| China is a developing country with a large number of populations and relative shortage of resources which have become a major bottleneck that constrains the economic development of our country. In order to implement State Council's decision on strengthening geological work, many drilling of deep hard rock must be carried out. During deep-hole drilling of hard rock about 70% of the time is spent on drilling and pulling out bit from the hole. So the quality accident of a drill bit will cause serious damage in the drilling process. Cost of deep-hole exploration drilling is normally more expensive.The damage of drill bit causes great economic losses itself. Putting down and pulling out the dill bit is a waste of a lot of manpower and material resources. Finding the accident and finding a suitable drill bit to replace the damaged drill bit will take a lot of time. These factors have led to delays in schedules that delay the completion of production plans. It can be seen that quality of drill bit is very important during drilling. We must develop high efficient and long life drill bits which can achieve high speed and efficiency.Impregnated diamond drill bits are mostly used in hard rock drilling in China, and the technology is relatively mature with little room for improvement. While PDC (Polycrystalline Diamond Compact) drill drilling efficiency is several times higher than the traditional diamond drill bit when drilling the soft-medium hard rock. But the PDC coring bits of current level are not suitable for drilling hard rock and very hard rock. When drilling these formations, the drill bit gets collapse teeth easily, wears fast, and drills with slow speed. So using PDC bit in these formations is uneconomical from efficiency and economic factors. We must develop the PDC coring bits technology exteriorly if we want to achieve that kind of drilling results in hard rock such as in soft-medium hard rock. The purpose of this research project is to study matrix PDC Coring Bits based on hard rock drilling that hopes to enhance its ability for drilling hard rock and obtain a better drilling effect.For the purpose of drilling hard rock and based on previous studies, laboratory equipment, Pro/engineering and AutoCAD mapping software, Ansys software are used to study the physical and mechanical properties of hard rock, simulate and analyze the breaking capacity of bit structure on rock, study the material requirements surrounding hard rock, enforce a bit of the manufacturing process and micro-drilling tests, design a field drill bit and discuss its working status and stress.The first chapter summarizes the research status and trends for the PDC bit at home and abroad, including four areas as the rock drillability, drill design, manufacture and working status of drill bit.The second chapter is about Drillability research of hard rocks. Drillability of rocks it's ability to resist breaking during drilling, which indicates the ease of crushing rock. The purpose of study is to determine whether it is hard rock which can provide physical and mechanical parameters of rock samples for the design of drill bit.Eight kinds of hard rock samples are selected for testing in order to understand their physical components, structure, and their names by slice analysis. Moh's hardness that is calculated through rock mineral composition respective is as a basis for a preliminary understanding of the extent of soft and hard rock.Drillability level of rock is determined by the main indicators of the joint rocks combined with the ball hardness and ductility coefficient, the PDC Rock DRILLABILITY tables of rocks which was issued by the Ministry of Geology of DRILLABILITY in 1984. Then, the extent of soft and hard rock is determined according to Drillability level, and these rocks are identified by a comprehensive mechanical indicator. The rock uniaxial compressive strength is used to verify the composite indicator of classification. We can see the method that indentates hardness as the main indicators, putting the ball joint rock hardness and ductility coefficient integrated to determine drillability level is reliable coMParing with the results from the compressive strength of rock lithology and comprehensive analysis of indicators. Rock samples of numberl,8 are hardest followed by 4,5,7, and 2,3,6 the softest.The third chapter is about theory research on design of matrix PDC coring bit. The conventional PDC coring bit is only applicable to soft-medium hard rock. We must consider the actual working state of drill bit during drilling if we want to use it for hard rock drilling. Combination of hard rock's physical and mechanical properties, using experimental and finite element analysis and theoretical analysis and other methods we design the matrix PDC coring bit. The main design contents include the lip surface, cutting tooth, matrix materials, and waterway system.Difficult points of bit lip lies in increasing free cutting face and particularity of drilling hard rock. PDC wears fast when drill bit is used to drill hard rock. Bit lip can acquire more free cutting face by adopt step lip or double-loop bit lip. Exposed height of PDC should be on a plane to avoid stress concentration that is shared on PDC because of the large bit pressure of drilling hard rock.Research contents around drilling hard rock to study the cutting teeths include selection of suitable PDC, PDC arrangement, caster angle and bypass angle of PDC, and the exposed height of PDC in order that all aspects of cutting teeths can meet the good effects of breaking rock. It's found that the wear resistance of PDC is strong; short-term wear and tear of grinding on the PDC is negligible. PDC is structured suitable for cutting rock by cutting test.Right typical categories of coring bit are sharpening and self-sharp-style-type drill bits among which needle-like bit, dig and drill bit, row-like bit show strong capacity when drilling hard rock. Bit with row-like structure is more appropriate in hard rock drilling regarding PDC as special carbide to design drill bits. Law of force of the rock in the process that PDC with different angle and height of the drill bit cuts the rock is acquired by drawing model of drill bit and rock with Pro/engineering software and importing the model into the ANSYS software for stress analysis coMParison. Observing stress distribution maps and coMParing Mises stress generate from change of caster angle, the locations of the maximum stress of the rock are basically the same, indicating rock damage is most likely to start here during process of breaking rock except the model of 1537540; the maximum stress of rock increases at first, and then becomes smaller. From the point of the maximum stress of the rock, it's more reasonable for PDC bit to select 15.1°as caster angle. Observing stress distribution maps and coMParing Mises stress generate from bypass angles the locations of the maximum stress of the rock are basically the same which indicate rock damage is most likely to start here during process of breaking rock except model of 1537240; the maximum stress of rock increases along with bypass angle except the model of 1537540, subjecting to maximum stress of the rock with the bypass angle increases. Cconsidering the point of the maximum stress of rock, the bigger PDC's bypass angle is the larger the stress of breaking rock of the bit is. Observing stress distribution maps and coMParing Mises stress generates from exposed height of PDC, the rock by the position change of the maximum stress is relatively large; remove model 1537537, the maximum stress of rocks increases at first, and then decreases. The exposed height of 4.0mm is a sub-interface. Considering from the point of maximum stress of rock, PDC's exposed height of 4.0mm is a more appropriate choice.About matrix material design, analyzing test result, from different formulations, we can see the average hardness of the histogram increases with the increasing of WC content. The hardness and density matrix express upward trend when content of Cu-Sn alloy reduce; with content of WC increasing and content of Cu-Sn alloy decreasing, iMPact resistance and flexural toughness strength of matrix express downward trend from the average bending strength of different formulations and different histograms formula, and the average iMPact toughness of the histogram.About design of waterway system of bit, design of discharge area expresses in design of areas mainly. The paper discusses the relationship between the PDC number, PDC in size, the support size of after each piece part of PDC, the volume of PDC in the matrix, the depth of PDC cutting into the rocks and discharge area, and points out that layouts of cutting teeth on the lips of bit should be conducive to exclude debris. Because bit is used in hard rock drilling, full flush-type outlet, also known as plum-type outlet is used taking into account the first outlet layout of pregnant diamond that drills hard rock.This outlet is characterized by forcing the washing fluid flow out along the edge of the PDC, and form flow between the gap of the matrix and the hole at the end of the formation of rock which can fully cool PDC and remove debris. Gap on the inner and outer ring, inner and outer ring gap of drill bit should be designed to ensure the realization of the function of drill fluid.The fourth chapter is about pilot study of micro-drill. There are three aims to carry out micro-drilling tests on the drill bit, first, to be familiar with manufacturing processes of drill-bit, and second, to study the arrangement of PDC by using micro-drill bit in hard rock drilling, and finally to understand the requirements of hard-rock drilling on the drill bit further according to the status of micro-drilling processes.Three small bits are designed. Each bit has 6 PDC per one, caster angle is 15.1°, by-pass angle is 7.5°, the exposed height is 4mm which remain unchanged, thickness of he bit lip surface and the arrangement of PDC on the bit lip surface is changed, and single-loop and double-loop layout are used respectively.Preparations of the construction material of drill bit include designing and manufacturing mold at first. Two aspects must be taken into account:one is whether the graphite mold can bear the sintering pressure which the powder needed during the sintering process to form bit. That is to say the mold won't be crushed because of low endurance in the range of sintering pressure; the second is whether the temperature of large-diameter drill graphite mold can drill up to the required sintering temperature that the formula needs during sintering process.Bit body as a support body of PDC delivers axial force and torque to each cutting tools, and suffers a reaction and the micro-containing counter-effect during breaking rocks, but also lies in the environment of a long time in the debris, rock powder flow and pore-wall friction, therefore, we must choose appropriate steel body.45# steel is used as bit body in micro-drill pilot. Because it is micro-drilling tests indoor, and the total footage of bit is short, requirement to performance of matrix is lower than that in the wild-drilling. Matrix formulation of 1#-1 is chosen.How much of the powder is calculated according to three-dimensional maps of drill bit and matrix formula. Powder is loaded and the installation path layer are inserted after powder is mixed and graphite mold is fabricated, and then a good bit processing steel body, and then hot-pressing sintering method is selected to sinter the bit with SM-100E medium-frequency induction sintering equipment.In order to welding PDC firmly, there are several difficulties, firstly, it is how to ensure solderability liquid filling the gap between the matrix and the PDC to form a large welding surface since about half of the height of the PDC into the matrix. There is no question about the traditional drill because the depth of alloy into the matrix is very small, or the alloy forms the bit with the matrix directly at once. So this is a new problem; secondly, it is how to avoid burning PDC during the welding process. Welding temperature should never exceed 750℃since conventional thermal stability of PDC of industrial production is around 750℃, and now conventional approach is to control the temperature of molten solder. In this paper silver melting flux is used to maintain the low temperature with medium frequency induction heating power supply ring; lastly, it is how to reduce oxidation to PDC during the welding process. The current methods are in vacuum welding, welding and other means of hydrogen environment commonly.There are certain conclusions through the micro-drilling tests:specific energy of single ring bits is far less than the double-loop bit which are designed to drill hard rock; comparing with single-ring drill bit under same WOB and speed, double-loop bit receives larger stress of rock, resistance passed to the drill pipe is also lager, require higher strength of the joint of bit, and low-intensity drill pipe and joints are damaged easily; according to the concept of the effective rock heart rateζ,ζbigger the better drill bits in the drilling process of same parameters, cutting teeth and the number under the same conditions; suitable drilling pressure and torque are needed to so that the bit can break rock smoothly and efficiently with small reaction force; hard rock expresses brittle, and become rock powder when PDC cut through it in the absence of confining pressure circumstances.Chapter V is research about the field drill bit. According to research results in the preceding chapters, field matrix PDC coring bits is designed, and refer to a hard-rock, the paper discusses the relationship between WOB, surface force of PDC and the largest force of the whole bit and the thread subject which provide reference for imposing appropriate drilling pressure and speed.Compared with micro-drilling bit drill diameter of field bit should be lager in order to meeting the needs of a larger core diameter. Specifications of the selected drill bit isφ94/70 which used PDC ofφ10, labial surface of flat-bottomed shape, caster angle 15.1°, and 5mm as the exposed height of PDC according to the aforementioned results. We select 7.5°as the size of the bypass angle by analyzing favorable factors and unfavorable factors of bypass angle combining with some achievements of the predecessors. Nine PDC are fixed up on the lip surface totally. Single-loop arrangement of bit is selected according to the conclusions of micro-drilling tests that the biggerζis the better is the bit, so that the thickness of lip surface is thinnest.It's found that PDC breaks rock mainly by compressive-shear affect through theoretical analysis that the cutting tooths break hard rock. Finally Ansys software is used to analyze mechanical force of bit mainly by changing the WOB and surface force of PDC to obtain the greatest stress and the stress of the bit and change of force on the thread. By observing nephograms of Mises stress on the selected boundary rate of change, the maximum Mises stress of the whole bit and internal thread receive a tremendous influence of surface force of PDC which is basically the same in the rate of change but less affected by the drilling pressure.In summary, based on hard rock drilling tests, this paper makes some achievements on matrix PDC Coring Bits research by a large number of tests, theoretical analysis and analysis with Ansys software.
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