Simex’s new TF 2500 cutter head lived up to expectations on a site in Switzerland where it showed off its production capacity on a tough excavation job. Lucio Garofalo reports.
Cutter heads are effective solutions when excavation using a hydraulic breaker or the blasting method is hampered by the level of fracturing or looseness of the rock mass. These attachments can also produce excellent results when tackling compact and hard sedimentary materials, provided that the teeth exert an effective cutting action. Apart from the geotechnical considerations, cutter heads also have advantages when it comes to the applications themselves. Breakers and explosives are not suitable when ground vibrations (the former continuous but low-intensity, the latter short but high-intensity) risk impacting buildings or other structures adjacent to the excavation site. These were precisely the conditions on a job site near Ürnasch in the Swiss canton of Appenzell Ausserhodem, where the contracting firm Æschbacher, used a TF 2500 cutter head (the first to be operated in Switzerland) to excavate rock in preparation for the construction of a new residential building. The attachment proved an efficient solution because, besides avoiding environmental impact (noise and dust) in the surrounding area, it demonstrated terrific productivity while maintaining a high degree of precision, a key condition of project specifications on the excavation measurements.
Like other regions in Switzerland, the Umasch area has natural conglomerates which were deposited following the glacial periods. These clastic sedimentary formations are composed of different-sized grains, called clasts, cemented by a matrix formed of much smaller grains (usually sand or clay when the clasts are cobbles) which fills the spaces between larger elements. Solutions formed in the sediment cause salts to precipitate, eventually creating a cementation effect and leading to a formation of a conglomerate similar to concrete, with the accompanying high levels of strength and compaction. In the case of the conglomerate on the Ürnasch job site, the point load tests performed by Simex’s R&D department, resulted in values close to 100MPa. With these levels of compressive strength of the mass combined with the substantial compaction of the rock to be excavated, using a breaker would not have ensured a satisfactory output; and neither would a hydraulic breaker have been an appropriate choice due to the clast composition of the rock mass, because it would have, unavoidably, propelled smaller fragments during excavation, constituting a safety hazard.
The TF 2500 supplied to the contractor Æschbacher, by Simex dealer Hydremag based in Waldstatt, was fitted with an HP type drum and teeth suited to the application. Part of the Simex cutter head range, the attachment is designed to extend and improve the product offer. With a rotation torque of 31.7kNm and a cutting force of 837kN, the TF 2500 delivers the power to take on the toughest excavation jobs, as exemplified by the Urnasch site. Considering the amount of material excavated and the degree of the rock’s strength and compaction, the cutter head performed successfully in an exceptionally tough application.
Like all cutter heads of the Simex range, the TF 2500 has patented features in its design and construction that make it very productive in relation to its weight and size. This is thanks to the high torque and efficiency provided by the integrated high displacement hydraulic piston motor which is fitted in a coaxial position with respect to the drums. As a result, the drums are not moved by a mechanical drive system and can exploit the advantages of the hydraulic drive. The coaxial layout of the motor also allows the shaft, featuring double bearings to support both drums, to transmit only the motion to the drums and prevents it from bearing any load. The TF 2500 also includes an oil flow limit valve that avoids risks and thus possible damage related to any over-revving of the hydraulic motor, ensuring longevity. Simex cutter heads are also fitted with mechanical seals on the drums making them dust-tight when fully submerged into the ground; they also avoid foreign objects from penetrating even when working in mud. Another advantage is the special shape of the frame, which allows hoses to be connected at both sides and at the front.
