SU954138A1 - Heat hardenable mixture for producing casting moulds and cores - Google Patents

Description

in the form of quartz sand, a binder based on a silica compound with sodium oxide and water contains finely ground tridymite and / or cristobalite with a sodium oxide content of 2-6 by mass of binder in the following ratio as a binder based on a silica compound with sodium oxide ingredients, masd: finely ground tridimite and / or cristobalite with sodium oxide content of 2-6 by weight of binder 5-15 Water Refractory filler in the form of quartz sand, Else Tridimite and / or cristobalite with the indicated oxide content on three have a specific surface of 3,, 5 thousand The blend in the composition of the inventive mixture is obtained by burning a material based on crystalline silica, for example quartz sand, in the presence of sodium carbonate at a temperature sufficient to structurally convert quartz to cristobal and / or tridymite (about 1300 s). At the same time, to obtain the material, primitively based on tridymite, requires longer firing and, accordingly, higher energy consumption by 30-35 ° o) than to obtain material, mainly based on cristobalite. The alkaline-silica ingredient obtained with the silica module 40 is subjected to grinding and crushing to form a dispersed powder. It should be noted that the strength of contact point bonds between particles of a sintered mass is relatively small, so its crushing and grinding does not cause great difficulties. The finely ground powder thus obtained, when mixed with water in the above ratios, acquires binding properties. After mixing with water (preliminary or negligently in the process of mixing with quartz sand), the suspension binder has a silica module 16–50, a density of 2.32, 5 g / cm /, pH of pH 10.2–11.6, freezing temperature 4lc , heat resistance 1600-1650 ° C. Forms and from the proposed mixture are cured during heat treatment for 25-30 minutes. After the removal of the bulk of the moisture, the mixture has almost zero gassing and chemical inertness to the liquid metal (steel). The content of sodium oxide in the binder is provided within 2-6 (by weight of the dry binder). When the content of sodium oxide in the binder is below the lower limit, the strength of the molds and cores does not satisfy the production requirements, and when it is above the upper limit, the knockability of the molds and cores from castings (mainly steel) deteriorates. The content of the dry binder in the composition of the mixture is provided within 5-15 May D. The minimum content of the binder in the mixture (5) provides the necessary strength to the crown when they are inserted and poured with metal, and the following light knockability. The maximum binder content in the mixture (15) provides the necessary strength for thin-walled rods. At the same time, bendability is satisfactory. A further increase in the content of the binder in the mixture is impractical due to the deterioration of knockability. The dispersion of the material based on tridimite and cristobalite has a significant impact on its binding ability. Dispersity should be in the range of 5 thousand cm / g. The dispersion of dry binder, below 3.5 thousand, leads to a drastic decrease in the strength of the mixture in wet and dry conditions, and the production of a material with a dispersion of more than 5.5 thousand cm / g under production conditions (on existing grinding equipment of the type ball mills) is practically difficult, and besides, when using a material with dispersion higher than 5i5 thousand, there is no further significant improvement in the strength characteristics of the molds and cores. In order to reduce the emission of harmful dust of tridimite and / or cristobalite during the preparation of the mixture, it is possible that the water intended for introduction into the mixture is introduced at the preliminary stage of grinding tridymite and / or cristobalite. When this occurs, the hydration of this material occurs and a further improvement in its binding properties is noted, and, accordingly, an increase in the strength of the forms

and rods at 10-12. In this case, the preparation of the mixture is carried out by mixing the quartz sand with the aqueous suspension of tridymite and / or cristobalite.

PRI me R. Binder for the proposed mixture is obtained by calcining the composition from 91 mass media of quartz sand, 5 mass% of technical sodium carbonate and k mass water. The firing is carried out for 20 minutes at TZOO C. A product is obtained with the content, in wt%, of sodium oxide, tridymite 50-60, and cristobalite else.

The grinding of this material is carried out to obtain a powder binder with a dispersity of 000.

The compositions proposed (1-3) and known 4 and 5) mixtures are given in table. one.

In tab. 2 shows the results of tests of the proposed (1-3) and known and 5) mixtures.

In tab. Figure 3 shows additional details characterizing the dry compressive strength of the proposed mixtures 1-3 depending on the dispersion of the powder binder.

As can be seen from the data table. 2, the proposed mixture has lower residual strength and, consequently, improved knockability (it is advisable to compare mixtures with the same binder content, for example, 1 and j. Especially pronounced decrease in the residual strength of the proposed mixture when it is heated to 800 C (followed by slow cooling to room temperature: it decreases by an average of 5 times compared with the analogous parameter for the prototype. This allows the proposed mixture to be used in the manufacture of rod shapes for casting ceiling elements, since in this case high temperatures are achieved, and warming the mixture, respectively, it is lightweight vybivaemost.

Production tests of the proposed and known mixtures are as follows. Molds with rods made from mixtures whose composition is listed in Table. 1, poured steel. After cooling, the castings are loaded into a tumbling drum. After the tumbling drum passes, the rods from the liquid-glass mixture remain in the castings. Their knocking out is a very laborious operation. In addition, the surface of the castings from the side of the liquid-glass mixture has a great burn-in and requires additional machining. On the contrary, stainless steel, made of tridymite mixture, after casting them with steel and cooling the castings, is easily removed from it, and the surface of the castings in places formed by these rods does not have a burn. Surface finish corresponds to -L 3-D according to GOST 2789-73. As a result, the complexity of cleaning castings using the proposed mixture is reduced by 6.5 times.

Thus, the proposed blend ensures the achievement of the improved embossability of the castings (. Primarily steel) and the improved purity of P (the top of the steel cast.

Table 1

Quartz sand

The material is based on tridimite and cristabalite with a content of sodium oxide C ° 4 and a specific surface of 4 thousand cm / g

8k

93

95

79

15

ten

Water

Liquid glass module 2.8, density 1.4 g / cm

59-61 88-92 e-Strength for compression in a dry state (drying temperature 200 ° C, kgf / cm, with a specific surface of the powder binder, cm / g: 3500

AOOO

5500

95P388

Continued table. 1 5 7

 65-67 37-93

122-128

81-83

140-Y5

88-32 J8-152 92-96

156-160

98-102

9EZ PV-10

Claims (2)

1. A mixture of heat curing for sodium 2% by weight of the manufacture of casting molds and cores, I including refractory filler in Water4 ° quartz sand binding at s. Refractory filler the basis of the combination of silica with hydroxy-. in the form of quartz sand The rest of the house is sodium and water, o tl and h aa sch 2. A mixture of pop. 1, I distinguish with TeMj that, in order to improve your well-being, so that tridymite and / or beemability of forms and rods, advantageous cristobalite with the mentioned content of steel castings, and the improvement of sodium oxide has a specific surface cleanness of the steel surface, n 3,. S cm / g. it contains as a binder on the basis of the combination of silica with oxide Sources of information . finely ground tridime sprites into consideration during examination and / or cristobalite containing oxy- js Yes, sodium 2-6% by weight of binder. Quick-hardening agents with the following ratio of ingredients - “„ instant mixtures. M .. Mechanical Engineering, Comrade, May. 280-29E. Finely divided tri-, dimite and / or cristobalite2. There we, with. 95-105.