to, or slightly
greater than the wall thickness of the pipe 27 to be cut plus the
clearance distance between the interior of the pipe 27 and the
surface of the cylindrical portion 45b when within the pipe 27. The
slitter 60 is a standard pipe cutting wheel having a diameter of
21/4" and blade thickness of about 1/8". As are the fixed blades 56
or 59, the slitter 60 is made of hardened steel, hardened to
Rockwell "C" 57 so that the material is tough, though not brittle.
As is the longitudinal location of the fixed blade 56a with respect
to the conical spreader portion 50, the location along the length
of the cylindrical portion 45b of the slitter 60 is functionally
related to the operation of the tool 21. That is, the axial center
C of the slitter 60 is preferably positioned forward of the blade
cutting edge point P a distance which is at least equal to the
longest length of any pipe coupling 33 or pipe clamp 34 (FIG. 1)
which the tool 21 may be expected to encounter when passing through
the length of pipe 27, as will be explained. In general, this
distance will be at least equal to one and one-half times the
diameter of the pipe 27, and may be greater.
The main body of the pipe bursting tool 21, including its spreader
portion 50 and fixed cylindrical portion 45a are preferably made by
casting A.I.S.I 4140 or 4340 low alloy steel. Alternatively, these
parts, as well as the removable cylindrical portion 45b, may be
made using machined steel components, welded together and hardening
necessary.
As illustrated in FIGS. 2 and 4, longitudinally extending so-called
"junk slots" 65 are formed within the tool body as shown, extending
from the forward end 21a rearward at least to a location as seen in
FIG. 2 corresponding to about one-half of the length of the conical
portion 50. These openings permit longitudinal passage through and
beyond the travelling tool 21 of rust, scale and dirt deposits as
may have accumulated within the deteriorated pipe 27 being cut, as
will be understood. The junk slot function might alternatively be
achieved using additional longitudinally extending skids, such as
skids 47b and 47c (FIG. 11), or built-up lines of weld along the
length of the tool, instead of by grooves as shown. Of course, the
circumferential locations of the junk slots, and the number of junk
slots provided on the tool may be varied appropriately to suit
particular anticipated conditions.
At its rearward end 21b the pipe bursting tool 21 has a threaded
aperture 70 for removable connection of the threaded nose rod 71 of
the impact ram 22. To provide a more rigid connection between the
tool 21 and the impact ram 22 the tool 21 is provided at its
rearward end 21b with an additional threaded aperture 72, disposed
concentrically with respect to the threaded aperture 70, for
receiving a rigid steel ram support pipe 73 at its correspondingly
threaded forward end 73a. The inside diameter of the support pipe
73 closely surrounds the cylindrical body 22a of the ram 22 to
avoid bending of the latter with respect to tool 21, especially at
the threaded nose portion 71.
In addition, a cylindrical pipe receiving flange 75 is attached to
the rearward end 21b of the bursting tool 21, as shown in FIGS. 2,
3 and 5, for temporary connection, as by screws 76, of the plastic
tubular liner or plastic replacement pipe 77 which the tool 21 will
progressively insert into the enlarged pipe tunnel (not shown)
which is formed as the tool 21 spreads, and effectively removes the
deteriorated underground pipe 27.
The operation of the pipe bursting and inserting tool and ancillary
apparatus will now be described particularly with reference to
FIGS. 1, 10 and 11.
As will be generally understood from FIG. 1, after the launching
pit 32a and receiving pit 32b have been excavated and the frame 40
and wire rope puller 28 are positioned as shown, the wire rope 25
is fed off from the winding drum 31 through the rope puller 38,
around the pulleys 42, 41, and then into the exit end 27d of the
pipe 27 to be removed. The wire rope and its free end connector 26
are fed or "fished" in any known manner through the pipe 27 to
emerge from the entrance opening 27c within the launching pit 32a.
The connector 26 is then threadedly connected to the threaded nose
48 of the tool 21, using the cylindrical threaded connector 49
(FIG. 2). The impact ram 22 and pipe liner or replacement piping 77
are attached to the rearward end 21b of the tool 21, and pneumatic
power from the compressed air supply 23 is connected to the ram
22.
The hydraulic pump 29 is then activated to operate the wire rope
puller 28 to exert pulling force on the wire rope 25, whereupon the
tool forward end 21a is guided into the pipe 27 at its entrance end
27c. Although the tool 21 may be oriented in any circumferential or
"roll" position as, for example, with its cutting blade 56 and
slitter 60 facing upwardly as seen in FIG. 10, as it enters the
pipe 27 the tool 21 is preferably oriented as illustrated in FIG.
1, with its eccentric spreader portion 50, cutter 56 and slitter 60
facing downwardly so as to slit the pipe 27 along its lowermost
longitudinal element. However, for convenience of illustration, the
operation will be described as it would be conducted with these
tool elements facing upwardly as shown in FIG. 10. It will be
understood, however, that the cutting action of the tool will be
the same regardless of its "roll" orientation.
As the pulling force exerted by the rope puller 28 on the wire rope
23 is increased to between 5 and 40 tons, the rotary slitter 60,
which first engages the pipe 27 will not likely cut through, but
will be found to squeeze the pipe upwardly along the longitudinal
line of cut 80 as seen in FIG. 11, and to form a groove 81 along
the interior pipe surface element immediately below the line of cut
80, as also indicated in FIG. 11. Backing force for the action of
the slitter wheel 60 and the action of blade 56 is provided by the
sliding engagement of the skid 47 and 47a with the opposite
interior surface of the pipe 27, as also seen in FIG. 11. It will
be found that this grooving action of the rotary pipe slitter 60 is
continuous along the length of the pipe 27 during the slitting and
spreading action of the tool 21.
Those skilled in the art will appreciate that it is possible to
replace sliding skid 47 with one or more rolling idler elements or
wheels .[.(not shown).]. .Iadd.as illustrated by dotted line
showing 47b in FIG. 12.Iaddend.. These idler wheels would also
provide the backing force for the action of slitter wheel 60 and
blade 56, with the added advantage of lower friction but with the
disadvantage of increased cost and susceptability to dirt and
foreign matter. Likewise, practice of the invention has shown that
the addition of auxilliary skids such as 47b and 47c (FIG. 11) can
help maintain the pipe crossection in a circular shape, thereby
assisting the action of slitter wheel 60.
It will be understood that the forming of the interior groove 81
thins the pipe wall thickness along the line of cut 80 so that the
curing action of the knife blade 56a therealong is facilitated,
thus requiring less power to pull the knife blade through the pipe
27, and imposing less wear on the fixed blade 56.
Moreover, as will be understood from FIG. 10, the subsequent
lateral spreading apart of the slit pipe 27 by the spreader portion
50 of the tool 21 exerts a longitudinal tearing action on the
intended line of cut along the as yet unslit pipe, immediately
forward of the blade cutting edge 56a, thereby significantly
increasing hoop tension within the pipe 27 at that point, which
further facilitates the cutting action. As previously noted, this
establishment of hoop tension immediately in front of the fixed
cutting blade is determined by the positioning of the blade at a
fixed distance forwardly of the tool spreader portion 50,
considering the conical shape of the spreader portion. That is, if
the fixed knife blade 56 is located too far forwardly, the spreader
portion 50 will have no effect on the pipe immediately forward of
the cutting blade, and the action of the fixed blade will not
benefit from the tension. If the knife blade 56 is positioned too
far rearwardly, the hoop tension induced by the spreader portion 50
will tend to be established at a location too far forwardly of the
knife blade, in which case slitting of the pipe occurs only because
of the tearing action of the spreader portion and not due to any
knife blade action at all. In the latter case the ability of the
tool to split couplings and clamps is severely compromised or
defeated because the tearing action of the spreader portion 50, and
hence the forward progress of the entire tool, will likely be
halted when the spreading/tearing action encounters the local pipe
reinfrocment represented by a coupling or clamp. The optimum tool
proportions and blade locations cited herein permit the fixed blade
56 to enter and cut a coupling before the spreading/tearing action
(and forward progress) are halted, yet stiff allow the spreading
action and resulting hoop tension to facilitate the cutting action
of the fixed blade. It becomes apparent that if the cone angle of
the spreader is changed, the fixed position of the knife blade
should also be changed to a location either farther from or nearer
to the spreader. If the cone angle of the spreader is made
shallower, the knife blade should be positioned farther in front of
the spreader; if the cone angle is made wider, the blade should be
moved closer to the spreader. In this regard it will be noted that
shallower cone angles impart greater "wedging action", and
therefore generally induce greater hoop tension in the pipe for a
given rope pulling force. As previously mentioned, it is believed
that a spreader cone angle within the range of between ten degrees
(10.degree.) and twenty degrees (20.degree.) affords good wedging
action, with the preferred angle being fifteen degrees
(15.degree.), and that for such shallow cone angles the cutting
blade should be positioned at a distance of between one and
one-half (11/2) and two (2) times the nominal diameter of the pipe
27, forwardly of the truncated apex end 50a of the conical
spreader.
Depending upon the soil resistance encountered, supplemental
ramming force of the impact ram 22 may or may not be required. That
is, in less dense and/or less compacted soil, such as sandy soil,
the force exerted by the rope puller 28 may be entirely adequate to
pull the pipe burster tool 21 in its cutting action through the
wall thickness of the pipe 27. In such instances the removable
cylindrical portion 45b and the slitter 60 mounted thereon, may be
removed. On the other hand, in dense, or compacted, or hard clay
soil as well as in instances in which pipe couplings 33 and clamps
34 may be encountered as aforesaid, the augmenting repeated
hammering force of the impact ram 22 may be required to slit the
pipe wall. In the presently described embodiment wherein 4"
diameter steel pipe is being split a typical impact ram 22 would be
a Pierce Airrow PA-4 pneumatic underground piercing tool which
exerts 420 blows per minute, each with an impact force of 190 lbs.
Other typical Pierce Airrow tools as may be used for up to 6"
diameter pipe provide up to 620 blows per minute, with impact
forces of from 70 to 190 lbs. Larger rams may be employed for
larger pipe sizes.
As noted, the grooving action of the slitter wheel 60 is intended
to be performed considerably in advance of the actual slitting
apart of the pipe 27. It becomes apparent that such grooving can be
performed in an operation which is conducted in advance of and
separate from the cutting and bursting action of the fixed blade 56
and conical spreader portion 50. Thus, referring again to FIG. 1,
such two-stage operation could be conducted by utilizing an
unmodified standard rod pusher (not shown) within the receiving pit
32b, in alignment with the pipe exit end 27d and pushing connected
lengths of rod through the pipe 27, with only the removable
cylindrical portion 45b (FIG. 2) connected to the leading end of
the first length of rod to be introduced into the pipe end 27d. The
slitter wheel 60 thereon would be pushed through by the connected
rods and would groove the pipe 27 from its exit end 27d to its
entrance end 27c, whereupon the cylindrical portion 45b would be
detached therefrom within the launching pit 32a, and the forward
end of the pipe bursting tool cylindrical portion 45a would be
attached to the rod end. The rod pusher would then be reversed so
.[.a.]. .Iadd.as .Iaddend.to pull the lengths of rod and the
bursting tool back through the pipe 27 to the receiving pit 32b so
that the pipe is thereby slit and laterally expanded by its fixed
knife blade 56 and its conical spreader portion 50. In this way the
more fragile slitter wheel 60 would not be subjected to the
pounding delivered by the impact ram 22 if its use is necessary
during the slitting and bursting operation. Of course, the same
two-stage operation of grooving and then slitting and bursting the
pipe could also be performed using two pulling passes with the wire
rope 28, the first pulling the detached cylindrical portion 45b
with its slitter wheel 60 through the pipe, and the second pass
being made with only the fixed cylindrical portion 45a and its
conjoining spreader portion 50 to slit and burst the pipe.
Referring again to FIG. 10, using the preferred cone angle of the
spreader portion 50 and the preferred position of the blade member
56 as previously described, it will be found that the conical
spreader portion 50 induces a small longitudinal tear, indicated by
reference numeral 82, immediately in front of the contact point P
of the blade cutting edge 56a, so that the force required to move
the blade along the line of cut 80, 82 is significantly
reduced.
Using the combined pulling action of the wire rope 25 and the
hammering action of the impact ram 22, it will be found that the
tool 21 easily slits through and spreads apart any pipe coupling 33
or pipe clamp 34 (FIG. 1) as may be encountered along the length of
the pipe 27. As previously pointed out, the cutting action of the
knife blade 56a and the conical spreader portion 50 through any
coupling 33 or pipe clamp 34 is augmented by the grooving 81 and
consequent weakening of the pipe wall thickness along the intended
line of cut 80 as the slitter 60 passes beneath the end rings 33b
and middle ring 33a of the coupling 33 in advance of any contact of
the knife blade cutting edge 56a with the coupling or the
clamp.
The amount of pulling force required is also significantly reduced
by the fact that the tool 21 is required to cut along only a single
line of cut 80 through the pipe 27, and by the eccentrically
arranged spreader portion 50 whose spreading action is concentrated
along that one line of cut and only the adjacent side wall portions
of the pipe.
The eccentric disposition of the conical spreader portion 50 as
shown and described, and which provides a completely straight
reaction edge along its opposite side, additionally prevents
pitching or nosing-over movement of the tool 21 as it is pulled and
rammed through the pipe 27.
Further, the cutting of the pipe 27 along only one line of cut 80
produces an arch-like expanded shape of the slit pipe, as indicated
by reference numeral 85 in FIG. 10, which affords a smooth interior
surface along which the plastic liner or replacement pipe 77 may
slide as it is inserted, thereby further reducing required forces.
The arch-like form 85 of the slit pipe when produced as an inverted
U-shape as indicated in FIG. 1, has the additional advantage of
shielding the thus produced pipe tunnel from rebound or other entry
of dirt from the surrounding compacted soil.
With reference to FIG. 8 it will be noted that, when using the flat
top blade 59, the line of cut 80 of the pipe 27 is actually made by
only one of the its longitudinal, angularly disposed edges 59c or
59d. Of course, the grooving action of the slitter wheel 60 along
the line of cut 80 in advance of the knife 59 reduces the cutting
force required by the flat top cutter.
Thus has been described an underground pipe bursting tool, an
apparatus, and a method which achieve all of the objects of the
invention.
* * * * *