Research and Development: A Sneak Peek at the Next Generation of Disc Cutters
R & D is important in any industry, and it is no less true for the tunneling industry. Evolution, even if it is incremental, is where most research and development successes are made. Such improvement forms part of the competitiveness among manufacturers and thus begets further improvements. I also believe it is our obligation, as equipment manufacturers, to assist the market in driving down the costs of tunneling in general by improved product performance and product life.
Take, for example the research and development going on with our disc cutters: Robbins disc cutters have improved dramatically since the 1950s when they achieved their first success at 11 inches in diameter in crystalline limestone of 190 MPa (28,000 psi) UCS. Today’s disc cutters do reach 20 inches in diameter and cost-effectively excavate rock strengths of 400 MPa (60,000 psi) UCS, all while lasting much longer than their predecessors.
That being said, we believe there is always room for improvement. We are working hard right now to develop customized cutters for EPB tunneling in soft and mixed ground, and to optimize those designs so they can excavate under high pressure. In hard rock, we are researching and testing new steels, and developing monitoring systems to allow contractors to plan cutter changes.
Here’s a snapshot of what research and development is going on in the cutter department, both in the lab and in the field:
Working with the University of Trondheim and the Norwegian government, we are commencing a program of laboratory and field testing to improve the materials making up the disc ring itself. We are always testing new materials in order to find the most durable materials based on the ground conditions. An example of past cutter research in the lab can be seen below:
Pressure Compensated Disc Cutters
We are currently developing improved disc cutters specifically for use on EPB and Slurry TBMs at high pressures of plus 10 bars, using a testing module in our Kent, Washington facility. The module duplicates a pressurized operational environment so that we can analyze how the cutter seals perform under pressure—the design is in its 3rd or 4th generation with continuous improvements being made.
Remote Cutter Monitoring
Our remote cutter monitoring system is a breakthrough that we have been field testing for four years. The system is now undergoing full scale testing on three Main Beam TBMs at Malaysia’s Pahang Selangor Raw Water Tunnel. The setup allows crews to more closely monitor the actual working conditions and cutter wear. We project, through this system, to increase the TBM utilization of each machine by 3 to 4% and to reduce cutter cost by 10%.
We’re also working on expanding this wireless system to EPB and Slurry machines, so that monitoring of cutter wear and rotation can be used while those machines are in closed mode. This would be a highly beneficial development, because under pressure the detection of tool wear is difficult. Our goal here is to reduce or better plan interventions because of tool wear.
Robbins Atmospheric Cutter Change System (RACCS)
Finally, we are developing a system to allow cutter changes at atmospheric pressure on large diameter EPBs. This atmospheric cutter change system is superior to other systems on the market because it allows muck to flow through. Other systems on the market are very prone to clogging. Each spoke of an EPB cutterhead will contain a chamber at atmospheric pressure. Cutters can be rotated from the pressure zone into the chamber to allow for efficient and relatively fast cutter changes.
The development is also significant because a huge cost of operating large diameter EPBs is associated with intervention for cutter inspection and change. We are currently building a large test fixture for this system, which will analyze how RACCS reacts in sand, gravel, boulders, clay, and mud conditions under pressure.
These research and development projects are all aimed at solving a particular problem or shortfall—with the objective to bore more meters per month. It is not the only area where we have research and development underway, as we have similar programs to investigate improvements of the probe drilling and lube systems on our TBMs. The process is usually rigorous, as designs need to be tested and re-tested in both the lab and the field.
I am not a big believer in “Big Step” research and development as was tried in earlier days at Robbins with the Mobile Miner and the Bore Pack. Such “Big Step” research and development usually leads to disappointment and heavy cost for the client and the company.
However, improvements like the 19” cutters and the cutter monitoring systems are and will be big wins for the contractors and for Robbins.