人工合成ダイヤモンド製細棒植込み型ビットの基本的性能に関する研究
1989 年 54 巻 3 号 p. 240-253
詳細
1989 年 54 巻 3 号 p. 240-253
New type of polycrystalline-diamond-compact (PDC) bits are tested for drilling hard rocks in laboratory conditions. Slender cylindrical inserts are used as cutters, so the bits are called as polycrystalline-diamond-insert (PDI) bits in this study. The inserts are 3-3.5mm in diameter, and 5mm in length in the test bit of 6cm in diameter. The inserts are composed of PDC and tungsten carbide (WC). Four types of inserts are tested: PDC sheathed by WC coaxially, PDC coverd by WC eccentrically, semicircular PDC welded with semicircular WC, and circular PDC.
Drilling rate and bit life are measured of nine test bits with different profiles. The bit profile is designed considering inserts distribution pattern, cuttings removal, stable motion of bit, breakage of a center plug of bottom-hole rock and so on. No. 8 bit drilled about 30m of granite, of which compressive strength ranges from 130MPa to 160MPa, with drilling rate of about 2.2m/h at bit weight of 25-15kN and rotating speed of 99rpm. No. 9bit shows high drilling ability of 4m/h in granite, of which compressive strength is about 130MPa, at bit weight of 12kN and rotating speed of 99rpm. The bit has stable drilling rate and torque during long periods, when an adequate combination of bit weight and rotating speed is applied. Low bit weight is apt to wear off inserts faster than matrix, and high bit weight is apt to wear off matrix. At optimum conditions, inserts and matrix seem to wear off slowly keeping the relative height of inserts from the matrix.
