No-bake foundry mixes and their use

This invention relates to polyurethane-forming foundry binder systems and foundry mixes which comprise a foundry aggregate, said foundry binder system, and a liquid amine curing catalyst. The binder system comprises a polyol component containing a polyether polyol and a monomeric glycol, and an organic polyisocyanate component. The foundry mixes are used to prepare foundry shapes made from foundry mixes by a no-bake process.

FIELD OF THE INVENTION 
This invention relates to polyurethane-forming foundry binder systems and 
foundry mixes which comprise a foundry aggregate, said foundry binder 
system, and a liquid amine curing catalyst. The binder system comprises a 
polyol component containing a polyether polyol and a monomeric polyol, and 
an organic polyisocyanate component. The foundry mixes are used to prepare 
foundry shapes made from foundry mixes by a no-bake process. 
BACKGROUND OF THE INVENTION 
In the foundry industry, one of the processes used for making metal parts 
is sand casting. In sand casting, disposable foundry shapes (usually 
characterized as molds and cores) are made by shaping and curing a foundry 
mix which is a mixture of sand and an organic or inorganic binder. 
One of the processes used in sand casting for making molds and cores is the 
no-bake process. In this process, a foundry aggregate, binder, and liquid 
curing catalyst are mixed and compacted to produce a cured mold and/or 
core. In the no-bake process, it is important to formulate a foundry mix 
which will provide sufficient worktime to allow shaping. Worktime is the 
time between when mixing begins and when the mixture can no longer be 
effectively shaped to fill a mold or core. 
A binder commonly used in the no-bake process is a polyurethane binder 
derived by curing a polyurethane-forming binder with a liquid tertiary 
amine catalyst. Such polyurethane-forming binders used in the no-bake 
process, have proven satisfactory for casting such metals as iron or steel 
which are normally cast at temperatures exceeding about 1370.degree. C. 
They are also useful in the casting of light-weight metals, such as 
aluminum, which have melting points of less than 815.degree. C. 
The polyurethane-forming binder usually consists of a phenolic resin 
component and polyisocyanate component which are mixed with sand prior to 
compacting and curing. Both the phenolic resin component and 
polyisocyanate component generally contain a substantial amount of organic 
solvent which can be obnoxious to smell and can create stress for the 
environment such as smoke when the binder is cured. Because of this, there 
is an interest in developing binders which do not require the use of 
organic solvents. 
U.S. Pat. No. 5,455,287 discloses no-bake foundry mixes where the binder 
comprises (a) polyether polyol having a hydroxyl number between 200-600 
and a viscosity of 100-1000 centipoise at 25.degree. C., (b) an organic 
polyisocyanate component, and (c) a liquid tertiary amine catalyst, 
preferably a bicyclic tertiary amine. 
SUMMARY OF THE INVENTION 
This invention relates to a foundry mix comprising as a mixture: 
(1) a foundry aggregate; 
(2) a polyurethane binder comprising: 
(a) a polyol component comprising: 
(i) a polyether polyol; and 
(ii) a monomeric polyol; and 
(b) an organic polyisocyanate component; 
(c) a catalytically effective amount of a liquid tertiary amine catalyst, 
wherein components (a) and (b) are compatible with each other. 
The invention also relates foundry binder systems used in the foundry mixes 
and to the use of these foundry mixes in a no-bake process for preparing 
foundry shapes. Additionally, the invention also relates to the use of 
these foundry shapes to cast metal parts. 
The foundry binder has a lower viscosity than those utilized in U.S. Pat. 
No. 5,455,287 which allows for easier pumping (even in the winter) and 
mixing of the sand and binder, and improves the bonding between the sand 
and the binder. Comparison experiments show that immediate, 1 hour, and 3 
hour tensiles strengths are improved by combining the polyether polyol and 
the monomeric polyol. 
The binders of the foundry mixes are most preferably free of free 
formaldehyde and free phenol. However, they may small amounts of free 
formaldehyde, i.e. no more than 2 weight percent free formaldehyde, 
preferably no more than 1 percent, and no more than 2 weight percent free 
phenol, preferably no more than 1 percent. Preferably, the binders do not 
contain solvents and thus are low in odor when mixing with sand, and do 
not produce much smoke during pour off which creates less stress to the 
environment than conventional polyurethane-forming binders. The sand 
shakes out from the castings effectively and the surface finish of the 
casting is good. 
BEST MODE AND OTHER MODES 
The polyether polyols which are used in the polyurethane-forming foundry 
binders are liquid polyether polyols or blends of liquid polyether polyols 
having a hydroxyl number of from about 200 to about 600, preferably about 
300 to about 500 milligrams of KOH based upon one gram of polyether 
polyol. The viscosity of the polyether polyol is from 100 to 1,000 
centipoise, preferably from 200 to 700 centipoise, most preferably 300 to 
500 centipoise. The polyether polyols may have primary and/or secondary 
hydroxyl groups. 
These polyols are commercially available and their method of preparation 
and determining their hydroxyl value is well known. The polyether polyols 
are prepared by reacting an alkylene oxide with a polyhydric alcohol in 
the presence of an appropriate catalyst such as sodium methoxide according 
to methods well known in the art. Any suitable alkylene oxide or mixtures 
of alkylene oxides may be reacted with the polyhydric alcohol to prepare 
the polyether polyols. The alkylene oxides used to prepare the polyether 
polyols typically have from two to six carbon atoms. Representative 
examples include ethylene oxide, propylene oxide, butylene oxide, amylene 
oxide, styrene oxide, or mixtures thereof. The polyhydric alcohols 
typically used to prepare the polyether polyols generally have a 
functionality greater than 2.0, preferably from 2.5 to 5.0, most 
preferably from 2.5 to 4.5. Examples include ethylene glycol, diethylene 
glycol, propylene glycol, trimethylol propane, and glycerine. 
The monomeric polyols used in the polyol component have an average 
functionality of 2 to 4, hydroxyl numbers from 500 to 2000, more 
preferably from 700 to 1200, and viscosities less than 200 centipoise at 
25.degree. C., preferably less than 100 centipoise at 25.degree. C. 
Examples of such monomeric polyols include ethylene glycol, diethylene 
glycol, triethylene glycol, 1,3-propane diol, 1,4-butanediol, 
1,2,4-butanetriol, dipropylene glycol, tripropylene glycol, glycerin, 
tetraethylene glycol, and mixtures thereof. 
The weight ratio of the polyether polyol to the monomeric polyol in the 
polyol component is from 70:30 to 30:70, preferably from 60:40 to 40:60. 
Although not preferred, minor amounts of phenolic resin and/or amine-based 
polyols can be added to the polyether polyol. By minor amounts, it is 
meant that less than 15 weight percent, preferably less than 5 weight 
percent, said weight percent based upon the weight of the polyether polyol 
component. If a phenolic resin is added to the polyether polyol, the 
preferred phenolic resins used are benzylic ether phenolic resins which 
are specifically described in U.S. Pat. No. 3,485,797 which is hereby 
incorporated by reference into this disclosure. 
Although not preferred, organic solvents may be added to the polyol 
component, particularly if a benzylic ether phenolic resin is used. The 
amount of solvent used is generally less than 15 weight percent based upon 
the total weight of the polyol component, preferably less that 5 weight 
percent. 
Other optional ingredients which may be added to the polyether include 
release agents and adhesion promoters, such as silanes described in U.S. 
Pat. No. 4,540,724 which is hereby incorporated into this disclosure by 
reference, to improve humidity resistance. 
Organic polyisocyanates used in the organic polyisocyanate component are 
liquid polyisocyanates having a functionality of two or more, preferably 2 
to 5. They may be aliphatic, cycloaliphatic, aromatic, or a hybrid 
polyisocyanate. Mixtures of such polyisocyanates may be used. The 
polyisocyanates should have a viscosity of about 100 to about 1,000, 
preferably about 200 to about 600. 
Representative examples of polyisocyanates which can be used are aliphatic 
polyisocyanates such as hexamethylene diisocyanate, alicyclic 
polyisocyanates such as 4,4'-dicyclohexylmethane diisocyanate, and 
aromatic polyisocyanates such as 2,4- and 2,6-toluene diisocyanate, 
diphenylmethane diisocyanate, and dimethyl derivates thereof. Other 
examples of suitable polyisocyanates are 1,5-naphthalene diisocyanate, 
triphenylmethane triisocyanate, xylylene diisocyanate, and the methyl 
derivates thereof, polymethylenepolyphenyl isocyanates, 
chlorophenylene-2,4-diisocyanate, and the like. 
The polyisocyanates are used in sufficient concentrations to react with the 
polyether polyol and cure in the presence of the liquid amine curing 
catalyst. In general the isocyanate ratio of the polyisocyanate to the 
hydroxyl of the polyol component (NCO/OH ratio), is from 1.25:1.0 to 
0.60:1.0, preferably about 0.9:1.0 to 1.1:1.0, and most preferably about 
1.0:1:0. 
The polyisocyanate component may contains a natural oil Representative 
examples of natural oils which are used in the isocyanate component are 
linseed oil including refined linseed oil, epoxidized linseed oil, alkali 
refined linseed oil, soybean oil, cottonseed oil, RBD Canola oil, refined 
sunflower oil, tung oil, and dehydrated castor oil. 
Optional ingredients such as release agents and solvents may also be used 
in the organic polyisocyanate component. 
Although not preferred, solvents may be used in the organic polyisocyanate 
component and/or polyol component. If solvents are used in either, those 
skilled in the art will know how to select them. Typical organic solvents 
which are used include aromatic solvents, esters, or ethers, preferably 
mixtures of these solvents. Preferably, these solvents are used in amounts 
less than about preferably less than 15 weight percent based upon the 
weight of the isocyanate component, more preferably less that 5 weight 
percent. 
The binder is preferably made available as a three package system with the 
polyol component in one package, the organic polyisocyanate component in 
the second package, and the catalyst in the third package. When making 
foundry mixes, usually the binder components are combined and then mixed 
with sand or a similar aggregate to form the foundry mix or the mix can be 
formed by sequentially mixing the components with the aggregate. 
Preferably the polyether polyol and catalyst are first mixed with the sand 
before mixing the isocyanate component with the sand. Methods of 
distributing the binder on the aggregate particles are well-known to those 
skilled in the art. The mix can, optionally, contain other ingredients 
such as iron oxide, ground flax fibers, wood cereals, pitch, refractory 
flours, and the like. 
The liquid amine catalyst is a base having a pK.sub.b value generally in 
the range of about 7 to about 11. The term "liquid amine" is meant to 
include amines which are liquid at ambient temperature or those in solid 
form which are dissolved in appropriate solvents. The pK.sub.b value is 
the negative logarithm of the dissociation constant of the base and is a 
well-known measure of the basicity of a basic material. The higher this 
number is, the weaker the base. The bases falling within this range are 
generally organic compounds containing one or more nitrogen atoms. 
Specific examples of bases which have pK.sub.b values within the necessary 
range include 4-alkyl pyridines wherein the alkyl group has from one to 
four carbon atoms, isoquinoline, arylpyridines such as phenyl pyridine, 
pyridine, acridine, 2-methoxypyridine, pyridazine, 3-chloro pyridine, 
quinoline, N-methyl imidazole, N-ethyl imidazole, 4,4'-dipyridine, 
4-phenylpropylpyridine, 1-methylbenzimidazole, and 1,4-thiazine. 
Preferably used as the liquid tertiary amine catalyst is an aliphatic 
tertiary amine, particularly POLYCAT 9 tris (3-dimethylamino) 
propylamine)! catalyst sold by Air Products. 
In view of the varying catalytic activity and varying catalytic effect 
desired, catalyst concentrations will vary widely. In general, the lower 
the pK.sub.b value is, the shorter will be the worktime of the composition 
and the faster, more complete will be the cure. In general, catalyst 
concentrations will be a catalytically effective amount which generally 
will range from about 0.2 to about 5.0 percent by weight of the polyether 
polyol, preferably 1.0 percent by weight to 4.0 percent by weight, most 
preferably 2.0 percent by weight to 3.5 percent by weight based upon the 
weight of the polyether polyol. 
In a preferred embodiment of the invention, the catalyst level is adjusted 
to provide a worktime for the foundry mix of 3 minutes to 10 minutes, 
preferably 8 minutes to about 10 minutes, and a striptime of about 4 
minutes to 12 minutes, preferably 9 minutes to about 10 minutes. Worktime 
is defined as the time interval after mixing the polyisocyanate, 
polyether, and catalyst and the time when the foundry shape reaches a 
level of 60 on the Green Hardness "B" Scale Gauge sold by Harry W. Dietert 
Co., Detroit, Mich. Striptime is time interval after mixing the 
polyisocyanate, polyether, and catalyst and the time when the foundry 
shape reaches a level of 90 on the Green Hardness "B" Scale Gauge. 
In this preferred embodiment, the ratio of the isocyanate groups of the 
polyisocyanate to hydroxyl groups of the polyol is preferably about 
0.9:1.0 to about 1.1:1.0, most preferably about 1.0:1:0, the hydroxyl 
number of the polyol is from about 200 to about 500, and the weight ratio 
of polyisocyanate to polyether polyol is from about 65:35 to about 35:65, 
preferably about 45:55. These parameters provide optimum worktime, 
striptime, and tensile properties. 
Various types of aggregate and amounts of binder are used to prepare 
foundry mixes by methods well known in the art. Ordinary shapes, shapes 
for precision casting, and refractory shapes can be prepared by using the 
binder systems and proper aggregate. The amount of binder and the type of 
aggregate used is known to those skilled in the art. The preferred 
aggregate employed for preparing foundry mixes is sand wherein at least 
about 70 weight percent, and preferably at least about 85 weight percent, 
of the sand is silica. Other suitable aggregate materials for ordinary 
foundry shapes include zircon, olivine, aluminosilicate, chromite sand, 
and the like. 
In ordinary sand type foundry applications, the amount of binder is 
generally no greater than about 10% by weight and frequently within the 
range of about 0.5% to about 7% by weight based upon the weight of the 
aggregate. Most often, the binder content for ordinary sand foundry shapes 
ranges from about 0.6% to about 5% by weight based upon the weight of the 
aggregate in ordinary sand-type foundry shapes. 
The aggregate employed with the catalyzed binder in producing the foundry 
mix should be sufficiently dry so that a handleable foundry shape results 
after a worktime of 3 to 10 minutes and a strip time of 4 to 12 minutes. 
Generally the amounts of moisture in the aggregate is less than about 0.5 
percent by weight, preferably less than about 0.2 percent by weight, and 
most preferably less than about 0.1 percent by weight based on the weight 
of the sand.

EXAMPLES 
The examples which follow will illustrate specific embodiments of the 
invention. These examples along with the written description will enable 
one skilled in the art to practice the invention. It is contemplated that 
many other embodiments of the invention will be operable besides those 
specifically disclosed. 
In all of the examples, the test specimens, unless otherwise indicated, 
were produced by the no-bake process using 3.5 weight percent, based on 
the Part I, of POLYCAT 9 catalyst sold by Air Products which is 12.5 
weight percent tris (3-dimethylamino) propylamine in dipropylene glycol. 
All parts are by weight and all temperatures are in .degree.C. unless 
otherwise specified. 
Unless otherwise indicated, the foundry mixes were prepared by first mixing 
4000 parts WEDRON 540 sand with the polyol component and the catalyst for 
about 2 minutes. Then the MONDUR MR was mixed with the mixture of sand, 
polyol component, and catalyst for about 2 minutes. The composition of the 
polyol component and the binder level, where appropriate, is specified in 
Tables I and II. The amount of polyol component and polyisocyanate was 
such that the ratio of hydroxyl groups of the polyol component to 
isocyanato groups of the polyisocyanate was about 1:1 and the weight ratio 
of polyol to polyisocyanate was about 41:59. 
Measuring the tensile strength of the dog bone shapes enables one to 
predict how the mixture of sand and binder will work in actual foundry 
operations. The foundry shapes were stored 0.5 hour, 1 hour, 3 hours and 
24 hours in a constant temperature room at a relative humidity of 50% and 
a temperature of 25.degree. C. before measuring their tensile strengths. 
Unless otherwise specified, the tensile strengths were also measured on 
shapes stored 24 hours at a relative humidity (RH) of 100%. 
The following terms were used in the examples: 
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BOS = based on sand. 
DEG = diethylene glycol having OH # of 
1058, functionality of 2 and viscosity of 
28 cps. 
DPG = dipropylene glycol. 
MONDUR MR = an organic polyisocyanate commercially 
available from BAYER AG having a 
functionality of 2.5 to 2.7. 
PEP = polyether polyol. 
PLURACOL POLYOL 
= a polyether polyol, sold commercially by 
TP-440 BASF, having an OH value 
of 398, prepared 
by reacting propylene oxide with 
trimethylol propane. 
RH = relative humidity. 
ST = striptime. 
TEG = triethylene glycol having an OH # of 
748, a functionality 2, and a viscosity 
of 35 cps. 
VIS = viscosity. 
WT = worktime. 
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CONTROL A AND B AND EXAMPLE 1 
Control A is based upon the teachings of U.S. Pat. No. 5,455,287 and does 
not contain a glycol while Control B uses a glycol, trethylene glycol, but 
does not use a polyether polyol. Table I shows the results of Control A 
and B compared to the formulations of Example 1 where a mixture of a 
polyether polyol and were used as the polyol component at a binder level 
of 1.3 weight percent based upon the weight of the sand. 
TABLE I 
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TENSILE PROPERTIES OF CORES 
VIS TENSILE (PSI) 
EXAMPLE PEP TEG (cps) 
WT/ST 30' 1 HR 3 HR 
______________________________________ 
Control A 
100 0 632 13.25/23.00 
100 254 302 
Control B 
0 100 35 6.25/11.50 
15 27 45 
1 50 50 100 4.25/7.50 
257 322 353 
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The data in Table I indicate that the foundry binder binders containing the 
mixture of polyether polyol and glycol have lower viscosities and improved 
tensile strengths even though they are solventless. This result is 
surprising in view of the low tensile strengths that result when 
triethylene glycol is used alone. Such binders are clearly more 
environmentally friendly and create less odor and smoke. 
EXAMPLE 2 
Example 2 was essentially repeated except diethylene glycol was used as the 
glycol instead of triethylene glycol. The binder consisted of polyether 
polyol TP-440 and diethylene glycol at 60/40 blend. Table II shows this 
binder performed well in sand tensile strength development too. 
TABLE II 
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TENSILE PROPERTIES OF CORES 
VIS TENSILE (PSI) 
EXAMPLE PEP DEG (cps) 
WT/ST 30' 1 HR 3 HR 
______________________________________ 
2 60 40 83 3.3/5.8 
105 152 176 
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EXAMPLES 3-5 
Examples 3-5 show the effect of changing the binder level in the 
formulations containing the polyether polyol and the glycol. In these 
examples, triethylene glycol was used as a 50/50 blend with the polyether 
polyol. Table III shows that reducing binder levels from 1.5 to 1.0% 
resulted in minor decreases of the sand tensile strengths as well as an 
increase of the WT/ST). 
TABLE III 
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TENSILE PROPERTIES OF CORES AT VARYING BINDER LEVELS 
EX- BIND- TENSILE (PSI) 
AM- ER VIS 24 24 HR 
PLE LEVEL (cps) WT/ST 30 1 HR 3 HR HR 100% RH 
______________________________________ 
3 1.5 100 3.5/5.5 
282 278 321 317 40 
4 1.25 100 4.3/7.5 
224 270 318 307 41 
5 1.0 100 5.5/10.2 
148 207 225 287 40 
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The data in Examples 3-5 indicate that worktime/striptime increases with 
decreasing binder level and the tensile strengths of the test specimens 
increase with increasing binder level.