WO2006058664A2 - Use of poorly soluble salts in combination with liquid glass for producing moulds and cores used in casting methods - Google Patents

Abstract

The invention relates to the use of liquid glass and/or one or more precursors of the latter during the production of moulds and/or cores used for casting purposes. According to said method, liquid glass, acting as component (1) and/or one or more precursors of the latter and one or more poorly soluble metallic salts, acting as component (2) and/or mixtures of components (1) and (2) are blended with particulate materials that act as component (3) and do not melt during the casting process, in order to produce moulds that can be removed after the casting process and/or cores for casting purposes. The invention also relates to a method for producing corresponding moulds and/or cores, to corresponding moulds and cores, in addition to other inventive embodiments that are covered by the description.

Description

 Use of sparingly soluble salts in combination with water glass in the production of molds and cores for the foundry industry

The invention relates to the use of waterglass and / or precursors thereof in the production of castable molds and / or cores for foundry purposes, to methods of making corresponding molds and / or cores, and to corresponding molds and cores, and to other inventive embodiments described below.

Water glass, an aqueous solution of alkali metal silicates, obtainable, for example, as a reaction product of

Silica and alkali metal bases, such as ammonium, sodium and / or potassium bases, such as the corresponding hydroxides, are known as binding materials, for example in the construction industry. Thus, water glass can be cured in combination with carbon dioxide, which is not particularly good

Curing leads, for example, because the reaction takes place only superficially (see O. Henning and D. Knöfel,

"Building Materials Chemistry - An Introduction for Civil Engineers and

Architects ", Verlag für Bauwesen, Berlin, and Bauverlag GmbH, Wiesbaden and Berlin 1997, p. 129).

Also known is the use of water glass as a binder material for the production of molds and cores based on sand or other ("refractory") particulate materials under heating in the casting process. For example, attempts have been made to use phosphates or borates as water glass hardeners so the benefits of the hardness of Water glass and the dispersibility due to an addition of phosphates and / or borates, see US 6,139,619. Here, however, only molds or cores can be obtained which have a strong adhesion tendency with metals to be cast, so that the foundry products have adhesions of sand and sand burns, which lead to an impure and rough surface, which is unacceptable for many purposes. Another feature of the hitherto known cores and forms is that they are difficult to disintegrate upon extensive or complete curing and are not water-soluble or dispersible, so that they are difficult to remove. This can lead to problems especially in femteiligen or strongly undercutting forms and / or cores, which can be difficult to remove completely.

Therefore, an effort has hitherto been directed to avoid complete hardening of the cores and / or molds, which in turn increases the adhesion to the castings and, on the other hand, is difficult to avoid when pouring the hot molten metals or alloys.

Against this background, the object is to provide new compositions for molds and / or cores which can be used in the foundry, which have a sufficient hardness for the casting process and are still easily removable after the casting process and without residues on the foundry products.

It has now surprisingly been found that this object can be achieved by the use of water glass, and / or one or more precursors thereof, in the production of molds and / or cores for foundry purposes, wherein (or by in that said use comprises that as component (1) water glass and / or one or more precursors thereof, and as component (2) one or more sparingly soluble metal salts, in particular those metals which can form silicates, and / or mixtures of component (1) and (2), for the production of castable molds and / or cores for foundry purposes, to be mixed with non-melting ("refractory") particulate materials as component (3) during the casting process.

It has been found that when the three components mentioned are used, to which one or more further customary additives, in particular flowability improvers, can be added as further component (s), at temperatures below the temperatures of the molten casting material used in casting ( For example, in particular the below referred to as preferred temperatures), for example, a metal or alloy melt, sufficiently solid "green" shapes and / or cores can be obtained, but surprisingly after subsequent casting (preferably light) by mechanical action, such as vibration, ultrasound or other vibration, can be transferred into a pourable form (condition) and thus easily removed, yet they are stable enough for the molten metal to be poured during the casting process, at least until they cool with the molds and / or nuclei sufficiently solidify in their contact area in order to ensure sufficient inherent dimensional stability.

The ease of conversion to a pourable form is surprising, even in the light of the hitherto severe water glass curing problems. Without being bound to this explanation An explanation for this may be that at elevated temperature during the casting and the subsequent cooling metal cations from the sparingly soluble salts can be released more. The anions of the sparingly soluble metal salts can form more readily soluble alkali metal salts with the alkali metal ions of the waterglass and / or its reaction products. As a result, the "green" forms and / or cores obtainable by the precuring can be brought into the mold, which can easily be converted into pourable form by mechanical action, during the casting process and the subsequent cooling, and then removed.

A further advantage of the forms and / or cores which can be produced according to the invention is that the composition used can be excellently compatible with various agents for increasing the flowability in the molds and / or cores. Finally, it is possible to effectively avoid gas formation, especially with a smaller proportion of water in the glass of water and / or a smaller proportion of the water glass in the overall composition of the molds and / or cores. The molds and / or cores available during the casting process can be removed without the addition of water. It is also advantageous that after removal of the cores (conversion into a free-flowing form) separation of the particulate material, e.g. Sand, can be reached from the remaining material residues, for example, by simple sifting.

Waterglass, a mixture of ammonium or alkali metal (such as sodium and / or potassium silicates, favoring less gas evolution), may be used as component (1) in dried form (which would fall under the definition of water glass precursors) or directly as aqueous Solution can be used. In case of using a dried Form, the addition of water before adding additional components or after the addition of one or more of the components. It is also possible that, as precursors for the preparation of water glass, silicon dioxide (for example amorphous silica or microsilica) and one or more alkali metal bases, in particular one or more alkali metal (such as sodium or potassium) hydroxides, directly one or more of the other components ( 2), (3) and optionally further additives are added, so that the water glass is formed only in admixture with one or more of these further components. All combinations of these mixture variants are conceivable and encompassed by the present invention. The molar water glass module can be used to influence the properties of the available shapes and / or cores.

The one or more metal salts used as component 2 are preferably a by itself or by Coatmg, for example, with organic polymers of a suitable melting point, for example having a melting point in the range of used in the production of green forms and / or cores temperatures, eg from at least 100 ⁰ C. , and / or with inorganic Coatmg materials such as titanium dioxide and / or alumina sparingly soluble (= especially at room temperature sparingly soluble in water) hydroxide, carbonate (such as magnesium calcium carbonate, eg dolomite), sulfate (such as kieserite) (carbonates or Sulfates are also conceivable in particular as additives for other sparingly soluble salts) and / or in particular fluoride of a metal, or mixtures of two or more thereof, wherein as (the cation in the salt supplying) metals are preferred: in particular calcium and / or aluminum, further Magnesium, or zinc or iron. The (preferably uncoated) hydroxides and / or fluorides are particularly Partly, as well as magnesium oxide (particularly advantageous in the cast iron foundry, preferably used as sintered magnesium, also, if mentioned below), since they do not lead to the formation of gases during casting or the production of molds and / or cores, as for example (otherwise also usable) sparingly soluble salts of organic acids, such as hydroxycarboxylic acids, for example lactates, or the like may be the case. The said sparingly soluble salts are preferably chosen so that they are so sparingly soluble that they can not react at room temperature (either because of a coating or preferably on their own) or not to a disturbing extent with the water glass. Particularly advantageous are calcium fluoride and / or aluminum fluoride, as these can cause a particularly low sand adhesion to the molds products after casting. In addition to the metal oxides mentioned, hydroxides of alkali metals, such as sodium hydroxide, may be added, for example (based on one part by weight of sparingly soluble metal salts as 1 part by weight) in a proportion by weight of 0.05 to 1, preferably 0.1 to 0.3, additional parts by weight ,

Component (1) and component (2) may be added separately to the mixture, or they may be pre-determined (with or without water content in water glass, ie as dry mix (obtainable eg by spray-drying), for example as dry powder, or with the water content, which is also longer Time, for example, several weeks, gives stable compositions which can also be used for adding the two components) and thus added to the other component (s). Such mixtures of component (1) and (2) as such (binder mixtures) are also a preferred embodiment of the invention. It is advantageous if the proportions of component (1) and component (2) are matched to one another, in particular in such a way that a coordinated ratio of cation of the sparingly soluble metal salt to anion in the water glass (silicates, in particular polymethyl and Polydisilikate etc.) becomes. For example, it is advantageous if, based on the dry weight of component (1), the weight ratio of component (2) to the dry matter proportions in component (1) is in the ratio of 1: 4 to 3: 1, for example in a possible preferred one Embodiment in the weight ratios of the two said components (2) to (1) at 0.6 to 2 to 1, 4 to 0.6, so at about 1 to 1 to 2. If component 1 in aqueous form before, is - Example of a preferred weight ratio of component (1) with water to the weight of component (2) at 5 to 1 to 1 to 2, for example at 3 to 1 to 1, 5 to 1.

The proportion of the components (1) and (2) in the mixture for molds and / or cores may in principle be arbitrary. Thus, based on the weight of component (3), it may be present in a proportion by weight of from 0.1 to 6% by weight, or, for example, in another possible preferred embodiment in a proportion by weight of from 0.5 to 5% by weight. , eg from 2 to 4% by weight.

Component 3, one or more non-melting ("refractory") particulate materials in the casting process, are, for example, refractory granular materials such as chromite sand, alumina, zircon sand, alumium silicate, chamotte, silicon carbide, mullite, graphite, fosterite, synthetic ceramic sand, or especially heat resistant Sands, such as quartz or foundry sand, metal beads or granules, for example of iron or copper, but also soluble salts, such as sodium chloride, or Mixtures of two or more of such components.

Further optional additives are, in particular, agents for increasing the flowability, for example corresponding surfactants or wetting agents, such as anionic, cationic, amphoteric or nonionic surfactants, or two or more thereof, along with further additives, such as water, or the like, which are preferably based on the total mass of the component (3), for example, in a proportion of a total of or preferably a total of 0 to 5 wt .-% may be added, such as from 0.01 to 1 wt .-%, in water, for example to 4 %.

Preferably, after mixing the components in a further step, the use according to the invention comprises that the available mixture is introduced into a molding or core tool, for example by encasing. Even more preferred is a use in which, simultaneously with the introduction into a mold or core tool and / or subsequently thereto, the mixture is heated to temperatures below the temperature of the molten metal or alloy to be cast, for example in one possible preferred embodiment more than 200 ^° C. below this temperature, for example (absolute) at 250 ^° C. or below, in one possible preferred example the temperature is between 80 ° and 200 ^° C., for example 100 ° and 100 ° with 150 ° C. All that is important is that a temperature required for the reaction, which leads to pourability at relatively high heat, is not exceeded too long, which would result in unstable shapes and / or cores, since the conversion into a readily pourable state is already possible would progress too far. In this way, "green" shapes and / or cores obtained, which have a sufficient stability for foundry purposes.

The available green molds and / or cores are suitable for use and, in a still further preferred embodiment of the invention, if necessary after removal from the mold or core tool, are used to make a foundry product (for example, without limitation Suction pipes for engines, cooling pipes, door hinges, nozzles for filling stations, cast iron pipes, faucets, hydraulic valves or the like may be mentioned) by casting arbitrary melts of metals or metal alloys, in particular tin, lead, zinc, bronze, iron, gray cast iron, steel or Aluminum or aluminum alloys. For example, particularly good results can be obtained with aluminum or alloys, especially when calcium fluoride is used, or with higher melting metals or alloys, such as iron or steel with higher melting with aluminum fluoride or aluminum hydroxide, with magnesium oxide with iron casting, so that their uses are particularly preferred embodiments relate to the invention.

In the subsequent casting using the molds and / or cores available as above, which together with the above steps as an additional step to the already mentioned another particular embodiment of the invention, the temperature of the molds and / or cores increases so far that starting with the casting process and also during the cooling phase, for example by reactions of liberated cations and / or anions of the sparingly soluble metal salts as described above, the molds and / or cores used are converted into such a state that they are in a further, corresponding to a still further preferred embodiment of the present use invention step of demolding then easily transferred into a pourable form and so mechanically, for example by shaking, ultrasound or knock, or the like, can be removed.

The invention also relates to the "green" molds and / or cores obtainable by the above process, processes for their preparation comprising the steps of the above and below use invention, in particular their preferred embodiments, the use of such "green" molds and / or cores Casting of castings and their demolding.

Where, above and below, forms and / or cores are mentioned, this also implies that only one form and / or one core (in singular) can be meant - the invention therefore also refers to individual cores and individual forms.

Hereinafter, some preferred embodiments of the invention will be described, wherein by the above (in particular as preferred or for example characterized) definitions, one or more general terms or proportions may be replaced by more specific ones, resulting in particularly preferred embodiments.

A preferred embodiment of the invention relates to the use of water glass, and / or one or more precursors thereof, in the production of molds and / or cores for foundry purposes, said use comprising as component (1) water glass and / or one or more precursors thereof, and as component (2) one or a plurality of sparingly soluble metal salts, and / or mixtures of components (1) and (2), for the production of castable molds and / or cores for foundry purposes, with particulate materials which do not melt during casting as component (3).

Preferred is the use according to the preceding paragraph, wherein as component (2) one or more hydroxides, carbonates (such as magnesium calcium carbonates, for example dolomite), sulfates (such as kieserite), metal fluorides and / or hydroxides, in particular

Hydroxides and / or preferably fluorides, preferably of

Calcium, aluminum, magnesium, iron or

Zinc, or magnesium oxide can be used free or

(less preferably) can also be present in coated form.

More preferred is a use according to one of the two preceding paragraphs, wherein as component (2) calcium fluoride, aluminum fluoride or a mixture is used, or magnesium oxide.

Even more preferred is a use according to any one of the preceding 3 paragraphs, wherein component (1) and component (2) are added to component (3) as a mixture or individually.

A further preferred embodiment of the invention relates to a use according to one of the preceding four paragraphs, wherein the molar water glass module of the component (1) used, e.g. is 1 to 4, and / or wherein the proportion of component (2) to the dry matter proportions in component (1) is 3 to 1 to 1 to 4.

Very preferred is also the use according to one of the preceding five paragraphs, wherein the components (1) and (2), based on the proportion by weight of component (3), for example m present in a proportion by weight of 0.1 to 6 wt .-%, in particular in a proportion of 0.5 to 5 wt .-%, for example in a proportion of 2 to 4 wt .-%.

A use according to any one of the preceding six paragraphs, wherein as component (3) a heat-resistant granular material, in particular sand, is added, is also a very preferred embodiment.

Also, a use according to any one of the above seven paragraphs, wherein as a further component a means for increasing the flowability is added, is very preferred.

Also preferred is a use according to one of the above eight paragraphs, wherein in a further step, the available mixture is introduced into a mold or core tool, in particular, wherein also simultaneously with the introduction into the mold or core tool and / or then the mixture Temperatures of 200 or more degrees Celsius ( ⁰ C) below the temperature of the metal or alloy melt used for casting a foundry product is heated, in particular to temperatures of 80 to 200 ⁰ C, preferably from 100 to 150 ⁰ C and so a green form and or a green core is produced, and more preferably, where the green form and / or the green core is further used to cast a foundry product.

Another advantageous embodiment of the invention relates to a method for producing a green mold or a green core for foundry purposes, comprising the steps according to one of the preceding nine paragraphs, or a green form obtainable thereby or a green obtainable thereby Core for foundry purposes.

A binder mixture comprising as component (1) water glass and as component (2) a sparingly soluble metal salt is particularly preferred, in particular one in which component (2) is a sparingly soluble hydroxide and / or preferably fluoride of a metal, in particular a fluoride of Calcium or aluminum, or a mixture of such Fuoride, or very preferably, wherein the weight ratio of component (2) to the weight of Trockenmatenalanteile in component (1) is 3 to 1 to 1 to 3.

A variant of the invention according to the last paragraph relates to a corresponding binder mixture in the dry state, another to a corresponding aqueous binder mixture.

Particular preference is also given to the subject invention shown in the examples.

The following examples serve to illustrate the invention without limiting its scope (all% data are in% by weight, proportions are by weight):

Example 1: Binder formulation with calcium fluoride: The binder mixture is one of 70% liquid sodium silicate (modulus 2.5) as component (1) and 29.6% calcium fluoride as component (2) with 0.4% surfactant (sodium lauryl ether sulfate). made as a further additive.

Example 2: Binder formulation with sparingly soluble aluminum salts: The binder mixture is one of 70% liquid Potassium silicate (modulus 3.0) as component (1), 20% aluminum fluoride and 5% aluminum hydroxide as component (2), 3.8% water and 0.2% surfactant (glycoside) prepared as a further additive.

Example 3 _j Binder formulation with sparingly soluble

Magnesium salt: The binder mixture is one prepared from 70% liquid sodium silicate (modulus 2.0) as component (1) and 30% magnesium hydroxide and 10% aluminum hydroxide as component (2).

Example 4j Powdered binder formulation with

Calcium fluoride: The binder mixture is a dry powder of 35% silica (pyrogenic or precipitated) and 30% concentrated sodium hydroxide solution (dry powder) as component 1 and 35% calcium fluoride as component (2).

Prior to use, 1 part of water is added to 3 parts of this mixture, either prior to mixing with the foundry sand or after mixing the powdered binder with the foundry sand. It is important that a uniform wetting of the grains of sand is achieved. The finished binder mixtures from Examples 1 to 4 are storable.

Example 5: Preparation of mixtures of binders and foundry sand: The finished binder mixture according to one of Examples 1 to 4 is mixed in a weight fraction of 2 to 4%, based on the proportion of foundry sand, with foundry sand (quartz sand) by means of conventional mixers (paddle stirrers).

Example 6 Preparation of Cores or Shapes: The mixtures obtained according to Example 5 are injected into mold or core tools and turned into green at about 130 ^° C. Hardened molds or cores. In this case, strengths of 200 to 500 N / cm ^{2 are} achieved. Also, a rapid curing in the tool is achieved, for example, only by the penetration of heat and / or hot purge air.

Example 7: Casting of moldings and removal of molds and / or cores: An aluminum melt is brought into contact with molds and / or cores according to Example 6 to produce a molded article. After cooling, the cores and / or molds are transferred by simple tapping into a flowable mold and removed.

Example 8:

A quartz sand is mixed with 2.5% of a binder of the following composition:

70% Na silicate

20% calcium fluoride ground

5% aluminum fluoride 5% sodium hydroxide solution

This mixture can be stored for several years, as it begins to react only by heat above 100 ⁰ C.

Put in a hot tool (130 - 200 ⁰ C), this mixture hardens after 30 - 60 sec., So that you can remove these already from the tool. In the following hour, the strength still increases, up to a bending fracture value of about 350 N / cm ² .

When used as a molded and core part of this product, the parts made therewith do not show any common sand buildup on contact with the liquid metal (Aluminum and cast iron), and the molds or cores disintegrate after some time (30 - 60 min) and collapse so that they can be easily removed from the casting again. This disintegration happens because the heat of action of the liquid metal (Al at about 700 ⁰ C), the components of the binder mainly to calcium and aluminum silicate connect, which are porous and show no strength. Also, these reaction products can be easily separated from the sand, making it easy to regenerate and reuse. As gas does not develop during casting, the castings have a better surface and less porosity than when made with conventional organic binders.

Claims

claims Use of water glass, and / or one or more precursors thereof, in the production of molds and / or cores for foundry purposes, said use comprising as component (1) waterglass and / or one or more precursors thereof, and as component (2) one or more metal salts difficult to dissolve on and / or by coating, and / or mixtures of components (1) and (2) for the production of casting molds and / or cores for foundry purposes during the casting process non-melting particulate materials are mixed as component (3). 2. Use according to claim 1, wherein as component (2) one or more hydroxides, carbonates (such as magnesium calcium carbonates, eg dolomite), sulfates (such as kieserite), metal fluorides and / or hydroxides, in particular hydroxides and / or preferably fluorides preferably of Calcium, aluminum, magnesium, iron or zinc. 3. Use according to one of claims 1 or 2, wherein as component (2) calcium fluoride, aluminum fluoride or a Mixture of it is used. 4. Use according to one of the preceding claims 1 to 3, wherein component (1) and component (2) are added to component (3) as a mixture or individually. 5. Use according to one of claims 1 to 4, wherein the water glass module of the component used (1) at molar Water glass module of the component (1) used, for example, is 1 to 4. 6. Use according to any one of claims 1 to 5, wherein the quantitative ratio of component (2) to the Dry matter proportions in component (1) is 3 to 1 to 1 to 4. 7. Use according to one of claims 1 to 6, wherein the components (1) and (2), based on the weight fraction of the component (3), in a weight fraction of 0.1 to 6 wt .-%, especially in one Proportion of 0.5 to 5 wt .-%. 8. Use according to one of claims 1 to 7, wherein as component (3) a heat-resistant granular material, in particular sand, is added. 9. Use according to one of claims 1 to 8, wherein as a further component a means for increasing the Flowability is added. 10. Use according to one of claims 1 to 9, wherein m a further step, the obtainable mixture is introduced into a mold or core tool. 11. Use according to claim 10, wherein simultaneously with the introduction into the mold or core tool and / or subsequently the mixture is heated to temperatures of 200 or more ⁰ C below the temperature of the metal or alloy melt used for casting a foundry product, in particular Temperatures of 80 to 200 ⁰ C, preferably from 100 to 1 BO ⁰ C and so a green form and / or a green core is produced. 12. Use according to claim 11, wherein the green mold and / or the green core continue to pour a Foundry product is used. 13. Use according to any one of claims 1 to 12, wherein the molds and cores can be transferred after subsequent casting by mechanical action in a pourable form. 14. Use according to any one of claims 1 to 13, wherein the sparingly soluble metal salts used are those which are so sparingly soluble that they can not react at room temperature because of a coating or, preferably, not to any extent to a disturbing extent with the water glass. 15. Use according to any one of claims 1 to 9 or 11 to 14, wherein the obtainable mixture is introduced into a mold or core tool and at the same time with the introduction m inn mold or core tool and / or then the mixture is heated to temperatures, which are below the temperature of the metal or alloy melts to be cast. Use according to any one of claims 1 to 10 or 11 to 15, wherein green molds or cores obtained after heating are used in the casting of castings and are then transferred to a pourable form and mechanically removed. 17. A method for producing a green mold or a green core for foundry purposes, comprising the steps according to one of claims 1 to 11 or 12 to 16. 18. Green mold or green core for foundry purposes, obtainable by the process according to claim 17. 19. Binder mixture comprising as component (1) water glass and as component (2) a sparingly soluble metal salt. 20. Binder mixture according to claim 20, wherein component (2) is a sparingly soluble hydroxide and / or preferably fluoride of a metal or magnesium oxide. The binder mixture of claim 19 or claim 20, wherein component (2) is a fluoride of calcium or aluminum, or a mixture of such fluorides. 22. A binder mixture according to any one of claims 19 to 21, wherein the weight ratio of component (2) to the weight of Dry matter content m component (1) is 3 to 1 to 1 to 3. 23. binder mixture according to any one of claims 19 to 22 in the dry state. 24.Wässrige binder mixture according to any one of claims 19 to 22.