Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ ~ ~350~
This application relates generally to the manufacture
of molds and cores for t~e casting o~ metals.
Metals such as light alloys, aluminum, bronze, gray
irons and steels are frequently cast with the aid of casting
forms such as cores and molds made of particles of a foundry sand
bound together with a suitable binder. One type of binder which
has been extensively used in the foundry industry is an aqueous
solution of a soluble silicate such as sodium silicate, i.e.,
water glass.
Aqueous solutions of alkaline silicates are generally
known to have adhesive properties, see, for example, Houwink et
al. "Adhesion and Adhesives", Elsevier Publishing Co. 1965;
Volume I, chapter 8; Vail "Soluble Silicates" Reinhold Publishing
Co. 1952. Adhesion must be developed, however, by slow drying
below the boiling point of water to avoid destruction of the ad-
hesive film. (Vail supra, Vol. II; page 411). Because of the need
for relatively 510w drying, other means of rapid hardening the
sodium silicate are required. To provide the rapid hardening re-
quired in practical foundry operation, it has become known to use
an acidic gas such as carbon dioxide or hydrochloric acid which
rapidly converts the sili~ate into silica gel with a liberation
of water and an alkaline carbonate. After an initial set has
been obtained, the mold may then be baked to prepare it for use.
The carbon dioxide-hardened, silicate-bound foundry
6and, however, has generally been recogni~ed to lack adequate
~trength particularly under the conditions of high production
- volume such as encountered in the automotive industry. Accor-
dingly, for the past twenty years foundry sand users have sought
alternatives to the use of silicate as a binder for foundry sands.
These alternatives have resided largely in the use of a variety
- of synthetic resins which are cured to provide the desired set
to the mold.
~143507
One such technique ~hich has been sug~ested is a so-
called hot box procedure in ~hich a li~uid resinous composition,
typically of the phenol or ~uran type, is mixed with the foundry
sand and packed into a mold ~ox. Alternately, others have sug~
gested using dry powdered resinous compositions blended with the
- sand. In any ev~nt, the resinous composi~ions are heated to fuse
the resin, sometimes using a liquid or gaseous material to facil-
itate hardening of the mold. Heat curing, however, presents
handling difficulties, since the ~orker must take precautions to
avoid ~eing burned by the hot heated cured mold. Moreover,
during casting, the hot metal causes decomposition of the resin
binder. This can result in the release of noxious gases that must
be disposed of and in some cases, require special safety pre-
cautions to avoid exposure of the workers involved. Not infre-
quently, the resinous systems also present fire hazards.
Powdered resins have other disadvantages as well. The
powder resin, since it has a substantially different density from
the foundry sand, tends to segregate during mixing and handling
which results in an uneven distribution of binder and an im-
2Q properly bond mold. Further, the powdered resins separates ordusts out during handling and mixing, and the resin dust resul-
ting creates an additional air pollution hazard.
Still another procedure which has been proposed for
binding foundry sands is described in U.S. Patent 3,409,579,
which concerns a binder composition containiny a phenolic resin
which combines with a polyiKx~anate to cross link without heating.
The procedure of this patent avoids the necessity of the hot box
curing. ~owever, curing in this case requires the use of a ter-
tiary amine which has liquid triethylamine which presents serious
difficulties in handling from the safety standpoint.
The use of furan resin bonded sands which are hardened
with sulfur dioxide have a~so been proposed. Here also there
~1~3507
are obvious drawbacks associated with use and disposition o~ a
noxious gas used to harden the ~and.
Summary of ~he Inven*ion
I ha~e now discovered a new method for preparing rapidly
hardened silicate bound sands in which only a relatively low
amDunt of silic ~ is required -- usually less than 3% by weight of
the sand. In accordance with thP present invention a green foun-
dry sand is prepared using an aqueous silicate binder and packed
into a mold box containing the pattern to be duplicated using com-
mercial techniques such as blowing, etc. Optionally, (and pre-
ferably) adjuvants which are more fully described below are used
to impro~e the setting and shake-out propertieS of the mold. The
sand is cured by rapidly removing water from it sufficiently to
cause the sand to set. Typically, such rapid setting is achieved
by removing 30~ or more of the water in less than 10 minutes; in
preferred practice, less than one to two minutes. The present
in~ention provides a method by which silicate-bonded sands will
yield instant tensile strength substantially in excess of the
instant tensile strength obtainable with the corresponding sands
hardened by carbon dioxide gassing.
The present invention~ in one aspect, resides in a
method for manufacturing foundry molds or cores comprising
(a) forming a green foundry sand around a pattern in a
box having at least two air permeable faces, said sand comprising
from 94 to 99.9~ of a refractory foundry sand and having 0.1% to
6% by weight of an aqueous solution containing a soluble silicate
as a binder, said silicate containing an alkali metal, ammonium,
an ammonium complex, or mixtures thereof as a cation and a sili-
cate as the anion, the anion to cation mole ratio being between
1:1 and 4:1, said fioluble silicate further containing ~rom 47 to
70% water. and
~43507
(b) applying 8 diferenti~1 pxe5sure ~et~een fiaid air
permeable fac~s suficient to force air therebet~een at a rate
~ufficient in less than two minutes to remove at lea6t 30% of the
water contained in said a~ueous solution ~nd to barden the same to
~n instant tensile strength in excess o~ that obtainable from
hardening said green sand by carbon dioxide gassing.
The invention, in another ~spect, resides in a method
for forming a desired shape from a particulate material selected
from ~and, charcoal, uood, ores, refractory oxides, fiberglass,
vermiculite, diatomaceous earth and asbestos, comprising
(a) molding a green mixture of said particulate mater-
ial and an aqueous solution of a soluble silicate as a binder into
said desired shape, said green mixture containing from 6 to 100
parts by weight of aid aqueous solution for each 100 parts by
weight of said particulate material, the amount of said
aqueous solution being sufficient to form a porous,
plastic mass when combined with said particulate material, said
soluble silicate containing an alkali metal, ammonium, an ammoniumf
complex, or mixtures thereof as a cation, and a silicate as the
anion, the anion to cation mole ratio being between 1:1 and 4:1,
said soluble silicate further containing ~rom 47 to 70~ water;
(b) said green mixture being molded in a box having an
air premeable face with an open area of at least 1.5%; and
(c) subjecting said molded shape to a force drying
period of not more than about two minutes, during which at least
30% of the water in said aqueous solution is evaporated and said
molded ~hape is hardened to a tensile ~trength of at least 20
pounds per ~quare in~h.
-- 5 --
: L1435i07
These aspects of the invention are also disclosed, and
are claimed, in Canadian Patent Application No. 330,753, filed
June 28, 1979, of which the present application is a divisional.
The procedure of the present invention is quite surpris-
ing since the only example known to me. previously of using air
dried silicate binders in foundry practice i5 in the construction
of investment molds fiuch as described for example in U. S. patent
2,945,273 to HerzmRrk et nl. In inYestment casting usually two
- Sa -
~l1435~7
or three layers of a sand-~ter ~la~ muxture ~r~ applied t~ a
wax pattern and hardened by exposure to an acidic gas such as
carbon dioxide or hydrochloric acid. Additional layers of the
sand-water glass mix are then applied and hardened ~y a current of
warm air. In this instance, air hardening of the investment mold
iS 810w, requiring as much as 30 to 40 minutes under the influence
of the warm air stream to harden each layer, and is limited to
drying of relatiYely thin films. So far as I am aware, drying
three dimensional permeable objects bonded by soluble silicates,
in the manner of the present invention has not heretofore been
~uggested.
Detailed Description of the Invention
As indicated generally above, the present invention in-
vol~es combining foundry sands, silicate binders and, optionally,
adjuvants, which are cured in a novel manner to produce molds and
cores having high initial strength and scratch resistance. In
more detail, the materials used in the invention are the following:
Foundry sands
The present invention is applicable generally to the
conventional foundry sands available in the art. Many such sands
are known. Those denoted as subangular are industrially used, as
well as those containing a higher percentage of spherical or
rounded particles. Lake sand, Wedron sand, and Ottawa sands are
all especially desirable. Also usable are refractory material
such as zircon sands, olivine sands, carbon, refractory oxides
and other refractory particulate substances. It is preferred that
the sand not contain significant portions of impurities such as
organic matter, silt, clays or other colloidal matter, lime and
the like. Some impurities are especially undesirable as they tend
to react with or to absorb the silicate binder, or interfere with
its coating capacity and binding strength.
~143507
Foundr~ sands are pre~erablx dr~ and ~ree ~lowin~.
Their size may be varied according to the particular usage and
may range from coarse (from 50 to 70 mesh~ to fine (as 150 mesh)
and even as fine as 250 mesh. However, because the present inven-
tion depends on rapid ~ithdra~al of ~ater from the silicate binder
in the interior of the mold, it is preferable to avoid fine mesh
sands unless they are necessary to the surface finish of the cast
article. Relatively coarse sands, for example, having an average
mesh size of 50-70, permit passage of drying air through the mold
and cores more easily than do fine sands, such as sands having an
average particle size of 120 mesh which generally doubles the
drying time at a fixed pressure drop.
-Silicate Binder
The simplest silicate binders for purposes of the pre-
sent invention are exemplified by water glass, i.e., sodium sili-
cate containing silica, sodium oxide and water in varying propor-
tions. It is, of course, well known that there are a variety of
alkali metal silicates, and all of these may be used in substitu-
tion for sodium silicate. Such other common alkali metal sili-
cates are potassium silicate and lithium silicate. Also usableare "ammoniated" sîlicates, that is, alkali metal silicates to
which G onium hydroxide has been added. These generally, and
preferably, have a high ratio of silica to soda (or alkali metal
oxide~ such as 2.2 or higher. Also quaternary ammonium silicates
can be used in combination with the alkali metal silicates. Such
quaternary ammonium silicates are described, for example, in U. S.
patents 3,239,521, 3,345,194 and 3,372,038.
Silicate binders generally have silica to metallic ox-
ides mole ratios o~ 1:1 to 4:1, and preferably from 2.2:1 to
3.2:1. These proportions correspond generally to metasilicates,
disilicates, trisilicates or higher silicates. Such silicates in
solution are characterized by increasing amounts of branched rings
~35V~7
and complex structures charactexized as "pol~silicate anions", and
it is believed that it is the ~ranched ring and complex structures
which give rise to the ~ind~ng properties of aqueous silicates.
The silicate binder also contains water to form a syrup-
like aqueous composition having colloidal or gel-like film-forming
eharacteristics. In commercially practicable silicates, there is
generally from 47 to 70~ water, the soluble silicate solution
having a viscosity ranging from 100 up to 50,Q00-70,000, depen-
ding upon the amount of water and the composition of the silicate.
I have had best results in using, as the soluble silicates, sodium
silica~e "N", sodium silicate "R", sodium silicate "RU" and sodium
silicate "D" of the Philadelphia Quartz Company. The grade "N"
soluble silicate contains silica to sodium oxide in a 3.22 weight
ratio, the syrup containing 37.2% sodium silicate solids, having
a density of ~1.0Be and a viscosity of 180cp. Grade "K" has a
SiO2:Na2O ratio of 2.~8 and contains 42.7~ solids. Grade "RU"
has a silicate to sodium oxide weight ratio of 2.40, a solids
content of 47%, a density of 52.0Be and a viscosity of 2100 cp.
Grade "D" has a SiO2:Na2O ratio of 2.0 and contains 44.1~ solids.
Sodium oxide when present in a soluble silicate binder
tends to reduce the melting point of the foundry sand. This im-
parts adverse shake-out properties, and is more severe with more
alkaline water glasses, notwithstanding that the more alkaline
silicates produce better tensile properties in the mold. At the
same time, however, while a soluble silicate containing a high
ratio of silicate to soda such as 3.6, for example, affords fa-
vorable ~hake-out characteristics, it tends to produce relatively
weak binding. Accordingly, there is a desire notwithstanding the
adverse effect of soda to use a soluble silicate of the highest
practical alkalinity -- lowest practical ratio of silicate to soda.
In part, this difficulty can be mitigated by replacing
some of the sodium oxide of water glass by other alkali metal
~35~7
oxides such as potassium. Such other alkali metals have a lesser
tendency than does sodium to flux the foundry sand and lower its
fusion point, but they add to the expense of the binder.
It is preferred, and an important discovery in its own
ri~ht in accordance with the present invention, to add ammonia
or a quaternary ammonium compound to the sodium silicate for the
purpose of increasing its alkalinity ~ithout introduction of ad-
verse quantities of ~odium oxide. In this aspec~ of the inven-
tion it is preferred, therefore, to use a sodium silicate con-
taining a silica to sodium ratio of 2.2 or higher (but preferablynot Aigher than 3.2) to which ammonia is added up to an amount
which increases the effective alkalinity of the mixture to the
equivalent of a sodium silicate having silica to metal oxide ratio
of 1.8 to 2.2. This is calculated by treating 1 mole of ammonia
as the equivalent of 1 mole of sodium hydroxide. This aspect of
the invention is particularly surprising because it had been
thought heretofore that addition of ammonia to sodium silicate
tended to convert the sodium silicate to an insoluble gel. I have
found that, upon addition of ammonia, if a mixture is stirred vig-
orously for at least 30 minutes if gellation occurs, and is allowedto age for several hours (or preferably a day or more) at room
temperature, the homogeneity of the ammoniated sodium silicate re-
appears and the mixture indeed becomes less viscous than the ori-
ginal sodium silicate.
The ammoniated silicate provides a binder with excep-
tiona~l tensile properties. Moreover, because the ammonia is vola-
tile under the influence of sand drying and heat of casting, the
ammonia evaporates leaving behind a mold of excellent shake-out
properties and because the introduction of soda is limited, the
foundry sand retains its reuseability for a greater period of time.
Adjuvants
Another method which I ~an use for reducing the tendency
1~435~7
of the ~ilicate binder to ~orm glass-like sub~tances durin~ cast-
lng is to include in it adjuvants ~ich improve the shake-out
characteristics of the silicate binder. In general such binders,
under the influence of heat during casting will decompose in a
manner that disrupts $he strength of the film or binding action of
the silicate. ~or example, additives carbonize upon exposure to
temperatures of the casting metal, and may evolve small amounts of
gases at such temperatures. This facilitates shake-out of the mold
and cores from the finished casting. According to this invention,
preferred adjuvants are film forming materials which will also
enh~nce the drying and strength properties of the silicate binder,
so that the same or even improved strength is obtained with re~
duced amount of silicate.
The additives are preferably miscible with the silicate
binder or dispersible therein, and have no detrimental effect on
it. It has been found that a small amount of gas formed in the
sand of the mold and core contributes to good casting. However,
excessively gassy adjuvants should be avoided since large amounts
of gas will cause porous cas~ings, and adversely affect the cast
surfaces and dimensional integrity of the casting. Additives
rich in nitrogen, for example, are not preferred for this reason.
A great number of additives have been used in silicate
binders. These are:
1. Alumina, borax, and various inorganic clays, such
as kaolin, bentonite, iron oxide, silica flour, and graphite.
2. Resinous or polymeric film forming compositions ex-
emplified by phenol-formaldehyde resins, urea-formaldehyde resins,
ureaphenol-formaldehyde resins, urea-furfural resins, bituminous
resins, 'osin, shellac, sytrene-butadiene latexes, and polyvinyl
acetate.
3. Sugars such as sucrose, dextrose, and glucose, in-
cluding forms of commercial glucose produced by hydrolysis of
-- 10 --
~L~4350~
carbohydrates, fructose, lactose, m~ose, levulose and maltose
and blends thereo~. Also ~uitable are substances such as corn
syrup containing one or more of the foregoing, as well as poly-
saccharides when used in combination with urea resins. The reduc-
ing sugar reaction with the formaldehyde to provide a binder en-
hances the binding properties of the silicate used as a primary
binder.
4. Special additives more fully described below which I
have discovered for use with silicate binders in accordance with
the present invention provide exceptional results and are preferred.
5. Various mixtures of the foregoing materials can also
be used if desired.
The preferred adjuvants are generally those of the second
through fourth class described above~ The additives of the first
category -- i.e. various inorganic substances~ have the disadvan-
- tage that they tend to add fines to the sand, and because of thist
their use must be limited so as not to reduce permeability and in-
crease resistance to air flow of the green sand. These charac-
teristics interfere with the desired rapid drying of the silicate
binder in accordance with the present invention.
Adjuvants of groups 2 through 4, when used, are desir-
able because they permit blending of a binder composition con-
taining reduced amounts of ~ilicate. Thus, for example, a sand
may be formed using 3%-5% binder of which possibly one-half may
constitute the adjuvant, the remaining major portion being a sili-
cate binder. Thus, the effective silicate content of the binder
is reduced so that upon reuse of the foundry sand after the cas~-
ing- has been completed, the accumulation of low melting alkali
metal oxides is reduced.
One class of adjuvant useful in the present invention
are those described in my British Patent 1,309,606. Such adju-
vants are a condensation product of a ~yrupy mixture composed of
-- 11 --
li~3507
44-77~ reducing sugar, 5-22~ urea~ A~19% ~ormaldehxde~ and 9-18%
water. The mixture is reacted at a pH of 5~16 for 15-120 minutes
at 110-118C. For application in the present process these may
be modified by reducing the amount of urea and formaldehyde.
As indicated, however, preferred adjuvants are those
which`have been specially formulated for use with foundry sands
bound by a soluble silicate in accordance with the present inven-
tion. These preferred adjuvants are formed from ~i) a reducing
sugar such as glucose, pure syrup or other reducing sugars such
as mentioned above; (ii~ a lower dibasic carboxylic acid or acid
anhydride such as maleic acid, maleic anhydride, succinic acid,
succinic anhydride, glutaric acid or anhydride, citric acid, tar-
tariC acid, etc. and; tiii~ a stabilizer to pre~ent carameliza-
tion of the reducing sugar that the process and temperatures re-
quired, I have found that boric acid is generally suitable as a
stabilizer. In general, the lower dibasic carboxylic acid should
contain from 3 to 6 carbon atoms, be miscible with the reducing
sugar at the processing temperature, and may contain hydroxy
groups. Optionally there may also be included polyhydric alcohols
containing 2 to 8 carbon atoms and 2 to 6 hydroxy groups, which
alcohols ~unction as a plasticizer. Typical such alcohols are
ethylene glycol, propylene glycol, glycerine, pentaerythritol and
sorbitol.
The foregoing ingredients are blended together to form a
mixture containins (on a dry weight basis) from 1 to 12~ of the
dibasic carboxylic acid anhydride and preferably from 1 to 3%;
from 1/2 to ~ of the stabilizer (such as boric acid), and pre-
ferably from 1/2 to 1%; and from 0 to 6% of the optional poly-
hydric alcohol preferably from 0 to 4%. The balance of the com-
position is made up of the reducing sugar. The reducing sugarmay be either as a dry powder or as an aqueous syrup containing
up to 20% water. The foregoing proportions are based on the
weight of the dry ingr~dientæ.
- 12 -
11435V'7
The mixture is heated to remove an~ water contained in
the reducing ~ugar as well as t~e ~ater condensation~ Heating
generally is for a period of 30 to 90 minutes at a temperature
of 110 to 150C. The heating step should preferably not be
carried on as long as to cause caramelization or thermodegregation
of the adjuvant. After heating to remove water, while the reac-
tion mixture is still hot, an aqueous alkali is then added, such
as an alkali metal hydroxide (NaOH, XOH, etc.~ or ammonia. The
amount of alkali and water added at this stage should be suffi-
cie~t to provide from 10 to 25~ water in the final produc~, and
from about 1/2 to 2% alkali. The amount of alkali added should
be sufficient to neutralize unreacted carboxylic acids and to aid
in the dilution process. After cooling, the finished product is
a syrupy fluid.
The present invention, in a further aspect, resides in
a composition of matter for use in binding a particulate
composition prepared by
(a) combining (i) a reducing sugar, (ii) a lower
dibasic carboxylic acid or acid anhydride, and (iii) a
stabilizer effective to prevent caramelization of the sugar
during reaction, said dibasic carboxylic acid or acid
anhydride being, on a dry weight basis, from 1 to 12% by weight
of said mixture, and said stabilizer being on a dry weight basis,
from 1/2 to 2% by weight of said mixture, the balance thereof
being made up of said reducing sugar;
(b) heating said mixture to remove water therefrom;
and
(c) thereafter adding an alkali and water to
provide a final product containing from 10% to 25% water and
from about 1/2% to 2% of said alkali.
- 13 -
11~3507
Formulation
The sand, silicate bindex and toptionally) adjuvants,
are mixed in standard mixers or mullers. It is desirable to
accomplish the mixing at rapid speeds to minimize costs and in-
crease output for higher production foundry sands. Thorough mix-
ing in about 1-2 minutes is a desirable and readily attainable
standard.
Generally, the silicate binder composition i8 provided
in an amount sufficient to yield a green sand containing fromO.1%
to 6% silicate. However, in preferred foundry practice, the green
sand will contain 0.5% to 3% by weight of silicate binder or more
preferably 1-3% by weight. The lowest binder content consistent
with the requisite strength is desirable because too high a binder
content destroys the porosity of the foundry sand. Reduced poros-
ity restricts the gas flow required to set the sand, as well as
gas flow through the mold when contacted by hot metal.
The adjuvant is used in proportions generally sufficient
to promote breakup of the binder under the influence of the heat
- 13a -
~1~350~
of the molten metal. The adjuvant preferably has film-f~rming
and plasticizing characteristics ~hich aid the strength of the
silicate binder prior to the casting, and, upon casting, decom-
poses to break up the film of silicate binding material thereby
pro~iding improved shake-out characteristics to the mold. The
adjuvant is used in proportions generally sufficient to promote
the breakup of the bînder under the influence of heat of the
molten metal during casting. Depending on the adjuvant selected,
the desired portion of adjuvant may range from 25% to as much as
200~ adjuvant based on the weight of the silicate binder, prefer-
ably from 5Q% to 150% adjuvant. As indicated above, an advantage
of using an adjuvant is that it decreases the amount of silicate
required for binding in a particular sand composition, thereby
reducing the accumulation of alkali metal oxides when the sand is
reused. For this reason, therefore, it may be preferred to in-
crease the amount of ad~uvant relative to the amount of silicate
consistent with the requirements of good casting performance.
Dehydration and ~ardening
-
In accordance with the present invention, it has been
found that green sands prepared with an aqueous soluble silicate
binder should be rapidly hardened, in the space of a few minutes
or seconds by forced evaporation of water from the silicate binder.
It has been found, surprisingly, that if the green sand
is force-dried to remove water rapidly, vastly improved results
are obtained. Rapid water removal can be accomplished by elec-
tronic heating, for example, by microwave heating, which generates
heat, volumetrically within the mass of the mold and core. In
this embodiment, the green sand is packed in a mold box, using a
pattern, of wood, plastic or other non-conductiye materials,
which are porous and thereby permit the escape of water ~apor as
it is evaporated from the sodium silicate. When electronic
heating is used, obviously metal must be excluded from the mold
- 14 -
~3S0~7
box as ~ell as the general vicinit~ D~ the mold box area and
therefore from the standpoint of practical foundry practice has
certain disadvantages. Electronic heating is ~est applied on
6ilicate bonded cores which have been taken out of the mold box
~na which retain their shape prior to hardening by virtue of the
cohesiveness and the green strength of the sand.
Preferred practice, therefore, is to construct a mold
~ox having two or more air permeable sides adapted to permit air
to be forced or drawn through the body of the mold and core by
application of air pressure or vacuum. A simple mold box is il-
lustrated in Figures 1 and 2 in which
Figure l is a plan view of ~he mold box showing, by
broken-away sections, the air permeable faces and mold cavity; and
Figur`e 2 is a side view through line 2-2 of Figure 1.
In the simple embodiment illustrated in Figures 1 and 2
of this application~ the top 1 and bottom 2 of the mold box are
provided with perforated faces. Typically, perforations are
spaced on 1/10 in. to 1/4 in. centers, the perforations being
sufficient in size to provide at least 1.5 to 10% open area. Pre-
2a ferably 3 1/2% or greater open area is provided. Greater openarea can be added, but does not materially improve results~
Slots providing equivalent ventilation of the mold faces 1 and 2
may also be used. Better results are obtained if the perforations
are more closely spaced. Alternately, the faces 1 and 2 of the
mold may be of air permeable substances such as sintered metal,
sintered glass, open-cell plastic foams, or wire screen of various
composite materials. For best results, the mold box is designed
so that the area of the opposing ventilation faces relative to
the Yolume of the core and mold to ~e hardened is as large as
practical. This will ordinarily result if the ventilated faces
of the mold box are positioned so that air is ~orced or drawn
across the thinnest section of the mold.
- 15 - -
11~*3507
According to this invention, the core and mold can ~e
fully or partially hardened before removal. Silicate binders
rapidly reach their potential strength in the practice of this
invention with adequate air ventilation in less than 40 ~econds.
Ventilation of the mold and core for a shorter period of time,
for example, 10 seconds, will result in a core which has been
hardened in the vicinity of the face ~here air enters, but may
still be soft or plastic on the exit face of the mold. Such
molds and cores, ho~ever, continue to harden after removal from
the mold box and rapidly reach their ultimate strength character-
istics.
While the present invention can be practiced using air
at ambient temperatures, more rapid curing is obtained when using
air at temperatures of 100 to 230F., or such other temperature
as is suitable provided that the mold is not heated during harden-
inq by the warm air to a point which creates a handling problem
when removing the hardened mold from the mold box.
For most purposes, in the practice of the present inven-
tion, it will be sufficient to provide for an air flow rate in the
range of lQ0 CFM to about 1500 CFM. The flow rate of air required
is dependent to some extent on the amount of sand to be cured and
the thickness of the mold which the drying air must traverse. Air
may be supplied either by a ~uitable blower and compressor provid-
ing air at su~ficient pressure, bearing in mind the permeability
of the mold and the mold faces which the air must traverse to pro-
vide the desired hardening. Ordinarily, 5 to 30 lbs. pressure
will be quite adequate. Under some conditions it may be desirable
to employ higher pressure; however in such cases, of course, the
mold box must have sufficient mechanical strength to withstand
3Q the pressure drop across it during hardening r Alternately, air
may be drawn through the mold box by applying ~uction to one
face.
1~3507
The air is orced throu~h the mold box containin~ a
green sana for a period of 5 seconds to several minutes, during
which time the mold and core will achieve an initial set suffi~
cient to permit handling and to evaporate 25~ or more of the water
originally present in the binder. The water content of the sili-
cate binder should usually be decreased so that the "dried" binder
is at least 54~ solids. Accordingly, the more dilute silicates
may require a more extensive drying to set than the more concen-
trated silicates. Preferably drying is sufficient to evaporate
50~-70~ of the water content of the binder, while the preferred
drying time is less than one or two minutes. Surprisingly, when
the mold and core parts are set aside, they will then continue to
gain in tensile strength.
By way of illustration, for example, in one series of
tests a foundry sand bound with RU grade sodium silicate, has an
initial water content of 13 moles of water for each mold of sodium
silicate. If sufficient water was removed to reduce the water
content of the silicate in the green sand to 9.5 moles per mole
of sodium silicate, an initial set strength of 20 psi was obtained.
When drying was continued to decrease the water content of the
sodium silicate to 7 moles, the initial set strength was 45-60
pounds. Further drying decreasing the water content to 4 moles
increased the set stren~th to over 100 psi. The experiment was
discontinued when the water content of the sodium silicate had
been reduced to 2.3 moles, at which point a set strength of 150
pounds per square inch had been obtained.
When working in a comparable series with grade N sodium
silicate, more water was present, and less strength was obtained.
~rade N sodium silicate initially contained 23 moles of water per
3~ mole of sodium silicate. I was able to dry a green sand using
grade N sodium silicate as a binder to the point where the sili-
cate contained only 7 moles of water, at which point the set
- 17 -
~1~3507
strength of the mold ~as 78 p~unds pex s~uare inch. Dif~iculty
was experienced, however, in ~urther reducing the water contellt
of the grade N sodium silicate.
The present invention has applications in areas other
than construction of foundry molds. One application o~ it, for
example, is in the manufacture of pl~wood. Laminates of wood may
be adhered, for example, with silicates in accordance with the
present invention. In this case, a layer of a silicate binding
agent is cast or otherwise applied to the surface of the wood
laminates to be adhered, and then they are pressed and, electron-
ically heated, for example, by microwave heating, to rapidly ex-
tract the water. Rapid extraction of water from the adhesive
layer is accelerated when wood is bound using the present invention
because of the wicking or absorbing characteristics of the wood,
which tends to extract water from the silicate.
It has been found, in this connection, that silicates
tend to be brittle. For this reason, bond stabilization of the
silicates can be provided, thereby reducing brittleness. Such
stabilization is obtained by addition of one or more of the adju-
vants described above.
The present invention is also applicable in the manufac-
ture of composites of various shapes, such as charcoal briquettes,
particle board, ore briquettes, and the like. The proce~ure in
manufacturing such briquettes is generally the same as that followed
in the manufacture of foundry molds. In such cases, it may be de-
sirable to increase the amount of silicate binder generally to a
range of 6-100 parts by weight for each 100 parts by weight of
the particulate material to be bound into a composite. The green
mixture should be o~ a putty-like consistency and retain sufficient
porosity that water vapor within the interstices of the desired
shape can escape during the rapid drying ctep described above.
In the case of such evaporation, the drying time may be extended
for up to ~ive to ten minutes.
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~1~35~'~
The selection of ~ilicate binders follows the same
general principles, bearing in mind that particularly in the
case of ores that some ores may be reactive with the 601uble
~ilicates, and in such cases the silicate mus~ be ~elected so
that it will retain its binding capacity in the presence of the
~re to be briquetted.
.... ... .
EXa~ple_l
One kilo of a foundry sand from Martin-Marietta Company
identified as Portage-60 having an average particle size of about
60 mesh, was combined with 20.4 grams of Type RU soluble silicate,
Philadelphia Quartz Company, and 13.6 grams of an adjuvant pre-
pared in accordance with Exam~le 5 of British patent No. 1,309,606.
Type RU is a sodium silicate having a silica to sodium oxide ratio
of 2.4 and containing 47% solids. The green sand was packed into
ample molds in the shape of standard A.~.S. tensile test speci-
mens. The top and bottom of the mold box were "Plexiglas "* per-
forated with 90 holes having an open space of about 5~ of the
face of the sample.
Hot air at 2209F. was ~ucked through the mold at a
rate of about 100 CFM by the aid of a vacuum pump at the bottom
face of the mold box such as shown in Figure 1 for a period of
time between 10 and 60 ~econds. The samples were tested immedi-
ately for water loss and their instant tensile strength loss.
* Trademark for poly (methyl methacrylate) resin in ~heet
form; it has exceptional transparency.
-- 19 --
3507
The ~ollowing result~ were obtained:
Instantaneous
Tensile
Strength ~si Water Loss Percentage*
10 seconds 30 psi O.43 gms. 304
n 32 0 ~ 56 39 . 4 %
~I 58 n 0 ~ 70 ~ 49 ~ 2P6
n 88 n 0 ~90 n 63
a 128 ~ 00 n 709~
o 50 ~ 174 n 1~ 09 77 ~ 7%
n (no break)**1.19 n ~3. 9%
- * The percentaqe of water loss is based on the total amount
of water initially present in the green 6and.
** Tensile strength over 400 psi
- l9a -
~35(~7
Improved results were obtained when the perforated
"Plexiglas "**~ faces of the mold box were replaced by a wire
screen.
~xample 2
1-1/2 kilograms of New Jersey silica 50 (New Jersey
Silica Company, average particle size 50) was combined with 24~2
gms. of a soluble silicate prepared by evaporating 12 gms. of
water from 2Q0 gms. of Type RV soluble silicate (Philadelphia
Quartz Companyl and adding 2 gms. sodium hydroxide thereto. In
addition, 17.6 gms. of adjuvant P-13 were blended into the green
sand.
P-13 adjuvant was prepared by combining 400 gms. of
glucose (9% water), 6.6 gms. of maleic anhydride and 2.66 gms.
of boric acid, the mixture was heated to 122-131C. for one hour
during which 22.6 gms. of water was lost. While still hot, 40 cc.
of 10~ sodium hydroxide and 34 cc. of water were added. The mix-
ture, when cooled to room temperature, was tacky and capable of
d~ying in air.
The green ~and was packed into a mold for tensile bar
samples and hardened by drying air therethrough at 220~., as
described in Example 1, for 10 to 45 seconds. The following re-
sults were obtained:
Instantaneous
Tensile Water Loss,
Drying TimeStrength psi grams
10 seconds 24 psi 0.4 gms.
" 40 " 0.55 "
n 46 0-57
9~ 58 n O .64 n
n 10 4 ~ 0.86 "
Example 3
1.0 kilograms of Wedron sand ~Wedron Silica Company:
120 average particle size) was comhined with Type N soluble
silicate (Philadelphia Quartz Company). Type N soluble silicate
***Trademark
- 20 -
~143S~7
has a 8ilica to sodium oxide ratio cf 3.22 and contains 374
solids. The green 6and in this example contains a 4.43~ of the
silicate binder.
The green sand was packed into tensile bars and hardened
using air which had been heated to 220F. ac described in Example
1. The fo~lowing results were o~tained:
Instantaneous
Tensile Water Content, moles
Drying Time Strength psi Water/Mole N*
20 seconds 12 psi 17.6
30 n 30 n 15 .
45 ~ 36 ~ 12.8
55 n 40 n 11.8
-78 6~7
*The amount of drying in this example is reported as the amount
of water remaining in the 6ilicate binder expressed as a molar
ratio of water to silicate solids. For Type N silicate the
initial ratio is 23
Fxample 4
The effect of varying the porosity of the top and bottom
faces of the mold was investigated. Standard tensilè bars were
prepared in molds in which the porosity of the top and bottom
faces were increased by increasing the number of perforations
drilled. For purposes of this test, a green sand was used pre-
pared from one kilogram of 26 average particle size Portage sand
(as in Example 1) combined with 34.6 gms. of Type RU soluble 8ili-
cate. The samples were packed into standard tensile bars and
hardened with 220F. air for 40 seconds as in Example 1. The
following results were obtained:
Instantaneous Percentage
No. of ~olesTensile Strength psi Water Loss
14 0 16.3%
34 20 25.6%
96 160 59.9%
190 312 64.8%
In the foregoing table, the hole ~ize used in each ~ase
was the same. When 190 holes had been drilled in the top and
bottom faces, th~ open area within the 6ample area was 10%.
- 21 -
35(~7
Example 5
The effect o Varying drying conditions were further
studied in the ~ollowing series of experiment~:
One kilogr~m of Portage sand average particle &ize 60,
20.4 grams Type R~ sod;um silicate and 13.6 grams of P-14 adju-
vant were com~ined to make a green sand. The green sand was
cured in standard tensile bar moles using 220F. air as in Example
1.
The P-14 adjuvant used in this ex2mple was prepared by
combining 400 grams of glucose (9% water), 6.6 grams citric acid
and 2.66 grams of ~oric acid. The reaction was carried out as
described in Example 2.
(A~ In a first test, the sample was treated in the
normal manner, the top and bottom plates containing 190 holes
having 10~ open area. During 50 seconds curing time, the sample
lost one gram of water and achieved a tensile strength of 220 psi.
(B~ The test A was repeated using, however, room tem-
perature air rather than 220F~ air. In 60 seconds only 0.62
grams were lost, and the tensile strength achieved was only 80 psi.
(C) Test B was repeated using the same vacuum pump, but
replacing the top plate of the mold with a plate ha~ing no per-
forations at all. In this test the water los~ was further redu~-
ed, to 0.53 gram~ and the tensile strength achieved in 60 seconds
~as only 60 psi.
Example 6
An ammoniated silicate for use in accordance with the
present invention was prepared as follows:
38 grams of Type N 601uble silicate (silica to sodium
oxide ratio 2.33, 37% solids) were combined with 3.8 grams of
concentrated ammonium hydroxide (28% ammonia). The mixture was
shaken intensely for a minute or two. At this point a slight
amount of gel appeared. The mixture was then allowed to set
22 -
il~3S~)7
overnight. The following da~ the gel had disappeared and a homo-
genous solution resulted ~ich was more fluid than the original
Type N ~oluble silicate.
Example 7
41 grams of a sodium, ammonium silicate prepared as in
Example 6 were combined with 1 kg. Portage sand of average par-
ticle size 60. The mixture was packed into stan~ b~ile test molds
and hardened in 220F. aîr a~ described in Example 1. The follow-
ing results were obtained:
Instantaneous Water Loss
Drying TimeTensile Strength psi Grams Percent
20 seconds 24 0.89 34.4
n 60 1. 30 50 . 3
n 93 1.69 65.5
" 125 1. 97 76 . 3
" 190 2.12 82.1
~ 16~ 2.23 86.4
For comparison purposes, a similar sample was made
using Type N soluble silicate as a binder without any ammonia
having been added thereto. When these samples were tested for
- strength, the following results were obtained:
Instantaneous
Drying TimeTensile Strength psi
20 seconds 18
" 40
n 64
~5 ~ 88
n 88
n 116
Example 8
Following generally the procedures of Examples 6 and 7 ~
an ammoniated silicate was prepared from Type RV soluble silicate
to which ammonia had been added to provide an ammoniated silicate
containing 2% ammonia. 20 grams of the ammoniated sodium silicate
were combined with 1 kg. of Portage sand. The mixture was packed
into standard tensile test molds and dried in 220F~ air as des-
cribed in Example 1. For comparison purposes, corresponding sam-
ples were made for a mixture of 1 kilogram of Portage sand with
- 23 -
1~350~7
22 grams of Type RU soluble silicate~ The follo~in~ results
were obtained:
Drying Time Instantaneous Tensile ~tren~th ps
Type RU plus
2% ammonia pe RU
10 seconds 26 18
" 52 32
" 80 48
" 98 62
" 98 84
n 160 B4
Example 9
Portage sand (average particle size 60) was used to
make a green foundry sand of the following composition:
1~5~ Type RU soluble silicate
0.68~ of an adjuvant prepared in accordance
with Example 5 of British Patent
1,309,606
0.1~ borax
0.24% of a styrene butadiene resin latex,
known as "Dylex 553"***, from the
Arco Chemical Company
The green sand contained 1.093% water. It was packed
into standard tensile bar molds and hardened in 220F. air in
accordance with Example 1. The following results were obtained:
Instantaneous
Tensile Strength psi _ Water Loss
Instan- After After
Drying Timetaneous 1 hr.** 24 hrs.** Grams Percent*
-
10 seconds 20 - - 0.36 33%
n 28 - - 0.46 42%
n 52 80 - 0.60 54.9%
n _ 100 124
n 78 - - 0~83 75.9~
n 88 - - 0.89 8i,4%
*Expressed as percent of total water present
**Tensile strength of these samples were also measured after the
samples had been allowed to age for the indicated period of
time at ambient conditions which at the time of the test were
30 70F. relative humidity 64%.
~**Trademark
- 24 -
5U7
Green sands suita~le ~or use in the present invention
can be prepared of the following compositions generally in accor-
dance with the procedures of Examples 1 and 2:
A L C D
_ _ .
Sand 1.5 kg. 1.5 kg. 1.5 kg.1.5 kg.
Silicate ~inder 28.2 gms. 28.2 gms. 28.2 gms. 28.2 gms.
Sucrose 15 gms.
Glucose 16 gms.
10 Corn Syrup 17 gms.
Urea furfural resins 15 gms.
Example 11
- 1.5 kilograms of foundry sand from the New Jersey
Silica Company having an average particle size of 50 were com-
bined with 40.3 grams of a binder prepared by blending the
following:
28 grams of a soluble silicate prepared as described
in Example 2.
14 grams of a quaternary ammonium silicate prepared in
20 accordance with V. S. patent 3,239,521 obtained from the
Philadelphia Quartz Company and identified as "Q-220"*.
20 grams of an adjuvant prepared in accordance with
Example 5 of British Patent 1,309,606.
The green sand was packed into standard tensile bar
molds and hardened by forcing cold air through it at a flow rate
; of 30 to 40 cu. ft. per minutes. The following results were ob-
tained:
Drying TimeTensile Strength, psiWater Loss, gms.
1 min. 12 0.4
1' 30" 30 0~57
2' 52 approx. 0.6
*Trademark
~35~7
Since the standard tensile ~est ~ar contains about
100 grams of material ~AFS Mold and Core Test Handbook, Section
11), the ventilation rates in this example correspond to flow
rates through the sample of at least about 30 cubic feet per
minute per 100 grams of sand~
Example 12
In accordance with the present invention, the amount of
silicate in the binder may be varied, particularly where adju-
~ants were used. In some cases, the adjuvant was P-13 (see
Example 2). In other cases the adjuvants of Example 5 of British
Patent No. 1,309,606. The following sample~ were prepared gen-
erally following the procedure of Example 1 (percentages being
expressed as weight percent of the green sand):
A B C D E F
Soluble Silicate
Binder 2.14% 1.88% 1.61% 0.813% 0.546% 0
Adjuvant 0.84% 1.0% 1.17~ 1.67~ 1.8% 2.4%
Tensile Strength134 145 104 78 72 64*
at 45 seconds psi psi psi psi psi psi
*After 30 minutes the strength had risen to 96 psi.
Example 13
A series of ammoniated sodium silicates were prepared
by adding ammonium hydroxide (28%) to various sodium silicate
solutions. Immediately following addition of the ammonium hy-
droxide, the mixture was vigorously stirred by hand for 30 to 40
minutes and then allowed to age at least 3 to 4 hrs. (In some
samples aging was overnight). The amount added was sufficient,
in each sample to increase the alkalinity to the equivalent of a
2.1 ratio silicate.
Tensile test bars were then prepared using sand contain-
ing about 1 1/2% silicate binder (dry olid basis). For compari~
son purposes, a similar series of samples were prepared from the
sodium silicates employed in these tests before ammonia had been
- ~6 ~
3~ 7
added. The following results were obtained:
SodiumSoda/Silica Sample Drying Tensile Strength
Silicate Ratio Time Initial Ammoniated
Type Sodium Sodium
Silicate Silicate
. _
Type ~U 2.4 45 sec. 84 160
Type R 2.88 120 1I 110 178
Type N 3.2 45 " 64 93
Type S-35 3.75 9O n 22 28
Example 14
.
Plywood was prepared in accordance with the present
invention by bonding 1/8" laminates of wood, in one case with
soluble silicate Type RU (identified below as sample A) and in
the second case, soluble silicate Type N (identified below as
sample B). Additional samples were prepared in which 10 parts
of Type RU soluble silicate or Type N soluble silicate were re-
s~ectlvely combined with 5 parts of the adjuvant described in
Example 5 of British Patent No. 1,309,606. These samples are
respectively identified as samples C and D below. Still further
examples of plywood were prepared in accordance with the present
invention using an adhesive prepared from 10 parts Type RU or 10
parts of Type N soluble silicate respectively combined with 5
parts of the adjuvant of Example 5 of the British Patent No.
- 1,309,606 and 1.5 parts of a styrene butadiene resin.
Each of the samples thus prepared was heated in a home
microwave oven for 25 seconds to harden the silicate. The oven
operated at a frequency of 2450 megacycles and was rated at 1500
watts. In parallel with the heating of samples, a small watch
glass having 1.5 grams of the binder was heated to provide a
measure of water lost from the binder caused by the microwave
heating.
After each test the wa~ch glass was reweighed to deter-
mine water 10SB. After 24 hrs. each of ~he samples was sawed
- 27 -
~35~7
into strips of approximatel~ 1 in. ~idth ~ox further testin~.
Additionally, the loss of water from the hinder was estimated.
The following results were obtained:
Sample- A - The weight loss determination showed that sample A
had lost sufficient water that the soluble silicates
remaining were 60% solids (Type RU silica initially
contains 47% solids). Sample A could not be cut into
test samples because the laminates shattered under the
~ibration of the saw.
-Sample B - The water loss measurement showed that the soluble
silicate remaining in sample B after heating contained
514 water (Type N soluble silic~te contains 37.6~
solids). Sample B could not be cut into test pieces
because the silicate bond shattered under the saw
vibration.
Sample C - Water loss measurements showed that the solids content
of the silicate binder plus adjuvant increased from
53% to 89%. No splitting occurred when the sample was
cut into test pieces. The test sample delaminated
after immersion in water for 24 hrs.
Sample D - Water loss measurements showed that the solids content
of the soluble silicate -- binder mixture increased
during drying from 50% to 76%. No splitting occurred
when the sample was cut into pieces. After immersion
in water for 10 days, the sample had not delaminated.
Sample E - Water loss measurements showed that the solids content
of the soluble silicate --adjuvant mixture increased
from 57% to 89%. No splitting occurred when the sample
was cut under test pieces. Samples immersed in water
showed delamination after two days.
-S&mple F - Water loss measurements showed that the solid content
of the binder-adjuvant mixturQ increased from 60% to
- 28 -
~35V7
80~. No splitting occurred upon cutting into test
pieces. Test pieces did not show delamination e~en
after water immersion for 10 days.
Example 15
50 grams of wood shavings with fines removed were com-
bined with 30 grams of ammoniated Type N soluble silicate pre-
pared in accordance with Example 6. In addition, 12 grams of an
adjuvant prepared in accordance with Example 5 of British Patent
No. 1,309,606 were included in the binder system. The mixture
had a putty-like consistency, but was porous. Samples were packed
into standard tensile test specimens and air dried by drawing air
across the sample under vacuum at 230F. for 3 minutes.
The specimens could be sawn within 2 hrs., or could be
sanded or otherwise worked~
Additional samples were tested for flammability. It
was found that the sample was non-flammable and did not lose its
strength under flaming conditions.
The materials produced are porous and could be valuable
~or their thermal and sound insulating properties, as well as for
their mechanical properties. Such adhesively bonded composites
can be useful in making molds for the present invention because
of their porosity.
It will be recognized that similar component particle
compositions can be made from fiberglass, vermiculite, diatomac-
eouS earth, asbestos and the like in accordance with the fore-
going example.
29
