Percussive down-the-hole hammer and a piston and drill bit...

Details Percussive down-the-hole hammer and a piston and drill bit... Percussive down-the-hole hammer and a piston and drill bit...

1999-02-02

2001-04-03

Batson, Victor (Department: 3671)

Boring or penetrating the earth

Below-ground impact members

Fluid-operated

C175S092000, C173S091000

Reexamination Certificate

active

06209666

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a percussive down-the-hole hammer and a piston and drill bit therefor.
PRIOR ART
During drilling with down-the-hole hammers under ground, such as in tunnels, the dust generated by the drilling operation often is bound together by the use of water mixed into the pressurized air driving the hammer and flushing the dust away. The down-the-hole hammer is provided with a plastic foot valve located in a central passageway in a drill bit anvil and projecting from the impact surface of the anvil. The foot valve is repeatedly enclosed by a central bore of the reciprocating piston to transfer spent pressurized driving air through the drill bit. When drilling downwardly, water is deposited on the impact surface between successive impacts such that each impact will create a jet stream of water away from the impact surface. The part of the jet stream traveling radially inwardly, however, will cut into the plastic foot valve and finally the valve will break such that the hammer will stop impacting.
OBJECTS OF THE INVENTION
An object of the present invention is to provide a drill bit for a down-the-hole hammer which provide for extended lifespan of the foot valve,
Another object of the present invention is to provide a drill bit for a down-the-hole hammer that will have a longer life between service than hitherto known hammers.
These and other objects of the drill bit and the down-the-hole hammer according to the present invention will become apparent from the following detailed description of a preferred embodiment thereof in connection with the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention relates to an air actuated down-the-hole hammer for rock drilling. The hammer comprises a generally cylindrical casing which defines an axis. A drill sub is mounted to a rear end of the casing. A drill chuck is mounted to a front end of the casing. A drill bit is mounted in the drill chuck and includes a front cutting face and a rear anvil portion. The anvil portion includes a rearwardly facing anvil surface. The drill bit includes a first central passageway extending through the anvil surface. A piston is mounted in the casing behind the drill bit. The piston includes a forwardly facing impact surface and a second central passage extending through the impact surface and aligned with the first central passage. A foot valve extends partially in the first central passage and partially in the second central passage when the impact surface impacts the anvil surface, for transferring pressurized air from the second central passage to the first central passage. The piston is mounted for axial reciprocation toward and away from the drill bit, causing the impact surface to impact the anvil surface during a forward stroke of the piston whereby at least some fluid disposed between the impact surface and the anvil surface is forced radially inwardly toward the foot valve. Either the impact surface or the anvil surface includes a projection extending around a radially inner peripheral edge thereof for deflecting the radially inwardly forced fluid in a direction having an axial component to minimize an impact force against the foot valve.
The present invention also relates to a percussive drill bit which includes the projection, and also relates to a piston which includes the projection.


REFERENCES:
patent: 4819746 (1989-04-01), Brown et al.
patent: 4878550 (1989-11-01), Chuang
patent: 4921056 (1990-05-01), Ennis
patent: 5115875 (1992-05-01), Ennis
patent: 5131476 (1992-07-01), Harrington
patent: 5435402 (1995-07-01), Ziegenfuss

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