ROCK BIT TIP AND ROCK BIT
A rock bit tip includes a mounting portion, an end portion converging from a top end of the mounting portion to form a work surface and at least one recess in a bottom of the mounting portion, the recess extending towards the end portion. Particularly, there are more than one recess. The disclosure further relates to a rock bit.
The present disclosure relates to tips in rock or mining bits for use in a rock excavation apparatus.
The disclosure particularly relates to tips with hollow bases.
BACKGROUNDThere are several different methods used for drilling in earth formations. Some use rotary movement and some use a combination of rotary and percussive movement. One common aspect of these methods is that a drill bit rotates at an end of a drill string.
Rotary drilling is conducted by rotating a rigid string of tubular rods to which a rock-cutting bit is attached. The rotary drill imparts two basic actions through the drill rod and bit into the rock, i.e. axial thrust and rotational torque. Percussive drills break rock predominantly by crushing and chipping rock with the repeated application of high-frequency, high-energy blows through a drill bit. The impact energy is developed by a piston that strikes the bit (down-the-hole drill) or drill steel (surface-mounted drill).
To improve the wear resistance and increase the lifetime of such drill bits, cutting elements in the form of tips or inserts are attached to the drill bit body. These tips are often made of cemented carbide, most commonly tungsten carbide, due to its excellent combination of high hardness and high toughness. The tips can also be made of polycrystalline diamond (PCD). The purpose of the tips is mainly to apply pressure to and fracture rock. Sometimes tips are also positioned on the drill bit body as protection for the surrounding steel. The tips must therefore withstand high compressive and transverse loads.
The tungsten carbide tips are commonly mounted in cylindrical recesses in the outer surface of the drill bit body. The tips can be made a few hundredths of a mm larger than the recess and are pressed in to have a tight interference fit to prevent loosening during usage.
Tungsten carbide tips are also used for soft cutting conditions such as excavation of coal. The tips are, in this application, often named caps and are often adhesively bonded to a pick body by, for example, brazing or welding.
Several standard shapes are used for tungsten carbide tips, such as a part-spherical, conical, a double cone, a ballistic and a chisel crest. Common for these different shapes is that the base, also called mounting portion, of the tip is generally cylindrical.
In many applications it is advantageous to use tips having a diameter of about 2 cm or larger. The advantages being that fewer tips need to be used and also that the protrusion of the tip from the surface of the bit body can be greater while maintaining adequate strength to avoid transverse failure during the excavation operation. Having large tips concentrates the load to fewer tips and greater rock penetration can be obtained without engagement of the steel surface, resulting in improved excavation rate. Having large tips that extend a greater distance from the bit also increases the lifetime of the bit as the large tips can accommodate appreciable wear before they are worn out.
One problem with large diameter tips is that they are expensive. This is due to the high cost of the material required to manufacture a tip. The material quantity required increases with the square of the diameter of the tip. When using tungsten carbide tips it is more costly to use few tips with a diameter of about 2 cm than using a larger amount of small tips.
This problem is addressed in U.S. Pat. No. 4,150,728. Here tungsten carbide tips with hollow bases are shown. Such a tip has a cavity opening to the inner end of the tip with a volume in the range of from about 15 to 30% of the volume of the base portion of the tip.
The present inventor has surprisingly found that several prominent problems occur at tips with hollow bases. One is that the base of the tip tends to get oval in shape. Another problem is that the form of the tip tends to get conical, i.e. the diameter of the mounting portion decreases when approaching the very bottom of the tip. Ovality and conicity in the mounting portion decreases the force for pulling the tip from the drill bit body and therefore loosening of the tip is an unfavorable consequence.
Another problem is that the mounting portion may crack when a tip is press fitted into a recess in the drill bit body.
These and other aspects of, and advantages with the present invention will be apparent from the detailed description and the accompanying drawings.
SUMMARYOne object of the present invention is to provide a hollow tip concept, which has better strength than known hollow tips. Another object is to provide a hollow tip concept which can be produced at a lower cost compared to solid tips, thus solving the above mentioned problems.
According to a first aspect, there is provided a rock bit tip comprising: a mounting portion, an end portion converging from a top end of the mounting portion to form a work surface and at least one recess in a bottom of the mounting portion, the recess extending towards said end portion, wherein there are more than one recess.
In a second aspect, there is provided a rock bit comprising a tip with more than one recess.
In the detailed description of the present invention reference will be made to the accompanying drawings, wherein,
The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which:
The number of recesses, and their sizes, may be altered compared to the examples described in the above-captioned embodiments. It is also possible to combine recesses with different sizes and shapes into a new embodiment. The depth of the recesses can also be varied, but the recesses are always of the blind hole type.
The present invention is not limited to the above described embodiments. Different alternatives, modifications and equivalents might be used. The above mentioned embodiments should therefore, not be considered limiting to the scope of the invention, which is defined by the patent claims.
Claims
1. A rock bit tip comprising:
- a mounting portion;
- an end portion converging from a top end of the mounting portion to form a work surface; and
- at least one recess in a bottom of the mounting portion, the recess extending towards said end portion, wherein there are a plurality of recesses.
2. The tip as set forth in claim 1, wherein the plurality of recesses are spaced apart by a support structure, the support structure being integral with the mounting portion and the end portion.
3. The tip as set forth in claim 1, wherein at least one recess has a cross section, parallel to the bottom of the mounting portion between a bottom of the mounting portion and the end portion, at least one recess having a geometrical centre separate from a longitudinal tip centre axis.
4. The tip as set forth in claim 1, wherein at least one recess has a cross section, parallel to the bottom of the mounting portion, at the bottom of the mounting portion, that is a circle sector.
5. The tip as set forth in claim 1, wherein at least one recess has a cross section, parallel to the bottom of the mounting portion, at the bottom of the mounting portion, that is a truncated circle ring.
6. The tip as set forth in claim 1, wherein at least one recess has a cross section, parallel to the bottom of the mounting portion, at the bottom of the mounting portion, that is hexagonal.
7. The tip as set forth in claim 1, wherein at least one recess has a cross section, parallel to the bottom of the mounting portion, at the bottom of the mounting portion, that is circular.
8. The tip as set forth in claim 1, wherein the tip comprises cemented carbide and/or polycrystalline diamond (PCD).
9. The tip as set forth in claim 8, wherein the tip comprises tungsten carbide.
10. A rock bit comprising a tip having a mounting portion, an end portion converging from a top end of the mounting portion to form a work surface, and at least one recess in a bottom of the mounting portion, the recess extending towards said end portion, wherein there are a plurality of recesses.
11. The rock bit as set forth in claim 10, wherein the rock bit is selected from the group of a bit for rotary drilling, a bit for percussive drilling or a mining pick.
Type: Application
Filed: Nov 26, 2013
Publication Date: Oct 29, 2015
Inventor: Karl-Oskar FINNMAN (The Woodlands, TX)
Application Number: 14/649,589