Abstract:
A cutter head according to the invention is particularly suitable for breaking relatively hard ground, is self-sharpening and has an extended service life.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a §371 national stage entry of International Application No. PCT/EP2010/059568 filed Jul. 5, 2010, which claims priority from BE 2009/0412 filed Jul. 6, 2009, both of which are hereby incorporated by reference in their entirety, for all purposes herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a cutter head for dredging ground under the water surface, this cutter head being suitable for attachment to the ladder of a cutter suction dredger and for being moved over the ground therewith in a lateral sweeping movement. The invention also relates to a cutter suction dredger provided with such a cutter head, and to the use of the cutter head for dredging ground, in particular relatively hard ground. 
         [0003]    A cutter head of the type described in the preamble is for instance known from NL-1031253. The known cutter head is a revolving body which is rotatable around a central axis and formed by a base ring and a hub placed at a distance therefrom and concentrically thereto, between which extend a number of support arms provided with cutting tools. The known cutting tools are bit-like, which means that they comprise a flattened part at their free outer end, with the end surface of which they make contact with the ground over a determined linear distance. For a good cutting action the cutting tools must be first to come into contact with the ground during rotation of the known cutter head. The cutting tools are therefore situated on a leading part of the support arms as seen in the direction of rotation of the cutter head. 
         [0004]    The cutter head is applied in combination with a cutter suction dredger (also referred to as cutter dredger). A cutter suction dredger comprises a vessel anchored in the ground by means of so-called spud posts. Owing to this anchoring the reaction forces occurring during dredging can be absorbed and transmitted to the ground. Attached to the ladder of the cutter suction dredger is a suction conduit which is connected to the cutter head and along which the dredged ground is removed. During dredging the cutter head is set into rotation and with ladder and suction conduit lowered into the water at a generally oblique angle until it touches the ground. The cutter head is dragged through the ground by hauling the ladder alternately from port side to starboard side using winches. Because the cutter head rotates about the axis of the cutter head—the line connecting the centres of rotation of the base ring and the hub—the end surfaces of the cutting tools strike the ground with great force under the weight of the cutter head, ladder and suction conduit. Via passage openings between the support arms the hereby formed fragments are suctioned up and discharged by the suction conduit. A whole ground surface can be dredged by moving the cutter suction dredger over a determined distance at a time and repeating the above stated sweeping movement. 
       BACKGROUND OF THE INVENTION 
       [0005]    U.S. Pat. No. 4,319,415 discloses a cutter head for a cutter. The cutter head comprises a revolving body that is rotatable around an axis of revolution and which is formed by a base ring and a hub located at a distance thereof, between which a number of support arms extend. The support arms are provided with teeth holders for cutting teeth. The teeth holders have a T-shaped profile with which they can be releasably attached to the support arms. 
         [0006]    WO 2005/035884 A describes a robotic manipulator for removing a worn tooth from a dredger cutter head, and for replacing the removed tooth with a new tooth. The manipulator is installed on a dredger vessel. The disclosed cutter heads are of the usual type including about 5 support arms carrying about 8 teeth each. 
         [0007]    GB-A-2 032 492 discloses a cutter head comprising a central hub onto which at least one spiral-helical web is mounted. The web is provided with an array of cutter bits spaced along the web and projecting therefrom such that in use successive bits on the same web cut deeper than a previous bit. 
         [0008]    NL-A-8 104 969 discloses a conventional cutter head for a cutter suction dredger, the cutter head comprising the usual amount of 5 support arms with about 8 teeth attached to it. 
         [0009]    U.S. Pat. No. 4,470,210 discloses an adapter for a cutter head. The adapter is rotatable around a longitudinal and a transverse axis, such that the optimum cutting angle of the cutting teeth can be adjusted. 
         [0010]    U.S. Pat. No. 4,986,011 discloses a cutting tooth for a cutter dredger that may be attached to a support arm of a cutter head by clamping part of it in an adapter, making use of an intermittent flexible element. 
         [0011]    The known cutter head has the drawback that relatively hard ground, such as for instance rock, defined in the context of the present application as ground with an Unconfined Compressive Strength (UCS) of at least 50 MPa, either cannot be dredged or can only be dredged with limited efficiency. The UCS is a concept known to the skilled person and represents the compressive strength of a ground mass, the side walls of which are not supported during compression. Efficiency is understood in the context of this application to mean the volume of ground dredged per unit of time and unit of power. 
         [0012]    The present invention has for its object to provide a cutter head for a cutter suction dredger which, in addition to other advantages, can dredge ground surfaces more efficiently and which makes it particularly possible to dredge relatively hard types of ground with an increased efficiency relative to the known cutter head. 
         [0013]    According to the invention there is provided for this purpose a cutter head which comprises a revolving body which is rotatable around a central axis and which is formed by a base ring and a hub placed at a distance therefrom, between which extend a number of support arms provided with cutting tools, wherein the cutter head comprises at least 50 cutting tools, which cutting tools are axisymmetrical at least at their free outer end, and preferably along their entire length, thereby allowing free rotation around their longitudinal axis. It has been found that, by providing inter alia the support arms of the cutter head with cutting tools that are axisymmetrical at the soil contact side thereof, relatively hard ground in particular, such as for instance rock, can be dredged with an increased efficiency relative to the known cutter head. The axisymmetry of the cutting tools has been found to have a favourable effect on the breaking of the ground, and particularly relatively hard ground. 
         [0014]    The known cutting tools are relatively wide at their free outer end to be able to withstand the great forces to which they are subjected during the dredging. The weight of the underwater components of the cutter suction dredger is after all distributed over the contact surface area between the cutting tools and the ground. By giving the known cutting tool a relatively wide free outer end this contact surface area is relatively large, whereby the force transmitted to the ground is distributed over a relatively large surface area. The average pressure on the contact surface is thus kept limited, whereby breaking of the cutting tools is prevented. 
         [0015]    Because the cutting tools according to the invention are axisymmetrical at least at their free outer end, and come into contact with the ground with this part, the cutting tools already penetrate the ground at relatively low forces. The pressure exerted locally on the ground is moreover relatively high, whereby the ground, and particularly relatively hard ground, is crushed effectively. 
         [0016]    It should be mentioned that US-A-4 488 608 describes a rotary stone-cutting head for cutting dry rock and the like, the cutting head carrying conical cutting tools, a part of which comprise a hardened (Tungsten carbide) insert. The tools having the inserts are placed in a somewhat retracted position vis-a-vis the other cutter tools to avoid early breakage when coming in contact with an irregular rock surface. 
         [0017]    DE 10 2005 051450 A1 discloses an axisymmetrical cutting tool that can be rotated freely around its axis of rotation symmetry in a case, whereas U.S. Pat. No. 4,575,156 relates to a similar axisymmetrical cutting tool for use in coal mining Both documents do not suggest using such tools in underwater dredging. 
         [0018]    A preferred embodiment of the cutter head has the feature that the cutting tools are rotation-symmetrical, and are more preferably of conical form. Such a geometry allows higher average pressures to be transmitted to the ground than is possible with the known cutting tool. A further advantage of the cutting tool according to the invention, and particularly the conical preferred variant, is that, owing to its shape, it takes up less space than the known cutting tool. It hereby becomes possible to provide the cutter head with a large number of cutting tools, and this has been found advantageous for the dredging efficiency of the cutter head. For the same reason the passage openings which are present between the support arms of the cutter head and along which the dredged ground is discharged can likewise be smaller than is the case in the known cutter head. This is because the cutting tools according to the invention obstruct the passage less. The number of support arms can hereby also increase. 
         [0019]    According to another preferred embodiment of the invention, the cutting tools comprise a substantially cylindrical shank part with a reduced diameter with respect to a conical top part. The cutting tool according to this embodiment is arranged with its cylindrical shank part in coupling means, provided on the arms of the cutter head. The coupling means preferably comprise a block socket with a central bore in which the cylindrical shank part is inserted for ready rotation. In this embodiment, the conical part will protrude outside the block socket over an active length, which is relatively short in comparison with the total length of the cutting tool. This has the advantage that much larger forces can be withstood than with the state of the art cutting teeth. The block socket moreover effectively supports the cutting tool against bending deformations. In a preferred embodiment the cutting tools have a length protruding outside its holder lying between 10 and 500 mm, more preferably between 20 and 250 mm, and most preferably between 50 and 150 mm. 
         [0020]    In a particularly preferred embodiment, the cutting tool is arranged, preferably in its socket, such that it can be rotated freely or at least readily around its axis of rotation-symmetry. This is possible due to the fact that the cutting tools are rotation-symmetric. Allowing free or ready rotation of the tools during operation reduces the risk for breakage and also self-sharpens the soil-contacting tip of the cutting tools by friction with the soil. The useful life of the cutting tools is hereby extended and precious time is saved in not having to replace broken or blunt cutting tools frequently. 
         [0021]    The conical part of the cutting tool is preferably provided with a hardened tip at the outer end which comes into contact with the soil. The tip may for instance be made of carbide. 
         [0022]    In another preferred embodiment the cutter head according to the invention is characterized in that the top part of the conical cutting tools has a radius of curvature of a maximum of 500 mm, more preferably of a maximum of 350 mm, still more preferably of a maximum of 100 mm, and most preferably of a maximum of 50 mm. Yet another preferred variant comprises conical cutting tools, the top part of which has a radius of curvature lying between 1 and 100 mm, and more preferably between 5 and 80 mm. In yet another preferred variant the cutting tools comprise a holder in which a conical hard metal insert is received. 
         [0023]    A preferred embodiment of the cutter head according to the invention has the feature that the cutter head comprises at least 5 support arms, more preferably at least 10 support arms, and most preferably at least 15 support arms. It is even possible for the cutter head to comprise a revolving surface provided with passage openings between the base ring and the hub. The part of the revolving surface lying between the openings then forms the ‘support arms’ of the cutter head. Another option is to provide the cutter head with axially running support arms on which are mounted transverse arms running in the peripheral direction. 
         [0024]    The number of cutting tools can be varied within broad limits, wherein it is advantageous if the number of cutting tools is as high as possible. In a preferred embodiment the cutter head according to the invention comprises at least 100 cutting tools, still more preferably at least 140 cutting tools, and most preferably at least 180 cutting tools. The cutting tools can here be distributed regularly, but also irregularly, over the revolving surface of the cutter head. The number of cutting tools per support arm preferably comprises at least 10 cutting tools, more preferably at least 15 cutting tools, still more preferably at least 20 cutting tools, and most preferably at least 25 cutting tools. 
         [0025]    The cutter head according to the invention cuts the ground in a fundamentally different manner than the known cutter head. Where the known cutter head strikes large fragments out of the ground with great force, the cutter head according to the invention will break off much smaller pieces of ground. Owing to the greater number of cutting tools in the direction of rotation of the cutter head the ground is moreover cut in more rapid succession. This operation is found to result in a higher efficiency, particularly in harder grounds. 
         [0026]    It has further been found advantageous for the support arms to comprise a first series of cutting tools on a leading part as seen in the direction of rotation of the cutter head, and at least one support arm comprises a second series of cutting tools on a part facing away from the central axis. Although it is unusual to provide a part of a support arm facing away from the central axis with cutting tools, an improved efficiency is obtained. It has been found, surprisingly, that the connection of the cutting tools to the part of the support arm facing away from the central axis is sufficiently strong to transmit to the support arm the forces resulting from the cutting tools striking against particularly hard ground such as rock. More cutting tools can in this way be placed on a single support arm than according to the prior art. This provides advantages, particularly in the dredging of relatively hard ground. 
         [0027]    In an advantageous embodiment the cutting tools of the first series on a support arm are offset relative to the cutting tools of the second series. This further increases the efficiency of the dredging process. Because the cutting tools are offset, an increased working area of the cutting tools is obtained. This is because cutting tools of the second series are not obstructed by cutting tools of the first series. 
         [0028]    In yet another embodiment the support arms have a length and the cutting tools are located on either side of the middle of the support arms along a maximum of 80% of the length of the support arm. The absence of cutting tools close to the outer ends of the support arms is not found to adversely affect the efficiency of the cutter head, while owing to this measure the construction of the cutter becomes simpler and therefore cheaper. On the other hand, the presence of cutting tools close to the hub of the cutter head is advantageous for the progression of the cutter head. 
         [0029]    The cutting tools can be formed integrally with the support arms of the cutter head. Another method is to connect them directly to the support arms, for instance by welding cutting tools embodied substantially in steel to support arms manufactured substantially from steel, this resulting in a strong connection. The cutting tools can particularly be connected to the support arms via coupling means. Cutting tools can hereby be replaced easily, which may be necessary as a result of wear or damage. It is advantageous here to connect the coupling means themselves integrally with the support arms, such as by making use of a welded connection. 
         [0030]    In a preferred embodiment of the cutter head according to the invention the support arms of the cutter head are provided with guides on which the coupling means and/or the cutting tools are displaceably mounted. A suitable guide comprises for instance a guide rail over which the coupling means and/or the cutting tools can slide. The present preferred variant has the advantage that the coupling means and/or the cutting tools can be displaced easily. The intermediate distance between the cutting tools can thus be adjusted in simple manner depending on the properties, and in particular the hardness, of the ground. 
         [0031]    The invention also relates to the use of a cutter head according to the present invention for cutting into ground parts a ground with an Unconfined Compressive Strength (UCS) of between 50-200 MPa, preferably between 60-150 MPa and most preferably 80-100 MPa. For the advantages of the use of the cutter head reference is made to the advantages already stated above of the cutter head according to the present invention. 
         [0032]    The invention also relates to a cutter suction dredger provided with a cutter head according to the present invention. With a cutter suction dredger provided with a cutter head according to the present invention ground, and in particular relatively hard ground, i.e. a ground with a UCS of more than 50 MPa, can be dredged with an improved efficiency. 
       SUMMARY OF THE INVENTION 
       [0033]    The invention will now be further elucidated with reference to the following figures and description of preferred embodiments, without the invention otherwise being limited thereto. The figures are not necessarily drawn to scale. In the figures: 
         [0034]      FIG. 1  is a schematic side view of a part of a cutter suction dredger with a ladder attached thereto and provided with a cutter head according to the invention; 
         [0035]      FIG. 2  is a perspective view of a cutter head according to the invention; 
         [0036]      FIG. 3  is a side view of a detail of a cutting tool according to the invention; 
         [0037]      FIG. 4  is a side view of a detail of a cutting tool according to another embodiment of the invention; and 
         [0038]      FIG. 5  is a side view of a detail of a cutting tool according to still another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION 
       [0039]      FIG. 1  shows a cutter suction dredger  1  on which a ladder  2  is mounted pivotally around a horizontal shaft  3 . Ladder  2  is provided with a suction pipe  4  which can suction up the loosened ground parts to a level above water surface  100 , after which they are discharged. Ladder  2  is hauled over the ground surface  9  for dredging or breaking by means of a winch  5  which is arranged on the deck of cutter suction dredger  1  and is provided with a number of swing winches (not shown) and ladder winch  8 . Ladder  2  is provided on the outer end thereof with a cutter head  10  according to the invention. Cutter head  10  can be lowered under water by means of the ladder winch cables  8  and moved during use over ground surface  9  in a reciprocating, sweeping movement from the port side to the starboard side of cutter suction dredger  1  and back. In order to be able to absorb the forces generated here on the ground surface, cutter suction dredger  1  is anchored in the ground by means of a spud post  101 .  FIG. 1  shows the left-hand (starboard) spud post in unanchored position and the right-hand (port side) spud post in anchored position. 
         [0040]    Referring to  FIG. 2 , cutter head  10  according to the invention comprises a revolving body  11  which can be set into rotation around its rotation axis  12  by means of drive means (not shown). Rotation axis  12  herein coincides with the central axis of cutter head  10 . In the shown embodiment revolving body  11  is set into rotation in clockwise direction R as seen from the bridge. Support arms  15  extend spirally between a base ring  13  and a hub  14  located at a distance from base ring  13 , these support arms  15  being connected to base ring  13  and hub  14 . Support arms  15  are here arcuate, wherein the convex sides are directed in the rotation direction R. Base ring  13 , hub  14  and support arms  15  are manufactured substantially from steel. This not only makes cutter head  10  strong but also gives cutter head  10  a great weight, whereby during dredging the cutter head  10  is urged in the direction of the ground for dredging under the influence of the gravitational force. Support arms  15  are herein placed regularly round the periphery of cutter head  10 . Passage openings  16  are located between support arms  15 . Coupling means  17  manufactured substantially from steel are welded to a leading edge  15   a  of support arms  15  relative to the rotation direction of cutter head  10  for the purpose of coupling a first series of cutting tools to support arms  15 . Coupling means  17  likewise manufactured substantially from steel are welded to the edge  15   b  of support arms  15  facing away from the central axis of cutter head  10  for the purpose of coupling a second series of cutting tools  20  to support arms  15 . Coupling means  17  are oriented such that the front side or striking side of cutting tools  20  of the first and second series are directed in rotation direction R. 
         [0041]    Referring to  FIG. 3 , an embodiment of a cutting tool  20  is shown. The shown cutting tool  20  with overall length  27  comprises a substantially cylindrical part  22  with diameter  25 , and a conical second part  23 . Cutting tool  20  can be arranged with cylindrical part  22  in an above described coupling means  17  of cutter head  1 , for instance by means of a snap connection  220 . A permanent connection is also possible, or other form of releasable connection. In the situation where cutting tool  20  is arranged in coupling means  17 , conical part  23  will protrude outside the coupling means or holder  17  over an active length  26 . Conical part  23  of cutting tool  20  is provided with a hardened tip  28  at the outer end which comes into contact with the soil. The appropriate radius of curvature of the tops of cutting tools  20  depends on, among other factors, the properties of the ground and on the specific design of the cutter head, but preferably lies between 1 and 100 mm. A suitable overall length  27  of a cutting tool  20  preferably amounts to between 20 and 400 mm. Suitable transverse dimensions  25  preferably amount to between 10 and 100 mm. In a preferred embodiment the cutting tools  20  have a length  26  protruding outside holder  17  lying between 10 and 500 mm, more preferably between 20 and 250 mm, and most preferably between 50 and 150 mm. 
         [0042]    As shown in  FIGS. 4 and 5 , the cutting tool  20  is preferably coupled to the support arms  15  through coupling means  17  in the form of a block socket with a central bore  170  in which the cylindrical shank part  22  of a cutting tool  20  is inserted for ready rotation. In the embodiment of  FIG. 4 , the conical part  23  with the carbide tip  28  protrudes outside the block socket over an active length that is relatively short in comparison with the total length of the cutting tool  20 . The block socket  17  supports the cutting tool  20  against bending deformations and allows to transfer large compressive forces in the axial direction  171  of the cutting tool  20 . The cutting tool  20  is inserted into the central bore  170  from the left until the snap connection  220  engages a corresponding annular groove  221  in the socket. In the engaged state, the cutting tool  20  is free to rotate around the axis  171  in the central bore  170 , due to the fact that the cutting tool  20  is rotation-symmetric. This rotation may be hindered somewhat by frictional forces between the outer surface of the shank part  22  and the inner surface of the central bore  170 , or between the contact surfaces of socket and conical part  23 , but is essential a free rotation. 
         [0043]    Another embodiment shown in  FIG. 5 , uses a separate holding ring  172  with a slot  173  such that it may be made smaller by compressing it. Once engaged with a corresponding annular groove  221  (as in the embodiment shown in  FIG. 4 ) it expands and leaves the outer surface of the shank part  22  free to rotate. Locking of the cutting tool  20  in the axial direction  171  is accomplished by engagement of the rear part  222  of cutting tool  20  against the annular ring  172 .