(1) Hot-pressing right-angled trapezoidal teeth with diamond bit.
1. bit structure design
The cutting unit of this drill is a right-angled trapezoidal tooth. Compared with isosceles trapezoid, the cross-sectional area of right-angled trapezoid teeth is smaller, which can improve the drilling specific pressure under the same WOB. Right-angled trapezoidal teeth can be divided into two parts: cuboid and triangle. Cuboid is the main part of broken rock, and triangle supports cuboid and participates in broken rock, which improves the bending strength of pick. The right-angle trapezoidal drill bit is shown in Figure 6-24. This type of drilling rig has obtained the national utility model patent (patent number ZL20 1320 108265.4).
Figure 6-24 Shape of Right Angle Trapezoidal Tooth Bit
Force analysis of (1) right-angled trapezoidal tooth
Assume that the right-angle side height of the right-angle trapezoidal tooth is H, the width of the top of the trapezoid is L, and the oblique angle of the trapezoid is α, which is influenced by the vertical WOB P and the rotating force W (Figure 6-25). In order to facilitate the calculation and analysis, the vibration, bending and other alternating stresses of the right-angle trapezoidal tooth bit at the bottom of the hole are ignored.
Figure 6-25 Schematic Diagram of Force Analysis of Right Angle Trapezoidal Tooth
As shown in Figure 6-26, the right-angled trapezoidal ABCD assumes that the end face of B bears uniform axial pressure, and its resultant force P acts in a symmetrical position. When drilling, the drill tooth can be regarded as a cantilever beam with a fixed root at the left end and a free right end. Under the combined action of rotating torque and WOB, the cantilever beam bears axial compression and bending. According to the mechanical analysis of materials, the dangerous section of the beam when it is deformed is the fixed end A section.
Figure 6-26 Force Analysis of Plane Right-angle Trapezoidal Teeth
Generally, the α angle of drilling teeth is large, so the neutral axis of bending deformation on the left section of variable cross-section beam can be approximately considered to be symmetrical up and down in section, that is, y = h1/2; The internal force on the cross section is:
Axial force (pressure) N = P；; Shear force (bending) Q = F；;
Bending moment (bending) m = p e-f (l-x) x = 0 = p e-f l.
If the influence of shear force Q on material strength is ignored, the normal stress of each point on this section is:
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Where: a = b h1= b (h+l/tan α);
e = h 1/2-h/2 =(h 1-h)/2 =(h+l/tanα-h)/2 = l/2 tanα；
iz = b/ 12；
H2 = l/tanα；
h 1=h+h2=h+l/tanα.
Figure 6-27 Cross-section of drill tooth A end
Assume that the cross section of end A is rectangular (Figure 6-27), and the normal stress of each point on the cross section of end A is:
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The maximum tensile stress on the cross section is located at every point of the upper edge line, and the maximum compressive stress is located at every point of the lower edge line. The absolute values of the two are equal. Then:
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Substituting h 1 for simplification, we get:
Deep core drilling technology and management
Deep core drilling technology and management
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Using the derived formula (6-5), combined with the specifications, structure, matrix mechanical properties and physical and mechanical properties of the drilled rock, the tooth profile specifications of the right-angle trapezoidal tooth bit can be designed.
(2) The structural design and analysis of right-angle trapezoidal teeth.
Considering that the compressive strength of bit matrix is generally very high, far exceeding the axial stress caused by WOB, that is, the compressive strength of trapezoidal cutting teeth can meet the drilling requirements, so the axial pressure of trapezoidal cutting teeth is not analyzed too much. Let the dimensions of right-angle trapezoidal teeth be: trapezoidal top width h, trapezoidal tooth thickness b, trapezoidal bottom angle α and right-angle trapezoidal height L. Take a hot-pressed diamond bit with a specification of φ77/48mm as an example, and b = (77-48)/2 = 14.5mm..l is determined by the working height and the water gap. If the working height is10mm and the water gap is 3mm, then L is13mm ... The only remaining variables are the α angle and the width h of the trapezoid top. Equation (6-3) can be written as:
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Substitute the above data into Equation (6-6) to obtain:
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The width h at the top of the trapezoid determines the initial contact area between the drill bit and the rock. For rocks with drillability grade ⅶ ~ ⅶ, the value of H is between 8 ~12 mm. Taking rock drillability grade VIII h= 10mm as an example, Equation (6-7) can be written as follows:
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The trapezoid bottom angle α can be selected between 55 and 70 according to the mechanical properties of the rock and the specifications of the drill bit. When the value of H is constant, the smaller α is, the greater the bending capacity of right-angled trapezoidal teeth is, but it is limited by the bit nozzle. Therefore, when designing a right-angle trapezoidal tooth bit, the stress σ of the trapezoidal tooth can be obtained as long as the magnitude of F force and α angle are known, and the trapezoidal tooth is safe as long as the actual bending strength of the trapezoidal tooth is greater than σ. Among them, F force mainly depends on the shear strength of rock and the friction between teeth and the bottom of hole. Usually, a trial-and-error algorithm is used to determine the α angle.
For example, when drilling a φ77/48mm drill bit of Grade VIII granite, taking α = 60 for trial calculation, it is known that the shear strength of the rock is about 3 15 MPa, and the stress borne by the trapezoidal teeth is about 553MPa, which is obviously lower than the minimum bending strength (700MPa) required by the bit matrix. Therefore, this design is safe.
2. Diamond parameter design of drill bit
1) The right-angled trapezoidal tooth consists of two parts: a rectangle m and a triangle n (Figure 6-28). Their carcass components and properties are the same, while the diamond concentration in the M part is higher and the diamond concentration in the N part is lower. At the initial stage of drilling, only BDFG plane is in contact with rocks, with small area and high specific pressure, and high drilling efficiency in hard and dense rocks. With the wear of the drill bit, the contact area will gradually increase and the ROP will decrease. However, due to the low wear resistance of N part, ROP has not been greatly reduced (in the range of 15% ~ 18%). At this time, the role of N part is to support M part of rock mass, increase its bending strength and impact toughness, and play an auxiliary role in rock breaking. Therefore, the design of this kind of drill mainly depends on the ratio of M to N and its performance according to the rock properties.
Figure 6-28 Schematic Diagram of Diamond Distribution
2) For hard, medium to strong abrasive rocks, the matrix properties of cuboid M and triangle N can be designed to be the same. For hard to hard and weakly abrasive rocks, the matrix of cuboid M should be hard and the diamond concentration should be high. The matrix of N part of triangle is soft and the diamond concentration is low.
3) By changing the ratio of cuboid M to triangle N and the size of α angle, the performance and drilling effect of the bit can be adjusted. The smaller the cuboid m is, the larger the α angle is, and the higher the drilling speed will be, and vice versa.
4) The adjustable structural parameters of this drill are: cuboid m, triangle n, α angle, diamond and matrix performance parameters. General bit nozzle 6 ~ 8mm；; The alpha angle is 75-65; Male: female = 3: 2 or 5: 3. The basic rules of diamond particle size, grade and concentration are the same as those of ordinary drills. For hard to hard and weakly abrasive rocks, the concentration of diamond-grade SMD35 in cubic M is 60% ~ 65%, the particle size of 40/50 mesh is 50% ~ 60%, and the particle size of 50/60 mesh is 40% ~ 50%. Triangle n diamond grade SMD 30 ~ SMD 35, the concentration is 45% ~ 50%; Particle size: 50/60 mesh accounts for 45% ~ 50%, and 40/50 mesh accounts for 50% ~ 55%. For hard, moderately strong abrasive rocks, the characteristics of these two parts are the same. The concentration of diamond-grade SMD30~SMD35 is 75% ~ 85%, and the particle size is 20% ~ 25% for 30/35 mesh, 50% ~ 60% for 40/50 mesh and 20% ~ 25% for 50/60 mesh.
5) The drilling specification parameters of this drill should be determined according to the hardness and abrasiveness of the rock. For rocks with medium hardness and poor integrity, WOB and rotation speed should be low to prevent cutting teeth from cutting into the rock too deeply and hindering drilling. However, for hard and dense formations, higher WOB and rotation speed can be used to obtain higher ROP.
(2) hot press impregnated broken polycrystalline diamond bit
Broken polycrystalline materials are inferior products in the process of polycrystalline synthesis, but they are also valuable because of their high hardness and high wear rate. Most of the fragments are cylinders with diameter-height ratio close to 1, which can be used to manufacture impregnated drill bits. It has good adaptability to medium hard to hard and medium abrasive rocks.
1. The principle of broken particles breaking rocks
Similar to the ordinary impregnated coarse-grained diamond drill bit, the broken particles are arranged in disorder in the matrix of impregnated drill bit. There may be three basic forms of broken particles randomly distributed near the cylinder in the hot pressing matrix: vertical, horizontal and at a certain angle with the bottom of the hole (Figure 6-29), and the mechanism and effect of breaking rocks are also different.
1) vertical crushing. The principle of vertically crushing aggregate particles to break rocks is basically the same as that of complete aggregate crystals. It cuts into the rock to a certain depth under the action of WOB P and shears and breaks the rock under the action of horizontal force Q [Figure 6-29(a)]. The bigger the WOB, the deeper the cutting, the bigger the shear body and the better the crushing effect.
Figure 6-29 Different forms of broken polycrystals in matrix and broken rocks.
2) The grains are aggregated at a certain angle. At the initial stage of drilling, the contact area between the broken aggregate particles with a certain angle and the rock is the smallest [Figure 6-29(b)], and it has certain sharp edges and corners, so it is easy to cut into the rock and the drilling efficiency is high. With the blunt tip angle of debris, the ROP gradually decreases, but the overall drilling efficiency is still high.
3) Particles are broken and aggregated in the recumbent state. The principle of horizontally placed broken particles breaking rocks is different from that of vertically placed broken particles breaking rocks. At the initial stage of drilling, the contact area between horizontally placed broken particles and rocks is much smaller than that of vertically placed broken particles [Figure 6-29(c)], and the drilling efficiency is high. With the passage of drilling time, the contact area between broken particles and rocks gradually increases, and the ROP decreases, but the overall drilling efficiency is still high. The broken particles lying horizontally are not easy to collapse, and the borehole is relatively stable. When the debris wears more than half, the contact area with the bottom of the hole will gradually decrease and the drilling speed will increase.
The rock-breaking mechanism and rock-breaking effect of the above three randomly distributed aggregate particles are different, which can complement each other and maintain a relatively stable and high drilling speed in relatively complete rocks (such as marble, limestone, basalt, sandstone, etc.). ) is lower than drillability grade VIII. It is suitable for a wider range of rock formations than a broken alloy bit. As long as the matrix performance design is reasonable, it can also be used to drill hard, brittle and broken abrasive rock layers.
2. Performance design of broken polycrystalline impregnated drill bit matrix.
The particle size of broken polycrystalline is coarser than that of diamond single crystal, but finer than that of broken alloy particles. Therefore, the performance of matrix is between ordinary diamond bit and broken alloy bit, with medium hardness and wear resistance. The hardness is designed as HRC 25 ~ HRC 30, and the wear resistance can be designed as (0.55 ~ 0.6) × 10-5. When tested by MPX-2000 friction and wear tester, the wear resistance can be designed as 420 mg ~ 450 mg.
Because of its high compressive strength and wear rate of 20,000 ~ 80,000, it can theoretically drill into any rock. However, due to its coarse particles, great resistance to cutting into the rock and obvious aging effect of breaking hard rock, the drilling rock grade is limited to some extent, and it is suitable for drilling rock strata below Grade VIII, with medium to strong abrasiveness and complete to relatively complete.
3. Design of parameters of broken polycrystalline.
According to the principle of diamond crushing rocks, coarse-grained diamonds are mostly used to drill soft and low abrasive rocks. Generally, the diameter of the broken polycrystalline bit is φ 1.5 ~ φ 2.5 mm and the height is 2 ~ 2.5 mm, that is, the diameter-height ratio is close to 1. This particle size is close to the particle size of natural diamond in surface inlaid bit. Because its hardness and wear rate are far less than that of natural diamond, only impregnated drill heads can be manufactured. The volume concentration of rocks with drillability of Grade VI and below is 20%, and that of rocks with drillability of Grade VI ~ VIII is 25%. Considering that it is difficult to ensure the uniform distribution of coarse-grained broken polycrystals in the matrix of the drill bit during random mixing, it is necessary to use a granulator as shown in Figure 6-30 to spray metal powder and binder while rotating, so that the broken polycrystals are wrapped by a thick metal film to achieve the purpose of uniform distribution of particles in the matrix.
Figure 6-30 granulator
4. Structural design of broken polycrystalline bit
In production practice, people hope that the new bit can be drilled effectively after drilling, but the traditional impregnated broken polycrystalline bit must have a grinding process before it can enter normal drilling. In order to change this situation, the broken polycrystalline bit can be designed as a combination of surface insert and impregnated insert, that is, the first layer is in the form of ordered surface insert, while the working layer behind it is in the form of disordered impregnated insert. According to this idea, the graphite mold is also designed as a common mold and a first-layer surface insert mold (as shown in Figure 6-3 1). The structure of coring broken polycrystalline diamond bit is shown in Figure 6-32.
Fig. 6-3 1 coring and crushing polycrystalline bit
Using the first layer mold
Figure 6-32 Structure Diagram of Core-type Broken Polycrystalline Bit
1 steel body; 2-bit matrix material; 3- with broken polycrystals; 4- The surface is inlaid with broken polycrystals; 5- single crystal diamond; 6— Gauge-retaining material for drill bit; 7-position nozzle
In the structure of hot crushing polycrystalline drill, SMD30 grade single crystal diamond with particle size of 30/40 mesh and concentration of 20% ~ 25% is embedded in addition to crushing polycrystalline main abrasive. This part of diamond not only participates in rock breaking, but also keeps the balance and wear of the working layer and improves the use effect of the drill bit. The impregnated broken polycrystalline bit has obtained the national utility model patent with the patent number ZL 201320109451.x.
(3) Alumina hollow ball hot pressing diamond bit.
Alumina hollow sphere is a pore-forming agent in powder metallurgy materials, which has low hardness and high brittleness and basically does not react with other matrix materials. Mixing it evenly with matrix material and diamond, and then putting it into a mold for hot pressing sintering (Figure 6-33) can improve the porosity of matrix material and weaken the wear resistance.
Figure 6-33 Schematic diagram of action mechanism of alumina hollow sphere
1- diamond; 2- alumina hollow sphere
Because the compressive strength of alumina hollow spheres is much lower than that of diamond, some crushed hollow spheres will form weak lattice during hot pressing. These weak lattices will easily fall off with the wear of the matrix, leaving many holes on the surface of the bottom lip, which will make it rough, improve the friction coefficient, accelerate the wear of the matrix and make the diamond cutting effect better. In addition, the contact surface with the bottom of the hole is reduced, which is beneficial to improve the drilling efficiency in hard and dense rocks. Alumina hollow ball hot pressing diamond bit has obtained the national utility model patent, patent number ZL20 122065 1088. X+0088.x。
Parameter design of 1. alumina hollow sphere
(1) Particle size of alumina hollow sphere
Alumina hollow spheres with different particle sizes in the market are shown in Figure 6-34 and Figure 6-35. The particle size of hollow spheres has obvious influence on the wear resistance and strength of weakened carcass. When the concentration is constant, the particle size of hollow spheres is small and the specific surface area is large, which shows that the dispersibility is good, and the cavities formed on the lip surface of the carcass are small and many, which will improve the effect of weakening the wear resistance of the carcass. But if the pore size is too small, the weakening effect on the carcass is not obvious. However, if the particle size is too large, the dispersibility will become worse, which is not conducive to weakening the carcass. Therefore, the particle size of hollow spheres should be 0.2 ~ 1.0 mm, which is equivalent to the diamond particle size of 70 ~ 20 mesh. The harder and denser the rock, the coarser the particle size of the hollow ball, the rougher the worn bottom lip surface and the more the wear resistance of the matrix decreases, which is beneficial to the cutting of working diamond and the improvement of drilling speed.
Figure 6-34 Coarse-grained alumina hollow spheres
Figure 6-35 Mixed Particle Size Alumina Hollow Spheres
(2) the concentration of alumina hollow spheres
The higher the concentration of hollow balls in the matrix, the higher the weakening degree of the matrix, but the higher the concentration, the lower the strength of the matrix and the normal use of the diamond drill. However, the low concentration of hollow spheres has little effect on weakening the wear resistance of the matrix. It is generally considered that the volume concentration of 12% ~ 18% is reasonable. The harder and denser the rock, the higher the content of hollow balls in the matrix, which makes the wear resistance of the matrix decrease obviously and the better the diamond cutting effect.
(3) Experimental study on parameters of alumina hollow spheres.
Alumina hollow spheres with particle sizes of 0.3mm, 0.6mm and 0.9mm and concentrations of 10%, 20% and 30% were selected for experimental design. Formula of carcass: FeCuNi accounts for 40%, FeCu30 accounts for 40%, and CUSN 10 accounts for 20%. According to the experimental design, the tire blocks were sintered separately and their wear resistance was tested. See Table 6-5 for the influence of carcass weakening. The histogram drawn according to the data in the table is shown in Figure 6-36.
Table 6-5 Weakening Test Design Table of Bit Matrix Wear Resistance
Figure 6-36 Relationship between Particle Size and Content of Alumina Hollow Spheres and Wear Resistance
Particle size: a-0.3mm; B-0.6 mm; C-0.9 mm
As can be seen from Figure 6-36, with the increase of alumina hollow sphere concentration, the wear amount of the matrix increases and the wear resistance shows a downward trend. No matter how the content changes, as long as the particle size of hollow spheres increases, the wear resistance of the matrix tends to improve. It can be seen that the concentration of alumina hollow spheres has a significant effect on the weakening of the matrix, and the particle size of hollow spheres is also an important factor affecting the performance of the matrix.
2. Design of diamond parameters of drill bit
Hot-pressed diamond bits containing alumina hollow spheres are mainly designed for hard and dense "sliding" rocks. It must be clear that even with high rotating speed, it is impossible to obtain high penetration rate in hard and dense rocks. Only by micro-pressure crushing the rock in a micro-volume way can a good crushing effect be achieved.
Particle size design of (1) diamond
In hard and dense rocks, coarse diamond bits are extremely difficult to self-sharpen, but the drilling efficiency is very low. Therefore, it is necessary to choose a finer diamond, but if it is too fine, the contact area between the diamond and the matrix is very small, and it will soon decrease with the wear of the matrix. So choose more 50/60 mesh and 60/70 mesh diamonds.
(2) Design of diamond concentration
It is generally believed that low diamond concentration should be used to drill hard and dense rocks, but how low the concentration is still needs to be studied. Although the pressure on each diamond with low concentration increases under the same WOB condition, it is easier to cut into the rock. However, if the concentration is too low, drilling efficiency and bit life will also decrease. Therefore, the diamond concentration should have an optimal value. When designing the concentration, the pore-forming effect of the added materials must also be considered. Because the porosity of matrix increases after pore-forming, the concentration of diamond should be reduced appropriately to ensure its inlay strength is not affected. In addition, the concentration and particle size of diamonds are interdependent. The finer the particle size of a diamond, the lower its concentration.
(3) Diamond design
Hard and dense rocks have high compressive hardness, so high-grade diamonds must be used. The compressive strength of a single diamond can not be lower than 300N, and the TTi value of a diamond can reach 85%.
To sum up, the diamond parameters are designed as follows: the particle size is 50/60 mesh to 60/70 mesh, of which 50/60 mesh accounts for 40% and 60/70 mesh accounts for 60%; The concentration is 60-70%; The diamond grade is not less than SMD35.