High-flying screen

1 The high-flying ST3.5 mobile screen from Metso

2 The Lokotrack jaw crusher in action, processing aggregates for the expansion of the Linth-Limmern power plants

3 The ST3.5 with upstream Lokotrack

Back in December 2010, Metso’s exclusive distributor for Switzerland, Drossard Sales & Service GmbH, caused quite a stir when the LT96 jaw crusher really took off. Contracted by Martitechnik AG, the Metso distributor transported the LT96 by cableway to its assigned operating site at an altitude of 2474 m in the Swiss Alps. In September 2011, the distributor was able to repeat this extraordinary action in Switzerland, this time taking Metso’s ST3.5 mobile screen to a height of just under 1857 m (Fig. 1). The realization of this project was preceded by meticulous planning – especially as two cableways with different capacity requirements were involved in the transport of the machine. Besides the necessary technical data such as the load centre of gravity, stability aspects and dimensions, it was important to take into consideration the weather and the necessary light as the cableway only transports loads in daylight.

The new ST3.5 screen is supporting the “Linthal 2015” project. The mobile Lokotrack is involved in the expansion of the Linth-Limmern power plants, where it is helping with the preparation of the terrain for the major construction site and for the processing of aggregate (Fig. 2). This unique power plant project – a joint venture between the Swiss Canton of Glarus and Axpo AG – is aimed at increasing power generation at the Linth-Limmern hydropower plant (KKL), thus assuring the future power supply for North-Eastern and Central Switzerland. The project is to be completed within five years and will employ a total of 250 people. The total costs of the project amount to around 2.1 bill. Swiss francs.

The new ST3.5 mobile screen, which Drossard Sales & Service GmbH transported by cableway, is also the first one in Switzerland. Not only the type name ST3.5 (3 stands for the number of products/double-deck screen; 5 for the screen width – corresponding to around 1500 mm) differs from the predecessor model tested ST352. A string of technical modifications to the screen improve its efficiency and environmental friendliness. Precondition for this is the improved combination of high-efficiency circular vibrating screen, selected quality components and the proven Lokotrack structure.

It is powered by a CAT C4.4, which with around 75 kW may seem oversized at the first glance. But it makes sure that the operator has adequate drive power even when working in the toughest and most difficult conditions. Besides the new engine, the hydraulics were optimized with a triple fixed displacement pump. As a result, the fuel consumption is around 33 % lower than for the predecessor model. The facilities for remote control (cable or radio) are still available, but manual operation of the screen is still the first choice for most operators. The intelligent arrangement of filter and the design of the engine casing optimally protect the drive system against dust.

For set-up, dismantling and transport of the screen, there are reliable fixtures and operating functions: the operating levers for the hydraulic folding of components during the set-up of the mobile screen are, for example, arranged so that the motional processes remain clearly visible. This also includes the obligatory platform at the screen and ample clearly labelled emergency stop switches. Good accessibility of lubrication points, maintenance points as well as for changing the screen meshes reduce downtime and increase working safety. The screen frames of the double-decker with 5.3 m² screening area are suitable for fitting different screening surfaces. The same size of the screen meshes on the two decks enables economic storage.

The ST3.5 is suitable for excavator or wheel loader feeding and can be operated both as a stand-alone component and with upstream and downstream equipment – e.g. with high-performance Lokotracks – in a closed circuit (Fig. 3). For this, longer discharge belts are available as an option, with which larger volumes can be stockpiled. For environmental friendly operation near residential areas, numerous options are available, such as dust covers for the feed and fines conveyors and water spraying with minimal water consumption. Customized modification in line with specific working conditions is available ex works. In future a double-deck vibrating grizzly will be available for mounting on the feed bin to ensure efficient pre-screening.