WO2008090159A1

WO2008090159A1 - Catalytic system for making foundry shaped cores and casting metals

Info

Publication number: WO2008090159A1
Application number: PCT/EP2008/050720
Authority: WO
Inventors: Bruno Van Hemelryck; Pierre-Henri Vacelet; Jean-Claude Roze; Jens Muller; Diether Koch
Original assignee: Arkema France
Priority date: 2007-01-22
Filing date: 2008-01-22
Publication date: 2008-07-31
Also published as: EP1955791A1

Abstract

This invention relates to the use of a catalytic system as curing agent for binder compositions useful in the foundry art for making cores that harden at room temperature (Cold Box Process). The present invention also relates to binder compositions useful in the foundry art for making cores which harden at room temperature, to combinations of a foundry aggregate and a binder which may be used in making metal castings.

Description

CATALYTIC SYSTEM FOR MAKING FOUNDRY SHAPED CORES

AND CASTING METALS

[0001] This invention relates to the use of a catalytic system as curing agent for binder compositions useful in the foundry art for making cores that harden at room temperature. The present invention also relates to binder compositions useful in the foundry art for making cores which harden at room temperature, to combinations of a foundry aggregate such as sand and a binder based generally on phenolic (phenol-aldehyde) resins and polyisocyanates which, on being formed into a coherent mass with the aggregate in a mould, generally a steel mould, is capable of being cured at room temperature by a curing agent. The self-supported as obtained, the cores, can be used in making metal castings. [0002] When the cured resins are based on both phenolic resins and polyisocyanates, the above process utilized in foundries is named Polyurethane Cold Box Process (PUCB)

[0003] According to this method, a two-component polyurethane binder system is used for the bonding of sand. The first component consists of a solution of a polyol, which contains at least two OH groups per molecule. The second component is a solution of an isocyanate having at least two NCO groups per molecule.

[0004] The use of tertiary volatile amines as curing agents has long been known in PUCB: see for example US 3,429,848; US 3,485,797; US 3,676,392; and US 3,432,457. These tertiary amines are sometimes utilized with metal salts and provide a fast curing of phenol formaldehyde and polyisocyanate resins at room temperature. They can be added to the binder system before the moulding stage, in order to bring the two components to reaction (US 3,676,392) or they can pass in a gaseous form through a shaped mixture of an aggregate and the binder (US 3,409,579). [0005] Generally, phenolic resins are used as polyols, which are prepared through condensation of phenol with aldehydes, preferably formaldehyde, in the liquid phase, at temperatures of up to around 130 ⁰C, in the presence of divalent metal catalysts. The manufacture of such phenolic resins is described in detail in US 3,485,797. In addition to unsubstituted phenol, substituted phenols, especially o-cresol and p-nonyl phenol, can be used (see for example EP-A-O 183 782). [0006] As additional reaction components, according to EP-B-O 177 871 , aliphatic monoalcohols with one to eight carbon atoms can be used to prepare alkoxylated phenolic resins. According to this patent, the use of alkoxylated phenolic resins in the binder results in binders that have a higher thermal stability. [0007] As solvents for the phenolic components, mixtures of high-boiling point polar solvents (for example, esters and ketones) and high boiling point aromatic hydrocarbons are typically used. [0008] Preferred tertiary amines for curing polyurethane cold box (PUCB) processes are trimethylamine (TMA), dimethylethylamine (DMEA), dimethylisopropylamine (DMIPA), triethylamine (TEA). They are used individually. [0009] The catalyst is usually introduced as a combination of one inert gas and one amine gas. The boiling point of the amine is preferably below 100 ⁰C to permit evaporation and to achieve satisfactory concentration of amine in the amine-inert gas mixture injected into the steel mould. A boiling point below 100 ⁰C also helps to avoid condensation of the amine when it contacts the steel moulds. [0010] However, the boiling point of the amine preferably must be high enough to facilitate handling of the amine. Trimethylamine (TMA) is a gas at normal ambient temperature (boiling point (Bp) 2.87 ⁰C), which makes it difficult to handle. Other drawback can be found with low boiling tertiary amines: the well-known low boiling tertiary amine DMEA (Bp 37°C) has undesirable organoleptic characteristics. In particular, it has a strong ammonia odor. Furthermore, this amine is very easily impregnated in the skin and in the clothing, making an unpleasant working environment when it is utilized.

[0011] On the other hand, the 89 ⁰C boiling point of triethylamine (TEA) is probably the highest practical boiling point because TEA tends to condensate out of the gas mixture in the piping which carries the amine-inert gas mixture to the steel mould in cold conditions, and in addition badly cured spots are found in sand cores produced in the steel mould. The molecular weight of the amine must be low enough to permit ready diffusion of the amine through sand in the steel mould, especially in the corners and edges of the mould.

[0012] TEA, with molecular weight of 101 is probably the highest molecular weight amine permissible for the so-called Cold Process; it has a very low odor intensity and very low amine smell but displays lower curing ability than the tertiary amines with lower Molecular weight and lower Boiling point. [0013] On an industrial point of view, DMIPA (Molecular weight: 87, Bp: 67 ⁰C) is a good compromise tertiary amine in the field of catalytic gassing agents for curing resins in cold box processes. More volatile than TEA, DMIPA requires less energy input and lower gassing temperatures when carried out in PUCB equipment. DMIPA has a better reactivity than TEA: 1 kg of DMIPA is capable of curing approximately 1200 kg of sand/resin mixture, while 1 kg of TEA is capable of curing only 900 kg of the same sand/resin mixture. DMIPA is less odorant than tertiary amine DMEA.

[0014] However, there still is a need to provide a tertiary amine with both an improved catalyst efficiency in comparison with DMIPA, i.e which catalyses binding resins more quickly than DMIPA, and which does not possess the strong, irritating, and itching ammonia odor associated with dimethylethylamine (DMEA). [0015] The present invention therefore first relates to the use of an amine catalyst for curing a composite resin composition, especially for preparing a foundry shape by the cold box process, said amine catalyst having an improved catalytic efficiency and presenting safer handling conditions. [0016] The use of the present invention has many advantages, among other a less odorant and safer catalyst, and allows a faster curing, as compared to the known catalysts used in the art.

[0017] More particularly, the curing catalyst system used in the present invention is based on diethylmethylamine (DEMA). [0018] The invention further relates to a process for preparing a foundry shape by the cold box process.

[0019] The cores produced according to the present process display a lower water sensitivity than with DMIPA, as seen from higher flexural strength after having been exposed to humidity. [0020] More precisely, the invention relates to a process for preparing a foundry shape by the cold box process, which comprises the following steps:

(a) forming a foundry mix with the binder and an aggregate, preferably sand,

(b) forming a foundry shape by introducing the foundry mix obtained from step (a) into a pattern, (c) contacting the shaped foundry mix with a curing catalyst comprising DEMA, in a liquid or preferably in a gaseous form, optionally carried out with an inert carrier,

(d) hardening the aggregate-resins mix into a hard, solid, cured shape, (e) removing the hardened foundry shape of step (d) from the pattern.

[0021] The binder system comprises at least a phenolic resin component and at least an isocyanate component.

[0022] Phenolic resins are manufactured by condensation of phenols and aldehydes (Ullmann's Encyclopedia of Industrial Chemistry, Bd. A19, pages 371 ff, 5th, edition, VCH Publishing House, Weinheim). Substituted phenols and mixtures thereof can also be used. All conventionally used substituted phenols are suitable. [0023] The phenolic binders are generally not substituted, either in both ortho- positions or in one ortho- and in the para-position, in order to enable the polymerization. The remaining ring sites can be substituted. There is no particular limitation on the choice of substituent, as long as the substituent does not negatively influence the polymerization of the phenol and the aldehyde. [0024] Examples of substituted phenols are alkyl-substituted phenols, aryl- substituted phenols, cycloalkyl-substituted phenols, alkenyl-substituted phenols, alkoxy-substituted phenols, aryloxy-substituted phenols and halogen-substituted phenols.

[0025] The above named substituents have 1 to 26, and preferably 1 to 12, carbon atoms. Examples of suitable phenols, in addition to the especially preferred unsubstituted phenols, are o-cresol, m-cresol, p-cresol, 3,5-xylol, 3,4-xylol, 3,4,5- trimethyl phenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutyl- phenol, p-amylphenol, cyclohexylphenol, p-octylphenol, 3,5-dicyclohexylphenol, p-crotylphenol, p-phenylphenol, 3,5-dimethoxyphenol, 3,4,5-thmethoxyphenol, p-ethoxyphenol, p-butoxyphenol, 3-methyl-4-methoxyphenol, and p-phenoxy- phenol. Especially preferred is phenol itself. [0026] All aldehydes, which are traditionally used for the manufacture of phenolic resins, can be used within the scope of the invention. Examples of this are formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. Preferably, the aldehydes commonly used should have the general formula R'CHO, where R' is hydrogen or a hydrocarbon radical with 1 -8 carbon atoms. Particularly preferred is formaldehyde, either in its diluted aqueous form or as paraformaldehyde.

[0027] In order to prepare the phenolic resole resins, a molar ratio aldehyde to phenol of at least 1.0 should be used. A molar ratio of aldehyde to phenol is preferred of at least 1 :1.0, with at least 1 :0.58 being the most preferable.

[0028] In order to obtain alkoxy-modified phenolic resins, primary and secondary aliphatic alcohols are used having an OH-group containing from 1 to 10 carbon atoms. Suitable primary or secondary alcohols include, for example, methanol, ethanol, n-propanol, isopropanol, n-butanol, and hexanol. Alcohols with 1 to 8 carbon atoms are preferred, in particular, methanol and butanol.

[0029] The manufacture of alkoxy-modified phenolic resins is described in EP-B-O 177 871. They can be manufactured using either a one-step or a two-step process. With the one-step-process, the phenolic components, the aldehyde and the alcohol are brought to a reaction in the presence of suitable catalysts. With the two-step-process, an unmodified resin is first manufactured, which is subsequently treated with alcohol.

[0030] The ratio of alcohol to phenol influences the properties of the resin as well as the speed of the reaction. Preferably, the molar ratio of alcohol to phenol amounts to less than 0.25. A molar ratio of from 0.18-0.25 is most preferred. If the molar ratio of alcohol to phenol amounts to more than 0.25, the moisture resistance decreases.

[0031] Suitable catalysts are divalent salts of Mn, Zn, Cd, Mg, Co, Ni, Fe, Pb, Ca and Ba. Zinc acetate is preferred. [0032] Alkoxylation leads to resins with a low viscosity. The resins predominantly exhibit ortho-ortho benzyl ether bridges and furthermore, in ortho- and para- position to the phenolic OH-groups, they exhibit alkoxymethylene groups with the general formula -(CH₂O)_nR. In this case R is the alkyl group of the alcohol, and n is a small whole number in the range of 1 to 5. [0033] All solvents, which are conventionally used in binder systems in the field of foundry technology, can be used. It is even possible to use aromatic hydrocarbons in large quantities as essential elements in the solution, except that those solvents are not preferred because of environmental considerations. For that reason, the use of oxygen-rich, polar, organic solvents are preferred as solvents for the phenolic resin components. The most suitable are dicarboxylic acid ester, glycol ether ester, glycol diester, glycol diether, cyclic ketone, cyclic ester (lactone) or cyclic carbonate.

[0034] Cyclic ketone and cyclic carbonate are preferred. Dicarboxylic acid ester exhibits the formula R1OOC-R2-COOR1, where the Ri, independently from one another, represent an alkyl group with 1 -12, and preferably 1 -6 carbon atoms, and R2 is an alkylene group with 1-4 carbon atoms. Examples are dimethyl ester from carboxylic acids with 4 to 6 carbon atoms, which can, for example, be obtained under the name dibasic ester from DuPont. [0035] Glycol ether esters are binders with the formula Rs-O-R₄-OOCR₅, where R3 represents an alkyl group with 1 -4 carbon atoms, R₄ is an alkylene group with 2-4 carbon atoms, and R₅ is an alkyl group with 1 -3 carbon atoms (for example butyl glycolacetate), with glycol etheracetate being preferred. [0036] Glycol diesters exhibit the general formula R₅COO-R₄-OOCR₅ where R₄ and R₅ are as defined above and the remaining R₅, are selected, independently of each other (for example, propyleneglycol diacetate), with glycol diacetate being preferred.

[0037] Glycol diether is characterized by the formula R3-O-R₄-O-R3, where R3 and R₄ are as defined above and the remaining R₃ are selected independent of each other (for example, dipropyleneglycol dimethyl ether). Cyclic ketone, cyclic ester and cyclic carbonate with 4-5 carbon atoms are likewise suitable (for example, propylene carbonate). The alkyl- and alkylene groups can be branched or unbranched.

[0038] These organic polar solvents can preferably be used either as stand-alone solvents for the phenolic resin or in combination with fatty acid esters, where the content of oxygen-rich solvents in a solvent mixture should predominate. The content of oxygen-rich solvents is preferably at least 50% by weight, more preferably at least 55% by weight of the total solvents.

[0039] Reducing the content of solvents in binder systems can have a positive effect on the development of smoke. Whereas conventional phenolic resins generally contain around 45% by weight and, sometimes, up to 55% by weight of solvents, in order to achieve an acceptable process viscosity (of up to 400 mPa.s), the amount of solvent in the phenolic-component can be restricted to at most 40% by weight, and preferably even 35% by weight, through the use of the low viscosity phenolic resins described herein, where the dynamic viscosity is determined by the Brookfield Head Spindle Process. If conventional non alkoxy-modified phenolic resins are used, the viscosity with reduced quantities of solvent lies well outside the range, which is favourable for technical applications of up to around 400 mPa.s. [0040] In some parts, the solubility is also so bad that at room temperature phase separation can be observed. At the same time the immediate strength of the cores manufactured with this binder system is very low. Suitable binder systems exhibit an immediate strength of at least 150 N/cm² when 0.8 part by weight each of the phenolic resin and isocyanate component are used for 100 parts by weight of an aggregate, like, for example, Quarzsand H32 (see for instance: EP 0 771 599 or DE 43 27 292).

[0041] The addition of fatty acid ester to the solvent of the phenolic component leads to especially good release properties. Fatty acids are suitable, such as, for example, those with 8 to 22 carbons, which are esterified with an aliphatic alcohol. Usually fatty acids with a natural origin are used, like, for example, those from tall oil, rapeseed oil, sunflower oil, germ oil, and coconut oil. Instead of the natural oils, which are found in most mixtures of various fatty acids, single fatty acids, like palmitic fatty acid or myristic fatty acid can, of course, be used. [0042] Aliphatic mono alcohols with 1 to 12 carbons are particularly suitable for the estehfication of fatty acids. Alcohols with 1 to 10 carbon atoms are preferred, with alcohols with 4 to 10 carton atoms being especially preferred. Based on the low polarity of fatty acid esters, whose alcohol components exhibit 4 to 10 carbon atoms, it is possible to reduce the quantity of fatty acid esters, and to reduce the build-up of smoke. A line of fatty acid esters is commercially obtainable. [0043] Fatty acid esters, whose alcohol components contain from 4 to 10 carbon atoms, are especially advantageous, since they also give binder systems excellent release properties, when their content in the solvent component of the phenolic component amounts to less than 50% by weight based upon the total amount of solvents in the phenolic resin component. As examples of fatty acid esters with longer alcohol components, are the butyl esters of oleic acids and tall oil fatty acid, as well as the mixed octyl-decylesters of tall oil fatty acids.

[0044] By using the alkoxy-modified phenolic resins described herein, aromatic hydrocarbons can be avoided as solvents for the phenolic component. This is because of the excellent polarity of the binders. Oxygen-rich organic, polar solvents, can now be used as stand-alone solvents. Through the use of the alkoxy-modified phenolic resins, the quantity of solvents required can be restricted to less than 35 % by weight of the phenolic component. This is made possible by the low viscosity of the resins. The use of aromatic hydrocarbons can, moreover, be avoided. The use of binder systems with at least 50% by weight of the above named oxygen-rich, polar, organic solvents as components in the solvents of the phenolic components leads, moreover, to a doubtlessly lower development of smoke, in comparison with conventional systems with a high proportion of fatty acid esters in the solvent. [0045] The two components of the binder system include an aliphatic, cycloaliphatic or aromatic polyisocyanate, preferably with 2 to 5 isocyanate groups. Based on the desired properties, each can also include mixtures of organic isocyanates. Suitable polyisocyanates include aliphatic polyisocyanates, like, for example, hexamethylenediisocyanate, alicyclic polyisocyanates like, for example, 4,4'-dicyclohexylmethanediisocyanate, and dimethyl dehvates thereof. [0046] Examples of suitable aromatic polyisocyanates are toluol-2,4-diisocyanate, toluol-2,6-diisocyanate, 1 ,5-napththalenediisocyanate, thphenylmethane- triisocyanate, xylylenediisocyanate and its methyl derivatives, polymethylene- polyphenyl isocyanate and chlorophenylene-2,4-diisocyanate. Preferred polyisocyanates are aromatic polyisocyanates, in particular, polymethylene- polyphenyl polyisocyanates such as diphenylmethane diisocyanate. [0047] In general 10-500% by weight of the polyisocyanates compared to the weight of the phenolic resins are used. 20-300% by weight of the polyisocyanates is preferred. Liquid polyisocyanates can be used in undiluted form, whereas solid or viscous polyisocyanates can be dissolved in organic solvents. The solvent can consist of up to 80% by weight of the isocyanate components. [0048] As solvents for the polyisocyanate, either the above-named fatty acid esters or a mixture of fatty acid esters and up to 50% by weight of aromatic solvents can be used. Suitable aromatic solvents are naphthalene, alkyl- substituted naphthalenes, alkyl-substituted benzenes, and mixtures thereof. Especially preferred are aromatic solvents, which consist of mixtures of the above named aromatic solvents and which have a boiling point range of between 140 and 230 ⁰C. However, preferably no aromatic solvents are used. Preferably, the amount of polyisocyanate used results in the number of the isocyanate group being from 80% to 120% with respect to the number of the free hydroxyl group of the resin.

[0049] In addition to the already mentioned components, the binder systems can include conventional additives, like, for example, silane (see for instance US 4,540,724), drying oils (US 4,268,425) or "Komplexbildner" (WO 95/03903). [0050] The binder systems are offered, preferably, as two-component-systems, whereby the solution of the phenolic resin represents one component and the polyisocyanate, also in solution, if appropriate, is the other component. Both components are combined and subsequently mixed with sand or a similar aggregate, in order to produce the moulding compound.

[0051] The moulding compound contains an effective binding quantity of up to 15% by weight of the binder system with respect to the weight of the aggregate. It is also possible to subsequently mix the components with quantities of sand or aggregates and then to join these two mixtures. Processes for obtaining a uniform mixture of components and aggregates are known to the expert. In addition, if appropriate, the mixture can contain other conventional ingredients, like iron oxide, ground flax fibre, xylem, pitch and refractory meal (powder). [0052] In order to manufacture foundry-moulded pieces from sand, the aggregate should exhibit a sufficiently large particle size. In this way, the founded piece has sufficient porosity, and fugitive gasses can escape during the casting process. In general at least 80% by weight and preferably 90% by weight of the aggregate should have an average particle size of less than or equal to 290 μm. The average particle size of the aggregate should have between 100 μm and 300 μm. [0053] For standard-founded pieces, sand is preferred as the aggregate material to be used, where at least 70% by weight, and preferably more than 80% by weight of the sand is silicon dioxide. Zircon, olivine, aluminosilicate sands and chromite sands are likewise suitable as aggregate materials. [0054] The aggregate material is the main component in founded pieces. In founded pieces from sand for standard applications, the proportion of binder in general amounts to up to 15% by weight, and often between 0.5% and 7% by weight, with respect to the weight of the aggregate. Especially preferred is 0.6% to 5% by weight of binder compared to the weight of the aggregate. [0055] Although the aggregate is primarily added dry, up to 0.1 % by weight of moisture can be tolerated, with respect to the weight of the aggregate. The founded piece is cured so that it retains its exterior shape after being removed from the mould.

[0056] As explained above and according to the present invention, the liquid or gaseous curing system used for hardening in the binder system is based on diethylmethylamine (DEMA).

[0057] Unexpectedly, DEMA appears to cure phenol formaldehyde and polyisocyanate resins faster than DMIPA. This is a main advantage for foundry cores having complex moulding shapes.

[0058] Moreover, given that DEMA displays superior catalytic activity than DMIPA, a lower water sensitivity of cores and moulds at storage is shown when curing with DEMA instead of DMIPA.

[0059] These results are surprising and unexpected when considering:

- the molecular weight of DEMA which is identical to the one of DMIPA,

- the boiling point of DEMA (65 ⁰C) which is quite similar to the one of DMIPA (67 °C), and

- the density of DEMA which is also very close to that of DMIPA, density which is another important property for PUCB catalysis (Borden, "Bulletin d'information 2000", page 9) (density of DEMA 0,706, density of DMIPA 0,710 as measured on a Mettler Toledo DA 100M). [0060] DEMA can be carried out in a liquid state or preferably in a gaseous state and in any desired predetermined concentration, alone or preferably in combination with an inert carrier.

[0061] The inert gaseous carrier can be nitrogen or air, but carbon dioxide, less expensive than nitrogen, is sometimes utilized. [0062] When DEMA is utilized as a liquid, a liquid carrier can optionally be utilized.

[0063] The present invention also encompasses the use of a mixture comprising, in addition to DEMA, up to 25%, and preferably up to 10% by weight of at least another amine, primary, secondary and/or tertiary, although the concentration of the at least another amine impurities represents preferably less than 0.5% by weight of the mixture comprising DEMA.

[0064] The DEMA used in the invention may also contain small amounts of water: the concentration of water in DEMA is preferably kept below 0.2% by weight. [0065] After removing the piece from the mould, further hardening can take place in the well-known way, for instance by heating, finally resulting in the finished piece or core or mould. [0066] According to a preferred embodiment, silane with the general formula therefore -(R'-O)3-Si-R- is added to the moulding compound before the curing begins. Here, R' is a hydrocarbon radical, preferably an alkyl radical with 1 -6 carbon atoms, and R is an alkyl radical, an alkoxy-substituted alkyl radical or an alkyl amine-substituted amine radical with alkyl groups, which have 1 -6 carbon atoms. The addition of from 0.1 to 2 % by weight with respect to the weight of the binder system and catalysts, reduces the moisture sensitivity of the system.

[0067] Examples of commercially obtainable silanes are Dow Corning Z6040 and Union Carbide A-187 (Y-glycidoxypropylthmethoxysilane), Union Carbide A-1 100 (γ-aminopropyl triethoxysilane), Union Carbide A-1 120 (N-β-(aminoethyl)-γ-amino- propyltrimethoxysilane) and Union Carbide A1 160 (ureidosilane). [0068] If applicable, other additives can be used, including wetting agents and sand mixture extending additives (English Benchlife-additives), such as those disclosed in US 4,683,252 or US 4,540,724. In addition, mould release agents like fatty acids, fatty alcohols and their derivatives can be used, but as a rule, they are not necessary. [0069] The present invention also relates to a process of casting a metal, said process comprising the following steps: a) preparing a foundry shape as described above in steps (a) to (e), b) pouring said metal while in the liquid state into said foundry shape; c) allowing said metal to cool and solidify; and d) then separating the moulded article from the said foundry shape.

[0070] The invention is now further illustrated by the following examples, which are not intented to bring any limitation to the present invention.

EXAMPLES

Example 1 : Bulk curing test

[0071] A test was carried out for the measurement of the percentage of sand- resins mixture sand cured for a defined volume (0.1 ml_ or 0.2 ml_) of a tertiary amine (either DMEA or DEMA or DMIPA) in order to show the kinetics of the curing. The amine concentrations used in the present test are on purpose at a default level, i.e. lower than the amount necessary to the full curing of the sand- resin mixtures. [0072] The resins used for this test are commercial resins from Ashland-Avebene (Usine du Goulet, 20, rue Croix du Vallot, 27600 St Pierre-la-Garenne, France) sold under the trade name Avecure^®; these resins are composed of a formo- phenolic polyol and an isocyanate resins in accordance with the present description. [0073] For each resin, the following results were obtained: full curing of a 1.870- 1.880 kg cylinder (length 300 mm x diameter 70 mm) of sand LA32 (Silfraco) + binder needs about 0.3-0.5 ml_ of DMEA whereas it requires up to 1 ml_ of DMIPA and up to 2 ml_ of TEA.

[0074] A fixed amount of sand-resins mixture with a predetermined amount of resins per mass unit of sand (normally between 0.5% and 2% by weight of each resin based on the amount of sand mixed) is placed in a long cylindrical shaped mould, the amine is poured as liquid ahead of the sand-resins cylinder in a U tube; a heated stream of carrier gas (normally nitrogen) at a fixed and predetermined rate is passed through the amine loaded U tubing. [0075] The carrier gas stream brings the volatilised amine to the cylinder filled with sand-resin during a fixed time. Test cores were prepared as follows:

[0076] Into a laboratory mixer, 0.8 part by weight of the phenolic resin solution and 0,8 part by weight of the polyisocyanate solution are added to 100 parts by weight of sand LA32 (Silfraco), in the order given, and mixed intensively for 3 minutes. 6 kg of fresh sand are used for each resin to be cured. This quantity allows 3 gassings of 1.870-1.880 kg of sand + binder for repeatability sake. The 3 gassings are made at 5.5 bars (static) equivalent to 4.8 bars (dynamic). 2 purgings of 10 seconds each are applied between each gassing operation. Gassing itself lasts 10 seconds at 1.5 bars (dynamic). Carrier gas heater is adjusted to 75 ⁰C ± 3 ⁰C. [0077] This test is a "Bulk curing test": the weight of the sand-resin mix which is cured is measured and the results given in Tables 1 and 2 are expressed in % by weight of solid bound sand. - Table 1 --

(Volume of Amine 0,1 ml_)

Resϊh — — __Am/ne_ DMEA DEMA DMIPA

Avecure^s ^} 353/653 67.0% 43.8% 39.1 %

Avecure^s ^} 333/633 54.4% 46.7% 38.9%

Avecure^s ' 331/631 57.8% 40.2% 37.8%

Avecure^s ^} 363/663 63.0% 65.7% 61.2%

-- Table 2 --

(Volume of Amine 0.2 ml_)

Resϊn — — __Am/ne_ DMEA DEMA DMIPA

Avecure^s ^} 353/653 85.9% 58 .1 % 49 .5%

Avecure^s ^} 333/633 77.5% 62 .8% 53 .2%

Avecure^s ' 331/631 79.8% 54 .9% 51 .0%

Avecure^s ^} 363/663 98.1 % 82 .0% 78 .4%

[0078] From the results of Example 1 above, it can be clearly seen that for low volumes of amine, a significantly higher level of curing is systematically attained with DEMA than with DMIPA for the same amount of amine carried out.

Example 2: Water sensitivity

[0079] In the following example, water sensitivity of a cured sand-binder core is evaluated through its mechanical resistance. The resistance test is carried out on a cured (sand-binder) sample which has been exposed to a 98% water saturated atmosphere at 20 ⁰C for 24 hours immediately after curing. Conditions of gassing are the same as for table 1 and 2, excepted that 0.5 ml_ of each amine catalyst is used.

[0080] PU Part 1 and 2 as indicated in Table 3 are the polyol and polyisocyanate components respectively of each PU resin type indicated as Resin 1 , 2, 3.

[0081] The resins used for this test are commercial resins from Ashland Sϋd-

Chemie sold under the trade names Askocure^® or Ecocure^®; these resins are composed of a formo-phenolic polyol and an isocyanate resins in accordance with the present description.

[0082] Transverse strength values have been measured twice for each resin and each amine curing and both results are mentioned in the table 3 (for instance, 290/300 for Resin 1 with DMIPA), the higher the value, the better in terms of mechanical resistance, so the better in terms of water resistance (ex. 460/470 for Resin 2 cured with DEMA indicates less water sensitivity than for the same resin cured with DMIPA as indicated by lower transverse strength values 420/440). [0083] The results are given in Table 3 below.

-- Table 3 --

[0084] As can be seen from the results of Table 3, water sensitivity of the sand- resins cured with DEMA is lower than with DMIPA in any cases. Moreover, as for Resin 3, DEMA gives less water sensitivity than the very reactive DMEA.

Claims

1. Use of diethylmethylamine in a catalyst curing system for preparing a foundry shape by the cold box process.

2. Use according to claim 1 , wherein diethylmethylamine is in a liquid state or preferably in a gaseous state and in any desired predetermined concentration, alone or preferably in combination with an inert carrier.

3. Use according to any of claim 1 or 2, wherein the curing catalyst system is a mixture comprising, in addition to DEMA, up to 25%, preferably up to 10% and advantageously up to 0.5% by weight of at least another amine, primary, secondary and/or tertiary.

4. Use according to any of claims 1 to 3, wherein the curing catalyst system contains 0.2 % by weight of water.

5. Process for preparing a foundry shape by the cold box process, which comprises the following steps:

(a) forming a foundry mix with a binder and an aggregate, preferably sand,

(b) forming a foundry shape by introducing the foundry mix obtained from step (a) into a pattern, (c) contacting the shaped foundry mix with a curing catalyst system comprising diethylmethylamine, in a liquid or preferably in a gaseous form, optionally carried out with an inert carrier,

(d) hardening the aggregate-resins mix into a hard, solid, cured shape,

(e) removing the hardened foundry shape of step (d) from the pattern.

6. Process according to claim 5, wherein the inert gaseous carrier is nitrogen, air and/or carbon dioxide.

7. Process according to any of claim 5 or 6, wherein the curing catalyst system is a mixture comprising, in addition to DEMA, up to 25 %, preferably up to 10 % and advantageously up to 0.5 % by weight of at least another amine, primary, secondary and/or tertiary.

8. Process according to any of claims 5 to 7, wherein the curing catalyst system contains 0.2 % by weight of water.

9. Process according to any of claims 5 to 8, for making a core or a mould comprising a further step of hardening the hardened foundry shape obtained from step (e).

10. Process of casting a metal, comprising the following steps: a) preparing a foundry shape in accordance with any of claims 5 to 9, b) pouring said metal while in the liquid state into a round said shape; c) allowing said metal to cool and solidify; and d) then separating the moulded article.