EP0187971B1 - Drill bit - Google Patents

Description

The invention relates to a drilling tool for hammer drilling machines, preferably with a double-start spiral gear at the tip of which a hard metal cutting plate with preferably two cutting surfaces is inserted transversely to the axial longitudinal direction of the drilling tool.

Drilling tools for use in hammer drills are equipped with a hard metal insert on the drill head. In the case of known drilling tools, this hard metal cutting insert is used parallel to the slot outlet, for example of a double-start spiral gear (see FIG. For this purpose, a transverse groove is made in the spiral body, into which the hard metal insert is soldered.

In order to increase the resistance against breaking out of the insert, the slot outlet on the drill head was designed asymmetrically with respect to the insert, so that the insert holder was made thicker in the area of greater stresses (see FIGS. 1b and 1c).

A known drilling tool as shown in principle in FIG. 1c of the present invention has become known from FR-A-1 118 255. According to FIG. 3 of this citation, the groove outlet of the spiral passage is arranged parallel to the hard metal cutting plate, the back surface of the cutting plate receptacle being reinforced.

A drilling tool is also known from EP-A 48 908, which has a parallel arrangement of the hard metal cutting plate to the respective two groove outlets. However, the groove outlets are not drawn to the hard metal cutting plate as strongly as is the case in the previously described publication (see FIG. 4 of EP-A-48 908).

The known drilling tools are used both in hammer drills in the higher weight class (e.g. 4 kg) and in hammer drills in the light weight class (e.g. 2 kg). In the case of hammer drills of the light class, the lower ram mass compared to the heavy class is compensated for by the firing pin being opened at a higher speed the drilling tool acts. The necessary energy is therefore achieved with increased firing pin speed.

When using the known drilling tools in hammer drilling machines of the light class, it has been shown that the drilling tools have a shorter service life than with the same load in hammer drilling machines of the heavy class. This lower fatigue strength stems from higher voltage peaks in the drill head, caused by the high impact speed with hammer drills of the lighter class.

The invention has for its object to provide a drilling tool which has increased stability or durability when used in hammer drills with high ram speed.

This object is achieved with a drilling tool of the type mentioned at the outset by the characterizing features of claim 1.

The main idea of the present invention lies in a fundamental redesign of the drill head of conventional drilling tools, in particular to increase the section modulus of the supporting or supporting surface. With conventional drilling tools, the hard metal cutting edge is always used parallel to the slot outlet in the drill head (see Fig. 1a). As a result, only a small web remains as lateral support for the cutting insert.

In contrast, in the present invention, the hard metal cutting insert is inserted into the drill head rotated by 90 ° compared to the arrangement in conventional drilling tools (see FIG. 2). As a result, the section modulus of the lateral support surface is considerably increased, which leads to longer service lives and increased fatigue strength of the drilling tool.

The drilling tool according to the invention also has the advantage that the end regions of the hard metal cutting plate protrude directly into the groove outlet surface. The drilling dust produced by the hard metal cutting insert is introduced directly into the groove outlet area of the drilling dust grooves in the area of origin without the need for a deflection as in conventional drilling tools. The removal of the drilling dust is therefore guaranteed to the full extent even with the modified construction of the drill head.

The measures listed in the subclaims enable advantageous further development and improvement of the drilling tool in accordance with the main claim. According to the design according to subclaim 2, in the case of a two-start twist drill, the hard metal cutting plate is arranged perpendicular to the groove run-out surface in order to produce a symmetrical drill head.

The further embodiment according to subclaim 3 provides that the lateral area of the receptacle for the hard metal cutting plate is ground, but the cross section of the drill material in the groove base of the hard metal cutting plate receptacle is not weakened. The highest shear forces occur in this area when the drill head is loaded.

Fig. 1a

bis c die Ausgestaltung von Bohrwerkzeugen nach dem Stande der Technik,

Fig. 2

eine prinzipielle Darstellung des erfindungsgemäßen Bohrwerkzeugs,

Fig. 3

eine Darstellung der Widerstandsmomente bei verschiedenen Konstruktionen,

Fig. 4

ein Ausführungsbeispiel der Erfindung in prinzipieller Darstellung,

Fig. 5

ein weiteres Ausführungsbeispiel der Erfindung mit angeschliffenem Bohrerkopf.

The invention is explained in more detail with reference to the figures and in the description below. Show it

Fig. 1a

to c the design of drilling tools according to the prior art,

Fig. 2

a basic representation of the drilling tool according to the invention,

Fig. 3

a representation of the moments of resistance in different constructions,

Fig. 4

an embodiment of the invention in principle,

Fig. 5

a further embodiment of the invention with a ground drill head.

In the prior art shown schematically in FIG. 1, the hard metal cutting plate 11 is introduced into the spiral passage of a two-speed drilling tool in such a way that it is arranged parallel to the two groove run-out surfaces 12, 13. The webs 15, 16 arranged on both sides of the groove 14 for receiving the hard metal cutting plate 11 are kept very narrow in their effective shear surface. To increase the section modulus of the web surfaces 15, 16, these are wedge-shaped according to FIGS. 1b and 1c (15 ', 15' ', 16', 16 ''). However, the measures according to FIGS. 1b and 1c are not sufficient to avoid shearing off the drill head in the area of the groove base of the groove 14.

According to the invention, the hard metal cutting plate 11 - as shown in FIG. 2 - is therefore arranged transversely to the groove run-out surface 12, 13. As a result, the entire remaining circular cross section is present on the side of the hard metal cutting plate, formed by the webs 17, 18.

Das Widerstandsmoment gemäß der Darstellung nach Fig. 2 ergibt sich aus der Fläche h₂ x b₂ und daraus das Widerstandsmoment $\text{W₂ = 1/6 (b₂ x h₂²).}$

In the representation acc. 3, the different resistance moments according to the embodiment according to FIG. 1 (prior art) and FIG. 2 (invention) are compared. 1a results in an effective area for calculating the section modulus, the area h 1 x b 1 with a section modulus of
$\text{W₁ = 1/6 x (b₁ x h₁²).}$

The section modulus as shown in FIG. 2 results from the area h₂ x b₂ and from it the section modulus $\text{W₂ = 1/6 (b₂ x h₂²).}$

From this it can be seen that the web width on the side of the hard metal cutting plate 11 (here h 1 and h 2) is entered as a square value in the formula for the section modulus. To avoid shearing of the webs 17, 18, they must therefore be made as wide as possible, which is achieved according to the invention in that the hard metal cutting plate 11 is arranged transversely to the slot outlet of the spiral passage.

A schematic representation of the invention is also shown in FIG. 4. As can be seen from FIG. 4b, the drilling tool 10 according to the invention has a drill head 19, in which the hard metal cutting plate 11 is arranged transversely or perpendicularly to the groove outlet surfaces 12, 13 of the groove outlet surfaces of the spiral passages 20, 21. As a result, the full remaining material thickness h 2 of the drill material is present at the base 22 of the groove 14, so that there is a high moment of resistance to shearing or vibration breakage in this area.

4a shows a side view of the representation acc. Fig. 4b. 4c, the drilling head 19 is shown in a top view, the drilling dust grooves 12, 13 formed by the groove outlet surfaces of the spiral passages 20, 21 being shown. Furthermore, the two cutting edges 23, 24 of the hard metal cutting plate 11 are shown (see also FIG. 4a).

In the embodiment according to 5, the lateral areas 17, 18 for supporting the hard metal cutting plate 11 are ground. The bevel angle ∝₁ with respect to the longitudinal axis 25 of the drill is approximately 20 to 40 °, in particular 30 °. The surfaces 26, 27 thus ground continue to run relative to the longitudinal plane 28 of the hard metal cutting plate 11 and one acute angle ∝₂ ≈ 15 to 30 °, especially ∝₂ = 20 °. At the level of the groove base 22 of the groove 14, however, the full material thickness of the spiral diameter is present on the side of the hard metal insert. The drilling dust is transported via the groove outlet surfaces of the spiral passages 20, 21.

The invention does not extend to the exemplary embodiment. Rather, it encompasses all professional developments and embodiments which result from the teaching of the claimed invention without further and without inventive step.

Claims (4)

1. Drill bit for hammer drills, comprising a single-start or two-start helical thread (20, 21), at the tip of which a hard metal cutting plate (11) having two cutting surfaces (23, 24) is fitted transversely to the axial longitudinal direction of the drill bit, characterized in that the hard metal cutting plate (11) is disposed substantially perpendicularly to the groove run-out (12, 13) of the helical thread (20, 21).
2. Drill bit according to Claim 1, characterized in that, in the case of a two-start drill bit, the hard metal cutting plate (11) extends perpendicularly to the groove run-out surface (12, 13) to form a symmetrical bit head (19), the lateral ends (29, 30) of the hard metal cutting plate (11) projecting into the groove run-out (12, 13).
3. Drill bit according to Claim 1 or 2, characterized in that the ribs (17, 18), disposed laterally of the hard metal cutting plate, are ground at an angle of ∝₁ ≈ 20 to 40°, especially ∝₁ = 30°, to the bit longitudinal axis (25) and these surfaces (26, 27) are ground at an angle of ∝₂ ≈ 15 to 30°, especially ∝₂ = 20°, to the longitudinal plane (28) of the hard metal cutting plate (11).
4. Drill bit according to one or more of Claims 1 to 3, characterized in that the effective resistance moment area $\text{b₂ x h₂}$

   

   in the region of the groove base (22) of the insertion groove (14) for seating the hard metal cutting plate (11) is not weakened by the groove run-out surfaces.

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