For more than 100 years the family-owned enterprise Lucht quarries sand and gravel at various locations in the Dithmarschen district. Ultra-fine sand is the main product of the current operation at Buchholz with up to 250 000 t/a. Since 2011, two crawler-mounted doublescreen plants, type Sandvik QA340, including pile belt conveyors have been used. They were supplied and are serviced by the Quickborn-based Sandvik partner Oppermann & Fuss (Fig. 1).
Today the Lucht gravel works at Buchholz comprise a little more than 13 ha of open area (Fig. 2). They were opened in 1998. The material is extracted by wheeled loaders of 5.0 m³ at various levels. With face heights of up to 6 m, the pit has a depth of 25 m. Two wheeled loaders with calibrated weighing equipment are operated in quarrying, handling and loading. They are supported by a crawler excavator, which is predominantly used for slope stabilization and areal layout. Jens Lucht and the Senior Partner Reimer Lucht are the permanent staff of the family-owned enterprise. With 30 ha of approved local quarrying area and more reserves in the surrounding countryside, the continued existence of the company is ensured beyond the present 5th generation.
The regular in-situ material has a rock content of only about 5 % and no organic portions worth mentioning. Thus, Lucht has specialized in the economic dry processing as regards the own production. The main products are unwashed sands with a size range of 0/2 and 0/3, which are mainly used as filling sand in the Dithmarschen district and sold and supplied within radii of up to 25 km. As regards the gravel portions, the company does not upgrade them either. The larger screen fractions of the Lucht supply range of building materials are completed by the uncrushed road gravel as well as by purchased products and those stored at the company (amongst other things antifreeze agents).
Efficient, mobile screening plants have determined the mineral processing at the Lucht gravel works for a long time. First they used wheeled units, later plants with crawler chassis which could be easily placed and which, furthermore, can be installed in the gravel works without any expensive preparation of the ground. Although the screen-specific requirements seem to be clear, the all-year operation is consistently aligned to a high production output with a profitability as large as possible.
Today, two doublescreen plants QA340 from Sandvik ensure production peaks of 500 t/h regarding gravel screening and 350 t of sand on average (Fig. 3). After the first unit in 2011, the Lucht gravel works took over the second plant again from the Quickborn-based Sandvik dealer Oppermann & Fuss at the end of last year. According to the Senior Partner Reimer Lucht, in particular the patented doublescreen technology was the deciding factor to be able to adapt the screening behaviour of the 27-ton plant exactly to the given quality.
“In 2005 we purchased the first doublescreen plant. Especially as regards sand, the two separated screen frames with their separate drives are convincing due to the high acceleration of the material being screened. Depending on the condition of the feed, we are additionally able to arrange a steep angle of the first screen frame and achieve an even higher efficiency,” explained Reimer Lucht (Fig. 4). The dimensions of the total screening surfaces on the lower and upper deck amount to close to 5 x 1.5 m each (Fig. 5). Their screening media can easily be replaced by hydraulic lifting and lowering of the main belt conveyor or the undersize discharge unit. As standard of the Sandvik QA340 in the quarry Buchholzer Sand is a square mesh of 40 mm on top and a harp screen of 3 mm on the lower deck. Furthermore, both plants have a double-deck vibrating grate (bar screen/80 mm square) on the feeder with a max. volume of 7 m³ (Fig. 6). The function of the latter is controlled from the wheeled loader. With this equipment, the plants achieve average outputs of 350 t/h of sand for the fractions 0/2, 2/35 and 35/80.
With two mobile pile belt conveyors Reimer Lucht handles these high production outputs: “With 350 t/h, the combined feeding and pile operation with a one-wheeled loader only is simply uneconomic and the screen runs empty too quickly.” Therefore, the pile reserve amounts to up to 10 000 t for the finished product 0/2. It is achieved at the banquette edge of 6 m height by the 24-m pile belt conveyors (discharge height 10 m) varnished with the typical Sandvik colours and delivered by a third supplier. “If I additionally compare the consumption of the pile belt conveyor of 5 l/h and the just over 20 l/h of the wheeled loader, I clearly operate the screening plant at a more favourable cost.”
Reimer Lucht also knows the consumption values of his Sandvik QA340: On a long-term average both plants of 75 kW need 15 l/h. One plant runs almost “stationary” with perhaps two location changes per year, while the second unit more frequently follows the extraction or is used for the production of defined gravel sizes after a short retrofit.
With an annual production of about 200 000 t to 250 000 t, the exclusive use of the Sandvik mineral processing technology is also a mark of confidence for the responsible dealer and service partner Oppermann & Fuss headquartered in Quickborn at a distance of about 80 km. This partnership has existed for about five years and, above all, is based on the high flexibility of the aftersales service and of the supply of parts (Fig. 7). The regular maintenance and major overhauls are carried out by the mobile service of O & F. For minor work Lucht has installed a well-sorted workshop container for each QA340 in the Sandvik colours with all the small parts, consumables and tools required.