Schäfer & Schmitt KG has been using Bell Equipment high-capacity articulated dump truck (ADT) technology in basalt quarrying for a good two years now. Following good experience gained using the Bell B45D, the company, based in Elbtal-Elbgrund, western Hesse, has now also purchased a larger Bell B50D (Fig. 1) to replace a 40 t rigid dump truck. Both of these 6 x 6-drives are in year-round service at the Elbgrund quarry, where the haulage route is characterised by difficult topography, special equipment requirements and a high stripping ratio of 1:3.
High-quality basalt has been quarried at Elbtal-Elbgrund, on the eastern edge of the Westerwald forest, for over eighty years. Schäfer & Schmitt GmbH & Co. KG is now part of the Schmidt Basalt group of medium-sized enterprises, which employs a total of eighty-five persons here, at its other quarry near Thalheim, at a building-materials recycling yard in Wiesbaden, and in its large delivery fleet (35 vehicles). The radius for deliveries of high-grade building materials and aggregates for asphalt and concrete extends up to 100 km, and Schmidt Basalt even supplies quality-controlled minerals and rail-track ballast via the River Rhine, as far as the Netherlands.
This consistent quality strategy also has immediate implications for operational organisation at the Elbgrund quarry. Only some 30 % of the annual around 450 000 t of product mineral are used in building-materials mixtures; the remainder is passed through the multi-stage processing plant (throughput: up to 2300 t/d), which was completely rebuilt in 2005/2006. The mineral face is quarried in accordance with strict product specifications on three levels with an overall thickness of up to 50 m on a total site of 18 ha. A 70 t backhoe (4.8 m3) loads the blasted material onto heavy-duty earthmoving trucks, which tackle the 12 % maximum gradients fully laden on their 700 and 1400 m trips to the pre-crusher (Fig. 2).
In addition to selective getting and production planning, which demands high haulage route availability even under adverse weather conditions, Schäfer & Schmitt CEO Klaus Horneck and facility manager Hubert Duda are also obliged to include yet another specific challenge at the Elbgrund facility in their calculations: the overburden above the basalt is 15-20 m in thickness, and the regular stripping volume of a good 150 000 m3/a is largely handled using the quarry’s own resources during the lower-sales winter months from December to February. Up to now, two or three rented 25-30 t class ADTs have boosted the quarry’s own capacities, consisting of a rigid dump truck (approx. 41 t payload) and the Bell B45D, with a similar rating, acquired in late 2011.
2 Good in-service experience
“The B45D replaced in its turn a Bell B40D, which had served a total of ten years with the Schmidt group, and had ultimately been permanently assigned to the Elbgrund quarry from 2009 onward”, notes Horneck. “The 40-t machine completed 12 000 h of operation without any serious problems, which eased our decision to move into Bell’s next highest size range which, in addition, met our needs precisely”. This is true, for Elbgrund, of the slim-line design of the articulated vehicle’s bin, in particular, since this makes discharge into the narrow pre-crusher installation, which was taken over from another Schmidt plant when the works was constructed in 2005, easier than when the wide bodies of “classical” 4 x 2-drives are used (Fig. 3).
“The Bell B45D also offered convincing advantages in terms of performance and road-holding over our existing rigid dump truck, with a comparable tonnage rate. And this was true not only of overburden handling for new takes and of waste disposal, it also applied during normal operation”, he adds. Working fully laden uphill, the 6 x 6-drive runs, he says, “as if on rails”, especially in wet weather, when the high tuff content of the rock quickly makes the terrain at Elbgrund both sticky and slippery. Horneck also awards the 375 kW Bell high-capacity ADT with its Blu@dvantage exhaust-gas clean-up system good grades for cost-efficiency: “Average consumption after nearly 4000 h of service was around 18 l, whereas our ten-year-old 4 x 2-drives needed more than 30 l/h for the same trip”.
The management at Schäfer & Schmitt decided to replace the company’s rigid dump truck early this year. “The technical alternative would have been a 4 x 2-drive sixty-tonne machine, but that would have caused us enormous problems with the pre-crusher’s feed width”, explains Klaus Horneck. The company therefore opted for a high-capacity articulated type and, after a detailed market survey, again chose Bell Equipment. “We decided on a Bell B50D, because it fits extremely well into our operational organisation as a production machine”. The dumper’s tailgate fitting boosts its capacity to just on 30 m3, while the design payload of 45.4 t provides adequate reserves for basalt and stripped overburden. The 4.8 m3 backhoe performs eight loading movements (Fig. 4) to fill the 3.77 m wide bin (loading height: 3.30 m) from the fine-particled freshly quarried material (1.8 t/m3).
The Bell B50D has been in service on 9 h dayshifts as the main production machine at Elbgrund since early July, and passed its 800 h mark in mid-November. The tried-and-proven Bell B45D remains on standby for the most diverse range of work. “Our entire operational organisation has benefited immensely from our 100 % changeover to Bell high-capacity ADTs”, comments Horneck. “Full availability of our haulage route for normal operation is still assured under all weather conditions and, in addition, we can now adapt our haulage capacity even more flexibly to cope with peak production levels”. He mentions as an example a special, urgent 30 000 t shipment of rail-track ballast which, shortly after the changeover, necessitated the parallel operation of both articulated machines for several days. The remaining handling tasks, such as dumping of pre-screening waste, stripping operations, and site clearance for new takes outside the winter months previously reserved for this work, can now also be planned and implemented with greater flexibility. Even then, Schäfer & Schmitt continues to reap benefits: “We’re almost certain that the two high-capacity ADTs will mean that we need only one additional rented machine, at most”.
The Bell B50D also hits the fuel economy target: the standard-equipment Fleetm@tic vehicle management system indicates 18.5 l/h for the first months of operation at full capacity, a direct 40 % saving compared to the rigid dump truck previously used. There are also cost-savings on servicing and maintenance: “The extensive commonality of power-train, running-gear and peripherals technology with the B45D was naturally an important argument for us. Our mechanics also know the Mercedes-Benz engines extremely thoroughly, in addition to their many years of experience with Bell machines”. Bell Equipment Germany, indeed, acknowledged this when the performance of guarantee-relevant periodic on-site maintenance (after 500 h, for example) using original Bell spares and operating fluids was agreed with the Schmidt group’s certified specialist heavy-vehicle workshop.