Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The normal way of Inaking a foundry mould or
core comprises shaping a mixture of foundry sand and of
binder in a mould or core box and allowing the mixture
to set, preferably at room temperature. It is often
preferred to use an organic resin condensate as the
binder in which event the mixture has to include also an
acid catalyst to promote setting. The normal way of making
such a mixture is to disperse the catalyst uniformly
through the sand and then to add binder. If the mix
is formed the other way round, with the acid catalyst
being added to a preformed mix of binder and sand,
localised curing of the binder startsimmediately the
acid contacts the mixture and so non-uniform curing
occurs.
Conventional mixtures of sand and binder that
are to be shaped behave substantially as solids and have
to be rammed or otherwise mechanically forced into the
core or mould box. In British Patent Specification No.
1,085,651 and U.S. Patent Specification No. 3,424,600 Liass
disclosed the concept of making a fluid sand composition
in which the aqueous phase was foamed, as a result of
which the composition could be shaped merely by pouring
it into the box. Unfortunately the specific compositions
described by Liass are not entirely satisfactory, even
when the mould is vibrated. In the process of Liass
and subsequent proposals of making fluid mixtures of
foundry sand and a foamed aqueous phase it seems generally
to have been considered desirable or necessary that the
materials used and the conditions of mixing should be such
that the foam collapses soon after its formation and
usually quickly, e.g. a few seconds or minutes, after
being poured into the mould or core box. Thus the
foam collapses before setting and as a result a permeable
set structure is obtained that is substantially denser
3s and stronger than would be ohtainable if the foam had
not collapsed before setting. Also in these processes
the usual order of mixing the sand, binder and catalyst
(i.e. catalyst first) seems to have been generally accepted
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as being necessary and indeed the only disclosures of
which we are aware of processes in which the acid is
added to a preformed fluid mix of sand and foamed
aqueous phase containing binder are Examples 12 and 13
of British Patent Specification No. 1,430,841 and it -is
stated in that specification that the compressive
strength of the products of these Examples is inferior
to the compressive strength of the products of the
other Examples in that specification (in which acid is
mixed with the sand before the binder was added) even
though more acid was used.
In British Patent Specification No. 1,373,647
we have described how improved results can be achieved
if the compositions contains a silane and in the
described process the foam is stable, that is to say
it does not break until the composition sets, the foam
bubbles breaking during setting. Such processes are
very advantageous because the stability of the foam
means that the composition will conform accurately to
the mould during setting and will not shrink away from
complex shapes before setting, and the preferred
compositions described in that specification, using a
silane and, preferably, a sodium lauryl ether sulphate
foaming agent, are capable of giving good overall
st~ength and in particular good surface smoothness
and strength. The conventional method of forming
foundry mixtures was described in that specification,
the acid being mixed with the sand before addition of
the binder.
In a first aspect of the invention we have
now found that when making a foundry mould or core by
~ a process comprising forming a fluid mixture that is
`~ stable against collapse before setting and that comprises
fluid sand and an aqueous phase comprising resin
condensate, foaming agent and an acid catalyst, pouring
the fluid mixture into a mould or core box-and allowing
the mixture to set, particularly advantageous results
are obtained if the fluid mixture is made by forming a
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fluid mixture of the sand and a foamed aqueous phase
comprising the resin condensate and foaming agent and
then mixing the acid curing agent into this. Thus the
acid is added to a preformed mixture of sand and binder
in contradistinction to the conventional methods in
which it is mixed with the sand before the binder is
added.
When all other conditions are constant, this
new order of mixing yields a mixture having improved
fluidity compared to that obtainable with the
conventional order of mixing and thus the mixture will
more readily flow into the mould or core and conform
more accurately to its shape without the need for
mechanical assistance, e.g. ramming or vibration of
the mould or core box. Accordingly in the preferred
process no consolidation techniques are applied and
the mould or core box remains immobile throughout.
The reason for the ~emarkable improvement
in fluidity is not known, but surprisingly the new
order of mixing does not seem to yield good fluidity
in the more usual, unstable, foams that collapse
substan*ially immediately on pouring, and indeed tests
we have conducted show that it may often give worse -~-
fluidity *han is obtained by the conventional order of
mixing.
Another surprising advantage of the invention
is tha* it is possible to reduce the amount of all
components in the mixture other than sand, and thereby
achieve substantial economies, without detrimentally
affecting the quality of the cured product, and indeed
this reduction can often be achieved together with
improvement in the quality of the product. Thus the
new order of mixing permits the amount of foaming
agent necessary to achieve a mix of adequate fluidity
to be reduced and as the foaming agent does not
contribute *o the strength of the cured mixture, and
indeed may result in weakening of it due to disruption
of the continuity of the resin, this reduction in the
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amount of ~oaming agent compared to that necessary with
the conventional order of mixing can result in a product
of improved strength. Accordingly some reduction in
the quantity of bonding agent is permissible while
still obtaining a product o~ equivalent or better
strength than that obtainable with the conventional
order of mixing and similarly a reduction in the
quantity of catalyst is also possible. Thus by
reversing the order of mixing when making a stable
fluid mixture it is possible to obtain much greater
fluidity in the mixture or to use less foaming agent
and obtain a stronger mixture or, and this is generally
preferred, to achieve increases both in the fluidity
and strength accompanied by a decrease in the amount of
foaming agent and generaily also binder and catalyst.
A number of foaming agents are capable
of giving fluid mixtures that are stable against
collapse before setting, including certain fatty
amido alkyl betaines, such as that sold under the
trade name "Lorapon AMB13" which is a cocoamide alkyl
betaine, and certain substituted imidazolines such as
those sold under the trade names "Crodateric ~" and
"Crodateric L" but the strength of the cured product
with these may not be as high as is desirable even when
used in the composition of British Patent Specification
No. 1,373,647, and best results are obtainable when
using a lauryl ether sulphate, generally sodium lauryl
ether sulphate.
Suitable sodium lauryl ether sulphates are
those obtained by ethoxylating lauryl alcohol with, for
instance, a chain of three ethoxy groups, and sulphating
the product. Examples of such materials are those
sold by Lankro Chemicals under the trade name "PerlanXrol
~SD" and t~ose sold by Albright & Wilson Limited under
the trade names "Empimin KSN 27" and "Empimin KSN 60".
They are all an industrial grade of sodium lauryl ether
sulphate based on a narrow cut lauryl alcohol,
"Perlankrol ESD" and "Empimin KSN 27" being 27
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aqueous solutions and "Empimin 60" being a 60~o aqueous
solution containing about 10% ethanol.
The amount of foaming agent will be chosen
having regard to the stability that is desired upon
pouring and having regard to the choice of foaming agent
and other components in the mix. Generally the amount
is from 0.05 to 0.5~, preferably 0.1 to 0.5% dry weight
based on the weight of foundry sand. In general
rather more foaming agent is needed when the resin
10 is a phenolic resin than when it is, for instance, a
urea formaldehyde and/or furfuryl alcohol resin.
The resin condensates used are preferably
furfuryl alcohol/formaldehyde, phenol/formaldehyde
or urea/formaldehyde resin condensates but it can be
advantageous for the binder composition also to
contain free furfuryl alcohol. The resin condensates
are usually water-soluble and are normally available
and used in the form of aqueous compositions, e.g. ---
solutions, containing from 1 to 30~ by weight of
water. The aqueous resin condensate composition is
usually used in an amount of 1 to 5~ based on the
weight of the fo~ndry sand e.g. 0.75 to 4.5~ resin
solids. Preferably we use 0.8 to 2~, preferably 1
to 1.75~, of aqueous resin condensate~ the condensate
usually containing 20~ water if the resin comprises
urea formaldehyde and 10~ water if the resin comprises
phenol formaldehyde.
In order to obtain products of good strength,
and especially good surface stren~th, it is preferred
to include a silane in the fluid mixture, for
instance as described in British Patent Specification
No. 1,373,~47. The silane is best dissolved in the
resin before the resin is mixed with the sand. Especially-
when the resin is not a urea formaldehyde resin, i.e.
when it is a phenol and/or furfuryl alcohol-formaldehyde
resin, the silane is preferably mixed with the resin
only just before the resin is mixed with the sand.
The silane must be one that will improve the
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strength of a composition containing the binder, some
silanes being more suitable for use with some binders
than others. In general the silane will be preferably
of general formula R'Si(OR)3 in which R' is a C2-C6
alkylene group bonded to an amino, epoxy, meTcapto,
hydroxy, hydroxy-Cl-C6 alkylamino, amino-Cl-C6 alkylamino,
C2-C6 alkenyl or C2-C6 alkenylcarboxy group and the
groups R may be the same or different and are
selected from Cl-C6 alkyl and Cl-C6 alkoxy-substituted
Cl-C6 alkyl. The amount of silane used is usually
from 0.05 to 0.5%, preferably from 0.1 to 0.2%, based
on the total weight of aqueous resin condensate
composition and silane.
Any acid that will serve as a curing agent
for the resin condensate may be used in the invention
and many such acid curing agents are known. Preferred
curing agents comprise one or more of phosphoric acid,
~-toluene sulphonic acid and sulphuric acid, mixtures
of the last two being particularly preferred. The
; 20 amount of curing agent, on a non-aqueous basis, is
generally from 10 to 150%, preferably 50 to 75~ by
weight based on the amount of ~esin solids or 0.3
to 2% based on the weight of foundry sand. However the
curing agents are preferably int~oduced as aqueous
solutions generally containing 15 to 40% water. The
amount of aqueous curing agent is generally 10 to
150%, preferably 50 to 75%, based on aqueous resin
condensate or 0.5 to 2.5% based on the weight of
foundry sand.
The amount of water used in the invention is
critical to success. If too much is used, above 2%,
the fluidity of the sand may be quite satisfactory
but the final strength of the product will be wholly
unsatisfactory. If too little is used, which in
practice means if less than about 0.9 or 1~ is used,
it will be impossible to make a fluid mixture since
an appropriate foamed aqueous phase will not exist.
Water is usually introduced both with the resin
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condensate and the curing agent and so preferably no
additional water is added.
We have now surprisingly found that,
possibly due in some instances at least to the reduction
in the amount of binder that can be used while
obtaining satisfactory fluidity, the amount of water
in the total mixture can be reduced far below the
2.0~ figure suggested in our British Patent
Specification No. 1,373,647. While 1.3 to 1.8~ s often
a convenient range for many systems, ~hen the binder
is free of urea and is a condensate of two or more
of phenol, formaldehyde and furfuryl alcohol an even
lower amount of water is preferred. Accordingly a
second aspect of the invention resides in a process
in which a fluid mixture is formed that contains such a
binder, and preferably also silane, and that is stable
against collapse befoTe setting and in which the
; total amount of water in the mix is from 0.9 to 1.5~
and most preferably 0.9 to 1.25~. This mix is preferably
- 20 formed by the defined order of mixing (euring agent
last) but this is not essential.
Any particulate inorganic material suitable
for use as the sand of a foundry mould or core may be
used in the in~ention, conventional sand being
preferred.
To make a foundry mould or core in the
invention preferably the sand, binder, silane and
foaming agent are mixed together under conditions
and for a duration sufficient to obtain adequate
distribution of the components and a foamed aqueous
phase, the acid catalyst is then added and further
mixing is conducted, and the mixture is then poured.
The duration of each mixing step depends inter alia
upon the type of mixer being used. Conventional mixers
are satisfactory. The first mixing stage often lasts
from 1 second to 3 minutes, e.g. 1 to 30 seconds in
a continuous mixer or 1 to 3 minutes in a batch mixer,
while the second mixing stage, after or during adding
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the acid, often lasts 1 to 90 seconds, e.g. 1 to 30
seconds in a continuous mixer or 30 to 90 seconds in
a batch mixer.
In the preferred processes of the invention
the mixture has very high stability against collapse
before curing, and as a result it is not necessary
to select the quantity of each component as critically
as has to be done with many conventional processes,
where the foam is designed to collapse, or at least
does collapse, very quickly. Whether or nGt foam
has collapsed can be determined by measuring the
permeability of the cured mould, since if curing
occurs before there is any substantial collapse the
permeability and density of the mould will be low
whilst if there has been substantial collapse of the
foam before the mix starts setting the density (and
strength) and permeability would be higher.
The following are Examples of the invention.
In these the viscosity figure is the time in seconds
during which 2 kg sand drops from the mixer in the test
described below. It is desirable for the figure to be as
low as possible since low figures indicate low viscosity
and therefore a mixture which will pour easily and
conform accurately to an intricately shaped mould.
The viscosity test uses a viscometer which consists
of mild steel vessel with an opening at the bottom.
The shape of the vessel ic a cylinder of 170 mm diameter
180 mm high finishing at the bottom with a cone 65 mm
high and cut for the outlet. The diameter of the outlet
is 45 mm and it is closed by a shutter connected
electrically with a stop watch. Inside the cylinder
there is a stirrer with 8 blades round the vertical
shaft and which rotates at 85 revs per minute.
The mixer serves to prepare a mix of 4000
grammes of fluid sand. When ready (after 42 mins of
mixing) the shutter is opened manually and sets the
stop watch in motion. The sand drops into a tared
container. Its bottom is placed 350 mm below the opening
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of the mixer. The container is placed on a scale
having a dish which, when it receives a weight of
2 ~g of sand, tilts and electrically stops the stop
watch to record the viscosity figure that is quoted.
Examples 1, 3, 11, 13, 15, 19, 20 and 21
are Examples of the invention whilst the remaining
examples are comparati~e.
Examples 1 to 4
4 kg sand, binder (B), foaming agent (F)
and 60 g (1.5~) curing agent (C) were mixed in the
amounts and order given below in Table 1 in the vessel
described above the ~iscosity of the mix was measured
as described above. The binder was a phenol formaldehyde
furfuryl alcohol binder containing 10~ water and 0.2~
silane (the product sold as AllO0), the foaming agent
~ was the 27~ solution of sodium lauryl ether sulphate
sold under the trade name "Perlankrol ESD" and the
curing agent was a composition having 33.13~ water
content and formed from 83.34% paratoluene sulphonic
acid~ 14.32~ of 77~ sulphuric acid and 2.34~ water.
The total amount of water in each mix was about 1.4
based on the weight of sand.
In Examples 2 and 4 the foaming agent and
catalyst were first mixed with the sand thoroughly
by a paddle mixer for 2~ minutes, by which time the
aqueous phase has foamed and the mixture fluid, and
the binder and silane were then added and mixed with
the paddle mixer for another minute, whereupon the
viscosity was measured and the mixture was poured into
a mould or core and left to set. Examples 1 and 3
were carried out in the same manner except that the
binder, silane and foaming agent were mixed with the
sand in the initial 21 minute mixing period and the
curing agent was added afterwards, for the final
minute mixing. The results obtained are shown in
Table 1.
Comparison of Example 1 with 2 and of
Examples 3 with 4 shows that by adding the catalyst at
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the end, instead of at the beginning, the viscosity
is almost halved in these examples and this is an
indication of the great increase in fluidity obtainable
by the invention.
TABLE 1
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Example Binder (B) Foam Agent (F) Order of Viscosity
g % g __ Addition _ _
1 71.5- 1.7875 38.5 0.9625 B+F;C 13z
2 71.5 1.7875 38.5 0.9625 F+C;B 26
3 70 1.75 36 0.9 B~F;C 15
4 70 1.75 36 0.9 F+C;B 28
i,
In each of Examples 1 to 4 the composition
was poured into a mould and upon curing in the mould
a product having good compression strength and having
` very high surface finish but having low density was
obtained.
Examples 5 to 16
4 kg of Chelford 50 sand were mixed with
the binder used in Example 1 and with foaming agent,
and acid in the amounts and order specified in Table II
in the vessel described above and the viscosity of the
mix was measured as described above. When the acid (C)
was mixed with the sand and foaming agent (F) before
the binder (B), C and F were introduced together by
adding 22%, based on sand, of a mixture of 40% of a
27% solids solution of foaming agent, 50% of 67%
solids paratoluene sulphonic acid, 8.6% of 77% sulphuric
acid and 1.4% water, and 1.75% of the binder added after
21 minutes and the product mixed for a further 1' minutes.
When the binder and foaming agent were added first 70 g
(1.75~ of binder and 40 g (1%) of the surfactant were
added and after 2~ minutes mixing 60 g (12~ of the same
acid mixture was added and the mix mixed for a further
1~ minutes.
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TABLE I I
Example Foaming Agent Order of Viscosity Stability
_ Addition of foam
Cordanol SBL 35 B+F;C 77 unstable
6 .. C+F;B not fluid _ r
7 Armac * C B+F;C 35 unstable
8 ., C~F;B 15' more stable
9 Armeen*12D B+F;C 19 unstable
.. C+F;B 16 more stable
11 Lorapon AMB13 B~F;C 161 stable
12 .. C+F;B 20 stable
13 Empicol*ES B3 B~F;C 48 stable
14 .. C+F;B 58 less stable
Empimin hSN 27 B+F;C 13' stable
16 _ _ _ C+P;B 18' stable
* Trade Mark
Cordanol SBL 35 is a fatty acid alkanolamide sulpho-
succinate.
"Armac"C is an acetate salt of C6_18 coconut amine.
"Armeen"12 D is 97~ lauryl amine.
Lorapon AM B13 is cocoamido alkyl betaine.
"Empicol"ES B3 is sodium ethoxylated lauryl alcohol, and
Empimin KSN 27 is sodium lauryl ether sulphate.
After pouring and curing the product of
Examples 15 and 16 had the best strength, but it is
clear that Example 15 gave the mixture having the
greatest fluidity.
Examples 5, 7 and 9 used the surfactants
and the order of mixing proposed in Examples 12 and 13
of British Patent Specification No. 1,430,841, which
are the only disclosures of which we are aware showing
the addition of curing agent to a preformed fluid mixture
of sand and foamed aqueous phase containing foaming
agent and binder, but as is apparent from each of
these Examples the fluid mixture was in fact unstable,
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as defined above. This is only to be expected as it
is clear that Specification No. 1,430,841 is concerned
solely with unstable foams as it requires that the
foam shall substantially completely subside before
the sand begins to set. Example 6 shows that if the
order of mixing in F.xample 5 is reversed a non-fluid
mix is obtained whilst Examples 8 and 10 show that
if the order of mixing in Examples 7 and 9 respectively
is reversed a more stable foam is obtained having
greater fluidity than the mixes in Examples 7 and 9,
that is to say the addition of the curing agent to
the preformed fluid mixture reduces the fluidity of
the mix, whereas in the stable foams of the invention
it increases the fluidity of the mix. In Example 5
the fluidity of the system was so low that the mould
had to be vibrated. Examples 11 to 16 all give stable
foams and in each instance it is clear that a more fluid
mixture is obtained when the curing agent is added last
than when it is added first.
Example 17
In this Example 13 of British Patent
Specification No. 1,430,841 is reproduced more accurately
than in the preceding Examples. The mixtures were foTmed
using the same technique as above from the recipe
50 parts of sand
1 part of binder (45~ ureaformaldehyde resin
plus 55~ furfuryl alcohol)
1 part of catalyst (18~ phosphoric acid, 18%
sulphuric acid, 64~ water)
0.05 foaming agent
0.05 water
In tests A and B the foaming agent was lauryl amine
acetate ~Armac*C) while in tests B and C the foaming
agent was 97~ lauryl amine (Armeen*12D). The results
are as follows:
* Trade Mark
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TABLF, III
Test Order of Mixing Viscosity
17A B4F;C 39z
17B C+F;B 31
17C B+F;C 312
17D C+F;B 26
In all instances the foam was unstable
and adding the curing agent last, instead of before
the binder, made the mixture less fluid.
Examples 18 to 21
In these Examples the binder and foaming
agent and apparatus used were broadly as descIibed in
Example 1, the catalyst was p-toluene sulphonic acid
and the compressive strength after 24 hours ~as
recorded in pounds per square inch. In Example 18
the binder was added last while in Examples 19 to 21
the curing agent was added last, and the amount of
foaming agent and curing agent was reduced in
Examples 19 and 20 and in Example 21 the amount of
binder was also reduced. The results are given in
Table IV. In Example 18 the amount of water in the
mixture is about 1.4~ but in the other Examples it is
from about 0.9 to about 1.2% -
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TABLE IV
Example 18 19 20 21
Binder 1.75~ 1.75 1.75 1.5
Foaming agent 1.0 0.6 0.7 0.8
Acid 1.5 1.0 1.0 1.0
PTSA C+F;B B+F;C B+F;C B+F;C
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Viscosity 213- 23 181 17
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Compresslve Strength 320 370 350 320
Example 19 shows that by mixing in the invention it is
possible to have a very large reduction in the amount
of foaming agent and curing agent, with a very small
increase in viscosity and a significant increase in
compTessive strength, while Examples 20 and 21 show
th~t by having a slightly smaller decrease in the
amount of foaming agent one can obtain a desirable
decrease in viscosity and improved compresssive
strength or, with less binder, an equivalent compressive
strength and even greater reduction in viscosity.
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