Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
a) Field of the invention
~ The present invention relates to a new heat-
resistant composition particularly useful to produce heat-
resistant boards, sleeves or linings capable of resisting
to high temperatures for substantial periods of time. The
invention also relates to the boards, sleeves, linings and
similar articles obtained from such a composition by vacuum
forming.
b) Brief description of the invention
Canadian patent application serial number 577,693
filed on September 16, 1988 in the name of the same
Applicant, discloses and claims a fibrous-like synthetic
forsterite product which is particularly useful as an
insulating material. This product which is presently
offered for sale under the trademark FRITMAG and will be
called as such hereinafter, is obtained by subjecting
chrysotile asbestos fibers of any commercial grade, having
an MgO: SiO2 ratio lower than 1:1, to calcination at a
temperature of from 650 to 1450C.
FRITMAG has a raw loose density of from 3 to 40
pounds per cubic foot, a thermal conductivity K factor of
from 0.25 to 0.40 BTU. in/hr.F.ft and a fusion point of
about 1600 to 1700C. It possesses a somewhat fibrous
structure ressembling that of the chrysotile asbestos
fibers from which it derives, although this fibrous
structure has shown to disappear upon rough manipulation,
when subjected to pressure, or when mixed with other
material. Then, the fibrous structure is lost but the
product has and always retains a high insulating value
,
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which is quite superior to granular forsterite, or similar
to KAOWOOL ttrademark) or rockwool.
In the above-mentioned canadian patent application,
it is mentioned that FRITMAG may be used as a substitute
for asbestos, whenever a fibrous material to be used in
bulk and having high insulating qualities is needed.
Indeed, FRITMAG is fibrous and has a loose density range
substantially identical to asbestos. It also has high
insulating properties and is devoided of all the
undesirable health problems allegedly attributed to
asbestos.
In the above-mentioned canadian patent application,
it is also suggested to mix FRITMAG with an inert filler
and a binder in order to form an insulating composition
adapted to be shooted onto any surface to be insulated or
to be moulded in the form of slabs for roof insulation.
However, no specific example of such a composition is
given, except for a short reference made in the
specification to a possible mixing with other materials,
such as Portland cement. Similarly, no method of
manufacturing slabs from such a composition is disclosed,
although it is obvious that some of the methods presently
used on an industrial scale to manufacture slabs may not be
applicable if FRITMAG is part of the combination, because
of the change of structure that has been noticed in this
product when it is subjected to pressure or mixed with
other materials.
SUMMARY OF THE INVENTION
The present invention derives from further
studies that have been conducted on FRITMAG since it was
first synthetized.
In accordance with the present invention, it has
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been found that heat-resistant boards, sleeves, linings and,
more generally, any kind of heat-resistant articles capable
of resisting to very high temperatures over substantial
periods of time can be produced from a new heat-resistant
composition processable by vacuum forming and consisting of
an aqueous suspension containing from 1 to 10% by weight of
a mixture comprising from 30 to 70% by weight of FRITMAG,
the balance consisting mainly of colloidal silica as a
binder.
The heat-resistant composition according to the
invention may also comprise reinforcing fibers preferably
selected from the group consisting of cellulose, glasswool,
refractory fibers such as ceramic fibers, rockwool and
their mixtures, in such an amount as to give sufficient
strength, especially tensile strength, to the composition
to make the article produced therefrom operative depending
on its intended use.
In accordance with the invention, it has also
been surprisingly found that the vacuum forming method
commonly used for manufacturing heat-resistant boards,
sleeves, linings or articles of any specific shape from
any heat-resistant composition can also be used with
success if use is made of the heat-resistant composition
according to the invention as defined hereinabove as
starting material. This vacuum forming method which is
also used industrially worldwidely, basically consists in
subjecting to vacuum an aqueous suspension containing from
1 to 10% by weight of solids. This vacuum forming method
is particularly useful to produce boards, sleeves or any
hollow shaped articles.
Surprisingly, it has been found that FRITMAG can
effectively be used as a substitute for asbestos to produce
boards, sleeves or hollow articles through such a vacuum
forming method. As a matter of fact, it has been found
that FRITMAG behaves as asbestos when subjected to vacuum
and gives heat-resistant sleeves, boards or hollow articles
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that can be subjected to very high temperatures over
substantial periods of time and behave as effectively as
any similar article made from "standard asbestos
composition", such as the one presently sold as MILLBOARD.
As aforesaid, the composition according to the
invention may further comprise reinforcing fibers.
Advantageously, the amount of reinforcing fibers may be
adjusted at will, so as to give sufficient strength,
especially tensile strength, to the resulting article to
make it operative depending on its intended use. This
amount of fibers added to the composition may be very
small. Indeed, the addition of such reinforcing fiber is
not required by any of the manufacturing methods mentioned
hereinabove, but exclusively by the desiderata of the
consumer.
Of course, the kind of fibers incorporated into
the composition depends on the intended use of the boards,
sleeves or heat-resistant articles produced from the
composition. As a binder, use is made of colloidal silica
like the one sold under the trademark LUDOX. If desired,
additional binders such as starch may be used together with
colloidal silica.
As aforesaid, the vacuum forming method may be
used to produce boards and sleeves. It may also be used to
produce other hollow articles of more complicated shape,
such as casting molds, furnace insulating components and
the like.
The composition according to the invention may
further comprise inert fillers and additives known per se
in this very specific field. Examples of such additives
are siliceous dust, quartz, crushed stones, kaolin, blast
furnace slag, etc.
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EXAMPLE 1:
Plates of 30 cm X 30 cm having a thickness of
0.3 cm were produced by vacuum forming, using the
composition given hereinafter as starting material.
FRITMAG 10.0 kg
FIBERFRAX~ 4.0 kg
Starch (EMPRESO ~ 0.8 kg
LUDOX HSR-40 2.8 kg
More particularly, the plates were prepared as
follows.
Starch previously dissolved into water were
added into the process water. FRITMAG and reinforcing
fibers of trademark FIBERFARX and LUDOX HS-40 were
subsequently added in this order. The concentration of
solid in the process water was kept to about 3% and the
elements were mixed for a period of time of 5 to 10
minutes prior to being subjected to vacuum forming .
The mixture was then subjected to vacuum forming
to produce the requested plates. The resulting plates were
compressed to have a volumic weight of 1.25g/cm3 and were
dried at 105C for 24 hours.
The tensile and bending strengths of these
plates are given in Table I and are compared with the
mechanical properties of similar plates obtained from a
commercial asbestos-containing MILLBOARD.
After heating at 8 hours at 1000C, the
resulting plates kept about 80% of their mechanical
properties. In contrast, the plates obtained from the
asbestos-containing MILLBOARD were reduced to dust after
heating at 800 C for 5 hours.
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TABLE I
MECHANICAL PROPERTIES AFTER DRYING AT 105C
Volume Bending Tensile
weight strength strength
gr/cm MPa MPa
Composition
according to the
invention 1.25 4.5 2.6
Asbestos-containing
MILLBOARD
(comparative) 0.90 5.6 3.0
EXAMPLE 2:
Cylindrical sleeves having a length of 35 cm, an
internal diameter of 10 cm and an external diameter of 14
cm were produced by vacuum forming, starting from the
compositions given in Table II hereinafter. Each of the
compositions was processed as disclosed in Example
hereinabove, prior to being subjected to vacuum forming.
The resulting sleeves were dried for 24 hours at
105C.
~ 33~ 3
TABLE II
COMPOSITION
A B C
Starch (kg) 0. 37 0.370.37
FRITMA ~ (kg) 3.68 4.655.56
Rock Wool (kg) 2.83 1.860.95
LUDOX HS-4 ~ (kg) 1. 30 1.301.30
Water (liters) 163.00 163.00 163.00
The volumic weight of the sleeves produced from
compositions A, B and C were equal to 18, 20 and 36 pcf
respectively.
EXAMPLE 3:
Cylindrical sleeves similar to those disclosed
in Example 2 were produced by vacuum forming, using, as
starting materials, compositions given in Table III
hereinafter. The sleeves were dried for 24 hours at 105 C.
The volumic weight of the sleeves produced from
compositions D, E and F were equal to 12, 20 and 19 pcf
respectively.
TABLE III
COMPOSITION
D E F
Starch (kg) 0. 37 0.37 0.37
FRITMA ~ (kg) ---- 4. 65 ----
-
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Rock Wool (kg) 6.51 1.86
Fibers (MANVILLE
No. 6)~ (kg) ---- ____ 6.51
LUDOX HS-4 ~ (kg) 1.30 1.30 1.30
Water (liters) 163.00 163.00 163.00
The sleeves that were so obtained were
hermatically closed at their bottom and aluminum was casted
in molded form at a temperature about 800C inside the
same. A temperature sensor was placed into the aluminum to
follow the evolution of the temperature. The result of
these tests are reported in Table IV.
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TABLE IV
VARIATION OF THE ALUMINUM TEMPERATURE INSIDE THE SLEEVES
Time (in minute) COMPOSITION
D E F
C C C
2.5 673 750 750
5.0 657 725 715
7.5 650 700 680
10.0 650 675 660
12.5 650 660 650
15.0 650 650 650
20.0 649 650 650
25.0 648 650 650
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As can be noted, the sleeves made from
composition E had a behaviour that was equal to or slightly
better than the the behaviour of the sleeves made from
composition F. Both of these sleeves had undergone very
small degradation after complete cooling of the aluminum.
The sleeves made from composition E (i.e. from the
composition containing FRITMAG) had a behaviour much
superior to the sleeves made from composition D. The
sleeves made from this composition D underwent substantial
degradation after cooling of the aluminum.
