MANUFACTURE OF DRILLING BIT

PURPOSE:To manufacture a drilling bit which is excellent in the fixing force by flowing out the initial part of the molten metal into a flow off provided in a mold. CONSTITUTION:Zirconia powder is dissolved in 5% sodium silicate solution, and in addition, 2% boric acid is added. This solution is coated three times on a mold by the spray coating, and after that, a cemented carbide tip 4 which is cleaned through the ultrasonic vibration in acetone is set in the mold. The molten cast steel is poured at the pouring temperature of 1630-1650 deg.C. Then, 30% of the total poured molten metal which is brought into contact with the cemented carbide tip 4 at first is flowed off into a flow off 3. The molten metal is successively poured until the void part 2 is filled. This constitution provides a drilling bit 7 where the cemented carbide tip 4 is fixed to a base metal part 6 made of cast steel. The molten metal is filled in an anchor hole 5 of the cemented carbide tip 4 and solidified, and the cemented carbide tip 4 is integrated with the base metal part 6 by this mechanical fitting and the diffusion bonding of the contacted surface.