U.S. patent application number 14/001241 was filed with the patent office on 2014-01-16 for foundry binder systems.
This patent application is currently assigned to RHODIA POLIAMIDA E ESPECIALIDADES LTDA. The applicant listed for this patent is Cristina Maria Schuch, Luciane Sereda, Suelbi Silva, Denilson Jose Vicentim. Invention is credited to Cristina Maria Schuch, Luciane Sereda, Suelbi Silva, Denilson Jose Vicentim.
Application Number | 20140018468 14/001241 |
Document ID | / |
Family ID | 44169081 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140018468 |
Kind Code |
A1 |
Schuch; Cristina Maria ; et
al. |
January 16, 2014 |
FOUNDRY BINDER SYSTEMS
Abstract
The present invention relates to foundry binder systems forming
a curable polyurethane with a catalytically effective amount of a
curing catalyst, comprising at least one phenolic resin component
comprising at least: a phenolic resin and a solvent of triacetin
type and a polyisocyanate component. The invention also relates to
foundry mixtures prepared from the binder and an aggregate, to
foundry forms such as cores and molds prepared via the no-bake or
cold-box processes, and also to the respective processes. The
foundry forms obtained by the present invention are especially used
for manufacturing metallic components, especially for the casting
of metallic components.
Inventors: |
Schuch; Cristina Maria;
(Campinas, BR) ; Vicentim; Denilson Jose;
(Campinas, BR) ; Sereda; Luciane; (Campinas,
BR) ; Silva; Suelbi; (Itatiba, BR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schuch; Cristina Maria
Vicentim; Denilson Jose
Sereda; Luciane
Silva; Suelbi |
Campinas
Campinas
Campinas
Itatiba |
|
BR
BR
BR
BR |
|
|
Assignee: |
RHODIA POLIAMIDA E ESPECIALIDADES
LTDA
Sao Paulo
BR
|
Family ID: |
44169081 |
Appl. No.: |
14/001241 |
Filed: |
March 20, 2012 |
PCT Filed: |
March 20, 2012 |
PCT NO: |
PCT/IB12/00539 |
371 Date: |
September 26, 2013 |
Current U.S.
Class: |
523/143 ;
252/182.2; 560/263 |
Current CPC
Class: |
B22C 1/2253 20130101;
C08G 18/542 20130101; C08G 18/0852 20130101; B22C 1/2273
20130101 |
Class at
Publication: |
523/143 ;
252/182.2; 560/263 |
International
Class: |
B22C 1/22 20060101
B22C001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 22, 2011 |
FR |
1152347 |
Claims
1. Foundry binder system forming a curable polyurethane with a
catalytically effective amount of a curing catalyst, comprising at
least: A. a phenolic resin component comprising at least: (1) a
phenolic resin: and (2) a solvent comprising at least triacetin:
and B. a polyisocyanate component
2. A foundry binder system as defined by claim 1, in which the
triacetin is obtained from a process using crude glycerol.
3. A foundry binder system as defined by claim 1, in which the
solvent is a mixture comprising at least 80% by weight of
triacetin.
4. A foundry binder system as defined by claim 1, in which the
solvent is a mixture comprising 80% to 95% by weight of triacetin,
5% to 15% by weight of diacetin and less than 5% by weight of
monoacetin, relative to the total weight of the mixture.
5. A foundry binder system as defined by claim 1, in which the said
component A also comprises a solvent that is a mixture of dimethyl
esters, especially dimethyl adipate, dimethyl glutarate and
dimethyl succinate.
6. A foundry binder system as defined by claim 5, in which the
ratio of the solvent comprising at least triacetin and of the said
mixture of dimethyl esters ranges from 1:20 to 20:1.
7. A foundry binder system as defined by claim 1, in which the said
component A also comprises one or more aromatic hydrocarbon-based
solvents.
8. A foundry binder system as defined by claim 1, in which the
solvent comprising at least triacetin represents from 10% to 30% by
weight relative to the weight of component A.
9. A foundry binder system as defined by claim 1, in which the said
phenolic resin is a resol phenolic resin.
10. A foundry binder defined by claim 1, in which the said
polyisocyanate component comprises a polyisocyanate and a
polyisocyanate solvent,
11. A foundry binder system as defined by claim 10, in which the
said polyisocyanate solvent is a mixture of aromatic hydrocarbons,
chosen especially from benzene, toluene, xylene and alkylbenzenes,
and mixtures thereof.
12. Foundry mixture comprising a polyurethane-forming binder system
as defined by claim 1, and an aggregate,
13. A foundry mixture as defined by claim 12, in which the said
aggregate is sand.
14. Process for preparing a foundry form via the cold-box process,
in which the binder is as defined by claim 1, and the curing
catalyst is a gaseous amine.
15. Process for preparing a foundry form via the no-bake process,
in which the binder is as defined by claim 1, and the curing
catalyst is a liquid amine.
16. Foundry form prepared via the process as defined by claim
14.
17. Use of a mixture comprising at least triacetin as a solvent
that is useful for phenolic resins in polyurethane-forming foundry
binder systems, alone or as a mixture with other solvents.
Description
[0001] The present invention relates to foundry binder systems
forming a curable polyurethane with a catalytically effective
amount of a curing catalyst, comprising at least one phenolic resin
component comprising at least: a phenolic resin and a solvent of
triacetin type for the phenolic resin and a polyisocyanate
component. The invention also relates to foundry mixtures prepared
from the binder and an aggregate, foundry forms such as cores and
moulds prepared via processes without baking or in a cold box, and
also to the respective processes. The foundry forms obtained by the
present invention are especially used for manufacturing metallic
components, especially for casting metallic components.
BACKGROUND OF THE INVENTION
[0002] A standard process used in the foundry industry for
manufacturing metallic components is sand casting. In sand casting,
disposable foundry forms, such as moulds and cores, are produced by
the shaping and curing of a foundry binder system consisting of a
mixture of sand and binder. The binder is used to reinforce the
moulds and cores. The steps that follow the curing of the binder
are the following: [0003] the molten metal is cast to fill the
cured mould, [0004] the cast material is cooled, [0005] the cast
material thus obtained is removed, and the corresponding mould is
destroyed, [0006] the sand is optionally reused in another binder
system.
[0007] Two of the main processes used, in sand casting to produce
moulds and cores are the "no-bake" process and the "cold-box"
process. In the no-bake process, a liquid curing agent is mixed
with an aggregate, generally sand, and shaped to produce a cured
core and/or mould. The no-bake process is based on the
room-temperature curing of two or more binder components after they
have been combined with sand. The curing of the binder system
begins immediately after the addition of a liquid curing agent to
all the components, producing a cured mould and/or a core. In the
cold-box process, a gaseous curing agent is passed through a shaped
compacted mixture so as to form a cured core and/or mould. The term
"cold-box process" implies the room-temperature curing of a mixture
of binder and sand accelerated with a vapour or gaseous catalyst
that is passed through the sand. The binders forming polyurethane,
cured with a gaseous tertiary amine catalyst, are often used in the
cold-box process to keep the foundry aggregates together in mould
or core form as described in American patent U.S. Pat. No.
3,409,579. The binder system forming polyurethane generally
consists of a phenolic resin component and a polyisocyanate
component that are mixed with sand before compacting and curing to
form a foundry binder system.
[0008] A person skilled in the art knows that the best use of a
solvent is that which is suitable both for the phenolic resin
component and for the polyisocyanate component and, if need be, for
other binder additives, for example the polyisocyanate curing
component.
[0009] The oldest class of solvents in this technique is probably
that of aromatic hydrocarbon-based compounds, for example benzene,
toluene, xylene and ethylbenzene.
[0010] Certain particular esters are also known as solvents for the
phenolic resin used in polyurethane-forming foundry binder systems.
A few examples of these are dioctyl adipate and propylene glycol
monomethyl ether acetate (WO 89/07626), dibasic esters (WO
91/09908); ethyl acetate (EP 1 809 456); methyl decanoate, methyl
undecanoate and vinyl decanoate (RD425045); 1,2-diisobutyl
phthalate, dibasic esters and butyldiglycol acetate (EP 1 074 568),
and dialkyl esters (U.S. Pat. No. 55,168, U.S. Pat. No.
4,852,629).
[0011] Moreover, another class of esters, i.e. acetic acid diesters
such as glyceryl triacetate (or triacetin, RN102-76-1), glyceryl
diacetate (or diacetin, RN2539531-7) and glyceryl monoacetate (or
monoacetin, RN 26446-35-5), alone or as a mixture, are also known
as being able to be used in foundry binder systems, but only as
curing agents, for example as described in patents JP 4198531, U.S.
Pat. No. 5,602,192, U.S. Pat. No. 5,169,880, U.S. Pat. No.
5,043,412, CS 258845, JP 03018530, U.S. Pat. No. 4,468,359 and U.S.
Pat. No. 3920,460. The typical content of triacetin as catalyst in
the prior art is 0.5% by weight relative to the weight of the
phenolic resin.
INVENTION
[0012] The present invention relates to the discovery, not
disclosed or suggested in the prior art, that triacetin or mixtures
of mono-, di- and triacetin, are solvents that are useful for
phenolic resins in polyurethane-forming foundry binder systems,
alone or as a mixture with other solvents.
[0013] The present invention thus relates to the use of a mixture
comprising at least triacetin as solvent that is useful for
phenolic resins in polyurethane-forming foundry binder systems,
alone or as a mixture with other solvents.
[0014] The present invention also relates to a polyurethane foundry
binder system that is curable with a catalytically effective amount
of a curing catalyst comprising at least: [0015] A. a phenolic
resin component comprising at least: [0016] (1) a phenolic resin;
and [0017] (2) a solvent comprising at least triacetin; and [0018]
B. a polyisocyanate component.
[0019] Another aspect of the present invention relates to foundry
mixtures comprising components A and B above with an aggregate, for
example sand.
[0020] In yet another aspect, the present invention relates to a
process for preparing a foundry form by the cold-box process or by
the no-bake process, which involves the curing of moulds and cores
prepared with the above binder, or the above foundry mixture.
[0021] In the cold-box process, the catalyst is in particular a
tertiary amine.
[0022] The qualities of the triacetin solvent for the phenolic
resin according to the present invention are the following, in
comparison with the solvents of the prior art: [0023] compatibility
with the phenolic resin, [0024] absence of nitrogenous compounds
(N2), which contribute towards the production of gas during
casting, thus giving rise to the appearance of defects in the
metallic component, [0025] acceleration of the catalytic process
for the reaction between the phenolic resin and the polyisocyanate,
[0026] absence or low content of OH-, which reacts with
polyisocyanate (for example MDI) and promotes the loss of
properties, [0027] low hygroscopicity, reducing the possibility of
reaction between water and a polyisocyanate, promoting the loss of
properties, or the generation of gas during casting, thus giving
rise to the appearance of defects in the metallic component, [0028]
flash point of greater than 120.degree. C., which reduces the
flammability, low content of volatile organic compounds, [0029] low
emission of smoke; smoke gives rise to defects in the metallic
component, [0030] solvability: the viscosity of the resin+solvent
mixture is sufficient to ensure the coating of the sand, [0031]
very low release of odour, [0032] readily biodegradable, [0033]
non-biocumulative, [0034] not classed as carcinogenic, [0035] not
classed as mutagenic, [0036] low aquatic toxicity, [0037] virtually
non-irritant to the eyes or the skin.
[0038] The chemical compounds mentioned in this text, such as
triacetin, should be used with care and precaution in the process
of the present invention, according to the technical norms.
Solvent
[0039] The solvent according to the invention thus comprises at
least triacetin. This triacetin may be obtained via a process using
crude glycerol, for example the process described in patent
application EP 2 272 818. The solvent may be a mixture comprising
at least triacetin, and monoacetin and/or diacetin. The solvent may
be a mixture comprising at least 80% by weight of triacetin.
[0040] Preferentially, the mixture comprises triacetin, monoacetin
and diacetin.
[0041] In one particular embodiment, the solvent is a mixture of
80% to 95% by weight of triacetin, 5% to 15% by weight of diacetin
and less than 5% by weight of monoacetin, relative to the total
weight of the said mixture. Triacetin has the formula
(AcO)--CH.sub.2--CH(OAc)--CH.sub.2(OAc). Diacetin has the formula
(AcO)--CH.sub.2--CH(OH)--CH.sub.2(OAc). Monoacetin has the formula
(AcO)--CH.sub.2--CH(OH)--CH.sub.2(OH). In the above formulae, Ac
denotes CH.sub.3C(.dbd.O). Triacetin known as "industrial
triacetin" is a mixture containing from 80% to 95% by weight of
triacetin, 5% to 15% by weight of diacetin and less than 5% by
weight of monoacetin, relative to the total weight of the said
mixture. It is advantageously used as a solvent for the phenolic
resin in the foundry binder system according to the invention.
[0042] A suitable mixture of solvents for phenolic resins according
to the present invention, without excluding any other, concerns
triacetin and esters such as those that are known and generally
used in this type of application. Examples that may be mentioned
include dioctyl adipate and propylene glycol monomethyl ether
acetate (WO 89/07626), dibasic esters (WO 91/09908); ethyl acetate
(EP 1 809 456); methyl decanoate, methyl undecanoate and vinyl
decanoate (RD425045); 1,2-diisobutyl phthalate, dibasic esters and
butyldiglycol acetate (EP 1 074 568), and dialkyl esters (U.S. Pat.
No. 55168 and U.S. Pat. No. 4,852,629).
[0043] A particular suitable mixture of solvents for phenolic
resins according to the present invention, without excluding any
other, comprises triacetin and a mixture of dimethyl esters, for
example the product sold in Brazil under the brand name Rhodiasolv
RPDE, comprising dimethyl adipate (RN 627-93-0), dimethyl glutarate
(RN1119-40-0) and dimethyl succinate (RN 106-65-0), also used as
phenolic resin solvent that is useful in polyurethane-forming
foundry binder systems, in particular in the no-bake or cold-box
process. Without, however, excluding the others, the appropriate
proportions between the triacetin solvent and the said mixture of
dimethyl ester ranges from 1:20 to 20:1.
[0044] According to the present invention, other phenolic resin
solvents, for example aromatic hydrocarbons such as benzene,
toluene, xylene, alkylbenzenes such as ethylbenzene, may also be
used with triacetin, or with a mixture of solvents comprising
triacetin and dimethyl esters.
Phenolic Resin
[0045] The phenolic resin component of the present invention is
used as a solution of triacetin organic solvent, per se or with
cosolvents.
[0046] The appropriate phenolic resins are those that are known to
a person skilled in the art, which are solid or liquid, but soluble
in organic solvents. The amount of solvent used in component A
should be sufficient to result in a binder composition that allows
uniform coating thereof on the aggregate and a uniform reaction of
the mixture. Despite the fact that the concentration of specific
solvents varies according to the type of phenolic resin used and
its molecular weight, the concentration of solvent in component A
in general may be up to 60% by weight of the resin solution, and is
typically in the range from 10% to 40% and preferably from 10% to
30%.
[0047] A particular phenolic resin used in sand casting according
to the present invention is a resol phenolic resin, known under the
name resol phenolic resins of benzyl ether type, prepared by
reacting an excess of aldehyde with a phenol in the presence of an
alkaline catalyst or a metallic catalyst. Without, however,
excluding the others, the appropriate phenolic resins are
preferably substantially free of water. Examples of phenolic resins
used in the binder compositions under consideration are well known
to those skilled in the art, such as those described in U.S. Pat.
No. 3,485,797. These resins predominantly contain bridges
connecting the phenolic nuclei of the polymer, which are
ortho-ortho benzyl ether bridges. Generally, they are prepared by
reacting an aldehyde and a phenol in an aldehyde/phenol mole ratio
of from 1.3:1 to 2.3:1 in the presence of a metal-ion catalyst,
preferably a divalent metal ion such as zinc, lead, manganese,
copper, tin, magnesium, cobalt, calcium or barium.
[0048] As known to those skilled in the art, the phenols used for
preparing the resol phenolic resins comprise one or more of the
phenols that were used hitherto in the formation of phenolic resins
and that are not substituted either on two ortho positions or on
one ortho position and on the para position. These unsubstituted
positions are necessary for the polymerization reaction. Any of the
remaining carbon atoms of the phenolic ring may be substituted. The
nature of the substituent may vary widely on condition that the
substituent does not seriously interfere with the polymerization of
the aldehyde with the phenol on the ortho and/or para position. The
substituted phenols used in the formation of the phenolic resins
comprise substituted alkylphenols, substituted arylphenols,
substituted cycloalkylphenols, substituted aryloxy-phenols and
substituted halophenols, these substituents containing from 1 to 26
carbon atoms and preferably from 1 to 12 carbon atoms.
[0049] Particular examples of suitable phenols comprise phenol,
2,6-xylenol, o-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol,
2,3,4-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol,
p-butylphenol, 3,5-dibutylphenol, p-amylphenol, p-cyclohexylphenol,
p-octylphenol, 3,5-dicyclohexylphenol, p-phenylphenol,
p-crotylphenol, 3,5-dimethoxyphenol, 3,4,5-trimethoxyphenol,
p-ethoxy-phenol, p-butoxyphenol, 3-methyl-4-methoxyphenol and
p-phenoxyphenol. Multi-ring phenols such as bisphenol A are also
suitable.
[0050] The appropriate aldehydes used for reacting with the phenol
in order to obtain a resol phenolic resin have the formula R--CHO
in which R is a hydrogen atom or a hydrocarbon-based radical
containing 1 to 8 carbon atoms. The aldehydes that react with the
phenol may comprise one of the aldehydes used hitherto in the
formation of phenol resins, such as formaldehyde, acetaldehyde,
propionaldehyde, furfuraldehyde and benzaldehyde.
Polyisocyanate
[0051] The polyisocyanate component of the binder according to the
present invention comprises a polyisocyanate, a polyisocyanate
solvent and optional ingredients. The polyisocyanate has a
functionality of two or more, preferably from 2 to 5. It may be
aliphatic, cycloaliphatic or aromatic, or a hybrid polyisocyanate.
The polyisocyanates may also be protected polyisocyanates,
polyisocyanate prepolymers and polyisocyanate quasi-prepolymers.
Mixtures of polyisocyanates are also covered by the present
invention.
[0052] The polyisocyanate component of the foundry binder comprises
a polyisocyanate, generally an organic polyisocyanate, and an
organic solvent, generally comprising aromatic hydrocarbons, such
as benzene, toluene, xylene and/or alkylbenzenes, in amounts
typically ranging from 0% by weight to about 80% by weight,
relative to the weight of the polyisocyanate. Optional ingredients
such as release agents and working-life extenders may also be used
in the polyisocyanate component.
[0053] Representative examples of polyisocyanates used in the
present invention 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 the dimethyl derivatives thereof. Other examples
of polyisocyanates are 1,5-naphthalene diisocyanate,
triphenylmethane triisocyanate, xylylene, and the methyl
derivatives thereof, polymethylenepolyphenyl isocyanates,
chlorophenylene 2,4-diisocyanate, etc.
[0054] The polyisocyanates are used in concentrations that are
sufficient to bring about curing of the resin after passage of the
gas or when in contact with the liquid curing catalyst. In general,
the ratio between the polyisocyanate and the hydroxyl of the
phenolic resin is from 1.25:1 to 1:1.25. The amount of
polyisocyanate used is generally from 10% to 500% by weight
relative to the weight of the phenolic resin.
[0055] The appropriate polyisocyanates are used in particular in
liquid from, which may be used in undiluted form, whereas solid or
viscous polyisocyanates are used in the form of solutions of
organic solvents. Without excluding other possibilities, the
adequate solvents for polyisocyanate are AB9 and AB10 (alkylbenzene
compounds containing an alkyl substituent that comprises,
respectively, 9 and 10 carbon atoms, for example sold under the
brand name Solvesso 100).
[0056] A person skilled in the art knows that the difference in
polarity between the polyisocyanate and the phenolic resins
restricts the choice of solvents with which the two components are
compatible. This compatibility is necessary in order to achieve a
complete reaction and curing of the binder compositions of the
present invention. Polar solvents, either of the protic or aprotic
type, are good solvents for the phenolic resin, but have limited
compatibility with polyisocyanate. Aromatic solvents, although
compatible with polyisocyanate, are less compatible with phenol
resins. It is thus preferable to use combinations of solvents and
in particular combinations of aromatic and polar solvents.
[0057] Examples of aromatic solvents for polyisocyanates comprise
benzene, toluene, xylene and alkylbenzenes, and mixtures thereof.
The aromatic solvents are preferably a mixture of aromatic solvents
whose boiling point ranges from 125.degree. C. to 250.degree. C. As
cosolvents, the polar solvents should not be extremely polar, which
would make them incompatible with the aromatic solvent. The
appropriate polar solvents are generally those classed in the prior
art as coupling solvents and include furfural, furfuryl alcohol,
2-ethoxyethyl acetate (Cellosolve.TM. acetate), 2-butoxyethanol
(butyl Cellosolve.TM.), diethylene glycol monobutyl ether (butyl
Carbitol.TM.), diacetone alcohol and 2,2,4-trimethyl-1,3-diol
monoisobutyrate (Texano.TM.). Cellosolve, Carbitol and Texanol are
trade names.
[0058] The polyisocyanate component B optionally comprises an
aromatic hydrocarbon-based compound.
Process
[0059] An optional element for a polyurethane-forming foundry
binder system is a natural oil. The natural oil is used in the
phenolic resin component, the isocyanate component, or in both, in
an effective amount that is sufficient to improve the tensile
strength of the binder-based foundry forms. This amount is
generally between about 1% by weight to about 15% by weight
relative to the weight of the isocyanate compound. In general,
smaller amounts of natural oil are used in the phenolic resin
component, generally about 1% by weight to about 5% by weight,
relative to the weight of the phenolic resin. The compatible
natural oils are also adequate. A natural oil is considered as
being compatible with the organic isocyanate and/or the phenolic
resin if the mixture does not separate into two phases at room
temperature, and preferably if it does not separate at temperatures
between 30.degree. C. and 0.degree. C. Natural oils include
unmodified natural oils and also the various known modifications
thereof, for example oils thickened by heat, blown with air or
oxygen, such as blown linseed oil and blown soybean oil. They are
generally classified as ethylenically unsaturated fatty acid
esters. The appropriate viscosities of the natural oil range from A
to J according to the Gardner Holt viscosity index. The acidity
value of the natural oil generally ranges from 0 to 10, as measured
by the number of milligrams of potassium hydroxide required to
neutralize a sample of 1 gram of natural oil.
[0060] As representative examples of the natural oils that are used
in the isocyanate component, mention may be made of linseed oil,
including refined linseed oil, epoxidized linseed oil, refined
linseed oil with alkali, soybean oil, cottonseed oil, RBD (refined,
blanched and deodorized) canola oil, refined sunflower oil, tung
oil and dehydrated castor oil. As natural oils that are
particularly used, mention may be made of purer forms of natural
oils that are treated to remove the fatty acids and other
impurities, generally consisting of triglycerides and of less than
1% by weight of impurities such as fatty acids and other
impurities. As particular examples of these pure natural oils,
mention may be made of polymerized linseed oils (PLO) such as
supreme linseed oil with an acidity value of about 0.30 and a
maximum viscosity of A, and purified soybean oils such as refined
soybean oil with an acidity value of less than 0.1 and a viscosity
of A to B. As is already known, this increases the tensile forces
of foundry forms.
[0061] It should be added that the drying oils as described in
patent U.S. Pat. No. 4,268,425 may be included in the binder in one
of the solvents mentioned herein. These drying oils comprise fatty
acid glycerides containing two or more double bonds. In addition,
ethylenically unsaturated fatty acid esters such as pine oil esters
of polyhydric or monohydric alcohols may be used as drying oils.
Generally, the drying oils are used at between about 35% and about
50% by weight of the total amount of solvent.
[0062] The binder may also contain a silane, generally added to the
phenolic resin component, for example as described in patent U.S.
Pat. No. 6,288,139. For example, the silane is added to the
phenolic resin component in amounts of 0.01% to 2% by weight
relative to the weight of the phenolic resin.
[0063] During the preparation of an ordinary foundry form of the
sand type, it is common practice to use the aggregate with a
relatively large particle size in order to provide a porosity that
is sufficient for the foundry form, so as to enable the evacuation
of the volatile materials from the form during the casting
operation. The term "ordinary foundry forms of sand type" as used
herein refers to foundry forms that have a porosity that is
sufficient to enable the evacuation of the volatile materials
during the casting operation. In general, at least about 80% by
weight of the aggregates used for foundry forms have a mean
particle size not less than about 50 and at about 150 mesh (Tyler
Screen Mesh).
[0064] An adequate aggregate used for ordinary foundry forms is
silica in which about 70% by weight of the sand consists of silica.
Other suitable materials include zircon, olivine, aluminosilicate,
sand, chromite sand, etc. Although the best results are often
obtained when the aggregate used is dry, it may contain small
amounts of moisture.
[0065] In the moulding compositions, the aggregate constitutes the
main constituent, the binder being present in a relatively small
amount. In foundry applications of the sand type, the amount of
binder generally does not exceed about 10% by weight and is
frequently in the range from 0.5% to 7% by weight relative to the
weight of the aggregate, in particular 1.0% to 1.8%.
[0066] The binder compositions are preferably provided as a
two-packet system with the phenolic resin component in one packet
and the polyisocyanate component in the other. Usually, the
phenolic resin component is mixed with the aggregate, and the
polyisocyanate component is then added. The methods for
distributing the binder over the aggregate particles are well known
to those skilled in the art.
[0067] Another aspect of the present invention relates to processes
for obtaining forms by sand casting, using the novel binder system,
which is moulded in the desired shape, such as a mould or core, and
cured. Curing via the cold-box process is performed by passing a
volatile tertiary amine, for example triethylamine,
1-dimethylamino-2-propanol (DMA-2P), monoethanolamine or
dimethylaminopropylamine (DMAPA), through the form in the mould as
described in U.S. Pat. No. 3,409,579. Curing via the no-bake
process is performed by mixing a liquid amine curing catalyst into
the foundry binder system, which is then shaped, and cured.
[0068] In accordance with the binder system according to the
invention, the term "catalytically effective amount of a curing
catalyst" means a concentration of the catalyst preferentially
between 0.2% and 5.0% by weight of the phenolic resin.
[0069] The useful liquid amine curing catalysts have a pKb value
generally of the order of 7 to 11. Particular examples of these
amines that may be mentioned include 4-alkylpyridines,
isoquinoline, arylpyridines, 1-methylbenzimidazole and
1,4-thiazine. A liquid tertiary amine that is particularly used as
catalyst is an aliphatic tertiary amine such as
tris(3-dimethyl-amino)propylamine. In general, the concentration of
the liquid amine catalyst ranges from 0.2% to 5.0% by weight of the
phenolic resin, in particular from 1.0% to 4.0% by weight and more
particularly from 2.0% to 3.5% by weight relative to the weight of
the polyether polyol. Catalysts such as triethylamine or
dimethyl-ethylamine are used in a range of from 0.05% to 0.15% by
weight relative to the weight of the binder.
[0070] Specific language is used in the description so as to
facilitate the understanding of the principle of the invention. It
should be understood, however, that no limitation of the scope of
the invention is envisaged by the use of this specific language.
Modifications, improvements and perfections may especially be
envisaged by a person skilled in the technical field concerned on
the basis of his own general knowledge.
[0071] The term "and/or" includes the meanings "and" and "or", and
also all the other possible combinations of elements connected with
this term.
[0072] Other details or advantages of the invention will emerge
more clearly in the light of the examples given below, purely for
indicative purposes.
EXPERIMENTAL SECTION
[0073] The example that follows represents a particular embodiment
of the invention, without any limiting nature, as described in the
set of claims presented later.
[0074] The solubilizing power of the solvents tested in this
example was determined by simulation using the Solsys.RTM. software
(Rhodia). It is based on the theory of solubility parameters and
the Hansen three-dimensional system. Specifically, as is known to
those skilled in the art, the cohesion energy parameters most
widely used for the characterization of solvents are those
developed by Hansen (for example in the book "Hansen Solubility
Parameters: A user's handbook" Hansen, Charles Second Edition 2007
Boca Raton, FL, United States. CRC Press). There are three figures
which, together, are known as the HSP. They fully describe the way
in which a solvent behaves relative to that which is dissolved if
their HSP values are known or can be estimated: [0075]
.delta.D--the dispersion energy of the bonds between the molecules
[0076] .delta.P--the energy of the intermolecular dipolar force
between molecules [0077] .delta.H--the energy of hydrogen bonds
between molecules.
[0078] Hansen demonstrated that the substances are characterized by
.delta.D, .delta.P and .delta.H.
[0079] The technique for determining the solubility parameters D, P
and H of a substance, namely of a phenolic resin in this example,
consists in testing the solubility of the said substance in a
series of pure solvents that belong to different chemical groups
(for example hydrocarbons, ketones, esters, alcohols and glycols).
The evaluation is made by considering the solvents that fully or
partially dissolve or that do not dissolve the substance to be
dissolved. The Solsys.RTM. software makes it possible to determine
the solubility volume of the substance and, as a consequence, it
makes it possible to determine the best solvent for dissolving the
substance. The solubility volume is represented by a sphere
(three-dimensional system) whose centre corresponds to a
"normalized distance" equal to 0 and reflects the solubility
maximum. All the points located on the surface of the sphere
correspond to a "normalized distance" equal to 1 and reflect the
solubility limit. The sphere is represented on a graph whose axes
correspond to .delta.D, .delta.P and .delta.H. The solubility of
the resin in the solvent will be proportionately greater the closer
the solubility volume is to the centre (normalized distance equal
to 0). Beyond the surface of the sphere (normalized distance equal
to 1), the resin is no longer soluble in the solvent.
[0080] The "normalized distance" values are used to evaluate the
solubilizing power of a substance, namely of the phenolic resin in
the present case, in a solvent. The closer the value of the
normalized distance to 0, the more soluble the resin in the
solvent.
[0081] Table I below shows the solubility parameter values for a
commercial mixture of dimethyl esters, relative to triacetin with a
purity of greater than 99.5% and industrial triacetin. The
normalized distances were obtained for a resol phenolic resin.
TABLE-US-00001 TABLE I Rhodiasolv Triacetin Solubility RPDE (*)
(purity Industrial parameters (comparative) >99.5%) triacetin
(**) .delta.D 16.87 16.5 16.5 .delta.P 4.87 4.5 8.7 .delta.H 10.02
9.1 11.5 Normalized distance 0.13 0.15 0.08 (*) 62% by weight of
dimethyl glutarate, 23% by weight of dimethyl succinate, 15% by
weight of dimethyl adipate. (**) About 86% by weight of triacetin,
10% by weight of diacetin, 4% by weight of monoacetin.
[0082] The general formulae of the solvents RPDE, triacetin and
industrial triacetin are given below.
##STR00001##
[0083] As is seen, the solubility parameter values for the mixture
of commercial dimethyl ester solvents are similar to those obtained
for triacetin. This means that the solvents are partially or
totally interchangeable, for the majority of applications, in
particular as a mixture, which depends on the commercial
conditions. The normalized distances are also very similar,
especially for the solubility in RPDE and triacetin of purity
greater than 99.5%.
[0084] Furthermore, it was demonstrated that industrial triacetin
has a greater solubilizing power. Specifically, the normalized
distance obtained is less than that obtained with RPDE and
triacetin alone, which makes it possible to reduce the amount of
solvent to dissolve the phenolic resin, when compared with
Rhodiasolv RPDE and triacetin, without loss of performance.
[0085] The presence of hydroxyl groups (--OH) in monoacetin and
diacetin justifies the increase in polarity (.delta.P value--Table
I) and of the solubilizing power of industrial triacetin. By
respecting the concentration range of triacetin in industrial
triacetin (from 80% to 95% by weight), no adverse reaction is
observed between the free --OH groups and the polyisocyanate.
[0086] With the information given here, a person skilled in the art
is capable of reproducing the invention in various ways, but for
the same purpose to achieve similar results. These equivalent
embodiments are also covered by the claims below.
* * * * *