GB2075409A - Drills - Google Patents

Abstract

A drill comprises at least one helical spline (3) for removal of rock drillings, a cross-head working tip provided by hard metal inserts (5), and two pairs of the diametrally opposed flutes (8, 8b; 8a, 8c) connecting the tip to the helical spline (3). The helix angle of each flute is greater than that of the helical spine but less than 90 DEG , and may be different to the helix angle of other flutes. The side edges of the flutes may diverge towards the tip and the end of the drill may have chamfers which slope away from the tip and towards the flutes. <IMAGE>

Description

SPECIFICATION Drills The present invention relates to drills for use in construction work, as well as in mining practice for drilling holes in hard rock.

According to the invention there is provided a drill for drilling holes in material, such as hard rock, comprising at least spline extending helically therealong for removal of rock drillings, a crosshead working tip and two pairs of diametrally opposed flutes connecting said at least one spline to the tip, each of said flutes extending along a helical path having a helix angle greater than that of the helix angle of said at least one spline, but less than 900.

The flutes improve the removal of rock drillings due to the fact that drillings move along a shorter pathway from the point of their chipping to the helical spline, which in turn increases the drilling speed and prevents the angular space between the walls of the hole being drilled and the bit head clogging. A cross-head tip is known to be most favourable for drilling as the use of such head reduces vibration due to the fact that identical angles of cutting edges of the cross bit head provide for a uniform distribution force at the drill at the moment of impact.

For a drill having two helical splines it is expedient that flutes of each pair have equal helix angles, and for the flutes of different pairs to have different helix angles.

For a drill having a single helical spline all the four flutes preferably have different angles of helix.

In a preferred drill each of the flutes is defined by a concave surface with side edges which diverge gradually towards the working tip. Also the end of the drill can be provided with chamfers which slope away from the tip and towards the flutes.

The invention is described in more detail below by way of example, with reference being made to the accompanying drawings, wherein Figure 1 is a perspective view of a spiral drill, according to the invention; Figure 2 is an enlarged view of the bit head of the spiral drill of Figure 1; Figures 3 and 4 are front and rear elevations .respectively, of the bit head of a spiral drill having four longitudinal flutes merging into the same helical spline of the drill body; Figure 5 illustrates an embodiment of the spiral drill provided with helical splines featuring varying cross-section and curvilinear generating surface; and Figure 6 illustrates an embodiment of the spiral drill provided with longitudinal flutes having an enlarged portion conjugated with the end face of the cutter bit at the front and back cutting edges of each of the hard metal inserts, respectively.

The spiral drill (Fig. 1) comprises a shank shaped as a hexagon or cylinder and adapted to be clamped in a bushing of a rotary hammer (not shown in the drawing), a body 2 provided with two helical splines 3 and 3' for rock drillings from the bit head to pass. The spiral drill has a cross bit head 4 known construction, provided with inserts 5 usually made of a hard metal, each of said inserts having a front cutting edge 6 and a back cutting edge 7, respectively. The cutting edges and 6 and 7 have an edge angle ranging within 90 to 1200 depending upon the hardness of the rock being drilled. The body of the cross bit head 4 is provided with four longitudinal flutes 8, 8a, 8b and 8c, said flutes being arranged in pairs diametrally opposite to each other, i.e., the flutes 8 and 8b are diametrally opposite, and the flutes 8a and 8c are diametrally opposite, too.Besides, the adjacent flutes 8 and 8a communicate with one of the helical splines while the adjacent flutes 8b and 8c, with the other helical spline, i.e., the adjacent longitudinal flutes communicate with the same helical spline. As it can be seen from Fig. 1 all the four longitudinal flutes have the helix angle exceeding that of the drill body helical spline, but less than 900. The helix angle of a longitudinal flute implies an angle bounded by the flute axis and the projection of said axis on the plane normal to the drill longitudinal axis. Practical experience has defined the helix angle of a helical spline to vary within 17 to 600 depending upon the bit head diameter, degree of rock hardness, drill rotational speed, and some other factors.

The spiral drill of the present invention operates as follows.

When a hammer (not shown) delivers a blow against the shank 1 the resulted impact energy is imparted to the cross bit head 4, whereby the latter penetrates into the rock for a depth of from 0.3610-2 to 1810-2 cm. Further blows and drill rotation carry out rock crushing and chipping by virtue of the front edges 6 and the back edges 7 of the bit inserts.

When the drill performs reciprocating motion which is combined with the rotary motion thereof the disintegrated rock solids are conveyed along all the four longitudinal flutes 8, 8a, 8b and 8c which are arranged as described above. Inasmuch as the helix angle of the longitudinal flute exceeds that of the helical spline the solid particles travel along a shorter pathway from the place of their chipping at a best throughout capacity of the longitudinal flutes.

In the given case the cross bit head may be considered as a set of wedges working on the pattern of a two-sided rock chipping with respect to the edges of the wedge inserts.

Rock drillings resulting from rock crushing by the bit, head are pressed out into the annular space between the borehole walls and the rotary cross bit, head.

Provision of two pairs of the diametrally opposite flutes 8, 8a, 8b and 8c allows the rock drillings to be removed of round the entire perimeter of the bottom hole and the flows of said drillings to be distributed uniformly in the annular space.

On the other hand, application of a cross bit head having the edges with the edge angle ranging within 90 to 110 degrees is instrumental in reducing possible running out of straight of the drill body in the borehole, attaining better centre aligning of the bit head with respect to the face and prevents the drill from getting jammed, especially when drilling through variable-hardness rock.

Fig. 2 represents an enlarged view of the bit head of the spiral drill illustrated in Fig. 1. A distinguishing feature of said bit head resides in the fact that each of the two diametrally opposite longitudinal flutes communicating with the helical spline, has similar helix angles, and the adjacent longitudinal flutes have different helix angles. It ensures from Fig. 2 that the flutes 8 and 8b, as well as the flutes 8a and 8c have equal helix angles, and the adjacent flutes 8 and 8a, as well as 8b and 8c have different helix angles. In this case each of the two pairs of the longitudinal flutes (8, 8a) and (8b, 8c) merge into their own helical spline of the drill body.Such an arrangement of the longitudinal flutes makes it possible not only to increase their throughout capacity but also to simplify their manufacture by using highly productive equipment for cutting helical splines of the drill body.

In another embodiment of the spiral drill illustrated in Figs. 3 and 4, all the four longitudinal flutes (8, 8a, 8b, 8c) merge into the single-start helical spline 3. As becomes evident from Figs. 3 and 4 the longitudinal flutes have different helix angles a, P, y, 6, said angles featuring the following relationship with respect to one another: > y > O. Such an embodiment of the longitudinal flutes adds to the throughput capacity thereof and improves the technological process for their production.

Fig. 5 represents an embodiment of the spiral drill, wherein the longitudinal flutes 8 communicating with the helical splines 3 of the drill body, feature varying cross section and a curvilinear generating surface 9 gradually expanding towards the cutting edges.

Such an embodiment of the longitudinal flutes 8 favours the collection, conveying and expelling of the drillings in the annylar space round the entire perimeter of the face being drilled and eventually adds to the throughput capacity of the longitudinal flutes.

Fig. 6 illustrates one more embodiment of the spiral drill, wherein the longitudinal flutes 8 have an enlarged portion 10 facing the cutting edges 6 and 7 conjugated with the end face of the bit head at the front and back cutting edges, respectively. That is the end of the body has chamfers which slope away from the tip and towards the flutes.

Said embodiment of the longitudinal flutes favours the removal of the drillings from the face when drilling through the medium-hardness rock or materials (such as grade 1 50 concrete).

It becomes obvious from the disclosure set forth hereinbefore that the spiral drill according to the present invention is capable of high drilling speed, reduced vibration, enables simple manufacturing process for making longitudinal flutes in a batch production of said spiral drills having both single-and double-start helical splines for passing the drillings, favourable conditions for expelling the drill cuttings into the annular space between the borehole walls and the bit head surface and for removal of the drillings from the face in case of drilling through medium hardness rock, etc.

Although the present invention has been described hereinabove with reference to some specific embodiments of the proposed spiral drill which are in fact exemplary and illustrative ones and must therefore by no means be considered as limiting the scope of the present invention, so that those skilled in the art may introduce some minor changes and modifications without departing from the spirit and scope of the invention as defined in the appended claims.

Production tests applied to the spiral drills manufactured in accordance with the present invention have demonstrated that the proposed spiral drill provide for accomplishing of the essential object of the invention, viz., an increased drilling speed and reduced vibration imparted to the rotary hammer.

Claims (6)

Claims

1. A drill for drilling holes in material, such as hard rock, comprising at least one spline extending helically therealong for removal of rock drillings, a cross-head working tip and two pairs of diametrically opposed flutes connecting said at least one spline to the tip, each of said flutes extending along a helical path having a helix angle greater than that of the helix angle of said at least one spline, but less than 900.

2. A drill as claimed in claim 1, wherein two helical splines are provided, and the flutes of each pair have the same helix angle which is different to the helix angle of the flutes of the other pair.

3. A drill as claimed in claim 1, wherein a single helical spline is provided, and the flutes are all connected to the spline and all have different helix angles.

4. A drill as claimed in any one of claims 1 to 3, wherein each of the flutes is defined by a concave surface, the side edges of which diverge gradually towards the tip.

5. A drill as claimed in any one of claims 1 to 4, wherein chamfers are provided at the working tip and slope downwardly away from the tip and towards the flutes.

6. A drill substantially as herein described with reference to the accompanying drawings.