DRILL TOOL

Abstract: A drilling tool for a sinker drill is provided with a drill-bit section (1) or broaching-bit section and a shaft section (2). According to the present invention a reliable drill tool with longer service life is obtained by making the drill-bit section (1) and the shaft section (2) or broaching-bit section and shaft section in two parts joined together by means of a screw joint in such a manner that the shaft section (2) reaches the bottom of the drill-bit section (1) or said broaching-bit section.

Description: Drill tool The present Invention relates to a drill tool for sinker drills. Such drill tools, consisting of a drill bit and a shaft or a broaching bit and a shaft, are manufactured in one piece. The drill tool Is connected to a sinker drill hammer and the following extension rod. An annular gap is formed between the cavity wall and the extension rod, through which cuttings are removed. A hammer acts on the free end of the drill-tool shaft. This part Is thus subjected to great impact, energy and must therefore be made of wear-resistant material. The drill bit or broaching bilr, on the other hand, should be made of a ductile material such as structural steel. In practice the requirements of the drill bit or broaching bit governs the choice of material. This entails high drill- tool costs since the whole tool must be replaced when the drill bit or broaching bit has become worn. The object of the present invention is to provide a reliable and less expensive drill tool with longer service life. In practice this is achieved by making the drill tool out of a drill-bit section or broaching- bit section having a recess in axial direction, and a tubular shaft section, these parts being detachably secured to each other by means of a screw joint, the drill-bit or broaching-bit section being provided with internal threading in said recess and the shaft section being provided with external threading. When fully screwed in, the shaft section reaches the bottom of the drill-bit or broaching-bit section. This construction allows the best material to be selected for each part of the drill tool. A ductile construction steel material can thus be se- lected for the drill-bit or broaching-bit section, while a hard-tempered rod steel can be selected for the shaft section. This choice enables one shaft section to be used for about three drill-bit or broaching-bit sec¬ tions and also permits different sizes of drill bits or broaching bits to be fitted. Additional characteristics of the present invention are revealed in the following claims. A preferred embodiment of the invention will be described In more detail with reference to the accompanying drawings, in which Figure 1 shows a drill tool according to the invention, partially In section, Figure 2 shows a drill-bit section seen obliquely from above, Figure 3 shows a drill-bit section seen obliquely from b.elow, Figure -1 shows a shaft section: seen obliquely from above; and Figure 5 shows a shaft section seen obliquely from below. In the drawings, 1 designates the drill-bit section of the drill tool and 2 Its shaft section. The drill-bit section 1 is provided in conventional manner on the lower side with an optional number of hard metal pins 8-13. Flushing channels 14,15 also emerge on the lower side, these channels communicating via the shaft section 2 with an extension rod (not shown) supplying compressed air. The drill-bit section is provided with a recess in axial direction, provided with Internal threading. The other ends of flushing channels 14 and 15 emerge in the bottom of the recess 3. The upper side 7 of the drill-bit section 1 is flat and annular. The shaft section 2, which is tubular, is provided at one end with external threading 4. At the junction between the external threading 4 and the flat peripheral surface of the shaft section 2 is an annular peripheral flange 5. The peripheral flange Is disc-shaped with flat surfaces 6 and 16. The surface 16 may be shaped alternatively. The shaft section 2 Is provided conventionally with splines 20, 21, 22 for the transfer of torsional moment. The upper end surface 26 is flat. An axial channel 25 runs the length of .the shaft section for the supply of compressed air and flushing medium. When the drill-bit section 1 and shaft section 2 are screwed together, as shown In Figure 1, the sha t section 2 reaches the bottom of the recess In the drill-bit section 1. When screwed together, a gap of say 0.3 -___■ Is formed between the upper side 7 of the drill-bit section and the lower side 6 of the peripheral flange. When impact energy is transmitted from the shaft to the bottom plane of the drill bit in the Internally threaded hole, this plane will be marked by the tightening of the screw joint. The type of steel used for the drill bit will permit elastic deformation and the shaft will be prevented from screwing further by the lower side 6 of the flange one the gap opening of say 0.3 mm has been used up. The purpose of this is to prevent continued screwing to an extent exceeding the yield limit of the threaded recess of the drill bit, resulting in fractures. The drill tool formed by screwing the two sections together is attached in conventional manner to a drill chamber and extension rod. When the drill tool is subjected to impacting both the drill-bit section and the shaft section will become worn. However, suitable choices of material and hardness in respective sections enable the service life to be optimized and costs thus kept down. When in operation the drill-bit section and shaft section are held ;Ln clamped position by material deformation. According to the invention, the threads in the screw joint have a shallow angle C. , so that the axial and radial forces are distributed more evenly during loading. The expression "shallow angle of thread" implies that the total angle is greater than 90 , i.e. that c is greater than 90 . The screw joint may have one or more entries. This facilitates manufac¬ ture since only one thread profileis then required, irrespective of the size of drill tool and thus screw joint. Furthermore, several thread entries also ensures greater pitch and the joint will therefore not be so tightly screwed. This in turn facilitates removal of the drill bit.

Claims: CLAIMS 1. A drill tool for a sinker drill, c h a r a c t e r i s e d In that said drill tool is In several pieces and consists of a drill-bit section (1) or broaching-bit section having a recess In axial direction, and a tubular shaft section (2), said parts being detachably secured to each other by means of a screw joint, the drill-bit section (1) or broaching-bit section being provided with internal threading (3) In said recesa and the shaft seetion (2) for attachment to said drill-bit section or to said broaching-bit section being provided " with external threading (4), said screw-threads (3, 4) being so designed " that the shaf * section (2) reaches the bottom of said drill-bit section (1) or said- broaching-bit section when fully screwed in. 2. A drill tool according to claim 1, c h a r a c t e r i s e d in that said shaft section (2) is provided with a substantially annular peripheral- flange (5) arranged at or clos.e to said external thread (4), said peripheral flange (5) having a substantially flat end surface (6) facing the upwardly facing surface (7) of said drill-bit section (1) or said broaching-bit section, the end surface (7) also being substantially flat, a gap being formed between end surface (6) and end surface (7) when the two drill sections are screwed together. 3. A drill tool according to claim 1 or 2, c h a r a c t e ¬ r i s e d in that the angle of thread (< ) in said screw joint is greater than 90°.

Inventors: LOEF UNO, LOEF, UNO
Applicants: LOEVAB LOEF OCH OESTLUND AB
Application year: 1987
Main classification: E21B17
IPC codes: E21B4, E21B17