OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 6 4 4 Ta b l e 1 Results of comparative tests of physical and chemical properties of carbide teeth sintered under diff erent conditions Analysed parameters Properties of teeth sintered by method 1 Properties of teeth sintered by method 2 Technical requirements for the VK10 (90 %W; 10 % Co) alloy Density, g/cm3 14.55 14.51 14.43–14.63 Hardness, HRA 87.8 87.8 87.4–88.2 Coercive force, E 87 80 70–90 Average grain size, μm 4.3 4.2 Not regulated Microstructure Equiaxial grain structure Equiaxial grain structure Homogeneous, without coarse grains and cobalt clusters Ctotal , % 5.40 5.52 5.46–5.54 Comparative tests of bits manufactured using diff erent technologies A 3D model of a pin crown and a programme for its manufacture on a fi ve-axis CNC machine (SNKexl 80) were developed for the production of steel crown bodies. The experimental crowns were made of 0.35 C-Cr-Mn-Si steel with the subsequent hardening and grinding up to Ra of 1.6. The fi nal assembly of KNSh 40×25 bits was performed by the cold pressing of teeth, sharpened to a tooth cone angle of 39 degrees. Experimental batches of KNSh 40×25 bits were manufactured for production testing and underwent operational tests at several mines. Several batches of experimental KNSh 40×25 bits were tested at Kyzyl-Olma mines of the Angren Mining Administration, when drilling rocks with a hardness of f` = 14–15, with a drilling result of 48.2 meters, as well as for rocks with f` = 12–16 with a result of 46.3 meters, with wear of 10–15 %. The bits were also tested while drilling the rocks a hardness of f`=14-17 in conditions of the Kauldy mine with an average result of four penetrations of 49.5 meters. Fifteen KNSh 40×25 bits were also tested at the Chadak mine in adits with a rock hardness of f` =16–18, the drilling results ranged from 47 to 58 meters. The certifi cates of industrial tests for the suitability of KNSh 40×25 drill bits manufactured at NPP for work at the Angren, Kauldi and Chadak mines were received. The work performed on the industrial operation of the experimental bits showed that its durability is inferior to the bits manufactured by Atlas Copco (Sweden) by no more than 14-17 %. When mastering the production of hard-alloy pin bits (KNSh 40×25) at Almalyk MMC JSC enterprise, it is expected that a signifi cant annual economic eff ect will be obtained due to its lower cost in comparison with Atlas Copco bits (Sweden). Conclusion Based on the results of the conducted research, the main reasons for the rapid failure of the drill bit teeth produced by NPO AGMK were identifi ed. Studies showed that the main reasons for its destruction are a poor structure (coarse grains and the presence of microdefects). Also, the unsuccessful shape of the tooth surface signifi cantly reduces the resistance. The work carried out to optimize the technology for manufacturing the teeth of the bits made it possible to signifi cantly increase its durability. For manufacturing, a purer tungsten powder of lower dispersion was used, the shape of the tooth surface was optimized to semi-ballistic. Changes were also made to the sintering mode and subsequent agening of the teeth. As a result, an improved technology for manufacturing teeth from hard alloy VK10-KS was developed. The teeth manufactured using the developed technology showed comparable resistance to the teeth manufactured by European manufacturers (Atlas Copco, Sweden). At the same time, the cost of bits with teeth manufactured using the NPO AGMK technology is signifi cantly lower.
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