CH652053A5 - Preparations for the manufacture or treatment of foundry articles - Google Patents

Description

The invention relates to a preparation for the manufacture or treatment of articles for the foundry, hereinafter also referred to as foundry articles, for. B. casting molds, die-casting molds, refractory parts of ovens or ladles, ceramic mold cores and the like articles, which enables an improvement in the high temperature strength and the fire resistance of such articles. The preparation according to the invention is characterized by the features specified in claim 1.

Various types of silicate-containing compositions are known for treating and producing articles for the foundry, such as casting molds, e.g. For example, the preparations described in U.S. Patent Nos. 4,114,499,4,111,705, 3,961,968, 3,957,715, 3,682,668, 3,576,652, 3,211,560, and 2,842,445. In some of the methods described in the above patents, silicate-containing preparations are incorporated into the molding sand or other crushed refractory material used to make the mold, as a binder, or as an impregnation or coating of a mold made from such material. The silicate-containing preparations described contain various other components or percentage-defined compositions and are generally effective for the intended purpose. Furthermore, some of these methods described can avoid the need to thermoset the molds, i.e. in other words, air-curable or non-baked forms can be obtained. With some of the known methods, however, air-curable molds are obtained whose molded skin or treated surface has an insufficient resistance to certain conditions that are frequently encountered in the foundry. For example, some known formulations do not obtain a molded skin that can withstand the intense heat and erosion caused by the movement of the hot, turbulent molten metal that is poured into the mold cavity. Other known preparations lead to multi-part skin structures that tend to crack when heated. Other known preparations allow the undesired penetration of metal into the molding sand or disadvantageous chemical reactions or the splitting or breaking up of the surface of the mold cavity.

The silicate contained in the preparation according to the invention is a hybrid silicate and / or silicon metaphosphate and the refractory aggregate is preferably selected from zirconium, silicon dioxide, aluminum oxide silicates, graphite, molten silicon dioxide, aluminum oxide, chromite, fibrous aluminum oxide silicates and mixtures thereof. In addition, the refractory aggregates preferably have a particle diameter size distribution of between approximately 10 and 3000 micrometers.

A hybrid silicate particularly suitable for use in preparations according to the invention is described in US Pat. No. 3,961,968 and can e.g. can be produced as follows:

Component weight% (approximation)

Alkyl silicate (ethyl silicate, type 40) 7-9

acidic silica sol (colloidal silica 45-55 water 0.5-1

Glycol ether 35-45

Sulfuric acid (37%) 0.25

Ethanol or isopropanol 5

Here, a reaction vessel was used, which has a cooling device in order to keep the reaction mixture at a temperature between 20 and 27 ° C. This reaction vessel was charged with a premix of 0.25% concentrated sulfuric acid (37%), 0.75% water and 5% isopropanol. With stirring, 40% of ethylene glycol monoethyl ether and then 8% of Type 40 ethyl silicate (available from Union Carbide Company) were added to the above mixture and mixed for an additional 30 minutes. The resulting mixture was then left to stand for 48 hours and then 51% of an acid-stabilized silica solution was added, the mixture being kept at temperatures between 20 and 27 ° C.

The silicon metaphosphate can e.g. be produced according to the following procedure:

Component weight% (approximation)

Sulfuric acid (37%) 0.25

Water (distilled, deionized) 0.99

colloidal silica sol (acidic) 49.05

Ethylene glycol monoethyl ether 30.01

Phosphoric acid (85%) 11.60

Ethyl silicate, type 40 8.10

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652 053

In a water-cooled reaction chamber, 0.25% concentrated sulfuric acid (37%) was combined with 0.99% distilled and deionized water. While stirring, 22.50% glycol ether was added to the reaction chamber and then immediately 8.10% ethyl silicate, type 40 (available from Union Carbide Company) was added. The mixture was then stirred for 30 minutes at a temperature carefully kept between 20 and 27 ° C. After 30 minutes, this mixture was kept at 20-27 ° C for 48 hours, whereupon 49.05% acidic colloidal silica sol was slowly introduced into the reaction chamber. The mixture was then stirred for a further 2 hours while maintaining the temperature of the reaction mixture at 20-27 ° C. When this reaction is almost complete, a mixture of 11.60% concentrated phosphoric acid and 7.51% glycol ether is introduced and the whole is reacted for 30 minutes. The product finally obtained was allowed to cool to room temperature and stored until the coating preparation was produced.

In addition, the following components can be implemented to produce a silicon metaphosphate suitable here:

The mixture may also contain a predetermined amount of an additive to increase wet strength, e.g. Polyvinyl acetate, polyvinyl alcohol or clay. Furthermore, the mixture can contain a surfactant in order to better wet the aggregates 5 during the production of the coating preparation. Suitable surfactants are the usual sodium soaps of fatty acids, carboxymethyl cellulose, sodium sulfates, sodium tripolyphosphates and synthetic detergents, such as "Victawet" from Stauffer Chemical Company, "Wet-io sit" from Nopco Chemical Company, and "Lestoil" from Noxell Corporation. Suitable fatty acid surfactants include "Wetanol" from Clyco Chemicals, Inc., "Surfact" from Casting Supply House, New York, and "Westasep" from West Chemical Products, Inc. Preferred synthetic surfactants are those with a straight line Chain and 10 or more carbon atoms in the chain.

The coating preparation just described can contain the following special components and can be produced in the manner specified below:

component

% By weight (approximation)

component

Hydrochloric acid (37%) ethyl silicate, type 40 colloidal silica sol (alkaline or acidic) isopropanol (anhydrous) phosphoric acid (85%)

fireproof unit 75-90

% By weight (approximation) polyvinyl acetate or polyvinyl alcohol 0.5

25 hybrid silicate 10-25

Surfactant 0.1

0.15 27.42

10.63 41.83 19.94

The preparation was worked up as follows: 0.15% concentrated hydrochloric acid (37%) was carefully mixed with 10.63% alkaline colloidal silica in a reaction vessel equipped with a cooling device. With stirring, 20.92% isopropanol was fed into the reaction vessel and stirred for 10 minutes. A premix of 20.92% isopropanol and 19.94% phosphoric acid was then introduced into the reaction vessel and the contents were stirred for 30 minutes. The resulting mixture was then kept at a temperature between 20 and 27 ° C. for 24 hours. After 24 hours, 27.42% type 40 ethyl silicate was slowly fed into the reaction vessel, maintaining the temperature between 20 and 27 ° C. The contents of the reaction vessel were then thoroughly mixed for 1 hour, kept between 20 and 27 ° C. for 24 hours and then stored for use in the preparation of the coating preparation.

The silicon metaphosphate has the formula

OH

O II

OH I

Si -

1

0

1

- en-

1

0

1

1

- Si - OH I

1

OH

0

1

OH

n in which n = 1, 2, 3 or 4.

To produce a coating preparation according to one embodiment of the invention, a predetermined amount of the hybrid silicate and one of the above-mentioned refractory aggregates or a combination of such aggregates is mixed to form a slurry which is to be applied to the surface of the mold cavity of a casting mold or to the surface part to be treated a similar foundry article is suitable.

40.9% refractory aggregate was mixed with 18.5% hybrid silicate over 15 minutes in a reactor kettle equipped with a cooler to keep the reaction mixture below 30 ° C at all times. 5% polyvinyl acetate were fed into the reaction vessel. The resulting mixture was stirred for 5 minutes, whereupon 0.1% surfactant was added and mixing was continued for a further 5 minutes. The refractory aggregate was added to this preparation as the remaining portion and the aggregate mixture was worked through for 15 min. After thorough mixing, the product was allowed to cool to room temperature.

The coating preparation produced in this way is in the form of a slurry and can be applied in any suitable manner to a specific surface part of the casting mold, the core or similar foundry articles to be treated.

In the drawing, as an example of a 45 foundry article to be treated, a casting mold 10 in the form of a compact made of quartz sand 12 or other crushed refractory material, as is usually used for the foundry technology, is shown in a shaped bottle 14. If the foundry article to be treated is a mold, at least the surface of the mold cavity 16 intended for receiving the molten metal and, if applicable, all parts of the mold which surround the mold cavity, as well as the mold inlet or sprue channel 18 and main channel 20 with the described preparation , e.g. B. coated by coating, 55 painting, spraying or other application methods. The thus coated mold is then allowed to air dry for about 20 minutes, resulting in a mold which has a skin or coating 22 with a thickness of approximately 0.4 to 0.8 mm in the surface parts treated in this way, and which is provided with the hybrid silicate to a depth of about 5 cm to increase the bond strength of the mold. Casting molds treated in this way have an improved surface quality and show considerable resistance to the penetration of turbulent molten metal into the surface of the mold and to peeling and erosion. Furthermore, the casting mold treated in this way has a considerably higher fire resistance than the corresponding non-treated casting mold.

652 053

For a coating preparation made according to an embodiment other than the one illustrated in the example above, the silicon metaphosphate is used together with a refractory aggregate or a combination of such aggregates to form the coating slurry. The mixture may also contain a predetermined amount or type of additive to increase wet strength, e.g. B. polyvinyl acetate, polyvinyl alcohol or clay. The mixture may also contain a surfactant for better wetting of the aggregates during the preparation of the coating preparation. Suitable surfactants are given above.

The coating just described using silicon metaphosphate can contain the following special components and can be produced as described below:

Component weight% (approximation)

fireproof aggregate 75-90 polyvinyl acetate or polyvinyl alcohol 0.5

Silicon metaphosphate 10-25 surfactant 0.1

In a reactor vessel which contains a cooling device in order to keep the reaction mixture below 30 ° C. at any time, 40.9% refractory aggregate were added to 18.5% silicon metaphosphate with stirring and the whole was mixed for 15 minutes. Then stirring was stopped and 0.5% polyvinyl acetate was slowly introduced into the vessel. The resulting mixture was stirred for 5 minutes and 0.1% surfactant was added, whereupon the mixture was stirred for a further 5 minutes. Then the remaining portion of the refractory aggregate was added to the preparation and the resulting mixture was mixed for 15 minutes. After thorough mixing of the product, it was allowed to cool to room temperature.

The coating preparation prepared in the manner just described and containing silicon metaphosphate is in the form of a slurry and can be applied in the same way to the surface or a part of the surface of the casting mold, core or similar foundry articles to be treated according to the above for those made of hybrid silicate and refractory Methods called aggregate-prepared coating preparation are applied. As with the coating method with the coating preparation made of hybrid silicate and refractory aggregate, the surface of the mold cavity and any other surrounding parts of the mold are coated with the preparation made of silicon metaphosphate and refractory aggregate either by spreading, brushing, spraying or by another application method. The mold or core or a similar foundry article treated in this way is then left to air dry for about 20 minutes. The foundry article obtained in this way has the same advantageous properties as the article treated with the preparation based on hybrid silicate and refractory aggregate, including increased resistance to layer separation, cracking, erosion, disadvantageous heat effects and impregnation with the silicon metaphosphate to a depth of about 5 cm, whereby the shape or the article shows an increased bond strength. In fact, the wet or raw strength of molds and similar foundry articles treated in this way is three times higher. When the molds treated in this way are heated, the strength of the mold increases over tenfold and proves to be resistant to temperatures of over 1650 ° C. without deformation due to high-temperature softening.

An important advantage of silicon metaphosphate is its inert behavior against molten steel. It inhibits any adverse chemical reactions between the parts of the foundry articles containing this substance and certain components in the molten metal, such as titanium and aluminum in molten steel, which could oxidize in an undesirable manner. Silicon metaphosphate also improves the radiographic properties of the casting by reducing the amount of exfoliated molding material that would be embedded in the casting during casting.

The foundry articles can also be produced entirely from the preparation according to the invention by mixing the silicon metaphosphate with the molding sand or another comminuted refractory aggregate and the article, e.g. produces a casting mold under compression. The silicon metaphosphate is expediently used in an amount which is suitable for achieving the desired consistency of the preparation to be compacted. A mold produced in this way shows a comparatively higher bond strength and fire resistance as well as all properties of foundry articles which, according to the above information, have been produced or treated using preparations with silicon metaphosphate, such as faster air drying, higher raw strength and resistance to temperatures above 1650 ° C.

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Claims (8)

652 053 1. Preparation for the manufacture or treatment of articles for the foundry, characterized in that it contains at least one silicate component which is a hybrid silicate and / or silicon metaphosphate mixed with at least one refractory aggregate, the latter forming the major part of the preparation. 2. Preparation according to claim 1, characterized in that the silicate component present as hybrid silicate is a mixture of an acidic colloidal silica sol, a water-miscible organic solvent and an alkyl silicate. 2nd PATENT CLAIMS 3. Preparation according to claim 1, characterized in that the silicate component present as silicon metaphosphate is a reaction product of an acidic colloidal silica, a water-miscible organic solvent and phosphoric acid. 4. Preparation according to one of claims 1 to 3, characterized in that the refractory aggregate is selected from zirconium, silicon dioxide, aluminum oxide silicates, graphite, fused silicon dioxide, aluminum oxide, chromite, fibrous aluminum oxide silicates and mixtures thereof. 5. Preparation according to one of claims 1 to 4, characterized in that it consists of: up to 30% by weight, preferably from 10-25% by weight, of the said silicate component, 0-5% by weight of a first additive from the group poly- vinyl alcohol, polyvinyl acetate and clay, 0-5% by weight of a second additive from the group of Fatty acid soaps and synthetic surfactants, and consists of the refractory aggregate as the rest. 6. Preparation according to claim 5, characterized in that the first and / or second additive is present in each case in a proportion of up to 3% by weight. 7. A method for producing articles for the foundry, characterized in that the articles are formed from a preparation according to claim 1. 8. A method for treating articles for the foundry, characterized in that surface parts of the articles are coated with a preparation according to claim 1.