Note: Descriptions are shown in the official language in which they were submitted.
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MOLDING SAND SUITABLE FOR MANUFACTURING
CORES AND CHILL-MOLDS
FIELD OF THE INVENTION
This invention is related to the manufacture of
iron casting and, specifically, it refers to a molding sand
for casting, suitable for manufacturing cores and chill
molds, incorporating hollow microspheres of aluminum
silicate.
BACKGROUND OF THE INVENTION
The iron casting obtained by using cores
manufactured with molding sand, generally have a series of
defects in their shape, such that it is necessary to subject
them to machining to obtain a dimensionally correct piece.
These defects are produced due to the heating the core
suffers due to the effect of the molten metal poured over
it, provoking its expansion and hence, the appearance of
fissures on its surface. The molten metal penetrates these
fissures, hence forming a kind of partition wall or laminas
on the surface of the piece obtained. This undesired effect
is known "veining" or "rat's tail".
At present, the cores are manufactured using
molding sands and gas- or heat-cured resins, or self-curing
resins, together with additives destined to improve the
characteristics of the piece obtained.
To prevent the formation of "veining", a series of
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techniques are known and used, such as:
- The use of iron oxide as an additive.
The iron oxides used as additives, are destined to
minimize the problems created by the expansion of the silica
contained in the sands, being used for such a purpose red,
black, yellow iron oxides or iron oxide from Sierra Leone,
which are incorporated to the mixture in percentages varying
from 1 to 30. These oxides act as a factor for the formation
of feyalite, such that the "veining" is minimized during the
formation of the fissure. Nevertheless, this technique
besides not eliminating "veining" in some cases, has as a
disadvantage that the iron oxide reduces the mechanical
resistance of the core and moreover the formation of
feyalite increases the tendency to penetration, causing the
external surface of the piece obtained to present
irregularities, which should be treated later.
- Use of wood flours and coal powder.
According to this technique, wood flour or coal
powders are added in proportions varying from 1 to 3o. These
flours burn during melting, hence leaving free gaps
distributed throughout the volume of the core, permitting
that the expansion of the silica is produced in these gaps
without the need to increase the external size, hence
avoiding the appearance of fissures provoking "veining". The
main disadvantage of this technique is that when the flours
burn, a large amount of gas is produced which, on
circulating, may result in dimensional problems in the
pieces obtained. Likewise, with this type of additive, a
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reduction in the mechanical resistance of the cores is
produced.
- Use of titanium oxide as an additive
This new technique described in the US Patent
Number 4.735.973, is based on the use of titanium oxide
additives, the additive being present at percentages varying
between 0.5 and 50 of the total amount of sand and said
additive containing between 15 and 95=o titanium oxide. With
this technique, thermal expansion is reduced, preventing, as
a result "veining", maintaining the mechanical resistance of
the cores and not producing an increase in gas production.
The disadvantage of this technique lies in the fact that the
cores obtained possesses a certain tendency to penetration,
it being necessary to apply paints or other treatments on
the surface of the cores obtained before proceeding to
melting the piece.
- Use of natural sands of low expansion
This new technique uses for the formation of the
core, special sands of the rounded of sub-angular silica
type, chromite sands, zirconium sands and olivine sands,
which, due to their different degrees of thermal expansion,
result in the reduction of "veining", and even to its total
elimination. The basic disadvantage of this technique is
the high cost of this type of sand, with the consequent
increase in the cost to obtain the gores.
- Use of electrofused sands of low expansion
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According to this technique, the silica sand
normally used for the manufacture of cores is melted in
electric ovens, until obtaining a kind of paste without
expansion capacity. Then, the paste obtained is ground until
obtaining a sand powder which is mixed approximately at 50
with silica sand. In this way, the expansion of the core is
avoided, since the powder obtained from the silica paste
does not have a capacity for expansion and hence, neither
produces fissures nor the corresponding veining. The basic
disadvantage of this technique is the greater complexity of
the production process, which makes the final cost to obtain
the cores more expensive.
As may be appreciated, the techniques normally
used to prevent the formation of "veining" consist either in
the use of additives (iron oxide, titanium oxide, wood
flours and coal powder) or in the use of special sands
(natural sands of low expansion or electrofused sands of low
expansion).
Now it has been found that it is possible to
improve the quality of the iron casting by using cores or
molds manufactured with molding sands incorporating hollow
microspheres of aluminum silicate.
As a result, a purpose of this invention comprises
a molding sand for casting which incorporates hollcw
microspheres of aluminum silicate.
An additional purpose of this invention comprises
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a process to manufacture cores or chill molds including the
use of the molding sand indicated above. The resulting
cores and molds also comprise a purpose of this invention.
Another additional purpose of this invention
comprises a process to manufacture iron casting including
the use of the cores or molds mentioned above. The
resulting iron casting also comprises a purpose of this
invention.
SUI~iARY OF THE INVENTION
According to a first aspect of the present
invention, there is provided a composition for the
manufacture of cores and chill molds which comprises a
molding sand, a resin and hollow microspheres of aluminum
silicate, said hollow microspheres of aluminum silicate
being present in the composition in an amount between 1 and
30~ by weight of the total amount of the composition and
having an aluminum content between 15 and 45~ by weight of
the microspheres to absorb expansion when the core or chill
mold is heated by a molten casting metal and thereby to
prevent formation of fissures in the core or chill mold and
veining of a cast article.
According to a second aspect of the present
invention, there is provided a cold process for the
manufacture of a core or chill mold comprising: introducing
a composition for the manufacture of cores and chill molds
according to the first aspect of the invention, in a forming
mold to form a non-cured core or mold; contacting said non-
cured core or mold with a gaseous curing catalyst until said
core or mold may be handled; and separating said core or
chill mold from the forming mold.
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According to a third aspect of the present
invention, there is provided a core or chill mold produced
according to the process of the second embodiment.
According to a further aspect of the invention,
there is provided a process for the manufacture of an iron
casting, which comprises: inserting the core or chill mold,
according to the third embodiment, in a casting device;
pouring an iron casting composition in a liquid state, in
said casting device; allowing the casting composition poured
into the casting device to cool and solidify; and removing
the casting composition thus solidified from the casting
device as the target iron casting.
According to a further aspect of the present
invention, there is provided a method of producing an iron
casting comprising: introducing a molding sand into a
forming mold, said molding sand having a composition
comprising: sand, a resin and hollow microspheres of
aluminum silicate, said hollow microspheres of aluminum
silicate being present in the composition in an amount
between 1 and 30~ by weight of the total amount of the
composition and having an aluminum content between 15 and 45%
by weight of the microspheres, forming a non-cured core or
mold in said composition, contacting said non-cured core or
mold with a gaseous curing catalyst until said core or mold
may be handled, inserting the core or mold in a casting
device, pouring an iron casting composition in a liquid
state, in said casting device; allowing the iron casting
composition poured into the casting device to cool and
solidify; and removing the thus solidified iron casting from
the casting device, said iron casting being free of surface
defects including veining due to smoothness of the care or
mold as a result of absorption of expansion by said
microspheres when the core or mold is heated by the casting
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metal, whereby the iron casting is the target product as is
without need for machining.
According to still another aspect of the present
invention, there is provided a method of reducing surface
defects including veining in the surface of an iron casting
produced by a method comprising: introducing a molding
composition into a forming mold, forming a non-cured core or
mold of said composition, contacting said non-cured core or
mold with a gaseous curing catalyst until said core or mold
may be handled, inserting the core or mold in a casting
device, pouring an iron casting composition in a liquid
state, into said casting device; allowing the iron casting
composition poured into the casting device to cool and
solidify; and removing the thus solidified iron casting from
the casting device, said iron casting being free of surface
defects including veining by forming said molding composition
as follows: sand, a resin and hollow microspheres of
aluminum silicate, said hollow microspheres of aluminum
silicate being present in the molding composition in an
amount between 1 and 30% by weight of the total amount of the
molding composition and having an aluminum content between 15
and 45% by weight of the microspheres the presence of said
microspheres in the molding composition as aforesaid
producing a smoothness of the core or mold as a result of
absorption of expansion by said microspheres when the core or
mold is heated by the casting metal, whereby the iron casting
is obtained as the target product, as is, without need for
machining.
The invention provides a molding sand for casting
which incorporates hollow microspheres of aluminum silicate
in an amount between 1 and 30% by weight with respect to the
total amount of molding sand.
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The molding sand, purpose of this invention, is
suitable to manufacture cores and chill molds which, in turn,
may be used in the manufacture of iron casting.
The use of hollow microspheres of aluminum silicate
prevents the appearance of fissures during core expansion,
but without increasing gas production and maintaining the
mechanical properties of the core obtained. During melting
of the piece, the expansion of the silica in the molding sand
does not cause an increase of the core, but the expansion is
absorbed by the internal spaces of the hollow microspheres,
by which the appearance of fissures on the core surface is
totally prevented and, as a result, "veining".
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With the molding sand of the invention, cores or
molds are obtained of lesser density, by which gas
production is reduced, but without decreasing its mechanical
resistance. Likewise, the penetration of the piece obtained
is reduced, due to the fact that the hollow microspheres of
aluminum silicate cover the interstitial spaces of the core
producing an effect similar to that of paint, improving the
surface of the piece obtained. Therefore, the quality of
the resulting iron casting is improved due to the reduction
of the defects caused by core expansion and gas production.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a bar diagram in which the
"veining" effect is seen for different techniques of core
shaping, position 04 corresponding to the technique based on
the use of a molding sand of the invention containing loo by
weight, of hollow microspheres of aluminum silicate.
Figure 2 shows a bar diagram in which the
mechanical resistance obtained is seen according to the
different techniques of core manufacture, the position 04
corresponding to the technique based on the use of a molding
sand of the invention containing 10° by weight of hollow
microspheres of aluminum silicate.
Figure 3 shows a bar diagram in which the density
of the cores obtained is shown, according to the different
manufacturing techniques.
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Figure 4 shows a comparative diagram of "veining"
and penetration obtained with molding sands containing
hollow microspheres of aluminum silicate (invention) and
molding sands containing titanium oxide according the US
patent 4.735.973.
Figure 5 shows a bar diagram in which the tensile
strength of cores obtained with molding sands of this
invention is shown, containing different percentages of
hollow microspheres of aluminum silicate, the curves
corresponding to the tensile strength at the exit of the
box, after 24 hours and with a relative humidity of 1003
being represented.
DETAILED DESCRIPTION OF THE INVENTION
The invention provides a molding sand for casting
incorporating hollow microspheres of aluminum silicate at an
amount between 1 and 30° by weight with respect to the total
amount of sand, preferably between 5 and 25~ and more
preferably, between 10 and 20'x, by weight.
Preliminary tests intended to prevent the
formation of "veining" on the iron casting surface showed
the possibility of using hollow microspheres of aluminum
silicate as an additive for molding sands destined to
manufacture cores and chill molds.
Further tests permitted the verification that good
results are obtained when the hollow microspheres of
aluminum silicate used have an aluminum content between 15
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and 45$ by weight, based on the weight of the hollow
microspheres of aluminum silicate, preferably between 20 and
35a by weight.
For their use in this invention, all kinds of
hollow microspheres of aluminum silicate may be used,
preferably those satisfying the aforementioned
characteristics, such as those marketed by the PQ
Corporation under the trade mark Extendospheres, and those
marketed by Microfine Minerals Limited under the trade mark
Metaspheres 50. In Table l, the main characteristics of the
different microspheres used in the tests carried cut are
indicated.
Contrary to that expected, it was surprising to
verify that the hollow microspheres of aluminum silicate of
the best quality, understanding as such those microspheres
with a relatively high aluminum content, typically between
35 and 45o by weight, give worse results than when hollow
microspheres of aluminum silicate of less quality are used,
that is, with an aluminum content less than 35~ by weight.
The tests performed with different hollow
microspheres of aluminum silicate, incorporated at different
proportions to the molding sand have shown that,
surprisingly, the microspheres with a low content in
aluminum (25-330) give, in general, the best results
regarding "veining" and penetration, in turn maintaining the
mechanical properties of the core obtained, moreover
observing that an increase in the percentage of aluminum in
the microspheres does not imply an improvement in the
results of said effects ("veining" and penetration), but, on
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occasions, the opposite occurs [see Table 5, (Example 5)).
Moreover, the studies performed showed that the
best results regarding veining and penetration do not only
depend on the aluminum content, but other factors also have
an influence, such as the size of the microspheres and the
thickness of their walls. Particularly, it has been
observed that hollow microspheres of aluminum silicate are
suitable having a wall thickness between 3 and l00 of the
microsphere diameter and a particle size between 10 and 350
micrometers (~.un) .
As may be seen in Table 4 (Example 4), the
microspheres giving the best results are those identified as
Metaspheres 50 and Extendospheres SG,, since they have a
crushing strength of 189.37 kg/cm2 (2.700 psi) with an
aluminum content between 25 and 30° by weight, a wall
thickness of 50, with respect to the particle diameter
(Extendospheres SG) and from 3 to 7°. with respect to the
diameter of the particle (Metaspheres 50), and an average
particle size of 150 ~,~m (Extendospheres SG) and between 10
and 250 ~.un (Metaspheres 50) .
The molding sand of the invention may also contain
other conventional components, like casting aggregates,
binders and other optional components used in this sector of
the technique.
The invention also provides a process .o
manufacture a core or chill mold by means of a cold process
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comprising:
(A) introducing the molding sand, purpose of this
invention, into a mold to form a core or non-
cured mold
(B) placing said core or non-cured mold of stage
(A) into contact with a gaseous cured
catalyst;
(C) permitting said core or non-cured mold
resulting from stage B) to cure until said
core or mold may be handled; and
(D) separating said core or mold from the mold.
In another embodiment, the invention also provides
a process to manufacture iron casting comprising:
(A) inserting the core or mold manufactured from
the molding sand, purpose of this invention,
in a casting device;
(B) pouring the metal, in a liquid state, in
said casting device;
(C) letting the metal poured into the casting
device cool and solidify; and
(D) separating the molten metal piece
from the casting device.
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The following examples serve to illustrate the
invention. In Table 1, the main characteristics of the
hollow microspheres of aluminum silicate used in the
execution of these examples are shown.
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EXAMPLE 1
Study of the use of hollow microspheres of
aluminum silicate as an additive for molding sands
To assess the possible use of hollow microspheres
of aluminum silicate as an additive for molding sands,
destined to manufacture casting cores, on the one hand some
cores were formed using different resins and conventional
additives, and on the other hand, other cores from a molding
sand, to which hollow microspheres of aluminum silicate had
been added, then studying "veining" and the tensile strength
of the cores obtained. The techniques used to manufacture
the different cores were conventional for each case.
The distinctive components for the different
mixtures used to manufacture the cores, are summarized below
(Table 2). In all the cases, 2-° resin was used. The
catalyst used in preparation 02 and 03 was S02 (gas) whilst
in the remaining preparations, the catalyst used was gaseous
methylethylamine (DMEA).
Table 2
Starting mixtures
Preparation Resin Molding sand
Ol Phenolic Silica sand (*)
urethane
02 Epoxy acrylic Silica sand (*)
03 Acrylic Silica sand (*)
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Tablo 2 ~cont.)
Preparation Resin Molding sand
09 Phenolic Silica sand (*) + 10% hollow
urethane microspheres of aluminum
silicate (invention)
05 Phenolic Recovered furanic sand
urethane
06 Phenolic 70/30 silica sand
urethane (*)/Chromite
07 Phenolic 50/50 silica sand
urethane (*)/Chromite
08 Phenolic Silica sand (*) + 2% HR-022
urethane
09 Phenolic Silica sand (*) + 2% coal
urethane
Phenolic Beggar clay
urethane
11 Phenolic 50/50 electrofused silica
urethane
12 Phenolic treated olivine
uxethane
13 Phenolic Thermally recovered sand
'urethane ,
19 Phenolic Silica sand i*) + 10% VeinsealT""
urethane 14000
(*): Silica sand AFA=50 rounded type, %Si>97%
5
Once the piece was prepared, the results were studied
giving the value "10" to the maximum value of "veiningp and a
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value "0" to the minimum value of "veining". Besides "veining",
tensile strength was evaluated.
In Figures 1 and 2, bar diagrams are shown indicating
the "veining" effect and tensile strength of the cores obtained.
In the position 04, the properties obtained with the core
obtained from molding sand containing microspheres of aluminum
silicate at a percentage of 10'~ are shown, it being possible to
observe the total absence of the "veining" effect and some good
tensile strength properties.
EXAMPLE 2
Density of different cores
The density of different cores obtained according to
different manufacturing techniques has been determined
including, for comparative purposes, a core manufactured from a
molding sand containing hollow microspheres of aluminum
silicate, purpose of this inventicn. The cores, whose density
has been evaluated were prepared using the sands and additives
listed below:
[1]: Additives of titanium oxide [US 4.735.973] (Veinseal).
[2]: Hollow microspheres of aluminum silicate (Inventicr:).
[3]: Rounded silica.
[4]: Sub-angular silica.
[5]: 70/30 Rounded silica/chromite.
[6]: 90/10 Silica/Additive of titanium oxide [US 4.735.973]
(Veinseal) .
[7]: 90/10 Silica/Hollow microspheres of aluminum silicate
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(Invention) .
The results obtained are shown in Figure 3, where it
may be appreciated that the cores manufactured from molding
sands containing hollow microspheres of aluminum silicate, have
a very reduced density with respect to that of the other cores,
a density permitting the reduction. of gas production and
penetration in the piece obtained.
EXAMPLE 3
Comparative example
Some cores were prepared as from some molding sands
containing different amounts (0, 5',, 10? y 200) of an additive
selected between:
(i) hollow microspheres of aluminum
silicate, and
(ii) additives of titanium oxide
according to the forth American Patent US
4.735.973 (Veinseal), and the effect of the same,
both on "veining" and penetration has been
evaluated.
The cores were prepared by mixing the sand (C-55) with
0.50, l00 or 20o by weight of the additive in question and to
the resulting mixtures, the suitably resins were added, formed
and cured.
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Once the different pieces were prepared, the results
were evaluated, giving the value "10" to the maximum level of
"veining" and penetration and the value "0" to the minimum level
of "veining" and penetration. To determine the penetration of
the metal in the mold, the test "Penetration 2 x 2 test
casting" [AFS Transactions] was used, in which the cavities of
the core in the test mold were visually examined for the
existence of metal penetration.
The results obtained are shown in Figure 4, where it
is clearly seen that the "veinir:a" in both techniques is very
similar and is gradually reduced until it disappears when the
percentage of additive gradually increases until reaching 10o.
However, the penetration using additives of titanium oxide
increases as the percentage of additive increases, whilst when
using hollow microspheres of alu:~~inum silicate as an additive,
the penetration remains constant and at a very reduced level.
EXAMPLE 4
Preparation of cores using ho':~low microspheres of aluminum
silicate as an additive
Some cores were prepared (crushing trials) consisting
of molding sand, to which different amounts (0.5~, 10° and 20o)
of hollow microspheres of aiuminvm si 1 icate had been added, and
the incidence thereof on the =ensile strength of the cores
obtained was evaluated.
The test pieces were ~repared by mixing the sand (C-
55) with 0.50, 10a or 20o by weight of some hollow microspheres
of aluminum silicate and to the resulting mixture, the
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appropriate resin mixture was added. With the mixture obtained,
the crushing trials were prepared which were cured with the
suitable gas.
The results obtained are collected in Figure 5, where
the tensile strength of the cores obtained with different
percentages of the additive, purpose of the invent;-on, are
shown, representing the curves corresponding to the tensile
strength at the exit of the box, after 24 hours and with a
relative humidity of 1000.
By means of a process similar to the above, some cores
were prepared as from the molding sands indicated in Table 3,
obtained by mixing the sand (C-55) with 0.50, l00 or 20o by
weight of hollow microspheres of aluminum silicate. In all
cases, to Isocure~ 325 (Ashland) resin and to Isocure~ 625
(Ashland) resin, and DMEA as a catalyst were used.
Table 3
Molding sands
Composition C-55 sand ('r by weight) Additive (by
weight;
I 100 0
II 95 5
III 90 10
IV 80 20
The cores obtained were submitted to some abrasion
resistance tests (Scratch Hardness, SH) and tensile strength
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tests (Tensile Hardness, TS). The results obtained are shown in
Table 4.
Table 4
Mechanical resistances
Resistance I II III IV
composition TS SH TS SH TS SH TS SH
2 cc. 302 68 94 56 93 54 92 44 90
1 hour 76 95 72 94 74 96 60 92
24 hours 88 98 95 97 98 97 85 96
~
1 h. Air 23 73 35 86 30 79 26 74
and 24 h.
100
humidity
Test piece 448,9 425 ,0 385, 8 318 ,8
weight
10
The following examples were made with the purpose of
selecting the most suitable hollow microspheres of aluminum
silicate for their use as an additive in molding sands.
EXAMPLE 5
Evaluation of different hollow microspheres of aluminum
silicate as an "anti-veining" additive
To evaluate the 'anti-veining" behavicr of different
types of microspheres of aluminum silicate, some test pieces for
crushing tests were prepared, consisting of molding sand to
i , , CA 02248329 1998-08-27
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which different amounts of the microspheres to be evaluated had
been added.
The test pieces were prepared by mixing the sand (C-
55) with 100 or 20o by weight of the microspheres and to the
resulting mixture 0.750 Isocure~ 325 (Ashland) and 0.750
Isocure~ 625 (Ashland) were added. With the mixture obtained,
some test pieces for crushing were made, gassing them with
Isocure~ 720 (Ashland). Afterwards, they were placed in a mold
for their melting with gray iron at 1,420°C.
Once the piece had been cooled, the results were
evaluated, giving the value "10" to the maximum level of
"veining" and penetration and the value "0" to the minimum level
of "veining" and penetration. To determine the penetration of
the metal in the mold, the test "Penetration 2 x 2 test casting"
[AFS Transactions] was used, in which the cavities of the core
were examined in the test mold to visually examined the
existence of metal penetration.
The results obtained are shown in Table 5, where it
may be appreciated that the best results regarding "veining" and
penetration (that is, those in which "veining" and penetration
was obtained with a value of zerc or very near to zero) were
obtained when using 20o by weight cf the hollow microspheres of
aluminum silicate with an aluminum content between 25 and 33~
(Extendospheres SG and Metaspheres SLG, SL180 and SL150, with an
aluminum content near to 45=: by ~Neight) which gave the worse
results in general.
CA 02248329 1998-08-27
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CA 02248329 1998-08-27
- 22 -
EXAMPLE 6
Evaluation of the mechanical resistance of "anti-veini
a ..t : a- , ..,., ~.
To evaluate the mechanical resistance of different
types of microspheres of aluminum silicate, some tensile
strength test pieces were prepared, consisting of sand to which
different amounts of the microspheres to be evaluated had been
added.
The test pieces were prepared by mixing the sand (C-
55) with loo or 20o by weight of the microspheres and to the
resulting mixture, 0.750 Isocure~ 325 (Ashland) and 0.750
Isocure~ 625 (Ashland) were added. The catalyst used was
DMEA. With the mixture obtained, some tensile strength test
pieces were made, which were subjected to abrasion resistance
(SH) and tensile strength (TH) tests. The result obtained are
shown in Table 6, where it is observed that in spite of the good
results obtained in the "veining" and penetration effects, also
satisfactory mechanical resistances were obtained, for the cores
prepared from the molding sands of the invention.
30
CA 02248329 1998-08-27
- 23 -
N N
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' CA 02248329 1998-08-27
- 24 -
EXAMPLE 7
Evaluation of mechanical resistances of different hollow
microspheres of aluminum silicate
To evaluate the mechanical resistance of different
hollow microspheres of aluminum silicate at 1000, some
tensile strength test pieces were prepared, by mixing the
microspheres (1000 to be evaluated with 3° Isocure~ 323
(Ashland) and 3o Isocure~ 623 (Ashland). With the
mixtures obtained, some tensile strength test pieces were
made which were gassed with Isocure~ 702 (Ashland). The
test pieces obtained were submitted to abrasion resistance
(SH) and tensile strength (TH) tests. The result obtained
are shown in Table 7, where it may be appreciated that the
best results were obtained with Extendospheres XEG
microspheres, having an average particle size (162 Eun)
greater than the Extendospheres SG microspheres(130 ~.im).
25
CA 02248329 1998-08-27
- 25 -
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