DE102004057669B3 - Use of sparingly soluble salts in combination with water glass in the production of molds and cores for the foundry industry - Google Patents

Abstract

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 more sparingly soluble metal salts and / or mixtures of components (1) and (2) for the production of castable molds and / or cores for foundry purposes are mixed with particulate materials which do not melt in the casting process as component (3); corresponding shapes and / or cores, and corresponding shapes and cores, and other inventive embodiments described in the specification.

Description

The The invention relates to the use of water glass and / or precursors of which in the manufacture of molds removable after a casting process and / or kernels for Foundry purposes, as set forth below.

Water glass, an aqueous one solution of alkali silicates, available 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, or corresponding carbonates, such as soda, is used as the material for bonding known in the construction industry, for example. So can Water glass to be cured in combination with carbon dioxide, which, however, does not lead to particularly good curing, for example because the reaction only superficially (see O. Henning and D. Knöfel, "Baustoffchemie - An Introduction for Civil Engineers and Architects ", Publisher for 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 to combine the advantages 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 finely divided or strongly undercutting shapes and / or cores, which can be difficult to remove completely.

on the other hand is known from DE-OS 1 571 607 the use of water glass, in the presence of mineral powders, such as perlite dust or ferrosilicon, especially in the presence of metal silicide, to form silica and as possible strong bodies, like solid and moisture resistant plates and the like. From DE-OS 1 508 637 are molding sand mixtures in which water glass in the presence of reactive binders, such as cement, and other components used to make high strength molds become.

Therefore So far, an effort has been directed to a complete curing of the Cores and / or shapes to avoid, in turn, the attachment to increases the castings and on the other hand while pouring the hot ones Metal melts or alloys can hardly be avoided, or if possible make solid shapes.

In front The object of this background is to provide novel compositions for in the foundry to provide useable shapes and / or cores that have sufficient Hardness for the casting process and still light and without residue after the casting process the foundry products are removable.

It was now surprising found that solved this task can be through the use of water glass, and / or one or several precursors of which, in the manufacture of molds and / or cores for foundry purposes, the following casting process easily converted by mechanical action in a pourable form and so easily removable are, wherein (or characterized in that) the said use comprising that as component (1) water glass and / or one or more precursor thereof, and as component (2) one or more sparingly soluble metal salts, the so sparingly soluble They are at room temperature because of a coating or on their own not or not in disturbing Extent with can react to the glass of water, in particular those metals which can form silicates, and / or Mixtures of component (1) and (2), for the preparation of a casting process Removable molds and / or cores for foundry purposes with the casting process non-melting ("refractory") particulate materials are mixed as component (3), the obtainable mixture in a molding or Core tool is introduced and simultaneously with the introduction in a mold or core tool and / or subsequently the mixture Temperatures warmed up which is below the temperatures of the molten metal or alloy to be cast lie.

It has been found that when using the three components mentioned, 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, a metal or alloy melt, initially sufficiently solid "green" shapes and / or cores can be obtained, but surprisingly after subsequent casting easily by mechanical action, such as vibration, ultrasound or otherwise vibration, transferred to a pourable form (state) and Nevertheless, they are sufficiently stable during the casting of molten metals during the casting process, at least until they cool sufficiently solidify in their contact area melting in contact with the molds and / or cores in order to ensure sufficient inherent dimensional stability.

The easy transferability in a pourable form is, also in view of the previous problems with strong hardening of Water glass, surprising. Without this explanation An explanation for this may be that at increased Temperature during of the casting and the subsequent cooling Metal cations from the sparingly soluble Salts can be released more often. These cations can then be used with previously as a hardener acting, in the formation of the "green" forms and / or the cores available water glass and its reaction products, in particular the silicate content, react. At the same time the anions of the sparingly soluble Metal salts with the alkali metal ions of the water glass and / or form more readily soluble alkali metal salts of its reaction products. This allows through the pre-hardening available "green" shapes and / or Cores during the casting process and the subsequent one Cooling brought in easily converted by mechanical action in pourable form convertible form and then removed become.

One Another advantage of the inventively producible forms and / or Cores is that the composition used is excellent with various means for increasing the flowability in the forms and / or cores. Finally is it is possible to avoid gas formation effectively, especially at lower water content in a glass of water and / or a smaller proportion of the water glass at the Overall composition of the forms and / or cores. The casting process available Shapes and / or cores can be without Addition of water to be removed. It is also advantageous that after removing the cores (transfer to a pourable form) especially easy separation of the particulate material, e.g. Sand, from the rest Material residues can be achieved, for example by simple Views. Waterglass, a mixture of ammonium or (in favor of lesser Gas evolution preferably) alkali metal, such as sodium and / or Potassium silicates, as component (1) in dried form (which is under the definition of precursors of water glass would fall) or directly as watery solution be used. In case of using a dried form can the addition of water before adding other components or after the addition of one or more of the components. It is also possible, that as precursors for the production of water glass silicon dioxide (For example, amorphous silica or micro-silica) 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 further components (2), (3) and optionally further additives be added so that the waterglass first in mixture with a or more of these other components arises. All combinations These mixture variants are conceivable and of the present Invention. Through the molten water glass module, the Properties of the available Shapes and / or cores are influenced.

The or the metal salts used as component 2 are preferred one by itself or by coating, for example with organic Polymers of a suitable melting point, e.g. with a melting point in the range of temperatures used in the production of green forms and / or cores, e.g. from at least 100 ° C, and / or with inorganic coating materials, such as titanium dioxide and / or alumina sparingly soluble (= difficult to dissolve in water at room temperature) hydroxide, carbonate (such as magnesium calcium carbonates, e.g. Dolomite), sulphate (such as kieserite) (where carbonates or sulphates also especially as additives for others slightly soluble Salts are conceivable) 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 the following: in particular calcium and / or aluminum, also magnesium, or zinc or iron. The (preferably uncoated) hydroxides and / or fluorides are especially advantageous because they are not used to form gases during casting or lead to the production of molds and / or cores, as for example in (otherwise also usable) sparingly soluble salts of organic acids, such as hydroxycarboxylic acids, e.g. Lactates, or the like may be the case. The mentioned slightly soluble Salts are chosen that they are so sparingly soluble are that they are at room temperature (be it because of a coating or preferably by itself) not or not to a disturbing extent with the Water glass can react.

Component (1) and component (2) can be added separately to the mixture, or they can be obtained in advance (with or without water content in the water glass, ie as a dry mixture (available eg by spray-drying), for example as a dry powder, or with the water content, which likewise gives a longer time, for example several weeks, stable compositions which can also be used for adding the two components) and thus added to the other component (s).

Advantageous is when the proportions of Component (1) and component (2) are coordinated, in particular in such a way that a coordinated ratio of cation of the sparingly soluble Metal salt to anion in a glass of water (silicates, especially polymethyl and polydisilicates, etc.). For example, it is advantageous if, based on the dry weight of component (1), the weight ratio of Component (2), to the dry matter contents in component (1) in relation to from 1 to 4 to 3 to 1, for example in one possible preferred embodiment at the weight ratios 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. Is Component 1 in aqueous Form ago, is an example of one preferred weight ratio of component (1) with water to weight of component (2) at 5 to 1 to 1 to 2, such as at 3 to 1 to 1.5 to 1.

Of the Proportion of components (1) and (2) in the mixture for molds and / or cores can be arbitrary in principle. That's the way he relates on the weight of component (3), in a weight percentage of 0.1 to 6 wt .-%, or for example in another potential preferred embodiment in a proportion by weight of 0.5 to 5% by weight, e.g. from 2 to 4% by weight.

component 3, one or more during the casting process non-melting ("refractory") particulate materials, For example, they are heat resistant grained Materials such as chromite sand, alumina, zircon sand, aluminum silicate, Chamotte, silicon carbide, mullite, graphite, fosterite, synthetic Ceramic sand or, in particular, heat-resistant sands, such as quartz or foundry sand, but also soluble Salts, such as sodium chloride, or mixtures of two or more of these Components.

When further optional additives In particular, there are agents for increasing the flowability into consideration, for example corresponding surfactants or wetting agents, such as anionic, cationic, amphoteric or nonionic surfactants, or two or more thereof, along with other additives such as quartz flour, clay, talc, Water, other solubilizers, such as alcohols, or the like, which are preferably based on the Total mass of the component (3), for example in a proportion of in total, or preferably, a total of 0 to 5 wt .-% added can be such as from 0.01 to 1% by weight, in the case of water, e.g. to 4%.

As mentioned, includes the use according to the invention after mixing the components in a further step, that the available mixtures is introduced into a mold or core tool, for example by shooting. simultaneously with the introduction into a mold or core tool and / or subsequently thereto The mixture is heated to temperatures below the temperature the one to be poured Metal or alloy melt lie, for example, in a potential preferred embodiment the invention more than 200 ° C. below this temperature, for example (absolute) at 250 ° C or below, in a possible preferred example between and from 80 to and 200 ° C, for example from and with 100 to and with 150 ° C. The important thing is that one for the reaction, which is greater heat for pourability leads, required temperature is not exceeded for too long, resulting in unstable Would give shapes and / or cores, since the conversion into a form easily convertible into a pourable state already going too far. On these are "green" shapes and / or cores obtained, which have a sufficient stability for foundry purposes.

The available green Shapes and / or cores are suitable for use and are used in a still further preferred embodiment of the invention, if necessary after removal from the forming or core tool used for manufacturing a foundry product (as examples are here, without this restricting effect should, suction pipes about for Motors, cooling tubes, Door hinges, Fuel nozzles for Petrol stations, cast iron pipes, taps, Hydraulic valves or the like) by pouring any Melting of metals or metal alloys, in particular tin, lead, zinc, bronze, iron, gray cast iron, steel or aluminum or aluminum alloys. For example, in aluminum or alloys thereof achieve particularly good results, in particular, if Calcium fluoride is used, or in higher melting metals or Alloys, such as iron or steel, with higher melting aluminum fluoride or aluminum hydroxide so that their uses are particularly preferred Embodiments of Concern 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 down Lung phase, for example, as described above reactions of released cations and / or anions of the sparingly soluble metal salts, the forms used and / or cores are converted into such a state that they in a further, belonging to a still further preferred embodiment of the present use invention step of Removal then easily transferred into a pourable form and so mechanically, for example, by shaking, ultrasound or tapping, or the like, can be removed.

Where above and below is referred to forms and / or cores includes This also means that only one form and / or one core (in singular) can be - the The invention therefore also relates to individual cores and individual ones To shape.

following will be some preferred embodiments of the invention, wherein by the above (in particular as preferred or for example characterized) definitions individual or more general expressions or proportions may be replaced by more specific ones to particularly preferred embodiments leads.

A preferred embodiment The invention relates to the use according to the invention as claimed 1, wherein as component (2) one or more hydroxides, carbonates (such as magnesium-calcium carbonates, e.g., dolomite), sulphates (such as kieserite), Metal fluorides and / or hydroxides, especially hydroxides and / or preferably fluorides, preferably of calcium, of aluminum, of magnesium, iron or zinc, which are used may be free or in coated form.

More preferred is a use according to the preceding paragraph, wherein as component (2) Calcium fluoride, aluminum fluoride or a mixture is used.

Yet stronger preferred is a use according to any of the preceding two paragraphs, wherein component (1) and component (2) to component (3) as a mixture or individually be added.

A Another preferred embodiment of This invention relates to a use according to any one of the preceding three paragraphs, wherein the molar water glass module of the component (1) used e.g. is 1 to 4, and / or wherein the ratio of Component (2) to the dry matter contents in component (1) at 3 to 1 to 1 to 4.

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

A Use according to one of the preceding five paragraphs, wherein as component (3) a heat resistant grained Material, especially sand, is added, is also one very preferred embodiment.

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

Prefers is also a use according to one of the preceding seven paragraphs, wherein the available one Mixture is introduced into a mold or core tool, wherein also simultaneously with the introduction into the mold or core tool and / or subsequently the Mixture at temperatures of 200 or more degrees Celsius (° C) below the Temperature of the pouring a foundry product used metal or alloy melt is heated, in particular on Temperatures from 80 to 200 ° C, preferably from 100 to 150 ° C and a green one Shape and / or a green one Core is made, and even more preferably, where the green form and / or the green one Core continues to pour a foundry product is used.

Especially the subject matter of the invention is also preferred.

The The following examples serve to illustrate the invention, without to limit their scope (all% data are in wt .-%, proportions are based on By weight):

Example 1: Preparation a binder formulation with calcium fluoride as part of a use according to the invention for the Further use according to Examples 5 and 6:

 When Binder mixture will be one of 70% liquid sodium silicate (mod 2.5) as component (1) and 29.6 calcium fluoride as component (2) prepared with 0.4% surfactant (sodium lauryl ether sulfate) as a further additive.

Example 2: Preparation of a binder formulation with sparingly soluble aluminum salts as part of an invention Use according to the invention for further use according to Examples 5 and 6:

When Binder mixture will be one of 70% liquid potassium silicate (mod 3.0) as component (1), 20% aluminum fluoride and 5% aluminum hydroxide as component (2), 3.8% water and 0.2% surfactant (glycoside) as further Additive made.

Example 3: Production a binder formulation with sparingly soluble magnesium salt as a part a use according to the invention for the Further use according to Examples 5 and 6:

When Binder mixture will be one of 70% liquid sodium silicate (mod 2.0) as component (1) and 30% magnesium hydroxide and 10% aluminum hydroxide produced as component (2).

Example 4: Preparation a powdery one Binder formulation with calcium fluoride as part of a use according to the invention for the Further use according to Examples 5 and 6:

When Binder mixture is a dry powder of 35 silica (pyrogenic or felled) and 30% concentrated sodium hydroxide solution (dry powder) as a component 1 and 35 calcium fluoride prepared as component (2).

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

Example 5: Preparation of mixtures of binders and foundry sand as part of a use according to the invention:

The finished binder mixture according to one of Examples 1 to 4 is in Weight proportion of 2 to 4%, based on the proportion of foundry sand, with foundry sand (Quartz sand) by means of conventional Mixer (paddle) mixed.

Example 6: Preparation of cores or molds as part of a use according to the invention:

The mixtures obtained according to Example 5 are injected into forming or core tools and hardened to "green" shapes or cores at about 130 ° C. Strengths of 200 to 500 N / cm ^{2 are} achieved in this case achieved, for example, only by the introduction of heat and / or hot purging air.

Example 7: Pouring from Moldings and removal of molds and / or cores as part of a preferred use according to the invention:

A Aluminum melt is used with molds and / or cores according to example 6 brought into contact for the production of a molded part. After this Cool down the cores and / or forms converted by simple tapping in a flowable mold and away.

Claims (11)

Use of water glass, and / or one or several precursors of which, in the manufacture of molds and / or cores for foundry purposes, the after subsequent casting process easily converted by mechanical action in a pourable form and so easily removable the said use comprising, as component (1) Water glass and / or one or more precursors thereof, and as a component (2) one or more metal salts sparingly soluble on its own and / or by coating, the so sparingly soluble They are at room temperature because of a coating or on their own not or not in disturbing Extent with can react to the glass of water, for the production of molds which can be removed after a casting process and / or Cores for foundry purposes with the casting process non-melting particulate Materials are mixed as component (3), the available Mixture is introduced into a mold or core tool and simultaneously with the introduction into a mold or core tool and / or subsequently thereto the mixture is heated to temperatures below that Temperatures of the metal to be cast or alloy melts lie. Use according to claim 1, wherein those obtained after heating green Molds and cores when pouring of castings used and then transferred into a pourable form and mechanically be removed. Use according to claim 1 or 2, wherein as component (2) one or more hydroxides, carbonates, especially magnesium-calcium carbonates (e.g. Dolomite), sulphates, in particular kieserite, metal fluorides and / or hydroxides, in particular hydroxides and / or preferably fluorides, preferably of calcium, aluminum, magnesium, iron or Zinc be used. Use according to one of claims 1 to 3, wherein as component (2) Calcium fluoride, aluminum fluoride or a mixture thereof used becomes. Use according to one of the preceding Claims 1 to 4, wherein component (1) and component (2) are added to component (3) as a mixture or individually. Use according to any one of claims 1 to 5, wherein the molar Water glass module of the component (1) used is 1 to 4. Use according to any one of claims 1 to 6, wherein the proportion of Component (2) to the dry matter proportions in component (1) at 3 to 1 to 1 to 4. Use according to any one of claims 1 to 7, wherein the components (1) and (2), based on the proportion by weight of component (3), in a proportion by weight of 0.1 to 6 wt .-%, in particular in a proportion of 0.5 to 5 wt .-%. Use according to one of claims 1 to 8, wherein as component (3) a heat-resistant granular material, especially sand, is added. Use according to any one of claims 1 to 9, wherein as further Component a means of increasing the fluidity is added. Use according to any one of claims 1 to 10, wherein simultaneously with the introduction into the mold or core tool and / or subsequently the Mixture at temperatures of 200 or more ° C below the temperature of the for casting a foundry product used metal or alloy melt is heated, in particular on Temperatures from 80 to 200 ° C, preferably from 100 to 150 ° C and a green one Shape and / or a green one Core is made.