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Refractories is a generic term for (with very few exceptions)
non-metallic materials that are used industrially at long-term
temperatures of over 800°C. They are always extremely
hard and brittle materials
with a Mohs' hardness of above 4 or 5.
Applications for these materials are:
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a) |
Raw materials
such as all types of clays, kaolin, magnesium carbonate,
etc., for the manufacture of refractory products.
The product fineness values are in the millimetre range,
whereby dependent on the application, particle sizes
of up to 20 µm are also common.
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| b) |
Intermediate
products as the starting material for the manufacture
of semi-finished products such as pipes, nozzles, shaped
parts, etc. In this case, spinel, mullite and magnesite
are used with fineness values ranging from 300 to 500
µm.
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| c) |
Sprayable
products for coatings, etc. based on different ultrafine
oxide mixtures such as Al2O3,
Al2O3/spinel, Al2O2 /spinel/magnesia and Al2O3/SiO2.
The fineness values demanded here are generally under
5 µm.
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The
fineness and particle size distribution have a critical
influence on the packing density and thus also on the
thermal properties of refractory materials.
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Another important
factor is the contamination-free (iron-contamination-free)
processing of the above-mentioned products. A number of
different grinding technologies are available, e.g. with
the fluidised bed opposed jet mill or a combination of
the high-compression roller mill ECP, table roller mill
AWM and/or ball mill S.O. with fine or ultrafine classifiers.
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As an example, the diagrams
below depict the processing
sequence of a complete processing system for magnesite,
whereby Alpine delivers the fine grinding and classifying
steps.
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