Field of the invention

The invention relates to a clamping device for clamping a tool to be drilled into the ground. The invention also relates to an auger and a pile drilling apparatus.

Background of the invention

In various methods for installing bored piles, the tool to be driven into the ground by an auger (e.g. an auger bit or a tube with a drill bit) is rotated and simultaneously in many cases also pressed into the ground during driving the tool into the ground. In order to drive a sufficient length of the tool into the ground, it is necessary to release the grip of the wrench that rotates the tool every now and then, and to move the clamping point between the wrench and the tool. For this reason, the wrench in such apparatuses is normally equipped with a clamping device for clamping the tool, whereby the grip of the tool can be released every now and then and the tool can then be re- clamped at a suitable point, from which the tool can be allowed to sink deeper into the ground than at the preceding stage. Therefore, the clamping device is based on surfaces clamping the tool, whereby upon clamping the tool, the surfaces clamping the tool have to be clamped against the tool by a sufficient force so that the frictional force between the surfaces is sufficient to transmit the driving torque from the wrench to the tool. The grip of the tool has to be releasable after the work has been completed. Thus, the clamping force of the clamping device, effective between the clamping surfaces and the tool, has to be releasable.

Clamping devices of prior art have the disadvantage that the clamping of the clamping members clamping the tool normally requires a hydraulic actuator and a continuous pressure of the pressurized medium effective in it, in order to maintain the necessary clamping force even during the use of the wrench. This is difficult, because the wrench and the clamping device connected to it are normally moved together with the tool to be rotated in its longitudinal direction. Moreover, the tool to be rotated by the wrench and comprising the clamping surfaces rotates with respect to the frame of the wrench. Therefore, the pressurized medium hoses of the hydraulic actuators maintaining the clamping force would be twisted around the tool if they were continuously connected to the actuators pressing the clamping devices against the tool. For this reason, in clamping devices of prior art, the pressurized medium hoses have to be detached from the clamping device for the time of rotation of the tool so that the pressure of the pressurized medium is maintained in the actuators generating the clamping force in the clamping members.

Brief summary of the invention

It is an aim of the invention to provide a novel clamping device for clamping a tool to be rotated by a wrenching device, such as the wrench for an auger in a pile drilling apparatus, which is simpler and more advantageous than before and which does not require continuous pressing of the gripping surfaces by a hydraulic actuator against the tool to be rotated. The objective clamping device of the invention is intended for use particularly in pile drilling apparatuses, but it may also be applied in other such technology areas in which an elongated tool, such as e.g. a bit, a tube, or a tubular auger, is pressed and/or driven by rotating into soil or other material that can be drilled in a corresponding way. The aim of the invention is achieved by a clamping device, wherein the clamping device comprises a self-retarding mechanical tightening arrangement for providing a clamping force in the clamping members clamping the tool, whereby the self-retarding tightening means, tightening the clamping members against the tool, is movable by actuators from a state in which the tool can be fitted between the clamping members, to a state in which the clamping members subject the tool to a sufficiently high clamping force so that the frictional force between the clamping members and the tool is higher than the combined effect of the forces caused by the rotation and pressing of the tool, and wherein said self-retarding tightening means is returnable from this state back to the state in which the tool can be fitted between the clamping members. To put it more precisely, the clamping device according to the invention is characterized by what will be presented in the independent claim 1 , the auger by what will be presented in the independent claim 13, and the pile drilling apparatus by what will be presented in the independent claim 16. Dependent claims 2 to 12 disclose some preferred embodiments of the clamping device according to the invention, and dependent claims 14 and 15 disclose preferred embodiments of the auger according to the invention.

The clamping device according to the invention has the advantage of providing a frictional grip, clamping the clamping members mechanically against the tool, in the tool rotated by the wrenching device so that the maintenance of the clamping force does not require continuous power production by actuators. This simplifies the use of the wrenching device, because the clamping grip of the tool is maintained even if the pressurized medium hoses of the hydraulic actuators tightening the clamping members are removed from the hydraulic actuators tightening the clamping members, so that the pressure of the pressurized medium effective in the actuators drops to zero.

Description of the drawings

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a clamping device in connection with a pile drilling apparatus according to the invention, in a slanted view from the side;

Fig. 2 shows a vertical cross section of the clamping device according to Fig. 1 (that is, in the longitudinal direction of the tool to be installed in the clamping device);

Fig. 3 shows a device for tightening the clamping members to be used in the clamping device according to Figs. 1 and 2, in a slanted view from above;

Fig. 4 shows the clamping members inside the frame of the clamping device in a slanted view from above, the clamping device being detached from the wrench of the auger; and Fig. 5 shows the clamping device in a slanted view from below, the clamping device being moved to a position in which it does not tension the clamping members fitted in the frame of the clamping device.

A detailed description of preferred embodiments of the invention

Figure 1 shows an auger 10 for a pile drilling apparatus, typically configured to move in the longitudinal direction of a rig belonging to the pile drilling apparatus and held in the vertical position or in a slanted position. The auger 10 comprises a wrench 1 1 and a clamping device 12 connected to it by a universal joint, as well as a tool to be drilled into the ground, such as an auger bit or a tube with a drill bit. The clamping device 12 shown in the figures comprises a frame 13, clamping members 14, a tightening means 15 and a transfer means 16, as well as actuators 17 with linear movements for moving the transfer means 16 and thereby the tightening means 15 with respect to the clamping members 14 and the frame 13 of the clamping device 12. In this embodiment, the frame 13 of the clamping device 12 is a sleeve-like plate structure connected to the rotary part 18 of the wrench 1 1 of the auger by a universal joint 19 that allows its turning with possible movements of the symmetry axis of the tool to be rotated. For the clamping members 14, the frame 13 is provided with openings 20, through which the clamping members 14 are configured to extend from the outside to the inside of the frame 13. On both sides of the openings 20, fastening holes 21 are provided for fastening the clamping members 14 to the frame 13 by fastening members 22 provided in the clamping members 14 and allowing the movement thereof. An upper flange 23 and a lower flange 24 are provided in the upper part and the lower part of the frame 13, respectively. The upper flange 23 extends inwards and the lower flange 24 outwards from the side wall 25 of the frame 13. The upper flange 23 and the lower flange 24 secure that the loads (particularly torque) caused by the clamping members 12 and the universal joint 19 on the frame 13 do not subject the frame 13 to deformations that would hamper the operation of the clamping device 12. In this embodiment, six clamping members 14 are provided at regular intervals around the frame. The clamping members 14 comprise transmitting elements 26 which are primarily outside the frame 13, and gripping elements 27 inside the frame 13. The outer surface of the transmitting elements 26 is formed by a guide surface 30 which is wedge-like, seen from the side, so that the guide surface 30 extends farther away from the lower part than the upper part of the transmitting elements 26, seen in the transverse direction in the figure. On both sides of the transmitting elements 26, fastening members 22 are provided, which allow a movement and by which the clamping members 14 are fastened to the frame 13 of the clamping device 12. The gripping elements 27 are connected to the transmitting elements 26 through openings 20 in the frame. The gripping elements 27 are equipped with contact elements 29 formed by curved plate elements inside the frame 13. The contact elements 29 comprise gripping surfaces 31 to be placed against the tool. Their dimension in the circumferential direction is selected so that a sufficient gap is left between each contact element 29 to provide a small clearance between the side edges of the contact elements 29 even when the clamping members 14 are moved to the clamping position (i.e. their first extreme position). Thus, all the clamping force transmitted from the clamping members 14 is applied to the tool remaining clamped between the contact elements 29. In this case, the clamping members 14 are designed for a tool that is a tube or a bar with a circular cross section. However, the size of the contact elements 29 and the shape (curvature) of their gripping surface 31 always depends on the shape of the outer surface and the size of the cross- section of the tool to be clamped (e.g. in the case of a tool with a circular cross-section, its diameter). The guide surface 30 of the transmitting elements 26 is also curved in the direction of the circumference of the frame 13. The radius of curvature is determined as a function of space reservation, processibility, surface pressure, and tensile stress.

The fastening of the clamping members 14 to the frame 13 is implemented by fastening members 22 allowing the movement of the clamping members 14 in the clamping direction (transverse to the rotation axis of the tool). In this case, it is implemented by fastening screws 32 driven between fastening lugs 33 in the transmitting members 26 and the gripping elements 27 inside the frame 13, via fastening holes 21 aligned with these in the frame. The fastening holes 21 provided for the fastening screws 32 in the frame 13 are loose so that the fastening screws 32 and thereby the clamping members are movable by the distance between the fastening lugs 32 in the transmitting elements 26 and the inner surface of the gripping elements 27, in the clamp- ing direction of the clamping members 14. As shown by Figs. 1 and 5, restoring springs 35 are also provided between the fastening lugs 33 and the frame 13. In this case, they are pressure springs which press the fastening lugs 33 in the transmitting elements 26 away from the frame 13. Thanks to this, the clamping members 14 always tend to move outward from the frame 13 (that is, to a position releasing the tool from the clamping) if the tightening means 15 is moved in the direction of its second extreme position (that is, upwards in this embodiment). The function of the restoring springs 35 is thus to provide the return movement of the clamping members 14, whereas the clamping of the tool is performed by moving the tightening means 15 in the direction of its first extreme position by means of the transfer means 16 along the guide surfaces 30 of the transmitting elements 26 of the clamping members 14.

In this embodiment, the tightening means 15 is, as shown in Fig. 3, a circular wedge frame having a conical shape when seen from the side and the shape of a hexagon with curved edges when seen from above. Consequently, curved wedging parts 36 are provided in the area of the angles of the tightening means 15, and straight intermediate parts 37 between them. The radius of curvature of the inside of the wedging parts 36 corresponds to the radius of curvature of the guide surfaces 30 of the clamping members 14. The conical shape, in turn, corresponds to the skew (wedging) of the guide surfaces of the clamping members 14. Thus, when the tightening means 15 is fitted onto the clamping members 14 so that its each wedging part 36 (in this case, 6 parts) comes on top of the guide surface 30 of the transmitting elements 26 of each clamping member (also 6 members), the wedging parts 36 follow the shape of the guide surfaces fairly well. As a result, moving the tightening means 15 in a first direction (i.e. in this case downwards) in the longitudinal direction of the symmetry axis of the tool to be clamped by the clamping members 14, will force the clamping members 14 to move towards the outer surface of the tool (i.e. inwards with respect to the frame) and to be clamped against the tool fitted in the clamping device 12. On the other hand, moving the tightening means 15 in a second direction (i.e. upwards) will release the clamping members 14 to move outward from the frame 13, that is, away from the outer surface of the tool fitted in the clamping device 12 (by the effect of the restoring springs 35 in the fastening members 22 of the clamping members 14). On the lower edge of the tightening means 15, at the intermediate parts 37, specific transfer protrusions 38 are provided for moving the tightening means 15.

When the tightening means 15 is moved in the first direction (i.e. downwards in this embodiment), the first extreme position in which it presses the clamping members 14 through the frame 13 or at least against the tool fitted at the clamping members 14 by a force causing a frictional force between the gripping surfaces 31 of the gripping elements 27 of the clamping members 14 and the tool, sufficient to rotate the tool when it is driven into the ground or corresponding material. When moved in the second direction (i.e. upwards in this embodiment), the tightening means 15 has a second extreme position, in which the clamping members 14 are movable, by the restoring springs 35 between them and the frame 13 of the clamping device 12, so far out of the frame 13 that the gripping surfaces 31 of their gripping elements 27 no longer prevent the movement and rotation of the tool between the clamping members 14.

To make the tightening means 15 self-retarding, the conical shape of the tightening means 15 and the corresponding wedge-like shape of the guide surfaces 30 of the clamping member 14 are smaller than the angle of friction between these surfaces. Thus, the transverse forces caused by the clamping members 14 on the wedge frame 15 cannot, in spite of its slightly conical shape, move it off the first extreme position retaining the clamping members against the tool. Consequently, the wedge frame 15 always remains, with respect to the clamping members 14, in the position to which it was moved by the transfer means 16. The conicality of the tightening means 15 and the wedge-like shape of the guide surface 30 of the clamping members 14 may vary, depending on the quality of the inner surface of the tightening means 15, the material of the tightening means 15, the surface quality of the guide surfaces 30 of the clamping members 14, and the material of the transmitting elements 26 of the clamping members 14. When the tightening means 15 is used for pressing the clamping members 14 against the tool, the tightening means 15 is subjected to a high tensile stress in the direction of its circumference. The curved shape of the wedging parts 36 of the tightening means 15 provides uniform distribution of the tensile stress, and prevents critical tensile stresses formed between the wedging parts 36 and the intermediate parts 37 in view of the strength of the clamping device 12. This has been demonstrated by strength calculations (FEM modelling) for the tightening means 15 and empirical tests supporting the same.

In this embodiment, the transfer means 16 is a ring-shaped transfer frame to be fitted around the tightening means 15. Its lower part is formed of a grooved ring 39 with an L-shaped cross-sectional profile, wherein the horizontal part of the letter L in the profile points in the direction of the symmetry axis of the clamping device (i.e. inwards). A locking ring 40 whose inner diameter is smaller than the L-shaped groove ring 39 but whose outer diameter corresponds to the grooved ring 30, is fastened onto the grooved ring 39 by a removable screw fastening. Thus, the combination of the grooved ring 39 and the locking ring 40 constitutes the transfer means 16 with a C-shaped cross-section, which can be installed (by first removing the locking ring 40 from the transfer means 16) around the tightening means 15 so that the transfer protrusions 38 of the tightening means 15 are locked in the groove formed by the grooved ring 39 and the locking ring 40. Four actuator lugs 41 extend from the outer surface of the transfer means 16 (the grooved ring 39), to which lugs the second end 43 of the actuators 17 with linear movements, moving the transfer means 16, is fastened for moving the transfer means 16 by means of the actuators 17 with linear movements. The clamping device 12 according to Figs. 1 to 5 also comprises the above mentioned actuators 17 with linear movements, which are in this case double-acting hydraulic cylinders. They are driven by pressurized medium which is in this case provided by a hydraulic system supplying pressurized medium to the different actuators of the pile drilling apparatus. Thus, the control of the actuators 17 with linear movements is arranged by means of the hydraulic system of the base machine on which said pile drilling apparatus is mounted.

The actuators 17 with linear movements determine the first extreme position and the second extreme position of the transfer means 16 and thereby also the tightening means 15. In this embodiment, the movable end of each actuator 17 with linear movements is, in the first extreme position, moved from the inside of the cylinder part to the outermost position, and in the second extreme position, entirely inside the cylinder part. It should be noted, however, that in another embodiment of the clamping device according to the invention, similar to this embodiment, the first extreme position and/or the second extreme position of the tightening means may not necessarily correspond to the extreme positions of the movable end of the actuators with linear movements, but the range of movement of the transfer means may be limited by means of some control technique, for example by limit switches, to be shorter than the range of movement of the movable end of the actuators with linear movements.

In an auger equipped with the clamping device 12 according to Figs. 1 to 5, the first end 42 of each actuator 17 with linear movements is fastened to the body 50 of the wrench 1 1 of the auger 10, and the second end 43, in the above mentioned way, to the actuator lugs 41 extending outwards from the outer surface of the grooved ring 39 of the transfer means 16. The fastening implemented by means of the actuator lugs 41 allows the transfer means 16 to turn and to move in the lateral direction with the frame 13 of the clamping device 12. Also, the fastening at the first end 42 of each actuator 17 with linear movements to the body 50 of the wrench 1 1 is implemented with corresponding actuator lugs 44. However, the rotation of the transfer means 16 with respect to the longitudinal axis of the frame 13 of the clamping device 12 (and the tool) is prevented by a specific rotation stopper 45. The rotation stopper 45 is a plate element between the body 50 of the wrench 1 1 and the transfer means 16 (Fig. 1 ), allowing the transfer means 16 to move in the direction of the longitudinal symmetry axis of the tool, but preventing the transfer means 16 from rotating with respect to said axis. For allowing said movement in the longitudinal direction, the connection between the rotation stopper 45 and the transfer means 16 is implemented by means of a retaining hoop 46 so that the retaining element 47 of the rotation stopper 45 on the side of the transfer means 16 is fitted through this retaining hoop 46, whose inner width corresponds to the width of the retaining element 47, as shown in Fig. 1 . Thus, the rotation stopper 45, which is wider at its end on the side of the body 50 of the wrench 1 1 than the retaining element 47 fitted through the retaining hoop 46, as shown in Fig. 1 , prevents the transfer means 16 from rotating with respect to the longitudinal symmetry axis of the frame 13 of the clamping device 12, but allows the movement of the transfer means 16 in the direction of the symmetry axis (i.e. the vertical direction), with respect to the stopper 45. It is important to prevent the rotation, because otherwise the transfer means 16 might rotate with respect to said longitudinal axis of the frame when pressed down by the actuators 17 with linear movements. Such rotating would cause that the transfer means 16 would no longer move the tightening means 15 in the direction of the longitudinal symmetry axis of the frame 13 of the clamping device 12 (and the tool extending through the same) in the desired way, for pressing the clamping members 14 against the outer surface of the tool.

Using an auger 10 for a pile drilling apparatus, equipped with the clamping device 12 of Figs. 1 to 5, it is possible to fasten a tool, e.g. a steel pipe to be drilled into the ground and having a drill bit, to the auger 10. Such a steel pipe can be used as the tool e.g. in driving bored piles into the soil by displacement. Thus, the steel pipe being driven into the ground displaces the soil around it, when sinking into the ground. After the tip of the pipe has reached the desired depth, the tube is provided with reinforcement. After this, fresh concrete is supplied into the pipe, and at the same time, said steel pipe is lifted off the ground. At the drilling stage, it may be necessary to release the grip on the steel pipe every now and then, and to move the gripping point to an upper part of the steel pipe. The clamping device 12 of the auger 10 plays a significant role in this operation, because it makes the drilling of the steel pipe into the ground faster and easier than before.

When the bored pipe is clamped by the clamping device 12 of the auger according to the Figs. 1 to 5, the clamping members 14 of the clamping device 12 are released by moving the tightening means 15 to the second extreme position (upwards) by means of the transfer means 16 and the actuators 17 with linear movements, moving the same. Thus, the restoring springs 35 in the fastening members 22 of the clamping members 14 return the clamping members 14 to their outermost position, whereby the tool, e.g. a steel pipe with a drill bit, is released from the grip of the clamping members 14. After this, the auger 10 and the clamping device 12 connected to its wrench 1 1 can be freely moved around the tool, in a desired direction. For example, if a certain length of the tool has already been driven into the ground and one wants to grip the tool at a different, upper point, the auger 10 is moved along the guide tracks of the rig upwards to the desired point. After the auger 10 has been moved to a suitable point, the tightening means 15 is moved by moving the transfer means 16 by the actuators 17 with linear movements to the first extreme position (i.e. downwards, when drilling vertically into the ground). Thus, the tightening means 15 forces the clamping members 14 to move against the outer surface of the tool, whereby the clamping force locks the tool to the gripping elements 27 of the clamping members 14 and thereby the auger 10 to the frame 13 of the clamping device 12 rotatable by the wrench 1 1 . When moving along the wedge-like guide surface 30 of the transmitting elements 26 of the clamping members 14, the tightening means 15 presses the clamping means 14 against the tool to be clamped by a force that generates a frictional force between the clamping members 14 and the tool, which frictional force is higher than the combined effect of the forces and torques applied on the clamping device 12 by the tool when the tool is drilled into the ground or corresponding material. In other words, a sufficiently firm grip of the tool is obtained, for implementing the desired drilling operation. Because the tightening means 15 is self-retarding in the above mentioned way, the actuators 17 with linear movements for moving the transfer means 16 do not need to have an effective pressure to keep the tightening means 15 moved onto the clamping members 14. As a result, the pressure of the pressurized medium may and should be released, because the pressure between the transfer means 16 and the tightening means 15 is thereby released as well and the tightening means 15 is allowed to rotate freely with respect to the transfer means 16. This is because the outer dimensions of the transfer protrusions 38 in the tightening means 15 are smaller than the groove formed between the grooved ring 39 and the locking ring 40 of the transfer means 16 (i.e. a clearance is formed between these when the effective pressure of the actuators 17 with linear movements is released). After these steps it is possible to continue the drilling of the tool into the ground by rotating the frame 13 of the clamping device 12 by the rotating part of the wrench 1 1 and by simultaneously moving (and, if necessary, pressing) the auger 10 at a corresponding speed along the rig in the direction of drilling of the tool when it is driven by the threading in the drill bit. After the desired drilling of the tool into ground has been completed, the rotating movement of the wrench 1 1 of the auger 10 is stopped. After this, the clamping device 12 may be removed from the tool by moving the transfer means 16 in said second direction (upwards) again, to a point corresponding to the second extreme position of the tightening means. Thus, the transfer means 16 also forces the tightening means 15 to move to said second extreme position, whereby the clamping force applied on the tool by the clamping members 14 is released, and the tool is released from the grip formed by the gripping elements 27 of the clamping members 14. After this, the tool can be gripped at a new desired point again by moving the auger 10 along the rig to the desired point. Now, the tool can be gripped e.g. at a lower point again, if the tool is to be lifted off the ground again, or at a higher point if, for example, the tool still extending upwards through the opening in the centre of the auger 10 is to be driven even deeper into the ground. On the other hand, if the tool is e.g. a tube that is to be left in the ground, the released auger 10 may be moved along the rig to a position above the upper end of the tool, whereby the pile drilling apparatus is released around said tool and may be e.g. moved to a location where the next tool is to be drilled into the ground.

The apparatus according to the invention may be implemented, in many respects, deviating from the example embodiment presented above. The clamping device according to the invention may also be used in connection with apparatuses other than the auger of a pile drilling apparatus, in the case of corresponding clamping of an elongated tool to be drilled into the ground or corresponding material, such as the clamping of various tubes, tubes equipped with a drill bit, bits to be drilled, or the like, when said tool is to be rotated upon driving into said material, and/or when a corresponding method of fastening the tool is needed, whereby the tool has to be fastened by clamping members to the apparatus rotating the tool and driving it into the material to be drilled. The tightening means holding the clamping members of the clamping device in the first or second position may also be different from the wedge frame used in the embodiment shown in Figs. 1 to 5. The tightening means may consist of, for example, a mechanism in which the clamping members are forced against the tool to be held in place with respect to the frame of the clamping device, by means of a bar, a lever or the like in contact with the guide surfaces of the clamping members tensioned by screws, a worm gear and gear racks, or wedges for each clamping member. In another embodiment similar to Figs. 1 to 5, a tightening means may be provided, which is moved by a transfer means threaded in an auxiliary frame connected to the wrench and rotated by an actuator placed in the body of the wrench and generating a rotary motion. Furthermore, there are also other alternatives for implementing a self-retarding tightening means. Thus, the number of actuators used for moving the transfer or tightening means may vary, i.e. be one or more.

The other parts of the clamping device may also be implemented in a way different from the example embodiments shown in Figs. 1 to 5. For example, the number of clamping members may vary. However, particularly in the case of a tubular tool, it is preferable to provide three or more clamping members, because the grip of the tool thus does not distort its cross-sectional shape. This improves the strength of the tubular tool having a circular cross-section, because distortion of the shape of the tubular tool reduces its torsional stiffness.

In embodiments similar to Figs. 1 to 5, the wedge-like shape of the outer surface of the guide parts of the clamping members, as well as the direction of the wedge shape, may vary. In some cases, the first position of the tightening means (i.e. the position in which the tightening means forces the clamping members to be pressed against the tool) may be achieved by moving the tightening means from below upwards (i.e. for example by pulling by actuators fastened to the frame of the auger). Thus, the direction of the wedge shape of the guide surface should be opposite to that in the embodiments of Figs. 1 to 5. Furthermore, the movable fastening of the clamping members and the gripping surfaces of the clamping part may be implemented in a variety of ways. Instead of fastening with fastening screws and restoring springs, it would be possible to apply, for example, bars fastened to the structures of the frame and sleeves fastened to the clamping members, configured to be movable along bars fastened to the frame. In the embodiment according to Figs. 1 to 5, the restoring springs 35 of the clamping members could be replaced by mechanical control. Thus, the tightening means 15 consisting of a wedge frame is provided with a second wedge surface configured to keep the inner surface and the guide surfaces of the tightening members against each other when the tightening means is moved from its first extreme position in the direction of its second extreme position (i.e. in the second direction). As a result, the clamping members 14 would move away from the tool without the restoring springs 35 provided in the embodiment shown in Figs. 1 to 5. In other words, the clamping device according to the invention is not limited to the example embodiments presented above, but it may vary within the scope of the appended claims.