Effects of increasing sintering pressure on the performance of impregnated diamond bit

The matrix formulas of conventional hot-pressed impregnated diamond bits are mostly elemental metal systems, using WC or YG8 as the skeleton materials, Cu alloys as the bonding materials, and Ni, Co, Fe and Mn as the intermediate materials. Due to the compositions and contents of the bonding and skeleton materials in the formulas, the suitable sintering pressure is limited (≤16 MPa), while the sintering temperature is relatively high (≥ 930℃), resulting in a lower relative ratio of the actual and theoretical densities (≤98%) for the diamond bit matrix. However, the high sintering temperature will cause thermal damage to the diamonds, making it difficult for the impregnated diamond bits to take into account the rate of penetration (ROP) and the service life at the same time. Therefore, two full pre-alloyed diamond bit matrix formulas were selected by the mixture regression test method, and the hardness (HRC), amount of wear, and relative density of the bit matrix were employed as evaluation indexes. On this basis, the single factor tests were carried out for the sintering temperature and sintering pressure for the above two formulas. Meanwhile, the optimization tests were also conducted to the sintering temperature (930, 940 and 950℃) and sintering pressure (17, 18, 19 and 20 MPa) for Formula 2. The test results show that the maximum indentation hardness of the bit matrix samples can be as high as 30.1 HRC, with the amount of wear and relative density of 134 mg and 99.1% respectively. Based on this, three ordinary double-tube bits (ø75/49 mm) were fabricated in trial according to Formula 2 with the optimized hot-pressing sintering parameters, and with these bits, field drilling test was performed at a gold exploration site in Luoyang, with the average ROP and service life of 2.02 m/h and 121.4 m obtained. However, the average ROP and service life of the diamond bits of other manufacturers used on the same drilling platform were only 1.81 m/h and 89 m respectively. The field drilling test results indicate that the impregnated diamond bits fabricated according to the full pre-alloyed matrix formula system and the optimized sintering pressure and temperature have more advantages than the conventional impregnated diamond bits of other manufacturers, thus capable of realizing drilling with high ROP and long service life.