Hydraulic and earth engineering – Subterranean or submarine pipe or cable laying – retrieving,...
Patent
1994-09-14
1996-01-02
Britts, Ramon S.
Hydraulic and earth engineering
Subterranean or submarine pipe or cable laying, retrieving,...
405184, 138 97, F16L 5518
Patent
active
054802636
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a soil displacement hammer for use in replacing underground pipes, such as gas mains or sewers.
Soil displacement hammers, commonly referred to as "moles", are impact-action self-propelled mechanisms for driving holes in the ground. They are generally pneumatically operated, although hydraulic, electric and other driving means are possible. They can be used to install pipes, cables or conduits in the ground without the necessity for excavating a continuous trench. Such moles are disclosed, for example, in GB-A-2 134 152 and GB-A-2 147 035.
The use of a mole in replacing underground pipes is described in GB-A-2 092 701. The mole is designed to pass through an existing underground pipe, and is provided with cutting edges at the front so as to cause the walls of the pipe to fracture as the mole moves therealong. A new pipe, or a liner therefor, is towed along behind the mole. The mole is driven through the pipe, for example by means of compressed air, in conventional manner, and is simultaneously guided and pulled along the pipe by a winch cable attached to the front of the mole.
The mole described in GB-A-2 092 701 is provided with fixed or moveable blades at its front to cause fracture of the existing pipe. However, such blades are not very effective, and particular problems are caused in fracturing thick flanges which are present at the joints between adjoining lengths of pipe. The blades have a high wear and fracture rate.
The present invention unexpectedly overcomes this problem by employing a mole in which the cutting edges are integral with the head. This solution is particularly unexpected because up to now, all moles have been provided with smoothly curved or frusto-conical heads. Indeed, in normal practice, a mole having a head portion with sharp edges would not be desirable, because it would be directionally unstable when passing through the ground.
The present invention thus provides a mole for use in replacing or preparing for replacement an existing underground pipe, the mole being adapted for insertion into and movement along the existing pipe, and having a front portion provided with a cutting face for engaging the internal wall of the existing pipe and arranged to cause the wall to fracture, and a rear portion provided with means for clamping to the mole a new pipe or a liner for the existing pipe, so that the mole can tow the new pipe or the liner through the fractured pipe as the mole moves therethrough, characterised in that a head portion of the mole is tapered towards the front and has flat or scalloped sides defining therebetween integral cutting edges, the angle of taper being from 2.degree. to 10.degree. and the number of cutting edges being from 3 to 8.
The angle of taper is preferably from 4.degree. to 6.degree.. The number of cutting edges is preferably from 3 to 6, in particular 4, and the tapered sides are preferably flat. Most preferably, the head portion of the mole is of tapered square section.
Reference is now made to the accompanying drawings, in which:
FIG. 1 is a side view of the front portion of a mole according to a preferred embodiment of the invention; and
FIG. 2 is a front view of the mole shown in FIG. 1.
Referring now to the drawings, the body of the mole comprises a cylindrical outer casing 1. The internal structure and pneumatic operation of the mole are conventional, and are therefore not described here. The rear end of the mole (not shown) includes means for clamping a new pipe or liner for towing behind the mole as it passes along the pipe to be replaced.
Immediately in front of the cylindrical casing 1, there is a frusto-conical portion 2, having an angle of taper of 20.degree.. Immediately in front of the frusto-conical section 2, there is a head portion 3 of square tapered section. The head portion 3 thus comprises four flat sides 4, 5, 6, 7, which define therebetween four straight cutting edges 8, 9, 10, 11 which are in the axial plane of the mole. The angle of taper of the head portion 3 is 4.degree..
Attached to the front of the
REFERENCES:
patent: 4648746 (1987-03-01), Abinett
patent: 4657436 (1987-04-01), Yarnell
patent: 4738565 (1988-04-01), Streatfield et al.
patent: 4848964 (1989-07-01), Yarnell
patent: 5054677 (1991-10-01), Carruthers
patent: 5112158 (1992-05-01), McConnell
Britts Ramon S.
Lagman Frederick L.
Powermole International Limited
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