Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
  • B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
  • B22C1/2233—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B22C1/224—Furan polymers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
  • B22C1/10—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for influencing the hardening tendency of the mould material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
  • B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/20—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents
  • B22C1/22—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins
  • B22C1/2233—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of organic agents of resins or rosins obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • B22C1/2246—Condensation polymers of aldehydes and ketones
  • B22C1/2253—Condensation polymers of aldehydes and ketones with phenols

Definitions

• the invention relates to a process for the production of cores and molds for the foundry industry and to a molding material mixture as used in the process.
• Molds for the production of metal bodies are composed of so-called cores and molds.
• the casting mold essentially represents a negative mold of the casting to be produced, wherein cores serve to form cavities in the interior of the casting, while the molds form the outer boundary.
• Different requirements are placed on the cores and molds.
• a relatively large surface area is available to dissipate gases that form during casting by the action of the hot metal.
• cores usually only a very small area is available, through which the gases can be derived. If there is too much gas, there is a risk that gas will transfer from the core into the liquid metal and there to form casting defects leads.
• the internal cavities are therefore imaged by cores solidified by cold-box binders, a polyurethane-based binder, while the outer contour of the casting is represented by lower cost forms, such as a green sand mold, a furan resin mold. or a phenol resin bound form or by a steel mold.
• Casting molds are made of a refractory material, such as quartz sand, whose grains are connected after molding of the mold by a suitable binder to ensure sufficient mechanical strength of the mold.
• a refractory molding material which is mixed with a suitable binder.
• the molding material mixture obtained from molding material and binder is preferably present in a free-flowing form, so that it can be filled into a suitable mold and compacted there.
• the binder produces a firm cohesion between the particles of the molding base material, so that the casting mold obtains the required mechanical stability.
• both organic and inorganic binders can be used, the curing of which can be effected by cold or hot processes.
• Cold processes are processes which are carried out essentially at room temperature without heating the molding material mixture.
• the curing is usually carried out by a chemical reaction, which can be triggered, for example, by passing a gaseous catalyst through the molding material mixture to be cured, or by adding a liquid catalyst to the molding material mixture.
• hot processes the molding material mixture is heated after molding to a sufficiently high temperature, for example, in the Drill binder contained solvents or to initiate a chemical reaction by which the binder is cured by crosslinking.
• organic binders e.g. Polyurethane, furan resin or epoxy-acrylate binders used in which the curing of the binder is carried out by adding a catalyst.
• binder depends on the shape and size of the casting to be produced, the conditions of production and the material used for the casting. For example, in the production of small castings that are produced in large numbers, polyurethane binders are often used because they allow fast cycle times and thus also a series production.
• Processes in which the curing of the molding material mixture by heat or by subsequent addition of a catalyst have the advantage that the processing of the molding material mixture is not subject to any special time restrictions.
• the molding material mixture can first be produced in larger quantities, which are then processed within a longer period of time, usually several hours.
• the curing of the molding material mixture takes place only after molding, with a rapid reaction is sought.
• the mold can be removed immediately after curing from the mold so that short cycle times can be realized. However, in order to obtain a good strength of the mold, the curing of the molding material mixture must be uniform within the mold. If the curing of the molding material mixture by subsequent addition of a catalyst, the mold is gassed after molding with the catalyst. For this purpose, the gaseous catalyst is passed through the casting mold.
• the molding material mixture hardens immediately after contact with the catalyst and can therefore be removed very quickly from the mold.
• the gassing times are prolonged, but can still arise sections in the mold, which are achieved very poorly or not at all by the gaseous catalyst.
• the amount of catalyst therefore increases sharply with increasing size of the mold.
• no-bake binders are used mostly.
• the refractory base molding material is first coated with a catalyst.
• the binder is added and distributed evenly by mixing on the already coated with the catalyst grains of the refractory base molding material.
• the molding material mixture can then be shaped into a shaped body. Since binder and catalyst are evenly distributed in the molding material mixture, the curing is largely uniform even with large moldings.
• the reaction rate can be influenced for a given amount of the binder and the refractory base molding material, for example, by the type and amount of the catalyst or by the addition of retarding components.
• the processing of the molding material mixture must be carried out under very controlled conditions, since the rate of curing is influenced, for example, by the temperature of the molding material mixture.
• the classic no-bake binders are based on furan resins and phenolic resins. They are offered as two-component systems, one component comprising a reactive furan resin and the other component an acid which acts as a catalyst for the curing of the reactive resin component.
• Furan and phenolic resins show very good disintegration properties during casting. Under the action of heat of the liquid metal, the furan or phenolic resin decomposes and the strength of the mold is lost. After casting, therefore, cores, possibly after prior shaking of the casting, pour out very well from cavities.
• furfuryl alcohol as an essential component.
• Furfuryl alcohol can react with itself under acid catalysis and form a polymer.
• furfuryl alcohol can react with itself under acid catalysis and form a polymer.
• furfuryl alcohol can react with itself under acid catalysis and form a polymer.
• furfuryl alcohol can react with itself under acid catalysis and form a polymer.
• furfuryl alcohol can react with itself under acid catalysis and form a polymer.
• furfuryl alcohol is generally not pure furfuryl alcohol used but added to the furfuryl alcohol further compounds which are polymerized into the resin. Examples of such compounds are aldehydes, such as formaldehyde or furfural, ketones, such as acetone, phenols, urea or even polyols, such as sugar alcohols or ethylene glycol.
• the resins may be added with other components that affect the properties of the resin, such as its elasticity. Melamine can be added, for example, to
• Furan no-bake binders are most often prepared by first producing furfuryl-containing precondensates from, for example, urea, formaldehyde, and furfuryl alcohol under acidic conditions. The reaction conditions are chosen so that only a slight polymerization of furfuryl alcohol occurs. These precondensates are then diluted with furfuryl alcohol.
• Resoles can also be used to prepare furan no-bake binders. Resoles are prepared by polymerization of mixtures of phenol and formaldehyde. These resoles are then diluted with furfuryl alcohol.
• the second component of the furan no-bake binder forms an acid.
• this acid neutralizes alkaline components which are contained in the refractory molding material and, on the other hand, catalyzes the crosslinking of the reactive furan resin.
• acids mostly aromatic sulfonic acids and in some special cases also phosphoric acid or sulfuric acid are used.
• Phosphoric acid is used in concentrated form, ie at concentrations greater than 75%.
• Sulfuric acid can be added as a relatively strong acid starter for the curing of furan resins to weaker acids.
• a smell typical of sulfur compounds develops.
• there is a risk that the casting material sulfur is absorbed, which affects its properties.
• aromatic sulfonic acids are used as catalysts. Because of their good availability and their high acidity especially toluene sulfonic acid, xylylene sulfonic acid and benzenesulfonic acid are used.
• the choice of catalyst has a great influence on the properties of the binder.
• the rate of curing can be influenced by the amount of acid and by the strength of the acid. Higher amounts of acid or stronger acids lead to an increase in the curing rate.
• the furan resin becomes brittle upon curing, which adversely affects the strength of the mold.
• the resin is not completely cured or the curing takes a long time which leads to a lower strength of the mold.
• Phenolic resins as the second large group of acid-catalyzed curable no-bake binders contain resoles as reactive resin components, ie phenolic resins which have been prepared with an excess of formaldehyde. Phenol resins show a significantly lower reactivity compared to furan resins and require strong sulfonic acids as catalysts. Phenolic resins show a relatively high viscosity, which is still with longer storage of the resin increases. Especially at temperatures below 20 ° C, the viscosity increases sharply, so that the sand must be heated in order to apply the binder evenly on the surface of the grains of sand can.
• the molding compound After the phenol no-bake binder has been applied to the refractory base molding material, the molding compound should be processed as promptly as possible so as not to suffer deterioration in the quality of the molding compound due to premature curing, resulting in deterioration of the strength of the molding compound mixture produced molds can lead.
• the flowability of the molding material mixture is usually poor. In the production of the mold, the molding material mixture must therefore be carefully compacted in order to achieve a high strength of the mold can.
• the preparation and processing of the molding material mixture should be carried out at temperatures in the range of 15 to 35 ° C. If the temperature is too low, the molding material mixture is difficult to process because of the high viscosity of the phenol no-bake resin. At temperatures of more than 35 ° C, the processing time is shortened by premature curing of the binder.
• molding mixtures based on phenol no-bake binders can also be worked up again, in which case mechanical or thermal or combined mechanical / thermal processes can also be used.
• the acid used as catalyst in the case of furan or phenol no-bake processes has a very great influence on the properties of the casting mold.
• the acid must have sufficient strength to ensure a sufficient rate of reaction in the curing of the mold.
• the curing must be well controllable, so that also sufficiently long processing times can be set. This is especially for the production of molds for very large Castings important, whose construction requires a longer period.
• the acid must not accumulate in the regeneration of the regeneration of old sands. If acid is introduced into the molding material mixture via the regenerate, this shortens the processing time and leads to a deterioration in the strength of the casting mold produced from the regenerate.
• the cured binder should decompose, so that the mold loses its strength.
• the aromatic sulfonic acids used as catalyst in particular p-toluenesulfonic acid, benzenesulfonic acid and xylenesulfonic acid, disintegrate under the influence of heat and the reducing atmosphere generated during casting and, in addition to sulfur dioxide, release aromatic pollutants such as benzene, toluene or xylene (BTX). Some of these decomposition products also remain in the used sand and can be released during reprocessing.
• the WO 97/31732 discloses furan-based binder for molding sands containing methanesulfonic acid as a hardener.
• the EP 1531018 A1 relates to acid hardeners for furan binders containing sulfuric acid, aliphatic carboxylic acid and arylsulphonic acid.
• the WO 97/31732 and the EP 1531013 A1 do not disclose the claimed manufacturing process.
• WO 97/31732 describes a self-hardening furan no-bake molding material mixture for the production of casting forums, which contains in addition to a furan-containing resin methanesulfonic acid as a catalytically active acid.
• the methanesulfonic acid may also be used in admixture with an organic sulfonic acid or an inorganic acid.
• organic sulfonic acids there are mentioned p-toluenesulfonic acid, benzenesulfonic acid and xylenesulfonic acid.
• sulfuric acid is mentioned.
• Methanesulfonic acid has a higher acid strength than, for example, p-toluenesulfonic acid. When using this acid, therefore, a faster curing of the furan no-bake binder is achieved or the curing can be achieved even at low temperatures, ie at temperatures below 25 ° C within acceptable periods.
• methanesulfonic acid is very problematic because of its high reactivity, especially in the production of very large casting molds, since it acts as a fast curing agent, thus allowing only relatively short processing periods.
• Another disadvantage is the use of methanesulfonic acid or methanesulfonic acid mixed with organic sulfonic acids for the emission of sulfur dioxide during casting.
• MAK maximum workplace concentration
• the invention was therefore based on the object to provide a method for the production of cores and molds for the foundry industry, which allows the production of molds, the casting a lower emission of pollutants show when this occurs with the use of currently conventional aromatic sulfonic acids.
• the emission of pollutants in particular the emission of sulfur dioxide and aromatic pollutants, such as benzene, toluene or xylene, can be drastically reduced during casting. As a result, the burden of used sand with these pollutants can be reduced.
• the acid used as a catalyst for the curing of the resin is a mixture of methanesulfonic acid and at least one further sulfur-free acid.
• refractory materials which are customary for the production of moldings for the foundry industry can be used as the refractory molding base material per se.
• suitable refractory mold bases are quartz sand, zircon sand, olivine sand, aluminum silicate sand and chrome ore sand or mixtures thereof.
• quartz sand is used.
• the refractory base molding material should have a sufficient particle size so that the molded article produced from the molding material mixture has a sufficiently high porosity to allow escape of volatile compounds during the casting process.
• at least 70 wt .-%, particularly preferably at least 80 wt .-% of the refractory molding base material has a particle size ⁇ 290 microns.
• the average particle size of the refractory base molding material should preferably be between 100 and 350 ⁇ m.
• the particle size can be determined, for example, by sieve analysis.
• the refractory base molding material should be present in free-flowing form, so that the catalyst or the acid-curable binder can be well applied, for example in a mixer to the grains of the refractory base molding material.
• Regenerated used sands are preferably used as refractory mold bases. From the used sand larger aggregates are removed and the used sand is separated into individual grains. After a mechanical or thermal treatment, the old sands are dedusted and can then be reused. Before reuse, the acid balance of the regenerated used sand is preferably tested. In particular, during thermal regeneration, by-products such as carbonates contained in the sand can be converted to the corresponding oxides, which then react alkaline and neutralize the acid added to the binder as a catalyst. Likewise, for example, in a mechanical regeneration, acid remain in the used sand, which should be considered in the preparation of the binder so as not to shorten the processing time of the molding material mixture.
• the refractory molding base should preferably be dry because the curing reaction is slowed by water.
• the refractory base molding material contains less than 1 wt .-% water.
• the refractory base molding material should not be too warm.
• the refractory base molding material should have a temperature in the range of 20 to 35 ° C. Possibly. the refractory molding material can be cooled or heated
• An acid is then applied to the free-flowing refractory to yield an acid-coated refractory molding base.
• the acid is applied by conventional methods to the refractory base molding material, for example, by spraying the acid onto the refractory base molding material.
• the Amount of acid is preferably selected in the range of 5 to 45 wt .-%, particularly preferably in the range of 20 to 30 wt .-%, based on the weight of the binder and calculated as the pure acid, ie without consideration of any solvent used , Unless the acid is already in liquid form and has a sufficiently low viscosity to be distributed in the form of a thin film on the grains of the refractory base molding material, the acid is dissolved in a suitable solvent.
• Exemplary solvents are water or alcohols or mixtures of water and alcohol.
• the solution is prepared as concentrated as possible in order to minimize the introduced into the binder or the molding material amount of water.
• the mixture of refractory base molding material and acid is well homogenized.
• An acid-curable binder is then applied to the acid-coated refractory base stock.
• the amount of the binder is preferably selected in the range of 0.25 to 5 wt .-%, particularly preferably in the range of 1 to 3 wt .-%, based on the refractory molding base material and calculated as the resin component.
• the acid-curable binder it is possible to use, as such, all acid-curable binders, especially those acid-curable binders which are already customary for the production of molding compounds for the foundry industry.
• the binder may also contain other customary components, for example solvents for adjusting the viscosity or extenders which replace part of the crosslinkable resin.
• the binder is applied to the acid coated refractory base stock and agitated by agitating the mixture onto the base
• Granules of refractory base molding material distributed in the form of a thin film.
• the amounts of binder and acid are chosen so that on the one hand sufficient strength of the casting mold and on the other hand a sufficient processing time of the molding material mixture is achieved.
• a processing time in the range of 5 to 45 minutes is suitable.
• the binder-coated refractory molding base stock is then formed into a shaped article by conventional methods.
• the molding material mixture can be introduced into a suitable mold and compacted there.
• the resulting molded body is then allowed to cure.
• the catalyst used is a mixture of methanesulfonic acid and at least one further sulfur-free acid.
• the use of the mixture can reduce both the emissions of aromatic pollutants, in particular BTX, produced during casting and the emissions of sulfur dioxide.
• BTX aromatic pollutants
• the proportion of methanesulfonic acid having high acid strength is reduced, sufficient reactivity is achieved to cure the binder within a time suitable for industrial applications.
• any acid can be used per se, as long as it does not comprise sulfur-containing groups. Both inorganic and organic acids can be used, with a good reactivity of the binder system being achieved even in the case of organic acids, although such organic acids usually have a relatively low acid strength.
• the proportion of methanesulfonic acid in the acid used as catalyst depends on the reactivity of the resin used in the binder, the at least one sulfur-free acid used in addition to the methanesulfonic acid and the amount of the acid used.
• the proportion of methanesulfonic acid in the acid used as catalyst is preferably less than 70% by weight, preferably less than 65% by weight, particularly preferably less chosen as 60 wt .-% and particularly preferably less than 55 wt .-%.
• the proportion of methanesulfonic acid in the acid used as the catalyst is preferably greater than 20 wt .-%, preferably greater than 30 wt .-%, more preferably greater than 35 wt .-% and particularly preferably greater than 40 wt .-% chosen.
• the proportion of the sulfur-free acid is preferably greater than 30 wt .-%, preferably greater than 35 wt .-%, more preferably greater than 40 wt .-%, and particularly preferably greater than 45 wt .-% selected.
• an aromatic sulfonic acid may also be present in a small proportion in the acid used as catalyst. This proportion is preferably less than 20% by weight, preferably less than 10% by weight and more preferably less than 5% by weight. Most preferably, no aromatic sulfonic acid is included in the acid used as a catalyst.
• Exemplary aromatic sulfonic acids are toluenesulfonic acid, benzenesulfonic acid and xylenesulfonic acid.
• the data refers to the anhydrous acids.
• any binder which can be cured by acid catalysis can be used per se in the process according to the invention.
• the acid-curable binder it is preferable to use a furan no-bake binder or a phenol no-bake binder.
• furan no-bake binder all furan resins can be used per se, as they are already used in furan no-bake binder systems.
• the furan resins used in technical furan no-bake binders are usually precondensates or mixtures of furfuryl alcohol with other monomers or precondensates.
• the precondensates contained in furan no-bake binders are prepared in a manner known per se.
• furfuryl alcohol is used in combination with urea and / or formaldehyde or urea / formaldehyde precondensates.
• Formaldehyde can be used both in monomeric form, for example in the form of a formalin solution, as well as in the form of its polymers, such as trioxane or paraformaldehyde.
• formaldehyde other aldehydes or ketones can be used.
• Suitable aldehydes are, for example, acetaldehyde, propionaldehyde, butyraldehyde, acrolein, crotonaldehyde, benzaldehyde, salicylaldehyde, cinnamaldehyde, glyoxal and mixtures of these aldehydes.
• Formaldehyde is preferred, this being preferably used in the form of paraformaldehyde.
• ketones As ketone component, all ketones can be used which have a sufficiently high reactivity. Exemplary ketones are methyl ethyl ketone, methyl propyl ketone and acetone, with acetone being preferred.
• the said aldehydes and ketones can be used as a single compound but also in admixture with each other.
• the molar ratio of aldehyde, in particular formaldehyde, or ketone to furfuryl alcohol can be selected within wide ranges.
• 0.4 to 4 moles of furfuryl alcohol, preferably 0.5 to 2 moles of furfuryl alcohol, may be used per mole of aldehyde.
• furfuryl alcohol, formaldehyde and urea can be heated to boiling, for example, after the pH has been adjusted to more than 4.5, water being continuously distilled off from the reaction mixture.
• the reaction time can be several hours, for example 2 hours. Under these reaction conditions occurs almost no polymerization of furfuryl alcohol. However, the furfuryl alcohol is condensed into a resin together with the formaldehyde and the urea.
• furfuryl alcohol, formaldehyde and urea are reacted at a pH of well below 4.5, for example at a pH of 2.0, in the heat, wherein the water formed in the condensation are distilled off under reduced pressure can.
• the reaction product has a relatively high viscosity and is diluted with furfuryl alcohol to produce the binder until the desired viscosity is achieved.
• phenol can be reacted under alkaline conditions, first with formaldehyde to a resole resin.
• This resol can then be treated with furfuryl alcohol or a furan group containing Resin reacted or mixed.
• furan group-containing resins can be obtained, for example, by the methods described above.
• phenols for example resorcinol, cresols or bisphenol A.
• the proportion of phenol or higher phenols to the binder is preferably in the range of up to 45 wt .-%, preferably up to 20 wt .-%, more preferably selected up to 10 wt .-%. According to one embodiment, the proportion of phenol or higher phenols can be greater than 2 wt .-%, according to a further embodiment greater than 4 wt .-% can be selected.
• condensates of aldehydes and ketones which are then mixed with furfuryl alcohol to produce the binder.
• Such condensates can be prepared by reacting aldehydes and ketones under alkaline conditions.
• the aldehyde used is preferably formaldehyde, in particular in the form of paraformaldehyde.
• the ketone used is preferably acetone.
• the relative molar ratio of aldehyde to ketone is preferably selected in the range of 7: 1 to 1: 1, preferably 1.2: 1 to 3.0: 1.
• the condensation is preferably carried out under alkaline conditions at pH values in the range of 8 to 11.5, preferably 9 to 11.
• a suitable base is, for example, sodium carbonate.
• the proportion of furfuryl alcohol on Binder in the range of 30 to 95 wt .-%, preferably 50 to 90 wt .-%, particularly preferably 60 to 85 wt .-% selected.
• the proportion of urea and / or formaldehyde in the binder is preferably selected in the range of 2 to 70 wt .-%, preferably 5 to 45 wt .-%, particularly preferably 15 to 30 wt .-%.
• the proportions include both the unbound portions of these compounds contained in the binder and those bound in the resin.
• the proportion of these extenders in the binder is therefore preferably less than 25% by weight, preferably less than 15% by weight and more preferably less than 10% by weight. In order to achieve a cost saving without having to put an excessive influence on the strength of the mold, the proportion of extenders is chosen according to an embodiment greater than 5 wt .-%.
• the furan no-bake binders may further contain water.
• the proportion of water is preferably chosen as low as possible.
• the proportion of water in the binder is preferably less than 20% by weight, preferably less than 15% by weight. From an economic point of view, an amount of water of more than 5% by weight in the binder can be tolerated.
• Resoles are mixtures of hydroxymethylphenols which are linked via methylene and methylene ether bridges and by Reaction of aldehydes and phenols in a molar ratio of 1: ⁇ 1, optionally in the presence of a catalyst, for example a basic catalyst, are available. They have a molecular weight M w of ⁇ 10,000 g / mol.
• phenolic resins For the preparation of phenolic resins, all conventionally used phenols are suitable. In addition to unsubstituted phenol, substituted phenols or mixtures thereof can be used. The phenolic compounds are unsubstituted either in both ortho positions or in an ortho and in the para position to allow polymerization. The remaining ring carbon atoms may be substituted. The choice of the substituent is not particularly limited so long as the substituent does not adversely affect the polymerization of the phenol or the aldehyde. Examples of substituted phenols are alkyl-substituted phenols, alkoxy-substituted phenols and aryloxy-substituted phenols.
• the abovementioned substituents have, for example, 1 to 26, preferably 1 to 15, carbon atoms.
• suitable phenols are o-cresol, m-cresol, p-cresol, 3,5-xylene, 3,4-xylene, 3,4,5-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol, cyclohexylphenol, p-octylphenol, p-nonylphenol, 3,5-dicyclohexylphenol, p-crotylphenol, p-phenylphenol, 3,5-dimethoxyphenol and p-phenoxyphenol.
• phenol itself.
• higher condensed phenols such as bisphenol A, are suitable.
• polyhydric phenols having more than one phenolic hydroxyl group are also suitable.
• Preferred polyhydric phenols have 2 to 4 phenolic hydroxyl groups.
• suitable polyhydric phenols are pyrocatechol, resorcinol, hydroquinone, pyrogallol, fluoroglycine, 2,5-dimethylresorcinol, 4,5-dimethylresorcinol, 5-methylresorcinol or 5-ethylresorcinol.
• Mixtures of various mono- and polyhydric and / or substituted and / or condensed phenolic components can also be used for the preparation of the polyol component.
• phenols of general formula I for the preparation of the phenolic resin component, wherein A, B and C independently of one another from a hydrogen atom, a branched or unbranched alkyl radical, which may have, for example 1 to 26, preferably 1 to 15 carbon atoms, a branched or unbranched alkoxy radical, for example 1 to 26, preferably having from 1 to 15 carbon atoms, a branched or unbranched alkenoxy radical which may, for example, have 1 to 26, preferably 1 to 15, carbon atoms, an aryl or alkylaryl radical, such as, for example, bisphenyls.
• a branched or unbranched alkyl radical which may have, for example 1 to 26, preferably 1 to 15 carbon atoms, a branched or unbranched alkoxy radical, for example 1 to 26, preferably having from 1 to 15 carbon atoms, a branched or unbranched alkenoxy radical which may, for example, have 1 to 26, preferably 1 to 15, carbon atoms,
• aldehydes for the production of the phenolic resin component are the same aldehydes as are used in the preparation of the furan resin component in furan no-bake binders.
• aldehydes of the formula: R-CHO wherein R is a hydrogen atom or a carbon atom radical having preferably 1 to 8, particularly preferably 1 to 3 carbon atoms.
• R is a hydrogen atom or a carbon atom radical having preferably 1 to 8, particularly preferably 1 to 3 carbon atoms.
• Specific examples are formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde and benzaldehyde. It is particularly preferred to use formaldehyde, either in its aqueous form, as para-formaldehyde or trioxane.
• the molar ratio of aldehyde to phenol is preferably 1: 1.0 to 2.5: 1, more preferably 1.1: 1 to 2.2: 1, particularly preferably 1.2: 1 to 2.0: 1.
• Sodium hydroxide, ammonia, sodium carbonate, calcium, magnesium and barium hydroxide or also tertiary amines can be used as bases in the preparation of the resoles.
• the resoles can also be modified by further compounds, for example nitrogen-containing compounds, such as urea.
• the resoles are preferably mixed with furfuryl alcohol in the preparation of the binder.
• the binders may contain other customary additives, for example silanes as adhesion promoters.
• Suitable silanes are, for example, aminosilanes, epoxysilanes, mercaptosilanes, hydroxysilanes and ureidosilanes, such as ⁇ -hydroxypropyltrimethoxysilane, ⁇ -aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, ⁇ -mercaptopropyltrimethoxysilane, ⁇ -glycidoxypropyltrimethoxysilane, ⁇ - (3,4-epoxycyclohexyl) trimethoxysilane, N- ⁇ - (aminoethyl) - ⁇ -aminopropyltrimethoxysilane.
• silane is added to the binder in a proportion of 0.1 to 3% by weight, preferably 0.1 to 1% by weight.
• the binders may also contain activators which accelerate the curing of the binder.
• activators are, for example, resorcinol, bisphenol A. It is also possible to use mixtures which remain in the bottom during the distillation of resorcinol or bisphenol A. These mixtures contain oligomers of resorcinol or bisphenol A, for example dimers, trimers or polymers.
• polyols may also be added to the binder, such as polyether polyols or polyester polyols.
• Polyester polyols can be prepared, for example, by reaction of a dicarboxylic acid or a dicarboxylic acid anhydride with a glycol. Suitable dicarboxylic acids are, for example, adipic acid or oxalic acid.
• Suitable glycols are, for example, ethylene glycol, propylene glycol or diethylene glycol. The molecular weight of these compounds is preferably in the range of 300 to 800.
• Polyether polyols are commercially available. They can be prepared by reaction of an alkylene oxide with a glycol. Suitable alkylene oxides are, for example, ethylene oxide, propylene oxide or butylene oxide. Examples of suitable glycols are ethylene glycol, diethylene glycol and propylene glycol.
• solvents may also be present in the binder.
• a suitable solvent is, for example, water or alcohols, such as methanol or ethanol.
• the binder may also contain plasticizers, for example monoethylene glycol or diisobutyl phthalate.
• the molding material mixture may contain other customary constituents.
• Exemplary further constituents are iron oxide, ground fibrous fibers, wood flour granules, ground coal or clay.
• organic acids are preferably used.
• Organic acids can easily be removed during the regeneration of the used sand, so that they do not accumulate in the regenerated used sand.
• the organic acids decompose into harmless compounds, ultimately water and carbon dioxide, so that when using organic acids no special measures must be taken, for example, to clean the exhaust air during regeneration.
• Organic acids are compounds based on hydrocarbons which comprise at least one carboxyl group.
• the organic acids may also comprise further functional groups, for example hydroxy groups, aldehyde groups, or even double bonds.
• the organic acids preferably comprise 1 to 10 carbon atoms, more preferably 2 to 8 carbon atoms.
• Saturated carboxylic acids are preferably used, since these are readily available and have a high stability, so that they can be stored for a long time without sacrificing quality.
• Sulfur-free acid used is preferably those organic acids which have a high acid strength.
• the organic acid preferably comprises, in addition to the at least one carboxyl group, at least one further electron-withdrawing group.
• the at least one further electron-withdrawing group is selected from the group of carboxyl group, hydroxy group, aldehyde group. Particular preference is given to using dicarboxylic acids, tricarboxylic acids or hydroxycarboxylic acids.
• the organic acid is selected from the group of citric acid, lactic acid, glycolic acid, glyoxylic acid, malic acid, oxalic acid.
• the acids can be used both individually and in admixture.
• the at least one further acid, in particular organic acid preferably has a pK s value of less than 4.5, preferably less than 4.0.
• the at least one further acid, in particular organic acid has a pK s value of more than 1.0, according to a further embodiment a pK s value of more than 2.
• the at least one further sulfur-free acid has a pK s value in the range from 3 to 4.
• the acid is preferably added in the form of a solution.
• a solution As the solvent, water is preferably used. Since water, as already explained, slows down the hardening of the molding material mixture, a concentrated solution of the acid is preferably used, the concentration of the acid in the solution preferably being chosen to be greater than 30% by weight.
• the temperature during the production and processing of the molding material mixture is preferably not too high.
• the curing of the molded body produced from the molding material should be as uniform as possible in order to achieve high strength.
• the curing of the shaped body is carried out at a temperature of less than 40 ° C, preferably in a temperature range of 15 to 30 ° C.
• a molding material mixture is used used, which is particularly suitable for the production of large molds, these molds show a reduced emission of defective compounds during casting, especially BTX and sulfur compounds.
• the invention relates to molds and cores, as obtained by the method according to the invention, as well as their use for metal casting, in particular iron and steel casting.
• the mold was filled with 4.3 kg of liquid iron (casting temperature: 1400 ° C), so that the weight ratio of mold and molten iron was about 1: 1.
• a defined partial flow was drawn off via a sampling probe and the substances contained in the partial flow were adsorbed on active carbon in accordance with the process according to DIN EN 14662-2.
• the qualitative and quantitative analysis of the adsorbed substances was carried out by gas chromatography.
• a partial flow was discharged from the exhaust gas and with a vacuum device in a Aspirated PE bag.
• the concentration of sulfur dioxide was determined by mass spectrometry.
• Table 2 Emissions of a casting mold during casting (Technikum scale) Molding material mixture 1 (not according to the invention) Molding material mixture 2 (according to the invention) Benzene [mg / m 3 ] 6095 560 Toluene [mg / m 3 ] 30000 300 Xylene [mg / m 3 ] 930 105.5 Sulfur dioxide [ppm by volume] 3600 1300
• Table 4 Emissions of a casting mold during casting (practical application) Molding material mixture 3 (not according to the invention) Molding material mixture 4 (according to the invention) Benzene [mg / m 3 ] 15.0 5.0 Toluene [mg / m 3 ] 18.0 6.0 Xylene [mg / m 3 ] ⁇ 0.5 ⁇ 0.5 Sulfur dioxide [ppm by volume] 22.5 19.1
• the molding material mixture is compacted in a mold, 100 mm in height and 100 mm in diameter, with a hand plate.
• the surface is checked at certain intervals with the surface hardness tester GF. If the test ball no longer penetrates into the core surface, the demolding time is given.
• the remaining remainder of the sand mixture after bending core production is assessed visually for its flowability and rolling behavior. If unrolling occurs like a scoop, the sand processing time is over.
• test bars were placed in a Georg Fischer strength tester equipped with a three-point bending device (DISA-Industrie AG, Schaffhausen, CH) and the force was measured, which resulted in the breakage of the test bars.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Mold Materials And Core Materials (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=40976944

Family Applications (1)

Country Status (13)

Families Citing this family (15)

Family Cites Families (10)

• 2008
  • 2008-05-23 DE DE102008024727A patent/DE102008024727A1/de not_active Withdrawn
• 2009
  • 2009-05-22 EP EP09749648.3A patent/EP2296836B1/de active Active
  • 2009-05-22 CN CN2009801246237A patent/CN102076440A/zh active Pending
  • 2009-05-22 UA UAA201015488A patent/UA101502C2/ru unknown
  • 2009-05-22 MX MX2010012742A patent/MX2010012742A/es active IP Right Grant
  • 2009-05-22 WO PCT/EP2009/003643 patent/WO2009141158A1/de active Application Filing
  • 2009-05-22 BR BRPI0912685-6A patent/BRPI0912685B1/pt not_active IP Right Cessation
  • 2009-05-22 EA EA201071344A patent/EA021549B1/ru not_active IP Right Cessation
  • 2009-05-22 US US12/993,994 patent/US8919421B2/en not_active Expired - Fee Related
  • 2009-05-22 PL PL09749648T patent/PL2296836T3/pl unknown
  • 2009-05-22 KR KR1020107028541A patent/KR101643703B1/ko active IP Right Grant
  • 2009-05-22 JP JP2011509899A patent/JP5557293B2/ja not_active Expired - Fee Related
• 2010
  • 2010-11-11 ZA ZA2010/08061A patent/ZA201008061B/en unknown

Also Published As

Similar Documents

Legal Events