(2) Carcass performance test
1 drill bit performance test is mainly the test of wear resistance and erosion resistance, which is the most important performance to ensure that the bit body is adapted to the stratum. The performance index of the carcass wear resistance is the relative wear rate (wear ratio). The index of erosion resistance is the erosion resistance index. These two indicators reflect the performance of the carcass more accurately than the carcass hardness. This is also the main performance indicator for the new carcass formula test institute to strive to improve.
2 Physical and mechanical properties test of carcass materials, including material linear expansion coefficient, flexural strength, impact toughness and shear strength.
(3) Measures to improve the performance of the carcass
1 The hardness of the bit body can be adjusted by the tap density of the skeleton powder. The higher the tap density, the higher the hardness of the carcass. The use of skeleton powders of different ratios and particle sizes is an effective method for improving the density of the drill bit.
2 The control of powder quality has a significant effect on tap density and sintering strength.
3 Strengthen the bit body to improve the performance of the carcass. Performance can be improved by strengthening and selecting the carcass and improving the impregnated alloy formulation. The strengthening of the bit matrix can be achieved by adding a small amount of trace elements (nickel Ni, cobalt Co, titanium Ti) which contribute to the dispersion strengthening and contribute to the wetting property of the carcass skeleton powder in the carcass powder.
4. Research on solid tooth technology The research of solid tooth technology is mainly to study the brazing process of polycrystalline diamond composite sheet, which is the key technology for manufacturing PDC bit. The bit body is a sintered body of cast tungsten carbide powder as a skeleton and an impregnated alloy. The composite sheet is a composite superhard material synthesized by a hard alloy substrate and a polycrystalline diamond thin layer under high temperature and high pressure, and the solid tooth technology can solve the two types. Composite brazing joint problem.
The most important form of PDC drill bit failure in the field to remove normal wear is the shedding, delamination and fracture of the composite sheet. The main reason for this phenomenon is the poor quality of brazing. At present, the most widely used drill bit manufacturers at home and abroad are direct brazing, using common silver-based brazing filler metal and general-purpose silver-based flux, supplemented by some composite sheet surface treatment technologies (such as sand blasting and pickling). Some also use special surface treatment techniques (coating or plating metal, etc.). Because the general brazing material does not ideally impregnate the composite sheet and the carcass, the brazing temperature is too high, and the thermal stability temperature limit of the composite sheet is 700 ° C, which leads to the performance degradation of the composite sheet and the delamination of the diamond layer, and the brazing Insufficient weld weld strength.
The exploration of the PDC brazing process is as follows.
(1) The surface modification work of the composite sheet improves the wettability of the composite sheet and the solder. According to the practice of brazing work for many years, in order to ensure the stability of the brazing quality in mass production, it is necessary to improve the wettability of the surface of the welded part, and secondly, it is necessary to improve the weld strength. Cemented carbides are easily infiltrated with the brazing filler metal during brazing at temperatures above 850 °C. However, for the brazing composite sheet, the brazing temperature must be stably controlled below 700 ° C, which is a difficult technical problem. The surface of cemented carbide and diamond is modified by electroplating, electroless plating, molten salt plating, immersion plating, vacuum deposition, vacuum sputtering and ion implantation. A method of ionic melt metallurgy coating has been developed in China for modification. After the activation treatment, the welding performance is obviously improved, the brazing temperature is lowered, the technical grade requirement for the worker is lowered, and the brazing quality is stably ensured. However, there is a problem that the wear ratio decreases after the composite sheet is processed, and further research is needed.
(2) Research on special flux and brazing filler metal A special flux and brazing filler metal suitable for brazing PDC bit ensure that the brazing temperature does not exceed 700 ° C, and has good wetting properties and sufficient weld strength.
(3) Application research of new brazing process At present, the brazing composite sheet generally adopts the method of manual flame brazing. Whether other more scientific and reliable methods can be adopted is also one of the topics that the bit manufacturing industry should explore. The possibility of vacuum diffusion brazing, electric resistance welding, high frequency induction heating brazing, laser brazing, plasma brazing, ultrasonic welding and the like applied to the brazing of composite sheets should be studied.
(4) Research on brazing temperature control method Brazing temperature control method is also an important part of research, so that the brazing process of the composite sheet is always controlled within a reasonable temperature line, the brazing quality is ensured, and the composite sheet is maintained. Performance is not compromised during brazing. Under the premise of ensuring the strength of the brazed weld, the performance of the composite sheet during the brazing process is not reduced or reduced, which is of great significance for improving the performance and life of the PDC bit.
The development of PDC drill bit, the first is the research of PDC bit design theory by Shenren, the development of special design analysis software, the development of solid simulation and working state simulation technology to make the design level up; the second is to strengthen the research work of bit foundation theory and manufacturing process technology. . Due to the incomplete research methods and insufficient research work, most of China's bit industry is in the stage of simple imitation and simple play. PDC drill bit is a multi-disciplinary edge technology involving geology, drilling, superhard materials, powder metallurgy, machinery and welding. Therefore, the manufacturer should carry out research and manufacturing departments and drilling geology departments of research institutes. Joint, breaking foreign monopoly, and establishing a scientific PDC bit design and manufacturing system, which has important practical significance and obvious economic benefits for improving the level and market competitiveness of domestic PDC bits.
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