Drilling apparatus especially for ground drilling

Abstract

Ground drilling apparatus where a drill unit is operated from within a casing pipe which is sunk into the hole drilled by the drill unit, the hole being wider than the casing pipe. The casing pipe is pulled without rotation into the hole by a drill bit of the drill unit. The drill bit includes a pilot bit having an axis which coincides with the center line of the drill hole and is parallel to and separate from the central axis of the drill unit which is the line of action of the percussion force.

Description

The present invention relates to drilling apparatus for drilling in the ground where a drill unit having a drill bit is driven by driving means and coacts with a casing pipe which is sinkable into a hole drilled by the drill unit, the hole having a diameter at least equal to the outside diameter of the casing pipe. The drill unit is guidable in the casing pipe and retractable into it and has a central axis substantially parallel with but spaced from the center line of the drill hole, the central axis being the line of action for a percussion force from the driving means to the drill unit in the working position of the latter.

When drilling holes in the ground, the problem often arises that the wall of the hole collapses, partly or completely filling the hole. In order to avoid this it has been a practice to feed a casing pipe into the drill hole as drilling takes place. The difficulty with this is in getting the casing pipe down the hole without using too much force. Inn loose soils having fine structure, it is possible to let a drill make a hole the same size as the inner diameter of the casing pipe, and simply force the casing pipe down the hole by blows and/or turning from somewhere above ground level. In more stony ground it becomes necessary to be able to drill a hole with a larger diameter than that of the outside diameter of the casing pipe, in order to allow the passage of the casing pipe unhindered by stones.

This problem has been solved by, among other methods, having a drill unit eccentrically mounted in the casing pipe, the drill unit being retractable into the casing pipe, but means for driving both the drill unit and the casing pipe have been placed above ground as before. The shaft connection which would then be necessary between drill unit and driving means gives rise to large percussion force transmission losses due to elasticity, play, etc., especially for deep holes. Force transmission losses are also significant for the casing pipe, due to its elasticity, and the casing pipe must be fairly heavy as well to withstand any compression loads which might arise. A further disadvantage of placing the driving means above ground is the noise problem thus created.

The object of this invention is to eliminate the above mentioned disadvantages, and construct a drilling apparatus which makes the successive introduction of the casing pipe into the drill hole simple and effective, while still maintaining good drill control.

A further object is to accomplish a drilling apparatus which works quietly and has small force transmission losses.

The drilling apparatus according to the invention is characterized in that the casing pipe is pullable without rotation into the hole drilled by the drill bit, and in that the drill bit has a ring bit from which protrudes downwards a pilot bit, the central axis of which conincides with the center line of the drill hole and is parallel to and spaced from the central axis of the drill unit and the line of action of the percussion force.

According to an especially advantageous embodiment, the casing pipe is constructed to house the driving means, which is so arranged as to operate the drill unit at the lower part of the casing pipe. Because the casing pipe is pulled into the drill hole, a thinner and lighter casing pipe than those previously used may be employed, and thereby less force will be required to pull the casing pipe down. Also, by placing the driving means in the casing pipe, the driving means does not have to set in motion a long shaft connection, and the whole drive force can thus be concentrated on the drill unit, thereby maximum the efficiency of the apparatus. This position of the driving means also makes effective silencing possible. By providing the drill bit with a special pilot bit, the whole drill unit will revolve about the central axis of the pilot bit, in this way facilitating guidance of the drill unit. At the same time, the percussion force from the driving means is directed along the central axis of the drill bit, thus eliminating slanting loads.

According to a further advantageous embodiment of the invention, the lower end of the casing pipe has a driving shoe provided with a supporting surface designed to coact, for pulling down the casing pipe, with engaging means arranged around the periphery of the drill unit and shaped to fit against the supporting surface. The supporting surface is shaped as a portion of the surface of a truncated cone having a downwardly directed apex to form a guiding surface whereby the drill unit is guided in the casing.

By providing the pipe casing with a driving shoe, it will be found that the casing pipe itself can be made even thinner and consequently cheaper and lighter, while the risk of damage to the lower end of the casing pipe is diminished. With the combined guidance of the supporting surface of the driving shoe and the pilot bit, the drill unit receives simple and effective guidance while not taking up space in the casing pipe.

Further advantages and advantageous embodiments of the invention may be seen from the appended description and claims.

In the following, the invention is explained more closely with the help of an embodiment example shown on the appended drawings in which:

FIG. 1 schematically shows a drilling apparatus in which the drill unit according to the invention is a part,

FIG. 2 shows a longitudinal section through the drill unit according to the invention,

FIG. 3 shows the drill unit according to FIG. 2 seen from below, and

FIG. 4 shows a section along the line IV--IV in FIG. 2.

The drilling apparatus 1 shown in FIG. 1 includes a casing pipe 2 guiding a drill unit 3, which is connected with and operated by driving means 4, preferably in the form of a sinker drill lowered into the casing pipe. The drill unit 3, as may be seen in FIG. 2, has two portions united to each other, an adaptor portion 5 and a drill bit 6, the drill bit 6 supporting a cutting unit 7 protruding from casing pipe 2. The cutting unit 7 in turn includes a ring bit 8 and protruding from this a pilot bit 9. A driving shoe 10 is attached to the lower portion of the casing pipe 2, the inside diameter of the shoe being larger than the diameter of the cutting unit 7, so that it is possible for the cutting unit to pass through the driving shoe, and to withdraw the whole of the drill unit 3 into the casing pipe 2. The drill unit 3 is guided in the casing pipe 2 by engaging means 11 that are arranged around the periphery of the drill bit 6 and rest against a supporting surface 12 on the upper part of the driving shoe 10, so that the central axis 13 of the drill unit 3 which is directed through the center of the cutting unit 7, is essentially parallel with but spaced from the center line 14 of the drill hole. The central axis 13 coincides with the central axis of the adapter portion 5 and is the line of action for a percussion force exerted on the drill unit 3 by the driving means 4.

The pilot bit 9, the center of which coincides with the center line 14 of the drill hole (see also FIG. 3), has a diameter which is less than that of the ring bit 8, and is removably attached to it. When in operation, the drill unit 3 will revolve about the center line of the pilot bit 9, and rotate about the central axis 13 so that the point 15 on the ring bit 8 will thereby move around the periphery of a drill hole, the diameter of which is made at least as great as the outside diameter of the casing pipe 2.

The adapter portion 5, which acts to transmit driving force from the driving means 4 to the drill unit 3 has, in the embodiment shown here, the shape of a generally cylindrical shaft, which in its lower end is provided with a substantially spherical ball 16. The ball 16 is housed in a recess 17 in the drill bit 6, and is retained in the recess by a retaining sleeve 18 encircling the adapter portion 5 and screwed or attached in some other way to the drill bit 6. In the position shown in FIG. 2 the ball 16 rests in the bottom of the recess 17 and is supported by a seat 19, the shape of which conforms to the shape of the ball thereby providing a large area for transferring percussive force. From FIG. 4 it may be seen that the ball 16 is provided with two substantially planar side surfaces 20, mutually parallel and parallel also to the longitudinal axis of the adapter portion 5. Side surfaces 20 each abut and act against locking plates 21 (shown with dotted lines in FIG. 2), in the drill bit 6.

By pulling the adapter portion 5 upwards, the side surfaces 20 are pulled along the locking plates 21 until the lower part of sleeve 18 comes into contact with the ball 16, arresting its continued motion upward. Upon continued pulling, with the adapter portion 5 remaining in its vertical position, the drill bit 6 will pivot in relation to the adapter portion as the ball 16 is pulled towards a lifting surface 22, which is part of the confining wall of the recess 17. The hole through the locking sleeve 18 is, as shown in FIG. 2, so shaped that it allows the drill bit to pivot relative to the adaptor portion around an axis essentially perpendicular to the longitudinal axis of the adapter portion. The pivoting movement described makes it possible to pull the whole drill unit 3 into the casing pipe 2 from the working position shown. The adapter portion 5 and the drill bit 6 remain, because of the locking plates 21, in continuous torque transmitting engagement with each other, and the drill bit can therefore be rotated the whole time to facilitate withdrawal or lowering of the drill unit.

The adapter portion 5 is provided with at least one longitudinal duct 23 for conducting compressed air from the driving means 4. The duct 23 terminates on the lower side of the ball 16, and from there transfers compressed air via a collecting duct 24 to at least one duct 25, and also to a duct 26 which opens into a longitudinal duct 27 through the pilot bit. From each of the ducts 25 and 27 there are a number of tranched ducts 28 and 29 which terminates on the lower sides of the crown ring bit 8 and the pilot bit 9 respectively, and which conduct the compressed air so that it may cool drilling teeth 30. The compressed air ejected from said ducts takes away drilling dust via openings 31 between engaging means 11.

To prevent foreign matter entering the recess 17, the sleeve 18 is provided with a ring seal 32, but it would also be possible to dispense with the seal 32 and to instead introduce, through one or more ducts in the adapter portion 5, comprssed air into recess 17, and let the air escape through the space between the adapter portion 5 and the sleeve 18. It would also be possible to arrange in the drill bit 6 compressed air ducts connected to the collecting duct 24 and to locate the mouths of these ducts adjacent the upper surface of the sleeve 18, thereby keeping the juncture between the sleeve and the adapter portion clean. It would of course, also be possible to use a combination of seal and introduction of compressed air.

Because the supporting surface 12 of the driving shoe 10 forms a section of the surface of a cone having a downwardly directed apex and as the engaging means 11 are shaped in a corresponding manner, the drill unit is simply and quickly guided to its correct working position in the casing pipe. A certain deformation of the supporting surface 12 is permitted, as it is normal practice to leave the casing pipe behind in the drill hole, there thus being no need to use the driving shoe again. The lower portion of the driving shoe can, if so desired, be equipped with cutting bits, but as a rule this is not necessary. By allowing the driving force on the casing pipe to be applied via the driving shoe, at the lower end of the casing pipe, a tensional load is applied to the pipe walls, and they can therefore be made thinner than a casing pipe that is pressed down by a force applied to the upper end of the casing pipe. If it is required, the casing pipe can also be given a certain degree of rotational movement by a suitable design of the driving shoe and support, or in some other way.

To drill a hole, the operation is begun by placing the casing pipe with its driving shoe against the ground. Then the drill unit and the driving means are lowered into the casing pipe so that the drill bit touches the ground (if necessary, the drill unit can be rotated slightly so that the drill bit can get through the driving shoe). Then the casing pipe is raised so that the engaging means 11 engage the support surface 12 and the ball 16 comes to rest against the seat 19. The casing pipe is then aimed in the right direction and drilling can begin. With the help of valves operated by the adapter portion, or in some other way not shown, it is advantageous to arrange that the adapter portion 5 not be subject to percussion force from the driving means 4 before the ball 16 really rests against the seat 19. This is to avoid possible damage to the casing pipe or the driving shoe upon displacement of the drill unit. Both the pilot bit 9 and the adapter portion 5 are suitably provided with teeth or the like to obtain torque transmitting engagement with the ring bit and the driving means respectively.

When drilling holes in certain types of ground it may be desirable to introduce a liquid stabilizer into the drill hole, and this can suitably take place using the described compressed air ducts or possibly special ducts. The invention described here can naturally be modified in a number of different ways by one skilled in the art within the scope of the following claims.

Claims

What is claimed is:

1. Apparatus for drilling a hole in the ground along a center line comprising

a casing pipe adapted to be disposed in the hole,

a drill unit received in said casing pipe and having an adaptor portion and a drill bit and a central axis parallel to and spaced from the center line of the hole,

driving means inside said casing pipe supplying torgue and percussive force to said drill unit through said adaptor portion and along the central axis of said drill unit,

a generally cylindrical driving shoe attached to the end of said casing pipe and having on its inner side a supporting surface in the general form of a downwardly directed truncated cone, and

engaging means on said drill unit engaging the supporting surface of said driving shoe to pull said casing pipe into the hole without rotation as the hole is drilled,

said drill bit including a ring bit with its center at the central axis of said drill unit and extending beyond said casing pipe to drill a hole wider than said casing pipe and a pilot bit extending from said ring bit with its center at the center line of the hole.

2. Drilling apparatus as claimed in claim 1 wherein

said drill bit is pivotable relative to said adaptor portion so that it may be withdrawn into said casing pipe, and

said engaging means acting on the supporting surface of said driving shoe causes said drill bit to assume its working position as it is extended from said casing pipe.

3. Drilling apparatus as claimed in claim 1

wherein ducts are provided through said adaptor portion and through said drill bit so that compressed air can be introduced through said drill unit to the drilling surface.

4. Apparatus for drilling a hole along a center line comprising

a casing pipe adapted to be disposed in the hole,

a drill unit received in and guided by said casing and including an adaptor portion and an drill bit,

driving means received in said casing pipe and supplying torgue and percussive force to said drill unit through said adaptor portion,

locking means on said drill bit preventing relative rotational movement between said adaptor portion and said drill bit but allowing pivoting of said drill bit relative to said adaptor portion,

said drill bit including a ring bit and a pilot bit extending therefrom, said ring bit extending outward beyond said casing pipe, and

engaging means on said drill bit to engage said casing pipe to pull it into the hole without rotation,

characterized in that it has a working position in which it extends out from said casing pipe and a retracted position inside said casing pipe and in that in said working position said adaptor portion, and said drill bit have a common central axis parallel to and spaced from the center line of the hole and that in the retracted position said drill bit pivots relative to said adaptor portion to allow said drill bit to be withdrawn into said casing pipe.

5. Apparatus for drilling a hole as claimed in claim 4 wherein

said adaptor portion has two ends, a first end operated by said driving means and a second end receiving in said drill bit,

said second end of said adaptor portion has thereon a generally spherical ball having flattened surfaces on opposite vertical sides, and

said locking means on said drill bit abut said flattened surfaces on said ball so that torque is transmitted from said adaptor portion to said drill bit.

6. Apparatus for drilling a hole as claimed in claim 4 wherein

a driving shoe is attached to said casing pipe and has an inner supporting surface in the form of a downwardly pointing truncated cone and

said engaging means engage the supporting surface on said driving shoe to pull the casing pipe into the hole.