CS218263B1 - Admixture in the foundry selfhardening forming and core mixtures - Google Patents

Abstract

Additive to foundry self-hardening molding and core blends with water glass · in the amount of 1.2 to 4.0% by weight. as binders and liquid based hardeners Organic esters. The essence of the solution lies in that the additive further contains amorphous silicon dioxide, of which the average silicon dioxide the particle diameter ranges from 1.10 "7 to 2.1O ~ 4 * * and is contained in the mixture in an amount of 0.2 to 0.5 5.0% by weight.

Description

The invention relates to an additive to a foundry self-hardening molding and core composition comprising water glass as a binder and a liquid organic substance as a hardener, for example based on glycerin esters or glycols or glyosal derivatives.

The use of self-hardening compounds is based on the prospective foundry technology of mold and core production, leading to increased productivity of casting production, reduction of laboriousness, elimination of strenuous work and reduction of qualification requirements. Self-hardening compositions eliminate the need to dry the molds and; and extend the field of applicability of raw casting. The most widespread self-hardening compositions contain waterglass as a binder, the advantage of which is low cost, hygienic safety during molding and casting. Certain organic substances, such as esters such as glycerin and glycol acetates or glyoxal derivatives, are used as the most preferred liquid waterglass hardeners. Compositions containing these hardeners provide molds and cores of high strength after curing, curing speed is reproducible and easy to control.

A disadvantage of existing waterglass and liquid hardener compositions is the relatively lower core and mold strength when removed from the cores in relation to the ultimate strength that the core obtains by drying our air. This deteriorates the disintegration of the mixtures, since the water glass content must be selected due to the desired handling dryness of the core and the mold in the non-dry state <and therefore not according to the final core strength values which would allow considerably lower water glass contents. A further disadvantage of the water glass and liquid hardener compositions used hitherto is the high tendency of the cores and molds removed from the modeling device and core box to deform at normal laboratory temperatures. Deformations occur even at otherwise sufficiently high strength of molds and cores, which can then manifest itself in loss of dimensions and accuracy of the core and mold. When casting with the effect of temperature and stress in the mold or core strongly increases the susceptibility of existing mixtures to deformation, which affects the quality of the castings and the occurrence of a number of difficulties and defects, especially when casting larger and more massive castings.

It is further known to use silica powder to increase the viscosity of resins or to adjust the theological properties of suspensions. E.g. čs. ΑΌ 111250 indicates use up to 5% by weight. of active silica into liquid mixtures for the production of fdrs and cores for precision casting.

Disadvantages of the conventional self-hardening molding and core mixtures of water glass and liquid hardeners removes the additive according to the invention whose principle consists in that, IB is formed powdered amorphous carbon 'silica of average particle diameter ranging from 1.10 ^-7 to 2.10Γ ⁴ meter and in the mixture % in an amount of 0.2 to 5 wt. of the total weight of the molding and core mixture.

As additives according to the invention, it is advantageous to use a flux from the production of crystalline silicon which is formed by isotropic spherical particles of amorphous silica powder of 0.2 to 2 microns, grouped in solid form in porous agglomerates of up to 50 microns. The specific surface area is 20 to 30 m ^a / g, the minimum SiO 2 content is 90%, the heat resistance is 1680 ° C.

The use of an additive in said self-hardening compositions achieves a number of advantages. The cure speed and strength of the cores at the time of removal from the core are increased without compromising the life of the mixture. This makes it possible to reduce the water glass content up to 2% in the mixture. This will improve the disintegration of the cores after casting and reduce the cost of cleaning the castings. Increased cure speed and strength of the cores at the moment of forming and removing the core from the core, the productivity of the production of cores and molds increases substantially. Another significant advantage is the increase of the resistance to deformation of the molds and cores by cold and after casting by the molten metal. The additive thus improves the dimensional accuracy of the castings, preventing the occurrence of defects, bulges and deformations. It allows extending the applicability of liquid hardener mixtures to more massive and thicker castings and more complex molds and cores, while reducing the cost of the mixture and increasing its disintegration.

The effect of the additive increases with its increasing content in the mixture. Typically, a sufficient content of the additive according to the invention in foundry compositions is 1% by weight of the composition.

The additive is applicable to mixtures containing all kinds of waterglass differing in module, density and reactivity. It is also effective when using various types of liquid hardeners of different chemical nature and cure speed. The compositions containing the additive according to the invention are useful in casting steel, cast iron and non-ferrous and light alloys.

In practical use of the additive, it is advantageous to embed it in the sand, then to add a hardener, water glass and possibly water. Testing with positive results is also mixing of the additive in water; This can, however, be advantageous only for short storage times of the waterglass and additive mixture, when the viscosity of the waterglass is not affected by the additive.

An exemplary use of the additive according to the invention is given in the following examples, which also show the effect of the additive compared to known mixtures.

Example 1

Composition of the mixture in parts by weight A mixture with an additive according to the invention known mixture quartz sand with a mean grain size of 0.36 mm 95 96 water glass of module 2,3 and density 5f) ° Bé 3.0 3.0 a diacetate and triacetate glycerin hardener 0.3 0.3 Addition of amorphous silica powder of spec. surface area 27 m ² / g 1.0 water 0.7 0.7

Compressive strength in MPa for standard rollers hardened in the core box

For doibu curing in h:

0.5 0.8 0.3 1.0 2.2 1.3 4.0 2.8 1,8 Pot life in min. 10 to 12 12 to 14 Time to destruction at 0.3 MPa load 4.0 0.8 and temperature 1000 ° C in minutes Temperature in ⁰ C at which the roller achieves a deformation of 3% at a load of 0.2 MPa 640 580 Example 2 Composition of the mixture in parts by weight mixture with additive known mixture according to the invention quartz sand with a mean grain size of 0.36 mm 96.3 97.5 water glass with module 2,2, 50 ° Bé 12.0 2,0 a diacetate and triacetate glycerin hardener 0.2 0.2 Addition of amorphous silica powder of spec. surface area 27 m ² / g 1,2 · water 0.3 0.3 Compressive strength in MPa for standard rollers cured in adipose in time of curing Setting in h: 0.5 0.7 0.2 1.0 1.4 0.8 4.0 1,8 1.3 Time to destruction at a load of 0.3 MPa and a temperature of 1000 ° C in minutes 5.0 2,0 Example 3 Composition of the mixture in parts by weight mixture with additive known mixture according to the invention quartz sand with a mean grain size of 0.36 mm 96.0 96.4 water glass on coagulation threshold 4.4% Na2O 2.5 3.0 glycerin triacetate 0.25 0.3 addition of amorphous powdered oxygen 1.0 - silicon niche spec. surface area 21 m ² / g water 0.25 0.3 Compressive strength in MPa for standard rollers cured in adipose in time of curing Production in h .: 0.5 0.8 0.1 1.0 1,2 0.7 4.0 1,8 1.4 Time to destruction at 0.3 MPa load and 1000 ° C in minutes 5.0 1.0 The temperature at which the roller reaches a deformation of 3% at a load of 0.2 MPa 620 570

He attaches

Composition of the mixture in parts by weight mixture with an additive known mixture according to the invention

medium size quartz sand 95.1 96.1 grain 0.36 mm water glass of module 2,3 and density of 50 ° Bé 3.0 3.0 METYLGLYOXAL 0.9 0.9 Addition of amorphous silica powder of spec. surface area ² µl m ² / g 1.0 Compressive strength of standard rollers in MPa per 24 hours i3,5 2.5 Time to destruction at 0.3 MPa load and 1000 ° C in minutes 2,0 0.6 Temperature at which the roller achieves a deformation of 3% at a load of 0.2 MPa 560 500

Example 5

Composition of the mixture in parts by weight

Sorted flake grit 93.2 water glass of module 2,3 and geese 3.0 total 90 ° Be Diacetate-based hardener 0.3 and glycerin triaoetate Amorphous powder additive 0.8 silicon dioxide a surface area of 27 m ² / g water 0.7

Subject

Claims (1)

Additive to foundry self-hardening molding and core mixtures with water glass in an amount of 1.2 to 4.0% by weight as binder and liquid hardeners based on organic esters, such as glycerine acetates or glycol derivatives based on glyoxal derivatives, such as the reaction product of glyoxal and acetone in an alkaline alkali environment in an amount of 0.1 to 1.0% by weight of the unreacted product, based on the content of the mixture, characterized in that it contains amorphous powdered silica with a mean particle diameter in the range of 1.10 ^-7 to 2.10 ^-4 m. it is present in the mixture in an amount of 0.2 to 5% by weight.