GB1338586A - Rock drill - Google Patents

Abstract

1338586 Rotary percussive drills HAWERA HARTMETALL - WERKZEUGFABRIK RAVENSBURG GmbH 29 Dec 1970 [30 Dec 1969] 61423/70 Heading B3C [Also in Divisions B4-B5] A bit for a percussive rotary rock drill comprises an insert 3, Fig. 2, e.g. of tungsten carbide, fixed, e.g. brazed, in a cross-slot at one end of a uniform cross-section shank 1, e.g. of steel. The shank has two diametrally opposed grooves 11, 12 for collecting and removing drilling chips and dust each groove being parallel with the longitudinal axis of the shank and extending from directly adjacent the insert 3 to the chucking end of the shank 1. The surface of each groove is shaped in cross-section as an elliptical arc and intersects the envelope surface 13, Fig. 4, of the shank to form a scraper edge 15 enclosing an angle γ of 20 to 70 degrees, preferably 40 to 60 degrees, e.g. 55 degrees. The grooves 11, 12 may each extend over an angle α of less than 90 degrees, e.g. 40 to 50 degrees, and may increase slightly in crosssection towards the chucking end of the shank. The ratio a/b of the semi axes of the ellipse E partly defined by one of the grooves is preferably 4 : 2 to 5 : 2 and the major axis A of the ellipse preferably intersects the median plane SS of the insert 3 at a distance e from the drill axis M where e is 20-30% of D the drill shank diameter. The angle # between the axis A and the plane SS is preferably 75 degrees. The radius of the shank may decrease slightly from each scraper edge 15 to the leading edge of the following groove, either continuously or stepwise.