SU1156801A1 - Ceramic mixture for making moulds and cores by permanent patterns - Google Patents

Abstract

CERAMIC MIXTURE FOR MANUFACTURING MOLDING CASTING FORMS BY CONSTANT DESIGNS, including a refractory filler, hydrolyzed ethyl silicate and a gelling agent from the class of inorganic bases, differing from that in order to increase its anti-burning cost, who will apply the cost of the application. ingredients, wt.%: Hydrolyzed ethyl silicate16, 8-34.5 Gelling agent from the class of inorganic bases 0.8-2.2 Chromite magnesium 5.2-20.0 Refractory oxide (L steel

Description

SP

O5 00

The invention relates to a foundry, in particular, to the composition of molding compounds for the manufacture of predominantly two-layer ceramic molds and cores according to constant models, and can be used in the production of preferably large-sized steel castings made from high-alloy steel grades.

Ceramic mixtures containing hydrolyzed ethyl silicate, a refractory filler, a gelling agent and various special additives are known in their composition. The disadvantage of known mixtures is that the molds and cores made from such mixtures need to be calcined at high temperature in order to reducing gas creation and removing moisture present in the composition of the liquid component of the mixture and promoting the formation of burns on the surface of the castings.

Closest to the invention by its technical nature and achievable, the result is a ceramic mixture 21 for the manufacture of casting molds and cores in constant models, containing, wt.%: Hydrolyzed ethyl silicate (ethyl silicate-40 solution) 17.0

Quartz sand 20.0 Dusty quartz 60.0 Gelling agent from the class of inorganic bases - 5% sodium hydroxide solution 3.0 The known mixture is most prevalent in the manufacture of molds and cores using constant models.

However, the disadvantage of this mixture is that the molds and cores obtained on its basis for the manufacture of large steel castings with a mass of up to 12 tons, including two-layer molds and cores, do not ensure the absence of burns on the cast surface without their high temperature lining.

The aim of the invention is to improve the non-stick properties of the mixture in the preparation of steel castings.

The goal is achieved by the fact that the ceramic mixture for "

production of casting molds and rods using permanent models, including a refractory filler, hydrolyzed ethyl silicate and a gelling agent from the class of inorganic bases, further contains magnesium chromite in the following ratio of ingredients, wt.%: Hydrolyzed ethyl silicate 16.8-34.5 Gelling agent from the class inorganic bases 0.8-2.2 Magnesium chromite 5.2-20.0 Refractory fillerOther Magnesium Chromite, cured by thermal dissociation of magnesium dichromate by reaction-.

MgCr OT-. MgCr04. + 0.5CrjOj + l 1.50i

2MgCrOj - MgCi: 4. + MgO + 30 is a highly dispersed powder (Sy. 2.5) with a high melting point of.

The content of impurities (GeO SiO, etc.) in the chromite magician does not exceed 0.4-0.9 wt.% (See TU 113-12-11, 007-82). Therefore, having a high refractoriness, a minimum content of impurities, a high specific surface area, magnesium chromite, introduced into the ceramic mixture, increases chemical inertness, to its metal and its oxides.

So, iron oxide FeO is inevitable; but appears at the metal-form interface, as a result of steel oxidation, water vapor and atmospheric oxygen primarily interacts with finely dispersed magnesium chromite, and, by the liquid phase, forms solid solutions of substitution by reaction

FeO + MgO-CrjOj- -FeCr.O + MgO FeO + MgO- (Mg, Fe) 0 Reaction products FeO c. magnesium chromite refractories (Tdd), do not dissolve in iron oxides and are not wetted by liquid steel (wetting angle Q 90), thereby reducing the adhesive strength between the casting and the mold.

In addition, as a result, the volume changes that occur in the case of the interaction between magnesium chromite and iron oxides, occur inside

stress, contributing to the separation of the stick layer from the surface of the casting.

When the content of magnesium chromite is less than 5.2 wt.%, The mixture has insufficient chemical inertness, which leads to the formation of a burn on the surface of the casting. When the content of magnesium chromite is more than 20 wt.%, Large cracks appear on the surface of the ceramic cladding after removing the volatiles, the surface of the molds wrinkles, and metal flows in the form of scallops appear on the surface of the castings.

Example. Getting ceramic suspension. The method of preparing a mixture of two-phase. First, hydrolyzed ethyl silicate is poured into a special mixer, then the refractory filler, magnesium chromite, and a part of the gelling agent are poured in and mixed for 10-20 minutes. As a refractory filler, electrocorundum, marshallite, and dietsilimanite are used. Then a gelling agent — an aqueous solution of alkalis, or Mg oxide, or a combination thereof — is introduced into the mixer, and the mixing is continued for another 0.5-1 min.

The finished mixture is poured into a model tooling, where it is solidified. After removing the model from the hardened mixture or releasing the rod from the core box, the mold and the rods are immediately ignited.

568014

High-temperature calcination of ceramic molds and rods is not carried out, replacing it with heat drying at 260 ° C for 4 hours. Durability

5 mixtures are determined by compression.

samples with a diameter of 20 and a height of 20 mm after the binder is burned out and cooled.

In tab. 1 shows a quantitative

0 | content of compounds 1-6. heading mixture.

As you can see, the forms and rods of the proposed ceramic mixture due to the increased non-stick

5 properties provide irocution of high-quality steel castings without performing a special labor-intensive - high-temperature calcination operation. The known mixture provides a similar high surface quality of steel castings only under the condition that the operation of high-temperature calcination of the molds and cores.

5 In table. 2 shows the properties of mixtures 1-6.

Thus, the use of the invention in production will allow to obtain large-sized shaped steel castings without a burner, without using a high-temperature gasket of keramegic PHO-4 grams of rods. With this, the weight and dimensional accuracy of the castings is increased, and the labor intensity of their manufacture is reduced by about 15-20%.

Table I

Hydrolyzed ethyl 16, 8 19.0 silicate Refractory filled 77, 2 59.8 tel - electrocorundum Marshallite - Distensilimanite 5.2 20.0 Chromite magnesium Gelling agent 1-5% solution of alkali 0, 8 chi 0.5 32, 5.32, five - - - . 61.0 52.8 - - - 54.0 49 7.0 13.0 9.5 16.5 - - - 1.

Composition for mixtures, wt.X

Ingredients

MgO

1.5% solution of alkali + MgO (1: 1 by weight) The prrchnodti limit on compression after burnout of volatile components is 11, 9 14.2 from the bottom, kgf / cm Fine Small Ceramic structure HAIR-HAIR Cracked cracks Prigara-Prigara Surface quality ra no no steel castings

Continued table. one

.

2.0

1.5

2.2 10.2 12.5 8.7 11.1 Minor Minor Minor Minor HAIR-HAIR-BOB-HAIR-HAIR-HAIR-HAIR-HAIR-HAIR-Prig-Prig-Prigar there is no time no fuck no

Claims (1)

CERAMIC MIXTURE FOR MANUFACTURE OF CASTING FORMS AND-RODS BY CONSTANT MODELS, including refractory filler, hydrolyzed ethyl silicate and gelling agent from the class of inorganic bases, characterized in that, with the aim of increasing its non-stick properties, it is obtained from mild alloys the following ratio of ingredients, wt.%: Hydrolyzed Ethyl Silicate 16.8-34.5 Inorganic base gelling agent Magnesium chromite Refractory filler 0, * 8-2.2 5.2-20.0 Rest SU ... 1156801>