Multi-indenter hammer drill bits and method of fabricating
11111729 · 2021-09-07
Assignee
Inventors
Cpc classification
International classification
Abstract
A multi-indenter drill bit includes a plurality of indenters arranged on a drilling surface of a bit face. The ratio of the total indenter area to the bit face area is defined by a parameter KPI.sub.1 (expressed as a percentage), and the ratio of the average individual indenter area to the bit face area is defined by a parameter KPI.sub.2, (expressed as a percentage). The relationship between KPI.sub.1 and KPI.sub.2 is defined by an equation.
Claims
1. A method of fabricating a down-the-hole hammer multi-indenter drill bit for use in down-the-hole hammer drilling of a hole, the drill bit including a plurality of indenters arranged on a drilling surface of a bit face, the method comprising: defining a drill bit face area; defining a number of drill bit indenters; defining a total area of the drill bit indenters, wherein a ratio, expressed as a percentage, of total indenter area to bit face area provides a value KPI.sub.1 (Key Performance Indicator 1), and a ratio, expressed as a percentage, defined by (the total area the drill bit indenters/the number of indenters)/(bit face area), provides a value KPI.sub.2 (Key Performance Indicator 2); and using the equation
KPI.sub.2<=1.353×10.sup.−6(KPI.sub.1).sup.5−1.527×10.sup.−4(KPI.sub.1).sup.4+6.586×10.sup.−3(KPI.sub.1).sup.3−1.301×10.sup.−1(KPI.sub.1).sup.2+1.185(KPI.sub.1)−3.960 to constrain a relationship between KPI.sub.1 and KPI.sub.2.
2. The method according to claim 1, further comprising defining the bit face area/the total number of indenters by a parameter KPI.sub.3, wherein a value of KPI.sub.3 is between 90 sq. mm/indenter and 5,000 sq. mm/indenter.
3. The method according to claim 2, wherein the value of KPI.sub.3 is between 90 sq. mm/indenter and 250 sq. mm/indenter.
4. The method according to claim 2, wherein the value of KPI.sub.3 is between 120 sq. mm/indenter and 500 sq. mm/indenter.
5. The method according to claim 2, wherein the value of KPI.sub.3 is between 130 sq. mm/indenter and 1,100 sq. mm/indenter.
6. The method according to claim 2, wherein the value of KPI.sub.3 is between 140 sq. mm/indenter and 1,400 sq. mm/indenter.
7. The method according to claim 2, KPI.sub.3 wherein the value of KPI.sub.3 is between 160 sq. mm/indenter and 1,700 sq. mm/indenter.
8. The method according to claim 2, wherein the value of KPI.sub.3 is between 180 sq. mm/indenter and 2,000 sq. mm/indenter.
9. The method according to claim 2, wherein the value of KPI.sub.3 is between 200 sq. mm/indenter and 2,300 sq. mm/indenter.
10. The method according to claim 2, wherein the value of KPI.sub.3 is between 250 sq. mm/indenter and 2,600 sq. mm/indenter.
11. The method according to claim 2, wherein the value of KPI.sub.3 is between 300 sq. mm/indenter and 2,900 sq. mm/indenter.
12. The method according to claim 2, wherein the value of KPI.sub.3 is between 400 sq. mm/indenter and 3,400 sq. mm/indenter.
13. The method according to claim 2, wherein the value of KPI.sub.3 is between 800 sq. mm/indenter and 4,000 sq. mm/indenter.
14. The method according to claim 2, wherein the value of KPI.sub.3 is between 1,000 sq. mm/indenter and 5,000 sq. mm/indenter.
15. The method according to claim 1, comprising using the drill bit in a hydraulic down-the-hole hammer.
Description
DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
(5)
(6)
DETAILED DESCRIPTION
(7) Many design options are available when designing a given drill bit. Parameters include the total area of the bit face, the number of indenters, the size of the indenters and the spacing between indenters relative to adjacent indenters. Altering each of these parameters will affect the functionality of the drill bit and will have an effect on the drilling efficiency of the bit. In studying these parameters and their effects, a number of Key Performance Indicators, or KPIs, between the bit features have been established which allow for the performance of drill bits to be investigated for improved performance over known bits. Drill bits are fabricated based on the optimum KPI values.
(8) KPI Values
(9) For any given rock type, and indenter loading, there is an optimum indenter spacing which provides for the greatest volume of chips to be removed or liberated during drilling due to coalescence of cracks. The area around each indenter is a measure of its ‘average’ spacing from the surrounding indenters. It follows that for a two-dimensional case there is also an optimum area around each indenter for maximum chip volume removal. It is also well known that a smaller diameter and/or sharper indenter will create chips more efficiently than one that is larger and/or more blunt. This suggests that a drill bit, with a fixed amount of input work available, can drill faster (i.e. liberate more chips), if the indenters are small in diameter and optimally spaced. Thus, multiple small indenters would appear to provide an optimum solution. However, there are also some other practical issues to consider in design of the drill bit with a large number of small diameter indenters; for example, as the indenter diameter decreases, the wear rate (of the indenters) increases. Also, the more indenters that are used, the lower the average input work available to each indenter.
(10) Considering all of the above relevant factors, three important Key Performance Indicators (KPIs) can be created which can be applied to drill bits of all sizes: 1. KPI.sub.1—Ratio of total indenter area to bit face area (expressed as a percentage)
(11) This provides a measure of the proportion of the bit face which is taken up with indenters, and, with that, an indication of the drill bit's wear resistance. i.e. [Total indenter area/Bit face area]. 2. KPI.sub.2—Ratio of (average) individual indenter area to bit face area (expressed as a percentage).
(12) Specifically, this is defined by [Total area of the indenters/Number of indenters]/Bit Face Area. This provides a measure of the average size of each indenter relative to the size of the bit (i.e. how ‘sharp’ are the indenters, on average, relative to the bit size). 3. KPI.sub.3—Bit face area per indenter
(13) This is defined by [Bit face area/Total number of indenters]. This provides a measure of the average area surrounding each indenter. This is not a ratio, but rather an absolute (average) area per indenter in mm.sup.2. This provides a ‘scale’ factor for the drill bit where it can be matched to the output of the impact mechanism it is fitted to.
(14) For the range of percussion mechanisms available it has been shown that drill bits can drill considerably faster if KPI.sub.2 and KPI.sub.3 are kept below a certain calculated value.
(15) It has also been shown that wear life of drill bits can be improved if KPI.sub.1 is kept above a certain calculated value.
EXAMPLE
(16) As an example,
(17) Calculating the area values for these bits provides: 1. BIT 1—Total bit face area: 21.382 mm.sup.2, total indenter area: 3.801 mm.sup.2, average indenter area: 95 mm.sup.2 2. BIT 2—Total bit face area: 21.382 mm.sup.2, total indenter area: 4.964 mm.sup.2, average indenter area: 236 mm.sup.2 3. BIT 3—Total bit face area: 21.382 mm.sup.2, total indenter area: 5416 mm.sup.2, average indenter area: 95 mm.sup.2
(18) Calculating the KPI's as above for each of these bits provides the following values.
(19) TABLE-US-00001 TABLE 1 KPI.sub.1 KPI.sub.2 KPI.sub.3 BIT 1 17.7% 0.44%, 534 mm.sup.2 BIT 2 23.2% 1.1%, 1,018 mm.sup.2 BIT 3 25.3% 0.44% 375 mm.sup.2
(20) Thus, on the basis of the above calculated KPIs it can be expected that in most rock types BIT 1 will drill faster than BIT 2 as BIT 1 has a lower KPI.sub.2 and KPI.sub.3 value. However, BIT 2 will have a better lifespan (i.e. less indenter wear) as BIT 2 has a comparatively higher KPI.sub.1 value. However, for BIT.sub.3 all three KPI's show an improvement over BIT 2.
(21) Thus, this indicates that a higher indenter count for a given bit face area compared to more conventional drill bits provides an improvement in each of KPI.sub.1, KPI.sub.2 and KPI.sub.3. Thus an optimum indenter count for a given bit face area may be derived which takes account of the disadvantages of a higher indenter count (i.e. lower average input work available to each indenter) while still providing for an improved drill bit performance.
(22) On this basis, KPI values are calculated for a number of drill bits based on a number of parameters; namely bit size (mm), number of indenters, bit area (sq mm) and total indenter area. These results are then compared to a conventional prior art drill bit.
(23) TABLE-US-00002 TABLE 2 Prior Art Bit Trial Bit 1 Trial Bit 2 Trial Bit 3 Bit size (mm) 165 165 165 165 Number of 20 30 40 55 indenters Bit area (sq mm) 21383 21383 21383 21383 Total indenter 5671 3800 3801 5227 area (sq mm) KPI 1: total 27% 18% 18% 24% indenter area/bit area KPI 2: (average 1.33% 0.59% 0.44% 0.44% area/indenter)/bit area.sup.2 KPI 3: bit area/no 1069 713 535 389 of indenters (sq mm ea)
(24) Thus, it can be seen when comparing Trial bit 1 and Trial bit 2 to the Prior Art bit that increasing the number of indenters leads to a corresponding increase in drilling performance, as KPI.sub.2 and KPI.sub.3 of Trial bits 1 and 2 are lower compared to the prior art bit. However, Trial bits 1 and 2 display increased wear as the KPI.sub.1 value for Trial bits 1 and 2 is lower than the prior art bit.
(25) If, however, Trial bit 3 is compared to the Prior Art bit, it can be seen that not only is improved drilling performance displayed (i.e. as evidenced by the lower KPI.sub.2 and .sub.3 values), but also Trial bit 3 shows comparable wear performance to that of the prior art bit.
(26) In effect increasing the number of indenters significantly (i.e. 55 indenters on Trial bit 3 compared to 20 indenters on the Prior Art bit) provides improved drilling performance without any significant decrease in wear performance. Typically, industrial bit design is normally a ‘trade off’ between drilling speed and bit wear life. The present invention however provides for enhanced drilling speed while also providing no significant decrease in wear life.
(27) Furthermore, it can be seen that calculating the KPI values in this manner provides information which can be used to select the most suitable drill bit for a given drilling task.
(28) For example, if faster drilling is required, a bit with a lower value of KPI.sub.2 and KPI.sub.3 may be selected and fabricated. Alternatively, if longer wear is the primary design requirement, a bit with a higher value of KPI.sub.1 may be selected and fabricated. Furthermore, the calculation of KPIs in this manner allows a drill bit with optimum KPI 1, 2 and 3 to be fabricated which provides both improved drilling and an optimised lifespan.
(29) Thus, calculating optimum KPI values provides that an equation may be derived defining a relationship between KPI values for optimum drilling performance. It has thus been calculated that a drill bit comprising a plurality of indenters about a bit face provides optimum performance wherein the ratio of the total indenter area to the bit face area, KPI.sub.1 and the ratio of the average individual indenter area to the bit face area, KPI.sub.2, (both expressed as a percentage) are related such that:
KPI.sub.2>=1.353×10.sup.−6(KPI.sub.1).sup.5−1.527×10.sup.−4(KPI.sub.1).sup.4+6.586×10.sup.−3(KPI.sub.1).sup.3−1.301×10.sup.−1(KPI.sub.1).sup.2+1.185(KPI.sub.1)−3.960 (Equation 1)
(30) As such, drill bits with KPI.sub.2 values falling on or below a curve defined by Equation 1 display enhanced performance compared to drill bits with KPI.sub.2 falling above the curve.
(31) Furthermore, drill bits with values defined as per Equation 1 may be produced with a range of KPI.sub.3 values scaled as appropriate for the impact mechanism to which the bit is fitted. Impact mechanisms are commonly manufactured in discrete sizes, correlating to the impact work they can deliver per blow, which is a function of the impact piston's mass. This is particularly the case with down-the-hole impact mechanisms, where the maximum diameter of the impact piston is constrained by the hole size being drilled. Manufacturers have generally standardised on a range of mechanism sizes, designated by the hole sizes (in inches) they are primarily designed to drill. Sizes 3″ (76.2 mm), 3.5″ (88.9 mm), 4″ (101.6 mm), 4.5″ (114.3 mm), 5″ (127 mm), 5.5″ (139.7 mm), 6″ (152.4 mm), 6.5″ (165.1 mm), 8″ (203.2 mm), 12″ (304.8 mm), 18″ (457.2 mm), 24″ (609.4 mm) are commonly produced. These down-the-hole impact mechanisms (known as down-the-hole hammers) deliver applied work per blow which increases with the designated size. It follows that the optimum KPI.sub.3 value for the drill bits used with these hammers will increase with the hammer size. So, for example, a drill bit manufactured for use in, say, a 6″ down-the-hole hammer, would have a smaller optimum KPI.sub.3 value when compared to a drill bit manufactured for use in a 6.5″ hammer, when drilling the same rock type.
(32) Provided the relationship between KPI.sub.2 and KPI.sub.1 is as described by Equation 1, bit performance and wear life will be improved over prior art designs. However, the performance of a drill bit in a particular rock type, used in a particular impact mechanism size is further enhanced when the KPI.sub.3 value is at an appropriate level.
(33) For a 3″ hammer, KPI.sub.3 may have a value between about 90 sq. mm/indenter and 250 sq. mm/indenter. For a 3.5″ hammer, KPI.sub.3 may have a value between about 120 sq. mm/indenter and 500 sq. mm/indenter. For a 4″ hammer, KPI.sub.3 may have a value between about 130 sq. mm/indenter and 1100 sq. mm/indenter. For a 4.5″ hammer, KPI.sub.3 may have a value between about 140 sq. mm/indenter and 1400 sq. mm/indenter. For a 5″ hammer, KPI.sub.3 may have a value between about 160 sq. mm/indenter and 1700 sq. mm/indenter. For a 5.5″ hammer, KPI.sub.3 may have a value between about 180 sq. mm/indenter and 2000 sq. mm/indenter. For a 6″ hammer, KPI.sub.3 may have a value between about 200 sq. mm/indenter and 2300 sq. mm/indenter. For a 6.5″ hammer, KPI.sub.3 may have a value between about 250 sq. mm/indenter and 2600 sq. mm/indenter. For an 8″ hammer, KPI.sub.3 may have a value between about 300 sq. mm/indenter and 2900 sq. mm/indenter. For a 12″ hammer, KPI.sub.3 may have a value between about 400 sq. mm/indenter and 3400 sq. mm/indenter. For an 18″ hammer, KPI.sub.3 may have a value between about 800 sq. mm/indenter and 4000 sq. mm/indenter. For a 24″ hammer, KPI.sub.3 may have a value between about 1000 sq. mm/indenter and 5000 sq. mm/indenter.
(34) Furthermore, a method of fabricating a multi-indenter drill bit is provided comprising the steps of defining a drill bit face area, defining a number of drill bit indenters and defining the size of the drill bit indenters; such that the relationship between KPI.sub.1 and KPI.sub.2 is defined by equation 1.
(35) Drill bits as described may be used with a variety of hammer types such a down-the-hole (DTH) hammers and hydraulic down-the-hole hammers.
(36) The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
(37) It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
REFERENCES
(38) [1]. Miller et al. Int. Journ. Rock Mech. Min. Sci. Vol. 5, pp. 375-398.
(39) [2]. Moon et al. Rock Mech Rock Eng (2012) 45:837-849, DOI 10.1007/s00603-011-0180-3