Boring or penetrating the earth – Boring without earth removal
Reexamination Certificate
2000-02-16
2001-08-14
Pezzuto, Robert E. (Department: 3671)
Boring or penetrating the earth
Boring without earth removal
Reexamination Certificate
active
06273201
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates, in general, to pneumatic impact tools and, in particular to a movable chisel head for a pneumatic impact tool.
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 body having a tapered nose and an open rear end, an air supply hose that 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 movement through the soil.
Some pneumatic tools incorporate movable bits or chisels at the tapered nose section of the tool to more easily penetrate hard ground. Although this concentration of force is useful for penetrating obstructions, total tool displacement per impact is reduced. This inefficiency causes slower tool speeds when the tool is not penetrating hard ground conditions. To the extent the movable chisel and bit mounted on it move outwardly from the tool body during impact, there is also a tendency for soil to enter the gap behind the bit between the bit and tool body and cause the chisel to become jammed. Spektor U.S. Pat. No. 5,031,706 describes using a resilient gasket confined under compression between the movable head and chisel adapter as a means of preventing soil from entering behind the chisel.
Some prior movable chisel tools have also relied on elaborate front end structures which are susceptible to breakage and more difficult to assemble and disassemble than tools wherein the anvil of the tool does not move. Another has the disadvantage of delivering direct impacts to the rear end of an anvil that is threadedly secured in a front end opening of the tool body, damaging the threaded connection and/or making it difficult to disengage the anvil when the chisel requires replacement. See, for example, U.S. Pat. No. 4,462,468.
In normal operation, the chisel is spring-biased to a position at which its rear end protrudes beyond the read end or impact surface of the anvil. If the chisel encounters an obstruction and is not moved all the way forward as a result of receiving an impact from the striker, then all of the striker's energy continues to be transferred to the chisel with each repeated forward stroke until the rear end of the chisel is flush with the impact surface of the anvil. The present invention provides a movable chisel of simple but durable design that allows the tool to penetrate hard ground and maintain tool performance better than other movable chisels currently in commercial use.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a ground piercing tool includes an elongated tubular tool housing, a striker disposed for reciprocation within an internal chamber of the housing to impart impacts to a front impact surface for driving the tool forwardly through the ground, and an air distributing mechanism that reciprocates the striker in response to a supply of compressed fluid. An anvil disposed in a front end opening of the tool housing, which anvil includes a rear, outer frustoconical portion which engages a like-shaped forwardly tapering inner wall of the housing whereby the anvil is held in the housing. The anvil has a lengthwise bore therein, and a rear end of the anvil defines the front impact surface for the striker. A chisel is slidably disposed in the bore of the anvil, which chisel is movable between a rearwardmost position at which a rear end portion of the chisel protrudes from the bore of the anvil to receive an initial impact from the striker, and a forwardmost position at which the striker can impact directly on the rear impact surface of the anvil. A spring may be confined in a space between the chisel and anvil to cause the rear end of the chisel to protrude rearwardly from the bore of the anvil a predetermined distance. The spring compresses as the striker delivers an impact to the chisel and moves the chisel forward until the striker contacts the rear end of the anvil.
Virtually all prior movable chisel ground piercing tools have used a spring. According to a further aspect of the invention, it has been found that the spring can be omitted and the chisel can be configured to return to a position at which a rear end of the chisel protrudes a short distance from the opening in the anvil. If the bit is held in place by the soil, the striker will impact the front anvil and can therefore drive the housing forward until it stops against the bit, thus resetting the chisel. If the bit is not secured by the soil, the striker impacts the chisel, and drives it forward through the already opened bore. Since the bore was already opened, very little energy is used in moving the bit and chisel. The striker will continue moving forward until it impacts the front anvil, driving the housing forward to catch up with the bit and chisel. In either case, the chisel is reset.
A ground piercing tool according to this aspect of the invention having a housing, striker and air distributing mechanism as described above includes an anvil disposed in a front end opening of the tool housing. The anvil has a lengthwise bore therein, and a rear end of the anvil defines the front impact surface for the striker. The chisel is slidably disposed in the bore of the anvil and is movable between a rearwardmost position at which a rear end portion of the chisel protrudes from the bore of the anvil to receive an initial impact from the striker, and a forwardmost position at which the striker can impact directly on a rear impact surface of the anvil. The chisel has an enlarged diameter rear end portion or stop that is in close sliding contact with an enlarged rear end portion of the anvil bore such that the enlarged diameter rear end portion of the chisel engages a step at the front end of the enlarged rear end portion of the anvil bore when the chisel is in its forwardmost position. Most preferably, the step and a contact surface of the enlarged diameter rear end portion of the chisel have a forwardly tapering, frustoconical shape with a sufficient taper to cause the chisel to become temporarily locked in its forwardmost position during rearward tool operation.
A bit is mounted on a front end portion of the chisel. The bit has an outer surface configured to engage the wall of a hole being bored so that as the striker first impacts the chisel and propels the chisel and bit forward, then impacts the impact surface of the anvil, and then moves rearwardly in preparation for another impact, the chisel and bit are propelled forward, increasing a gap between the bit and the front end of the housing. Thereafter, the housing is propelled forward, decreasing the gap between the bit and the front end of the housing and causing the chisel to assume its rearwardmost position without the aid of a spring. Removal of the spring improves the efficiency of operation because some of the striker's energy is lost in the process of compressing the spring on each impact.
The invention further provides a ground piercing tool provided with a wear cover configured to fit over the nose of the ground piercing tool housing, which nose includes a reduced diameter cylindrical front end portion and a forwardly tapering portion rearwardly thereof. The wear cover comprises a cylindrical sleeve having a forwardly tapering inner surface that engages the forwardly tapering portion of the nose of the housing. It can be friction fit over the nose and replaced when necessary. The invention also provides a two-pi
Crane Robert F.
Randa Mark D.
Wentworth Steven W.
Earth Tool Company L.L.C.
Meyers Philip G.
Pezzuto Robert E.
Philip G. Meyers Intellectual Property Law, P.C.
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