RU2791333C1 - Raw mixture for compressed gypsum products and method of manufacturing thereof - Google Patents

Abstract

FIELD: construction materials.

SUBSTANCE: group of inventions relates to the field of production of building materials and can be used in the production of gypsum products. Raw mixture for pressed gypsum products contains, wt.%: gypsum binder obtained by firing of citrogypsum at a temperature of 175°C, 64-72, filler - citrogypsum with a particle size of not more than 112 mcm, 8-16, water - the rest. A method for manufacturing pressed gypsum products from the above mixture includes mixing citrogypsum with a gypsum binder, introducing the resulting raw mixture into water, mixing, molding in a metal mold under a pressure of 5-7 MPa with holding at the specified pressure for 30 s, pressing out and drying the products in natural conditions to permanent weight.

EFFECT: technical result is an increase in the strength of products, reduced consumption of a binder, lower energy costs for pressing and reduced equipment wear.

2 cl, 2 tbl, 1 ex

Description

The present invention relates to the field of production of building materials and can be used in the production of gypsum products.

A known method and composition for the manufacture of gypsum products, while wet natural dihydrate gypsum or citrogypsum is mixed with sulfuric acid, and then sequentially with dry quicklime and mixing water, then the resulting raw mixture is pressed while removing excess mixing water (Patent RU No. 2132310 C1 , published 06/27/1999).

The disadvantage of this method is the complexity of the process of manufacturing products, high costs for their production, as well as low water resistance of products, low strength.

Also known is a method and composition for the manufacture of gypsum products, which consists in using expanded perlite (fine aggregate) with a granule size of 75-100 microns, which is pre-saturated with water, filtering out water not retained by expanded perlite granules, mixing water-saturated perlite with gypsum, serving the resulting mixture into a mold for further pressing and pressed at a pressure of at least 10 MPa (Patent RU No. 2525412 C1, publ. 10.08.2014, bull. No. 22).

The main disadvantages of this composition and method are low strength, high water-binding (water-gypsum) ratio, the presence of additional operations associated with the need for water saturation and filtration of water from perlite. Also, with this technological solution, it is difficult to ensure a constant water-gypsum ratio, this is due to the neglect of the weight of perlite, as well as the fact that filtration does not ensure complete removal of water from the surface of perlite, and when it is dosed, free moisture will remain on all equipment involved in this operation. . The fluctuation of the water-gypsum ratio has a negative impact on ensuring the constancy of the strength characteristics of the final products.

The technical solution closest to the proposed invention, taken as a prototype, is the composition and method of manufacturing gypsum products, which consists in the fact that the fine aggregate is a waste product of perlite production (perlite dust with a granule size of 5-100 microns, a bulk density of 75 kg / m ³ ) is mixed with water, followed by the introduction of a modified gypsum binder obtained by firing citrogypsum in a rotary kiln at a temperature of 120-140 ° C, with a specific surface of 600-650 m ² /kg and molded in molds under a pressure of 10 MPa, with keeping the products at specified pressure for 30 sec. (Patent RU No. 2693808 C1, published on July 4, 2019, Bull. No. 19).

The main disadvantages of this composition and method are low strength, increased binder consumption, increased energy costs for pressing, the need to use perlite dust, which increases the cost of raw materials associated with the purchase and transportation of perlite dust.

The invention is aimed at increasing the strength of products, reducing the consumption of a binder, the cost of raw materials, energy costs for pressing, reducing equipment wear.

This is achieved by the fact that the raw mix for pressed gypsum products contains a binder, a filler and water, while gypsum binder obtained by firing citrogypsum at a temperature of 175 ° C is used as a binder, citrogypsum with a particle size of not more than 112 microns is used as a filler, manufacturing the mixture is carried out at the following mass ratios of raw components, %:

gypsum binder 64–72 citrogypsum 8–16 water rest

The method for the manufacture of gypsum products includes the preparation of a molding mass, molding in a metal mold, pressing out, drying, while the preparation of the molding mass is carried out in the following sequence: preparation of a raw mix by mixing a binder and a filler, adding a raw mix to water, mixing, molding in a metal in a mold under a pressure of 5-7 MPa, with keeping the products at the specified pressure for 30 seconds, pressing out and drying in natural conditions to a constant weight.

Characteristics of the materials used.

1. Filler - a waste product of the biochemical synthesis of citric acid - citrogypsum, with a particle size of not more than 112 microns. The chemical composition of citrogypsum is presented in table 1.

Table 1

The chemical composition of citrogypsum

Content of oxides, %: CaO SO _{3 SiO2} MgO p.p.p. 50.85 48.32 0.317 0.146 rest

2. Gypsum binder - calcined citrogypsum with a specific surface area of 300-350 m ² /kg.

Gypsum binder is obtained by firing citrogypsum at a temperature of 175 °C.

3. Water GOST 23732-2011 “Water for concrete and mortar. Specifications".

The developed compositions of the raw mixture and the strength characteristics of the studied composition of products and the prototype are shown in table 2.

table 2

Compositions of the raw mix and physical and mechanical characteristics

investigated pressed gypsum products

Product type Material consumption % wt. Water binder
attitude Pressing pressure, MPa Compressive strength after 2 hours
pressing, MPa Compressive strength of dry products, MPa Gypsum binder Perlite dust Cytrogypsum Water research composition No. 1 72 - 8 20 0.28 7 16 26 study composition No. 2 64 - 16 20 0.31 5 13 23 prototype 83 1.5 - 15.5 0.18-0.19 10 15-16 19-20

Example (table 2, composition No. 1): citrogypsum in the amount of 0.8 kg (8% by weight) and gypsum binder in the amount of 7.2 kg (72% by weight) are mixed until a homogeneous mass is obtained. Next, the resulting raw mixture is poured into water, taken in an amount of 2 l (20% by weight), followed by thorough mixing until a homogeneous molding mass is obtained. After that, the resulting molding mass is sent to a metal mold and pressed under a pressure of 7 MPa, the duration of holding under the specified pressure is 30 seconds, then it is pressed out and dried in natural conditions to a constant weight.

The developed method for manufacturing products with the proposed ratio of components, the presence of citrogypsum in the system, which acts as a filler, reduces the adhesion of the mixture to the walls of the mold, facilitating the molding process, which contributes to an increase in the strength of the final products and an increase in the quality of their appearance.

The introduction of citrogypsum into the composition of the raw mixture also helps to reduce the cost of the product by reducing the consumption of gypsum binder and the costs associated with the purchase and transportation of perlite dust.

Based on the fact that citrogypsum is a waste product of the biochemical synthesis of citric acid, this invention also significantly reduces the burden on the environment.

The use of the specified pressure (5-7 MPa) and the mode of molding products helps to reduce equipment wear and reduce energy costs.

Reducing the pressing pressure below 5 MPa and increasing the content of the filler (citrogypsum) in the system above 16% contributes to a decrease in the average density of the products and, as a result, the strength is below the strength values of the prototype. At the same time, an increase in pressing pressure above 7 MPa and a decrease in the content of the filler (citrogypsum) increases the energy costs for production and the cost of raw materials - gypsum binder. With the complete exclusion of citrogypsum, due to the high adhesion of the gypsum binder to the metal mold, the number of defects on the surface of the products increases.

Claims (3)

1. A raw mix for pressed gypsum products containing a binder, a filler and water, characterized in that the raw mix uses a gypsum binder obtained by roasting citrogypsum at a temperature of 175 ° C, as a filler - citrogypsum with a particle size of not more than 112 microns, the production of the mixture is carried out at the following mass ratios of raw materials,%: gypsum binder 64-72 citrogypsum 8-16 water rest 2. The method of manufacturing pressed gypsum products according to claim 1, including the preparation of a molding mass, molding, pressing out, drying, characterized in that the preparation of the molding mass is carried out in the following sequence: mixing citrogypsum with a gypsum binder, introducing the resulting raw mixture into water, mixing, molding in a metal mold under a pressure of 5-7 MPa, keeping the products at the specified pressure for 30 s, pressing out and drying in natural conditions to a constant weight.