Boring or penetrating the earth – Below-ground impact members – Fluid-operated
Reexamination Certificate
1999-12-14
2001-09-18
Tsay, Frank S. (Department: 3672)
Boring or penetrating the earth
Below-ground impact members
Fluid-operated
C175S321000
Reexamination Certificate
active
06290005
ABSTRACT:
TITLE OF THE INVENTION
A pneumatic impact damping device for a drill column
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic impact damping device for a drill column, and, in particular, to an impact damping device used with a deep-hole hammer drill to divert the impacts and vibrations of the drill from the rotating machine rotating the drill column and from other parts of the drilling equipment.
U.S. Pat. No. 5,355,966 describes a drilling means with a deep-hole hammer drill at an inner drill column and a rotary percussion drill at an outer drill column. An impact damping device is provided that separates the impacts from the inner and the outer tube, respectively.
From German Patent 196 16 751, a device for superposed drilling is known wherein an outer column is connected with a head-piece onto which an percussion device may strike. Within the head-piece, a gas pressure reservoir is located having a hydraulic chamber in communication with a cylinder chamber. The hydraulic liquid In the cylinder chamber pushes forward a hydraulic piston to which the inner column is connected. The gas pressure reservoir separates the inner column, with the deep-hole hammer drill contained therein, from the impacts caused by the percussion device.
It is common with drill columns operated with a deep-hole hammer drill to arrange a pack of damping elements in front of the rotary drive, the elements keeping the deep-hole hammer drill impacts away from the rotary drive. The damping elements are rubber packages subjected to heavy wear.
A pneumatic impact damping device of the kind mentioned in the preamble of claim
1
is known from U.S. Pat. No. 4,055,338. This damping device comprises a cylinder chamber filled with gas, e.g. hydrogen, and sealed off by a piston. The piston is supported by a liquid buffer. Upon an axial movement of the cylinder, which is connected with a first portion of a drill column, the gas within the gas chamber is compressed thereby producing a spring and damping effect. This device has a gas chamber that is always closed, and it also has a liquid chamber always closed. Thus, it requires a certain maintenance to ensure the required volumes of gas and liquid.
It is the object of the present invention to provide a pneumatic impact damping device that is of simple structure and is functionally reliable while having a long service life.
SUMMARY OF THE INVENTION
The present impact damping device comprises a cylinder in which a piston is movable. The piston and the cylinder are penetrated by a longitudinally extending channel through which pressurized air may flow for supplying a connected deep-hole hammer drill with pressurized air. From the channel that carries the pressurized operating air, a passage extends into the cylinder chamber. This passage is closed off automatically when an axial thrust force is exerted from the rear end onto the drill column. Closing off the passage traps the pressurized air contained in the cylinder chamber, the air being compressed subsequently. The air flowing in the channel of the drill column is used as the pressure gas so that no closed gas pressure reservoir is needed. Neither is a closed liquid chamber needed. With the air trapped in the cylinder space, ain air cushion is formed that absorbs impacts. This air cushion is pre-stressed by the supply pressure of the pressurized air and also by the axial thrust force so that it can effectively dampen impacts and vibrations. The pre-compressed pressure may increase to a multiple of the operating pressure by closing the passage. Thus, the damping device may be made more compact.
According to a preferred development of the invention, the cylinder chamber contains a spring device pressing on the piston. This spring device tends to enlarge the cylinder chamber. It supports the damping effect of the pneumatic air cushion. Moreover, it presses the cylinder chamber apart when the thrust force is released. This guarantees that the impact damping device does not remain in the compressed state, but is always relaxed and open when used again.
In a preferred embodiment, the cylinder chamber includes a longitudinally extending bushing projecting through the piston and being provided with the passage in the form of at least one hole in the wall. This bushing is the channel for the pressurized air flowing through the drill column. At the same time, it acts as a control element to close off the cylinder chamber when a thrust force acts thereon.
The invention is generally applicable to drill columns, both double drill columns and single drill columns. Double drill columns have an inner tube and an outer tube rotated by a common rotary drive or by separate rotary drives.
REFERENCES:
patent: 4055338 (1977-10-01), Dyer
patent: 4194581 (1980-03-01), Walter
patent: 4231283 (1980-11-01), Malburg
patent: 4257245 (1981-03-01), Toelke et al.
patent: 5355966 (1994-10-01), Mathis
patent: 5715897 (1998-02-01), Gustafsson
patent: 19616751 (1996-04-01), None
Diller Ramik & Wight
Tsay Frank S.
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