Apparatus and Method for Boring Through the Taphole in a Molten Metal Blast Furnace

FIG. 1 is a schematic side elevational view of a taphole-opening apparatus including a drill shaft assembly in accordance with a preferred embodiment of the present invention.

FIG. 2 is a side view, partially in section, of a portion of the drill shaft assembly of FIG. 1, with a portion thereof broken away showing a preferred embodiment of the present invention.

FIG. 3 is an exploded view of a portion of the drill shaft assembly of FIG. 2.

FIG. 4 is a fragmented perspective view of the drill shaft of FIG. 2.

FIG. 5 is a side view, partially in section and partly fragmented, of a drill shaft of an alternative embodiment of the present invention.

FIG. 6 is a side view, partially in section, of a portion of a drill shaft assembly in accordance with another preferred embodiment of the present invention.

FIG. 7 is a cross-sectional view of the drill shaft of FIG. 6 taken along the lines 7--7 and viewed in the direction of the arrows.

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the princiPles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

Referring to FIG. 1 there is shown a taphole-opening apparatus 11 including a drill shaft assembly in accordance with a preferred embodiment of the present invention. A conventional blast furnace, partly shown and designated generally as 10, includes a taphole 12 through which molten metal may exit into a runner trough 13 disposed in the surrounding floor 14. During blast furnace operation, taphole 12 contains a plug 16 of refractory material. When withdrawal of molten metal from furnace 10 is desired a hole is drilled in plug 16 in the diameter desired for the cast.

Taphole opening apparatus 11 generally includes a percussion drill 17 which is slidably mounted on a rail 18. Rail 18 is pivotally mounted in the direction of arrow 19 to allow taphole-opening apparatus 11 to be swung in and out of position for drilling. As is known, a motor assembly (not shown) is provided to move percussion drill 17 along rail 18, toward and away from taphole 12. As is also known, a boom assembly (not shown) may be used to move the entire taphole opening apparatus 11.

In accordance with a preferred embodiment of the present invention, drill shaft apparatus 21 includes drill tool piece 22, coupling 23, and replaceable drill shaft 24. These components are secured to one another to form drill shaft apparatus 21 which acts as a unit and is mounted to percussion drill 17 by any appropriate means known in the art. One such manner of connecting drill shaft apparatus 21 is chuck 26, which is disclosed in U.S. Pat. No. 3,862,750 issued to Broom the disclosure of which is hereby expressly incorporated by reference. Drill shaft apparatus 21 is secured and driven at one end by chuck 26 and is supported intermediately by slotted guide member 27 which is secured at the end of rail 18. At the furthest end of drill shaft apparatus 21 is threadedly secured a rock bit 28 for drilling through plug 16.

To reduce the high cost of the prior art associated with the frequent destruction of expensive high alloy tool steel pipe drill shafts, the present invention is provided with intermediate directed air channel means for precluding binding of the drill bit due to the build up of dust and to preclude molten metal backwash. Referring to FIG. 2, the directed air channel means includes using a solid drill shaft 24 in place of the tool steel shaft with the central bore of the prior art. Drill shaft 24 in a preferred embodiment is made from a solid bar of 1018 cold rolled steel which is significantly less expensive than the steel pipe previously used. Since in the preferred embodiment, drill shaft 24 does not have a central bore and is solid, a lower grade and cheaper bar of steel can be used and still provide the same or greater shaft strength as higher grade and more expensive pipe. Of course, other suitable grades of solid bar may be used. The forward end 30 of drill shaft 24 is threaded for receipt of rock bit 28. (See FIGS. 1 and 4) The rearward end 31 of drill shaft 24 defines a continuous groove 33. Groove 33 extends diametrically across end face 34 of drill shaft 24 and then extends therefrom along opposite sides longitudinally toward forward end 30 of drill shaft 24. Rearward end 31 of drive shaft 24 is also threaded forward from end face 34, with grooves 33 extending farther toward forward end 30 than does threading 35.

Drill tool piece 22 in a preferred embodiment is made from A53 Butt Weld Pipe and is adapted at its rearward end 37 to be secured within chuck 26 in accordance with the disclosure in U.S. Pat. No. 3,862,750. Of course, other suitable materials may be used for drill tool piece shaft 22 and other known or equivalent thereto means for mating with the drill motor may also be used. Drill tool Piece 22 defines a central longitudinal passageway or bore 38 which is in communication at its rearward end with a source of pressurized air as is known (not shown). The pressurized air source is typically 80 to 110 pounds per square inch. At forward end 39 of drill tool piece 22 is defined a groove 42, similar to groove 33 of drill shaft 24, except that groove 42 extends only radially in end face 43 of forward end 39 and then longitudinally along one side of tool piece 22 toward rearward end 37. Forward end 39 of tool piece 22 is also threaded at 44, with groove 42 extending farther toward the rear than threading 44.

Hollow coupling 23 is made in the preferred embodiment of seamless tubing but of course other suitable materials may be used. Hollow coupling 23 is internally threaded at 46 along its entire length. The total longitudinal length 47 of threading 44 on tool piece 22 and the longitudinal length 48 of threading 35 on drill shaft 24 is greater than the longitudinal length 49 of threading 46 in coupling 23. This is to help Prevent coupling 23 from binding relative to tool piece 22 or drill shaft 24 when the three are secured together or during the drilling operation. In the prior art, the longitudinal distance of threading from end face 43 of tool piece 22 or from end face 34 of drill shaft 24 was such that a coupling, such as coupling 23, could be threadedly secured so far in one direction or another that the internal threading of coupling 23 was advanced onto a non-threaded portion of either tool piece 22 or shaft 24 resulting in severe binding. The length of threading of the present components assures adequate excess threading to prevent such binding.

Because the total drill shaft assembly is made of more than one part, it is possible to make the drill tool piece shaft 22 and drill shaft 24 of various combinations of lengths to achieve the overall length desired.

During the drilling operation, pressurized air is fed through bore 38 of tool piece 22. Within coupling 23, the air flow is directed primarily within groove 33, outward of coupling 23 and along arrows 51 toward forward end 30 of drill shaft 24. Operating under an air pressure of approximately 80 to 110 P.S.I., and due to the restriction in flow area, air flow 51 increases in speed and follows drill shaft 24 into bore 52 in plug 16, agitating and blowing the dust back out. This continues even as drill shaft apparatus 21 including coupling 23 bores deeply into plug 16.

A portion of the pressurized air flowing into coupling 23 also passes through groove 42 and rearwardly of coupling 23 blowing back in the direction of arrows 53. As drill shaft apparatus 22 bores through plug 16 and as coupling 23 passes into bore 52, rearward air flow 53 further aids the removal of the dust within bore 52.

Use of nitrogen instead of air allows pressures of 150 P.S.I. Higher pressure gas flow allows the air flow grooves to be farther back from the drill end 30 and thus longer drill shafts 24 may be used. As is readily apparent, the length of drill shafts, tool piece shafts and location of air flow grooves or holes can be adjusted based upon the particulars of the application.

As with the prior art rock bit 28 and often drill shaft 24 may become damaged from the excessive 2800.degree. F. heat of the molten metal within blast furnace 10. In the present invention, however, drill shaft 24 is much less expensive. The practice of changing the drill shaft and bit with a poking bar to break through the final skull in order to avoid total loss of the bit and drill shaft is now avoided because the drill shaft 24 of the present invention is expendable.

An alternative embodiment of the present invention is shown in FIG. 5. In the alternative embodiment of FIG. 5, drill shaft 24 is provided with a central axial bore 56 which extends from end face 34 for a portion of the drill shaft length toward forward end 30. Forward end 30 is still sealed. A pair of opposite and outwardly extending exit bores 57 extend from the forward end of central bore 56 slant forwardly and outwardly from drill shaft 24 to provide forwardly directed exits for high pressure air flow 51. Again a less expensive solid bar can be used instead of the pipe. The bore 56 and exit bores 57 can be readily drilled into the solid bar drill shaft 24. It is to be understood, that the air channel means of the present invention may be placed by appropriate means such as other tubing or holes in solid drill shafts at different locations along the assembly above the drill shaft either along the drill shaft 24 or even the drill tool piece shaft 22. In this manner, dust clearing air flow is available and the problem of molten backwash is minimized. Further, solid shafts can be adapted to be used in the place of the more expensive pipe shafts used in the prior art.

Such an alternative preferred embodiment is shown in FIGS. 6 and 7. There, a solid bar shaft is used for drill shaft 24. An outwardly extending longitudinal groove 60 which extends the entire length from end face 34 to forward end 30 of drill shaft 24 is cut into the solid bar. A metal air blast tube 61 is embedded into groove 60. Tubing 61 is sized to be pressure fit within groove 60 so that no artificial means are necessary to hold tubing 61 therewithin. In the alternative, one or more appropriate, spaced tabs or brackets (not shown) may be affixed (such as by welding) over both groove 60 and tubing 61 to hold tubing 61 firmly therewithin. In this manner the air blast can be provided as desicribed below, backwash is minimized and a lower drill shaft 24 is provided using less expensive materials than the more expensive pipe shaft of the prior art.

Tube 61 is sized so that its rearward end 62 is disposed slightly forward of end face 34 and its forward end 63 is disposed slightly rearward of rock bit 28. Rock bit 28 is held tightly on end 30 of shaft 24 by threaded engagement (65) therebetween. Threaded bore 66 of bit 28 is deeper than the male threaded end 30 of shaft 24. This provides flow communication between the numerous exit holes 67 of bit 28 and groove 60. A groove 69 extends partially diametrically across end face 34 of shaft 24 to provide flow communication between the incoming air flow through central bore 38 of drill tool piece 22 and tubing 61.

In operation, pressurized air forced through bore 38 passes through groove 69, into air blast tubing 61 and exits tubing 61 at forward end 63. Some portion of the pressurized air continues within groove 60 into bit 28 and through exit hole 67 while the remainder of the air passes outside of shaft 24 and bit 28. This configuration creates a circuit of forced air extending all the way down to rock bit 28. Once the final skull is penetrated and molten metal begins to flow upwards along shaft 24, the molten metal will flow more easily along the outside of shaft 24 rather than through the relatively small diameter of air blast tubing 61 thereby reducing the likelihood of molten backwash through the air channels and up to the drill motor.

While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.