SU807542A1 - Mold and core making sand - Google Patents

Abstract

MIXTURE FOR MANUFACTURING CASTING FORMS AND RODS, cured with a gaseous hardener, including a refractory filler and an integrated binder — a by-product of the production of crystalline silicon in combination with water and alkali, which, in order to increase strength and reduce -. after curing with gas while maintaining good knockability and high nonstick properties, the mixture contains the specified ingredients in the following ratio, wt.%: By-product of the production of crystalline silicon 1.1-1.4 Alkaline0.85-0.98Water .2 , 65-3,02 Fire-resistant fillerEverything else

Description

The invention relates to the field of foundry, namely, molding and core mixtures for the manufacture of casting molds and cores, cured with a gaseous hardener. Widely known are mixtures that are cured by carbon dioxide blowing, in vitro refractory filler, eg boar sand and KOMZineKCHoe binder based on a liquid glass of a military solution of alkali metal silicate and 10-20% aqueous solutions of caustic HaTpaftJ. Closest to the described invention, the technical essence and the achieved result is a mixture for the manufacture of casting molds and cores, cured by a gas-curing hardener, including a refractory filler and complex binder - a by-product of the production of crystalline silicon in combination with water and alkaline. A disadvantage of the known mixture is low strength and friability of the forms and rods after curing. The aim of the invention is to increase the strength and decrease the fritability of the molds and rods after gas curing while maintaining a good choice of antiburning properties. To achieve this goal, blends for the manufacture of casting molds and cores, hardened with a gaseous hardener, include refractory filler and a complex binder from the production of crystalline silicon in combination with these and alkali contain the specified ingredients in the following ratio, wt.%:. By-product of the production of crystalline silicon;, .- - 1.1-1.4 Caustic soda (20A-aqueous solution) 3.5-4.0 Refractory fillerOther Refractory filler - molding sand according to GOST 2138-74. The by-product of the production of crystalline silicon is a fine, non-porous, highly cremaceous amorphous dust of general chemical composition, wt.%: Carbon 3-10 Aluminum oxide 1-4 2 Iron oxide 1.5-1.6 Calcium oxide 0.3-1, 7 Silicon dioxide. Rest Bulk weight 160-170 kgf / m angle of repose - 40. Dust is not hygroscopic, prone to the formation of aggregates, has a gray grain dust: A by-product of the production of crystalline silicon is ocHoBHEtM component of the complex silica-containing binder in the proposed mixture. Particles of high-silica dust, in particular a by-product in the production of silicon from silica containing: compounds, are solid particles of hydrated amorphous silica-silica gel. During heat treatment in an alkaline medium, silica gel transforms into various forms of high molecular weight silicic acids in aqueous solution, which has clearly pronounced colloid in adhering properties after cooling. The alkaline medium in the complex silica-containing binder of the proposed mixture is {{a 20% aqueous solution of caustic is used. The pH of the medium at the selected ratio of binder components is pH 12.9-13 units. This ensures the transfer of high molecular weight silicic acids to the state with the main form of existence in the form of the 5i OI ion — with an active, non-saturated double bond Si O, capable of polymerization with a subsequent decrease in pH, for example, by blowing carbon dioxide () in the closed) structure of the initial particles of amorphous silica (silica gel) SiO. With carbon dioxide, the proposed mixture of silica binder polymerizes from the SiO 3 form to the solid polymer structures of the particles of amorphous silica - silica gel, which has the initial size of byproduct particles, the production of crystalline silicon. Simultaneously, carbonates of sodium are added in the binder film. When purging carbon dioxide with a gas of a known mixture, liquid glass-sodium silicate decomposes into a silica film with the formation of silica gel with an average particle size of silica of 80 A and carbonates. The much larger dimensions of a portion of the silica gel in the binder film of the substrate of the proposed mixture (3 μm 3 versus 80 A in the known mixture) provide them with greater energy stability. those. lower tendency to react with sodium carbonates at a usual temperature, and when filled with liquid metal - with metal oxides at the metal – form interface. In a known mixture, when it is flushed with carbon dioxide, along with the formation of silica gel from silicate, a reverse process also takes place at an ambient temperature, which is accelerated at a higher because of the low energy stability of silica gel particles, a product of decomposition of liquid glass. When the metal is poured with liquid metal, sodium silicate in a known mixture on the face of metal — the form forms strong ferrous silicates with oxides of metal, which promotes formation; durable burn mixture to casting. In the thickness of the mold or rod, when they are heated from the heat of casting, sodium silicate interacts with a filler — quartz sand; they form strong monoliths with a blurred border; the filler — the binder. When the proposed mixture is poured with liquid metal, the formation of a hardened casting crust ends more than the complete dissolution of small and large silica particles in the molten carbonate in the binder film with the formation of silicates at the metal-form interface. However, from the heat content of the cooling metal over time, the sodium silicate in the binder film in the mixture layer at the surface of the casting is formed by contact, it interacts with the filler, but the strong crust of the mixture with a clear boundary has a thickness of no more than 2-12 mm with a casting thickness of 15- 130 m and has a low grip. Pig of the mixture is easily removed. In the thickness of the mixture behind the crust in the binder film, changes do not occur. The film consists of a solid mixture of particles of amorphous silica and carbonates. with admixture of sili-. sodium cathode and easily destroyed. This contributes to the easy knockability of the proposed mixture of castings using conventional methods. The binder is prepared as follows. Caustic soda is dissolved in the calculated amount of water at room temperature. Next, amorphous dust, a by-product of the production of crystalline silicon, is introduced and dissolves it, continuously mixing until a homogeneous solution is obtained at a temperature of 80-90 ° C for 2.0-2.5 hours, providing a technologically acceptable viscosity of 25-30 centipoise. The finished binder, after cooling, is a stable colloidal solution in which the by-product particles of the crystalline silicon production are in the form of high molecular weight silicic acids. The binder components are mixed in a closed type mixer to prevent water from evaporating. The proposed mixture is prepared, in a conventional type of paddle or roller mixer, by mixing the refractory filler with the binder for 2 minutes. The preferred method of making rods and molds from the proposed mixture is by purging with carbon dioxide in a snap-in under high-volume, low-volume and mass production conditions. The invention is illustrated by the compositions and properties of the mixtures, which are listed in Tables 1 and 2. As follows from the tables, mixtures No. 1.3 and 4 have the best complex of properties. When the content of the house components is below the lower limit No. 1, the strength decreases after solidification by carbon dioxide blowing, and when the SRI contains their upper limits (mixture No. 5), a decrease in gas permeability is observed, a slight deterioration in selectability and sticking. The mixture in accordance with the invention has higher physical and technological properties after purging with carbon dioxide: compressive strength 4.2 times;

crumbling lower by more than 20 times, with little work

807542 "

on selectability and practical absence of sticking.

Table 1

Alkali (caustic

rub according to GOST

4328-66)

Water technical

Quartz sand

in accordance with GOST 2138-74 of Grimerchani

Compressive strength, after purging with carbon dioxide for 45 s, kgf / cm

252 230 228

3.5 0.3 0.16 6.9 0.5 0.36

0.760,850,915 0,981.12

2,342,652,735 3,023,48

95,995,4.95,09 94,693,9

table 2

16.8 18.5 18.9

14

230 217

190

0.11 0.08 0.04 0.26 0.19 0.16 e: The values of alkali and water given in the table correspond to a 20% aqueous solution of caustic soda. Beatability, kgm (for work expended on producing a mixture from a sample) Not with prigoreyamost (visual assessment) burns to the castings - samples with thicknesses of 20, 50 and 100 mm castings

807542

8 Continuation of the table, 2 By raising the mixture in casting specimens, the metal is removed to a clean surface by tapping in the form of a mixture of mixers that do not adhere to the mixture. tall with a crust Under the crust the surface of the metal is pure mixture

Claims (1)

A MIXTURE FOR THE PRODUCTION OF CASTING FORMS AND BARS, cured by a gaseous hardener, including a refractory filler and a complex binder - a by-product of the production of crystalline silicon in combination with water and alkali, characterized in that, in order to increase the strength and reduce the crumbling of molds and cores after gas curing, while maintaining good knockability and high non-stick properties, the mixture contains the indicated ingredients in the right ratio, wt.%: A crystalline silicon by-product 1.1-1.4 Alkali 0.85-0.98 Water 2.65-3.02 Refractory filler SU „„ 807542