Patent Description:
CSD's typically use a suction tube with a cutter head at the suction inlet. The cutter head may be connected to the dredger with a hub that is mounted on an axis with a drive to rotate the cutter head. The axis of rotation is referred to as the axial direction of the cutter head. The cutter head and suction inlet may be moveable with respect to the water bed being dredged. In order to draw the material into the suction tube, a wear-resistant pump may be provided, for example, a centrifugal pump. The material cut by the cutter head that has been drawn into the suction tube may then be transported away from the CSD, for example, by a floating pipe line to a dumping location.

A prior art cutter head is shown in <FIG>. Cutter head <NUM> includes a base ring <NUM> and a hub <NUM>, with backplate <NUM> which includes a suction opening (not shown). The hub <NUM> and base ring <NUM> are connected by a plurality of arms <NUM> extending in an axial direction. The arms <NUM> may be curved in a tangential and radial direction such that the arms spiral toward each other. In other cutter heads, the arms may be curved in the radial direction only, while being axially aligned or at a small angle with respect to the axial direction. Each arm <NUM> must be connected to the base ring <NUM> and to the hub <NUM>, typically by welding. The cutter head <NUM> may additionally be provided with different excavating tools <NUM>, for example, teeth in the shape of chisels or another shape to assist in the excavation. These cutting tools <NUM> can be attached to the arms <NUM>. The back plate is secured to a non-moving part such as a ladder, and does not rotate with the cutter head <NUM>, but instead forms a surface to expose the suction mouth to the material cut by the cutter head <NUM> as the cutter head <NUM> rotates.

During the excavation process of a cutter suction dredger, not all material cut by the cutter head will be sucked up directly by the suction mouth. This process is referred to as spill. The consequence of spill is that it lowers the production rate since the density of the mixture set by the cutter head suction mouth will lower due to sucking in additional water and less cut material. Spill also increases the time required for a given excavation depth as the spilled material needs to be removed by additional sweeps.

Other examples of cutter heads are provided in Japanese utility models <CIT>, <CIT> and <CIT>. Patent publication <CIT> discloses a dredger.

According to a first aspect of the invention, a cutter head arranged to rotate about an axis of rotation for removing material from a water bed comprises a base ring positioned with respect to the axis of rotation; a hub positioned with respect to the axis of rotation; a plurality of arms extending between the base ring and the hub, the arms comprising a plurality of cutting tools; and a plurality of skirts, each skirt extending from one of the plurality of arms to the hub to form a closed surface between the arm and the hub from a distal end of the cutter head toward the base ring and ending with a side configured to be parallel to a backplate that is angled toward the distal end of the cutter head from the base ring, leaving an open channel between the skirt and the backplate.

Such a cutter head with a plurality of skirts can result in more efficient dredging operations with less spill. The skirts form closed channels from the distal end of the cutter head toward where the cut material will be suctioned, helping to retain more of the cut material and send it toward the suction opening. Additionally, this helps to prevent the inflow of additional water with the cut material, resulting in increased production rates.

According to an embodiment, each skirt is shaped with a pitch angle. Optionally, each skirt is propeller shaped. Such configurations for the skirts can help to move the cut material toward the backplate where it will be suctioned, thereby helping to minimize spill in the dredging process.

According to an embodiment, a skirt extends between each of the plurality of arms and the hub to form a closed surface between each arm and the hub. By having a skirt extending between each arm and the hub, closed channels are formed between each arm and hub. This configuration can further increase the resistance to spillage.

According to an embodiment, the skirt extends over <NUM>-<NUM>% of each arm length from the distal end toward the base ring. The extent of the skirt can help to resist spillage over a large amount of the cutter head.

According to an embodiment, the arms extend rotatingly from the base ring to the hub. This configuration can help with the cutting ability of the cutter head.

According to an embodiment, the plurality of skirts comprise the same material as the plurality of arms. Optionally, the arms and the skirts could be formed integrally. By forming the arms and skirts of the same or similar materials, they will be able to equally withstand forces from cutting operations, and would generally require similar maintenance routines, making the overall cutter head more simple to maintain.

According to an embodiment, the cutter head is a part of a vessel with a ladder. Optionally, the vessel could be a cutter-suction dredger. Such a vessel with a cutter head would have more efficient dredging operations as the cutter head would result in less spillage and a more dense mixture being cleared and suctioned to the vessel.

According to an embodiment, the vessel further comprises a backplate secured to the ladder and extending between the base ring and the hub at a position to form the open channel with the skirts. The backplate comprises a suction opening. Such an arrangement forms an open channel between the skirts and the backplate which helps to funnel the cut mixture into the suction opening from the closed channels between spill skirts. Optionally, the height of the channel between the backplate and the skirt is between about <NUM>% and <NUM>% of the diameter of the base ring, and can depend on the size of the cutter head and the material to be cut amongst other factors.

According to an embodiment, the backplate is angled toward the distal end of the cutter head from the base ring. In such an embodiment, the end of the skirt would also likely be angled such that the height of the channel stays the same.

According to a further aspect of the invention, a method of forming an assembly of a cutter head with skirts and a backplate comprises obtaining a cutter head comprising a base ring, a hub, a plurality of arms extending between the base ring and the hub, and a plurality of cutting tools on the plurality of arms; obtaining a backplate; and connecting a plurality of skirts to the cutter head to form closed channels between at least some of the plurality of arms and the hub from a distal end of the cutter head toward the base ring ending with a surface configured to be parallel to a backplate and leave an open channel between the backplate and each skirt. Such a method can form a cutter head that minimizes spillage and increases the efficiency of a dredging operation.

According to an embodiment, the step of connecting the plurality of skirts comprises welding the plurality of skirts to the plurality of arms and to the hub. Welding can provide an effective means of connecting the skirts after they have been manufactured separately. Manufacturing skirts separately can be a simpler method of manufacture, particularly when the skirt will have a complex shape and/or bend.

According to an embodiment, the plurality of skirts are integrally formed with the plurality of arms, and the step of connecting a plurality of skirts comprises connecting a plurality of skirts to the hub to form closed channels between at least some of the plurality of arms and the hub from a distal end of the cutter head toward the base ring ending with a surface configured to be parallel to a backplate and leaving an open channel between the backplate and each skirt. Forming the plurality of arms integrally with the plurality of skirts ensures a strong connection between the arms and skirts for cutting operations.

According to an embodiment, the method further comprises connecting a plurality of cutting tools to the plurality of arms. Connecting cutting tools to the plurality of arms can ensure that the cutter head is able to effectively cut a bed, particularly when that bed is hard.

According to an embodiment, the step of connecting a plurality of skirts to the cutter head comprises connecting a skirt to form closed channels between each of the plurality of arms and the hub. Connecting a skirt to each arm to form a closed channel between each of the arms can ensure a very high resistance to spillage during a dredging operation with the cutter head.

According to a further aspect of the invention, a skirt for a cutter head comprises a rigid body configured to connect between an arm and a hub of a cutter head and extend from the distal end toward a backplate. Such a skirt can be connected to an existing cutter head to increase the resistance of spillage of such a cutter head.

According to an embodiment, the skirt is shaped to encourage flow from the distal end toward the backplate. The shape can be, for example, with a pitch angle, curve, propeller shape, and/or tapering thickness.

<FIG> shows a side view of a cutter head <NUM>, with base ring <NUM>, hub <NUM>, backplate <NUM> with suction opening <NUM>, arms <NUM>, cutting tools <NUM> and spill skirts <NUM>. <FIG> shows a back view of cutter head <NUM>, with backplate <NUM> removed, and <FIG> shows a side view of cutter head <NUM>, with arms <NUM> and base ring <NUM> removed.

Arms <NUM> extend between base ring <NUM> and hub <NUM>. Cutting tools <NUM> extend from arms <NUM> and can be formed integral or can be attached. Cutting tools <NUM> can take many different forms. Backplate <NUM> connects to a stationary part, for example, a ladder (see <FIG>).

Spill skirts <NUM> each connect to hub <NUM> and to one arm <NUM>, extending from distal end <NUM> toward base ring <NUM> to form a closed surface between arms <NUM> and hub <NUM>. This forms closed channels between adjacent arms <NUM> with spill skirts <NUM>. Spill skirts <NUM> end with a side <NUM> parallel to back plate <NUM>, and leaving an opening <NUM> between skirt <NUM> and backplate <NUM>. These openings <NUM> form a channel between skirts <NUM> and backplate <NUM>. The opening can be based on the diameter of the base ring <NUM>, and can be about <NUM>%-<NUM>% of the diameter of the base ring <NUM>.

Spill skirts <NUM> can be formed integral with arms <NUM> or can be formed separate, and connected to arms <NUM> and hub <NUM>, for example, by welding. Each spill skirt <NUM> is shaped with a propeller shaped pitch angle to influence flow, though in other embodiments skirts <NUM> may be shaped differently. Skirts <NUM> can be made of the same material as arms <NUM> or a different durable material (e.g., iron), and can extend over <NUM>% - <NUM>% of each arm length.

Cutter head <NUM> can be connected to a vessel, for example dredger <NUM>, shown in <FIG> for excavation. Cutter head <NUM> is connected to ladder <NUM>, and is used to cut hard surface materials, such as rock. Hub <NUM> is connected to and driven by a drive shaft (not shown) to rotate cutter head <NUM> around its axis of rotation RA. The cut material is then guided along closed channels between spill skirts <NUM> toward backplate <NUM>, where it will enter suction opening <NUM> and be transported away from cutter head <NUM>.

As mentioned in the background, the open space of the interior of prior art cutter heads lead to cut material more easily escaping from the cutter head before entering the suction opening. By closing the space between arms <NUM> with spill skirts <NUM>, cutter head <NUM> helps to minimize this spillage when performing a cutting operation. The cut material is guided toward the open channel between spill skirts <NUM> and backplate <NUM> by spill skirts <NUM>, thereby ensuring more of the cut material is suctioned through suction opening <NUM> when the suction opening passes by. This reduces water ingestion from the surroundings, and therefore ensures that the dredging mixture is higher in density and that entire dredging process is more efficient by requiring fewer sweeps to remove the desired amount of material.

The shape of spill skirts <NUM>, for example, spill skirts <NUM> with a pitch angle resembling a propeller shape can help further reduce spill. The shape can assist in accelerating cut material away from distal end <NUM> towards the area which will pass by suction opening <NUM>.

By using spill skirts <NUM> to minimize the cut material that spills out of cutter head during a cutting process, cutter head <NUM> helps to increase the density of the suctioned mixture and ensure that the overall dredging process is more efficient.

Cutter head <NUM> can be formed from prior art cutter heads by adding spill skirts <NUM> as described in relation to <FIG>. They can be incorporated, for example, by welding spill skirts <NUM> to a prior art cutter head. This can make for an economical way of improving dredging efficiency by reusing older cutter heads, and making them more efficient for a dredging process.

In summary, the addition of a plurality of spill skirts <NUM> help to retain cut material for suctioning through a suction opening <NUM>. Spill skirts <NUM> assist in retaining material in the closed channels between spill skirts <NUM> and hub <NUM>, thereby reducing spill. The open channel formed between spill skirts <NUM> lower side <NUM> and backplate <NUM> retain material for suctioning through suction opening <NUM> as cutter head <NUM> rotates, increasing production rates by minimizing spill of cutter head <NUM>.

While spill skirts <NUM> are shown as connected between every arm <NUM> and hub <NUM> in cutter head <NUM>, in other embodiments, cutter head <NUM> could have fewer spill skirts <NUM>, for example only forming channels between every other arm <NUM> as long as it was symmetrical around the axis of rotation. Using spill skirts with fewer than each arm <NUM> can help to decrease the weight of overall cutter head <NUM>, making movement and production easier and less expensive.

Spill skirts <NUM> can vary in thickness, from the thickness of the arms <NUM> to much less depending on the needs for cutter head <NUM>.

Claim 1:
An assembly comprising a cutter head (<NUM>) arranged to rotate about an axis of rotation (RA) for removing material from a water bed and a backplate (<NUM>) connectable to a vessel, the cutter head (<NUM>) comprising:
a base ring (<NUM>) positioned around the axis of rotation (RA); and
a hub (<NUM>) positioned to rotate the cutter head (<NUM>) about the axis of rotation (RA);
a plurality of arms (<NUM>) extending between the base ring (<NUM>) and the hub (<NUM>), the arms (<NUM>) comprising a plurality of cutting tools (<NUM>); and
a plurality of skirts (<NUM>), each skirt (<NUM>) extending from one of the plurality of arms (<NUM>) to the hub (<NUM>) to form a closed surface between the arm (<NUM>) and the hub (<NUM>) from a distal end (<NUM>) of the cutter head (<NUM>) toward the base ring (<NUM>),
characterized in that each skirt is ending with a side (<NUM>) configured to be parallel to the backplate (<NUM>) that is angled toward the distal end (<NUM>) of the cutter head (<NUM>) from the base ring (<NUM>), leaving an open channel (<NUM>) between the skirt (<NUM>) and the backplate.