RU2021234C1 - Method for manufacturing products based on magnesian binder - Google Patents

Abstract

FIELD: manufacture of constructional materials. SUBSTANCE: this method prescribes preparing molding mixture by admixing dry caustic magnesite and finely dispersed filler which may be either natural quartz or carbonate sand or rejects of these, introducing thus prepared dry mixture with vigorously stirring into magnesium chloride salt solution having specific gravity of 1,28-1,3g/cm³ and heated to temperature of 70 to 110 C. Desired product is molded from above mixture under vibration, molds are placed in prewarmed-up heater to harden products at temperature of 200 +/- 2 C during 20 min per each 10 mm of product thickness, and finally end products are rapidly cooled via walls of molds. Compressive strength of desired products after removal of molds accounts for 10 to 15 MPa. EFFECT: higher quality of surfaces of desired products. 1 tbl

Description

 The invention relates to methods for the manufacture of building products based on a magnesian binder with any finely divided filler and may find application in the building materials industry for the manufacture of mainly facing tiles, slabs, architectural details.

Known method for preparing the raw material mixture and products on its basis, preferably construction panels, by introducing caustic powdered magnesite (MoO) with vigorous stirring into the heated dol 70 ° ^C aqueous solution of a magnesium salt, followed by mixing with any filler and plasticizer - pre-neutralized with dilute alkali polyvinylacetate [1].

There is also a known method of manufacturing building products based on magnesian binder by pre-heating the mixture, including caustic magnesite, a salt of magnesium chloride or sulfate to 80-110 ^about With subsequent rapid cooling of the mixture [2].

 The disadvantages of this method are as follows: the long curing time of semi-finished products under environmental conditions (20-24 hours); low strength at the time of form removal (less than 5 MPa); low architectural appearance due to efflorescence, including on the surface in contact with the inner surface of the molds, as well as the possible application of the hardened mixture to the inner surface of pre-lubricated forms.

A known method of manufacturing building products based on magnesia binder by mixing a mixture of caustic magnesite with a finely divided filler with a solution of magnesium chloride, holding the mixture for 45 ... 90 minutes, molding and holding in the mold for 4 hours in a preheated oven at 30-40 ^about C. forms of form removal and subsequent aging for 24 hours at ⁵⁰ ° C to complete hardening. The known method allows you to speed up the process of curing strength of products to the possible dismantling within 4 hours, increases the fire resistance and nails of products [3].

 Along with the advantages of the known method, there are significant disadvantages: the lengthy process of curing products in molds when heated, which reduces the rate of turnover of forms - 4 hours and 24 hours without forms (only 28 hours); low strength at the time of form stripping (less than 2-3 MPa); low architectural appearance due to intensive salt formation, including on the surface in contact with the inner surface of the molds, as well as due to the adhesion of the mixture to the surface of non-lubricated molds.

Closest to the claimed is a method of obtaining products based on a magnesian binder, which consists in mixing a dry mixture containing caustic magnesite, a fine filler with an additive, a solution of hexahydrate magnesium chloride - MgCl ₂ ˙ 6H ₂ O, mixing, molding in molds and holding the mixture in molds in a furnace preheated to a temperature of 365 ± 2 K and holding at this temperature in air until the products completely harden for 15.5 hours (930 minutes).

 Along with the great advantages of the method (the process of complete hardening of products in molds is accelerated to 15.5 hours with the acquisition of strength at the time of stripping up to 12 MPa, there are significant disadvantages that preclude the use of the known method for the mass production of cladding plates, namely: a long term of complete hardening in molds when heated - 15.5 hours, which reduces the rate of mold turnover, especially when forming products by casting with fibration; low architectural appearance of products due to vysolobrazovaniya on surface, including contacting with the inner surface of the molds, as well as due to the adhesion of the mixture to the inner surface of non-lubricated molds.

 The purpose of the invention is to accelerate the curing process in molds without loss of strength during demolition, increase the architectural appearance of the surface in contact with the mold surface, by eliminating efflorescence and adhesion of the mixture to the mold surface not lubricated with grease.

For this purpose, a method of manufacturing products based on magnesia binder by applying a caustic magnesite with any particulate filler under vigorous stirring in hot with a temperature of 70-110 ^{° C} magnesium salt solution, subsequent quenching, formation and solidification in metal molds preheated in heat unit, curing forms preheated aggregate is carried out for 20 minutes for each 10 mm of thickness of products at a temperature of 473 ± 2 K (200 ± 2 ° ^C), and quenching the reaction mixture with o exist across the surface of the molds after the mixture has cured.

 When testing the proposed method was used (except for caustic magnesite and a solution of magnesium chloride) a large number of finely divided fillers of both mineral and organic origin, and from among industrial wastes, including natural ones (quartz and carbonate sands).

 In the tests of the proposed method, the following components were adopted.

1. Magnesium oxide (caustic magnesite). Highly dispersed with a specific surface of 6000 cm ² / g, contains at least 98% MgO. Low grade caustic magnesite P.M.K. III grade.

2. Ground basic granulated slag. The basicity modulus is 1.05-1.08, the specific surface area is 2800-3000 cm ² / g. The chemical composition is the following, wt.%: SiO ₂ 38,47. . .39.38; Al ₂ O ₃ 7.5 ... 9.05; CaO 42.26 ... 43.36; MgO 7.27 ... 7.9; FeO - 0.31. . .0.36; MgO - 0.23 ... 0.26; S is the rest. Bulk density 980-1000 kg / m ³ .

3. Koloshnikovy dust - waste blast furnace production of cast iron. Used blast furnace dust with a specific surface area of 2800-3000 cm ² / g

The chemical composition is the following, wt. %: SiO ₂ 6.00 ... 13.1; Al ₂ O ₃ 0.95 ... 1.78; CaO 10.45 ... 32.40; MgO 1.59 ... 1.72; FeO 2.21 ... 9.31; Fe ₂ O ₃ 33.00 ... 41.29; P ₂ O ₅ 0,053 ... 0,14; SO ₃ 1.08 ... 1.90; TiO ₂ 1.8 ... 2.23; S 0.4 ... 0.79; C 16.01 ... 18.50; Na ₂ O + Ca ₂ O 0.173 ... 0.32, MnO 0.07 ... 0.95.

4. Ferromanganese blast furnace dust is a waste product of ferromanganese cast iron production. The specific surface area is 1480 cm ² / g.

The chemical composition is the following, wt. %: SiO ₂ 9.89 ... 13.7; Fe ₂ O ₃ 5.86 ... 14.68; CaO 8.14 ... 9.44; S 0.84 ... 1.38; R ₂ O 4.13 ... 5.76; Al ₂ O ₃ 2.84 ... 2.89; FeO 2.16. . . 2.26; Mn ₃ O ₄ 25.84 ... 33.32; P 0.13 ... 0.15; C (coal) 25.2 ... 30.80.

5. Six-oxide oxide of magnesium chloride - (bischofite) MgCl ₂ ˙ 6H ₂ O. The usual - Karabogazgolsky deposit is accepted. A concentrated solution of the Volgograd field may also be suitable. The concentration of the solution for mixing is recommended 1.28-1.34 g / cm ^3.
6. Quartz sand - fine sand with a particle size of 1.5; contains 97-98% SiO ₂ .

7. Wood sawdust - coniferous sawdust is accepted, humidity 14%, bulk density 180-200 kg / m ³ , particle size less than 5 mm.

8. Carbonate sand - waste of stone crushing of limestone. Contains 98-98.5% CaCO ₃ . The ground calcium carbonate is sieved through a sieve with a mesh diameter of 0.5 mm.

 In production conditions, the proposed method is as follows.

 Caustic magnesite and finely dispersed inert filler such as quartz or carbonate sand, sawdust and other similar fillers with a particle size of 0 ... 5 mm are dosed. In the case of the manufacture of facade cladding tiles, fillers must be introduced, in addition to inert fillers, and any such filler, which contains silicates, calcium aluminates, which are activated by magnesium oxide, These fillers include ground main gravel slag, blast furnace dust or sludge gas treatment of blast furnaces, increasing the water resistance of magnesia binder.

Otdozirovannyh mixture of dry components is introduced with vigorous stirring into a hot solution of magnesium chloride at a density of 1.28 ... 1.3 g / cm ³ and a temperature not lower than 70 ^C and not higher than the boiling point of the solution, i.e., 110 ^about S.

The hot mixture is immediately formed immediately by casting with vibration in metallic non-lubricated forms having an ambient temperature. The shaped semifinished plates in molds was placed in preheated to a temperature of 473 ± 2 K (200 ± 2 ° ^C) oven and held at this temperature for at least 20 min to 10 mm thick slabs; 80 min for 40 mm thick boards, i.e. at the rate of 20 min for every 10 mm of thickness.

 For the specified time, the product acquires strength sufficient for operation. The hardened products are removed from the oven in the molds, the mold is sharply cooled, the products are removed from the mold and tested for strength, the presence of efflorescence is determined, and the surface that is in contact with the mold is defective.

 Molded products can be sent to the consumer without waiting for them to gain design strength (strength after 28 days. Hardening in an industrial environment). The strength of the products at the time of disassembling is 11 ... 15 MPa in compression and 3.5 ... 9.2 MPa in bending and is sufficient for tiles, especially if you take into account that the strength will increase over time.

PRI me R 1. Weighed 920 g (17.07%) of caustic magnesite, 1 kg 444 g (27.72%) of finely ground blast granulated (main) slag, 1 kg (18.55%) of expanded clay dust from cyclones , 400 g (7.42%) of quartz fine sand. Otdozirovannyh mixture components are fed into the preheated to ⁷⁰ ° C MgCl ₂ brine with a density of 1.28 g / cm ^2, taken in an amount of 1 kg 576 g including 526.24 based on MgCl ₂ (9.76%) and the rest was water 1049 kg 76 g (19.48%), taking into account chemically bound water introduced with six-water magnesium chloride MgCl _{2 2} 6H ₂ O (bischofite). In the process of supplying the dry mixture to a hot solution of magnesium salt, intensive mixing was carried out for 2 minutes and then a homogeneous cast mixture with an actual water-solid ratio of 0.24 was poured into metal cold non-lubricated molds with a size of 16 x 4 x 4 cm, the latter at the time of pouring vibrated.

Due to the increased temperature of the mixture, its mobility increased sharply, which simplified and accelerated the molding process, which lasted 30 s. Molded products - semi-finished products at a temperature of 50 ^{° C} was placed in the forms in a preheated 200 ^{° C} oven and held at this temperature for 80 minutes at a rate of 20 m per 10 mm of thickness of products, and then forms quickly cooled, making it possible to quickly raspalublivat molds and prevent adhesion of products to the surface of molds. Samples product was air-cooled to 20 ± 2 ^{° C} and then tested for durability, architectural view - the presence of efflorescence and defects on the front surface in contact with the inner surface of the molds. The test results are shown in the table (see experiment for mixture 2, property data in the numerator). In a similar manner and produced a mixture of N 3-8 were tested including prohibitive 1, wherein only accepted other lower MgCl ₂ solution temperature (60 ^{° C)} and the secondary heat treatment in an oven ^of 150 C, and for a mixture of 9 - 250 ^{° C} .

PRI me R 2. To test the known method (prototype) prepared a mixture similar to the composition of example 1, and until molding, the molding mixture was also prepared according to the method of example 1, and then the molded products were semi-finished by casting with vibration in non-lubricated forms with 16 x 4 x 4 cm was placed in a preheated to a temperature of 365 K (92 ° ^C) oven and held at this temperature until complete curing. Since the mixture was closed by the method of the known analogue (1), i.e. a hot solution of MgCl ₂ at 70 ^{° C} in an oven and were placed in a semi-finished forms at 50 ^{° C,} the product is not hardened after 15.5 hours (930 min), as is the case in the prior art, and after 10 h (600 min), i.e. 5.5 hours earlier, and in the absence of an environmentally harmful fluoride-containing additive - calcium fluoride or strontium. Then the products were removed from the oven and immediately dismantled without sudden cooling of the non-lubricated forms. After cooling models of articles to a temperature of 20 ± 2 ^{° C} was performed to test their strength and visually on architectural appearance.

 The products had efflorescences not only on the open surface, but also on the surface in contact with the surface of the molds, and there were also defects due to increased adhesion (adhesion) of the hardened mixture to the inner surface of non-lubricated forms (see the experiment example in the table for mixture N 2 - data in denominator).

As can be seen from the table:
1) Tests 1 and 9 are extremely high, since the temperature adopted for the mixing to 60 ^{° C} and 150 ^{° C} for secondary thermal processing under otherwise identical conditions of preparation of products of a mixture of 1 are low, because the surface of the articles in contact with the walls of mold are observed efflorescences and defects due to adhesion of the mixture to non-lubricated pre-forms.

When heat treated semi-finished molded in metal molds over 200 ^{° C} (at 250 ^C) observed product deformation, the presence of blistering. For these reasons, the manufacturing methods of the products described in examples 1 and 2 are beyond.

2) The inventive method of manufacturing products has the following advantages in comparison with the prototype:
the process of curing products in molds during heat treatment is reduced by 4 ... 7 times without loss of strength; on the surface in contact with the base of the form, and which is facial during operation, there are no efflorescences, sinks.

 The surface in contact with the inner surface of the molds is front, because when using molds with a smooth polished surface, respectively, the products acquire a smooth glossy surface.

The physicochemical nature of the technical solution to achieve the goal consists in the timely (until the time of setting) diffusion of soluble salts, including excess MgCl ₂ onto the open surface of the products not in contact with the internal surface of the form, by enhancing not only the moisture content gradient, but and by increasing the gradient of the temperature difference between the lower base of the form (metal) and, accordingly, the mixture in contact with the metal and the open surface of the molded mixture, i.e., in the adopted decision ii enhanced thermal process soluble salts on the exposed surface of articles and thereby promptly removed, these salts with the front surface of the products on a rear surface of the facing tiles.

 So, in the adopted technical solution, due to the double heat treatment of the mixture, and then the timely semi-finished product in the molds at a higher temperature, not only the curing process is accelerated, but also in a timely manner until the curing time, all soluble salts, efflorescence sources, diffuse with the front surface in contact with the base metal form, on the open (back) surface of the products, which is laid on the solution during lining. Timely removal of salts (diffusion) also contributes to a decrease in strength, since the diffusion of salts in the hardened product softens this product. For this reason, the strength of products hardening a shorter period in comparison with the product of the prototype method does not decrease, but increases.

In the prototype method, the ingredient factor of the temperature difference is insignificant in comparison with the claimed method, therefore, the thermal diffusion of soluble salts is correspondingly insignificant, i.e., in the known method, the curing factor is ahead of the diffusion factor of soluble salts on an open surface and part of the salts remains inside the hardened products, including and on a contact surface with a mold base. The remaining salts (MgCl ₂ , etc.) corrode with the base of the metal form and the adhesion of the mixture to the metal is enhanced, i.e. areas of adhering products remain on the surface of the molds, i.e. accordingly, defects are formed on the front surface of the products, in particular tiles.

 In the claimed method of defect-freeness, a sharp cooling of the metal form and the hardened mixture also contributes. Due to the different coefficients of linear thermal expansion and contraction of the metal and the hardened product, the latter easily lags behind the form.

The inventive method in comparison with the known method the base enterprises in which curing is performed by heating plates in plastic form and at a temperature not higher than 55 ± 5 ^{° C} have the following technical and economic benefits: increased productivity in 3 ... 5 times due to the acceleration the rate of mold turnover and the acceleration of the duration of complete cure by 15 times; the quality of the products increases due to the surface non-defectiveness; tiles are not required to process water; no lubrication of molds required; reduced total heat and energy consumption due to the acceleration of the curing process by 10 times.

 Due to these advantages, the cost of products is reduced by 64.3%.

Claims (1)

METHOD FOR PRODUCING PRODUCTS BASED ON MAGNESIUM BINDER by feeding with vigorous stirring caustic magnesite with a finely divided filler with a particle size of less than 5 mm into a solution of magnesium chloride heated to 70 - 110 ^o C, followed by rapid cooling, molding and curing pre-mixed in metallic form thermal unit, characterized in that the curing in molds in a preheated aggregate is carried out for 20 minutes for each 10 mm of thickness product at 200 ± 2 ^o C and quenched forms of conduct through the surface after the curing mixture.

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