Foundry mold or core compositions and method

Compositions and method for producing foundry sand cores or molds of initial high strength but with essentially no strength after casting metals above 700.degree. C. which involves shaping and setting a composition containing foundry sand and a binder comprising sodium, potassium, or lithium silicate and sufficient amorphous silica so that the fraction of the total silica in the binder solution which is present as amorphous silica is from 2 to 75%, the amorphous silica having a particle size in the range from about 2 nanometers to 500 nanometers and the binder having a molar ratio of silica to alkali metal oxide ranging from 3.5:1 to 10.1.

BACKGROUND OF THE INVENTION 
In the metal casting industry molten metal is cast into molds containing 
sand cores made from foundry sand and binders. These sand cores are 
conventionally bonded with organic resins which, during curing and during 
casting of the metal, decompose and evolve byproducts which are 
odoriferous, offensive fumes which are not only skin irritants but in most 
cases toxic. The molds themselves are made from foundry sand bonded with 
oils, clays and/or organic resins. Thus, during their use, similar 
problems can occur. 
A great percentage of the sand binders used by the foundry industry are 
made of phenol- and urea-formaldehyde resins, phenolic- and oil-isocyanate 
resins, and furan resins. Almost all these binders and their decomposition 
products such as ketones, aldehydes and ammonia are toxic. The principal 
effect on man is dermatitis which occurs not so much from completely 
polymerized resins, but rather from the excess of free phenol, free 
formaldehyde, alcohol or hexamethylenetramine used as a catalyst. 
Formaldehyde has an irritating effect on the eyes, mucous membrane and 
skin. It has a pungent and suffocating odor and numerous cases of 
dermatitis have been reported among workers handling it. Phenol is a 
well-known poison and is not only a skin irritant but is a local 
anesthetic as well, so that burns may not be felt until serious damage has 
been done. Besides being capable of causing dermatitis it can do organic 
damage to the body. Furfuryl alcohol defats the skin and contact with it 
has to be avoided. Hexamethylenetetramine is a primary skin irritant which 
can cause dermatitis by direct action on the skin at the site of contact. 
Urea decomposes to carbon dioxide and ammonia, the latter of which is 
intolerable in toxic concentrations. In addition to the binders, some 
processes use flammable gases such as triethylamine as a curing agent. 
Capturing or destroying gases, smoke and objectionable odors are only 
temporary, stop-gap expensive solutions. New binders are needed that 
completely eliminate the sources of offensive odors and toxic gases. 
Many of the organic binders are hot setting and therefore require heating 
to cure. Hot molds not only add hazards and complicate pollution control 
problems but add economical problems related to increased use of energy 
and increased equipment, maintenance and operation costs. 
An alternative is to use inorganic cold setting binders, such as sodium 
silicate, which set at room temperature without producing objectionable 
gases or vapors. The use of silicates, however, results in the silicate 
bond remaining too strong after casting, so that the core is still 
coherent, and has to be removed by use of violent mechanical agitation or 
by dissolving the silicate bond with a strong, hot aqueous alkali. The 
problem may be lessened to a degree by using sodium silicate solutions 
admixed with organic materials such as sugar, but even in this case the 
core is still coherent after casting and requires extreme measures for 
removal such as violent mechanical agitation. 
Thus, there is a need to create a binder for sand in making cores and molds 
for casting metals such as aluminum, bronze, or iron, that will have 
satisfactory high strength before the metal is cast, retain sufficient hot 
strength and dimensional stability during the hot metal pouring, but which 
will have strength after the metal has been cast and cooled, that the sand 
can be readily shaken out of the cavities formed by the cores; the binder 
also should be one that will not evolve unreasonable amounts of 
objectionable fumes when the sand cores and molds are subjected to molten 
metal. 
SUMMARY OF THE INVENTION 
I have discovered that molds and sand cores of initial high strength but 
with essentially no strength after casting metals above 700.degree. C. can 
be made by bonding foundry sand with an aqueous solution of sodium, 
potassium, or lithium silicate or their mixtures and amorphous colloidal 
silica the amounts of silicate and amorphous colloidal silica being such 
that the overall molar ratio of SiO.sub.2 /alkali metal oxide (M.sub.2 O) 
is from 3.5:1 to 10:1, preferably 4:1 to 6:1, the fraction of the total 
silica present as amorphous coloidal silica is from 2 to 75% by weight, 
preferably 2 to 50%, and most preferably 10 to 50%, the amorphous 
colloidal silica having a particle size in the range from about 2 
nanometers to 500 nanometers, and the 98 to 25% balance of the total 
silica being in the form of silicate ions. The amorphous colloidal silica 
in the binder comprises both the amorphous colloidal silica component of 
the mixture and the amorphous colloidal silica fraction inherently present 
in aqueous solution of alkali metal silicates of ratio more than about 
2.5. 
In alkali metal aqueous solutions containing more than 2.5 mols of 
SiO.sub.2 per mole of M.sub.2 O, it is found by ultrafiltration, according 
to a procedure referred to herein as the Gore Procedure, that at the 
concentrations used in this invention part of the silica in solution is 
ionic and part of it is colloidal, the colloidal fraction being retained 
by the ultrafilter while the ionic silicate passes through. In the case of 
sodium silicate for example, concentrated commercial silicate solutions 
are available having a SiO.sub.2 /Na.sub.2 O ratio as high as 3.8/1.0 and 
these concentrated solutions therefore contain a substantial proportion of 
the silica present in the colloidal state. The colloidal fraction consists 
of a range of sizes less than 5 nm diameter and down to near 1 nm, with a 
substantial amount of 2 or 3 nm diameter. These units are so small that 
solubility equilibrium is rapidly established so that if the solution is 
diluted with water the units pass into solutiom forming lower molecular 
weight ionic species. 
The higher the ratio of concentrated aqueous solutions of alkali metal 
silicates the higher the colloidal silica content, but for each ratio the 
colloidal silica content decreases with dilution of the solution. 
To prepare a binder having SiO.sub.2 /M.sub.2 O ratio of 3.5 to 3.8 it is 
therefore not necessary to add any colloidal silica if an alkali metal 
solution is used already in the ratio range. On the other hand, if an 
alkali metal silica solution with ratio lower than 3.5 is used, it is 
necessary to add at least some colloidal silica in the form of a sol to 
prepare our binder. 
Silica aquasols (water dispersions of colloidal amorphous silica) 
containing only a small amount of alkali as a stabilizer are commercially 
available and are described in the preferred aspects of this invention. 
In summary, binder compositions of our invention comprise (1) aqueous 
solutions of alkali metal oxide silicates with or without amorphous silica 
present therein and (2) amorphous colloidal silica, if the silicate does 
not have any amorphous silica present therein or if the level of amorphous 
silica in the silicate is not sufficient. 
The core and mold compositions of the invention have the additional 
advantage in that they can be made cold setting, i.e., heating to set the 
binder system is not necessary. Thus, they can be set with CO.sub.2 or a 
suitable acid releasing curing agent. 
Preferred for use in the compositions of the invention are binder wherein 
the alkali metal silicate is sodium silicate and at least 10% of the 
amorphous silica is obtained from a silica sol. 
In preferred embodiments of the composition of the invention carbonaceous 
materials and/or film forming resin adhesives are employed. These 
materials can add desirable properties with respect to shake-out and 
storage life. The employment of these optional, but preferred, materials 
is described in greater detail in the following paragraphs. 
Thus, I have found sand core or mold compositions of foundry sand and 
binder wherein the composition consists essentially of 85 to 97 parts by 
weight of foundry sand and 3 to 15 parts by weight of an aqueous binder 
comprising an aqueous sodium, potassium or lithium silicate solution or 
mixtures thereof and amorphous silica, the amorphous silica in the 
silicate solution determined by the Gore test procedure, the binder 
characterized by (1) a molar ratio of silica to alkali metal oxide of from 
3.5:1 10:1; (2) a weight fraction of the total silica present as amorphous 
silica is from 2 to 75%; and (3) a weight fraction of the total silica 
present as silicate ions is from 98 to 25% and the amorphous silica has a 
particle size of from 2 nanometers to 500 nanometers and the sand core of 
mold possesses a compressive strength sufficiently low to permit easy 
crushing after said core or mold is used in preparing a metal casting. 
Accordingly, the present invention also includes a method for making a sand 
core or a sand mold useful in the casting of molten metal which comprises 
mixing 85 to 97 parts by weight of foundry sand with 3 to 15 parts by 
weight of a binder which comprises am aqueous sodium, potassium or lithium 
silicate solution or mixtures thereof with amorphous silica having a 
particle size of from 2nanometers to 500 nanometers, the amount of 
silicate and amorphous silica being adjusted to form a binder with (1) a 
molar ratio of silica to alkali metal oxide ranging from 3.5:1 to 10:1, 
(2) the weight fraction of total silica present as amorphous silica of 
from 2 to 75%; and (3) a weight fraction of the total silica present as 
silicate ions of from 98 to 25%, the amorphous silica present in the 
silica solution is determined by the Gore test procedure, forming the sand 
and binder mixtures into the desired shape and setting the formed mixture. 
DESCRIPTION OF THE INVENTION 
Foundry Sand 
The compositions of the invention will contain between 85 and 97 parts by 
weight of foundry sand, preferably between 90 and 96 parts by weight. The 
amount of binder used is related to sand type and particle size in that 
with small sand particles and more angular surfaces, more binder mixture 
will be necessary. 
The type of foundry sand used is not critical and the useful foundry sands 
include all of the ones conventionally used in the metal casting industry. 
Thus, these sands can be zircon sands (zirconium silicates), silica sands, 
e.g., quartz, aluminum silicate, chromite, olivine, staurolite and their 
mixtures. 
The particle size of the foundry sand again is not critical and American 
Foundrymen's Society (AFS) particle sizes of 25 to 275 GFN can be 
employed. GFN stands for Grain Fineness Number and is approximately the 
number of meshes per inch of that sieve which would just pass the sample 
of its grains were of uniform size, i.e., the average of the sizes of 
grains in the sample. It is approximately proportional to the surface area 
per unit weight of sand exclusive of clay. 
The useful sands can be washed sands or they can be unwashed sands and 
contain small amount of impurities, i.e., clay. If recycle sands are used, 
an adjustment may have to be made to the binder mixture to take into 
account any silicate present in such sands. 
Various minerals can be used as sand additives to optimize mold or core 
performance. For instance, alumina or clay products can be used to improve 
the high temperature strength and shake-out characteristics of the sand 
cores. 
Conventional refractory grain alumina powders, kaolin, and Western 
bentonite can be used. Kaolin is preferred in amounts between 0.5 to 10% 
by weight of the sand. An example of a kaolin grade useful for this 
purpose is Freeport Kaolin Co.'s "Nusheen" unpulverized kaolin material 
which consists of kaolinite particles with a specific surface area of 
about 16 m.sup.2 /g. 
Binder System 
The compositions of the invention contain 3 to 15 parts, per 100 parts of 
sand binder mixture by weight, of a binder system comprising a water 
soluble alkali metal silicate and amorphous colloidal silica. The key is 
to have very finely divided amorphous silica particles of colloidal size 
dispersed within the alkali metal silicate bond. It is inherent in the 
nature of water soluble alkali metal silicates having a molar ratio 
SiO.sub.2 /alkali metal oxide (M.sub.2 O) above about 2.5, that colloidal 
silica is present. In the case of silicates having a ratio higher than 
3.5, the colloidal silica content is such that they may be employed 
without adding more colloidal silica, but in the case of alkali metal 
silicates of lower/silica/alkali metal oxide ratio there is little or no 
amorphous colloidal silica present so that amorphous colloidal silica must 
be added in order to produce the cores and molds of the present invention. 
In order for the foundry core or mold to become weak after heating and 
cooling, it is helpful to have crystalline silica such as cristobalite 
formed throughout the binder mass by spontaneous nucleation at high 
temperatures. Such nucleation apparently occurs at the surface of 
particles of amorphous colloidal silica. Hence, the larger the area of 
such surface, the weaker the resulting core after heating and cooling. If 
enough amorphous silica is colloidally subdivided and dispersed within the 
silicate, then within one gram of such silicate binder there can exist 
dozens of square meters of amorphous silica surface. The smaller the 
particles, the more rapid the loss of core strength after heating at 
700.degree. C. and cooling. 
The useful water soluble silicate component of the mixture includes the 
commercially available sodium, potassium or lithium silicate or their 
mixtures. Sodium silicate is preferred. These silicates are usually used 
as solutions; however, their hydrates can be used provided that water is 
mixed into the binder, either prior to or during application to the sand. 
The useful sodium silicate aqueous solutions have a weight ratio of silica 
to sodium oxide ranging from 1.9:1 to 3.75:1 and a concentration of silica 
and sodium oxide of about 30 to 50% by weight. As stated above, a fraction 
of the silica in the useful water soluble sodium silicate of SiO.sub.2 
/M.sub.2 O ratio higher than 2.5 is in the form of very small particle 
size amorphous colloidal silicate. Alkali metal silicates with SiO.sub.2 
/alkali metal oxide ratio higher than about 3.5:1 are referred to as high 
ratio alkali silicates or alkali polysilicates although they contain in 
fact a certain proportion of colloidal silica. In essence high ratio 
alkali metal silicate aqueous solutions can be conceived as mixtures of 
alkali metal ions, silicate ions and colloidal silica. High ratio alkali 
metal silicate solutions contain varying amounts of monomeric silicate 
ions, polysilicate ions and colloidal silica micelles or particles. The 
type, size of the ions and micelles or particles, and distribution depend 
for each alkali metal on ratio and concentration. Aqueous solutions of 
moderate concentration of the metasilicate ratio, namely SiO.sub.2 /alkali 
metal oxide 1:1, or more contain mainly the monomeric silicate ions. In 
disilicate aqueous solutions of moderate concentration, with SiO.sub.2 
/M.sub.2 O of 2/1 only the simple metasilicate and disilicate ions are 
present. Aqueous solution of silicates with greater ratios contain 
monomeric silicate ions, dimeric silicate ions, and polymeric silicate 
ions (trimers, tetramers, pentamers, etc.) 
The degree of polymerization of the silica is silicate solutions may be 
expressed as the number of silicate groups formed in the average molecule 
of silicic or polysilicic acid corresponding to the alkali metal silicate. 
The degree of polymerization increases with the silicate. Whereas for 
example a sodium silicate solution of ratio 0.5:1 may have an average 
silica molecular weight of 60 corresponding to one molecule of Si0.sub.2, 
sodium silicate solutions of ratio 1, 2, 3.5 and 4.0 are formed to have 
average molecular weights of about 70, 150, 325 and 400 respectively. This 
is the reason why as mentioned above high ratio silicates containing a 
large proportion of polymeric ions are also known as "polysilicates". 
Silicate polymer ions with a corresponding silica molecular weight above 
about 600 are sufficiently large to be considered as very small silica 
particles and will hereinafter be referred to as colloidal silica or 
colloidal SiO.sub.2. Colloidal particles are generally defined as 
particles with a particle size between about one nanometer and 500 to 1000 
nanometer. This particle size range constitutes the colloidal range and is 
not limited by a sharply defined boundary. 
Alkali metal silicates with an "average" silica molecular weight higher 
than around 200 to 300 have a fraction of their silicate ions present as 
polysilicate ions in the colloidal range. The higher the average molecular 
weight the higher the fraction of polysilicate ions in the colloidal range 
and the higher the molecular weight or particle size of polymer ions or 
particles in the colloidal range. For example, a sodium silicate solution 
ratio 3.25:1 may contain more than 2 and 3 and as much as 15 percent by 
weight of the total silicate or silica in the form of colloidal silica. 
Sodium silicate solutions ratios 3.75:1 and 5:9 may contain more than 8 or 
10 and 33 percent by weight of the total silica respectively in the form 
of polysilicate ions or colloidal silicate. Higher ratio sodium silicate 
solutions of various ratios eventually reach a state of equilibrium in 
which the colloidal silica fraction has a certain particle size 
distribution. In the case of sodium silicate aqueous solutions ratio 3.25 
to 4 at equilibrium the colloidal silica fraction has a particle size 
smaller than 5 nm. 
High ratio sodium silicate solutions may be prepared by simply adding 
dilute silica aquasols (colloidal dispersions of silica in water) to 
dilute low ratio sodium silicate solutions. In this case and until 
equilibrium is reached, average particle size of the collidal silica 
fraction will be determined by time and silica particle size distribution 
of the original sol and the original silicate solution. 
Increase in the ratio of alkali metal silicate solutions containing a 
constant concentration of silica causes an increase is viscosity even to 
the point of gelling or solidification. For this reason the maximum 
practical concentrations for alkali metal silicate solutions decrease with 
increasing ratio. Maximum practical concentration is the maximum 
concentration of siO.sub.2 plus Na.sub.2 O in solution at which the 
silicate solution flows like a fluid by gravity and is stable to gelation 
for long periods of time. The following table illustrates as an example 
the case of sodium silicate aqueous solutions. 
______________________________________ 
Approximate Approximate Maximum Practical 
SiO.sub.2 /Na.sub.2 O Molar Ratio 
Concentraton, % Wt. 
______________________________________ 
1.95 55 
2.40 47 
2.90 43 
3.25 39 
3.75 32 
5.0 &lt;20 
______________________________________ 
Above a certain concentration which decreases with increasing silica-soda 
ratio as explained above, sodium silicate aqueous solutions become very 
viscous and are stable for only a limited period of time. Stability in 
this case means resistance to gelling. More stable solutions can be made 
at lower sodium silicate concentrations but this may become impractical in 
a foundry binder. The high water content of very high ratio (more than 4 
to 5) sodium silicate solutions at practical viscosities prevent their 
extended use as a foundry binder in the present invention. Excessively 
high water content in a foundry binder means unacceptable weak sand molds 
or cores and detrimental quantities of steam evolving when the molten 
metal is poured into the sand mold-core assembly. 
I have discovered ways of using high ratio alkali metal silicates as 
foundry sand binders without introducing excessive amounts of water into 
the sand and without employing unstable commodities. 
A practical way of using high ratio silicate as binders for foundry sands 
is to mix concentrated silica aquasols and concentrated sodium silicate 
aqueous solutions in situ, that is on the surface of the sand grains, thus 
forming the high ratio silicate on the sand surface. 
Concentrated sodium silicate aqueous solutions cannot be mixed with 
concentrated silica aquasols without almost immediate gelling. It would be 
very impractical or simply impossible to mix gels formed in this manner 
with sand using the means available today in common foundry practice. 
However, I have discovered that effective mixing and binding effect is 
obtained with sand if the concentrated silica sol is mixed first with the 
sand to form a uniform and continuous film on the surface of the sand 
grains. The concentrated sodium silicate solution is then added to the 
sand mass in a second, separate step and the sodium silicate then mixed 
with the colloidal silica film on the surface of the sand, gelling in situ 
to form an intimately and uniformly mixed binder within the sand mass. The 
sand mix thus formed in the mixer can be molded by any of the various 
processes available in foundry practice and hardened to form strong molds 
or cores. 
When sand molds or cores made with low ratio (less than about 3.5) silicate 
binders get dry either by exposure to a dry atmosphere or by heating, they 
become harder. On the other hand, when sand molds or cores made with very 
high ratio silicate as binders get dry either by exposure to a dry 
atmosphere or by heating they tend to become weak and friable. This is 
because the overall strength of the mold or core is primarily dependent on 
the mechanical properties of the solid film formed by the silicate 
adhesive when it sets. The separation of adhesive bonds is rarely the 
breaking away of the solid-liquid interface but more generally a rupture 
either within the adhesive film or within the body of the material to 
which the adhesive was applied. Cracks or other faults within the adhesive 
film are more likely to account for low bond strength than rupture at the 
interface. 
The formation of crystalline silica within the mass of the binder 
contributes to weaken the bond between sand grains after heating and 
cooling the molds and/or cores, therefore, providing easier core shake-out 
and separation of the metal from the mold. Conventional sodium silicate 
binders form a glass on the surface of the sand grains when the molds or 
cores are heated to high temperatures. When the mold or core cools down to 
room temperature the glass becomes very rigid forming a very strong bond, 
therefore, hardening the mold or core. For this reason a core made with 
such a binder is very difficult to break up and remove from the cavity of 
a cast metal during the foundry operation known as shake-out. 
When colloidal silica is embedded in a matrix of sodium silicate it tends 
to crystallize and form cristobalite at the temperatures the cores reach 
when metals are cast. Due to the difference in thermal expansion 
coefficient, the expansions and contractions of the cristobalite crystals 
embedded in the glass matrix tend to crack the binder film surrounding the 
sand grains therefore weakening the mold or core. This weakening effect 
has to be added to the already mentioned weakening effect due to the 
cracking of high ratio silicate films on dehydration. Due to these 
weakening mechanisms a core made with the high ratio silicates covered by 
this invention is very easy to break up and remove or separate from the 
cast metal during the shake-out operation. 
Thus the difference in behavior between low and high ratio silicate binders 
for sand molds and cores can be understood by observing films formed on 
silica glass plates by slow evaporation of for example aqueous solutions 
of sodium silicate of various ratios. 
The low silicate/soda ratio (2.0) sodium silicate solution dries in air at 
room temperature very slowly forming a very viscous, smooth, clear film. 
At higher ratio (2.4) drying is faster and the silicate film obtained 
shows some cracks. At very high ratios (3.25 and 4.0) sodium silicate 
solutions include substantial amounts of very small particle size 
colloidal silica and drying is even faster: cracking is even more 
extensive and the film tends to lose integrity. A silica sol of particle 
size 14 nm and SiO.sub.2 /Na.sub.2 O ratio 90 does not form a continuous 
film under the same drying conditions. 
Low ratio silicate binders thus form on the sand surface viscous, smooth 
films which do not form cracks on drying. On the other hand, the films 
formed on the sand surface by high ratio silicate binders, crack on drying 
thus weakening the sand core or mold. For these reasons cores made with 
low ratio silicate binders outside the scope of the present invention 
become stronger when they are heated at high temperatures by molten metals 
in the pouring operation of the casting process. On the other hand, cores 
made with high ratio silicate binders within the present invention are 
reasonably strong when just made, but become weak and friable during the 
casting operation. 
In the practice of this invention a compromise has to be made when choosing 
a binder composition by selecting one with a SiO.sub.2 /Na.sub.2 O ratio 
not so high that the sand molds or cores will weaken to unacceptable 
levels by merely drying at room temperature when exposed to the 
atmosphere, and not so low that the sand molds or cores will form a 
cohesive, solid glass bond when the core or mold is heated in the casting 
operation so that the core or mold becomes very strong when cooled down to 
room temperature and cannot be separated easily from the metal casting. 
The room temperature, as-made strength of sand molds or cores obtained 
with high ratio silicate binders of this invention may be upgraded by the 
addition to the silicate bonded sand mix of a fugitive film-forming resin 
adhesive in the form of a water solution or water dispersion. In this 
case, as explained below in more detail, the molds or cores become 
stronger by drying at room temperature. However, when heated to high 
temperatures during the casting process the resin adhesive decomposes 
evolving harmless vapors and the weakened core and mold can be easily 
separated from the cast metal. 
If a preformed sodium polysilicate having a molar ratio of silica to alkali 
metal oxide in the range of 3.5 to 10 is employed before it gels, the same 
effects as with the amorphous silica sodium silicate system will be 
obtained. An aqueous sodium polysilicate containing 10 to 30% by weight 
silica and sodium oxide and having a silica to sodium oxide weight ratio 
of 4.2:1 to 6.0:1 can be produced as described in U.S. Pat. No. 3,492,137. 
Similarly, the high ratio lithium silicates of Iler U.S. Pat. No. 2,668,149 
or the potassium polysilicates of Woltersdorp, application Ser. No. 
728,926, filed May 14, 1968, now Defensive Publication 728,926, dated Jan. 
7, 1969, can be employed as the binder provided the requirements as to 
molar ratio, particle size and amount of amorphous silica are followed. 
Furthermore, alkali metal polysilicates stabilized by quaternary ammonium 
compounds or guanidine and its salts can also be employed. Some stabilized 
polysilicates of this type are described in U.S. Pat. No. 3,625,722. This 
method, however, has the disadvantage of producing unpleasant odors on 
casting due to the thermal decomposition of the organic molecule. 
Complexed metal ion stabilized alkali metal polysilicates can also be used, 
such as copper ethylenediamine hydroxide stabilized sodium polysilicate 
made by mixing copper ethylenediamine with colloidal silica and then the 
silicate, or the stabilized polysilicates of U.S. Pat. No. 3,715,224. 
The useful amorphous silica are those having a particle size in the range 
from about 2 nanometers to 500 nanometers. In addition to the amorphous 
silica already present in aqueous solutions of high ratio alkali metal 
silicates, such silicas can be obtained from silica sol (colloidal 
dispersions of silica in liquids), colloidal silica powders, or submicron 
particles of silica. The silica sols and colloidal silica powders, 
particularly the sols, are preferred in view of the shake-out properties 
of the binders made from them. 
Gore Procedure 
The amount of coloidal silica present in an aqueous solution of high ratio 
alkali metal silicate can be determined for example by ultrafiltration. 
Ultrafiltration refers to the efficient selective retention of solutes by 
solvent flow through an anisotropic "skinned" membrane such as the Amicon 
"Diaflo" ultrafiltration membranes made by the Amicon Corporation of 
Lexington, Massachusetts. In ultrafiltration solutes, colloids or 
particles of dimensions larger than the specified membrane "cut-off" are 
quantitatively retained in solution, while solutes smaller than the 
uniform minute skin pores pass unhindered with solvent through the 
supportive membrane substructure. 
Amicon "Diaflo" ultrafiltration membranes offer a selection of macrosolute 
retentions ranging from 500 to 300,000 molecular weight as calibrated with 
globular macrosolutes. These values correspond to pore sizes between about 
1 and 15 nm. Each membrane is characterized by its nominal cut-off, i.e., 
its ability to retain molecules larger than those of a given size. 
For effective ultrafiltration, equipment must be optimized to promote the 
highest transmembrane flow and selectivity. A major problem which must be 
overcome is concentration polarization, the accumulation of a gradient of 
retained macrosolute above the membrane. The extent of polarization is 
determined by the macrosolute concentration and diffusivity, temperature 
effects on solution viscosity and system geometry. If left undisturbed, 
concentration polarization restricts solvent and solute transport through 
the membrane and can even alter membrane selectivity by forming a gel 
layer on the membrane surface -- in effect, a secondary membrane -- 
increasing rejection of normally permeating species. 
An effective way of providing polarization control is the use of stirred 
cells. Magnetic stirring provides high ultrafiltration rates. 
A recommended procedure is to use an Amicon ultrafilter Model 202, with a 
pressure cell of 100 ml capacity and a 62 mm diameter ultrafilter membrane 
operated at 25.degree. C. with magnetic stirring with air pressure at 
around 50 psi. 
In the case of sodium silicate for example, an aqueous solution diluted 
with water, is placed in the cell. An Amicon PM-10 membrane, 1.8 nm 
diameter pores, is used. Pressure is applied and filtrate collected. In 
some cases, water is fed in to replace the volume passing through the 
filter into the filtrate. The solution in the filter cell is concentrated 
until the filtration rate is only a few ml per hour. 
The filtrate is collected in progressive fractions, and they and the final 
concentrated solution from the cell are examined: Volumes are noted and 
SiO.sub.2 and Na.sub.2 O concentrations in grams per ml are determined by 
chemical analysis. 
In some cases, the concentrated solution on the filter is further washed by 
adding water under pressure, as fast as filtrate is removed. In these 
cases there is further depolymerization or dissolution of the colloid 
fraction. 
The percentage of colloidal silica, based on total silica, is indicated by 
the amount of residual silica that does not pass through the filter. These 
represent maximum values for the amount of colloid present, since some 
ionic soluble silica is still present. In further examples the residual 
soluble silica is subtracted and the composition of the colloid is 
calculated. 
It is not necessary to isolate the pure colloid, but only to measure the 
concentration of SiO.sub.2 and Na.sub.2 O as ultrafiltration proceeds. 
Since the concentration of "soluble" sodium silicate in the filtrate is 
about the same as in the solution in the cell if this colloid is present 
only at low concentration, the amount and composition of colloid can be 
calculated by difference. 
Allowance should be made in interpreting results obtained with this method 
for the fact that every time water is added to the system some 
depolymerization of colloid or polysilicate ions probably occurs. 
The colloidal amorphous silicas useful in preparing the compositions of the 
invention have a specific surface area greater than 5 square meters per 
gram and generally in the range of 50 to 800 m.sup.2 /g and preferably in 
the range of 50 to 250 m.sup.2 /g. The specific surface area is determined 
by nitrogen adsorption according to the BET method. The ultimate particle 
size of the silica used is in the colloidal range, and is generally in the 
range of 20 to 500 nanometers, preferably 12 to 60 nanometers. Thus, the 
silica sols of the desired particle size range described by M. F. Bechtold 
and O. E. Snyder in U.S. Pat. No. 2,574,902; J. M. Rule in U.S. Pat. No. 
2,577,484; or G. B. Alexander in U.S. Pat. No. 2,750,345 can be used. 
Positive silica sols and alumina modified silica sols wherein the ultimate 
silica particles have been modified and/or made electrically positive by 
partially or completely coating the particle surface with aluminum 
compounds can also be used in the present invention as a source of 
amorphous silica. Such sols are described for example by G. B. Alexander 
and G. H. Bolt in U.S. Pat. No. 3,007,878 and by G. B. Alexander and R. K. 
Iler in U.S. Pat. No. 2,892,797. The advantage of these sols is that in 
some cases they form more stable mixtures with sodium silicate aqueous 
solutions than the unmodified silica sols. 
Certain very finely divided colloidal silica powders such as those made by 
the "fume process" by burning a mixture of silicon tetrachloride and 
methane, have a sufficiently discrete, particulate structure that such 
powders can be dispersed in water by colloid milling to give a sol useful 
in this invention. It is also obvious that such a powder can also be 
colloid milled directly into a solution of silicate. 
Very finely divided colloidal silica powders can also be obtained by 
treating certain silicate minerals such as clay or calcium silicate with 
acid, followed by suitable heat treatment in an alkaline medium. 
Similarly, finely divided colloidal silicas can be produced by 
precipitating silica from a solution of sodium silicate with carbon 
dioxide. Such precipitated silicas are commonly used as reinforcing 
fillers, for elastomers because they are extremely finely divided, and the 
ultimate particles are easily broken apart. Finely divided aerogels of 
silicas may be employed, such as those described by Kistler in U.S. Pat. 
Nos. 2,093,454 and 2,249,767. 
The finely divided colloidal silica powders useful in the composition of 
the invention are characterized by having specific surface areas as 
determined by nitrogen adsorption according to the BET method, of from 5 
to 800 m.sup.2 /g and preferably 50 to 250 m.sup.2 /g, and being further 
characterized by the fact that the aggregates of ultimate silica particles 
are generally less than 10 microns in diameter. 
The amounts and types of amorphous silica that can be dispersed within the 
soluble silicate depends to a considerable extent on the amount of 
grinding or mixing that is done to disintegrate and disperse particles of 
amorphous silica in the silicate bond. Thus, for example, it is possible 
to start with fused silica glass and grind it to the point where a 
substantial amount is present as particles smaller than a micron. The 
inclusion of a high concentration of this type of material can provide 
sufficient surface for nucleation of cristobalite or tridymite within the 
alkali metal silicate glass bond when the sand core or mold reaches high 
temperature during the metal casting operation. Also, finely divided 
natural forms of silica such as volcanic glasses which, in the presence of 
alkali silicates, can be devitrified, may be used, providing they are 
sufficiently finely divided and well dispersed in the sodium, potassium or 
lithium silicate solution used as the binder. 
The compositions of the invention will have 2 to 75% of the total silica 
present in the binder present as amorphous silica, preferably 10 to 50% 
the balance of the total silica being in the form of silicate ions. As the 
specific surface area of the amorphous silica increases, lesser amounts of 
it will be required in the binder mixture. 
There is a practical maximum concentration of amorphous silica that can be 
dispersed in the aqueous silicate solution. It is often desirable to 
incorporate as high a concentration of amorphous silica as possible, yet 
still have a workable fluid binder to apply to the sand. If the proportion 
of amorphous silica to soluble silicate is too low, then the shake-out 
will be adversely affected. On the other hand, if the ratio of amorphous 
silica to soluble silicate is too high, the mixture will be too viscous 
and must be thinned with water. Also, there will not be enough binder to 
fill the spaces between the amorphous silica particles in the bond, and it 
will be weak. In generaly, the higher the content of amorphous silica 
relative to sodium or potassium silicate, the weaker the initial bond as 
set by carbon dioxide. Conversely, the more silicate in the binder, the 
higher will be the initial and retained strengths. 
The binder system should have a molar ratio of silica to alkali metal oxide 
which ranges from 3.5 to 10, preferably 3.5 to 7. This ratio is 
significant because the ratios of soluble potassium, lithium or sodium 
silicates commercially available as solutions lie within a relatively 
narrow range. Most of sodium silicates are within the range of SiO.sub.2 
/Na.sub.2 O of about 2:1 to 3.75:1. Thus, overall ratios of binder 
compositions obtained by admixing colloidal silica, such as ratios 4:1, 
5:1, 7:1 are mainly an indication of what proportions of colloidal silica 
and soluble silicates were mixed since the amount of amorphous silica in 
the soluble silicate at ratios of 2:1 to 3.75:1 are small. 
However, in the ratio range of about 3.5:1 to 4.0:1, compositions of a 
specified ratio are not necessarily equivalent. Thus, a potassium silicate 
having an SiO.sub.2 /K.sub.2 O ratio of 3.9:1, in which there is a 
distribution of polysilicate ions, but relatively small amount of 
colloidal silica, differs considerably from a mixture made by mixing a 
potassium silicate solution of SiO.sub.2 /K.sub.2 O of 2.0:1 with 
colloidal silica having a particle size of, for example, 14 nanometers. In 
the latter case, the colloidal particles will remain as such in solution 
over a considerable period of time. Such a composition has two advantages 
over the more homogeneous one in that the low ratio of silicate has a 
higher binding power giving greater initial strength, while the higher 
content of colloidal particles results in a major reduction in the 
strength in the core after casting the metal. 
OPTIONAL ADDITIVES 
In the casting of some metals, e.g., iron or steel, very high casting 
temperatures are involved, i.e., 2500.degree. F. to 2900.degree. F. If the 
mass of the core is small relative to the mass of the cast metal during 
such high temperature casting, there may be some vitrification of the 
silicate thus creating shake-out problems. To alleviate this situation a 
carbonaceous material can be added to the core composition. These 
carbonaceous materials assist the binder of the invention in providing 
excellent shake-out, particularly after the core has been subjected to 
very high temperatures. 
The useful carbonaceous materials should have the following 
characteristics: 
(a) It should not interfere with the binder system. 
(b) It should have a particle size or primary aggregate equivalent diameter 
sufficiently large to leave discontinuities in the glass formed by the 
binder at very high temperatures, as it burns off partially or completely. 
It should also have a particle size which is not large enough to weaken 
the sand core as fabricated, and specially not larger than the particle 
size of the sand itself. Thus the particle size or primary aggregate 
equivalent diameter should range between 0.1 micron and 75 microns, 
preferably between 5 microns and 50 microns. When the ultimate particle 
size of the carbonaceous material is smaller than 0.1 micron it is 
generally coalesced or it tends to coalesce in the sand mix into primary 
aggregates larger than 0.1 micron. 
(c) It should not be too avid for water, otherwise it would subtract from 
the binder system, drying up the sand and making it impossible or 
difficult to mold. 
Preferred for use are pitch, tar, coal-tar pitch, pitch compounds, 
asphaltenes, carbon black, and sea coal, and most preferred are pitch and 
carbon black. 
Pitch is a by-product from coke making and oil refining and is distilled 
off at around 350.degree. F. It has a melting range of from 285.degree. 
F. to 315.degree. F., is highly volatile, high in carbon and extremely low 
in ash. Following is a typical analysis of coal-tar pitch in weight 
percent: 
______________________________________ 
Volatile 47.37% 
Fixed Carbon 52.43 
Ash 0.2 
Sulfur 0.5 
______________________________________ 
Pitch is a material resistant to moisture absorption and is often used as a 
binder or as an additive for foundry sand cores and molds. 
Sea coal is a common name used to describe any ground coal employed as an 
additive to foundry sands. Sea coal is used in foundry sands primarily to 
prevent wetting of the sand grains by the molten metal, thus preventing 
burnon and improving the surface finish of castings. It is also used as a 
stabilizer and to promote chilling of the metal. 
Following is a typical analysis of sea coal given on a dry basis: 
______________________________________ 
Weight Percent 
______________________________________ 
Ash 5.10% 
Sulfur 0.51 
Volatile carbonaceous material 
40.00 
Fixed Carbon 53.80 
______________________________________ 
______________________________________ 
Ultimate analysis: Weight Percent 
______________________________________ 
Hydrogen 5.20% 
Carbon 81.29 
Nitrogen 1.50 
Oxygen 6.40 
Sulfur 0.51 
Ash 5.00 
______________________________________ 
Tar is generally defined as a thick, heavy, dark brown or black liquid 
obtained by the distillation of wood, coal, peat, petroleum and other 
organic materials. The chemical composition of a tar varies with the 
temperature at which it is recovered and raw material from which it is 
obtained. 
Carbon blacks are a family of industrial carbons, essentially elemental 
carbon, produced either by partial combustion or thermal decomposition of 
liquid or gaseous hydrocarbons. They differ from commercial carbons such 
as cokes and charcoals by the fact that carbon blacks are particulate and 
are composed of spherical particles, quasigraphitic in structure and of 
colloidal dimensions. Many grades and types of carbon black are produced 
commercially ranging in ultimate particle size from less than 10 
nanometers to 400 nanometers. In most grades ultimate particles are 
coalesced or fused into primary aggregates, which are the smallest 
dispersible unit of carbon black. The number of ultimate particles making 
up the primary aggregate gives rise to "structure" -- the greater the 
number of particles per aggregate, the higher the structure of the carbon 
black. 
When mixed with sand fine particle size carbon blacks are coalesced into 
aggregates in the sand mix, therefore they leave discontinuities in the 
binder phase when burned off during the high temperature casting 
operation. 
An example of a commercial carbon black is Regal 660, sold by the Cabot 
Corporation of Boston, Mass., which has the following characteristics: 
______________________________________ 
Nigrometer Index: 83 
Nitrogen Surface Area: 
112 m.sup.2 /g 
Oil (DBP) Absorption: 62 cc/100 grams 
Fixed Carbon: 99% 
______________________________________ 
The carbonaceous material should be present in the core composition in the 
amount of 0.5 to 4 weight percent based on the foundry sand, preferably 1 
to 2 weight percent. 
The amount of carbonaceous material, e.g., pitch, needed depends, to some 
degree, on the refractoriness of the binder used which is in turn a 
function of the silica/alkali molar ratio, and on the temperature to which 
the core will be subjected during casting. When a SiO.sub.2 /Na.sub.2 O 
ratio of 5:1 sodium polysilicate is used as a binder, no pitch is needed 
if the core is used for nonferrous metal castings since in these cases the 
core temperature will not exceed about 1200.degree. C. If the same binder 
is used for small cores in massive iron castings, 2% of pitch is useful to 
help break up the silicate glass formed. 
In the event it is desirable to make cores and store them for extended 
periods of time prior to use, I have discovered that the addition of a 
film-forming resin adhesive in the form of a water solution or water 
dispersion, drastically extends the storage life of foundry sand cores 
made with the binder of the invention. Thus the use of these materials 
enable the formed cores to retain sufficient strength and hardness during 
storage. 
Useful film-forming resin adhesives include polyvinyl esters and ethers and 
their copolymers and interpolymers with ethylene and vinyl monomers, 
acrylic resins and their copolymers, polyvinyl alcohol, water dispersions 
of polyolefin resins, polystyrene copolymers such as polystyrene 
butadiene, polyamide resins, natural rubber dispersions, and natural and 
modified carbohydrartes (starch or carboxycellulose). Particularly 
preferred for use are aqueous dispersions of polyvinyl acetate and vinyl 
acetate-ethylene copolymers. 
The polymer resin should be in a state of subdivision suitable for uniform 
distribution on the sand grains to form an adhesive film and hold the sand 
grains strongly together. it is preferred that resin dispersions be 
between 40 and 60% by weight solids. The higher the concentration of 
solids, the better, as less water will have to be removed, however, with 
concentrations above 60% by weight it can be difficult to mix the 
dispersion into the sand. With resin solutions, e.g., solutions of 
polyvinyl alcohol, concentrations of 4 to 20% solids are preferred. 
Useful polyvinyl acetate dispersions are milkwhite, high-solids dispersions 
of vinyl acetate homopolymer in water. Such dispersions have excellent 
mechanical and chemical stability. Typical properties of a preferred 
polyvinyl acetate dispersion are given in the following table. 
Commercially available dispersions with similar characteristics are 
Monsanto's S-55L, Borden's "Polyco" 11755, Air Products' "Vynac" XX-210, 
and Seydel Wooley's "Seycorez" C-79 
TABLE 
______________________________________ 
Typical Properties of a Preferred 
Polyvinyl Acetate Homopolymer Aqueous Dispersion 
Solid, % 55 
Brookfield viscosity, P* 
8.5-10 
pH 4-6 
Molecular weight (number 
30,000-60,000 (mostly 
average) crosslinked) 
Average particle size, microns 
1-2 (range from 0.1 
to 4) 
Density (25.degree. C.), 
9.2 
approx. lb./gal. 
Surface tension (25.degree. C.), 
55 
approx. dynes/cm. 
Min. film formation temperature** 
.degree. C. 17 
.degree. F. 63 
Residual monomer as vinyl 
1.0 
acetate, % max. 
Particle charge essentially nonionic 
______________________________________ 
*Brookfield model LVF, No. 2 spindle at 6 rpm or No. 3 
**ASTM D2354. 
The useful vinyl acetate-ethylene copolymers are milk-white dispersions of 
55 w/o solids in water with a viscosity between 12 and 45 poises. Du 
Pont's "Elvace" is a commercially available dispersion with these 
characteristics. 
The useful polyvinyl alcohol (PVA) is a water soluble synthetic resin 85% 
to 99.8% hydrolyzed. Du Pont's "Elvanol" resins and Goshenol GL-05, 85% 
hydrolyzed, low viscosity PVA are examples of suitable commercially 
available materials. "Elvanol" grades give 4% water solutions with a 
viscosity ranging from 3.5 to 65 Cp at 20.degree. C. as measured by the 
Hoeppler falling ball method. Water solutions of PVA at low concentrations 
(up to about 10-15 weight percent) or concentrated aqueous colloidal 
dispersions of the water insoluble polymer resins mix uniformly with sand 
and provide good adhesion. Very concentrated water solutions of PVA 
(higher than 20 weight percent) are too viscous and do not mix well enough 
with sand. 
To obtain optimum adhesion, the film forming resin dispersion or solution 
should be added such that it does not gel or coagulate either the silica 
or the sodium silicate before adding them to the sand. For instance, the 
polymer resin dispersions can be mixed with the silica before adding to 
the sand because both are compatible and do not gel when mixed together. 
The mixtures can be added to sand and they will form an adhesive film on 
the surface of the sand grains. After the silica and the polymer resin 
dispersion have been mixed with the sand, the sodium silicate solution can 
be added to the sand and although it will thicken in contact with the 
silica and the polymer resin dispersion, it will do so in situ, that is, 
fairly uniformly distributed on a preformed film of silica and polymer 
resin. 
If before adding to the sand the sodium silicate is mixed with the 
concentrated polymer dispersion and the silica, it thickens and gels and 
it cannot subsequently be mixed adequately with the sand. Instead of 
distributing fairly uniformly on the surface of the sand grains, it would 
tend to form lumps and distribute unevenly in the sand. 
Alcoholic solutions of the polymer resins may be used but are not 
recommended as additives to the silica-sodium silicate binder because they 
get very thick in contact with the binder and tend to gel faster than the 
aqueous dispersions and therefore do not distribute as uniformly on the 
sand grains. However, dilute alcoholic solutions of polymer resins can be 
used as such or mixed with commercial zircon core washes to coat the 
surface of the cores and give improved hardness and storage life to the 
cores. In this case the gel forms on the surface of the sand core already 
set, and it air dries fairly fast or it is dried almost instantaneously by 
lighting the alcohol to extinction of the flame, therefore preventing the 
possible diffusion of the alcohol into the core. 
The use of a water solution or water dispersion of a polymer resin produces 
sand cores with the silica-sodium silicate binder having as gassed 
mechanical strength somewhat lower than that of sand cores made with 
silica-sodium silicate binder without the polymer resin solution or 
dispersion. This may be due to the weakening of the sodium silicate bond 
caused by the dilution produced by the water of the polymer resin solution 
or dispersion. However, drying of the core on storage, more than overcomes 
this effect and after very few days the cores show a much higher 
mechanical strength than the one obtained immediately after gassing with 
CO.sub.2. 
Two mechanisms may contribute to the hardening and strengthening on storage 
provided by the polymer resin. One is the thickening in situ of the 
adhesive film of silicapolymer resin-sodium silicate on the sand grains 
due to the "salting-out" effect caused by electrolyte formation on gassing 
with CO.sub.2. More important is the thickening and solidification of the 
film caused initially by the CO.sub.2 blown through the sand grains and 
specially the subsequent evaporation of the water from the sand core on 
storage. 
Under these conditions the polymer resin macromolecules and/or colloidal 
particles are expected to coalesce and form an effective adhesive bond 
between the sand grains and reinforce the sodium polysilicate binder. 
In the case of the polyvinyl esters the alkaline hydrolysis caused by the 
mixing with the sodium silicate will tend to form in the already formed 
uniform film, polyvinyl alcohol, perhaps an even better adhesive than the 
ester itself. 
The colloidal silica-resin, e.g., polyvinyl acetate components of the 
binder can be used in the form of a stable liquid mixture, the 
carbonaceous material being optionally present. Thus uniform mixtures 
containing colloidal silica and polyvinyl acetate within the relative 
amounts specified in this invention, such as 1.94 parts by weight of 40% 
aqueous colloidal silica and 2 parts by weight of 55% polyvinyl acetate 
aqueous dispersion, can be made by mixing the two components in a beaker. 
The mixture is stable and uniform and can be used within the working day. 
Overnight the mixture tends to separate in two layers and can be stirred 
up to make it uniform. 
One method of providing a stable, pourable mixture of colloidal 
silica-polyvinyl acetate with or without the carbonaceous material, e.g., 
pitch, is to make the liquid phase slightly thixotropic but not viscous. 
In other words, to make it so that it sets to a weak gel structure at once 
when undisturbed (to maintain all particles in uniform suspension) but 
when stirred, or even tilted to pour, the yield point is so weak as to 
permit ready transfer of the material and easy blending with the sand. 
Thixotropic suspensions with the characteristics described above can be 
prepared using a three component suspending agent system disclosed in U.S. 
Pat. No. 3,852,085, issued Dec. 3, 1974. This system consists of (a) 
carboxymethyl cellulose and (b) carboxyvinyl polymer in a total amount of 
about 36 to 65 weight percent with the relative amount of (a) to (b) 
varying from a weight percent ratio of about 1:4 to 4:1 and (c) magnesium 
montmorillonite clay in a concentration of about 35 to 64 weight percent. 
The useful compositions will contain between 95 and 991/2% by weight of the 
binder components and between 1/2 and 5% by weight of the suspending agent 
system. In a composition containing only the colloidal silica and resin, 
15 to 35% of the binder will be silica solids and 15 to 35% of the binder 
will be resin solids. In a three component binder, 5 to 20% will be silica 
solids, 5 to 20% resin solids and 5 to 40% will be carbonaceous matter. 
This suspension system can be used with dispersions containing a maximum 
solid content of 55 percent by weight of polymer resin and colloidal 
silica or polymer resin, colloidal silica and carbonaceous material such 
as pitch. The minimum solid content is only limited by the amount of water 
that is practical to add to the sand mix to obtain practical cores. 
For example, to prepare a colloidal silica-polyvinyl acetate-pitch 
suspension 0.67 parts by weight of "Benaqua" (magnesium montmorillonite 
sold by the National Lead Co.) can be dispersed in 235 parts by weight of 
water with low shear mixing; 0.67 parts by weight of CMC-7H (carboxymethyl 
cellulose) and 0.67 parts by weight of Carbopol 941 (water soluble 
carboxyvinyl polymer) can be added and dissolved using low shear mixing; 
0.15 parts by weight of a 1% solution of GE-60 (silicone-based emulsion) 
can be added as an antifoam agent; 194 parts by weight of "Ludox" HS-40 
(aqueous colloidal silica dispersion sold by E. I. du Pont de Nemours & 
Co.) can be added and mixed with moderate shear mixing; 200 parts by 
weight of Gelva S-55L (polyvinyl acetate aqueous dispersion sold by the 
Monsanto Company) can be added and mixed with moderate shear mixing; then 
200 parts by weight of "O" Pitch sold by the Ashland Chemical Company can 
be added and mixed with moderate shear mixing. A fluid suspension 
containing colloidal silicapolyvinyl acetate and pitch is obtained at a 
suitable ratio to be used as a component of the silicate binder system of 
the invention. 
Alternatively, 58 parts by weight of water can be used instead of 235 parts 
by weight of water and in this case a uniform, stable suspension is 
obtained which is more viscous than the previously described, but still 
pourable and mixes well with sand. 
Alternatively, pitch can be omitted from the preparation, and fluid 
suspensions containing colloidal silicapolyvinyl acetate are obtained at a 
suitable ratio to be used as components of the silicate binder system of 
the invention. 
Application of the Binder 
The binder mixture of the invention can be applied to the sand in various 
ways. Thus, if the binder mixture has sufficient shelf life, it can be 
formulated, stored, and applied to the sand when needed. The silicate and 
amorphous silica can be stored separately and then mixed together when 
needed and applied. Furthermore, they can be applied separately to the 
sand. If this latter procedure is used, it is preferred to first apply the 
amorphous silica, mix it into the sand, then apply the silicate and mix 
again. However, the silicate can be applied first. 
Uniform sand mixes can be prepared by adding the binder to the sand in 
conventional foundry mixer, muller, or mix-mixers, or laboratory or 
kitchen mixers, and mixing for sufficient time to obtain a good admixture 
of the sand and binder, e.g., for several minutes. When added separately, 
it is desirable to mix each component for less than two minutes to avoid 
undue drying. 
If an alkali metal polysilicate solution is used as a binder, it should be 
mixed directly with the sand. If on the other hand colloidal silica and 
sodium silicate solution are added separately to the sand, it is 
preferable to add the silica sol first and to mix it thoroughly with the 
sand before adding the sodium silicate. Once the sodium silicate is added, 
the mix should not be kept too long in the mixer. A period of two minutes 
stirring is generally optimum for the sodium silicate. 
Dry colloidal silicas such as pyrogenic amorphous silica do not mix well 
with the sand and in addition they tend to absorb water from the 
sand-binder system. Therefore, dry colloidal silica powders should be 
added to the sand in the form of a paste made with water or water should 
be added to the sand to help mix the dry silica powder. The amount of 
water made to use the paste should be enough to assure good mixing of the 
silica powder and yet not too much to affect the strength of the core or 
mold when it is hardened. Generally the amount of water needed in this 
case is no more than around 3% by weight of sand. 
When the film forming resin or pitch are incorporated into the core 
composition, if the components are added separately to the sand, the resin 
should be added to the sand before the silicate. The resin can be added to 
the sand before or after the colloidal silica. The order in which the 
pitch is added is not critical with respect to either the silica or the 
silicate. 
When materials such as clays or oxides are used as additives besides the 
binder, they should be mixed thoroughly with the sand in the sand mixer 
before adding the binder. 
In some cases it is found convenient to use a release agent mixed with the 
sand to prevent the core or mold from sticking to the core box or pattern 
after setting. In these cases a conventional core or mold release such as 
kerosene or Mabco Release Agent "G" supplied by the M. A. Bell Company of 
St. Louis, Mo., should be added to the sand mix in the last 20 seconds of 
the two minute period of mixing the sodium silicate. 
If the sand mix is not going to be used immediately, it should not be 
allowed to dry or react with atmospheric CO.sub.2. The mix should 
therefore be stored in a tightly closed container or plastic bag from 
where the air has been squeezed out before sealing until it is ready to be 
used. If a slightly hard layer forms on the top surface of the sand due to 
air left inside the container, the hard layer should be discarded before 
using the sand to make cores or molds. 
A practical way of checking uniformity of the sand mix and observe changes 
in the sand mix, such as reaction with the atmospheric CO.sub.2, is to add 
a few grams of an indicator such as phenolphthalein at the beginning of 
the mixing operation. The phenolphthalein can be added in the form of a 
fine powder before adding the sodium silicate or dissolved in the sodium 
silicate or in the silica sol. Usually 160 milligrams of phenolphthalein 
per kilogram of sand is sufficient to develop a deep pink color in the 
sand mix. 
Conventional foundry practice can be followed to form and set the sand core 
or mold. The sand can be compacted by being rammed, squeezed or pressed 
into the core box either by hand or automatically, or can be blown into 
the core box with air under pressure. 
The formed sand mix can be hardened very fast at room temperature by 
gassing the sand with CO.sub.2 for a few seconds. Optimum gassing time can 
be determined either by measuring the hardness or the strength of the core 
or by observing the change of color of the sand mix when an indicator such 
as phenolphthalein has been previously added to the sand. 
Thermal hardening can be used for cores made with the binder compositions 
of the invention instead of CO.sub.2 hardening. For instance, high 
strength cores can be obtained in a very short time by forming the sand 
mix in a hot box at temperatures between 100.degree. C. and 300.degree. C. 
In general, the higher the temperature the shorter the time required to 
achieve a certain strength level. On the other hand at a fixed temperature 
in general, the core strength increases with time of heating. However, 
thermal hardening is not a preferred setting process for the compositions 
of the invention because cores made in this way do not have as good 
shake-out characteristics as those made by CO.sub.2 hardening. 
Another fast hardening process that can be used is CO.sub.2 gassing in a 
warm box (about 60.degree. to 80.degree. C.) or gassing with heated 
CO.sub.2. 
When fast hardening is not required, cores with the binders of the 
invention can be set with other common curing agents used for the systems 
known in the art as silicate no-bakes. These curing agents are organic 
materials which are latent acids such as ethyl acetate, formamide, and 
acetins. Most of these agents contain glycerol mono-, di-, or tri-acetates 
or any other material which can release or decompose into an acid 
substance which in turn produces hardening of the alkali metal silicate. 
Furthermore, such a hardening process can produce cores having long shelf 
life without the need for a film-forming resin adhesive, i.e., polyvinyl 
acetate. 
Conventional water based on alcohol based core washes can be used to treat 
the surface of the cores. This type of treatment is in some cases to 
improve the surface of the metal casting or the hardness and shelf life of 
the core. Shelf life is the period of time after making for which the sand 
core is useful. 
Polyvinyl acetate homopolymers and copolymers can be used as core washes 
for sand cores as aqueous dispersions, in organic solvent solutions or 
mixed with zircon or graphite in aqueous or alcoholic suspensions. 
Polyvinyl alcohol or partially hydrolyzed polyvinyl alcohol can be used in 
aqueous solutions, organic solvent dispersions or mixed with zircon or 
graphite. 
Polyvinyl Alcohol or Hydrolyzed Polyvinyl Acetate: 
Five percent by weight to 20 percent by weight in water solutions or 5 
percent by weight to 40 percent by weight in alcoholic solutions. More 
concentrated solutions are too thick to obtain uniform coating of the 
cores, more dilute solutions are too thin to provide satisfactory 
protective coating on the core surface. 
Polymer Resin Aqueous Dispersions and Alcoholic Solutions: 
Five percent by weight to 40 percent by weight of polymer resin such as 
polyvinyl acetate homopolymer or copolymer in water solutions or 5 percent 
by weight to 25% by weight of polymer resin such as polyvinyl acetate 
homopolymer or copolymer in alcoholic solutions. 
Polymer Resin-Zircon or Graphite Mixtures: 
In water based core washes: 15 to 25 percent by weight of polymer resin 
such as polyvinyl acetate homopolymer or copolymer and 30 to 50 percent by 
weight of zircon (25 to 50 percent by weight of water). 
In alcohol based core washes: 5 to 10 percent by weight of polymer resin 
such as polyvinyl acetate homopolymer or copolymer and 30 to 50 percent by 
weight of zircon or graphite (40 to 60% alcohol). 
The alcohols useful in the above core washes include methanol and ethanol. 
Satisfactory polymer resin-zircon core washes are made for example by 
slurrying 1 part by weight of a commercial zircon core wash (as shipped by 
the supplier in the form of a wet powder) in 1 part by weight of 55% 
polyvinyl acetate aqueous dispersion if the core wash is intended to be 
used shortly after preparation. More dilute slurries are preferred for 
core wash compositions intended to be stored for some time before using. 
In this case the 1 part by weight of the zircon wet powder should be 
slurried in 1 part by weight of water before mixing with 1 part by weight 
of 55% polyvinyl acetate aqueous dispersion. 
Aqueous polyvinyl acetate or zircon-polyvinyl acetate or graphite-polyvinyl 
acetate core washes are applied on the core surface by common foundry 
practices such as dipping, spraying, brushing, etc., and allowing the core 
to air dry before using. 
Sand cores coated with alcohol base polyvinyl acetate or zircon-polyvinyl 
acetate are lighted immediately after one wash application as in common 
foundry practice with alcohol base zircon core washes. 
Concentration of polyvinyl alcohol aqueous solutions to give satisfactory 
core washes with adequate viscosity depends on molecular weight of the 
polymer. Polyvinyl alcohol solutions can also be used as a mixture with 
zircon or graphite core wash. 
Casting Metals 
Sand molds and cores made with the binder compositions of the invention can 
be used to cast most metals, such as gray, ductile and malleable iron, 
steel, aluminum, copper-based alloys such as brass or bronze. Steel is 
usually cast at around 2900.degree. F., iron at about 2650.degree. F., 
brass and bronze at around 2100.degree. F. and aluminum at about 
1300.degree. F. 
With the molds or cores of the invention it is desirable that the core have 
an initial strength such that it can be handled without undue care and 
that it will stand up during the casting of the molten metal, i.e., will 
not wash away or distort. In standard American Foundrymen's Society lab 
tests this means that the core should have a compressive strength of at 
least 100 psi and preferably over 150 psi. 
It is desirable that the hardness of freshly made cores exceed 5, 
preferably 10. The greater the hardness, the better, particularly at the 
time of metal pouring when it should exceed 10 and preferably 20. 
Scratch hardness of cured cores can be measured with commercial hardness 
tester No. 674 available from Harry W. Dietert Co., 9330 Roselawn Avenue, 
Detroit, Michigan. This is a practical, pocket-sized instrument for 
measuring the surface and sub-surface hardness of baked cores and dry sand 
molds. 
The tester has three abrading points which are loaded by a calibrated 
spring which exerts a constant pressure. These abrading points are rotated 
in a circle 3/8" in diameter. To obtain the hardness values, the lower end 
of the instrument is held against the sand surface and the abrading points 
are rotated three revolutions. The hardness values are actually obtained 
by measuring the depth to which the abrading points penetrate. The maximum 
hardness value indicated by this tester is 100 for zero penetration. When 
the abrading points move down a distance of 0.250 inches, the hardness of 
the core is 0. Intermediate values are read from the instrument dials. 
The core should, after the metal has been cast and cooled, have a retained 
strength such that it can be shaken out without the use of undue energy. 
This corresponds to a compressive strength in lab tests of, preferably, 
less than 50 psi.

The following examples are offered to illustrate various embodiments of the 
invention. All parts and percentages are by weight unless otherwise 
indicated. 
EXAMPLE 1 
This is an example of the use of guanidine stabilized sodium polysilicate 
(SiO.sub.2 /Na.sub.2 O ratio 5:1) prepared according to Example 1 of 
patent application Ser. No. 287,037, filed Sept. 7, 1972, as a binder for 
foundry sand cores. These sand cores were used to make aluminum castings 
in a nonferrous metal foundry. 
The binder sample was made with 1890 g of sodium silicate Du Pont Grade No. 
20 (SiO.sub.2 /Na.sub.2 O molar ratio 3.25:1, 28.4% SiO.sub.2, 8.7% 
Na.sub.2 O), 56 g of water, 539 g of 1.3 M guanidine hydroxide and 1015 g 
of Ludox.RTM. HS, a commercial colloidal silica sol containing 30% 
SiO.sub.2 of particle size of about 14 nanometers. 
The sand mix was prepared in the following way: 90 grams of kaolin and 2 
grams of phenolphthalein were added to 10 lbs. of sand while stirring in a 
10-lb. capacity Clearfield mixer. 0.5 Lbs. of binder solution were also 
added to the sand while stirring and the sand was mixed for a total of two 
minutes. 
The sand used was a mixture of 50 parts of Houston's subangular bank sand 
AFS No. 40-45 and 50 parts of No. 1 Millcreek, Oklahoma AFS 99 ground 
sand. The sand when used was at room temperature (75.degree. F.). Humidity 
of the room was about 80%. The binder mixed readily with the sand showing 
excellent mixing characteristics. Flowability of the mix was also 
excellent. 
The sand mix was placed in a polyethylene bag and sealed. The sand mix was 
used the following day to make sand cores. Three to four pound sand cores 
were made by filling wooden core boxes with the sand mix, compacting the 
sand by hand and gassing it for about 15-25 seconds with CO.sub.2 gas at 
an estimated pressure of 20-30 pounds. 
The color of the sand is deep pink due to the phenolphthalein added. After 
gassing the cores had the natural color of the original sand. Good release 
of the core was observed when the core box was opened to remove the core. 
The cores were immersed in a conventional alcohol zircon core wash and 
flamed before using. This is common practice with core washes for sodium 
silicate sand cores. 
The cores were assembled in a sand mold and used to make an aluminum 
casting. Aluminum was poured at a temperature of about 1375.degree. F. 
When pouring was completed the casting was allowed to cool for about 15 
minutes inside the sand mold assembly. The aluminum casting was removed 
from the mold when still hot and the sand core was observed before 
shake-out. Shake-out was very easy; the core broke up and flowed like 
unbounded sand upon touching. No offensive odors were noticed during the 
casting and cooling. 
The aluminum castings had very good surface finish and were used in normal 
production. 
EXAMPLE 2 
This is an example of the use of sand cores made with the binder solution 
of Example 1, to make gray iron castings. 
Two 10 lb. sand mix batches were made by adding 0.5 lbs. of the binder 
solution and 0.7 g of phenolphthalein to 10 lbs. of Houston subangular 
bank sand AFS 45-50, while stirring in a 10 lb. capacity Clearfield mixer 
and mixing for two minutes. The binder mixed very well with the sand and 
gave a uniform sand mix containing 5% of binder by weight of sand. The 
sand mix showed excellent flowability. The sand mix was kept in a closed 
polyethylene bag for four hours before using. 
Two more 10 lb. sand mix batches were made by adding 23 g of "Nusheen" 
kaolin powder furnished by the Freeport Kaolin Co., 0.5 lbs. of the binder 
solution and 0.7 g of phenolphthalein to 10 lbs. of the same Houston sand 
AFS 45-50, while stirring in a 10 lb. Clearfield mixer, and mixing for two 
minutes. The kaolin powder and the binder mixed readily with the sand and 
a uniform sand mix with excellent flowability containing 5% of binder and 
0.5% of kaolin by weight of sand was obtained in this manner. The sand mix 
was kept in a closed polyethylene bag for about four hours before using. 
Sand cores were made by placing the sand mixes into a half-bottle shaped 
aluminum core box with no parting agent, placing iron rods longitudinally 
in the mix, tapping the sand, and gassing the core with CO.sub.2 until the 
core surface developed enough hardness but the sand still had a light pink 
color. The gassing was accomplished by placing a CO.sub.2 probe for 5 to 
10 inches in different parts of the sand core until it was uniformly 
hardened. 
Six core halves with the shape of half-bottles were obtained in this manner 
and all were dried at 450.degree. F. for one minute. No core wash was 
applied to the surface of the cores. Two half-bottle shaped parts made 
with sand mix containing no kaolin were assembled and glued together with 
a conventional silicate core paste furnished by the M. A. Bell Co. of St. 
Louis, Mo. under the trade name of "Fast-Dry", to form a bottle-shaped 
sand core. 
Two half-bottle shaped parts made with sand mix containing 0.5% of kaolin 
by weight of sand were also assembled and glued together with the same 
core paste to form a second bottle-shaped sand core. 
A third bottle-shaped core was made by assembling and pasting together one 
half-bottle shaped core part prepared with sand containing 0.5% by weight 
of kaolin and one half-bottle shaped core part prepared with sand 
containing no kaolin. 
Three full bottle-shaped sand cores were obtained in this manner and they 
were assembled inside a sand mold. Gray iron at about 2650.degree. F. was 
poured into the mold and allowed to cool for about one hour before 
removing from the mold. Shake-out of all three cores, with and without 
kaolin, was very easy: The sand core broke up and flowed out when tapped 
with an iron bar. 
EXAMPLE 3 
This is an example of the use of a lithium polysilicate solution as a 
binder for foundry sand cores. The sand cores made with this binder were 
used to cast brass metal parts. 
The lithium polysilicate solution contained 20 weight percent of silica and 
2.1 weight percent of lithium oxide, therefore the SiO.sub.2 /Li.sub.2 O 
ratio was 4.8:1. Density of the solution is 9.8 lbs/gal (specific gravity 
1.17 g/cc); viscosity 10 cp; pH 11. 
The sand mix was prepared by adding 0.1 lb. of "Nusheen" kaolin powder, 2 
grams of phenolphthalein powder, and 1 lb. of lithium polysilicate binder 
solution to 10 lbs. of a sand mixture (50 weight percent Houston sand AFS 
50 and 50 weight percent #1 Millcreek, Oklahoma, sand AFS 90) in a 10 lb. 
Clearfield sand mixer while stirring. The mix was stirred for one minute 
and a half and 30 grams of a conventional release agent commercially 
available from the M. A. Bell Co. of St. Louis, Mo., under the trade name 
of Mabco Release Agent "G", was added while stirring. The mix was stirred 
for a total time of two minutes. 
During the operation it was observed that the binder mixed readily with the 
sand. The sand mix obtained had very good flowability and it was kept 
overnight in a closed polyethylene bag before using to make sand cores. 
Cores were made by ramming the sand mix with a tamper in a wood core box 
painted with aluminum paint. CO.sub.2 gassing was applied for 5 to 10 
seconds from each end of the U shaped cores or through a center hole in 
the case of cylindrical type cores. When the core boxes were opened, the 
hard, strong sand cores released without difficulty. The cores were 
immersed in a conventional zircon-alcohol core wash and flamed before 
using. 
The cores were assembled into sand molds and molten brass was poured at 
about 2100.degree. F. The metal was allowed to cool to about room 
temperature. The sand core broke up very easily and flowed from inside the 
casting without difficulty. 
EXAMPLE 4 
This is an example of the use of the guanidine stabilized sodium 
polysilicate (SiO.sub.2 /Na.sub.2 O ratio 5:1) of Example 1 to make sand 
cores and test them according to American Foundrymen's Society standard 
methods. 
The sand mix was prepared by adding 30 grams of the binder solution and 100 
mg of phenolphthalein powder to 570 g Portage 515 sand. Portage 515 is a 
sand from Portage, Wisconsin, with an AFS (American Foundrymen's Society) 
Grain Fineness Number as defined in page 5-8 of the seventh edition (1963) 
of the AFS Foundry Sand Handbook, of 67-71. In this example the AFS number 
was 68. Phenolphthalein is added only as an indicator for optimum gassing 
time with CO.sub.2. 
The addition of the sodium silicate to the sand was made gradually while 
the sand was stirred at speed setting 2 in a "Kitchenaid" mixer Hobart 
K45. The sand was mixed for a total of ten minutes. 
AFS standard and specimens for foundry sand mixtures were used for making 
tests. The specimens are cylindrically shaped and exactly 2 in..+-.0.001 
in. (508 cm) diameter and 2 in..+-.1/32 in. (5.08 cm) height prepared in a 
standard sand rammer. The standard sand rammer and the standard procedure 
to make test specimens are described in sections 4-5 and 4-9 respectively 
of the above-mentioned Foundry Sand Handbook. In this example 170 g of the 
sand mixed were used to fall within AFS specimen height specifications 
after ramming. 
AFS standard specimens prepared in this manner were strong enough to be 
handled and in this case they had a pink color due to the phenolphthalein 
indicator added to the alkaline mix. 
A Dietert CO.sub.2 gassing fixture set No. 655 supplied by the Harry W. 
Dietert Co. of Detroit, Michigan was used to harden the sand specimens by 
making CO.sub.2 gas flow through them at a controlled rate for an optimum 
period of time. The CO.sub.2 setting equipment consists of a pressure 
reducer and flow meter, and gassing fixtures for the standard 2 inch 
diameter precision specimen tube where the sand specimen is rammed. 
The flow meter is calibrated in terms of gas flow at atmospheric pressure 
from 0 to 15 liters per minute. A constant gas flow of 3 liters per minute 
was used and the optimum gassing time of each sand mix was determined by 
testing a number of cores made at different gassing times. The change of 
color of the phenolphthalein in the sand during gassing indicated the 
degree of neutralization reached by the alkaline silicate and could be 
used as a preliminary guidance to try to estimate the hardening of the 
sample. 
After gassing the compressive strength of the standard sand specimens was 
measured in a motor driven Dietert No. 400 Universal Sand Strength Machine 
equipped with a No. 410 high dry strength accessory to increase the range 
of compression strength to 280 psi. 
Evaluation of the shake-out characteristics of the sand cores made with the 
binder compositions was made with the AFS non-standard Retained Strength 
test. The standard, hardened-by-gassing, 2".times.2" sand specimens were 
soaked in an electric muffle furance at 850.degree. C. for 12 minutes in 
their own atmosphere, then removed from the furnace and allowed to cool to 
just above room temperature, and tested in the Universal Sand Strength 
Machine. 
Some specimens made with commercial silicates as a comparison sometimes 
gave strength values higher than 280 psi and were therefore tested in an 
Instron Machine. 
Gassing times and strength values obtained with guanidine stabilized sodium 
polysilicate bonded AFS 68 Portage 515 sand are given in the Table. 
Employing the methods of preparation of the sand mix, forming and hardening 
the sand core specimen, and testing compression strength given in this 
Example 4, different binder compositions of the invention were used to 
make and test sand cores. The binder compositions used are described 
below. Testing results obtained are included in the Table. 
Examples 
A. Kaolin (2% by weight) mixed with the sand before adding the 5% guanidine 
stabilized sodium polysilicate of this Example 4 and mixing for 2 minutes. 
B. 5% Tetramethylammonium hydroxide (TMAH) stabilized sodium polysilicate 
made according to teachings of U.S. Pat. No. 3,625,722. 
C. Kaolin (0.5% by weight) mixed with the sand before adding the T.M.A.H. 
stabilized sodium polysilicate of Sample B and mixing for 2 minutes. 
D. 5% Of sodium polysilicate SiO.sub.2 /Na.sub.2 O molar ratio 3.75:1 made 
by dissolving fine colloidal silica powder (HiSil 233) in sodium silicate 
SiO.sub.2 /Na.sub.2 O molar ratio 3.25:1. 
E. 5% Of sodium polysilicate SiO.sub.2 /Na.sub.2 O molar ratio 6.5:1 
stabilized with copper ethylenediamine hydroxide. 
F. 10% Of lithium polysilicate SiO.sub.2 /Li.sub.2 O molar ratio 4.8:1 made 
according to the teachings of U.S. Pat. No. 2,668,149. 
G. 10% Of potassium polysilicate SiO.sub.2 /K.sub.2 O molar ratio of 5:1. 
TABLE 
______________________________________ 
Compressive Strength 
psi 
Retained After 
Binder As Gased 850.degree. C. - 12 minutes 
______________________________________ 
guanidine stabilized 
sodium polysilicate 
160 10 
Example A 160 30 
Example B 190 30 
Example C 185 30 
Example D 160 10 
Example E 200 25 
Example F 180 10 
Example G 100 &lt;10 
______________________________________ 
EXAMPLE 5 
Amorphous silica-sodium silicate binder composition of SiO.sub.2 /Na.sub.2 
O ratio 5:1 can be formed directly on the sand by addition of colloidal 
silica sol of uniform particle diameter about 14 nm to the sand, mixing, 
and then adding sodium silicate SiO.sub.2 /Na.sub.2 O molar ratio 3.25:1 
and mixing for two minutes. 
14.96 g of Du Pont Ludox.RTM. HS-40 (40 w/o SiO.sub.2) poured into 745 g of 
Portage 515 sand in a Hobart K-45 mixer while stirring at speed setting 2. 
Then adding 40 g of Du Pont sodium silicate grade No. 20 (SiO.sub.2 
/Na.sub.2 O molar ratio 3.25:1) and mixing for 2 more minutes. 
Standard AFS 2".times.2" samples made by ramming, then gassing for 30 
seconds with CO.sub.2 at a flow rate of 3 liters/minute have a compressive 
strength of 200 psi and a retained compressive strength at room 
temperature after soaking in a furnace at 850.degree. C. for 12 minutes 
and cooling, of 20 psi. 
EXAMPLE 6 
Amorphous silica-sodium silicate binder composition of SiO.sub.2 /Na.sub.2 
O ratio 5:1 formed directly on the sand as in Example 5 but using a 
colloidal silica sol of uniform particle diameter about 25 nm instead of 
14 nm, with the same sodium silicate. 
12 g of Du Pont Ludox.RTM. TM-50 (50 w/o SiO.sub.2) 
40 g of Du Pont sodium silicate No. 20 
748 g of Portage 515 sand 
Co.sub.2 gassing time= 30 seconds 
Compressive strength= 230 psi 
Retained strength (850.degree. C.--12 minutes) = 15 psi 
Retained strength (1375.degree. C.--12 minutes) = 35 psi 
EXAMPLE 7 
Amorphous silica-sodium silicate binder composition of SiO.sub.2 /Na.sub.2 
O ratio 5:1 formed directly on the sand as in Example 5 but using a 
colloidal silica sol of uniform particle diameter about 25 nm instead of 
14 nm, and using sodium silicate SiO.sub.2 /Na.sub.2 O molar ratio 3.75:1 
instead of 3.25:1. 
6.76 g of Du Pont Ludox.RTM. TM-50 (50 w/o SiO.sub.2) 
40 g of Phila. Quartz Co. sodium silicate grade S 35 
753.24 g of Portage 515 sand 
Co.sub.2 gassing time= 30 seconds 
Compressive strength= 180 psi 
Retained strength (850.degree. C.--12 minutes)= 15 psi 
EXAMPLE 8 
Amorphous silica-sodium silicate binder composition made with the same 
components and using the same forming method directly on the sand as used 
in Example 5, except that relative amounts of silica sol and sodium 
silicate are calculated to give a final SiO.sub.2 /Na.sub.2 O molar ratio 
8:1 in the mixture. 
32 g of Du Pont Ludox.RTM. TM-50 
40 g of Du Pont sodium silicate No. 20 
728 g of Portage 515 sand 
Co.sub.2 gassing time= 30 seconds 
Compressive strength= 210 psi 
Retained strength (850.degree. C.--12 minutes)= 20 psi 
EXAMPLE 9 
Amorphous silica-sodium silicate binder compositions made by first mixing 
the colloidal amorphous silica as a paste with the sand, then adding the 
sodium silicate and mixing for two minutes. 
3.61 g of Cab-O-Sil M-5 pyrogenic silica powder mixed with 14.4 g of water 
made a thick paste which was mixed with 475 g of Portage 515 sand in a 
Hobart K-45 mixer. To the uniform sand-silica mixture, 25 g of Du Pont 
sodium silicate No. 20 added and mixed for two minutes. 
Standard AFS 2".times.2" samples made by ramming, then gassing for 30 
seconds with CO.sub.2 at a flow rate of 3 liters/minute. Compressive 
strength measured: 210 psi. Retained strength (850.degree. C.--12 
minutes): 15 psi. 
EXAMPLE 10 
This is an example of the use of an amorphous silica-sodium silicate 
composition of SiO.sub.2 /Na.sub.2 O ratio 5:1 as a binder for foundry 
sand cores, a polyvinyl acetate aqueous dispersion as a co-binder and 
additive for durability, and pitch as an aid to improve shake-out and 
casting surface finish. 
An amorphous silica-sodium silicate binder composition of SiO.sub.2 
/Na.sub.2 O ratio 5:1 is formed directly on the sand by addition of 
colloidal silica sol of uniform particle diameter about 15 nm to the sand, 
mixing, and then adding sodium silicate SiO.sub.2 /Na.sub.2 O molar ratio 
3.25:1 and mixing for an additional period of time. 
The sand mix is prepared in the following way: 16 grams of "O" Pitch sold 
by Ashland Chemical Company of Columbus, Ohio are added to 800 grams of 
Portage 515 sand supplied by Martin Marietta Aggregates of Rukton, 
Illinois, in a "Kitchen-Aid" Hobart K-45 mixer while stirring at speed 
setting 2 and mixed thoroughly with the sand. 
14.70 Grams of "Ludox" HS-40 colloidal silica sold by E. I. du Pont de 
Nemours and Company, and 16 grams of Gelva S-55L polyvinyl acetate aqueous 
dispersion, sold by Monsanto Chemical Company, are mixed in a plastic 
beaker, added to the sand-pitch mix and mixed in the Hobart mixer for 2 
minutes. 
Finally, 40 grams of Du Pont sodium silicate grade No. 9 (SiO.sub.2 
/Na.sub.2 O molar ratio 3.25:1) are added and mixed for 2 more minutes. 
AFS (American Foundrymen's Society) standard specimens for foundry sand 
mixtures are made immediately after the mixing is completed, as described 
in Example 4. The specimens are set by gassing with carbon dioxide using 
the equipment and procedure of Example 4. Optimum gassing time for the 
composition of this example is 20 seconds. 
Gassed cores are separated in two groups: one group of cores is left 
untreated, the second group of cores is coated by immersion in various 
core wash compositions given in Table 2. Cores coated with water based and 
methanol based core washes are allowed to air dry, whereas cores coated 
with ethanol based core washes are lighted immediately after removal from 
the core wash bath and the flame is allowed to extinguish. 
The compressive strength of the standard sand specimens is measured as 
described in Example 4. Tensile strength is determined by making AFS 
standard briquets, gassing with CO.sub.2 for 20 seconds and testing the 
briquets according to the standard AFS method (Briquet Method). 
Surface (and sub-surface) hardness of the cores is measured with a 
Dietert-Detroit Core Hardness Tester No. 674. 
Shelf life of the cores is evaluated by measuring core scratch hardness, 
compressive strength and in some cases tensile strength of cores stored in 
standard temperature-himidity condition as a function of elapsed time of 
storage. 
The compressive strength, tensile strength, and core scratch hardness 
obtained are given in Tables 1 and 2. 
Evaluation of the shake-out characteristics of the sand cores made with the 
binder compositions is made with the AFS nonstandard Retained Strength 
test. The standard, hardened-by-gassing, 2".times.2" sand specimens are 
soaked in an electric muffle furnace at 850.degree. C. or 1375.degree. C. 
for 12 minutes in their own atmosphere, then removed from the furnace and 
allowed to cool to just above room temperature, and tested in the 
Universal Sand Strength Machine. For all cores prepared as described in 
this example, both 850.degree. C. and 1375.degree. C. retained strength 
values were less than 25 psi. 
Some specimens made with commercial silicates as a comparison sometimes 
give retained strength values higher than 280 psi and are therefore tested 
on an Instron Machine. 
Table 1 
______________________________________ 
Example 10 
Mechanical properties versus elapsed time 
on storage at 73.degree. F. .+-. 2.degree. F. and 50% 
relative humidity of Portage 515 sand cores made with 
5% sodium silicate* - 1.94% silica sol** - 2% polyvinyl 
acetate aqueous dispersion** - 2% pitch**** 
Core Elapsed Time Since Making Core 
Mechanical 
Properties one one 
Properties 
As Made 1 day 2 days 
3 days 
week month 
______________________________________ 
Compres- 
165 180 200 260 260 275 
sive 
Strength, 
psi 
Core 30 40 45 45 45 45 
(Scratch) 
Hardness 
Tensile 25 25 40 45 45 45 
Strength, 
psi 
______________________________________ 
*Du Pont Sodium Silicate No. 9: 29 w/o SiO.sub.2 : 8.9 w/o Na.sub.2 O. 
**Du Pont Ludox.sup..RTM. HS-40: 40 w/o SiO.sub.2. 
***Monsanto Gelva S:55L: 55 w/o polyvinyl acetate. 
****Ashland Chemical "O" Pitch powder. 
Table 2 
__________________________________________________________________________ 
Example 10 
Compressive strength and core hardness versus elapsed time on storage at 
73.degree. F. .+-. 2.degree. F. 
and 50% relative humidity of Portage 515 sand cores made with 5% sodium 
silicate - 
1.94% silica sol - 2% polyvinyl acetate aqueous dispersion - 2% pitch 
uncoated and 
coated with various core washes (grades of binder components in Table 1) 
Core Time Elapsed on Storage 
Properties one one 
Core Wash As Made 
1 day 
2 days 
3 days 
week month 
__________________________________________________________________________ 
No core wash 
C.S.* 165 180 200 260 260 275 
Hardness* 
30 40 45 45 45 45 
Polyvinyl acetate 
Compr. Str. 
150 280 
water based core wash 
Hardness 
90 90 90 90 90 90 
(75% Monsanto 
Gelva S-55L in water) 
Commercial zircon 
C.S. 170 &gt;280 335 
core wash Hardness 
60 65 60 
(50% "Lite-Off" A 
ethanol dispersion)*** 
Commercial graphite 
C.S. 170 &gt;280 
core wash Hardness 
55 75 75 
(50% Pyrokote**** 
ethanol dispersion) 
Polyvinyl acetate 
C.S. 170 &gt;280 &gt;335 
alcohol based core 
Hardness 
&gt;100 &gt;100 &gt;100 
wash (75% Monsanto 
Gelva V7-M50 in 
methanol) 
Polyvinyl acetate-zircon 
C.S. 130 280 
water based core wash 
Hardness 
30 100 
(1 part Gelva S-55L, 
1 part Lite-Off A, 1 
part water) 
__________________________________________________________________________ 
*C.S. Compressive Strength, psi. American Foundrymen's Soceity Standard 
Method for Bulked Cores. 
**Hardness. Core (Scratch) Hardness. 
***Lite-Off A is a product of M. A. Bell Co., St. Louis, Mo. 
****Pyrokote Supreme 114-5X supplied by Penna. Foundry Supply and Sand 
Co., Philadelphia, Pennsylvania. 
EXAMPLE 11 
This example describes the preparation of sand cores bonded with amorphous 
silica, sodium silicate and polyvinyl acetate and their use in casting 
2.5" grey iron and brass pipe tees. The sand mix is prepared in a Carver 
"S" mixer by adding to 400 lbs. of sand (Whitehead Brothers "E" sand with 
an AFS number 92.2), a mixture consisting of 10.5 lbs. Du Pont "Ludox" 
HS-40 and 9 lbs. Monsanto Gelva S-55L polyvinyl acetate aqueous 
dispersion, and 9 lbs. of pitch (Ashland Chemicals "O" Grade). After five 
minutes 27 lbs. of Du Pont No. 9 sodium silicate are added and mixing is 
continued for a further five minutes. The free flowing, uniformly brown 
mix is then dischargd to a storage bin. 
The cores are formed by air blowing the mix into a steel pattern comprising 
twin 2 1/2" tees and gassing with carbondioxide at 65 psi for 3.5 seconds. 
The cores are immediately removed from the pattern and placed on storage 
trays. 150 cores are made in 18 minutes, each weighing about 2 1/4 lbs. No 
fumes or odors are detected during the mixing or core preparation and the 
cores have adequate strength for normal handling in the foundry. They have 
a very smooth surface with an AFS hardness number of about 20. The cores 
are positioned in oil bonded sand molds, enclosed by steel boxes and grey 
iron is poured at about 2700.degree. F. Ninety cores are used within a few 
hours of preparation and 58 are stored for three days at relative humidity 
of about 25% at about 18.degree. C. The cores which are stored for three 
days are both stronger and harder than when first made. 
After pouring the iron the cores are cooled almost to room temperture. No 
offensive odors are detected during metal pouring or cooling. The cores 
are then very weak and shake-out readily with excellent surface peel from 
the iron. After final cleanup by wet drum tumbling and shot blasting, the 
pipe tees have a much smoother internal surface than those made in normal 
production using a commercial, proprietary silicate binder. In addition to 
having a rougher surface some of the tees made using cores with the 
commercial binder still had sand adhering to the internal surface after 
cleanup. 
Two of the cores prepared as described above are coated by brushing on a 
slurry consisting of 50% zircon and 20% polyvinyl acetate methanolic 
dipersion (Monsanto Gelva V7-M50) and 30% methanol. The alcohol is allowed 
to air dry leaving a hard coating of zircon bonded with polyvinyl acetate. 
The hardness is measured as 90 AFS and shows no change after storing for 
three days at about 25% relative humidity and about 18.degree. C. 
The cores are positioned in molds, and brass is poured at 2120.degree. F. 
After cooling to room temperature the cores collapse readily and shake-out 
is easily accomplished with excellent peel from the metal surface. No 
offensive fumes are detected during metal pouring and cooling. The 
internal surface of the brass tees is very clean and smooth. 
EXAMPLE 12 
The procedure of Example 11 is repeated using Houston, subangular bank 
sand, AFS number 45, and omitting the pitch. Half of the cores are coated 
by immersing them in an agitated slurry containing 50% graphite 
(Pyrokote), 10% Monsanto Gelva S-55L polyvinyl acetate, and 40% alcohol, 
allowing them to drain and igniting the alcohol to burn off completely. 
The other half are similarly treated with an aqueous slurry containing 75% 
Monsanto (Gelva S-55L) polyvinyl acetate dispersion, allowing them to 
drain and air dry. 
After storing for two weeks at about 80% relative humidity and 30.degree. 
C. all the cores are strong and hard (AFS hardness number 80-90). The 
cores are positioned in the molds and brass is poured at 2150.degree. F. 
and allowed to cool to about room temperature. No offensive fumes are 
detected during metal pouring and cooling. Core breakdown is very easy in 
all cases and the shake-out sand is granular and free flowing. Surface 
peel and internal surface finish are excellent in the case of tees made 
from cores treated with the graphite polyvinyl acetete wash and very good 
for cores coated with polyvinyl acetate alone. No sand residues are 
observed on the internal surfaces of tees cast from any of the cores. 
EXAMPLE 13 
This example describes the preparation of sand cores bonded with colloidal 
silica powder, sodium silicate and polyvinyl acetate ethylene copolymer 
and their use in the production of cast iron end plates for boilers. 
Two thousand pounds of Portage No. 515 sand, AFS number 68 are charged to a 
batch muller. Forty pounds of pitch (Ashland Chemical Co. "O" grade) are 
thoroughly mixed with the sand over a period of three minutes. Twenty 
pounds of Cab-O-Sil M-5 pyrogenic silica powder, as a thick paste with 80 
pounds of water, and 40 pounds of Du Pont's "Elvace" 1873, a 55% aqueous 
dispersion of polyvinyl acetate/ethylene copolymer (13% ethylene) are then 
added to the mulled mixture over a period of two minutes. One hundred six 
pounds of Du Pont No. 20 sodium silicate are then added and the mixing 
continued for an additional two minutes. Half a minute from the end of the 
mixing period, 1.5 pounds of M. A. Bell's "G" grade flow agent are added. 
The free flowing mix is discharged into a bin. Cores are made by hand 
ramming the mix into the two halves of a split core box. The two halves 
are clamped together and the core is gassed with carbon dioxide at 30 psi 
for a period of 30 seconds. No fumes or odors are detected during mxing 
and core preparation. The core is then stripped from the pattern and after 
storing for several days at about 50% humidity and 25.degree. C. it is 
assembled in the mold. Iron is poured at 2650.degree. F. and after cooling 
to about 1500.degree. F. the molds are broken away. Examination of the 
cores shows them to be quite friable and they collapse immediately on a 
vibrator table and shake-out as granular lump free sand. The boiler end 
plates are free from defects, dimensionally accurate and have excellent 
surface finish. 
EXAMPLE 14 
This is an example of the use of esters as setting agents for the high 
ratio silicate binders of this invention. 
The sand mix is prepared by mixing 14.7 grams of "Ludox" HS-40 and 2 grams 
of Triacetin (glycerol triacetate sold by Eastman Kodak), with 760 grams 
of Portage 515 sand using a "Kitchen-Aid" mixer, Hobart K45. The sand is 
mixed for a total of 2 minutes and 40 grams of sodium silicate ratio 3.25 
(Du Pont No. 9) are then added. After an additional 2 minutes mixing the 
free flowing sand mix is used immediately to prepare standard 2" diameter 
cylinders as described in Example 4. Cores are similarly made using 2 
grams of ethyl acetate (ACS grade sold by Fisher Scientific Co.) in place 
of Triacetin. Cores are stored at 73.degree. F. and 50% relative humidity. 
The compressive strength, hardness and shake-out characteristics are 
evaluated as described in Example 4 and the results are tabulated in Table 
1. 
In addition to very good initial strength and hardness, both strength and 
hardness increase on storage and the loss of strength after heating the 
cores for 12 minutes at 850.degree. C. is indicative of good shake-out. 
TABLE 1 
__________________________________________________________________________ 
Example 14 
Mechanical properties versus elapsed time on storage at 73.degree. F. and 
50% relative 
humidity of Portage 515 sand cores made with 5.3% sodium silicate* - 
1.93% 
silica sol** and either 0.26% Triacetin*** or 0.26% ethyl acetate**** 
Elapsed Time 
Since Making Core 
Mechanical one 
After Heating 850.degree. C. 
Properties 1 day 
3 days 
5 days 
week 
for 12 min. 
__________________________________________________________________________ 
Compressive 
Triacetin 570 685 90 
Strength, psi 
Ethyl acetate 
260 685 
100 
Core (Scratch) 
Triacetin 80 85 
Hardness 
Ethyl acetate 
98 90 
__________________________________________________________________________ 
*Du Pont Sodium Silicate No. 9; 29 w/o SiO.sub.2 ; 8.9 w/o Na.sub.2 O. 
**Du Pont Ludox.sup..RTM. HS-40: 40 w/o SiO.sub.2. 
***Eastman Kodak glycerol triacetate. 
****Fisher Scientific Co. ACS grade ethyl acetate. 
A 400 pound sand mix is made in a Carver "S" mixer as described in Example 
11 adding 8 pounds of pitch in addition to "Ludox" HS-40, sodium silicate 
No. 9 and Triacetin at the same levels on the sand as described above. 
Cores for 2 1/2" pipe tees are made as described in Example 11 except that 
the cores are not gassed with CO.sub.2. After allowing them to harden in 
the pattern for 5 minutes the pattern is stripped and the cores are stored 
for three days before being assembled in the molds. Ductile iron is poured 
at about 2700.degree. C. and the castings are allowed to cool for about 
two hours inside the mold assembly. After removing the castings from the 
molds the cores collapse readily in a vibrator and the recovered sand is 
granular and free from lumps. No odors are produced during the entire 
operation and the castings have very good interior surface finish. 
EXAMPLE 15 
This is an example of heat setting the high ratio sodium silicate binder of 
this invention. 
A sand mix is prepared in a Hobart K45 mixer by adding 12 grams of "Ludox" 
TM-50, 16 grams of polyvinyl acetate dispersion (Monsanto Gelva S-55L) and 
40 grams of sodium silicate ratio 3.25 Du Pont No. 9) to 750 grams of 
Portage 515 sand. The mixing time is ten minutes and the free flowing mix 
is used to prepare standard 2" diameter cylinders as described in Example 
4. The cores are carefully removed from the compacting cylinder and heated 
for 1 hour in an air oven at 100.degree. C. The strength and hardness of 
the cured cores are as follows: 
Compressive strength = 1200 psi 
Afs hardness = 95 
Retained strength (850+ C. -- 12 minutes) = 150 psi 
Example 16 
This is an example of the use of dextrin with high ratio sodium silicate 
binder to produce cores which retain excellent strength and hardness when 
stored for several weeks. 
A sand mix is prepared as described in Example 14 by mixing 14.7 grams 
"Ludox" HS-40, 16 grams of 50% aqueous solution of dextrin (sold by 
Industrial Products Chemicals, Pikesville, Md.) previously mixed with 40 
grams of sodium silicate ratio 3.25 (Du Pont No. 9), with 760 grams of 
Portage 515 sand. Standard cores are prepared and set by gassing with 
carbon dioxide as described in Example 4. Compressive strength and 
hardness measurements when freshly made and after storing for one week at 
about 50% relative humidity and 23.degree. C. show these cores to have 
excellent storage life. Loss of strength after heating for 12 minutes at 
850.degree. C. and 1375.degree. C. in indicative of good shake-out. 
______________________________________ 
After 
Initial 
One Week 
______________________________________ 
Compressive Strength, psi 
135 150 
Core (Scratch) Hardness 
30 50 
Retained Strength (850.degree. C.-12 min.), psi 
20 
Retained Strength (1375.degree. C.-12 min.), psi 
50 
______________________________________ 
EXAMPLE 17 
Amorphous silica-sodium silicate-polyvinyl acetate of Si0.sub.2 /Na.sub.2 0 
molar ratio 5:1 formed directly on the sand by addition of a uniform, 
stable mixture of aqueous silica sol of uniform particle diameter about 12 
nanometers to the sand, mixing and then adding sodium silicate Si0.sub.2 
/Na.sub.2 O molar ratio 3.25:1 and mixing for two minutes. 
14.96 grams of Du Pont "Ludox" HS-40 (40 w/o SiO.sub. 2) are mixed in a 
beaker with 16 g. of Monsanto Gelva S-55L polyvinyl acetate aqueous 
dispersion (55 w/o polyvinyl acetate) and poured into 740 g. of Portage 
515 sand in a Hobart "Kitchen-Aid" K45 mixer, stirred at speed setting 2 
for two minutes. Then adding 40 g. of Du Pont sodium silicate grade No. 9 
(29 w/o Si0.sub.2, 8.9 w/o Na.sub.2 O) and mixing for 2 more minutes. 
Standard AFS 2" .times.2" samples made by ramming, then gassing for 20 
seconds with CO.sub. 2 at a flow rate of 5 liters/minute, are allowed to 
age at about 23.degree. C. and 50% humidity, others are immersed in 
polyvinyl acetate or polyvinyl acetate-zircon water-based core washes and 
allowed to air dry. Samples treated with core washes are allowed to age 
under the same conditions as the untreated specimens. Compressive strength 
and core scratch hardness, and in some cases tensile strength is 
determined the day of making the cores and after several periods of time. 
Results obtained are shown on the table. 
Example 17 
__________________________________________________________________________ 
Mechanical properties versus elapsed time on storage at 73.degree. F. 
.+-. 2.degree. F. and 50% relative 
humidity of Portage 515 sand cores made with 5% sodium silicate - 1.94% 
silica sol - 
2% polyvinyl acetate aqueous dispersion uncoated and coated with various 
core washes 
Mechanical 
Elapsed Time on Storage 
Properties one 
two one 
Core Wash As Made 
1 day 
2 days 
3 days 
week 
weeks 
month 
__________________________________________________________________________ 
Compressive 
170 170 180 200 260 
300 
Strength, 
psi 
Tensile 
30 40 50 55 60 
No core wash Strength, 
psi 
Core 35 50 50 50 50 
Scratch 
Hardness 
Polyvinyl acetate-zircon 
Compressive 
150 290 440 
water-based core wash (1 part 
Strength 
Monsanto Gelva S-55L; 1 
part "Lite-Off" A; 1 part 
Hardness 
25 95 95 95 
water) 
Polyvinyl acetate-zircon 
C.S. 170 425 450 
alcohol-based core wash 
(1.0 parts Gelva V7-50 
Hardness 100 100 
diluted with methanol to 
20% polyvinyl acetate; 1 
part "Lite-Off" A) 
Polyvinyl acetate 
C.S. 170 275 315 
water-based core wash 
(75% Gelva S-55L in 
Tensile 
25 60 140 
H.sub.2 O) 
Hardness 
100 100 
100 
Polyvinyl acetate 
C.S. 320 395 
alcohol-based core wash 
(75% Gelva V7-M50 in 
Hardness 100 100 
methanol) 
__________________________________________________________________________