by Refractory prefabricated parts have the advantages of convenient, fast and long service life.
They are more and more widely used in the field of high-temperature industrial furnaces.
The production process of fire-resistant prefabricated parts is relatively simple, which is basically carried out according to the process of batching, mixing, forming, drying and so on.
However, some problems are often encountered in the production process.
This paper mainly discusses the common problems and treatment methods in production.
1.
Powdered bauxite clinker with impurities in bauxite clinker is one of the commonly used refractory raw materials for refractory materials.
Its quality has a great impact on the performance of refractory products.
Bauxite clinker, i.e.
bauxite clinker, is made of bauxite calcined at high temperature, and its Al2O3 content shall be greater than 50%.
The content of impurities in the product shall not exceed 2%, and shall not be mixed with limestone, loess, high calcium and high iron and other foreign inclusions.
Due to the geological distribution characteristics of bauxite raw ore, it is often associated with limestone and loess.
If the selection after calcination is not sufficient, limestone and other impurities will be mixed into bauxite clinker.
Once used in fire-resistant prefabricated parts, during the process of water mixing, molding, drying, firing or use, local pit defects appear in the products due to the pulverization of limestone, which will not only affect the appearance quality of the products, but also affect the internal quality of the products.
Therefore, before using bauxite clinker, it is necessary to test the pulverization rate.
The method is to take the bauxite clinker particles with the weight of M1 (particle size + 3mm), immerse them in water for a period of time, then dry them at 110 ℃ and weigh the weight of the particles on the screen as M2 after passing through a 3mm screen.
Then the pulverization rate can be expressed as: pulverization rate (%) = (m1-m2) / M1 × 100%, the pulverization rate should not exceed 0.20%.
If the measured pulverization rate is high, in order to ensure the quality of the product, this batch of raw materials need to be pretreated.
It can be used after water impregnation, drying and screening.
2.
Pulverization of brown corundum in amorphous refractory materials, corundum is used as refractory aggregate and powder, which is more and more used and has achieved remarkable results.
Corundum is generally made of industrial alumina or bauxite after sintering or electrofusion, including white corundum, sub white corundum, plate corundum, high alumina corundum, brown corundum, etc.
Among them, brown corundum is produced by smelting with light burned high aluminum material, coal and iron filings as the main raw materials.
Smelting processes are divided into two types: shelling furnace and dumping furnace.
The crystallization degree of materials produced by shelling furnace varies greatly in different parts, and the iron distribution part is wide.
The brown corundum produced by the dumping furnace has uniform quality and good body density, but due to the uniform quality, there are few grades and the comprehensive index may be slightly poor.
According to the production practice, the pulverization probability of brown corundum produced by shelling furnace is much greater than that produced by dumping furnace.
If brown corundum with high pulverization rate is used to produce prefabricated parts, after high-temperature firing, local pulverization and cracking will occur on the surface of the products, which will not only affect the quality of the products, but also greatly reduce the firing qualification rate and increase the production cost.
It is necessary to detect the quality of corundum powder due to its serious hidden danger of browning.
At present, there is no test method and standard for pulverization rate.
The methods used in this paper are the following two: qualitative test: each batch of brown corundum is prefabricated into a piece of product according to a certain formula, dried and fired at a low temperature of 600 ℃ or 1000 ℃ to see whether there is disintegration, so as to judge whether the batch of brown corundum is pulverized.
Quantitative detection: take a certain particle size sample with a weight of M3, generally with a particle size of 3 ~ 1mm, and boil it in pressure cooker for 60min (or 1000 ℃ in electric furnace) × 1H treatment), observe the change of particle color and particle size after drying.
After passing through a 1mm screen, the weight of the material on the screen is recorded as M4, and the pulverization rate can be expressed as: pulverization rate (%) = (M3-M4) / m3 × 100% is qualified if the detected pulverization rate does not exceed 0.10%.
For different refractory products, the standards for pulverization rate control can be different.
3.
Delamination of magnesium aluminum preforms containing micro silicon powder during the production of magnesium aluminum preforms containing micro silicon powder, the forming surface often rises, resulting in product delamination, which will seriously affect the service life and yield of refractory products.
There are two kinds of SiO2 micro powder: one is made of high-purity silica, and the other is a by-product of metal silicon or ferrosilicon.
Generally, the silica powder used in refractories refers to the latter, which is hollow and spherical, active, non agglomerated, good filling performance, pozzolanic reaction at room temperature, and mullite formed with Al2O3 at high temperature, which is conducive to the improvement of castable strength.
However, it must have stable physical and chemical properties, otherwise it will affect the service performance of the product.
In the production process of refractory preforms, the molding performance of products fluctuates due to the batch replacement of silicon powder in raw materials.
Among them, the most obvious is the rise and stratification of the formed products.
The methods to deal with the problem of rising stratification are as follows: firstly, the silicon powder used is screened to homogenize its composition; Secondly, in the process of mixing, increase the amount of retarder, appropriately increase the amount of water, appropriately extend the wet mixing time, and then form; Finally, properly reduce the curing temperature of the products, which can basically solve the problem.
4.
The flashing of corundum spinel preform containing aluminum powder is in the production of amorphous refractory- α Al2O3 micro powder is also one of the commonly used refractory powders- α Al2O3 ultrafine powder is made by calcining industrial alumina.
It is characterized by good dispersion, small particles, easy sintering at high temperature and small volume effect..
