The construction of chimneys, industrial furnaces, fireplaces and other stone structures operating at high temperatures takes place using special materials. The use of ordinary ceramic or silicate stone in such buildings is unacceptable, since there is a possibility of its destruction. Specialists use refractory bricks, which are laid using the same heat-resistant mortars. The heat resistance of the material is achieved through firing and the use of special components in the production of stone.
Features
The refractory brick has different characteristics from ordinary artificial ceramic or silicate stone. White clay is an integral part of the material, and the properties and types of bricks depend on impurities. However, they all have one category - refractories, that is, the ability to maintain their original characteristics when exposed to high temperatures that exceed 1580 degrees.
They are mainly used inindustry, so high requirements are placed on the production of refractories. Since any failure in the operation of such materials is fraught with large losses, not only temporary, but also financial. Most importantly, they provide security. Refractory brick is a fire insulating material.
General characteristics of fire-resistant artificial stones:
- Low thermal conductivity - the ability to keep heat inside the thermal units.
- Heat resistance - maintaining the strength of a brick when exposed to temperatures above 1580 degrees.
- Thermal inertia - the ability of a refractory material to cool slowly and heat up quickly.
- Heat capacity is a characteristic that ensures the accumulation of heat by a brick for further return.
- Chemical resistance to hot gases, slag, metal.
- Constancy of volume, that is, the characteristic of refractory stones to not shrink or grow within the range of 0.5% to 1%.
Application
Refractory brick, whose characteristics are different from conventional masonry materials, has found its application in the construction of thermal units. In the metallurgical industry, for the melting of iron, nickel, copper, a temperature above 1500 degrees is required, therefore, furnaces in such a production are lined exclusively with dolomite, dinas, chrome-magnesite bricks. Dinas stone is used for arches and lining of furnaces working with acidic substances. It expands at temperature, but magnesite refractoryshrinks, so the arch with the use of the latter may collapse. That is, each type of this category of brick has different properties and uses.
In the non-metallurgical industry, refractory stone is used for laying chemical production equipment, municipal boiler houses, coke kilns; glassworks units.
Views
The refractory brick comes in four designs. The carbon type is made from coal tar with the addition of coke/anthracite powder. Such material is heat-resistant and slag-resistant. As a rule, it is used in the construction of blast furnaces. However, to protect it, another layer of fireclay products is laid out. Dinas (quartz) stone is made from quartz powder and milk of lime. The fire resistance of this material is 1730 degrees, and brick is used for laying equipment in contact with acidic environments.
Magnesite, chromite, chromium-magnesite brick is made from burnt minerals. There are also carborundum and graphite products. The fire resistance of these types is from 1500 to 2000 degrees.
The aluminous type includes a material popular in industry - refractory fireclay bricks. It contains more than 30% aluminum oxide (alumina) and the obligatory presence of special clay resistant to temperatures. Fire resistance - up to 1400 degrees.
Classification by chemical properties
Depending on the composition of the main components, artificial stones can bedivided into 3 groups: neutral, basic and acidic.
Dinas and quartz clay bricks belong to the acidic group of stone materials. They interact with acidic environments without damage to themselves.
Basic refractories made of dolomite, magnesite, chromomagnesite seamlessly contact the alkaline environment. They are used for laying thermal units that require a sharp change in temperature in their work.
The neutral group for chemical compatibility includes fireclay refractory brick, carbon and graphite stone material. They are resistant to both alkaline and acidic environments.
Product sizes
It is impossible to combine all types of refractory bricks under one universal size. Each type of product has its own GOST, according to the requirements of which the building material is manufactured and where its main parameters are determined. Plus, the dimensions of refractory bricks depend on the shape, which is not always rectangular. This is due to the complex design of the thermal unit, which requires arches and vaults.
For example, the dimensions of rectangular single products start from 230x65x65 mm and end with parameters of 345x150x75 mm. All dimensions of rectangular, wedge-shaped, hanging and other refractory products can be found in GOST 8691-73.
Marking
To answer the question of what kind of refractory brick to buy for a furnace, the price of which directly depends on the indicators of the material, it is necessaryknow the basic marking of the product. Each block has symbols. The first letter indicates the name and type of product. So, if the letter “Sh” is in the marking, then this refractory belongs to the group of fireclay stones; "D" - dinas, "M" - mullite.
The second letter defines the maximum application temperature of the material. Example for fireclay stones:
- SHA, SHAK - 1400 degrees.
- SB - 1350 degrees.
- SHUS, SHV - 1250 degrees.
- PB (semi-acid type) - 1350 degrees.
- PV - 1250 degrees.
The dimensions of refractory bricks are identified by a number preceded by the first two letters of the product brand. For example, ShA-5 refractory has parameters 230x114x65 mm, and ShA-8 - 250x124x65. ShB-22 characterizes the product in the form of an end wedge (trapezium), the dimensions of such material are 230x114x65x55 mm. After the number in the marking, letters follow, which are the abbreviation of the manufacturer.
Cost
For the construction of fireplaces, barbecues, stoves, refractory bricks are used. The price of the material depends on the brand, size, design features and manufacturer. To compare prices for October 2015 in Ukraine and Russia, 4 types of popular fireclay bricks were selected. When ordering a pallet, there are 350-360 bricks. Price is for 1 piece
- ShA-5 is a rectangular item in Russia, priced at 39.9 rubles.
- Similar to the previous refractory, SHA-8, which is slightly larger, costs 47.9 rubles.
- SHA-22(end wedge): price in Russia - 49 rubles.
- SHA-45 (end wedge): the cost of the product in Russia is 41.2 rubles.
Which refractory brick to choose for the furnace?
When constructing furnace devices, you can use normal-fired red brick, the standard dimensions of which are 250x120x65 mm. It should have clear edges, no chips, smooth edges and right angles. Otherwise, the masonry will be fragile. When broken, the brick must have a homogeneous structure, that is, be inside without cracks, voids and layers.
Zheleznik - a grade of burnt brick can only be used for the installation of furnace foundations, since it is difficult to bind to the mortar. Unburnt (scarlet) artificial stone, silicate, perforated and hollow bricks are not allowed to be used for laying stoves and chimneys.
Refractory brick for the furnace, the price of which is several times higher than red ceramic stone, is necessary for lining thermal units. That is, to create a protective shell, a refractory is used, which is wrapped around the furnace. Due to this, the heat flux created inside does not destroy the main walls of the furnace.
Solutions
Kiln refractory bricks must be laid into the structure using a homogeneous mortar that will firmly hold the masonry together and harden in due time. For household stoves, a clay solution is used, which is prepared, depending on the fat content of the clay, with the addition of sand in proportions of 1:1 or 1:2. The prepared solution is considered suitable if the ball rolled from it atdrying does not crack along the contour, and when thrown to the floor does not crumble. If there is an excess of sand, then the ball falls apart, cracks are caused by the presence of a large proportion of clay in the solution.
When laying industrial equipment, refractory bricks are fastened together using mortars - these are lime mortars designed to bind refractory products.
For laying the foundations of stoves, it is recommended to prepare lime mortars in a ratio of 1:2 - 1:4. Cement mixtures are used for the construction of foundations for thermal units subject to the influence of water, such as groundwater.
Masonry category
When building, repairing thermal units, the laying of refractory bricks takes place according to the following requirements, which determine its category:
- The maximum thickness of the joints from 0.5 to 1 mm corresponds to especially careful laying of the 1st category.
- 1-2 mm seams between bricks belong to category 2.
- Standard (ordinary) masonry is characterized by a joint thickness of up to 3 mm.
- The presence of a mortar between bricks over 3 mm corresponds to a simple refractory masonry.
Classes, grades of refractories, masonry category - all this information should be written in the working documentation. If there is none, then the thickness of the seams for different structural elements is determined based on special tables.
