Patent GB-525800-A (GB)
Title: Improvements in the construction of externally screw-threaded members
IPC: E21B17/042
Filed: 1939-03-01
Abstract: 525,800. Percussive drills. DREWETT, G. March 1, 1939, No. 6714. [Class 124] [Also in Groups XXII and XXV] In a method of forming an external screw thread, a rigid non- screw-threaded stem has a sleeve of thin metal applied thereto, the sleeve having a screw thread formed from the wall thereof and being fixed on the stem by being molecularly deformed to make binding frictional engagement therewith. As applied to securing a rockdrilling bit on a drill rod, or the drill rod to a machine spindle, the bit 7, Figs. 1 and 2, has a sleeve 13a forced thereon which is formed from drawn mild steel or alloy tubing of about 26 gauge and is pressed to the shape of an external screw thiead of uniform pitch. A similar screwed sleeve 13 is forced on the drill rod 9 and the two are screwed into a socket 8 with the end surfaces 23 abutting each other and engaging tapered surfaces 21 on an internal flange 22 in the socket. The members 7, 9 mav abut entirelv on their end surfaces without a flange 22, or the flange mayextend completely across the socket to form the abutment as shown in Fig. 3. The sleeves 13, 13a may be further secured to the members 7, 9 by filling the space under the thread with friction-exerting material such as lead or rubber, or the sleeves may be secured at one end by a few spot-welds 25, Fig. 2, or by pressing the ends into recesses 26, Fig. 3, but such fixing should allow the major portions of the sleeves to move axially on the members when the ends 23 abut. This resilience of the sleeves may be increased by one or more longitudinal slits 27, Fig. 2, formed partly therethrough. When the sleeves are applied to drill steel 11, Fig. 3, of polygonal cross-section, they are internally polygonal and have an externally circular screw thread, and the sleeves may then be formed of thick metal having a polygonal bore with the screw thread machined on the outside. The thick sleeves are longitudinally slit to allow them to be forced on the drill rods, &c. Force-fits assembling.-The screwed sleeves 13, Fig. 4 are forced in the cold state axially on the drill rods &c. 9 by means of a socket 16 having an internal screw thread 17 for support ing the sleeves against axial collapse. The sleeves are bell mouthed at 15 to.facilitate entry of the members 9 and the bases 18 of the threads are expanded throughout the thickness of the metal during assembly. The socket 16 may be removed after assembly or may form the permanent socket into which the member 9 is to be secured. Percussive-drills.-The drill shank 11, Fig. 1, is axially slidable in a polygonal socket and is hammered and rotated by the polygonal nose 6 of the hammer piston. The coupling 10 for attaching the drill rod 9 to the shank 11 is surrounded by a non-rotary sleeve 40, Figs. 1 and 3, packed at 41 and having a water inlet at 39 for supplying the cutting bit through the hollow drill rod and passages 37, 38 in the flange 22 of the coupling 10. The drill rods and shank &c. are made from steel in the hard rolled condition in which screw threads cannot easily be cut. Specification 519,214 is referred to.