GB2032492A

GB2032492A - Cutter Head for Suction Dredger

Info

Publication number: GB2032492A
Application number: GB7929046A
Authority: GB
Original assignee: WESTMINSTER DREDGING
Current assignee: WESTMINSTER DREDGING
Priority date: 1978-08-21
Filing date: 1979-08-21
Publication date: 1980-05-08
Also published as: GB2032492B

Abstract

A cutter head for a suction dredger which includes a central boss (11) mountable upon a power drive shaft (12) and suction head of the dredger, wherein the boss (11) carries at least one spiral-helical web (13) upon which is mounted an array of cutter bits (19) spaced at intervals along the web (13) and projecting therefrom so that their tips define a generally part-ellipsoidal envelope (15), the working direction of the bits (19) and the "hand" of the spiral-helix of the web (13) being such that in use the cuts made by successive bits (19) on the same web (13) are staggered relatively to one another, each succeeding cut being nearer to the larger diameter end of the cutter head. <IMAGE>

Description

SPECIFICATION Cutter Head for a Suction Dredger This invention relates to cutter heads for floating suction dredgers. A conventional cutter head consists of a set of curved spiral-helical blades mounted on an axial boss for rotation under power for the purpose of breaking up the sea or river bed, the broken fragments being removed from the head by suction and delivered to the dredger for disposal.

When the sea bed consists of soft clay or sand, a typical dredger can operate at what is considered a satisfactory output rate, but when harder conglomerates, or rock are encountered, then the rate of removai decreases very significantly. For example, with a hard rock, having a compressive strength of 2000-3000 Ib/sq.in. the rate may be reduced by as much as 90%, though it would still be generally regarded as an acceptable rate of working. For harder rocks the rate is even lower until one reaches rock compressive strengths approaching 7,000 Ibs/sq.

in., when other methods, such as blasting, must be adopted, which significantly increases the time and cost of the whole operation.

Attempts have been made to adopt dry rock cutting techniques, for example by fitting teeth or picks to the cutter blades, but these have not been particularly successful due in part to a lack of understanding of the physical properties of underwater rock formations.

It is an object of the present invention to provide an improved cutter head for a suction dredger which is capable of operating on harder rocks than at present possible, or which can achieve a higher rate of removal than can be obtained at present for a given rock strength.

The present invention consists in a cutter head for a suction dredger which includes a central boss mountable upon a power drive shaft and suction head of the dredger, wherein the boss carries at least one spiral-helical web upon which is mounted an array of cutter bits spaced at intervals along the web and projecting therefrom so that their tips define a generally part-ellipsoidal envelope, the working direction of the bits and the "hand" of the spiral-helix of the web being such that in use the cuts made by successive bits on the same web are staggered relatively to one another each succeeding cut being nearer to the larger diameter end of the cutter head.

In the accompanying drawings: Figure 1 is a side view of one form of cutter head according to the present invention, Figure 2 is a longitudinal section through the cutter head on Figure 1, and Figure 3 is a cross section taken in a spiral plane starting at line 3-3 of Figure 1.

In carrying the invention into effect according to one convenient mode by way of example, a cutter head for a suction dredger includes a central boss 11 adapted to be fitted on the drive shaft 12 of suction head of known form of a suction dredger.

Welded to the central boss are four interposed closely-spaced pairs of spiral-helical webs 1 3 of metal sheet or plate material thus forming a fourstart spiral-heiical channel system, between adjacent pairs of web pairs, each channel being of about 1 turns. At the larger diameter end the webs 13 are joined to a pair of annular rings 14 positioned coaxially with the axis of the boss 11 and at right angles thereto.

At the smaller diameter end the webs 13 are joined to a pair of conical rings 23 positioned coaxially with the axis of the boss, and whose included angle is about 600.

The webs 1 3 are so dimensioned that in longitudinal profile they define a curve 1 5 which is part of a near ellipse and is chosen so as to present the optimum angle of attack to the sea bed whatever the angle of the axis of the cutter to the horizontal in use.

The peripheries of the webs and the annular rings are provided with cut-outs 1 6 in which are welded mounting plates 1 7 each of which bridges the pair of webs or rings and upon which is mounted a block 1 8 holding a cutter bit 1 9 so that an array of cutter bits 19 is formed.

The cut-outs are so dimensioned that the tips of the cutter bits 1 9 project beyond the peripheries of the webs, the extent to which they project defining the maximum cutting depth of the bits, and the bits are angled in conventional manner as shown in Figure 3 so as to have a working direction (clockwise in figure 3). The tips of the cutter bits thus define a generally partellipsoidal envelope of the same form as curve 1 5.

The cutter bits 1 9 are spaced at intervals around the pairs of webs 1 3 and the working direction of the bits 19 and the "hand" of the spiral-helix of the webs are such that in use the cuts made by successive bits on the same web are staggered relatively to one another each succeeding cut being nearer to the larger diameter end of the cutter head.

The pairs of webs 13 are provided with apertures 20 to prevent "bridging" of material between adjacent pairs, and to allow the rearward flow of material to the mouth 21 of the suction head under the action of the suction from the head assisted by the helical form of the webs 1 3.

To assist this action scoops 22 are provided between adjacent pairs of scoops 22, but other arrangements may be advantageous.

Various modifications may be made within the scope of the present invention. For example, the cutter bits may be replaced by other forms of mining tools such as picks or chisels.

Claims

1. A cutter head for a suction dredger which includes a central boss mountable upon a power drive shaft and suction head of the dredger, wherein the boss carries at least one spiral-helical web upon which is mounted an array of cutter bits spaced at intervals along the web and projecting therefrom so that their tips define a generally part-ellipsoidal envelope, the working direction of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cutter Head for a Suction Dredger This invention relates to cutter heads for floating suction dredgers. A conventional cutter head consists of a set of curved spiral-helical blades mounted on an axial boss for rotation under power for the purpose of breaking up the sea or river bed, the broken fragments being removed from the head by suction and delivered to the dredger for disposal. When the sea bed consists of soft clay or sand, a typical dredger can operate at what is considered a satisfactory output rate, but when harder conglomerates, or rock are encountered, then the rate of removai decreases very significantly. For example, with a hard rock, having a compressive strength of 2000-3000 Ib/sq.in. the rate may be reduced by as much as 90%, though it would still be generally regarded as an acceptable rate of working. For harder rocks the rate is even lower until one reaches rock compressive strengths approaching 7,000 Ibs/sq. in., when other methods, such as blasting, must be adopted, which significantly increases the time and cost of the whole operation. Attempts have been made to adopt dry rock cutting techniques, for example by fitting teeth or picks to the cutter blades, but these have not been particularly successful due in part to a lack of understanding of the physical properties of underwater rock formations. It is an object of the present invention to provide an improved cutter head for a suction dredger which is capable of operating on harder rocks than at present possible, or which can achieve a higher rate of removal than can be obtained at present for a given rock strength. The present invention consists in a cutter head for a suction dredger which includes a central boss mountable upon a power drive shaft and suction head of the dredger, wherein the boss carries at least one spiral-helical web upon which is mounted an array of cutter bits spaced at intervals along the web and projecting therefrom so that their tips define a generally part-ellipsoidal envelope, the working direction of the bits and the "hand" of the spiral-helix of the web being such that in use the cuts made by successive bits on the same web are staggered relatively to one another each succeeding cut being nearer to the larger diameter end of the cutter head. In the accompanying drawings: Figure 1 is a side view of one form of cutter head according to the present invention, Figure 2 is a longitudinal section through the cutter head on Figure 1, and Figure 3 is a cross section taken in a spiral plane starting at line 3-3 of Figure 1. In carrying the invention into effect according to one convenient mode by way of example, a cutter head for a suction dredger includes a central boss 11 adapted to be fitted on the drive shaft 12 of suction head of known form of a suction dredger. Welded to the central boss are four interposed closely-spaced pairs of spiral-helical webs 1 3 of metal sheet or plate material thus forming a fourstart spiral-heiical channel system, between adjacent pairs of web pairs, each channel being of about 1 turns. At the larger diameter end the webs 13 are joined to a pair of annular rings 14 positioned coaxially with the axis of the boss 11 and at right angles thereto. At the smaller diameter end the webs 13 are joined to a pair of conical rings 23 positioned coaxially with the axis of the boss, and whose included angle is about 600. The webs 1 3 are so dimensioned that in longitudinal profile they define a curve 1 5 which is part of a near ellipse and is chosen so as to present the optimum angle of attack to the sea bed whatever the angle of the axis of the cutter to the horizontal in use. The peripheries of the webs and the annular rings are provided with cut-outs 1 6 in which are welded mounting plates 1 7 each of which bridges the pair of webs or rings and upon which is mounted a block 1 8 holding a cutter bit 1 9 so that an array of cutter bits 19 is formed. The cut-outs are so dimensioned that the tips of the cutter bits 1 9 project beyond the peripheries of the webs, the extent to which they project defining the maximum cutting depth of the bits, and the bits are angled in conventional manner as shown in Figure 3 so as to have a working direction (clockwise in figure 3). The tips of the cutter bits thus define a generally partellipsoidal envelope of the same form as curve 1 5. The cutter bits 1 9 are spaced at intervals around the pairs of webs 1 3 and the working direction of the bits 19 and the "hand" of the spiral-helix of the webs are such that in use the cuts made by successive bits on the same web are staggered relatively to one another each succeeding cut being nearer to the larger diameter end of the cutter head. The pairs of webs 13 are provided with apertures 20 to prevent "bridging" of material between adjacent pairs, and to allow the rearward flow of material to the mouth 21 of the suction head under the action of the suction from the head assisted by the helical form of the webs 1 3. To assist this action scoops 22 are provided between adjacent pairs of scoops 22, but other arrangements may be advantageous. Various modifications may be made within the scope of the present invention. For example, the cutter bits may be replaced by other forms of mining tools such as picks or chisels. Claims

1. A cutter head for a suction dredger which includes a central boss mountable upon a power drive shaft and suction head of the dredger, wherein the boss carries at least one spiral-helical web upon which is mounted an array of cutter bits spaced at intervals along the web and projecting therefrom so that their tips define a generally part-ellipsoidal envelope, the working direction of the bits and the "hand" of the spiral-helix of the web being such that in use the cuts made by successive bits on the same web are staggered relatively to one another, each succeeding cut being nearer to the larger diameter end of the cutter head.

2. A cutter head as claimed in claim 1, wherein the boss carries at least one pair of closely spaced webs and the cutter bits are mounted upon plates bridging the webs.

3. A cutter head as claimed in claim 1 or 2, wherein the cutter bits are mounted in cut-outs in the or each web.

4. A cutter head as claimed in claim 1, 2 or 3, wherein the or each web is provided with axial apertures.

5. A cutter head as claimed in any one of claims 1 to 4, wherein scoops are provided between adjacent turns of the web which, in use, serve to assist the flow of dredged material towards the section head mouth.

6. A cutter head substantially as described with reference to the accompanying drawings.