Cutterheads
A cutterhead is a rotating cutting tool literally at the forefront of the dredging process of a cutter suction dredger (CSD). The cutterhead’s aim is to loosen and dislodge the soil through a rotating motion, so that the slurry can be drawn into the suction pipe. The cutterhead is responsible for both excavation of the soil and slurry creation and, therefore, largely defines the performance of the dredger.
A cutterhead must be able to excavate the soil and mix a maximum amount of soil with a minimum cutting force and spillage. Different soil types demand different forms of penetration and to get the best results, various cutterheads are available for different circumstances.
Cutterhead design
In general, a cutterhead consists of various parts: a back ring; hub; blades; and specific cutting elements. The cutter is usually equipped with five or six blades that connect the hub with the ring. This must be able to rotate freely with respect to the suction mouth. The shape and the dimensions are based on, among other factors, the power and the speed of the cutter drive, the suction tube diameter and the tooth system to be applied. However, the type of soil is the decisive factor.
Selecting the right cutterhead for different soil types
- For harder soil types, such as sandstone, coral and soft rock, a high cutting force is needed. For these soil types, the contour of the cutter will be as small as possible and a narrow conical contour is commonly used. To fragment stone, coral or rock, the cutterhead is equipped with pick point-shaped teeth. Due to the high impact load of these harder soil types, wear will be substantial. That is why this type of cutterhead is fitted with a tooth adaptor system for easy replacement of the pick points.
- For cohesive soil, such as clay, wear will be limited, but there is a risk of clogging. The hydraulic design of the cutter plays a vital role. The cut chunks of clay must be as small as possible to facilitate subsequent transport. For this soil type, the contour of the cutterhead is relatively large and the cutter will be equipped with smooth cutting edges, serrated cutting edges or many small teeth.
- For non-cohesive soil, such as sand and gravel, wear is an important consideration. The cutter will have chisels or cutting edges with a large wearing volume and easily replaceable parts. The hydraulic design will be optimal, so high production rates can be achieved. For this soil, the contour of the cutter is usually relatively flat.
Multipurpose cutterhead
At a single dredge site, various types of soil may be encountered. That is where the multipurpose or multifunctional cutterhead comes in handy. This type of cutterhead is suited for several soil types, since it is equipped with a tooth system, so that the cutting edges can be replaced based on the soil type. The main teeth types are:
- flared chisels – used for peat, sand and soft clay
- narrow chisels – applied in packed sand and soft clay
- teeth with pick points – used for rock.
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