Moulding Materials

Silica sandry sands from the Upper Palatinate

The company Strobel Quarzsand in Freihung has been extracting sands for numerous different industries for more than 135 years. Today the company is one of the top suppliers in Germany.
Although Germany is commonly regarded as a country lacking in raw materials, there is no lack of silica sand, which can be refined to make high-quality industrial products. One of the around fourteen silica sand deposits where sands for use in foundries are mined is located in the Gebenbach and Freihung area in the Upper Palatinate region. This is where for more than 135 years the company Strobel has extracted sands for a wide variety of industrial applications.The range of products that Strobel Quarzsand GmbH offers today extends from products for foundries (40%), for the glass industry (35%), construction chemistry (20%) as well as to construction products and products for the areas of sport and leisure. Strobel Quarzsand GmbH is an owner-managed family company with around 70 employees. „Despite the lean organisational structure, every year we produce approx. 700000 t in our plant in Freihungsand, making us one of the top producers of silica sand in Germany,“ says Benjamin Forster, son of the two managing directors Lisselotte and Günter Forster.It has admittedly been a long road to get to this point. Back in the 19th century, „Freihung silica sand“, which is renowned for its high level of purity, was still mined underground. Today the silica sand is mined at Strobel exclusively in a total of six open-cast pits using state-of-the-art machinery. Only sands we mine ourselves
„We only offer sands which we have mined ourselves,“ says Benjamin Forster. Strobel Quarzsand GmbH has specialised in fine sand (AFS < 0.15 mm) and very fine sands (AFS < 0.1 mm) which are renowned for high SiO2 contents and low levels of impurities.
Nevertheless, the range that Strobel offers is continuously expanding. „Customers’ increasing demand for customised specifications has changed the requirements that are placed on our products,“ observes Benjamin Forster. „As well as the demand for more individual grades of sand, the customer base has also changed. Our products are increasingly in demand internationally, even though we do not actively seek to acquire new customers internationally.“ Individual sand processing
Sand is a natural product. This is why the compositions of the sands which are mined also differ to a certain extent, e.g. the fraction of clay and heavy minerals. To ensure that the end product has the required quality, the mined sands must first be classified and then processed. This is done by the company’s own admission by selectively applying the sands to different wet processing systems. The rest of the stages for processing the silica sand are pre-screening, de- sludging through different hydrocyclone stages, attrition of the sands for cleaning the grain surfaces, classification into individual grain fractions in hydrosizers, segregation of the magnetic impurities by means of wet magnetic separation and dewatering of the end product by means of vacuum belt filters or vibration screening machines. The desludged, classified and sorted silica sands are then temporarily stored in a large depot and dewatered in a drainage system.
The residual moisture content of the silica sands is subsequently reduced down to less than one per mille using rotary dryers. Finally, high-frequency machines ensure a very high level of screening accuracy. The company also adds that, depending on the customer requirements, grain sizes of between 0.09 and 1.6 mm are also screened.
The sands for use in the foundry sector are suitable for producing mouldings and cores with the binding agents bentonite, synthetic resin or water glass. They serve as the basis for ready-to-use sands for a wide range of different uses right through to rapid prototyping. Besides the standard grades in the grain size range of from AFS 0.09 mm to AFS 0.40 mm, Strobel also offers very fine special sands up to AFS 250 as an additive in green sand. The foundry sands are constantly examined in the company’s own laboratory in order to optimise their use for the production of cores and mouldings. According to Benjamin Forster, Strobel has also geared itself up to meet the requirements of additive manufacturing. „We have adapted existing types of sand to suit the demands of 3D printing.“ Outlook
Benjamin Forster sees the company as being well positioned for the future. There may well be a series of challenges, such as safeguarding deposits of raw materials, recruiting and retaining skilled employees and increasing statutory requirements.
But: „In the last few years, the demand has moved away from the standard grades and evolved more towards more individually tested and specified sand grades. Customers want an increasingly broader offering and a greater variety of sand types,“ says Benjamin Forster. All this makes Strobel a strong partner for the industry.
Gerd Theißen

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