US 3749190 A
Description (OCR text may contain errors)
United States Patent 1 Shipman [451 July 31, 1973 Inventor:
RETAINING CARBIDE IN ROCK DRILL BITS Clarence S. Shipman, Easton, Pa.
llngersoll-Rand Company, New York, NY.
Filed: May 6, 1971 Appl. No.: 140,793
U.S. Cl 175/410, 29/525, 175/374,
Int. Cl. E21c 13/02, E21c 13/06 Field of Search 175/329, 374, 410; 29/509, 512, 522, 525; 76/101 A, 108 A; 85/70, 77, 82; 287/203; 299/91; 285/3824, 382.5, DIG. 9
Reierences Cited UNITED STATES PATENTS 11/1951 Alexander et al. 175/410 FOREIGN PATENTS OR APPLICATIONS 642,770 9/1950 Great Britain 85/77 Primary Examiner-Marvin A. Champion Assistant Examiner-Jack E. Ebel Attorney-Frank S, Troidl and David W. Tibbott 2 Claims, 3 Drawing Figures PATENIEB JUL 31 I975 INVENTOR CLARENCE 5 SHIP/14A IV BY QM ATTORNEY RETAINING CARBIDE IN ROCK DRILL BITS This invention relates to rock drill bits, and in particular, to a rock drill bit having tapered carbide button inserts.
Conventional rock drill bits with carbide inserts are exposed to severe impact forces in operation which tend to extract the carbide buttons from the bits rendering the bits ineffective. Because the buttons are usually inserted by press-fit or shrink-fit into holes in the bit face that are machined to close tolerance, the bits must be made from a material soft enough to machine. This lower hardness makes the bit body more easily deformed and requires less force to extract a carbide button from its hole. Many steels may be heat treated to increase their strength, but such heat treatment tends to distort close tolerance dimensions. My invention eliminates the need for expensive close tolerance machining of holes, and permits the use of a material hardenable to higher strength for the bit body.
I have discovered that if a straight hole is provided with an undercut and a tapered carbide button is inserted in the hole with the large end of the button seated on the bottom of the hole, a sleeve may be wedged into the space between the button of the hole with sufficient force to extrude the sleeve material into the undercut. The sleeve thus retains the carbide button in the drill bit by its wedging action and by interlocking with the undercut in the drill bit. Because close tolerances are not required, the drill bit may be further strengthened by heat treating after the hole and undercut are machined and prior to insertion of the carbide button. The button cannot be extracted from its hole without removing the wedge sleeve, and the wedge sleeve cannot be removed without shearing across the generatrix of the undercut.
The invention as well as its advantages, may be further understood by reference to the following detailed description and drawings wherein like parts are represented by like numbers throughout the various views, and in which:
FIG. 1 is a perspective view of a rock drill bit with carbide inserts;
FIG. 2 is a sectional view of the carbide button inserted in a drill bit; and
FIG. 3 is a similar view with the sleeve extruded into the undercut.
Referring to the drawings, and particularly to FIG. 1, a drill bit has a plurality of tapered carbide buttons 12 projecting from the working face 14 of the bit. In FIG. 2, it can be seen that the carbide button is positioned in a straight hole 16 which has an undercut 18. The large end of the button 20 abuts the bottom of the hole 22 and a sleeve 24 is wedged between the tapered side 26 and the hole 16. FIG. 3 shows how the sleeve 24 has been pressed further into the hole with sufficient force to wedge it between the tapered side 26 of the button I2 and the straight side of the hole 16, and, more importantly, sufficient to extrude part of the sleeve into the undercut I8. Prior to application the sleeve may have a uniform wall thickness or a tapered wall.
In operation, when extractive forces are imposed on the carbide sides 26, the button will be retained in the hole until these forces exceed the shear strength of the sleeve across the shear line that spans the upper intersection 28 of the undercut with the straight hole wall 16 and the lower intersection 30 of the undercut with the hole wall. The larger the shear area, the greater will be the retaining strength of the sleeve. The use of a hardenable steel for the bit body 10 permits easy machining of hole 16 and undercut l8, and heat treatment for maximum strength to resist deformation near the hole by the extractive forces on the button.
1. A rock drill bit comprising:
A bit body having at least one hole formed therein:
a tapered carbide insert set in said one hole with a taper-defined larger end of said insert abutting the bottom of said one hole; and
a sleeve wedgingly retaining the carbide insert in said one hole; wherein said insert is circular in cross-section, and has a uniformly-diminishing diameter along a length thereof which is defined by the portion of said insert which is set in said one hole, said portion defining only a uniformly-diminishing cylindrical surface; said sleeve comprises an annulus which envelops substantially all of said portion of said insert, and which is compressed along the full length thereof, between said uniformly-diminishing cylindrical surface of said insert and the wall of said one hole, to secure said insert with a forceful constraint, about the full circumference thereof and along a substantial length of said portion thereof, in said one hole;
said one hole has an annular undercut formed in said wall a substantial distance from the bottom of said one hole;
said sleeve has an annular extrusion formed thereon which is compressively nested in said undercut; and
said extrusion and undercut are cooperative with said circumferential constraint of said insert by said sleeve and said lengthwise constraint of a substantial length of said portion of said insert by said sleeve to secure said insert in said one hole.
2. The method of retaining a carbide button, having an unformly-diminishing cylindrical surface, in a rock drill bit comprising:
forming a hole in the bit to receive the button;
forming an undercut in the hole a substantial distance from the bottom of said hole;
setting a tapered carbide button in the hole, with the taper-defined larger end of the button abutting the bottom of the hole, and with only said uniformlydiminishing cylindrical surface thereof within said hole;
forcing a sleeve, which has an inside diameter which is less than the outside diameter of said button, around the button; and
pressing the sleeve toward the bottom of the hole with a predetermined force, to cause part of the sleeve to extrude into the undercut, the sleeve to envelop substantially all of said uniformlydiminishing cylindrical surface, and the remainder of said sleeve to deform into an annular wedge forcefully constrained against the full circumference of said button, against and along a substantial length of said uniformly-diminishing cylindrical surface, and against the wall of the hole, retaining the button in the body.
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