SU1080911A1 - Mixture for producing moulds and cores by co@ process - Google Patents

Description

This invention relates to a foundry, in particular, to molding sand compositions using a CO2 process.

Known molding mixture fl according to the CO process, containing a refractory filler, water and a binder — slaked lime, which reacts with carbon dioxide by the reaction of Ca (OH) -, nlUO + COOCACOd

+ (h HI) ..

The disadvantage of such a mixture is its low strength immediately after carbon dioxide blowing, due to the fact that the calcium carbonate film, which forms during the second period of hardening on the surface of lime, makes it difficult for carbon dioxide to penetrate into its inner layers. Due to this, the carbonization process, which can be relatively intensive in the presence of a sufficient amount of carbon dioxide, is strongly inhibited and can be suspended, and non-carbonated calcium oxide hydrate and unrelated water remain in the mixture.

It is known to use cement, calcium chloride mixtures as a C2J hardening accelerator.

However, in this mixture it contributes to the formation of sparingly soluble salts in self-hardening mixtures, the use of which requires a certain time.

Closest to the invention to the technical essence and the achieved result is a molding mixture according to the SOL process, which includes a refractory filler, hydrated lime, water, and, as an additive, aluminate dsaltsi SZ.

However, the known mixture does not have high strength, in order to achieve which the mold and the rod need to be kept in air for 24 hours after flushing the COU.

The aim of the invention is to increase the strength of the molding mixture after purging with carbon dioxide.

To achieve this goal, the mixture for the manufacture of casting molds and cores according to the CO process, including a refractory filler, a binder based on slaked lime, water and a processing additive, additionally contains a sulphite-yeast brew, and calcium chloride as a processing aid. with the following ratio of ingredients, May.%:

Holy lime based on hydrated lime3-6

Water 3-6

SDB0,01-0,20

Calcium chloride 0.1-1.0

Refractory fillerOther

Moreover, the binder based on hydrated lime has the following composition / wt.%:

Calcium Oxide Hydrate 80-98 Calcium Carbonate 2-20

When this mixture is hardened on a high limestone binder with additives, the formation of complex hydrate compounds of the type of basic calcium carbonate, for example, x X Ca (OH) 2 OR OR -CaCOjCaC x X chNLO, is already important. In this case, calcium carbonate produces a multitude of crystallization centers, which promote the formation of calcium carbonate crystals in the hardening mixture. This contributes to the accelerated hardening of the mixture and its acquisition of increased strength, which is not observed when the content of carbotane calcium in the high limestone binder is less than 2 wt.% And calcium chloride in the mixture is less than 0.1 wt.%

When the content of calcium carbonate in the high limestone binder is more than 20 wt.%, The increased strength is not ensured due to the insufficient content of the basic phase of calcium oxide hydrate. The content of chloride is more than 1 wt.% In the mixture is undesirable because of the increased hygroscopicity of the mixture.

Calcium chloride lowers the temperature and accelerates the process of dissociation of CaCO and the softening of the mixture in the process of cooling the molds after pouring them with molten metal, which contributes to the ease of knocking out the mixture from the castings.

A high lime binder is obtained by calcining a natural raw material of an appropriate composition, followed by quenching} by calcining a mixture of an appropriate composition, followed by quenching; mixing in a predetermined ratio of pre-prepared components.

The introduction of high-limestone binder and water in the composition of the molding mixture in an amount of less than 3 wt.% Of each leads to a decrease in the strength characteristics of the molding sands, an increase in crumbling and brittleness. When the content of high limestone binder and water in an amount of more than 6 wt.% Of each leads to increased adhesion and gas-creation of the mixture, low gas permeability, and also impractical for economic reasons. considerations m.

As a surfactant, it is advisable to use a BDM, which is a catalyst for the carbonation of a lime binder due to the presence or the formation of sugars and calcium lignosulfonates. However, when the BDS content is more than 0.20 mass%, the gas permeability of the mixture decreases sharply, which reduces the penetration of the mixture after carbon dioxide blowing and leads to a deterioration in the quality of the casting due to the formation of gas holes in the castings and burner.

As a refractory filler in the preparation of molding compounds using quartz sand, chromite, chromium magnesite and other refractory materials. I

Example 1 A high lime binder is obtained by calcining at 900-1100 seconds from a mixture of the appropriate composition of individual components, followed by a solution to obtain the following composition, in% by weight:

Calcium Oxide Hydrate 90 Calcium carbonate 10 The firing mode should ensure that firing results in calcium in addition to CaO and calcium carbonates.

The high binder binder is mixed with molding quartz sand for 2 minutes, then a liquid composition of calcium chloride and DMB is added and mixed for an additional 1– 2 minutes. Standard specimens are filled from the mixture (H 50; 0 50 mm} for compressive strength immediately after flushing with carbon dioxide.

The compositions of the molding mixtures are listed in the label. one.

Table 1

A high limestone binder according to the example. Example 2. A high-steely T (G, BODY) binder is prepared according to example 1, it is carried out according to example 1 of the blowing composition, May.

Calcium oxide hydrate 80 Compositions. Forming mixtures

Calcium carbonate 20deny in the table. 2

High binder according to example 2

Add

Water

Calcium chloride

table 2

Example 3. A high lime binder is prepared according to Example 1 of the composition, wt%:

Calcium Oxide 98 Hydrate Carbonate 2

. 80.40

sand

waste at 3, 0 0.01 3.0 0.1

calcium

Physicomechanical

techno

lo.G1 chesky properties of mixes. h

14,016,5 iO, 0

12.5

14,017.0 11.0

13.0

14,517.5 13.0

13.5

26.029.0 2 & 0

25.0

0,53 0,48 0,60 0,45 0,40 0,50 0,35 0,35 0,45 0,20 0,25 0,20

The preparation of the mixture and samples is carried out as in Example 1,

The composition of the molding compounds predsgavleny in. Table. 3. Table 3

86.80

6.0

4.5 0.20 0.10 6.0 4.5 1.0 0.5

13

from tab.

Tables are given. four.

J a b l and c

12,013.0 15,012,513,514,5

12,513.0 15,513,014,014,5

13,513.5 l6,013,515,015.0

15.025.0 27.525.025.516.5

0.520,450,480,450,450,48

0.400,350,400,400,380.40

0,300,250,250,350,320,32

0,200,200,200,250,200,20

The gas permeability of the mixtures, as well as other properties, depends on the type of sand, and the use of 2K016A sand is 90119 units. ,

As shown by production tests, the survivability of the mixtures depends on the temperature of the sand and the environment and is 16-24 hours. When the samples are made up to 800, 1000 and 1200 ° C, the samples are completely dispersed.

As follows from the table. 4, the strength of samples from a mixture of the proposed composition is 20-50% higher than the strength of a known mixture, which promotes the use of mixtures under conditions of mass production without prior exposure to air to provide the necessary technological strength.

The economic efficiency from the application of the proposed molding sand compositions is 3–5 rubles per ton of useful material. I.

Claims (3)

1. MIXTURE FOR THE PRODUCTION OF CASTING FORMS AND RODS BY THE CO _£ -Process, comprising a refractory filler, a binder based on slaked lime, water and a technological additive, characterized in that, in order to increase the strength of the mixture after blowing with carbon dioxide, the mixture additionally contains sulfite yeast mash, and as a technological additive - calcium chloride in the following ratio of ingredients, May.%: Binder based on slaked lime Water Sulphite-yeast mash Calcium Chloride Refractory Filler 2. The mixture according to π. 1, , 3-6 3.-6 0.01-0.20 0.1-1.0 The rest of t and h a rout I with the fact that the binder based on slaked lime has the following composition, wt.%: Calcium Oxide Hydrate 80-98 Calcium Carbonate 2-20