Tool driving or impacting – Impacting devices – Selective axial direction of impact
Reexamination Certificate
1997-10-24
2001-08-07
Smith, Scott A. (Department: 3721)
Tool driving or impacting
Impacting devices
Selective axial direction of impact
C173S019000
Reexamination Certificate
active
06269889
ABSTRACT:
TECHNICAL FIELD
This invention relates to impact tools and methods of use of such tools, particularly self-propelled pneumatic ground piercing tools.
BACKGROUND OF THE INVENTION
Self-propelled pneumatic tools for making small diameter holes through soil are well known. Such tools are used to form holes for pipes or cables beneath roadways without need for digging a trench across the roadway. These tools include, as general components, a torpedo-shaped steel body having a tapered nose and an open rear end, an air supply hose which enters the rear of the tool and connects it to an air compressor, a piston or striker disposed for reciprocal movement within the tool, and an air distributing mechanism for causing the striker to move rapidly back and forth. The striker impacts against the front wall (anvil) of the interior of the tool body, causing the tool to move violently forward into the soil. The friction between the outside of the tool body and the surrounding soil tends to hold the tool in place as the striker moves back for another blow, resulting in incremental forward movement through the soil. Exhaust passages are provided in the tail assembly of the tool to allow spent compressed air to escape into the atmosphere.
Most impact boring tools of this type have an air distributing mechanism which utilizes a stepped air inlet. The step of the air inlet is in sliding, sealing contact with a tubular cavity in the rear of the striker. The striker has radial passages through the tubular wall surrounding this cavity, and an outer bearing surface of enlarged diameter at the rear end of the striker. This bearing surface engages the inner surface of the tool body.
Air fed into the tool enters the cavity in the striker through the air inlet, creating a constant pressure which urges the striker forward. When the striker has moved forward sufficiently far so that the radial passages clear the front end of the step, compressed air enters the space between the striker and the body ahead of the bearing surface at the rear of the striker. Since the cross-sectional area of the front of the striker is greater than the cross-sectional area of its rear cavity, the net force exerted by the compressed air now urges the striker backwards instead of forwards. This generally happens just after the striker has imparted a blow to the anvil at the front of the tool.
As the striker moves rearwardly, the radial holes pass back over the step and isolate the front chamber of the tool from the compressed air supply. The momentum of the striker carries it rearward until the radial holes clear the rear end of the step. At this time the pressure in the front chamber is relieved because the air therein rushes out through the radial holes and passes through exhaust passages at the rear of the tool into the atmosphere. The pressure in the rear cavity of the striker, which defines a constant pressure chamber together with the stepped air inlet, then causes the striker to move forwardly again, and the cycle is repeated.
In some prior tools, the air inlet includes a separate air inlet pipe, which is secured to the body by a radial flange having exhaust holes therethrough, and a stepped bushing connected to the air inlet pipe by a flexible hose. These tools have been made reversible by providing a threaded connection between the air inlet sleeve and the surrounding structure which holds the air inlet concentric with the tool body. The threaded connection allows the operator to rotate the air supply hose and thereby displace the stepped air inlet rearwardly relative to the striker. Since the stroke of the striker is determined by the position of the step, i.e., the positions at which the radial holes are uncovered, rearward displacement of the stepped air inlet causes the striker to hit against the tail nut at the rear of the tool instead of the front anvil, driving the tool rearward out of the hole. See, for example, Wentworth et al. U.S. Pat. Nos. 5,025,868 and 5,337,837.
Expanders are tapered, ring-shaped shells that fit over the tapered nose portion of an earth boring tool in order to widen the hole made by the tool as it passes through the ground. In this manner, a 4 inch diameter tool may be used to make a 6 or 8-inch diameter hole. The tool is often sent through to make an initial bore, and then sent through a second time with the expander in order to widen the existing hole and/or crack an existing pipe. According to a known method, a plastic pipe may be attached to the back of the expander with the above described reversible tool inside the pipe so that the pipe is installed as the tool moves through the soil, with or without additional widening of the bore.
The tool body of the pneumatic impact tool used in such pipe pulling operations is the single largest and most expensive component of the tool, weighing over 1000 pounds in a large diameter tool. Known tool bodies include a long tubular housing and a tapered nose, which may be integral with the housing or a separate assembly secured to it. The former are made by machining or by swaging as described in Wentworth et al. U.S. Pat. No. 5,487,430, issued Jan. 30, 1996. The present invention provides a pneumatic impact tool specially adapted for pipe pulling operations in which the traditional tubular steel tool body is eliminated.
SUMMARY OF THE INVENTION
A ground piercing tool of the invention includes an elongated tubular housing having front and rear openings, a head including an anvil secured in the front opening of the housing, a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to a rear impact surface of the anvil for driving the tool through the ground, a reciprocation mechanism for reciprocating the striker, and a tail assembly mounted in a rear end opening of the housing that secures the striker and reciprocation mechanism in the housing. According to the invention, a plastic tube forms the body of the housing, and suitable means are provided for securing the plastic tube to the head, which is made of steel or a material of comparable strength. The reciprocation mechanism is preferably an air distributing mechanism that uses compressed air to reciprocate the striker, but a hydraulic or electric reciprocating mechanism could also be used.
According to another aspect of the invention, a method using the foregoing tool is provided for installing an underground pipe. This method includes the steps of welding a front end of the replacement pipe coaxially to a rear end of the plastic tube, operating the tool over a run to pull the pipe into the ground, and when the tool has reached the end of the run, disconnecting the tool from the replacement pipe, preferably by sawing through either the plastic tube or the replacement pipe at the weld or a location proximate the weld.
Other objects, features and advantages of the invention will become apparent from the following detailed description. It should be understood, however, that the detailed description is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 4496007 (1985-01-01), Zinck
patent: 4693335 (1987-09-01), Almon
patent: 4854398 (1989-08-01), Holloway
patent: 5025868 (1991-06-01), Wentworth et al.
patent: 5249634 (1993-10-01), Bueter et al.
patent: 5465797 (1995-11-01), Wentworth et al.
patent: 5467831 (1995-11-01), Spektor
patent: 5487430 (1996-01-01), Wentworth et al.
patent: 5494116 (1996-02-01), Wentworth
patent: 5540294 (1996-07-01), Anderberg
Hammerhead Mole Accessories Catalog, pp. 11-20, Feb. 1995.
Earth Tool Company L.L.C.
Meyers Philip G.
Philip G. Meyers Intellectual Property Law, P.C.
Smith Scott A.
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