EP2892670B1 - Method for obtaining a foundry body from a granular mixture including a modified polycondensed resin and a formaldehyde sensor - Google Patents

Description

The present invention relates to a process for obtaining a foundry body from a granular mixture comprising a modified polycondensed resin, and a formaldehyde sensor, and the foundry body obtained by said method.

The processes for hot forming granular or fibrous substances are industrial processes leading to the manufacture of bodies that are most often solid. Among these, hot box type industrial processes (or hot box) use resins. In general, the resins are intimately mixed with the substance or substances to be agglomerated, or spread on the surface to be bonded, in association with a hardening agent whose function is most often to render the solid reaction medium in situ.

The substances to be formed or agglomerated, generally solid, most often comprise at least one granular or fibrous filler such as, for example, mineral or synthetic sands, glass micro-beads, ceramic micro-beads and fibers which are most often ligno-lined. cellulose.

After the incorporation of the resin and a possible hardening agent, and possibly at least one other additive, the substance to be agglomerated is generally fluid, most often viscous. The substance to be agglomerated is then brought into contact with or in a forming tool, and then heated, the heat being generally provided by the heating of the forming tool (or forming tooling).

The heat initiates curing of the resins by polymerization, and then the solid body thus formed is generally removed from the forming tool for later use. By "body" is meant according to the invention a material object occupying a portion of space and having particular properties. The body according to the invention is most often in a solid continuous medium, that is to say of clean form and substantially invariable volume. In contrast, a fluid body is generally a body constituting a deformable continuous medium.

One of the industrial processes is called " hot box" and uses resins condensed with formaldehyde. These thermoset resins hot and in acidic medium, by polymerization.

In the field of foundry, molds and cores are generally solid bodies, which can be manufactured by a " hot box" type process from a granular charge. When casting each metal part into or in contact with the mold or core, the corresponding mold or core is destroyed by burning the resin in contact with the metal. This involves producing a set of molds or kernels per piece produced. To promote this destruction, at industrial rate, and to limit the nuisance of the combustion gases, the resins content, calculated as dry extract, are extremely low, most often in a range of 0.3 to 3% by weight by weight. relative to the mass of the granular charge to be agglomerated. In addition, the chemical nature of the combustion gases is important, both for the quality of cast metal parts and for the health of workers.

Finally, in certain industries, such as the mass production industry, the production of molds and cores must be done at high speeds of up to a few thousand pieces per day. In this case, the forming tools or core boxes are metallic because the heating temperatures to obtain rapid polymerization of the resins are high, generally greater than 150 ° C and up to 380 ° C. This involves significant tooling costs and especially dimensional accuracy problems of molds and cores, related to the expansion of tools under the effect of heat. On the other hand, respiratory nuisances for people working in this environment have been deemed inadmissible.

This is why " hot box" processes were abandoned some forty years ago by the industry, in favor of " cold box" processes (or cold boxes). These "cold box" type processes proposed the use of cold binders, which at that time generated little nuisance, in terms of hygiene and safety, and above all compatible with a high industrial production rate.

However, at present, these cold box type alternative binders are also problematic in industrial processes because they have become incompatible with more stringent standards in terms of hygiene, safety and the environment.

In this context, the French patent application FR 2948307, published in January 2011 , describes an improved method of the " hot box " type, making it possible to solve the problems presented by the " hot box" type processes of the prior art, and overcoming the shortcomings of " cold box" type processes , particularly in the foundry industry.

Thus, the French patent application FR 2948307 relates to a process for producing a body comprising a conventional polycondensed resin, preferably a urea-formaldehyde resin, and a free formaldehyde sensor, which is preferably carbohydrazide.

However, this improvement claimed in the French patent application FR 2948307 is practically usable in the industry only in aluminum foundry. Indeed, it proved to be suitable for the industrial stage only for the casting of aluminum parts (ie at about 800 ° C). Its heat resistance is not suitable for casting parts of a metal alloy such as cast iron, whose melting temperature is significantly higher (about 1300 ° C). In addition, the nitrogen content generated by the urea-formaldehyde resin used in this context, proved too important for the industrial production of a cast iron part.

On the other hand, the patent application US 2007/0149644 discloses the use of tannin extract in a foundry mixture comprising an aggregate and a binder of tannin extract and furfuryl alcohol. This binder does not necessarily contain resin, because the two components of the binder react together at a temperature above 40 ° C. However, this invention can not be used in industry because furfuryl alcohol is a compound now classified as carcinogenic. In addition, the foundry mix of this document apparently does not generate free formaldehyde or phenol free. Thus, according to the text of this document, no formaldehyde sensor seems necessary in this context. In fact, the presence of free formaldehyde is proven and poses a problem, and, above all, the very low reactivity during the implementation of this process, which makes it necessary to heat up at high temperature and / or to use a powerful catalyst. , makes it incompatible with industrial use in mass production.

The patent application WO 2004/058843 discloses a resin-based composition comprising tannin, an amine compound, an aldehyde and a stabilizer. The compound containing amino groups may be urea or an oligomer derived from the urea-formaldehyde condensation. The stabilizer is preferably an amino-based heterocyclic compound. There is also described a method for preparing this composition, as well as the use of this composition for producing a mixture comprising particles, for the purpose of creating particle boards, including wood particles. However, the compositions of this document do not include a formaldehyde sensor, since it is explained that the free formaldehyde from the resin will react with the tannin during the formation of the composition. In fact, the presence of free formaldehyde is proven and is problematic.

It is in the context developed above that the Applicant has discovered an improved process of the patent application process. FR 2 948 307 previously described. This improved process overcomes the shortcomings of all the processes of the state of the art, especially in the foundry industry including cast iron.

• la préparation d'un mélange granulaire, comprenant :
  • a- au moins 90%, de préférence de 96 à 99%, en poids de grains, lesdits grains étant principalement composés d'au moins un oxyde minéral, et au moins 80% desdits grains ayant une taille de 10 à 3000 µm,
  • b- de 0,3 à 3%, de préférence de 0,6 à 1,5%, en poids d'au moins une résine polycondensée avec du formaldéhyde et/ou ses dérivés, le pourcentage étant calculé en extrait sec de résine,
  • c- de 0,001 à 3%, de préférence de 0,005 à 1%, en poids d'au moins un agent durcisseur, le pourcentage étant calculé en extrait sec d'agent durcisseur,
  • d- de 0,003 à 1%, de préférence de 0,01 à 0,15%, en poids d'au moins un composé capteur de formaldéhyde, et
  • f- de 0,2 à 3%, de préférence de 0,7 à 2%, en poids d'eau;
• la mise en contact dudit mélange granulaire avec au moins une surface d'un outil de formage, et
• l'insufflage dans le mélange granulaire d'au moins un flux de gaz à une température de 50°C à 380°C, pour une durée comprise de 1 à 300 secondes, pour assurer au moins partiellement le durcissement dudit mélange.
• de 0,003% à 1,5%, de préférence de 0,15% à 1%, en poids d'au moins une résine choisie dans le groupe formé par les tanins, les polyphénols naturels, et les lignines ;

Ledit procédé étant caractérisé en ce que la résine polycondensée (composant b-) dudit mélange est modifiée :

• Soit par la présence d'un composant e- dans le mélange, à une teneur de 0,003% à 1,5%, de préférence de 0,15% à 1%, en poids par rapport au poids total du mélange, d'au moins une résine choisie dans le groupe formé par les tanins, les polyphénols naturels, et les lignines,
• Soit par la présence lors de sa synthèse d'un composé comprenant au moins une unité phénolique et/ou polyphénolique, à une teneur de 1 à 30 % en poids par rapport au poids total de la résine polycondensée.

The present invention relates to a method for producing a body, preferably a casting mold and / or core, said method comprising at least the following successive steps:

• the preparation of a granular mixture, comprising:
  • a- at least 90%, preferably from 96 to 99% by weight of grains, said grains being composed mainly of at least one inorganic oxide, and at least 80% of said grains having a size of 10 to 3000 microns,
  • b- from 0.3 to 3%, preferably from 0.6 to 1.5%, by weight of at least one polycondensed resin with formaldehyde and / or its derivatives, the percentage being calculated as solids content of resin,
  • c- from 0.001 to 3%, preferably from 0.005 to 1% by weight of at least one curing agent, the percentage being calculated as solids curing agent,
  • d- from 0.003 to 1%, preferably from 0.01 to 0.15%, by weight of at least one formaldehyde-sensing compound, and
  • f- from 0.2 to 3%, preferably from 0.7 to 2% by weight of water;
• contacting said granular mixture with at least one surface of a forming tool, and
• blowing into the granular mixture at least one gas stream at a temperature of 50 ° C to 380 ° C, for a period of from 1 to 300 seconds, to at least partially cure said mixture.
• from 0.003% to 1.5%, preferably from 0.15% to 1%, by weight of at least one resin selected from the group consisting of tannins, natural polyphenols, and lignins;

Said method being characterized in that the polycondensed resin (component b -) of said mixture is modified:

• Either by the presence of a component e- in the mixture, at a content of 0.003% to 1.5%, preferably from 0.15% to 1%, by weight relative to the total weight of the mixture, from less a resin selected from the group consisting of tannins, natural polyphenols, and lignins,
• Or by the presence during its synthesis of a compound comprising at least one phenolic unit and / or polyphenol, at a content of 1 to 30% by weight relative to the total weight of the polycondensed resin.

It is thus possible according to the invention to modify the resin by one and / or the other of the two possibilities described above: presence of a component e- and / or presence of a compound comprising at least one unit phenolic and / or polyphenolic during the synthesis of the resin. At a minimum, one must both possibilities are present, but both possibilities can be present (simultaneously).

Thus, according to the invention, the polycondensed resin with formaldehyde and / or its derivatives (component b -) is modified by the presence of aromatic and / or polyaromatic groups in the mixture.

The polycondensed resin with formaldehyde and / or its derivatives (component b -) is preferably a furanic resin, an aminoplast, a phenoplast or a copolymer of at least two of these three compounds.

The formaldehyde sensor (component d -) is generally, according to the invention, a compound of the family of hydrazides, preferably chosen from the group formed by mono and dihydrazides, the said sensor being even more preferably the dihydrazide of the acid. adipic acid, succinic acid dihydrazide, or carbohydrazide. In a particularly preferred manner, the formaldehyde sensor is carbohydrazide.

The resin selected from the group consisting of tannins, natural polyphenols, and lignins (component e -) is preferably a tannin type resin, more preferably a condensed tannin type resin.

In the case, the component e) is a resin by itself, and is generally added to the component b) premix (such a diluent if the two components are liquid). Its presence modifies the behavior of the polycondensed resin (component b), which is therefore a "modified" resin during its use) in the mixture during the implementation of the process according to the invention.

According to the invention, it is possible to add components b), c) d) and f), and possibly e) to component a) separately (ie each component b), c) d) and f) and optionally e) is added one by one to the component a), or by at least one premix. Thus, it is possible to premix the components b) and e); or b), e) and f); or c) and e); or c), e) and f); or d) and e); or d), e) and f); or b) and f); or b), c) and f); or b) c) d) and f); and then mixing this premix with at least component a). In addition, the component f), which is water, may be previously incorporated, in whole or in part, at least one of the other components.

The blowing step makes it possible to implement at least partially at least one chemical reaction which ensures the at least partial hardening of said mixture.

As is known to those skilled in the art, these steps are generally followed by removal of the substantially solid body from the forming tool.

In a particularly advantageous manner, the process according to the invention makes it particularly possible, in the case of the use of the body thus obtained for cast iron casting, to reduce the production of formaldehyde during the reaction, to reduce the nitrogen content generated. in the formed body, to enrich the formed body in carbon and to improve the thermal resistance during the process.

Of course, the granular mixture may comprise any other additive known to those skilled in the art. In particular the granular mixture may comprise any additive, liquid or powder, known to those skilled in the art to promote the physico-chemical behavior of the mixture during its processing and its subsequent use.

The grains of the granular mixture according to the invention are generally natural or synthetic. Preferably, the grains are grains of inorganic oxide (s), most often natural siliceous sandy mixtures whose grains are composed mainly of silicon oxide and whose particle size AFS (acronym for " American Foundry Society"). Can range from 30 to 140.

The water is generally provided in the granular mixture mainly as a solvent of components b) to d), optionally e), of the granular mixture.

Indeed, insofar as the curing agent is generally incorporated at a very low level in the granular mixture, its dispersion is improved if it is previously diluted in aqueous solution. It is the same for the formaldehyde sensor and the component e), if it is provided in powder form.

The granular mixture according to the invention is generally in the form of at least one fluid aggregate.

The surface of the forming tool with which the granular mixture is in contact generally represents the "negative" of the part to be formed in the body manufactured according to the invention.

The step of blowing a flow of hot gas is generally such that the temperature and the flow rate of said flow are adjusted to cause the temperature rise in the heart of the granular mixture, substantially above ambient temperature (which is about 20 ° C) and preferably above 45 ° C.

The process according to the invention, by the presence in the granular mixture of at least one formaldehyde sensor and a modified polycondensed resin, advantageously makes it possible to significantly improve the thermal properties of the granular mixture and to limit the emission of formaldehyde free when performing formed bodies. In addition, the presence of a modified polycondensed resin makes it possible to significantly improve the thermal properties and to reduce the nitrogen content of the bodies formed. These characteristics make the use of the body thus obtained particularly advantageous for the casting of cast iron parts and in particular adaptable to the foundry mass production.

Preferably, the method according to the invention is such that, in addition, the forming tool is heated to a temperature in the range of 40 ° C to 180 ° C, preferably 50 ° C to 150 ° C. This is generally done in the contacting step, and at the latest during the blowing step.

Thus, the heat provided by the hot gas is supplemented by the heat of heating of the forming tool, so as to optimize, in a preferred version of the invention, the heating of the granular mixture.

The gas is preferably selected from the group consisting of air, a neutral gas and a gas involved in the acidification of the reaction medium.

According to the invention, the term "neutral gas" means a gas which does not participate in the reaction, for example chosen from dinitrogen and the so-called noble gases such as helium, neon and argon. By "gas involved in the acidification of the reaction medium" is meant according to the invention a gas for decreasing in situ the pH of the medium such as carbon dioxide or sulfur dioxide.

In a preferred embodiment of the invention, the method also comprises an additional step during which a stream of at least one gas is circulated within the at least partially hardened granular mixture at a temperature within a range of 5 ° C to 45 ° C, for a time in a range of 1 to 300 seconds, the gas being preferably selected from the group consisting of air, nitrogen and carbon dioxide. This step is most often carried out before the optional step of removing the body from the forming tool. The gas is usually not previously heated, and therefore substantially at room temperature, or possibly cooled.

Indeed, since the nuisance of formaldehyde can be exerted after the manufacture of the body during storage or subsequent handling, it is very useful and advantageous in the context of the invention to complete the action of the sensor. formaldehyde by blocking the polymerization reaction of the modified polycondensed resin by cooling the body after partial curing. In addition, this flow of gas advantageously makes it possible to wash with a flow of air, of nitrogen or of carbon dioxide, the free formaldehyde which may be residual.

The term polycondensed resin or polycondensed resin with formaldehyde and / or its derivatives, a composition of at least one resin having undergone a chemical reaction between a first element selected from urea and its derivatives, melamine, benzoguanamine, glycoluril, phenol and / or its derivatives, and furfuryl alcohol and / or its derivatives, and a second element selected from formaldehyde and / or its derivatives, wherein preferably the chain growth generally causes at each stage the release of a molecule of water.

This polycondensed resin is generally a thermosetting polymer, such as a furan resin or an aminoplast or a phenoplast or a copolymer of these compounds, preferably an aminoplast or a phenoplast or an aminoplast-phenoplast copolymer.

The aminoplasts are obtained by polycondensation of the first comonomer which is formaldehyde and the second comonomer carrying amino groups NH ₂ -. They are usually divided into two families compounds, namely urea-formaldehyde (or urea-formaldehyde) (UF) and melamine-formaldehyde (or melamine-formaldehyde) resins (MF).

Phenoplasts or phenol-formaldehyde resins (PF) are obtained by polycondensation between a first comonomer that is formaldehyde and a second comonomer that is phenol. There are two types of phenolic resins: novolacs, prepared by acid catalysis, and the resols, obtained by basic catalysis. The best known phenoplast is bakelite ^® (or polyoxybenzylmethylene glycol anhydride), which is the oldest industrial synthetic polymer material.

The furanic resin is obtained by polycondensation of the first comonomer furfuryl alcohol and the second comonomer is formaldehyde.

The component (s) of the polycondensed resin may remain free in excess in the polycondensed resin, or may have been added thereto after the polycondensation.

The polycondensed resin with formaldehyde and / or its derivatives is generally such that it thermosets in acidic medium. Such a polycondensed resin is generally commercially available.

The polycondensed resin may, according to the invention, be modified by the presence during its synthesis of a compound comprising at least one phenolic and / or polyphenolic unit, at a content of 1 to 30% by weight, preferably from 5 to 20% by weight, relative to the total weight of the modified polycondensate resin. This is not the polycondensed resin described in the French patent application FR 2948307 . Indeed, it comprises groups which are derived from the precursor groups that are the phenolic units and / or polyphenolic, preferably present in a compound such as vanillin and phloroglucinol. This compound is generally mixed with the resin prior to its synthesis and the derived groups "hang" on the resin during its synthesis.

The polycondensed resin may thus have been premixed with a compound, most often synthetic, such as vanillin or phloroglucinol. In this case, the presence in the granular mixture used in the process according to the invention a component e) according to the invention, ie the resin selected from the group formed by tannins, natural polyphenols, and lignins, is optional.

The phenolic and / or polyphenolic unit may be of natural or synthetic origin. The resin is thus in the form of a formophenolic copolymer. In the context of this embodiment, it is particularly preferred that the phenolic and / or polyphenolic unit be present in a compound selected from the group consisting of vanillin (4-hydroxy-3-methoxybenzaldehyde) and phloroglucinol (benzene- 1,3,5-triol).

The polycondensed resin with formaldehyde and / or its derivatives according to the invention may also optionally contain at least one additive chosen from solvents, diluents, stabilizers and solid particle fillers, which are usually used and known to those skilled in the art to obtain a particular effect. Thus, said polycondensed resin may contain at least one silane, which generally makes it possible to bridge, and thus optimize, the bond between the resin and the grains.

The resin selected from the group consisting of tannins, natural polyphenols, and lignins, is a natural polymer rich in aromatic rings (ie having at least two aromatic rings). In reality, this resin contains at least one aromatic nucleus per monomer unit of the polymer, thus a plurality of aromatic nuclei. This resin is chosen according to the invention from the group formed by tannins, which are generally of natural origin, preferably condensed and / or modified to make them soluble in water, such as extracts from the Quebracho tree, natural polyphenols, such as those extracted from araucaria angustifolia (Paraná pine) or pinus palustris (swamp pine), and lignins, modified or not.

The resin selected from the group formed by tannins, natural polyphenols, and lignins, is most often renewable. The term "renewable resin" means, according to the invention, either a natural resin whose stock can be reconstituted over a short period on a human scale, or a synthetic resin whose main synthetic starting materials are renewable components; in theory renewal must be done at least as fast as consumption.

In a preferred embodiment, the resin selected from the group consisting of tannins, natural polyphenols, and lignins, is a tannin-type resin, and even more preferably it is a condensed tannin-type resin.

The tannin type resin is usually a natural phenolic substance. It is usually a secondary metabolite of superior plant that is found practically in all parts of plants (bark, roots, leaves, stems, etc.). The tannins are polyphenol natural resins either monosaccharide type polyols and galloyl units or derivatives thereof, linked to flavonoids or triterpenoids, or oligomers or flavanol polymers. Preferably, the tannins used according to the invention are polyflavonoids, for example of the tannin type of the Quebracho tree.

Lignins are polymers based on one or more monolignols, such as paracoumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The lignins may, for example, be modified to lignosulphonates by reactions with bisulphites.

The resin selected from the group consisting of tannins, natural polyphenols, and lignins, may also be a thermoplastic resin, for example, an extract of araucaria angustifolia (Paraná pine) or pinus palustris (swamp pine).

The resin selected from the group consisting of tannins, natural polyphenols, and lignins, can be composed of long-chain aliphatic phenols such as cashew nut shell extract.

Thus, the resin selected from the group formed by tannins, natural polyphenols, and lignins, may be a commercial compound such as the following commercial products: Respine RLP from the company POLYTRADE (natural aromatic resin derived from araucaria angustifolia ); VINSOL ^® from HERCULES (consisting of approximately 57% polyphenols, 28% rosin and 15% terpenoid); QSF (alcohol-soluble part of tannins de Quebracho), FINTAN 737B (modified condensed tannin from Schinopsis lorentzii or Quebracho colorado powder) and FINTAN 737C (stabilized condensed tannin from Schinopsis lorentzii or Quebracho colorado in 45% solution) from INDUNOR; and CARDANOL (long-chain aliphatic phenols from cashew shells) from SAI CHEMICALS.

• les sels naturellement acides, tels que les sels d'ammonium, notamment les persulfates, les nitrates, les bisulfates, les sulfates et les chlorures ;
• les sels générant un acide par réaction avec un aldéhyde, tels que les sels d'hydroxylamine, notamment les sulfates, les chlorhydrates, les phosphates, les sulfonates et les nitrates d'hydroxylamine ;
• les acides sublimables, notamment l'acide oxalique et l'acide benzoïque ; et, éventuellement,
• les acides organiques compatibles avec le procédé au regard de leur réactivité et de leur toxicité, comme par exemple l'acide lactique et l'acide citrique.

The curing agent is generally selected from the group consisting of the following compounds:

• naturally acidic salts, such as ammonium salts, especially persulfates, nitrates, bisulphates, sulphates and chlorides;
• salts generating an acid by reaction with an aldehyde, such as hydroxylamine salts, especially sulphates, hydrochlorides, phosphates, sulphonates and hydroxylamine nitrates;
• sublimable acids, especially oxalic acid and benzoic acid; and eventually,
• organic acids compatible with the process with regard to their reactivity and toxicity, such as lactic acid and citric acid.

The curing agent is more generally such that it renders the reaction medium of the acid mixture, either by its own acidity, or by its ability to release acid during the polymerization process.

Particularly preferably, the curing agent is selected from the group consisting of hydroxylamine salts, and even more preferably, the curing agent is hydroxylamine sulfate. The hydroxylamine salts advantageously release an acid in the presence of formaldehyde.

In the preferred case where the curing agent is a hydroxylamine salt, it surprisingly appears according to the invention that the free formaldehyde available combines primarily with this hydroxylamine salt to release an acid, and that the formaldehyde sensor does not inhibit or little acid formation by said salt during the curing reaction.

In addition, the Applicant has found that the use of hydroxylamine salt significantly and advantageously improves the process according to the invention, by accelerating the hardening kinetics and by increasing the acidity of the reaction medium as the thermosetting reaction releases formaldehyde.

In addition, the addition of the formaldehyde sensor significantly improves the mechanical characteristics of the formed bodies.

Those skilled in the art are able to choose the resins b) and e), as well as the curing agent, which are suitable for the case which concerns it, in particular taking into account the reactivity of the binder system, that is to say that is, the resin (s) and hardening agent (s) incorporated in the granular mixture.

The production of the granular mixture according to the first step of the process of the invention is generally carried out in a manner known to those skilled in the art. Thus, conventionally, in the presence of conventional mixing equipment, those skilled in the art first introduce the granular part or parts into a mixer and then proceed to the introduction of liquid parts, the mixing time being a function of the material and preferably from 15 s to 5 min.

The invention particularly relates to a method of manufacturing a casting piece of metal, or metal alloy, molded, which comprises casting a metal, or metal alloy, liquid in at least one mold and / or core, characterized in that said mold is a body obtained by the process according to the invention as described above.

Preferably, such a method is such that the metal, or metal alloy, is selected from the group formed by aluminum, the ferrous alloys selected from the group consisting of steels and cast irons, non-ferrous metals, non-alloys ferrous, and, more preferably, the metal or metal alloy is selected from the group formed by the fonts.

The invention also relates to any molded metal part obtained by a manufacturing method as described above. The invention further relates to any mechanical assembly comprising at least one such piece.

The invention is illustrated by the Figure 1 attached, which is commented on in the examples below.

The Figure 1 represents curves A, B, C, D and E passing P (in percentage) as a function of time t (in minutes) for five different resins described in the examples, that is to say that each curve represents the percentage passing as a function of time for the resin concerned. This makes it possible to evaluate the thermal resistance.

The invention will be better understood in light of the following examples which illustrate the invention by way of non-limiting example.

Examples

The following examples were carried out by mixing each time 4 kg of SIFRACO LA 32 siliceous sand with the other components in the proportions indicated for each granular mixture.

For each example, a premix was made comprising mainly the polycondensed resin (component b) and optionally a resin selected from the group consisting of tannins, natural polyphenols, and lignins (component e)), and a second premix a was performed comprising the curing agent (component c)) and optionally a formaldehyde sensor compound (component d)). Water was generally present in these two premixes. Then, the granular mixture was made by mixing the siliceous sand, the first premix and the second premix. This granular mixture was carried out in a vibratory bowl mixer with a mixing time of 60 seconds. The granular mixture was then blown into a box equipped with a heating system and a supply of hot air (at 100-120 ° C) under a pressure of 1.5 bar (0.15 MPa), for a period of 60 seconds, containing two test pieces of standardized mechanical characteristics of square section 5 cm ² , on a ROPER machine.

Curing was performed according to the data indicated for each granular mixture.

The measurement of formaldehyde during mixing was carried out using the DRAGER model Accuro pump equipment equipped with DRAGER "formaldehyde" dosing tubes (0.2 / a). The range of measurements is 0.2 to 5 ppm. The measurements were made above the vibrating bowl of the mixer.

The formaldehyde removal measurement was carried out using the DRAGER model Accuro pump equipment fitted with DRAGER "formaldehyde" dosing tubes (0.2 / a or 2 / a), depending on the concentration to be measured in a 10 liter chamber in which circulated a flow of nitrogen of 0.5 L / min. A test tube was placed in the enclosure as soon as it came out of the box. The assay tube was used to measure formaldehyde in the enclosure air for 180 seconds. The results are given as such for the tube 0.2 / a (n = 20 strokes), and are multiplied by 4 for the tube 2 / a (n = 5 strokes).

All incorporation rates are percentages by weight.

The bending measurements were carried out according to the technical recommendations n ° 481 and 487 of December 1999 of the BNIF published and available from the Technical Center of the Foundry Industries located in Sèvres in France. The results are expressed in daN / cm ² .

It is considered that flexural strengths of about 10 daN / cm ² when hot from the outlet of the box are sufficient to allow the handling of the bodies formed, and that resistances of about 30 daN / cm ² when cold, either an hour after leaving the box, are often satisfactory to allow the casting of the metal.

The flexural strengths were measured both hot and cold after a cooking time of 15 seconds, 30 seconds, 60 seconds and 120 seconds in a can.

The detection at the end of dislocation (or extraction) of a content of formaldehyde (free) more than 20 times lower than the conventional hot box process is considered to make the shaped body suitable for industrial use.

The dry extract expressed in% by weight is the residue produced after heating one gram of product at 135 ° C. for one hour.

The test pieces obtained are solid formed bodies that can be assimilated to nuclei.

• Des corps moulés de forme parallélépipédique de section carrée 5 cm² ont été confectionnés. Les corps moulés ont ensuite été laissés 24 heures au repos.

The rate of disintegration of the granular body at 450 ° C was measured under the following conditions:

• Molded bodies of parallelepipedal shape of square section 5 cm ² were made. The molded bodies were then left for 24 hours at rest.

These cubes were then made into cubes adjusted to 23.5 g (± 0.5 g) per cube, omitting to use the ends of the moldings.

The cubes were placed separately in crucibles closed by a lid. The crucibles were spotted.

The crucibles were then placed in a muffle furnace regulated at 450 ° C, a timer having been triggered when the oven was closed.

The crucibles were taken out of the oven at regular intervals (eg 5-10-20-30-40 minutes ...) and allowed to cool to room temperature.

The contents of each crucible were then placed on a 1 mm mesh screen, and vibrated by a Retsch brand VS1000 laboratory sieve for 30 seconds.

The pass-through portion was recovered, weighed and the resulting mass converted to percent.

This measurement, which is representative of the heat resistance of the polycondensed resin, is given on the attached curve ( Figure 1 ) which illustrates the part P (in percentage) of formed body passing through the sieve as a function of time t (in minutes), maintenance in the oven for five different resins exemplified. The respective curves of these five resins are the curves A, B, C, D and E present on the diagram of the Figure 1 which shows the thermal behavior of five of the exemplified resins.

It is estimated that a percentage of formed body passing through the sieve, under these test conditions, less than 50%, after twenty minutes, allows the casting of cast iron parts.

Example 1 (comparative)

• Resin: Urea-formaldehyde resin, Cleantech 11 R26 commercial product, synthesized in an acidic medium with a formaldehyde / urea molar ratio of 2.37 (used at 2.0% relative to sand)
• Catalyst: Cleantech 14D38 commercial product from Hüttenes Albertus France containing 3% hydroxylamine sulfate, 15% carbohydrazide and 82% water (used at 0.4% relative to sand)

• Temperature box: 130 ° C
• Hot air temperature: 100-120 ° C

• Hot bending resistance at the box outlet: at 30, 60 and 120 seconds respectively: 18, 32 and 55 daN / cm ²
• Cold bending resistance, respectively 30, 60 and 120 seconds: 72, 80 and 72 daN / cm ²

• Formaldéhyde au malaxage : inférieur à 0,2 ppm (non détectable)
• Formaldéhyde au déboîtage : valeur comparative 0,2

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.

• Formaldehyde with mixing: less than 0.2 ppm (not detectable)
• Formaldehyde on release: comparative value 0.2

Formaldehyde emissions at mixing and disbudding are extremely low (at debugging approximately 600 times lower than the hot box process represented by Example 3).
% passing (P) at 20 minutes: 79% (see Curve A of the Figure 1 )

The thermal resistance, expressed by this percentage, is incompatible with the casting of cast iron casting parts.

Example 2 (comparative)

• Resin: Resin urea-melamine / formalin referenced FUM274 synthesized with a formaldehyde / urea molar ratio of 2.95 and a formaldehyde / melamine molar ratio of 3.45 (used at 2% relative to sand)
• Catalyst: referenced UFAC 12/268 containing (20%) hydroxylamine sulfate and (80%) water (used at 0.4% relative to sand)

• Box temperature: 120 ° C
• Hot air temperature: 100-120 ° C

• Hot bending resistance at the box outlet: at 30, 60 and 120 seconds respectively: 17, 24 and 44 daN / cm ²
• Cold bending strength at 30, 60 and 120 seconds respectively: 72, 70 and 53 daN / cm ²
• Formaldehyde with mixing: 1 ppm

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.
Formaldehyde in Deboxage: Comparative Value 80

Formaldehyde emissions during mixing and disbudding are high and problematic.
% passing (P) at 20 minutes: 37% (see curve C of the Figure 1 )

The thermal resistance, expressed by this percentage, is sufficient for the casting of cast iron casting parts.

Example 3 (comparative)

Resin: Urea-phenol / formaldehyde resin, commercial product Resital 12B62 from Hüttenes Albertus France.

This resin is characteristic of the "hot box" process, and was used at 2% compared to sand.

Catalyst: Commercial product Harter AT3B from Hüttenes Albertus France (50% magnesium lignosulfonate solution), urea and ammonium nitrate.

This catalyst was used at 0.5% with respect to the sand.

This resin is characteristic of the "hot box" process used in cast iron foundries.
Box temperature: 220 ° C

Hot bending resistance at the box outlet: at 30, 60 and 120 seconds respectively: 34, 51 and 61 daN / cm ²
Cold bending strength at 30, 60 and 120 seconds respectively: 70, 70 and 59 daN / cm ²

• Formaldéhyde au malaxage : 1 ppm
• Formaldéhyde au déboîtage : valeur comparative 120

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.

• Formaldehyde with mixing: 1 ppm
• Formaldehyde at the disposal: comparative value 120

Formaldehyde emissions during mixing and disintegration are incompatible with changes in hygiene and safety standards.

Example 4 (according to the invention)

Resin: Urea-formaldehyde resin comprising vanillin, which has been synthesized in an acidic medium with a formaldehyde / urea mole ratio of 2.37, and to which vanillin has been added in a molar ratio of urea to vanillin of 4, 5.

The vanillin content with respect to the resin is 11.3% by weight.

This resin was used at 2% relative to sand.
Catalyst: Catalyst consisting of 1.4% hydroxylamine in 50% solution, 1.7% p-toluenesulphonic acid in 65% solution, 15.1% carbohydrazide, 2.2% hydroxylamine sulfate and 79.7% water.

• Température Boîte : 120°C
• Température d'air chaud : 100-120°C

This catalyst was used at 0.4% relative to sand.

• Box temperature: 120 ° C
• Hot air temperature: 100-120 ° C

Hot bending resistance at the box outlet: at 30, 60 and 120 seconds respectively: 15, 30 and 45 daN / cm ²
Cold bending strength at 30, 60 and 120 seconds respectively: 55, 60 and 65 daN / cm ²

• Formaldéhyde au malaxage : inférieur à 0,2 ppm (non détectable)
• Formaldéhyde au déboîtage : valeur comparative 2,5

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.

• Formaldehyde with mixing: less than 0.2 ppm (not detectable)
• Formaldehyde in the process of deboning: comparative value 2.5

Formaldehyde emissions during mixing and disbudding are low (at debugging approximately 50 times lower than the hot box process represented by Example 3).
% passing (P) at 20 minutes: 43% (see Curve B of the Figure 1 )

The thermal resistance, expressed by this percentage, is considered sufficient for the casting of cast iron casting parts.

Example 5 (according to the invention)

Resin: Urea-melamine / formaldehyde resin, which was synthesized with a formaldehyde / urea molar ratio of 2.95 and to which was added melamine in a formaldehyde / melamine molar ratio of 3.45 then in which was added 3% modified tannin Fintan 737B, commercial product of the company Indunor (modified condensed tannin from Schinopsis lorentzii or Quebracho colorado powder).

This resin was used at 2.2% relative to the sand.
Catalyst: Catalyst containing 14% hydroxylamine sulfate, 20% carbohydrazide and 66% water.

• Température Boîte : 130°C
• Température d'air chaud : 100-120°C

This catalyst was used at 0.3% relative to sand.

• Temperature box: 130 ° C
• Hot air temperature: 100-120 ° C

Hot bending resistance at the box outlet: at 30, 60 and 120 seconds respectively: 15, 24 and 42 daN / cm ²
Bending resistance at 30, 60 and 120 seconds respectively: 75, 84 and 95 daN / cm ²

• Formaldéhyde au malaxage : inférieur à 0,2 ppm (non détectable)
• Formaldéhyde au déboîtage : valeur comparative 2,5

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.

• Formaldehyde with mixing: less than 0.2 ppm (not detectable)
• Formaldehyde in the process of deboning: comparative value 2.5

Formaldehyde emissions during mixing and disbudding are low (at debugging approximately 50 times lower than the hot box process represented by Example 3).
% passing (P) at 20 minutes: 40% (see Curve D of the Figure 1 )

The thermal resistance, expressed by this percentage, is considered sufficient for the casting of cast iron casting parts.

Example 6 (according to the invention)

Resin: Tannin-modified urea / formaldehyde resin, which was synthesized with a formaldehyde / urea molar ratio of 2.37, and in which 25% of modified tannin Fintan 737C, a commercial product of Indunor (stabilized condensed tannin derived from Schinopsis lorentzii or Quebracho colorado in 45% solution).

This resin was used at 2% relative to sand.
Catalyst: Catalyst containing 14% hydroxylamine sulfate, 20% carbohydrazide and 66% water.

• Température Boîte : 130°C
• Température d'air chaud : 100-120°C

• Résistance flexion à chaud en sortie de boîte: respectivement à 15, 30 et 60 secondes : 6, 13 et 21 daN/cm²
• Résistance flexion à froid, respectivement à 15, 30 et 60 secondes : 31, 40 et 45 daN/cm²

This catalyst was used at 0.3% relative to sand.

• Temperature box: 130 ° C
• Hot air temperature: 100-120 ° C

• Hot bending resistance at the box outlet: at 15, 30 and 60 seconds respectively: 6, 13 and 21 daN / cm ²
• Bending resistance at 15, 30 and 60 seconds respectively: 31, 40 and 45 daN / cm ²

• Formaldéhyde au malaxage : inférieur à 0,2 ppm (non détectable)
• Formaldéhyde au déboîtage : valeur comparative 2,5

The hot and cold bending resistances are sufficient to allow, respectively, the manipulation of the formed bodies and the casting of the metal.

• Formaldehyde with mixing: less than 0.2 ppm (not detectable)
• Formaldehyde in the process of deboning: comparative value 2.5

Formaldehyde emissions during mixing and disbudding are low (at debugging approximately 50 times lower than the hot box process represented by Example 3).
% passing (P) at 20 minutes: 50% (see Curve E on the Figure 1 )

The thermal resistance expressed by this percentage is considered sufficient for the casting of cast iron casting parts.

Claims (13)

1. Method for producing a foundry body, preferably a mould and/or core for a foundry piece, said method comprising at least the following successive steps:

   - preparing a granular mixture, comprising, in % weight with respect to the total weight of the mixture:

   a- at least 90%, preferably 96 to 99% by weight of grains, said grains being mainly composed of at least one mineral oxide, and at least 80% of said grains having a size from 10 to 3000 µm,

   b- 0.3 to 3%, preferably 0.6 to 1.5% by weight of at least one resin polycondensed with formaldehyde and/or its derivatives, the percentage being calculated in dry resin solids,

   c- 0.001 to 3%, preferably 0.005 to 1% by weight of at least one curing agent, the percentage being calculated in dry curing agent solids,

   d- 0.003 to 1%, preferably 0.01 to 0.15%, by weight of at least one formaldehyde scavenger compound, and

   f- 0.2 to 3%, preferably 0.7 to 2%, by weight of water;

   - placing said granular mixture in contact with at least one surface of a forming tool, and

   - blowing at least one gas stream into the granular mixture at a temperature of 50°C to 380°C, for a duration comprised from 1 to 300 seconds, in order to ensure at least partial curing of said mixture,

   Said method being characterized in that the polycondensed resin (component b-) of said mixture is modified:

   • Either by the presence of a component e- in the mixture, at a content from 0.003% to 1.5%, preferably from 0.15% to 1%, by weight with respect to the total weight of the mixture, of at least one resin chosen from the group consisting of tannins, natural polyphenols and lignins,

   • Or by the presence during its synthesis of a compound comprising at least one phenolic and/or polyphenolic unit, at a content from 1 to 30% by weight with respect to the total weight of the polycondensed resin.
2. Method according to claim 1, such that the formaldehyde scavenger (component d-) is a compound of the hydrazide family, preferably chosen from the group consisting of the mono- and dihydrazides, even more preferably adipic acid dihydrazide, succinic acid dihydrazide or carbohydrazide, particularly preferably carbohydrazide.
3. Method according to any one of the claims 1 or 2, such that the resin chosen from the group consisting of tannins, natural polyphenols and lignins (component e)) is a resin of the tannin type, preferably a resin of the condensed tannin type.
4. Method according to any one of claims 1 to 3, such that the forming tool is heated to a temperature comprised within a range from 40 to 180°C, preferably from 50 to 150°C.
5. Method according to any one of claims 1 to 4, such that said gas is chosen from the group consisting of air, an inert gas and a gas contributing to the acidification of the reaction medium.
6. Method according to any one of claims 1 to 5, comprising an additional step, during which a stream of at least one gas is circulated within the at least partially cured granular mixture, at a temperature comprised within a range from 5°C to 45°C, for a duration comprised within a range from 1 to 300 seconds, the gas being preferably chosen from the group consisting of air, dinitrogen and carbon dioxide.
7. Method according to any one of claims 1 to 6, in which the resin polycondensed with formaldehyde and/or its derivatives is a composition of at least one resin having undergone a chemical reaction between a first element chosen from urea and its derivatives, melamine, benzoguanamine, glycoluril, phenol and/or its derivatives, and furfuryl alcohol and/or its derivatives, and a second element chosen from formaldehyde and/or its derivatives.
8. Method according to any one of claims 1 to 7, such that the phenolic and/or polyphenolic unit is present in a compound chosen from the group consisting of the vanillin (4-hydroxy-3-methoxybenzaldehyde) and phloroglucinol (benzene-1,3,5-triol).
9. Method according to any one of claims 1 to 8, in which the resin chosen from the group consisting of tannins, natural polyphenols and lignins is chosen from the group consisting of tannins, preferably condensed and/or modified in order to render them soluble in water, such as extracts of the Quebracho tree, polyphenols, such as for example those extracted from araucaria angustifolia (Paraná pine) or from pinus palustris (longleaf pine), and the lignins, modified or not.
10. Method according to any one of claims 1 to 9, in which the curing agent is chosen from the group consisting of the following compounds:

    - naturally acid salts such as ammonium salts, in particular persulphates, nitrates, bisulphates, sulphates and chlorides;

    - salts generating an acid by reaction with an aldehyde, such as hydroxylamine salts, in particular hydroxylamine sulphates, hydrochlorides, phosphates, sulphonates and nitrates.

    - sublimable acids, in particular oxalic acid and benzoic acid; and, optionally,

    - organic acids compatible with the method with the regard to their reactivity and their toxicity, such as for example lactic acid and citric acid.

    the curing agent being preferably chosen from the group consisting of hydroxylamine salts, and even more preferably, the curing agent is hydroxylamine sulphate.
11. Method for the production of a cast metal, or metal alloy, foundry piece, which comprises pouring a liquid metal or metal alloy into at least one mould and/or core, characterized in that said mould and/or core is a solid body obtained by the method according to one of claims 1 to 10.
12. Method according to claim 11, such that said metal, or metal alloy, is chosen from the group consisting of aluminium, ferrous alloys chosen from the group consisting of steels and cast irons, non-ferrous metals, non-ferrous alloys, and preferably, said metal or metal alloy is chosen from the group consisting of the cast irons.
13. Cast metal part obtained by a production method according to one of claims 11 or 12.

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