IMPROVED CORE SAMPLING DRILL BIT
This invention relates to an improved earth drilling bit for obtaining core samples, and more specifically to an improved diamond impregnated drill bit for core sampling during ground drilling.
A conventional diamond impregnated drill bit is normally formed with a crown section having a height in the order of 10 mm, with the crown section being moulded with a plurality of crown segments which have radial end faces separated by radial waterways or channels which allow water to flow outwardly across the end face of the bit and remove the cuttings of the drilled rock. The number of waterways formed in the crown of the drill bit normally depend on the size of the bit. The height of the crown segment and the depth of these waterways is critical to the design strength of the drill bit. For example, with a conventional bit design, if the crown height is excessively increased, the overall strength of the segment is reduced such that the drill bit segment cannot withstand the forces involved in drilling. This reduced strength has been partially combated by adding a "fileable" waterway in some bit types. However, this requires the fileable waterway to be manually filed out partway through the drilling life of the bit. This of course stops drill production and also requires the removal of the drill bit from the drill hole. This is extremely time consuming and uneconomical.
It will be appreciated that with conventional drill bits, once the bit has been worn away to an extent where the waterways no longer exist, it is necessary for the drill rods of the drill string to be removed from the drill hole and the drill bit changed. Again, this stops drill production and is therefore very uneconomical.
It is the main object of the present invention to provide an improved core sampling drill bit of the diamond impregnated type which allows the crown segment height to be significantly increased to that of a conventional drill bit without
significantly affecting the design strength of the crown segment, and which can be drilled for a much longer period of time before having to be replaced, thereby increasing the productivity of the drill assembly and reducing the drill bit cost per metre of drilling.
It is another object of the present invention to provide an improved core sampling drill bit wherein the crown of the bit is formed with an increased number of waterways without substantially affecting or reducing the design strength of the crown segments.
Broadly according to this invention therefore, there is provided an improved core sampling drill bit of the type having a tubular body which at one end is connectable to a drill string and which terminates at its other end in an impregnated diamond segmented crown characterised by a first set of primary circumf erentially spaced waterway forming radial slots formed in a first section of the crown and each of which extends axially inwards from the outer end face of the drill bit, and a second set of circumf erentially spaced secondary waterway forming radial slots formed in a second section of the crown and axially offset relative to and partially overlapping (or nearly so) said primary waterway forming slots, arranged so that, in use, as the drill bit wears away and the height of the crown progressively decreases, the primary waterway slots wear away followed by the secondary waterway slots and waterflow across the working end face of the bit is therefore uninterrupted.
By having the primary and secondary waterway forming slots or channels axially offset and partially overlapping, the height of the crown of the drill bit can be significantly increased while still providing the requisite drilling strength, despite an increase in the number of waterways formed in the crown.
Desirably, the axial depths of the primary and secondary waterway forming slots or channels are approximately equal, eg approximately 15 mm, thereby giving a total overall crown height of around 30 mm which compares with around 10 mm for a conventional diamond impregnated drill bit.
The drill bit of this invention can be drilled for the entirety of its working life without having to be removed from the drill hole to remove any "fileable" waterways or replace the bit for the conventional bit design. This avoids having to remove the drill rods and bit from the drill hole and stop production.
By having a drill bit which has two sets of waterways in a staggered array ensures that water flow across the end-face of the bit will not be interrupted during drilling. Any interruption of water flow during drilling may cause the bit to burn due to the bit face becoming overheated.
In order to further illustrate the present invention, a preferred embodiment thereof is described hereunder in some further detail with reference to and as illustrated in the accompanying drawings wherein:
Figure 1 is a side view of a core sampling drill bit made in accordance with the present invention;
Figure 2 is a partly sectioned side elevational view of the drill bit shown in Figure 1; while
Figure 3 is a end elevational view of the drill bit.
Referring to the drawings, there is shown a diamond impregnated drill bit 10 having a metal tubular body 11 which is adapted for connection to a drill string member (not shown), and a radially segmented crown 12 integrally formed with the body 11 in accord with known art. The wall of the crown 11 has formed therein a set of primary circumf erentially spaced waterway channels or slots 13 in an upper
cutting matrix portion of the crown 12, and a set of secondary circumferentially spaced waterway slots or channels 14 in a lower cutting matrix portion of the crown 12, with the secondary waterway channels or slots 14 being axially offset or staggered in relation to the primary waterway channels or slots 13.
In this embodiment, each of the waterway slots or channels 13, 14 formed in the wall of the crown 12 of the drill bit 10 has an axial depth of approximately 15 mm, with the height of the crown slightly greater than 30 mm. Each of the primary waterway slots 13 extends axially inwards from the leading end face of the drill bit, with their inner ends overlapping with the upper leading ends of the secondary waterway slots 14. In this embodiment the amount of axial overlap is in the order of 1 mm. This ensures that once the primary waterway channels or slots 13 have been worn away, water flow continues across the radial end f ce of the drill bit by virtue of the "opening up" of the secondary waterway slots 14. It will be appreciated that the secondary waterway slots 14 form windows in the wall of the crown 12 and do not function until such time as the primary waterway slots have almost disappeared.
The arrangement of the waterway slots 13, 14 and their relative positioning are such that the overall design strength of the drill bit is not substantially reduced and will still be capable of withstanding the forces involved in drilling through rock formations.
It will be appreciated that the configuration of the waterway channels or slots 13, 14 could be varied in a number of ways and is not limited to the arrangement shown in Figures 1 and 2 where each secondary waterway slot 14 is centrally located between a pair of adjacent primary waterway slots 13 and equidistantly spaced from one another.
In accordance with known art, each primary waterway slot 13 joins to an axial watercourse forming groove 16 formed in the outer surface of the crown 12, with the bottom or trailing end of the groove 16 extending to the inner or bottom end of the crown 12, whereby water flowing through the waterway channels or slots 13 is able to flow downwardly past the drill bit along such watercourses. Similar watercourse grooves 16' are formed on the inner cylindrical surface of the crown 12.
In this embodiment, the initially closed ended slotted openings 14 do not extend to the bottom edge 18 of the crown 12 and terminate short thereof by approximately 2 to 3 mm. This 2 to 3 mm bottom section of the crown 12 can be formed of a backing matrix rather than the cutting matrix which is used for the portions of the crown 12 containing the waterways 13, 14. It has been found that by having the secondary waterways 14 terminate short of the bottom edge 18 of the crown 12, there is unlikely to be any loss of water pressure during drilling. Water pressure loss may occur if the slots 14 extend right through to the bottom edge 18 of the crown.
A brief consideration of the above described embodiment will indicate that the invention provides a vastly improved core sampling drill bit which has a substantially increased crown height achieved by having offset primary and secondary waterway channels or slots formed in upper and lower portions of the crown. With this invention, the drill bit has a substantially increased working life which increases drilling productivity and reduces the number of times the drill string has to be removed from the drill hole.