The present invention relates to a dredge cutterhead used to remove material from harbors, shipping channels, and other marine environments and mining operations.
Dredge cutterheads are generally hemispherical with a multiplicity of hard rock cutting teeth or replaceable edges projecting outwardly from helical support arms or blades disposed about the hemispherical surface of the cutterhead. An example of such a dredge cutterhead is disclosed in Bowes, Jr., U.S. Pat. No. 4,891,893. The cutterhead has a hub which fits around a shaft that provides the torque for turning the cutterhead in its operation of dredging. The cutterhead encounters all kinds of materials, including rock, sand and clay which must be removed from the bed being dredged.
Conventional cutterhead arms are shaped to minimize wear, but are not designed to move material. However, one of the problems encountered by cutterheads is that the material loosened by the cutting teeth must be directed into a suction pipe in order to be removed from the bottom of the waterway. As the cutterhead moves across the waterway bottom, the cutting teeth dig below the bed to loosen material. Unfortunately, a substantial portion of the material loosened by the cutting teeth does not reach the suction mouth, which is generally located adjacent to the lower side of the ring of the cutterhead. Instead, some of the loosened material quickly falls off the trailing edge of the digging arm and tumbles onto the following arm. When the cutterhead is operated at a steep ladder angle (for example as shown in
The result is that the finished bed depth provided by the dredge cutterhead is often limited to the depth of the mouth of the suction pipe, rather than the depth of cut achieved by the cutting teeth. Since the dredge cutterhead itself is large and is often operated at an inclined ladder angle during use, the difference between the depth of cut achieved by the cutting teeth and the depth of the suction mouth may be as large as three to four feet. Accordingly, in order to achieve a specified finished bed depth, it is often necessary to cut into the bed substantially below the specified finished bed depth so that a sufficient amount of material may be removed. This results in additional time and effort needed to achieve a specified finished bed depth.
One attempt to direct material inwardly from the cutterhead to the suction pipe is disclosed in Fray, U.S. Pat. No. 2,090,790, which discloses a rotary cutter comprised of a plurality of blades. The body of each blade extends substantially in the line of a helix taken around the center of rotation, and the cut material accumulates within the space defined by the cutting blades, to be discharged into the usual suction pipe. Each blade provides a plurality of rib formations which are intended to propel movement of the earth or other materials being handled to the suction pipe.
Another attempt to move dredged material is disclosed in Shiba et al., U.S. Pat. No. 4,702,024, which discloses scoop-in plates 7 coupled between helical vanes 3 and a ring 24. Earth and sand are scooped in by means of the scoop-in plate 7 so as to be directed toward the suction tube 5. However, the vanes themselves do not capture material so as to move the material toward the scoop-in plates.
Another dredge cutterhead has involved adding at the upper portion of the arm a wall at a sharp angle following a conventionally shaped cutterhead arm. The lower portion of the arm was shaped like that of a conventional cutterhead. Cross-sections of the arm of this prior art cutterhead are shown in
What is therefore desired is a dredge cutterhead that efficiently captures the loosened material within the cutterhead, that moves the dredged material to the mouth of the suction pipe, that supports and allows for the easy replacement of standard cutting teeth, and that is capable of withstanding the extreme forces encountered during dredging without breaking or becoming deformed.
The present invention overcomes the aforesaid drawbacks of the prior art by providing an improved dredge cutterhead.
In a first aspect of the invention, a dredge cutterhead comprises a hub, a ring, and a plurality of helical arms interconnecting the hub and the ring. Each of the helical arms has a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween. The arm is shaped such that the net force exerted on material in the trough portion pushes the material toward the ring substantially along the center of the trough portion. By “net force” is meant the force exerted on the material by the combination of gravity, buoyancy and centrifugal force.
In a second related aspect of the invention, a dredge cutterhead comprises a plurality of helical arms, the helical arms interconnecting a hub and a ring. Each of the helical arms has a leading edge for attachment of cutting teeth, a trailing edge, and a trough portion therebetween. Each arm has a degree of curvature near the ring of at least 10%.
These aspects of the invention provide several advantages. By shaping the arm so that the net force directs material toward the ring, the arm acts like a pump vane to move material efficiently toward the mouth of the suction pipe. In addition, by providing a relatively large degree of curvature near the ring, the trough portion of the arm is shaped so as to retain the dredged material within the cutterhead as it flows toward the suction pipe. Material loosened by the cutting teeth flows along the trough portion of the arm and toward the ring. The trough portion prevents the loose material from spilling over the trailing edge of the arm and out of the interior of the cutterhead. The cutterhead thus improves the efficiency of dredging and achieves a deeper finished bed depth for a given depth of cut.
In another aspect of the invention, a dredge cutterhead comprises a hub, a ring and a plurality of helical arms interconnecting the hub and the ring. Each of the helical arms is capable of supporting a plurality of cutting teeth. An annular channel is defined by the ring for retaining loosened material.
This aspect of the invention also serves to facilitate movement of loose, dredged material from the interior of the cutterhead into the suction pipe. Material loosened by the cutting teeth is transported along the arms toward the ring. Once the material enters the ring, the channel retains the loose material. Thus, notwithstanding the rotation of the cutterhead, the loose material remains inside the interior portion of the ring until it is removed by the suction pipe.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.
The present invention is directed toward a dredge cutterhead that improves the ability of the cutterhead to capture dredged, loosened material within the interior of the cutterhead and to move the loosened material toward the mouth of the suction pipe. The dredge cutterhead of the present invention may be used with any conventional dredger used for cutter-suction dredging.
Referring now to the drawings, wherein like numerals refer to like elements,
Mounted at the end of the ladder 18 is a conventional backing plate 38 which covers the rear opening of the cutterhead 20. The backing plate 38 has a conventional opening (not shown), which communicates with the entrance or mouth of the suction pipe 24. Thus, the backing plate 38 substantially prevents material from exiting the rear of the cutterhead except through the suction pipe mouth. The backing plate 38 and suction pipe mouth may be conventional. Material loosened by the teeth 36 enters the interior of the cutterhead 20, moves along the interior surface of the arms 32, and toward the suction pipe mouth, which then removes the loosened material to the dredger 10.
The cutterhead 20 of the present invention achieves its advantages by more efficiently moving, or “pumping,” the loosened material from the interior of the cutterhead along the interior surface of the arms 32 toward the suction pipe mouth, and by capturing more of the loosened material within the interior of the cutterhead. The cutterhead achieves these advantages through the use of a novel arm shape and a novel ring shape.
Turning now to the arms 32,
The arm 32 thus acts like the vane of a pump and causes the loosened material, upon entering the interior of the cutterhead 20, to be captured within the interior of the cutterhead and move along the arm 32 toward the mouth of the suction pipe 24. The result is that the cutterhead 20 achieves greater efficiency during dredging by capturing material that might otherwise pass out of the cutterhead 20, and allows the cutterhead 20 to achieve a finished bed depth that is deeper than the mouth of the suction pipe 24, as shown in
Turning to the arm 32 in more detail,
The interior face 49 of the arm 32 is sufficiently curved so as to retain material loosened by the cutting teeth, thus preventing material from falling off the trailing edge of the arm and exiting the cutterhead. By “curved” is meant the degree of curvature of the interior face 49 from the leading edge 40 to the trailing edge 42 of the arm. A degree of curvature (“D.C.”) of a section at any point along the arm may be determined by taking the ratio of (1) the depth of the trough portion 44 at that point and (2) the width of the interior face 49 of the arm at that point. The “depth” of the trough portion is determined by the greatest perpendicular distance between the inner-surface of the trough portion 44 and a straight line interconnecting the innermost surfaces of the leading edge and the trailing edge. For example,
By “sufficiently curved” is meant that the arm has a degree of curvature that is sufficient to retain material within the trough portion. In general, the degree of curvature near the hub is at least about 8%, and more preferably about 10 to 12%. The degree of curvature near the ring is at least about 10%, more preferably about 15%, and even more preferably, about 20 to 25%. A degree of curvature near the ring of at least 10% insures that the net force exerted on material near the ring will urge material toward the ring, and also allows the trough portion to accommodate the material flowing down the arm and also entering the arm over the leading edge near the ring. By “near the hub” is meant within the upper 20% of the arm length adjacent to the hub 28, and by “near the ring” is meant within the lower 20% of the arm length adjacent to the ring 30. For example, as shown in
Preferably, the degree of curvature generally increases along the arm 32 from the top near the hub 28 toward the bottom of the arm 32 near the ring 30. By “generally increases” is meant that the degree of curvature on average increases over at least the lower portion of the arm, that is from a location at about 50% of the arm length from the hub to the ring. More preferably, the degree of curvature on average increases over at least 70% of the length of the arm, and even more preferably on average increases over at least 90% of the length of the arm. While the degree of curvature increases on average, nevertheless the degree of curvature may vary over a given length, and may even decrease over short portions of the arm.
Increasing the degree of curvature along the arm allows the trough portion to retain the material flowing along the trough and admit additional loosened material entering the trough portion from the lower portion of the leading edge. Because the degree of curvature generally increases, the maximum degree of curvature is preferably located lower than the minimum degree of curvature. The degree of curvature near the ring 30 is preferably at least 1.5 times, and even more preferably at least 2 times, the degree of curvature near the hub 28.
For example,
Returning to the exemplary cross-section of
The leading portion 48 preferably curves inwardly to provide a space between each of the respective arms 32 for dredged material to enter the interior of the cutterhead. Preferably, the leading portion 48 is aligned with or follows the cutting teeth 36 of the arm, so as to minimize the wear of the arm. The leading portion 48 may have an interior radius of curvature RL which is similar to the conventional radius of curvature of the prior art arm 32′. The radius of curvature RL varies along the arm from the ring 30 to the hub 28, but in general is such that the arm 32 curves in a smooth helical fashion from the ring 30 to the hub 28. The width of the leading portion 48 may vary, but generally comprises from 10% to 35% of the width of the interior face 49.
In one preferred embodiment, the trough portion at any section further comprises three different areas, each having a different radius of curvature R1, R2 and R3. The first area 56 has a radius of curvature R1 that is much smaller than that of RL. As shown in
While FIGS. 4 and 6A-6D show an arm having an interior face comprising a leading portion and a trough portion, the requisite degree of curvature may be obtained without differentiating the arm into two such portions. Thus, the arm may have a uniform thickness. Nor is it necessary that the trailing edge curl inwardly. The interior surface 46 may be defined by any curve or combination of curves, and is not restricted to arcs and lines. While smooth surfaces are desired, it may be possible to obtain the requisite degree of curvature using a plurality of flat surfaces which transition at sharp angles along the interior surface of the trough.
In addition, while the figures show each arm having a trough portion, it is only necessary that a plurality of the arms be pumping in nature. Thus, for example, the cutterhead may be provided with three pumping arms having the degree of curvature described above, and three conventional arms.
The ability of the cutterhead 20 to efficiently move loosened material toward the ring, or its “pumping” nature, may be improved by optionally increasing the helix angle of the trough portion of the arm 32. As shown in
One method for effectively increasing the helix angle of the trough portion is to increase the width of the arm of the cutterhead from the top to the bottom of the arm. For example,
Another method for increasing the helix angle of the trough portion is to increase the helix angle of the leading edge. Preferably, the helix angle of the leading edge is at least 140°, and more preferably at least 145°.
Likewise, the pumping nature of the cutterhead may be improved by optionally increasing the aspect ratio (β) of the cutterhead 20. The aspect ratio of the cutterhead is the ratio of the outside diameter of the ring 30 to the height of the cutterhead 20. The height of the cutterhead is the distance along the rotational axis A through the hub 28 between the top 62 of the hub and a horizontal plane defined by the bottom of the ring 30 as shown in
The flow of material into the suction mouth may be enhanced by continuing the trough portion into the ring 30. As shown in particular in
In another separate aspect of the invention, the ring 30 of the cutterhead 20 defines an annular channel 66 preferably having a cross-section in the shape of a “half-pipe” as shown in
While
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.
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Number | Date | Country |
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0236692 | Sep 1987 | EP |
Entry |
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ESCO Dredge Products, 1997; ESCO Spherilok Rock Dredge Cutterheads; 5 Pages. |
ESCO, Helilok Sand and Clay Dredge Cutterheads; 1997; 2 Pages. |
ESCO, Spherilok Rock Dredge Cutterheads 1997; 2 Pages. |
Number | Date | Country | |
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Parent | 09776020 | Feb 2001 | US |
Child | 11153886 | US |