SU939154A1 - Self-hardenable mixture for producing casting moulds and cores - Google Patents

Description

The invention relates to foundry, in particular, core and molding mixtures with mineral binders to produce high-quality castings with regard to environmental requirements. The known mixture for the production of casting molds, containing refractory filler, water and hydraulic cement in which calcium aluminate fluoride present | 1 This mixture is characterized by slow hardening in air and difficult knock-out of castings in connection with the sintering of the specified type of cement with quartz sand. Also known is a self-hardening mixture containing quartz sand, gypsum (hydraulic binder as calcium salt, namely sulphate calcium) and water 2. This mixture is characterized by an excessively high content of gypsum (up to 70 wt.), Which determines their technological features and the possibility of using it only for color casting. The process of making molds from a mixture is labor intensive and requires increased energy consumption. Closest to the proposed technical essence and the achieved result is a self-hardening mixture for the manufacture of foundry molds and cores, containing, m.h: hydraulic refractory filler hydrating in the form of calcium salt, namely calcium sulphate high-strength gypsum) 6-10, fortifier KOS 0.5-2.5 water k, 7S-5i.7S H. . This mixture is characterized by relatively low strength properties during self-hardening, which degrades the quality of the molds and cores. The purpose of the invention is to increase the strength of the forms and rods at all stages, their hardening. 3 The goal is achieved by the fact that a self-hardening mixture for the manufacture of casting molds and cores, including a refractory filler, a hydraulic calcium calcining salt, and water, contains calcium as calcium salt — a compound based on calcium aluminate with the following the ratio of ingredients, ma.ch; Refractory filler 100 Calcium aluminate-based compound. Water -9 Mixture contains calcium sulfoaluminate as the calcium aluminate-based compound. The mixture contains calcium sulfoaluminate and calcium aluminate fluoride as a calcium aluminate compound in the following ratio. ingredients, mash.: Refractory filler 100 Calcium sulfoaluminate 2,, 5 Calcium aluminate fluoride 2.5-3.5 Water.4-7 When the content of the proposed mixture contains a compound based on calcium aluminate below the lower limit (5 m .) the required level of the strength characteristics of the molds and rods is not reached, and when its content is above the upper limit (9 wt.h.), the humidity and the gas-generating capacity of the mixture increase. Calcium sulfoaluminate is a solid phase sintering product for gypsum, limestone and bauxite, followed by grinding the product to a finely divided state (for example, to a specific surface area of 0.6) with the general formula 3 (CaOAI-j O) CaS (X. When interacting with water it forms high-sulfate forms of calcium hydrosulphoaluminate such as ettringite KaOAljz Oj-JCaSO.The high energy of water in this mineralogical formation allows obtaining high strengths of the forms and rods.The high water demand of calcium sulfaluminate requires an increased water sulfate ratio (, 81, 0), Increasing B / C over 1.0 results in 55

to slow down hardening, and a reduction in B / C below 0.8 increases the crumbling rate and reduces the strength of the mixture.

by stirring the mixture until water is evenly distributed by weight of the dry ingredients. A Calcium aluminate fluoride, which, like calcium sulfoaluminate, is a solid phase sintering product, has the formula 11Ca0 7A1 0-J. X Sar2. In the presence of water, such a fluoroaluminate. . Calcium very quickly hydrates with the formation of split spherulites of calcium hydroaluminates kCaOM () 2 and aluminum hydroxide gel, which leads to an energetic process of self-hardening of the mixture (another factor contributing to self-hardening is the formation of calcium sulfoaluminate from ettiringite, mentioned above). With an increase in the content of the sum of the specified binders over 7 May, h. the strength does not recover, since the rate of their hydration is high ahead of the rate of structure formation. Dilute the mixture with sand, i.e. By reducing the content of binders, it is possible to bring the growth rate of the nuclei of crystallohydrates into line with the growth rate of the growth crystals of the new growths. Reducing the content of the binders is less than 5 bpm. leads to a decrease in strength and increased shedding. High water demand for re-emittable aluminates requires a high water-aluminate ratio (B / C 0.8 - 1.0). An increase in B / A of over 1.0 results in a slower hardening and increase in the moisture content of the mixture. The value of B / A below 0.8 leads to an increase in flaking ability and a decrease in the strength of the mixture. In this case, the total amount of aluminates within the specified limits is significant, not their ratio in the mixture. Due to the high refractoriness of fluoride sulfoaluminates (they are produced by solid phase sintering at temperatures below the appearance of a liquid melt), they are easily ground to a high specific surface. About 0.6 m / g and can be stored in a closed container for a long time (do not lose their hydraulic ones). sting) properties. The mixture is prepared by mixing the dry ingredients (sand and powder in a calcium aluminate base) followed by the introduction of water and the final mixing. The invention is illustrated by the following example.

In table., T shows the compositions of the proposed mixtures 1-8 and the composition of the prototype, S

Properties of the mixtures are given in table 2.

From the data table. 2 it follows that the proposed mixture provides an increase in compressive strength in all

terms of hardening “ensures sufficient survivability of low shoveling, low residual moisture, high gas permeability and good selectability. The waste mixture is almost entirely recyclable. The mixture is recommended for making medium and large cores and shapes.

Ta 6 l and m a 2

Vitality, NIN 20 2S Compressive strength, IPa, through, h 0.30.20.05 0.60.50.3 0.80.70.0 0.90.80.7 3.02.83.0 " "TO 5.0 3.5 1.0 1.5 Gas permeability, UO 130 150 units 150 C to 15, 0.1 0 0.1 Residual strength after heating, 6 samples to 1350 C and cooling 0, 0 05 0.05 0.05 ni, MPa Approximate strength indicators in kgf / cm of MPa values 10 times.

invention formula

. 1, Self-hardening (a mixture for the production, preparation of casting molds and cores, including a refractory filler, which hydrates calcium salt and water, so that with the aim of increasing the strength of the molds and rods at all stages of hardening, it contains as a calcium salt in the form of a calcium salt as a hydraulic binder in the following ratio of ingredients m.ch: 30

Refractory filler 100. Calcium aluminate compound. 5-9 VodaA-9

2. A mixture according to claim 1, of which is that it contains

IB as a calcium aluminate based compound calcium sulfoaluminate.

3. A mixture of, characterized in that it contains calcium sulfoaluminate as a compound based on aluminum calcium

and calcium aluminate fluoride when barely. by blowing soot on ingredients, mac.ch: 0 20 35 25 0.05 Less About | 05 0.1 Less than 0.005 0.3 O, 0.1 0.20.009-0.013 0.5 0.60.2 Oh, 0.015-0.312 0 , 7 0,8 O, 0,7 2,9 3,2 2,8 3,10, W-1,0 3,05,0 5,0-6,0, 5 "" .O i; 0 0,5 0 , 51.0 160120 130 150 0.30 0.1 0.2 0.1 0.05 0.05 0.05 0.05 can be obtained by increasing

11 93915 12

Refractory filler 100. 2. Kestner O.E., Baradan Nts V.K.

Calcium sulfoaluminate 2, etc. Precision casting of non-ferrous alloys

Fluoride aluminate Cal-in plaster and ceramic forms, M.,

Qi 2.5-3.5 Mechanical Engineering, 1968, pp.10-35.

Water 3.Ivanov N.Kh. and Sidorenko B.M. Light Sources of information, poking fluid activated

taken into account in the examination of the mixture and equipment for their preparation1. Japan patent 1G50-38611, laziness. M., NIIMASH, 1971, p., 71,

cl. MA 112, published. 1E75.table 20, s, 73, tab. 20.

Claims (3)

claims <1. Self-hardening mixture for the manufacture of foundry molds and cores, including a refractory filler, a hydraulic binder in the form of calcium salt * and water, characterized in that, in order to increase the strength of the molds and cores at all stages of hardening, it contains as a hydraulic binder * in the form ^! calcium salts - a compound based on calcium aluminate in the following ratio of ingredients wt.h .: Refractory filler 100 Calcium Aluminate Compound .5 “9 Water 4-9 2. The mixture according to claim ^ characterized in that it contains calcium sulfoaluminate as a compound based on calcium aluminate. 3. The mixture according to claim 1, characterized in that it contains calcium sulfoaluminate and calcium aluminate fluoride when barely, as a compound based on calcium aluminite. the ratio of ingredients, parts by weight: 11 939 154 12 Refractory filler 100. Calcium sulfoaluminate 2.5 ~ 3.5 Calcium Aluminate Fluoride 2.5-3.5 Water 4-7