Rock Drilling Bit

Abstract

The present rock drilling bit has either one or two worms or screws extending helically around its shaft. Each worm is formed by a bottom surface and by substantially laterally extending flanks in such a manner that each bottom surface extends in parallel to the longitudinal axis of the shaft of the drill bit. The lateral flanks are inclined relative to said bottom surface substantially in the same manner, whereby the flank which is closer to the tip of the drill bit forms an acute angle relative to said bottom surface.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a rock drilling bit, and more specifically, to rock drilling bits which are suitable for use in connection with so called torsional impacting drilling machines. Moreover, the present rock drilling bits may comprise either a single or a double helix forming a worm around the solid shaft of the bit, whereby the worm serves for removing drilling chips or dust. The terms "drilling bit" and "drill bit" will be used interchangeably.

In order to increase the efficiency of moving the drilling chips or dust by means of such a rock drilling bit, it has been suggested in German Patent Publication No. 2,013,328 to make the two lateral flanks which form the worm of the drilling bit substantially symmetrical to each other and to assure that both flanks include between the flank proper and the generated surface of the drilling bit an acute angle. Moreover, the foot of each flank, that is, the area where the flank is connected to the core of the shaft, is rounded in a conventional manner. This type of construction provides a back taper for both flanks relative to the generated surface of the drill bit, whereby the space for the borings or drilling chips attains an optimum size. Moreover, an ejection or spattering of the borings is substantially prevented due to the fact that the lateral flanks slope outwardly in a converging manner. Although the just described conventional drill bit provides a very high feed performance or efficiency it has the drawback that the worm windings are so constructed that they have their weakest spot near the flank foot, that is, where the flanks are connected to the core of the shaft. This drawback limits the load capacity of the worm windings as well as the torsional strength of the drill bit.

Another conventional rock drilling bit is described in German Patent No. 1,291,707. This conventional drill bit comprises a single thread feed screw the worm of which is asymmetrical. The flank of the worm which carries the borings is slightly back tapered relative to the generating surface of the bit shaft. The flank foot is rounded off toward the core of the drill bit. The other lateral flank is shaped as a curve which bridges the entire worm toward the core of the bit so that the bottom surface of the worm is essentially a cone shaped surface which tapers toward the tip of the drill bit. Although this conventional rock drilling bit has a good load capacity of its worm windings, the space for receiving the borings is relatively small due to the curve shaped formation of one of its lateral flanks, whereby the feed capacity for the borings is reduced.

OBJECTS OF THE INVENTION

In view of the foregoing, it is the aim of the invention to achieve the following objects, singly or in combination:

TO REMOVE THE DRAWBACKS OF THE PRIOR ART AS OUTLINED ABOVE;

TO PROVIDE A ROCK DRILLING BIT WHICH IS ESPECIALLY SUITABLE FOR USE IN SO CALLED TORSIONAL IMPACT DRILLING MACHINES;

TO PROVIDE A ROCK DRILLING BIT WHICH HAS A GOOD FEEDING CAPACITY IN COMBINATION WITH A GOOD LOAD CAPACITY OF ITS WORM WINDINGS, STATED DIFFERENTLY, THE DRILL BIT ACCORDING TO THE INVENTION SHALL EFFICIENTLY REMOVE THE BORINGS WHILE SIMULTANEOUSLY HAVING AN IMPROVED STRUCTURAL STRENGTH AGAINST BREAKAGE;

TO PROVIDE A DRILL BIT WHICH MAY BE CONSTRUCTED TO COMPRISE A SINGLE FEED WORM WINDING OR A DOUBLE WORM WINDING WHILE SIMULTANEOUSLY HAVING A GOOD REMOVAL CAPACITY FOR THE BORINGS AND A GOOD STRUCTURAL STRENGTH;

TO PROVIDE A ROCK DRILLING BIT WITH LATERAL FLANKS WHICH EXTEND SUBSTANTIALLY PARALLEL TO EACH OTHER AND LATERALLY OUTWARDLY, WHEREAS THE BOTTOM SURFACE OF THE WORM EXTENDS IN PARALLEL TO THE LONGITUDINAL AXIS OF THE SHAFT OF THE BIT; AND

TO PROVIDE A DRILL BIT WHICH IS SO CONSTRUCTED THAT THE FOOT OF THE FLANKS, THAT IS, THE PORTION OF THE FLANKS WHICH MERGES INTO THE CORE OF THE BIT, HAS AN ENLARGED CROSS SECTIONAL AREA.

SUMMARY OF THE INVENTION

According to the invention there is provided a rock drilling bit, especially a rock drilling bit suitable for use in so called torsional impact drilling machines, wherein the bottom surface of each worm winding extends in parallel to the longitudinal axis of the drilling bit and wherein the lateral flanks of the worm winding slope in the same manner relative to said bottom surface, whereby the lateral flank which is closer to the tip of the drill bit includes together with the bottom surface an acute angle .gamma..

It is a surprising advantage of the present invention that the parallel extension of the bottom surface of the feed screw increases the feed volume or feed space for the borings as compared to prior art embodiments. Moreover, due to the fact that the lateral flanks extend substantially in parallel, it is possible to increase the cross sectional area of the flank foot of the screw windings so that the load capacity as well as the structural strength of the drill bit is also increased as compared to prior art embodiments.

SHORT FIGURE DESCRIPTION

In order that the invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a portion, partially in section, of a rock drilling bit according to the invention, whereby the upper part is shown in section and the lower part is illustrated as a side view; and

FIG. 2 is an enlarged partial sectional view of the encircled portion A shown in FIG. 1.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS:

To save space FIG. 1 merely illustrates a portion of a drill bit 10 according to the invention. The drill bit has a tip symbolized by the arrow 11 and a shank symbolized by the arrow 12. The central longitudinal axis of the drilling bit is indicated by the dashed line 13.

The example embodiment shown in FIG. 1 comprises two feed worms or screws best seen in the lower side view part of FIG. 1. One screw a surrounds the shaft or core 1 of the drill bit intermediate the other screw b.

The core 1 of the drill bit is surrounded by the bottom surface 2 of the worms or worm windings a and b. The lateral boundaries of the worms are formed by flanks 3 and 4. According to the invention, the bottom surface 2 extends in parallel to the longitudinal axis 13 as viewed in the sectional upper portion of the drill bit. Thus, the bottom surface 2 has a cylindrical shape. The lateral flanks 3 and 4 slope relative to the longitudinal axis 13 substantially in the same manner, that is, the flanks 3 and 4 each include an angle with a respective plane 14 or 15 extending perpendicularly to the longitudinal axis of the drilling bit. These angles .alpha. and .beta. are shown in the upper right hand portion of FIG. 1. The line which forms an extension of the respective flanks 3 or 4 and which includes the angle together with the respective plane, points toward the tip 11, relatively speaking, whereby the respective angles .alpha. and .beta. are acute angles. According to one embodiment of the invention, the angles .alpha. and .beta. may be selected to be equal to each other. In this embodiment, the angles between the lateral flanks on the one hand and the bottom surface 2 of a worm winding form angles which are complementary angles relative to each other.

FIG. 2 illustrates on an enlarged scale a partial sectional view substantially showing the portion surrounded by the circle A in FIG. 1 thus showing a section through one winding of the feed screw, whereby the following dimensions are selected according to the invention relative to the given outer diameter D of the drilling bit. Thus, the depth T of the worm winding is preferably about 0.2 to 0.3 times the outer diameter D. Smaller drill bits will be constructed so that said depth corresponds to the lower end of said given range, whereas larger drill bits will have a depth corresponding to the upper end of said range.

The worm windings 16 forming said flanks 3 and 4 preferably have a peripheral thickness S which is equal to about 0.07 to 0.2 times the outer diameter D. The angle .alpha. may, for example, in those instances where .alpha. and .beta. are not equal to each other be within the range of 4.degree. to 7.degree. whereas the angle .beta. then may be preferably within the range of 15.degree. to 20.degree..

As seen in FIG. 2 the footing of the winding 16 has an enlarged cross sectional area as compared to the peripheral thickness S, whereby the structural strength and the load capacity of the present drill bit is substantially improved as compared to the prior art. Moreover, the footing is shown to be rounded off as indicated by reference numerals 17 and 18.

Although the invention has been described with reference to specific examples, it is to be understood that it is intended to cover all equivalents and modifications within the scope of the appended claims.

Claims

What I claim is:

1. In a rock drilling bit having a shaft with a longitudinal axis and a given outer diameter, a tip at one end of the shaft and a shank at the other end of the shaft, as well as worm means extending around the shaft between the tip and the shank for removing drilling chips, each worm means comprising a bottom surface and two lateral flanks, said bottom surface extending in parallel to said longitudinal axis relative to any arbitrary axial section through the shaft, the improvement comprising a first angle ( .alpha. ) of about 4.degree. to 7.degree. included between any of said lateral flanks closer to said tip (11) and a first plane extending perpendicularly to said longitudinal axis, a second angle ( .beta. ) of about 15.degree. to 20.degree. included between the respective opposite flank closer to the shank (12) and a further plane extending in parallel to said first plane, all of said lateral flanks having a slope which points toward said tip, whereby an acute angle ( .gamma. , .gamma.') facing toward said tip is included between the slope of any one of said flanks and said longitudinal axis.

2. The rock drilling bit according to claim 1, wherein said worm means comprise a double helix.

3. The rock drilling bit according to claim 1, wherein said worm means comprise a single helix.

4. The rock drilling bit according to claim 1, wherein said worm means have a depth equal to 0.2 to 0.3 times said given diameter.

5. The rock drilling bit according to claim 1, wherein said flanks of said worm means have a peripheral thickness corresponding to 0.07 to 0.2 times said given diameter.