Chucks or sockets – With fluid-pressure actuator – Radially reciprocating jaws
Reexamination Certificate
2001-10-26
2004-04-13
Howell, Daniel W. (Department: 3721)
Chucks or sockets
With fluid-pressure actuator
Radially reciprocating jaws
C279S057000, C279S074000
Reexamination Certificate
active
06719303
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a chuck for rotating a drill string.
BACKGROUND OF THE INVENTION
To investigate geological structures, holes are drilled into the ground utilizing a drill string that carries a drill bit at one end. The drill string is made up of a number of drill rods threaded together with each of the drill rods typically being in the order of ten feet in length. In conventional drilling, a drill rig is employed which allows the rods of the drill string to be assembled end to end and provides for the rotation of the drill string. Rotation is imparted to the rods by a drill chuck that engages the outer surface of one of the rods and transmits torque to the rod from the drive unit. The position of the chuck on the rod must be adjustable so that as the string penetrates the ground the chuck can be released, moved along the rod, and reengaged.
In conventional drill rod chucks, the jaws of the chucks are moved to a closed position gripping the drill rod under the force of large a number of preloaded coiled springs or Belleville washers. An hydraulically actuated operator is utilized to compress the coiled springs or Belleville washers to thereby release the jaws from their closed drill rod gripping position and to open them for advance of the drill rod therethrough.
To provide adequate drill gripping force to rotate the drill string in the case of the coiled springs, a large number of springs are required, e.g. some 22 coiled springs, which have a significant height of 8 to 12 inches. Again, with the Belleville washers, a large number of stacks of washers, e.g. 18 stacks, of heights comparable to the coiled springs are required.
To accommodate the large number of springs or washer stacks conventional chucks are necessarily large, heavy and costly.
One of the problems with conventional chucks is that, in use over time, the initial force imparted by the coiled springs or Belleville washers deteriorates reducing the grip and hence the positiveness of the drive to the drill rod. Moreover, such deterioration is nonuniform from spring to spring so that the grip of the chuck jaws is not uniform around the rod.
Further, the force exerted by the coil springs or the Belleville washers is inherently less when they are extended so that in time worn drill rods may even slip through the chuck.
It will be understood that in order to provide the required chuck closing force, the springs or washers must be preloaded when assembled into the chuck so that they are under compressive force between a fixed surface or pressure pad and the jaw actuator. As a result, the chuck has a dangerous potential to fly apart and cause serious injury, for instance, when a retaining bolt is removed or bolt threads are stripped.
Again, in conventional chucks the bearing between the axially moveable non-rotating hydraulic operator and the chuck actuator is maintained in contact with the chuck actuator with the chuck in the closed position and driving the drill string from the drill rotation or drive unit. This results in generating very significant heat during the drilling operation. This heat added to the heat generated by the chuck driving unit renders their surfaces dangerous to the operator and capable of causing serious burns.
A further problem with conventional chucks is that, not only are the coiled springs or Belleville washers inherently subject to different rates of loss of resiliency or compressive forces as mentioned above, but they operate in an environment where they are subject to deterioration through corrosive damage due to contact with water and sludge shortening useful spring and washer life.
A still further problem with conventional chucks is that the jaws are not adequaately supported against the high cantilever and twisting forces causing loss of grip, eccentricity, run out virations, and jamming.
It is the object of the present invention to overcome the above disadvantages as well as others of conventional chucks as will hereinafter appear.
SUMMARY OF THE INVENTION
One important aspect of the present invention resides in eliminating the use of mechanical springs or washers with their inherent limitations and instead utilizes compressed gas to provide the force to close the chuck jaws to grip the drill rod.
With the utilization of compressed gas to provide the force to close the jaws of the chuck on a drill rod of a drill string, it has been found that the closing pressure can be both accurately set yet altered as desired. Further, the jaws can be moved uniformly to close on the drill rod to provide a balanced or uniform grip around the rod while maintaining an essentially constant gripping force throughout the jaw travel. As a result, the jaws can grip rods of different diameters with essentially equal and sufficient force not only to provide the requisite torque transfer regardless of such variations in drill rod diameters.
More particularly, in keeping with this aspect of the invention, the chuck actuator which moves axially longitudinally of the spindle to open and close the jaws is operated in the jaw closing direction by a source of compressed gas in the form of a plurality of compressed gas springs disposed symmetrically around the chuck actuator and acting between the jaw actuator and a suitable stop surface or pressure pad fixed to the spindle.
Compressed gas springs are commercially available and comprise cylinders into which compressed gas, eg. nitrogen, is introduced. The compressed gas forces a slideable small diameter cylindrical plunger or piston outwardly to a maximum position. Under the application of a force on the outer end of the plunger, the plunger can be displaced telescopically back into the cylinder against the force of the contained compressed gas. The travel of the plunger from its point of maximum projection to its point where it is fully retracted is the stroke of the plunger. Such gas springs using compressed nitrogen gas are sold, for example, by Hyson Products. These gas springs are extremely compact and provide much more force in a very much smaller area than conventional mechanical springs. For instance, a nitrogen gas spring having a diameter of 2¾ inches can provide the same force as from 8 to 10 coiled springs having a diameter of 2 inches.
In the case of coiled springs, for optimum life the springs should not be deflected more than 25% of their total length. Therefore, in the case of an application requiring a 3 inch stroke, the height of the spring should be 12 inches.
For a corresponding 3 inch stroke, the height of a gas spring is almost half that of the coiled spring.
It will be understood that on contact with the plunger of a gas spring the full force of the compressed gas in the cylinder is available to resist inward movement of the plunger whereas in a coiled spring, unless it is preloaded, there is no force on simple contact with the spring. Moreover, gas springs provide a nearly constant force resisting inward movement throughout the stroke of the plunger.
In addition, as the compressed gas within the cylinder of the gas spring is trapped from escaping, unlike coiled springs or washers whose force deteriorates with age and use, the force exerted by the gas spring remains constant with time and regardless of the frequency of its use. On the other hand, the force of the spring can be altered as desired by introducing a measured amount of compressed gas, eg. nitrogen gas, into the cylinder or exhausting a measured amount if desired. Thus, each spring can be calibrated to provide a precise spring force so that a number of identical gas springs having precisely the same spring force and other characteristics can be provided.
The jaws are moved by a jaw actuator in the form of a bowl or ring which cooperates with the jaws which are arranged at equally spaced intervals symmetrically around the spindle in a circular configuration. The jaw actuator or bowl opens the jaws as it is moved upwardly under hydraulic force and closes the jaws as it is moved downwardly under the force of a highly efficient compact arrangement o
Boart Longyear International Holdings, Inc.
Howell Daniel W.
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