After my last post1, I received some comments and questions about the actual products we are applying in our cutter systems for our CSD’s2. Indeed, from a pure physical perspective, last post cuts to the heart of the processes, but does not explain our design of the working tool that makes a cutter suction dredge do its work.
Over the years, there has been a lot of development in this tool. Originally, suction dredges were plain suction dredges, working in non-cohesive sand. When the soil was more cohesive than could be dug with the standard suction dredges, attaching a mechanical device for loosening the ground enabled the suction dredge to work in this environment. From this original concept, the cutter head was already recognisable as a crown with teeth on a back ring and a suction mouth in the centre. From there, a lot of experimentation was done, but ultimately it all came back to this concept. Although modern cutter heads have a vastly improved performance and lifetime.
The cutting process in a modern cutter head is a combination of the rotation of the head and the swing of the dredge. The teeth describe a compound path of translation and rotation and each individual tooth has its own set of cutting parameters for depth and angle varying over time. Moreover, the combination of teeth on the different arms, allow for a staggering of the teeth that each tooth cuts fresh material and optimising the use of the teeth and spreading the wear. This results in a complicated geometry of the arms and a intricate pattern of the teeth.
Once a cutter design has been chosen, there is still some tuning possible. Normally, the teeth are fitted on adapters and there are several teeth types available for a certain adapter. Pick points, Chisels and Flares. Most productivity can be expected from the wider teeth. However, the penetration of the wide teeth is less. So, for harder material you want to select narrower teeth.
Wear is also an issue3. And as the teeth are in direct contact with the fresh material, the wear rates can be severe. The disadvantage of a teeth and adapter system is that that are quite big. So, less teeth fit on an arm, reducing production on average. As most of our CSD’s are working in more gentle sands we selected a cutter system, that provides more teeth to engage in the action, increasing production. As these teeth are fitted directly on the arms, there are no adapters that wear also. Consequently having no adapters, simpler arms and dirt cheap teeth result in a low investment low OPEX cutter system. Although you might have to check the state of your teeth more often, in the end you spend less money on a cubic meter produced.
Teeth can be worn down to the root. Also they are not wearing evenly. Usually, they last longer on the outside, near the back ring. You might consider using different tooth forms over the arm. Experience and practice, will guide you in selecting the best combination. In line with the previous post, the analogy will be on the table. Just as you select different teeth for your fork, you can select different teeth on your cutter depending on the dish being served.
- Experiencing The Cutting Edge Of Dredging Technology, Discover Dredging
- Cutter Suction Dredger, Damen
- Wear of Rock Cutting Tools, Peter Verhoef