Study On Diamond Bit With Steel Bonded Carbide Type Of Matrix For Percussive-Rotary Drilling

Percussive-rotary drilling, a kind of advanced, high efficiency and low cost drilling technique, shows obvious advantages when drilling in hard formations, that has an excellent effects not only with respect to the improvement of drilling efficiency and core recovery percent but also the prevention of hole deviation and core blockage. Research on percussive-rotary drilling can be retraced to the late 1970s in China when it was popularized by geological department positively. At that time, the outlook that diamond bits could not be used for percussive-rotary drilling were hold by many researchers due to their limited recognition on diamond performances, ability of anti-impacting and anti-crushing as well as diamond bits because the application of diamond drilling technologies was still in its infancy. In recent years, investigations on impacters and percussive-rotary drilling technology centering on tungsten carbide bits have been implemented by geological and metallurgical departments etc. and a series of research results, such as different types of impacters with good qualities were obtained, which means percussive-rotary drilling technology has been considerably developed.Percussive-rotary drilling, wire line coring drilling and diamond drilling system have became indispensable to subsurface geological prospecting because of the development of modern drilling technologies. However, very few studies have been performed particularly on diamond bits used for percussive-rotary drilling for years such that there are neither corresponding research results nor patents were reported up to now, which restricts the superiority when percussive-rotary drilling are used for deep hole and hard formation. This paper aims to research into diamond bits used for percussive-rotary drilling in order to make contributions to percussive-rotary drilling technology.Design ideas and manufacturing technologies of traditional hot-pressed diamond bits were firstly depicted in this paper including shape of bit face, bit matrix compositions and matrix performances, bit waterway, diamond parameters and hot-pressing process. Analyses were also contained to find out the adaptive law between structural parameters of ordinary hot-pressed diamond bits and rock formations. Besides, comparative study was performed to find the difference between common rotary drilling and percussive-rotary drilling, which offers useful bases for trial-manufacture of diamond bit used for percussive-rotary drilling.Matrix compositions and their performances of diamond bit for percussive-rotary drilling were mainly studied in this paper. Characteristics of percussive-rotary drilling and requirements for diamond bit properties were elaborated. The effect of impact energy on diamond bits and drilling process were also analyzed combining correlative references in addition to the analyses of structural characteristics and matrix performances requirements of diamond bit for percussive-rotary drilling.Based on the analyses of performance and characters of steel bonded carbide, steel bonded carbide compositions were introduced to making hot-pressed diamond bit during matrix experiments. Primary experiments were performed and two basic phases of steel bonded carbide, namely hard phase and binding phase were studied intensively to achieve bit matrix formula of steel bonded carbide type.Research method for improvement of matrix performance was supplied and corresponding experiments were carried out. Compound skeleton material was used as hard phase of matrix, including tungsten carbide, titanium carbide and YG8, to improve matrix wear resistance as well as exposure of diamond grits. Draw lessons from high manganese steel with respect to its components and properties of binding phase in order to insure the proper overall mechanical performance. Copper-tin-rare earth pre-alloyed powder was used as the substitution for 663-Cu powder in order to improve matrix alloying extent and compact texture as well as reducing element segregation and components loss of alloy with low melting point. Silicon carbide fiber material was employed to improve matrix hardness, intensity and wear resistance.Basic and valuable research results on bit matrix for percussive-rotary drilling were obtained through a number of experiments, which lays a solid foundation for study and trial manufacture of bits used for percussive rotary drilling.Current research status about ordinary diamond bits were set forth in this paper, including more thorough expatiation that bit quality is not only closely associated with matrix formula but also well correlated to hot-pressing parameters. The influences of sintering parameters such as sintering temperature, pressure, heating-up speed, heat preservation time and outlet temperature on matrix alloying were analyzed, which indicates that the design of hot-pressing parameters is closely related to matrix composition and has substantial effect on matrix performance. These research processes can supply beneficial enlightenment for design of bit used in percussive-rotary drilling.Extreme vertices method of mixture regression was chosen to design bit matrix formula experiments after comparing with formula uniform design method. Mathematic analyses and tabling method were both used and compared to achieve consistent results. It can be seen that mixture regression method is an advanced and credible means to investigate the variation patterns between matrix components and matrix performances.Matrix composition of hard phase and that of binding phase in terms of mass percent were determined through experimental study. Regression analyses and nonlinear programming method were implemented to analyze the experimental results such that mathematic models between matrix hardness, wear resistance, anti-impact toughness and matrix components were obtained respectively. Significance test indicated that this research results are satisfying and reasonable.The ability of anti-dynamic impact loading of bit matrix under axial impact force was also taken into account particularly besides matrix anti-impact toughness to ensure enough ability of resisting impact force from impacter. Results showed that the anti-impact ability of matrix tested was completely sufficient and could guarantee normal percussive-rotary drilling.Wearing conditions of bits employed by China Continental Scientific Drilling project were analyzed in this paper, from which the conclusion was obtained that the structure of bit working lining must be considered to strengthen its anti-impact capability and gauge protection ability in addition to thinking about its other necessary performances for common rotary drilling. As a result, two types of diamond impregnated bit, CJ-A and CJ-B, were designed.To validate the rationality of the design technology and quality of bit, diamond bits for field tests were designed and trial-produced and field drilling were carried out in accordance with the geologic condition and property of rock formation of field drilling mining area. Property tests on rock samples from mining area contained indentation hardness using WYY-1 rock pression sclerometer, pendulum ball hardness and plasticity coefficients using WYQ-1 rock pendulum ball sclerometer. Rock drillability was rated gradeⅧ-Ⅸaccording to the tested rock mechanical properties. With regard to abrasiveness of rock sample, because most of its mineral particles were uniform and medium granularity through surface analyzing of rock samples as well as their mineral structure and crystallization, this kind of rock can be treated as medium to high abrasive rock formation.Matrix performance that adapts to certain rock formation was designed accordingly. Proper adjustment of matrix formula based on previous research was performed and final matrix formula and hot-pressing technology were determined as:42% hard phase,24% copper-tin-rare earth pre-alloyed powder,10% nickel and manganese,13% iron-phosphorus alloy,11% cobalt-molybdenum-titanium; sintering temperature was 980℃, pressure was 18MPa, heat preservation time was 7min and outlet temperature was 800℃.Bits produced with final formula were tested by field drilling in the mining area of eighth geological prospecting party, Fujian province. The result was that average penetration rate was 2.29m/h; average bit life was 63.82m. So this kind of bits has more obvious advantages than that made by the other two bit factories. The expected goal of design and experiments has been reached.