THREE-ROLLER BIT

FIELD: rock breaking tools, flushing systems of three-roller bits. SUBSTANCE: three-roller bit includes arms making up body of bit, rolling cutters supported in bearings and combined flushing system comprising two side and one central nozzles. Central nozzle has narrowing upper part, cylindrical middle and expanding lower parts with presence of three radial holes in cylindrical part. Area of outlet sections of holes is related to area of least diametrical cylindrical part of central nozzle by following relation Fd.p/∑Fr.h = 3/5 where Fd.p is area of outlet section of least diametrical cylindrical part of central nozzle, sq mm; ∑Fr.h is summary area of outlet sections of three radial holes of central nozzle, sq mm. Summary area of outlet sections of two hydraulic giant side nozzles and area of outlet section of least diametrical part of central nozzle are in the following relation SigmaFs.h/Fd.p = 1,6/1,8,, where SigmaFs.h is summary area of two side hydraulic giant nozzles, sq mm. EFFECT: raised operational reliability of three-roller bit thanks to rational distribution of downhole flows of flushing fluid by proposed combined hydraulic flushing system, improved counteraction to formation of balling across bit and bit fittings, enhanced technical and economical indices of drilling operations. 2 dwg