Trouble-free operation

Generation change in the crushing process

With around 3000 employees, the family-run Bachl Group is one of the most important companies in the construction industry, insulation technology and other independent business areas in Lower Bavaria. Among other things, Bachl operates three granite quarries within a radius of 4 km, of which the main quarry in Wotzdorf is operated exclusively on a stationary basis due to the stationary asphalt mixing plant and the required processing capacities of 350 000 t/a on average. The Group’s second quarry, a former quarry, has since been converted to bulk materials. Rock processing there is exclusively mobile. Operations in a third quarry are currently suspended. Around 70 % of all granite aggregates produced are utilised by the company itself, are mainly used for construction services in building construction and civil engineering or are used as aggregates for building material mixtures.


Retiring pioneers

For 26 years, the main quarry in Wotzdorf has been using crushing technologies from the Finnish manufacturer Metso for rock processing, which at that time still bore the brand names Lokomo or Nordberg. In recent years, however, there has been a need to replace the tried-and-tested pioneers with new systems. The last of three component changes took place in January 2023 – a stationary Metso Nordberg C150 jaw crusher went into operation at the beginning of the year. The predecessor machine from a competitor had to be replaced due to damage after decades of use. Only minor adjustments had to be made to the steel structure for the installation. The replacement itself then went smoothly. “We decided in favour of the C150 jaw crusher from Metso because the frame is bolted and not welded. Housing breakage or broken weld seams are simply ruled out here. And if something does get damaged inside the housing, you can replace every single component or assembly thanks to the modular design,” explains Josef Stockinger, the second retired plant manager.


Proven quality on the safe side

The new jaw crusher processes between 250 and 300 t/h and is in operation for up to 10 hours a day. The size of the blasted feed material for the 1st crushing stage is sometimes up to 1.3 to 1.4 m per lump. The C150 produces 0/300 mm material as a primary product, which is then fed to the Metso Nordberg GP300S stationary cone crusher, which was also installed in 2018. “The replacement of the new plant was completed in just 6 working days together with Metso,” says Martin Schlig, plant manager in Wotzdorf. “There were no further disruptions during commissioning and the start of production.”


In the 2nd crushing stage, fractions of 0/80 and 0/90 mm are produced from the 60/300 mm feed material, whereby a proportion of frost protection material from 0/56 mm is screened out. Further grain sizes from 11/56 to 11/60 mm are then available for the 3rd crushing stage for the production of high-grade chippings (8/11 mm) and other end products in the 0/32 mm range.


When replacing a crusher in the 3rd crushing stage in 2020, the choice was once again made in favour of a Metso plant. A joint decision was made to initially replace both pioneers – the old Lokomo G1211 and an H36 from Svedala – with a crusher for high-grade chippings production. However, the first attempt failed despite the throughput rate achieved, as the cubicity of the high-grade chippings did not consistently meet the customer’s requirements.


Task sharing in high-grade chippings production

After several conversions and quality tests, the decision was made to use two crushers in parallel operation for the high-grade chippings stage. Bachl decided in favour of a Metso Nordberg GP220 stationary cone crusher and another unit from a different manufacturer. Numerous tests were carried out on both new units in order to maintain a consistently high level of quality with regard to grain shape. The GP220 has a specially developed crushing chamber geometry to fulfil such requirements.


“Since 2021, the new IC50C control software has made a significant contribution to ensuring that the GP220 from Metso moves consistently and does not open the gap jerkily,” explains Martin Schlig. “With the software update, the device reacts less to overload peaks than before. The reaction to the spontaneously increased internal pressure was somewhat abrupt at the time and opened the gap immediately to 1 to 2 mm. Today, thanks to the new software, the crusher opens the gap in 0.5 mm steps. Since then, overload peaks have become less significant, as the software is more orientated towards an average value in the crushing cycle.”


Following the crusher replacement, Bachl entered into an extended warranty agreement with Metso for a period of 5 years, which covers individual assemblies. The state-of-the-art plant has been in trouble-free operation on the 15.2 ha site ever since and produces granite, covering and high-grade crushed sand, high-grade chippings, frost protection materials, aggregates, gravel, granite scrap and backfill materials in all grain sizes.

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