A Study On Hot-pressed Impregnated Diamond Drilling Bit In Designed Setting

It has been 40 years since the study on hot-pressed diamond bits had begun in the late 1960s in China. Widely employed in the fields of geological drilling, geological exploring, geotechnical drilling and construction,the hot pressing technology has long been the major methodology for the manufacturing of diamond bits which enjoy more flexibility in the adjustment of bit properties, stronger adaptability to different rocks, longer lifetime and higher working efficiency. However, with the traditional manufacturing technology, the distribution of diamonds in bit matrix is still uneven, which has greatly affected the bit's working efficiency. In recent years, the uniform distribution technology for diamond drilling bit, which has greatly improved the bit efficiency, has developed rapidly and come into the core of the study in this area.On the basis of the uniform distribution technology, this paper has conducted the research into the diamond positioning distribution technology in hot-pressed impregnated diamond drilling bit, by exploring the properties of hot-pressed impregnated diamond bit and studying the matrix formula, positioning arrangement of the bit, and the bit manufacturing process involved, so as to largely promote the quality of diamond bit. Since the diamond positioning distribution technology is a brand-new technique in promoting the quality of diamond, doing research in this field is of great significance in promoting the quality of diamond and the technological advancement in the related industries.This paper starts from the introduction of the domestic and foreign researches on the matrix formula, the positional parameters of diamond, and the structure of the hot-pressed impregnated diamond bit; it, then, proceeds to demonstrate the status quo of the uniform distribution technology and its application in manufacturing diamond tools at home and abroad; elaborating on the significance of studying the diamond positioning distribution technology, this paper adopts the following methodology in the present research.Firstly, the structure of hot-pressed impregnated diamond bit has been studied, with an analysis of its matrix in terms of primary matrix components and each of their effects, required matrix performance, and the major technical indicators in measuring its performance; with the further study of bit sintering process, the research has experimented on the IF furnace sintering in producing bit matrix, with a sintering temperature at 1000℃, the heating rate at 100-120℃/min, and the holding time of 5min; therefore, matrix hardness and wear resistance have been tested with the three matrix formulae, i.e. the Cu elemental powder formula, the pre-alloyed copper-nickel-manganese formula, and the pre-alloyed basis iron formula. Based on the above experiments, it has been justified that the change in matrix components leads to varied matrix performances.Next, the drilling mechanism and the matrix fragmentation have been elaborated. Therefore, the in-depth analysis of stress and abrasion of bit end, as well as the drilling effect of diamond distribution on bit bottom lip, has well justified the superiority in diamond positioning distribution, thus providing the theoretical support for the design of positioning distribution. To locate the diamond in the matrix, the study has initiated the use of three parameters, i.e. axial spacing, circumferential spacing and radial spacing, to analysis different effects on drilling bit performance caused by different parameters. After a systematic study on the diamond distribution on the bit bottom lip, in accordance with greater wear effects in inner-most and outer-most surfaces and the least wear effects in the middle part, this study has proposed the three-layered circular distribution of diamond grain,and different diamond parameters were used in inner, middle and outer ring of three different zones for the design of bits, so as to avoid unbalanced wear of bits. Positioning parameters for bit diamonds generally used in geological drilling have been designed, for diamond in particle size of 40/45 mesh, and for the diamond in particle size of 50/60 mesh, respectively. As to the positioning of the diamond in particle size of 40/45 mesh, the axial spacing is set as 0.4mm, radial spacing 1.0mm, with circumferential spacing of 1.2mm and radial spacing of 1.0mm in the middle layer; meanwhile, as to the distribution of the diamond in particle size of 50/60 mesh, the axial spacing is set as 0.3mm, radial spacing 0.7mm, with circumferential spacing of 1.0mm and radial spacing of 0.7mm in the middle layer. With the above new positioning of bit diamonds, the design of diamond bit is brought under control, more accurate and effective. Employing the diamond positioning distribution, the study has redesigned the manufacturing process of hot-pressed diamond bit, by adding to the manufacturing process of impregnated bit matrix a new procedure of diamond positioning distribution. The equipment involved in the new procedure of diamond positioning distribution include the equipment for pressing tablet mold, for the vacuum modeling of diamond distribution, for the cold composition and automatic ejection, which are used in respective procedure thus concerned. Based on a further study of the most widely used mold in bit manufacture, such as the tablet mold, the cold steel composition, and the sintering graphite mold, the sintering technology has been proposed with the sintering temperature of 1000℃for elemental powder formula and of 930℃for pre-alloy formula, and with an average stress at 150kgf/cm2 and the average holding time of 6min. In this study, the bit manufacturing process together with the equipment for diamond positioning distribution becomes an integrated system for optimal design and efficiency enhancement, which has been first utilized in geological drilling, featuring accurate positioning, high degree of mechanization and great productivity.Finally, 8 diamond bits, thus produced with positioning distribution technology, have been experimented in the field drilling tests at the coal-mining site in the Kongjia Hill of Linshui County in Sichuan Province, and that in Meng Village of Heng County in Guangxi Province. It has been found that the diamond bit, gains a longer lifetime by 34.38% and a higher drilling rate by 16.7% than conventional bit, when drilling the limestone layer with high content of flint; while drilling in shale layer, it reaches 33.06m in lifetime and 3.59m/h in drilling rate with an abrasion extent of 0.5mm; when drilling in granite layer, bit lifetime has increased by 100%, and the drilling rate increased by 50%. In this way, the bit performance has been greatly promoted by the application of bit positioning distribution technology. The experiments have shown that the performance and quality of hot-pressed impregnated diamond drilling bit have been improved significantly, and the diamond positioning distribute technology is of high practical value and wide prospect.