Improvements in Artificial Stone for Grinding or Abrading Purposes.
Year: 1897

page_text: COMPLETE SPECIFICATION.
Improvements in Artificial Stone for Grinding or Abrading Purposes.
We, CARL COWEN SCHIRM, Landscape Painter, and OTTO LESSING, Professor, both
of No. 51 Königin Augusta Strasse, Berlin, Germany, do hereby declare the nature
of our invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
Hitherto grinding agents have been employed in the industry consisting mainly
of natural agents, best suited for the particular purpose in view.
Since, however the stores of natural products are limited and in some cases soon
exhausted attempts have been made to replace natural by artificial products, which
attempts have, for many purposes been entirely successful, thus for instance the
artificial grindstones of the sandstone class, consisting of sand imbedded in cement or
other suitable material such as clay and the like.
For many purposes, however, it has not been possible to produce a suitable artificial
grinding medium, thus for instance in the manufacture of cellulose, paper, etc. a
particular kind of sandstone is necessary, which can only be found in Saxony and
Bohemia, in order to grind the wood pulp produced from the block. Even Norway is
obliged to import all this class of stone from the above mentioned places.
This stone possesses the pecularity that the grains of sand in their natural formation
are only cemented together at their points of contact one with the other, the
interstices remaining hollow, which is not the case with good hard sandstone. Further-
more the binding medium which cements the grains of sand together is of peculiar
hardness, exactly suited to the particular requirements of the case, the hardness
being such that if too much pressure is applied to the grindstone the grains of sand
will become detached. If the stone does not possess the prescribed porosity and if the
grains composing the same are too firmly cemented together, the stone will soon get
set full of wood pulp and become smooth, or the grains will tears fibres from the wood
rendering the pulp of an inferior class.
These conditions are of such importance for the above mentioned purpose that the
necessary stone can only be obtained from Saxony or Bohemia.
The total amount of this stone is relatively small and its price rises from year
to year, indeed it is not improbable that the whole store will be exhausted at no very
distant future.
Hitherto none of the artificial stones have been able to replace this natural product.
In every case the attempts have failed owing to the fact that imbedding the grains in
a mass, closes the pores of the product obtained, the binding mass has either been
too hard or too soft (only few masses exist at all which are suitable for the purpose)
in short, in this particular branch of the industry, as in many others the artificial
product has proved inadequate for the purpose.
The process forming the object of the present invention renders it possible to adapt
the artificial product to the particular requirements of the case.
In carrying out the process a flux, of suitable hardness such as glass flux or fluor-spar
is added to a granular grinding medium, the grain of which exactly suits the particular
purpose in view (sand, pulverized quartz, emery or the like) and the whole subsequently
heated to the fusing point of the flux so that the grains of the grinding agent will
either be baked together at their points of contact only, or, if the amount of flux
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page_text: added is increased, that the interstices will be more or less filled up, according to the
degree of porosity required.
The grinding agents are first formed of the above mentioned mass, i.e. moulded and
then fired at a temperature equal to the fusing point of the flux.
Fluxes of any desired hardness may be produced; the grain of the grinding medium
may be sieved to any desired degree of fineness and the porosity may be nicely adapted
to the particular object in view by varying the amount of the flux added.
Thus the present process provides means for adapting the nature of the artificial
grinding medium obtained, to any particular branch of the industry. Thus for instance
the grindstones for wood pulp works, can be turned out in such qualities as will be
capable of even exceeding the natural product in homogeny of the mass and evenness
of grain.
In carrying out the process parts of sieved quartz sand are advantageously mixed
with one part of a glass flux, or fluor spar having a fusing temperature of 850-900°
the mixture is moulded with the aid of water then dried and heated to about 900°.
The result is illustrated in the accompanying drawing: in which Figure 1 shows the
arrangement of the molecules A of the flux and those B of the grinding medium before
the mass is heated, whilst Fig. 2 shows the same arrangement after the mass has
been fired, C representing the interstices corresponding to the degree of porosity
required. As a rule 6 grains of the grinding agent will encircle one grain of the flux
the grinding agents being in contact with each other and with the molecule of flux as
illustrated. By this means and in view of the degree. of hardness of the flux, any
particular requirements of the industry may be met. It will be evident that, by.
varying the nature of the grinding agent and the hardness of the flux, the. grinding
agent may be made to suit any particular industrial purpose..
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is :-
A process .for producing grinding masses. by ceramical means, which consist in
mixing the granular grinding agent with a flux of the requisite hardness, in such
proportions as to attain the requisite porosity, moulding the inass thus attained and
heating it to the fusing point of the flux.