Improvements in and relating to the Production of Calcareous Sandstone.
Year: 1899

page_text: Date of Application, 6th Sept., 1899
Complete Specification Left, 6th June, 1900--Accepted, 6th Sept., 1900
PROVIDIONAL DIUIFICATION.
Improvements in and relating to the Production of Calcareous
Sandstone.
We, HANS CHRISTIAN MEURER, Chemist, and FRIEDRICH THEOPHIL BORMANN-
Zix, Merchant, both of Stadelhoferstrasse 40, Zürich, Switzerland, do hereby
declare the nature of this invention to be as follows: —
This invention has for object a process for the production of calcareous sandl-
stone by means of steam under pressure or of superheated steam. In preparing
the stone material according to this invention there is produced a complete and
rapid decomposition of the lime within the mixture of lime and sand, and a block
is turned out which is adapted for rapid hardening.
In the preparation of the stone-material it is, as is well known, of paramount
importance to rapidly and above all to completely slake the lime, so that no
unslaked sinter remains within the material which sinter would, when the block
was subjected to the action of the steam subsequently become slaked and would
scale off and destroy the stone or at least impair its firmness.
To overcome these defects we first of all intimately mix together dry "staub-
kalk" hereinafter called "air-slaked lime" and hot sand. The material in the
mixing apparatus is moistened with sufficient hot water, which water is always
at a temperature of something under 100° C., to exactly hydrate the lime and
the said material is then placed in a loose state in a closed \ receiver.
The
slaking of the lime is completed in a few minutes. The hot water for slaking is
always employed at a temperature of something under 100° C., in order to check
premature evaporation. The receiver, in which the slaking process is completed.
is also closed to prevent the escape of the steam generated and to oblige the said
steam to recondense. It is desirable that the material in the receiver should be
in a loose state in order to facilitate the flow of the steam through the said
material and also to permit said material to expand and thus avoid solidification.
The sand is heated previously to being mixed with the air slaked lime and is
hot at the time the mixing is effected. The degree of heat which may be want-
ing in the hot water is thus compensated and the evaporation of the water pro-
motes the breaking up of the lime. Evaporation, condensation, re-evaporation
&c., therefore go on throughout the slaking-vessel and this energetically accelo-
rates and completes the slaking process, so that under the action of the steami
and of the high temperature the lime throughout the entire mass is uniformly
hydrated and not an unslaked particle remains. It should, moreover, be observed
that in consequence of the dry state of the sand, due to its being heated before
mixing, a conglomeration &c., of the grains is prevented and hence a most inti-
mate mixture of sand and air-slaked lime is obtained. The proper manipulation
of this preliminary heating of the sand is of special value in connection with
smooth working in winter. The stone-material prepared in the manner herein-
before described leaves the receiver as a mixture in which each grain of sand is
surrounded by an envelope of slaked lime (lime-powder).

page_text: According to the method of shaping adapted (pressing, stamping, moulding
&c.) the pulverulent mass is repeatedly and thoroughly worked and moistened
with hot steam in a second mixing apparatus immediately before being shaped.
The block passes straight from the press to the hardening vessel It is impor-
tant that the steam in the said vessel which steam is under pressure or super
heated, should not come into contact with a cold block because in that case con-
siderable condensation of steam would take place and this would cause the block
to easily soften and break. The block must likewise be as dry as possible at the
commencement of this operation.
In the herein before described process of preparing stone-material, the said
material passes from the slaking vessel through the second mixing machine to
the press in a highly heated condition. The block which leaves the press and
reaches the hardening vessel dries itself in the most rapid manner and owing to
its high temperature any considerable condensation of the steam that impinges on
it is prevented. If it be impossible to immediately shape the stone-material pre-
pared in the slaking vessel, the said material must be kept in a hot state by
external means until it is shaped. This can be done by driving hot or superheated
steam through a double envelope surrounding the receiver or through heating
coils or some similar contrivance. This heating may also be applied during the
process of slaking so as to compensate for or prevent the transference of heat
from the material to the outside. It is further to be observed that in this
method of preparing the stone-material or block the breaking up of the quartz
ore silicic acid of the sand is started when the lime is slaked by the action of
the steam and high temperature and thenceforth until the completion of the
process in the hardening vessel the said decomposition continues uninterruptedly.
Hence according to this invention there is supplied a completely prepared stone
material or block previous to the hardening operation; the process also ensures
smooth working, in summer as well as in the winter and affords an entirely
mechanical and continuous method of manufacture. The manufactured article
obtained is a sandstone of great firmness, resistance to fire and durability.
Dated this 6th day of September 1899
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicants.
Improvements in and relating to the Froduction of Calcareous
Sandstone.
We, HANS CHRISTIAN MEURER, Chemist, and FRIEDRICH THEOPHIL BORMANN-
Zix, Merchant, both of Stadelhoferstrasse 40, Zürich, Switzerland, do hereby
declare the nature of this invention and in what manner the same is to be per-
formed to be particularly described and ascertained in and by the following
statement:
In hardening moulded blocks of calcareous sandstone by means of high pres-
sure steam experience has shown that the moulded blocks must comply with cer-
tain conditions if the firmness of their texture is not to be injured or perhaps
completely destroyed by the action of the high pressure steam.
Although there ought to be no particles of caustic lime remaining in the
hydrate of lime and sand mixture of the moulded block, since these particles
would become slaked by the action of the steam and would thereby destroy the
texture of the moulded block, there are two possible ways by which the moulded
blocks may be destroyed or spoiled in the hardening vessel viz., either in conse-

page_text: quence of the fact that the sand and hydrate of lime mixture of the moulded
block still contains hygroscopic water, which would be converted into steam by
the action of the high temperature in the hardening vessel and in expanding 'in
the interior of the newly made block would destroy its texture; or in conse-
quence of the fact that the high-pressure steam, which has a high temperature,
becomes cooled and condensed on the colder surface of the freshly moulded block
so as to soften the surface of the block in such a way that before the temperature
of the block is equal to that of the steam it may not only become deformed but
may break.
In order to avoid this risk of spoiling and destroying the newly made block a
process has been proposed for drying the wet moulded blocks by means of hot
air before subjecting them to the action of the high-pressure steam and for
simultaneously bringing them up to the temperature of the steam. According
to another proposed process the freshly made blocks are first heated by steam of
low pressure, while piled on waggons and protected by a finely perforated guard
adapted to keep the moisture of the low-pressure steam from the moulded blocks
and to impart only the heat to them. The high-pressure steam subsequently
admitted to the hardening vessel then passes through the perforations in the
guard to the previously dried and warmed block. Such preliminary treatment,
which has been found necessary, complicates and increases the cost of working
and is therefore unpractical; if, however, no preliminary treatment or protecting
device were used it might be expected that the stones would be spoilt or that
imperfect stones would be obtained even if made of a moister mortar or pressed
from a dryer material by using a higher pressure.
Now, this invention has for object to produce moulded blocks of calcareous
sandstone which are in such a state that without spoiling or injuring them and
without any preliminary treatment or the use of any protecting device they can
be subjected to the direct action of high-pressure steam for the purpose of quickly
petrifying them. The steam generators can therefore be constantly maintained at
the same pressure and the consumption of steam will be reduced in consequence
of the reduced time required for hardening.
According to this invention the stone material is prepared in a novel manner
suitable for manufacture on a large scale, so that the blocks pressed from this
material and coming from the press set at once, i.e., through the rapid and com-
plete 'decomposition of the lime and the consequent formation of a coherent
crystalline hydrate of lime throughout the moulded blocks, due to the rapid
evaporation of the hygroscopic water, they are converted into a more stonelike
condition. When the blocks in this condition are subjected to the action of high
pressure steam they contain no more hygroscopic water which can be converted
into steam and they are already so much hardened in texture that even a very
great condensation can no longer soften or deform them; the process of com-
pletely petrifying them takes place smoothly and uninterruptedly.
The experiments made by us as to the causes of the peculiar phenomena, the
so called "overburning" and the so-called "drowning" of the lime, when ordi-
narily burnt lime is slaked with too little or too much water, have shown that
both of these phenomena depend on the readiness of oxide of calcium to combine
with water to form crystals or a crystalline mass, and that the rapidity of the
formation of such combinations depends on the proximity of the molecules to one
another and on the height of the temperature acting thereupon. When" over-
burnt" lime is slaked it feels like a sandy powder and can no longer be made into a
soft lime paste by the addition of water in reality, in consequence of the crowded
state of the molecules of the calcium oxide and the action of the high temperature
produced, the calcium oxide combines immediately with the water to form
crystals or crystalline compounds which resist the absorption of more water.
When the lime is "drowned the opposite condition occurs; when calcium oxide
is treated with too much water the molecules are so far apart that a crystalline
compound cannot be formed. Such lime is useless for the preparation of mortar

page_text: even when again dried. It is assumed that the power of attraction of the mole-
cules of hydrate of lime has been completely lost. But the hardening of the
mortar made with air-slaked lime depends really on the formation of crystalline
compounds. The substitution of carbonic acid for the water of the hydrate occurs
only at a second stage. Our further experiments have shown that in order to
effect the instantaneous and regular formation of a crystalline compound it is
necessary to obtain a saturated solution of pure hydrate of lime at a high tem-
perature and preferably thoroughly mixed with sand or other similar filling
material, and that this formation takes place more rapidly and attains a greater
degree of hardness the higher the temperature at which it is carried out and the
higher the pressure to which it is subjected. A "saturated solution" is produced
when a mass of pure hydrate of limei.e., completely slaked and specifically
heavy hydrate of lime, in other words, a hydrate of lime, the molecules of which
have been kept as close together 'as possible by suitable slaking-contains an
excess (6 to 8%) of hygroscopic water. As the stone material is composed on the
average of 90% of sand to 10% of hydrate of lime, the quantity of hygroscopic
water to be added amounts to 6 to 8% in relation to the entire stone material.
When this material is mixed homogeneously with the filling material (the sand)
it insures regular and firm clinging surfaces in all parts of the compounds produced
Our process for the production of rapidly setting moulded blocks of calcareous
sandstone is based on the principles herein before described. In practice, how-
ever, we do not simply prepare this "saturated solution" from oxide of calcium
mixed with sand by slaking the lime at once with the total quantity of water
required, the hydrating water plus the addition mentioned and heating the
mixture during the slaking process, since the desired result could scarcely be
perfectly attained in this manner. On one hand by adding directly the total
quantity of water required a greater molecular separation of the lime being slaked
would result which might render a rapid and regular crystalline formation doubt-
ful, and on the other hand there would be a risk that separate formations might
occur in the hot mixture before pressing, especially as the material must always
lie for a short time for the purpose of completely hydrating all the molecules, i.e.,
for slaking even the more sinter-like particles of the lime.
In order to carry out the process smoothly every time and to attain the desired
result in every case independently of chance, we divide the production of the
stone material containing the saturated solution of pure hydrate of lime at a
high temperature mixed homogeneously with sand into two processes: (a) The
production of a homogeneous mixture of sand and hydrate of lime, the latter of
which is adapted, in consequence of its complete slaking, its molecular density
and its higher temperature, to form the saturated solution through the addition
of a definite quantity of water, which has also a high temperature. (b) The pre-
paration of this solution by adding a definite quantity (6-8%) of water at a high
temperature to the before-mentioned sand and hydrate of lime mixture imme-
diately before pressing into blocks.
In carrying out the process we start by using a uniformly dry sand as described
in the Specification of Letters Patent No. 12368 of 1896 in order to be indepen-
dent of the varying natural moistness of the sand and to enable us to add always
the same quantity of hydrate water in the charges of the mixture used by us for
the sake of simplicity in the manufacture.
23
We heat the sand-previously stored until dry or with its natural moisture-to
a high temperature, preferably by the direct action of furnace gases, mix it in
the proportion by volume of about 6:1 with "Staubkalk i.e., burnt lime that
has been powdered by air-slaking or otherwise-mix this mass in a mixing appa-
ratus so as to form a perfectly homogeneous mixture and then slake the lime to
form a dry hydrate by moistening it thoroughly and uniformly with the exact
quantity of warm water--on an average 32%-required for hydrating it.
object is to start the slaking process energetically and carry it through in the
shortest possible time while thoroughly slaking all parts. It is known that hot
The

page_text: "
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water causes the hydrating to start more energetically and to be completed more
rapidly. But it is disadvantageous to use it for the dry mixture of sand and
powdered lime because lumps would at once be formed which would absorb too
much water and keep it for a long time from the other parts. This would cause
a varying density in the position of the hydroxyl molecules in the entire mass
which would interfere with the subsequent regular formation of the crystalline
compound; moreover, there would be a risk of partial burning. In order to
obviate these disadvantages, on the one hand we moisten the powdered lime
thoroughly and uniformly throughout the entire mass by moving the mass as fast
as possible in the mixer, and using it in a finely powdered state, and on the other
hand we modify the action of the heat that expedites the slaking-i.e., the
chemical combination of the calcium oxide and the water-by employing
damp heat in the form of warm water whose temperature is always more or
less under 100° C. and to compensate for the reduction in temperature we provide
a source of "dry" heat by using hot sand mixed with the powdered lime; the
temperature of the slaking water must be in inverse ratio to that of the sand.
The water used for slaking must not be too hot, as otherwise a premature and
considerable evaporation would occur, since the steam generated would again
condense and act as hydrating water, which would retard the process.
possible escape of the steam generated is prevented since the mixer is closed in
order to prevent the mixture from being thrown out. In consequence of the
action of the two sources of heat and of the uniform moistening, the hydration is
completed in the shortest time and a stone mass is formed in which the sand
and the hydrate of lime are intimately combined and in which the latter appears
as a pure, completely slaked powder of the highest molecular density.
The
The stone mass leaves the mixing machine as a hot dry mixture in which each
particle of sand is enclosed in a coating of firmly adhering hydrate of lime, and
the said mass is conveyed to a hopper or receptacle which is arranged above the
press and from which it passes through another mixer to the press. In this
second mixer the hot saturated solution is obtained, the stone material entering
it being uniformly moistened with a certain quantity (6 to 8%) of hot water.
Perfect uniformity in moistening is also necessary in this case and it can be
effected here by a rapid movement of the mass and by the use of hot water in a
finely divided state. If the stone material issuing from the hopper or receptacle
should have cooled through standing for some time it must be again heated before
or during the treatment in the second mixer. For this purpose the mixer is pro-
vided with a jacket which can be heated by steam.
.
We
The prepared hot mixture is at once pressed into blocks; the pressing takes
place smoothly as the material has the most suitable consistency. The "setting"
is completed in the moulded block of calcareous sandstone coming from the press.
The compression of the stone material causes the hydrate to form thin layers
which bind together the several particles and are converted, while forming a hot
saturated solution, into a coherent crystalline mass throughout the entire moulded
block, the excess of water being separated out by rapid evaporation. The newly
made blocks are placed in the hardening vessel and are subjected to the direct
action of high-pressure steam for the purpose of rapidly petrifying them.
assume that this petrifaction depends mainly on a gradual hardening of the
hydrate of lime until it attains its greatest strength under the action of the high
temperature and the pressure of the steam. Furthermore, calcium hydrosilicate
is produced by the combination of the hydrate with the silicic acid of the sand.
The quantity of water required for the formation of this hydrosilicate cannot be
exactly determined but is supplied to the block partly as water of condensation,
since the high-pressure steam condenses and moistens the moulded block which
has already "set" like stone, and partly-which is important for the subsequent
duration of the hardening process when the steam has become dryer-as so called
priming" water which accompanies the steam to a greater or less extent in all
steam generators and is consequently conveyed to the hardening vessel.
"

page_text: Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed we declare that what
we claim is:-
-
1. A process for the manufacture of moulded blocks of calcareous sandstone,
which are adapted to be subjected without any previous treatment or protecting
device to the direct action of high-pressure steam for the purpose of rapidly har-
dening them, wherein the blocks are pressed out of a stone material consisting
of a hot and homogeneous mixture of sand and a saturated solution of pure
hydrate of lime.
2. In the process referred to in the preceding claim, the preparation of the
stone material described, by (a) slaking a homogeneous mixture of sand strongly
heated by the action of furnace gases, and burnt and powdered lime by moisten-
ing it with about 32% of warm water having a temperature in inverse ratio to
the temperature of the sand but always under 100° C.; and (b) uniformly moisten-
ing the dry powdered and hot stone material thus obtained, immediately before
pressing, with a certain quantity (6-8%) of hot water.
3. A modification of the process according to Claim 2, wherein the stone mate-
rial, which is obtained according to the portion (a) of Claim 2 but has become
cooled by lying for some time, is again heated in a suitable manner before or
during the treatment according to the portion (b) of Claim 2.
1 13
01
1000
い
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicants.