Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a binder com-
position for bonding molds, shapes, forms, etc. The
invention also relates -to refractory molds, shapes and
forms incorporating such a binder and to methods of
5 producing and using the binder and refractory compositions.
Alkyl silicates and colloidal sillca sols, among
others, are two of the kinds of materials that have been
used in binder compositions in preparing investment
casting molds and other refractory molds, shapes and
10 forms. Attempts have been made to combine these two
materials to obtain the advantageous properties of each
while minimizing the less desirable aspects. For example,
ethyl silicate provides high refractoriness and can be
quickly chemically hardened or air hardened, but it
15 provides low bond strength and limited s-tability in
refractory slurries. Colloidal silica sols, on the other
hand, provides high bond streng-th and good slurry stabil-
ity but cannot be chemically gelled to a single phase and
is only slowly air hardened.
In U.S. Patent No, 3,961,968 a hybrid system of
alkyl silicate and colloidal silica is disclosed in which
a binder composition including both alkyl silicate and
colloidal silica is produced by using various solvents
including alcohols, ethylene glycol monoethers and
25 diglycol die-thers. This binder composition provided a
desirable hybrid binder product when gelled, and at low
ethyl silicate levels of about 8% a stable binder
composition can be prepared which can be gelled -to a
single phase. On the other hand, the hybrid binder cloes
30 not have good long term stability when higher ethyl
silicate concentrations are employed, i.e., the binder of
a higher ethyl silicate concentration gels by ltself after
a short period of time without the addition of any gelllng
agent. Since higher ethyl silicate levels provi.de certain
35 desi.rable characteristics for binder and refractory
compositions, it would be desirable to provi.de a
composition which is stable against self-gellation bu-t
--2--
also which includes high amounts of ethyl silicate and
which gels on command to a single phase.
An improvement on the hybrid binder system of
lJ.S. Patent No. 3,961,968 is disclosed in U.S. Patent
5 No. 4,289,803 in which phosphoric acid is included in the
hybrid alkyl silicate/colloidal silica binder composit:on
to produce a phosphosilica-te composition, which is clis-
closed as enhancing mold strength and refractoriness of
the binder composition. The binder composJtions or U.S.
10 Patent No. 4,289,803 are stable at low ethyl silicate
levels but not at high ethyl silicate levels.
It has now been found that a binder compositlon
can be provided which has long term stability to
self-gellation, which can include high amounts of alkyl
15 silica-te and which gells, stiffens and sets predic-tably on
command at room temperature by heating or by addin~ a
chemical gelling agent. By gelling on command, we mean
-that the binder composition can be caused to ~el and set
within about 2 minu-tes, preferably about 30 seconds to
20 l minute by addition of a suitable gelling agen-t. These
characteristics are provided by a composition in accor-
dance wi-th the presen-t invention comprising colloiclal
silica, a liquid material con-taining Si-OH aroups.
solvent which is capable of solubilizing the 1iquid
25 material containing Si-OH groups ar;d -the colloidal sllica,
and at least one apro-tic, non-ionic, non-metallic, orqanic
compound which contains at least one element selected from
the group consisting o~ phosphoxus, sulfur, boxon, nitrogen
(identified hereinafter as P, S, B, N), and mixtures thereof
3~ and which stabilizes the binder composition agalrlst
self-gelling. The colloidal silica and the l:iquid materlal
containing Si-OH groups are present in a ratio by weiaht
of from about 1:12 to about 75:1, e.g., from about 1:10 to
about lO:1, respectively. The liquid material containing
3sSi-OH groups con-tains at least about 20% by weight SiO~,
and the colloidal silica contains at least about 15~
weight of SiO2. The solvent and the aprotic organlc
compound are present in amounts sufficient to solubilize
.'i~A ~ a
7~
the colloidal silica and the liquid material containing
Si-OH groups, to provide a binder composition which is
stable against self-gellation, and to provide a hinder
composition which gels to a single phase.
This binder composition can be mlxed ~r~lth
refractory filler, i.e., larger aggregate and/or fine
powders, to provide refractory cornpositions, which when
gelled can be used, for example, as investment casting
molds, as mold surface coatings, as refractory shapes, as
10 refractory foams, as a parting agent for stools in the
making of ingots in the steel industry, as a paint contain-
ing, e.g., Zn, for salt/brine resistant paints for shios,
as a binder in combination with sand to fill holes
quickly, for example, in an airport runway, as a binder
15 for the tiles on the heat resistant surfaces of reentry
rockets or ships, and as a component of a furan resin
binder system. The binder and filled compositions of the
invention provide a combination of very desirable proper-
ties to industry in that the compositions are stable
20 against self-gelling for long periods of time, but they
can include high alkyl silicate conten-ts and can be made
to gel on command to a single phase. Thus, the composi-
tions of the present invention can be packaged for later
use in predetermined concentrations to provide refractory
25 and binder composition of advantageous and known character-
istics, e.g., dimensional and strength characteristics.
The compositions of the invention can also include organic
compounds wh:ich decompose to provide for example boron or
phosphorus oxides, thus providing an added refractory on
30 the molecular level which become part of the chemical and
physical structure of the gelled composition.
In one embodiment of the present invention, the
binder composition prepared therefrom comprises from about
l to about 60% by weight, more preferably from abou-t 2 to
35 about 40%, e.g., from about 5 to about 40% by weight of
ethyl silicate which has been hydrated and which conta~ns
from about 28 to about 60% by weight of SiO2; from about 5
7~
--4--
to abou-t 75% by weight, more preferably from about =, to
about 60%, e.g., from about 5 to about 40% by weiqht of
colloidal silica containing from about 15 to about 60~ J
weight of SiO2; from about .5 to about 50% by weight, more
5preferably from about 1 to about 20%, e.g., from about .~
to about 10% by weight of dimethyl methyl phosphonate; and
from about 10 to about 93.5% by weight, more preferably
from about 20 to about 60%, e.g., from about 20 to about
55% by weight of a solvent selected from diethylene glycol
lOmonoethyl ether, propylene glycol monomethyl ether or
propylene glycol monopropyl ether.
As noted above, the binder composition of the
present invention includes as its basic elements a llquid
material containing Si-OH groups, colloidal silica, an
15appropriate solvent for -the liquid material and the
colloidal silica, and at least one aprotic, non-ionic,
non-metallic, organic compound which contains at least one
element selected from the group consisting of P, S, B, N,
and mixtures thereof and which stabilizes the binder
20compos:ition against self-gelling.
Any of the conventional liquid materlals contain-
ing Si-OH groups known in the art for binder compositions
can be employed in the presen-t invention. Preferably, the
liquid materials are silicate esters, e.g., alkyl silicate
25materials, which have been hydrated. Such liquld materials
should contain at least about 20% by weight Si02, and more
preferably, from about 28% to about 60% by weigh-t of Si02.
Suitable liquid materials containing Si-OH groups include
organooxysilanes (orthosilicic acid esters), and
30 poly(organooxysiloxanes) (polysilicic acid esters) which
have been hydrolyzed, see, for example, Chap-ter 11 of
"Chemistry and Technology of Silicones" by Walter Moll,
Academic Press, 1968. The liquid materials can be simple
molecules, but are usually polymeric in nature. Examples
35 of some commercially available alkyl silicates suitable
for use in the present invention include Ethyl Silicate 40
available from Stauffer Chemical Company and other ethyl
and propylsilicates available from Stauffer Chemical
Company, Kay-Fries, Inc., and Union Carbide Corporation.
Any conventional colloidal silica can be
employed in the present invention, including basi.c si.lica
5sols and acidic silica sols. Since the addition of base
can upset the stability of the hydrolyzed alkyl si.licates
if the pH is maintained for too long a per;od at about
pH 5-7, -the use of basic silica sol must be carefully
performed so that the pH of composition resulting from the
10 addition of the basic silica sol to th~ hydrolyzed alkyl
silicate does no-t cause gellation of the hydrolyzed alkyl
silicate and -therefore of the binder composition as a
whole. Preferably, -the colloidal silica contains at least
about 15% by weight of Si02, and more preferably, from
l5abou-t 15% to about 60% by weight SiO2. Examples of
suitable commercial colloidal silica compositi.ons include
Nalcoag*1129 and Nal.coa~ 1034-A ~which are water based
colloidal sili.ca sols) available from Nalco Chernical
Company, Nyacol*2034DI available from Nyacol Corporation,
20and Ludox*LS available from E.I. du Pont de Nemors and
Company. Acidic silica sols and si.lica sols in which the
particles themselves are non-charged are preferred for us~
in the present invention.
A solvent is used in the composition of the
25present invention which will solubilize both the liqui.d
material containing Si-OH groups and -the colloidal silica.
A preferred group of solvents are the water-miscible
organic solvents, especially aliphatic alcohols having
from 1 to 4 carbon atoms and glycol ethers. Examples of
30suitable solvents include ethanol, isopropanol, propylene
glycol monomethyl ether, propylene glycol monopropyl
ether, and diethylene glycol monoethyl ether. Propylene
glycol monome-thyl ether is particularly preferred in
situations calling for a high volatility solvent, while
35diethylene glycol monoethyl ether is preferred for
situati.ons requiring lower volatility solvents.
*trade marks
--6--
The binder composition of the present invent-on
also includes at least one aprotic, non-ionic,
non-metallic organic compound which contains at least one
element from the group consisting of P, S, B, ~, and
5 mix-tures thereof and which stabilizes the binder composi-
tion against self-gelling. The organic compounds are
preferably liquid at room temperature. The oraanic
portions of the molecules are not critical so long as the
organic compound along with -the solvent solubilizes the
lO colloidal silica and the licluid material containing Si-OH
groups and results in a binder composition which is stable
against self-gellation and which gels to a single phase.
In this regard, it has been found that organometallic
compounds in general are probably too ionic in nature or
15 too insoluble to be suitable for use in the invention.
Likewi.se, protic materials such as bu-tyl acid phosphate or
materials such as trimethyl phosphi-te (which ac-ts as a
fairly strong Lewis base) are not sui.table for use in the
i.nvention. Sui.table P containing organic compounds for use
20 in the present invention include, for example, fully
esterified phosphate, pyrophosphate, and phosphonate
esters. The B containing organic compounds suitable for
use in the invention include, for example, fully esterl-
fied borate and pyroborate esters. Suitable S containing
25 organic compounds include, for example, dialkyl or diaryl
sulfoxides, while sulfate esters may be -too ionic in
nature to be suitable. Dialkyl or diaryl amides of
alkanoic acids are examples of organic compounds cor.tain-
ing N which would be suitable for use in the present
30 invention. Preferably, the organic portions of the
compounds are alkyl straight or branched chain groups
containing from l to 6 carbon atoms, or are aryl groups
containing 6 to 8 carbon atc,ms, e.g., phenyl. Preferred
organic compounds are the organic compounds con-tai.ninq P
35 which when oxidized results in useful refractory oxi.des
thereof. Examples of suitable organic compounds containinc~
P, B, S and/or N include dimethyl methyl phosphon~te
7 ~ ~
-7-
(DMMP), triethyl phosphate, tributyl borate, dimethyl
sulfoxide and dimethyl formamide. It is believed that ~ne
organic compound stabilizes the binder composition by
inhibiting self-gellati.on while still allowing gelli.ng t~,y
5use of a gelling agent or by drying.
The binder composi-tion of the invention contain-
ing DM~P has been found to be par-ticul.arly advantageous. A
binder composition containing 21So by weiyht Ethyl
Silicate 40, 4.'7% by weight wa-ter, 37% by wei.ght diethyl-
10 ene glycol monoethyl e-ther, 30% by weight Nalcoag 1129,
7.2% by weight DMMP, and 0.1% by weight concentrated HCl
prepared in accordance with the present, invention has been
found by the conventional pyrometric cone equivalen-t, (PCE)
test to provide a PCE value of 32-33, whereas a bi.nder
15 composition without the DMMP only provided a PC~ value of
appro~ima-tely 2~. Similar PCE values are expected for
other compositions of the inven-t-,ion. This charac-teristic
of the bi.nder composi-tion of the present i.n~entioi-. .is
considered hiyhly advantageous because i-t means that the
20 binder composition of the invention can be used a-t hi.gher
-temperatures than conventional binder compositi.ons withcut
DMMP. For example, this charac-teristic makeci the binder
composition of -the invention suitable for use in casting
me-tal alloys requiring molten temperatures above 30GO or
25 even 3100F.
The binder composition of -the present invent,i.on
contains the colloidal silica and -the li.quid material
containing Si-O~I groups in a ratio by weight of from about
1:12 to about 75:1, e.g., from about 1:10 to about 10:1
30 respectively. Preferably, the bi.nder compositi.on contalns
from about 1 to about 60% by weight, e.g~, from about 2 to
about 60% by weight of the liquid material cont,ai.nlng
Si-OH groups, and more preferably, from about 2 to about
40% by weight, e.g., from about 5 to about 40%. The binder
35 composition also preferably con-tains from about 5 to about
75% by weight, e.g., from about 5 to about 55/0 by weiqht.
colloidal silica, and more preferably, from about 5 to
~z~
--8--
60% by weight, e.g., from abou-t 5 -to about 40%.
It has also been found that very good results
are obtained with rela-tively low amounts of the liquid
material containing Si-OH qroups. For example, a
5 composition prepared from a mixture of primary components
consistiny essentially of 4.1% by weiqht ethvl
silicate 40, 4.1% by weight DMr~P, 36.3% by wei-lht
propylene glycol monomethyl ether, and 55.3% by weight of
Nyacol 2034 (colloidal silica with 34% SiO2 and 66% H20),
10 when used as a wash for a sand mold provided a heavy steel
casting surface as good as an "as cast" surface. Because
of the low amounts of silicate ma-terial employed, such
compositions are easy to manufac-ture and are also very
economical. Although it can be found that the llquid
15 material containing Si-OH groups is a necessary part of
the binder composition of the invention, the lower
percentage weight limit of such liquid material has not
been determined exactly. On the other hand, because 4.1%
by weight performs well, it is believed -that a weiqht
20 percentage as low as 1% and perhaps even lower can be
employed while still providing good results as, e.g., an
investment casting wash.
The solvent and the organic compound are present
in -the binder composition of the present invention in
25 amounts sufficient to solubilize the colloidal silica and
the liquid material containing Si-OH groups, to provide a
binder composition which is stable against self-gellation,
and to provide a binder composition which gels to a slngle
phase. Preferably, -the binder composition is stable
30 against self-gellation for at leas-t about 3-9 months, more
preferably at least about 1 year or more. Sultable concen-
trations for the aprotic organic compounds in the binder
compositions of -the present invention include from ahout
.5% to about 50% by weight of the composition, and prefer-
35 ably, from about 1% to about 20% by weight, e.g., fromabout 5 to about 12%. Preferably, the composition of the
present invention includes from about 10% to about 93.5~
7~
g
by weight, e.g., from about 20 to about 55% by wei~ht of
solvent. Typically, when more aprotic organic compound is
employed less solvent and more preferably from ahout ~n ~"
about 60% is necessary.
It is sometimes advantaqeous to include a
thickening agent in preparing refractory compositions with
the binder composition of the invention. Preferably,
minimum amount of -thickening agent is employed so as not
- -to upset the system. Typically, amounts lower than about
10 0.1% by weight, preferably from about 0.01 to about 0.1~
by weight of thickening agent are employed in preparing
refractory compositions. Suitable thickening agerlts
include conventional non-ionic thickening aqents such dS
the hydroxyalkyl cellulose materials, for examp1e,
15 hydroxypropyl cellulose, e.g., Klucel*H available froln
Hercules. The thickening agent impar-ts a soft sett]~ng
charac-teristic to the refractory composition so that the
settling of -the added refractory, e.g., zircon powder,
from the composition is inhibited.
Various other materials can be included in the
binder composition of the present invention, e.q., the
reaction products from the hydration of the alkyl
silicate, surfactants, and viscosity modifiers to provide
a "paint" to which filler particles can be added to
2S provide refractory coatings. The amounts and types of such
other materials vary according to the purpose of the
additive and the ultimate application of the bincier
composi-tion.
The binder composition can be prepared by arly
30 method which will result in a stabilized mixture or
composition containing these four basic elements. ]~n one
method, a strong inorganic acid such as concentrated
sulfuric acid or hydrochloric acid is mixed with water.
Preferably, the water is distilled and deionized, and the
35 amount of water present is about the amount needed to
hydrate the ethyl silicate, i.e., large excesses of water
are avoided. The acid should be present so that the final
*trade mark
t~
--10--
pH of the binder composition is at a pH of from about 1 ~o
about 3. An appropriate solvent for the alkyl s;licate -nc~
the colloidal silica is then added, e.g., lso~ropyl
alcohol, die-thylene glycol monoethyl ether and~'or
5 propylene glycol monomethyl e-ther. This mixture is
agitated and an alkyl silicate such as ethyl silicate is
then added slowly and the temperature is controlled,
preferably between 15 C. and 31 C. During thi,s part of the
reaction, the alkyl silicate is being hydrated. This
10 hydration reaction is exothermic and therefore can be
monitored by use of a thermometer. When the system stops
giving off heat, the reaction is essentially complete.
However, in this method the hydrated al,kyl silicate
solution is preferably allowed to "rest" for a period of
15 time, e.g., 24 hours or lon~er, to stabilize -the hydrated
alkyl silicate thereby produced. After this period of
rest, the organic compound, preferably DMMP, is added w]th
agitation and then over a period of time the colloidal
silica is slowly added. This method results ln a very
20 stable binder composition.
In another embodiment, -the silica-te ester, the
concentra-ted acid, the solvent and the aprotic organic
compound can be placed in a reactor and the colloidal
silica can be added slowly to -the above reactants, e.g.,
25 by using a glass funnel with a petcock. Preferably, the
reaction mixture is formed by blending the s-ili,cate ester
with the solvent and/or aprotic organic compound and
adding the acid thereto. The acid acts as a catalyst for
the hydration reaction and i,s present in a suffic-ient
30 amount to provide a final pH of from about ~ to abo~t ~,
for the resulting binder composition. The colloidal sil?ca
provides substantially all of -the water necessary to
hydrate the silicate ester. Preferably, the reactor ~s
capable of being temperature controlled, e.~ a~,er
35 cooled. The temperature is preferably maintained frvm
about 15 to about 31 C, and during the entire reaction,
the reactants are agitated, e.g., with a mechanical
7.;~
s-tirrer. The colloidal silica is dripped into the re-:c-
tants at a slow rate, e.g., to provide a reaction ti~ne
from 1-2 hours. This assures hydration of the 31'.~yl
silicate without gelling the resulting binder compos~tion.
5 In the initial stages of the reaction, the colloidal
silica is hydrated. This hydration usually occurs in the
first 25% of the total reaction time. Again, during the
hydration period an exotherm usually occurs which is
readily discernable by using a thermometer. Thus, the
10 temperature of the reactants can be used to follow the
hydration reaction.
The binder composition could also be prepared by
starting with a hydrated alkyl silicate and just adding
the aprotic organic compound and colloidal silica thereto
15 as described above. One such hydrated alkyl silicate is
available from Stauffer Chemical Company under the name
Hydrated Ethyl Silicate Type E-5.
The binder composition of the present invention
can be used alone, for example, as a corrosion reslstant
20 adhesive, or can be used to prepare refractory composi-
tions for numerous applications, e.g., as investment
casting molds, as a refractory coating for the plastic
film in the well-known V-process, as coatings for sand
molds, as refractory shapes or as refrac-tory foams. These
25 refractory compositions basically comprise the binder
compositlon described above and filler particles, e.
larger aggrega-te and/or fine powders.
Additionally, the refractory compo:,itions can
include a predetermined quantity of an additive selected
30 from -the group consisting of polyvinyl acetate, polyvinyl
alcohol, gums, and clay for green streng-th. A surfactant
can also be included for wetting refractory powders during
the preparation and use of the compositions for coating
surfaces, e.g., of sand molds.
The selection of the filler particles depends on
the ultimate use to be made of the refractory composition
as is conventional in the ar-t. The filler Particles can
7~*
-12-
change and improve many of the properties of the binder
including the refractoriness, stability, crystallization,
strength, thermal shock resistance, permeability, and
toughness. Thus, if an investment casting mold is being
5prepared, combinations of fine powders and larger agqre-
gate will be most likely employed as is conventional in
the art, while powdered filler particles, for example,
zircon, ground to 100 mesh or finer will most like]y -to be
employed if a coating for -the surface of a sand mold is
lO contempla-ted. Addition of graphite can provide a
non-oxidizing type binder system for use, for example 7 in
making Ti metal castings, where the molten Ti might
normally be oxidized by the oxygen in the binder sys-tem.
Examples of suitable fil:Ler par-ticles include refractory
15 and non-refractory fillers. Examples of non-refractory
fillers include polystyrene (e.g., beads), mica, talc,
iron oxide and boric acid. Suitable refractory particles
include zircon, silica, olivine, clay, alumina-silicate,
graphite, fused silica, alurnina, chromite, fibrous-alumina
20 silicate, magnesia, or quartz. Combinations of -these
fi]ler materials can also be used.
The filler par-ticles can be mixed with the
binder composition of the present invention in any amount
suitable to provide a composition for the desired purpose
25 as is conventional in the ar-t. Typically, -the filled
compositions contain *rom about 5 to 50% by weight of the
binder composition.
The binder composition and filled composition -in
accordance with the present invention can be ~elled in any
30 conventional manner. For example, the binder and filled
compositions can be gelled by employing a gelling agent
such as ammonium hydroxide, MgO or ammonia gas. The
compositions can also be gelled by drying as is conven-
tional in the art.
The binder compositions of the present invention
bond together, without heat, the filler particles. The
filled compositions of -the invention are very advantageous
-13-
because they can be gelled on command, but are themselves
stable against gellation and can be employed in many
applications in either fired or non-fired conditions.
The filled compositions can be refractory
scompositions gelled in the desired shape, e.g., by the
'~lost wax process" or in the form of a refractory shape or
foam as described below. The gelled, shaped refractory
composition can be used as is or can be fired at a
temperature sufficient to oxldize the aprotic organic
lOcompounds therein to complex refractory oxides and/or
volatilized materials.
As noted above, the refractory compositions of
the invention can be used in conventional processes for
preparing investment casting molds, coatings for molds
15such as sand molds, refractory shapes, and refractory
foams. These processes are conventional in the art and
need not be detailed here. However, since the present
invention can be employed in such process, they are
briefly discussed below as they rela-te to the invention.
A number of important characteristics are
important in investment casting molds:
tl) They should be able to withstand high
temperatures, since some commercially important
metals become fluid at temperatures above about
1000F. and iron and steel above 2000F.
(2) The mold should also conform to specifi-
cations which approach those normally encoun-
tered with machine metal parts.
(3) The molds should faithfully reproduce
the shape and dimensions of the pattern of the
mold; and therefore the binder composition used
in preparing the mold should have sufficient
strength so that the refrac-tory composi,tion can
withstand the physical handling forces from
start to finish of the mold forming process.
(4) The mold should be able to be aener-
ated qui.ckly at ambient temperatures with suffi-
-14-
cient binder strength after forming to ~ithstand
the dewaxing stresses encountered when the
pattern is removed.
(5) The dewaxed mold should also be able
to withstand long periods of storage under
ambient conditions without deterioration.
These characteristics are provided by the binder
and refractory compositions of the present lnvention. In
particular, the refractory composi-tions of the present
10 invention can withstand temperatures of PCE 32-33 and have
sufficient strength to also withstand the ~lost wax
process" for preparing investment casting molds.
Investment casting molds are generally prepared
by the "lost wax process". In this process, a wax mold is
15prepared in the shape desired for the ultimate metal
casting. Binder is applied to this wax mold by dipping the
mold into a refractory slurry such as a refractory
composition of the invention. Filler particles such as
refractory particles are then applied to the slurry
20coating on the wax mold and the binder com~osition is
gelled. The wax mold is then again dipped into the
refractory slurry, more filler particles applied, and the
binder composition gelled again. These steps are repeated
until the desired characteristics of -the refractory invest-
25ment casting mold are achieved. Normally, -the size of the
filler particles increases from the inside to -the outside
of the casting mold.
The wax mold is then dewaxed by processes again
conventional in the ar-t. The refractory slurry of the
30invention provides sufficient strength to -the mold to
withstand the stresses during this dewaxing step.
The dewaxed investment mold prepared in accor-
dance with the invention can be stored for long periods of
time. It can then be used in a conventional investment
35casting process. During the casting process, the binder
and refractory compositions must withs-tand even greater
stresses.
7~'~
-15-
In preparing a fired investment mold, t'ne
dewaxed investment mold is first fired to burn out
temperatures of about 1800 F. This burn out accompllshes
three things:
(1) it rids the mold cavi-ty of all residual
organic matter;
(2) it oxidizes and recrystallizes all
refractory materials to their most stable high
temperature form; and
(3) it heats the mold to decrease thermal
shock from the molten metal during pour.
Thus, as is conventional in the art, due considera~lon
must be given during formulation of the binder to compen-
sate for the dimensional changes which take place within
15 the binder during the burnout period. Some mold failures
are characterized by such things as frac-tures, warpage,
passage restrictions, low strengths and perrneability
problems. To some degree, these failures have been traced
to refractory binders. 1`he present invention provides good
20 binder reliability.
In order to avoid the above problems, -the binder
in the investment mold should withstand high temperature
handling when the mold, which is normally at about
1800F., is moved from the burnout position~ which is
25 generally upside down, to the casting position, which is
right side up. All of this requires ri~idi-ty under
conditions which are prone towards plas-ticity because of
glass formation.
The binder should also withstand the rigors of
30 the pour. This means that the mold cavity should be able
to capture molten metal as it falls from the furnace or
ladle and to withstand the two shocks encountered in such
a fall. Thus, the binder should be able to withstand the
mechanical shock of being hit with a falling mass having a
35 specific gravity of from 5 to 9 and the thermal shock of
being hit with a very hot mass having a temperature
difference of up to about 1000F or greater.
-16-
The binder should further decrepitate after ~,he
metal solidifies so as not to place any undue mechanical
stresses on the hot metal during its cooling stage, ,when
it is shrinking and is prone to hot tears from the
5 stronger molding media.
The binder should not adhere to the metal
surfaces after shake-out. If it does, the castina will
have such defects as burn-ins, penetrations or other
surfaces blemishes. In other words, it should break awa~
~o clean.
The binder and refractory compositions of the
present ,invention provide these desirable results for
investment casting molds.
In the case of sand mold casting, si,milar but
15 less stringent mold re~uirements are needed than those
discussed above. Also, because there is a parting line and
the pattern can be rernoved from the mold intact prior to
closing and pouring, there are no dewaxina or burnout
stages, and the casting specificati,ons are not as demand-
20 ing. The sand mold is also normally at ambient temperaturewhen employed in casting. Generally, the strength of the
sand mold is only a small fraction of the strength of the
investment mold but is much more massive.
Casting molten metal into sand molds is a wiclely
25 used and accepted method of shaping parts. However, it
does have several limitations inherent in the process.
Sand molds are made from sand, the qrains of
which have a size of from about 30 to 100 per linear inch.
When these grains are compacted into a hard mass and held
30 together with a suitable binder the surface of the mold
cavity (whlch is exposed -to the molten me-tal and aqalnst
which this metal will solidify) will impart to the metal
the same smoothness as the grains of sand of which it lS
composed. In terms of metal surfaces, this is not smooth.
Several things happen when the molten metal is
poured into the sand mold cavity. At flrst, there is the
dynamic charge of the fluid as lt pours into the void.
-17-
Then, there is a "quiet time" of the fluid as it rests
against the sand walls and loses temperature, Finally,
there is the act of solidification, wherein the fluid
takes on the solid shape of the mold cavity, and ~ts
5 entire outside surface is in in-timate contact with the
sand surface of -the mold cavity. This surface to surface
contact is known as the metal/mold interface.
During the first dynamic stage when the mold
cavity is being filled, the rushing fluid has a tendency
10 to pull off loose grains of sand from the mold surface and
carry them along in the liqui~ metal. This causes
inclusions in the metal as well as damage to the metal/
mold interface. If erosion is severe enough, the dimen-
sions of the casting can be affected as well as the
15 integrity of the metal. Obviously, a sand mold surface
with enough strength to withstand this erosive effect is
required.
During the second static liquid stage when the
fluid metal has filled the cavity and is now quietly
20 losing heat -through the metal/mold interface, the mold
surface is being subjected to severe heat conditions. It
must be remembered that prior to the molten me-tal enterinq
the mold cavity, the sand surface was at amb-ient tempera-
ture of perhaps 80 F. Now only a few seconds later, the
25 interface is at the molten metal temperature of perhaps
2800 F., with the thermal gradient being very steep and
sweeping away fast from the metal. This is heat shock of
the worst kind. The interface is thus subjected to high
stresses, and in many cases the interface does not stand
30 up under such conditions. When failure of the mold surface
at the interface occurs, it results in quite a few unique
metal conditions. These are known by rather picturesque
names: rat-tail, scab, penetration, vain, burn-in,
orange-peel, nitrogen embrittlement, cill, cold shut,
35 porosity, and blow just to name a few. They a]l result jn
added difficulties and expenses to the foundryman.
During the third solidifica-tion stage when the
-18-
metal is becoming solid and taking on the shape and
surface aspect of the mold cavity - now altered by erosion
and heat-shock, the defects listed above are locked into
the casting.
If improvemen-ts are to be made -in the cast~nq
aspect relative to the weaknesses of the metal/mold
interface, it is obvious from the above that these improve-
ments must be made to the mold surface before the mold 1S
closed and the molten metal poured into the cavity. rhe
10 present invention provides such desirable interface
characteristics.
The refractory composition in accordance with
the invention formed from an admixture of the above
discussed ingredients may be combined wi-th a refractory
15 powder, as has been previously mentioned, -to produce a
slurry-like mixture for treating mold surfaces sometimes
referred to as a wash. Preferably, the refractory powder
is selec-ted from a group consisting of zircon, sillca,
alumina-silicate, graphite, fused silica, alumnina,
20 chromite, fibrous-alumina silicate, magnesia, or combina-
tion thereof. These refractory powders preferably are
ground to a size smaller than about lO0 mesh.
The slurry produced can be applied to coat the
sand mold surface of the cavity, e.g., by brush, spray,
25 dip, or swab methods. This coated surface is then allowed
to dry with or without hea-t being applied, i.e., the
refractory composition is gelled in place on the surface
of the mold. The mold surface so coated has properties
well suited to functioning as a metal/mold interface.
For example, the fine powdered refractories are
much smaller than the voids between the sand grains on the
surface of the mold. Therefore, the powdered refractories
tend to deposit in -these voids as well as lay on the top
surface of the uppermost sand grains. By so filling the
35 voids, a smooth surface resul-ts that is highly refractory
and impervious to penetration by either the :Liquid metal
or the metal vapors.
7~
--19--
Furthermore, with the present invention t'n s
wash affects more than just the top surface of the mold.
If a cross section of the mold surface is examined under
magnification, it can be seen that the fine powdered
5 refractory has penetrated to three or more sand grains
down into the molding media. This means that the voids on
the mold surface of the interface have been filled in ~J~ th
a high quality refractory to a depth of three or more sand
grains.
In addition, the liquid phase of the bi.nder
composition of the invention penetrates and bonds the molcl
sand mass from 1 lnch to several inches deep, depending
upon the characteristics of the molding media. As a result
of this deep mold i.nterface bonding, a hard mold surface
lS results, which can withstand considerable thermal and
mechanical shock.
~ y use of the lnventi.on in the form of a
refractory composition coating on sand molds, the sand is
bound -tightly together. Therefore, the sand will not erode
20 off the surface to become entrapped in the metal castlng
as an inclusion. Further, because of -the hardness, there
is less tendency for the surface of the mold to fracture,
thus eliminating expansion defec-ts normally associated
with a weak mold wall interface. As an added advarltage,
25 because the mold wall is smoo-th as a result of the
refractory powder filling in the gaps between sand qrains,
the solidification of the me-tal takes place agai.ns-t a
smooth surface and results in a smoo-th metal casting.
In still another embodimen-t of the i.nvention,
30 the binder composition of the invention is used in a
process known in the art as the V-process for preparlng
sand molds for lar~e metal castin~s. As is no-ted above,
the V-process is conventional in the art and basically
comprises the steps of: providing a pattern for the
35 product to be produced; placing an organic plasti.c film
over the pattern so that the plas-tic fil~ basically
conforms to the shape of the pattern, e.g., via heatln(~
3 ~
-20-
the film to provide a good elasticity and pulliny a vacuum
on the plastic through the mold pattern; coatin~ the
exposed surface of the plastic film with a refractory
wash; drying the refractory wash; placing a vacuum flas!~
5 so that it fits over and onto the plastic film and covers
the pattern, the vacuum flask having a first opening
suitable for receiving the pattern and a second openinq
for the addition of sand to the flask; addinq sand to the
flask through the second openin~ so that the sand is in
10 contact with the plastic film; vibrating the sand to
compact and conform the sand to the shape of the pattern,
closing the second opening so that at least a partial
vacuum can be drawn on the sand in the flask; pullin~ at
least a partial vacuum on the flask and the sand un-til the
15 sand is held in place against the refractory wash on the
plastic film opposite the Pattern; releasin~ the pattern
from the plastic film, e.g., by releasing the vacuum
pulled on the plas-tic film through the pattern. This
process provides a portion of a mold tha-t can be used
20 along with other similar molds in combination to provide
large metal castings as are known in the art. The
refractory washes which have been used in the past to coat
the plastic have not provided an effective h:iah
temperature vacuum seal in certain instances when the
25 metal for casting is placed in contact with the mold. For
example, when a large mold is involved or when -the mold
has sharp angles, etc., the heat of the molten metal
vaporizes and/or decomposes the plastic film. Because the
prior refractory washes employed did not provide an
30 effective vacuum barrier, -the vacuum seal created by the
plastic was broken. Because the vacuum is now ~roken prlor
to effective setting of solid metal, -the sand broke away
and defects occurred in the casting.
It has now been found that the refractory
35 compositions of the present invention can be used in place
of prior refractory washes to provide a superior metal/
mold interface as well as a good vacuum seal upon burninq
-21-
away of the plastic film during the castinq step of th_
V-process. Thus, the refractory composition of the present
invention main-tains a good vacuum in the sand ~nd prevents
drop off of sand due to lack of vacuum at crucial areas.
5 Thus, the problems of surface finish and sand drop off are
considerably alleviated with the presen-t invention. Thus,
another embodiment of the invention provides a process
comprising the steps of providing a pattern for the
product to be produced; placing an organic plastic film
10 over the pattern so that the plastic film conforms to the
shape of the pattern; coating the exposed surface of the
plastic film with a binder and/or refractory composition
comprising refractory partlcles and a binder composition,
said binder composition being in accordance with the
15 invention as described above; and gelling said blnder
and/or refractory composition. The remaininq steps of the
V-process described above can also be performed as is
conventional in thi.s art.
In still another embodiment, the refractory
20 composition of the present invention can also be used to
make fired or non-fired refractory shapes.
In current practice, refractory shapes are
generally manufactured by first mixing the refractory
materials with water to form the shape des-ired. Some
25drying is then entailed to make the green ware readY for
firing, which is the final s-tep. Although the in~redients
are not too expensive, the firing can be very expenslve,
especially in -the case of high -temperature refrac-tories.
As an alternative to firlng in the makina of
30 refractory shapes, several types of binder have been
proposed and/or used that set at room temperatures,
thereby eliminating the firing step in production. Some of
the current materials used for this purpose are:
(l) Sodium Silicate: This has sodium 1ons ln its
35matrix and therefore will form low temperature liquid
glass phase in the binder which severly restric-ts its
application in high temperature work.
7v~
-22-
(2) Calcium Aluminate: Although an improvement o-n
portland cement, which is a poor refractory cement, this
binder is limited to about the 27000F. range depending on
the manufacturer. The present invention will act as a
5 binder above 3100F, when desired.
(3) Various phosphates: These can be very useful
in refractory work below 3000F. The present invention
will act as a binder above 3100F.
(4) Ethyl Silicate: Although this binder has the
10 advantage of having only silicon dioxide as the refractory
adhesive, it does a relatively poor job of bonding to the
refractory aggregates. Therefore, shapes bonded with ethyl
silicate tend to be weak.
(5) Colloidal Silica Sol: This binder forms its
15 strength by drying, and in large thick masses, it both
takes a lonq time and shrinks. However, because the bond
is pure silicon dioxide, the final bond is a good one for
high temperature work.
(6) Hybrid Colloidal Silica/Ethyl Silicate (e.g.,
20 the hybrids disclosed in U.S. Patent Nos. 3,961,9~8 and
4,289,803 discussed above): Such a hybrid lacks the
advantage of having an aprotic organic compound, as is
present in the formulation of the invention, to provide
wider variability in the binder composition and contents
25 as well as to add stability to the solution.
Non-fired refractory shapes are useful to the
industrial community, because they make posslble fast
equipment repairs, accurate pattern contact curing, lower
cost field erection, automated in-plant fabrication,
30 energy savings, and a host of specialized saving and
advantages inherent to each need. Therefore, the closer
the non-fired refractory attributes come to the needs of
the users, the more non-fired shapes there will be in use
by industry. The compositions of the invention will
35 provide such useful characteristics.
In another application, the refractory composi-
tions of the present inven-tion can be used to prepare
non-fired refractory foams.
There has been a considerable amount of
industrial demand for foam type materials, either
materials foamed in place or bulk foamed. This foam
5 material can act as insulation, packing, filters,
strainers, screens, decorations, structures, containers,
etc. In other words, these foams have found a broad range
of usefulness. In line with the above, it has been found
useful to employ all manners of porous materials including
10 foams to strain liquids when temperatures do not exceed a
few hundred degrees F. As the temperature goes up,
however, this straining job becomes more difficult, until
at the temperatures at which most commercial metals are
liquid, there are very few materials available, if any, to
15 do the straining job. The present inven-tion provides a way
to make a continuous refractory foam of any pore size
desired and of any outside shape and dimension desired.
A refractory foam in accordance with the present
invention can be made, for example, by forming a slurry
20 refractory composition in accordance with the invention
using any refractory powder or combination of powders,
such as zircon, silica, olivine, chromi-te, mullite,
magnesium oxide, aluminum oxide, graphite, clay, etc.
Next, a piece o continuous porous organic foam is
25 provided having the pore size desired. The foam is cut and
trimmed to the outside dimensions and shape desired in the
finished refractory foam. The foam is dipped into the
slurry so as to cover all the organic surfaces and drained
so that the interior passage ways are not closed or
30 blocked. The piece is then gelled with a gelling agent or
set aside to cure and harden, or baked at low temperatures
to accelerate the cure. Once cured, the refractory foam is
ready for use as a preferred high temperature metal
strainer. For example, it can be placed in a stream of
35 metal to retain the entrained solids without burning away.
The following examples are presented to
illustrate, but not to limlt, the compositions and
processes of -the present invention.
24-
EXAMPLE 1
A refractory binder in accordance with the
present invention was prepared by utilizing the ingre-
dients listed below:
_ GREDIENTS PARTS BY WEIGHT
Water (distilled, deionized) 1.8
Sulfuric Acid, Concentrated 0.12
Diethylene glycol monoethyl ether (DE) 52.16
Ethyl Silicate 40 8.0
Dimethyl methyl phosphonate (DMMP) 8.64
Colloidal Silica Sol 30.0
1 Remet Chemical Company.
Nalcoag 1129 from Nalco Chemical Company
The water was placed into a water cooled reactor
15and the sulfuric acid was added. Then, the DE was added
and agitation turned on. Next, the ethyl silicate is
slowly added and the temperature monitored. The entire
reaction is kept at between 20C. and 24C. During this
part of the reaction, the ethyl silicate is hydrated. The
20DE is in the system to bring the oleophilic ethyl silicate
into solution with the water. Only enough water is added
to the system to hydrate the ethyl silicate. The reaction
is exothermic, and therefore can be monitored. When the
system stops giving off heat, the reaction is essentially
25complete. The agitator is then turned off and -the solution
is allowed to sit for 72 hours so as to stabilize the
hydrated ethyl silicate produced.
After 72 hours, the agitator is turned on again
and the dimethyl methyl phosphonate is added. Mixing is
30performed for 1 minute. Then, over a period of time of
about 6 minutes the colloidal silica sol was added. The
resulting composition is mixed for several minutes and
then stored.
This binder composition has been found to be
35stable against self-gellation for at least 6 months. The
composition also gelled on command by addition of a
gelling agent such as ammonium hydroxide to provide a
single phase gel.
-25-
EXAMPLE 2:
A refractory binder composition in accordance
with the present invention was prepared employing the
following ingredients:
INGREDIENTSPARTS BY VOLUME
Sulfuric Acid, Concentrated0.33 ml
Distilled Water 15.25 ml
Diethylene glycol monoethyl ether 275.00 ml
Ethyl Silicate 401 40.00 ml
Colloidal Silica 2 151.5 ml
DMMP 38.25 ml
Remet Chemical Company
2 Nalcoag 1129 from Nalco Chemical Company
These ingredients were mixed baslcally in
15 accordance with the procedure described in Example 1 above
except that DMMP was added at the start with the DE. The
resulting composition was found to he very stable against
self-gellation even in view of the high ethyl silicate
levels employed. The composition gelled on command with
20 ammonium hydroxide to provide a single phase gel.
EXAMPLE 3:
The procedure described in Example 1 above was
repeated to prepare four additional binder compositions A,
B, C and D employing the following ingredients-
25 INGREDIENTS PARTS BY WEIGHT
A B C D
DMMP 8.64 8.64 8.64 8.64
H20 2.48 3.38 4.05 4.73
ES40 11 15 18 21
30 DE 48.71 44.11 40.66 37.21
Nalcoag 1129 30 30 30 30
H2S04 .13 .14 .15 .16
All of the compositions A, B, C and D werestable against self-gellation and aelled on command by
35 addition o~ ammonium hydrox:ide to provide a single phase
gel.
i
-26-
lnterstab Zirco Drier Catalyst 24% was added t,o
Composition A above and Zirconium Cem-All 24% was added ~o
Composition B above. In each case, a small fall-out o~
solids occurred, probably because of a supersaturation,
5 ionic character or insolubility.
EXAMPLE 4:
A refrac-tory composition, e.g., for coating a
mold can be prepared from the following ingredients:
INGREDIENTSPARTS BY WEIGHT
Zircon Flour 75
Polyvinyl Alcohol 0.5
Binder Compostiion from Example 1 24.5
Surfactant4 0.01
3 Vinol*available from Air Products Chemicals, Inc.
S505LF*Poly-tergent surfactant available from Olin
Corporation
The above ingredients are mixed in a reactor
with an agitator and a water bath with the entire mix
maintained at from 20 to 30C. at all times. 24.5 grams
20 of the refractory binder from Example 1 is placed into the
reactor and 75 grams of a powdered zircon flour ground to
200 mesh is then mixed in. Mixing contlnues for
20 minutes, at which time 0.5 grams of polyvinyl alcohol
and 0.1 grams of the surfactant are added. After a further
25 20 minu-tes of mixing, the mi~ing is stopped and the
coating stored for use.
EXAMPLE 5:
A binder composition in accordance with the
present invention was prepared from the following inqre-
30 dients:
INGREDIENTS PA~TS BY WEIGllT
Ethyl Silicate 40 12
DMMP 2.5
Hydrochloric Acid (concentrated) 0.1 (40 drops !
35IPA (Isopropyl alcohol~ 51.9
Colloidal Silica Sol (Nalcoag 1129) 33.5
* trade marks
~ L_~
All the ingredients except the colloidal silicasol were placed in a reaction vessel equipped for
agitation, and a glass funnel with a petcock was
positioned above the reactor. The colloidal silica was
splaced in the glass funnel. A thermometer was located
permanently contacting the reactan-ts and readable from
outside the reaction. The reactors were capable of being
water cooled. With all apparatus in place, the colloidal
silica was dripped into the reactor so as to give a
10 relative reaction time of from 1-2 hours. During the
entire addition of colloidal silica sol, the reactor is
kept in a constant state of agitation. The first stage of
the reaction with the introduction of colloidal silica is
the hydration of the ethyl silicate in the presence of the
15 mutual solvent. The water is provided by the collcidal
silica sol. This hydration occurs over a period of about
the first 25% of the reaction time. During the hydration
period, exotherm occurs which is readily discernable
through the optical thermometer. The termination of
20 hydration is indicated through the peaking of temperature.
After all of the colloidal silica sol is added, the
resultant composition is capable of being used as a binder.
The resul-tant composition can be used as a
binder material for investment casting molds, as a binder
25material for mold washes, as a parting agen-t for s-teel
ingot stools and as a base for a corrosion resistant pain-t.
The resultant composition was mixed with zircon
flour of 325 mesh size in a ratio of 1:3, respectively.
This refractory composition was applied as a coa-tinq to an
30 organic binder sand mold and was qelled or cured thereon
by the application of heat. The resultant mold wash
coating the core proved to be ceramic in quality, being
very hard and deep penetrating and "rang" clearly like a
bell.
-28-
EXAMPLE 6:
The procedure of Example 5 was repeated, exceDt
that the following ingredients were employed and the water
was dripped into the ethyl silicate, PM, DMMP and acid
5 prior to addition of the colloidal silica:
INGREDIENTS PARTS BY WEIGHT
Ethyl silicate 40 377
PM ~propylene glycol monomethyl ether) 479
DMMP 170
10 Water (distilled) 60
H2S04 (concentrated) 1.5 (60 drops)
Colloidal Silica Sol (Nalcoag 1129) 832
The resulting composition has been stable
aga.inst self-gelling at ambient temperature for at least 2
15 months to this point.
EXAMPLE 7:
The procedure of Example 5 was repeated, except
that the following ingredients were used and i-t took about
5 hours to add the colloidal silica sol:
20 INGREDIENTS PARTS BY WEIG~IT
Ethyl Silicate 40 20
PM 22.1
DMMP 10
HCl (concentrated) 15 drops
25 Nalcoag 1034 47.9
The resulting composition was stable for
22 months. The composition was gelled to provide an
investment casting shell into which was poured 316 Series
stainless steel at 2975F. The shell did not crack and the
30 molten metal did not run out and provided an excellent
quality casting.
-29-
EXAMPLE 8:
. . .
The procedure of Example 5 was repeated, except
that the following ingredients were employed:
INGREDIENTS PARTS BY WEIGHT
5 Ethyl Silicate 40 20
EE (ethylene glycol monoethyl ether) 37
Tributyl Borate 10
Hydrochloric Acid (concentrated) 0.1 (20 drops)
Colloidal Silica Sol (Nalcoag 1034) 32.9
The above composition provided a binder com-
position which has been stable against self-gelling at
least 3 weeks to this point.
EXAMPLE 9:
The procedure of Example 5 was repeated, except
15 that the following ingredients were employed:
INGREDIENTSPARTS BY WEIGH r
-
Ethyl Silicate 40 20
Dimethylsulfoxide 10
PM (propylene monomethyl ether) 22
20 Hydrochloric Acid (concentrated) o,l (20 drops)
Colloidal Silica Sol (Nalcoag 1034) 47.9
The above composition provides a binder com-
position which has been stable against self-gelling for at
least 12 months to this point.
25 EXAMPLE 10:
The procedure of Example 5 was repea-ted, except
that the following ingredients were employed:
INGREDIENTSPARTS BY WEIGHT
Ethyl Silicate 40 20
30 Dimethylformamide 10
PM 22
Hydrochloric Acid (concentrated) 0.1 (20 drops)
Colloidal Silica Sol (Nalcoag 1034) 47.9
The above composition provides a hi.nder com-
35 position which was stable against self-gelling for at
least one month.
~ f~
-30-
EXAMPLE 11:
The procedure of Example 5 was repeated, except
that the following ingredients were employed:
INGREDIENTS PARTS BY WEIGHT
sEthyl Silicate 40 20
Triethylphosphate 10
EE 37
Hydrochloric Acid (concentrated) 0.1 (20 drops)
Colloidal Silica Sol (Nalcoag 1034) 32.9
The above composition provides a binder com-
position which has been stable against self-gelling for at
least three weeks to this point.
EXAMPLE 12:
Basically -the same proce`dare as described in
15 Example 6 above was employed, except tha-t instead of
dripping the colloidal silica sol into the reac-tor vessel
via the glass funnel, small portions of colloidal si,lica
sol were added by hand over a period of approximately 1
hours. The following ingredients were employed:
20 INGREDIENTS PARTS ~Y WEIGHT
Ethyl Silicate 40 20
DMMP ~
EE 22.1
Hydrochloric Acid (concentrated) 15 drops
25 Colloidal Silica Sol (Nalcoag 1034) 47.9
This composition was stable for at least three
months and was used successfully to make investment
casting shells. The relatively small amount of EE at 22.1%
reduced the stability significantly and the relatively
30 large amount of colloidal silica increased the water which
also reduced stability.
-31-
COMPARATIVE EXAMPLE 13:
A binder composition employing phosphoric acid
instead of DMMP and a relatively high ethyl silicate
concentration was also prepared from the followina
5 ingredients:
INGREDIENTS VOLUME %
Phosphoric acid (85%) 5.00 ml
Distilled Water 2.29 ml
Ethyl Alcohol (95%) 37.90 ml
lO Ethyl Silicate 40 43.91 ml
Colloidal Silica Sol2 10.90 ml
Remet Chemical Company
Nalcoag 1129 from Nalco Chemical Company
Half of the phosphoric acid and all of the
15 distilled water and ethyl alcohol were combined and the
ethyl silicate was added thereto. The hydration of the
ethyl silica-te was completed in about an hour. The
colloidal silica was then added. After about 20 minutes,
the second half of the acid was then added. After about
20 2-3 hours this solution gelled on its own.
COMPARATIVE EXAMPLE 14:
A binder composition including phosphoric acid
and a relatively low concentration of ethyl silicate was
prepared using the ingredients listed below. The water
25 acid and DE were placed in a reaction vessel. The ES-~O
was added slowly over a period of about 2 hours. Then, the
colloidal silica sol was slowly mixed in over about
4 minutes:
INGREDIENTS VOLUME %
.
Phosphoric acid (85%) 25.0 ml
Distilled Water 8.5 ml
DE 275.0 ml
Ethyl Silicate 401 40.0 ml
Colloidal Silica Sol2151.51 ml
Remet Chemical Company
Nalcoag 1129 from Nalco Chemical Company
-32-
The composition was found to be stable for at
least nine months, but as noted above, it contained only
8 volume % ethyl silicate and therefore a low percentage
of silica in the overall composition.
5 COMPARATIVE EXAMPLE 15:
The procedure of Example 5 was repeated, except
that the following ingredients were employed:
INGREDIENTS PARTS BY WEIGHT
Ethyl Silicate 40 20
10 TMP (trimethyl phosphite) 10
PM 22
Hydrochloric Acid (concentrated) 0.1 ( drops)
Colloidal Silica Sol (Nalcoag 1034) 47.9
This composition had a three phase separation,
15 gelled in three days, and was not useful as a binder.
COMPARATIVE EXAMPLE 16:
Basically the same procedure as described in
Example 5 above was employed, except that instead of
dripping the colloidal silica sol into the rea~tor vessel
20small portions of colloidal silica sol were added by hand
over a period of approximately 14 hours. The following
ingredients were employed:
INGREDIENTS PARTS BY WEIGHT
Ethyl Silicate 40 20
25BAP (butyl acid phosphate) lO
PM 22
Hydrochloric Acid (concentrated) 0.1 (30 dropsl
Colloidal Silica Sol (Nalcoag 1034) 47.9
This material was milky in color, was opaque and
30had the appearance of gelled colloidal silica. Eventually,
a separate solid phase se-ttled a-t the bottom.
~2~7~
-33-
COMPARATIVE EXAMPLE 17:
200 ml of the composition of Exam~le 12 above
was mixed with a solution of 2 grams of chromium acetyl-
acetonate in 20 ml of propylene glycol monomethyl ether.
5Also, 200 ml of the composition of Example 12 above :ia_
separately mlxed with a solution of 2 ml of me-thylcyclo-
pentadienyl manganese tricarbonyl in 20 ml of propylene
glycol monomethyl ether. The compositions containinq the
chromium or manganese compounds resulted in gels makina
10 the compositions unsuitable for use as binder compositions.
EXAMPLE 18:
The procedure of Example 5 above was repeated,
with the following changes and ingredients:
INGREDIENTSPAF~TS BY WEIGHT
15 Ethyl Silicate 40 4.1
PM 36.3
DMMP 4.1
HC1 .1
Nyacol 2034 ~Colloidal
20 Silica with 34% SiO2
and 66% H20) 55.3
Klucel H (hydroxypropyl
cellulose .1
The Klucel H was added wlth agitation to the
25 prepared binder composition after hydration of the Ethyl
Silicate 40 was completed and all of the colloidal s~ ca
had been added to the reactor. The propylene qlycol
monoethyl ether was added in two parts. The initial amount
of about 24.1 parts by weight was added ln preparinq the
30 binder compositions. The remaining 12.2 parts were added
after the Klucel H was added to clean up some cloudiness
that had developed upon addi-tion of the Klucel ~l.
The resultant binder composition (9.5 qrams) was
mixed with zircon flour (24.5 grams) to provide a
35 refractcry composition. This refractory composition was
"painted" in two coats onto the surface of a sand mold by
flooding the area to assure penetration into the sand
L r~
-34-
mass. The first coat was dried before application of the
second coat. This wash provided an excellent surface for
heavy steel casting. Moreover, application of the wash was
quick and easy and the wash composition is relatively
5 economical because of the low ratio of the costly
ingredients in the wash.
It will be understood that the embodiments
described herein are merely exemplary and that a person
skilled in the art may make many variations and
10 modifications without depar-ting from the spirit and scope
of the invention. All such modifications and variations
are intended to be included within the scope of the
invention as defined in the appended claims.
