1. Kiln loading

The so-called kiln loading refers to the process of reasonably arranging and stacking bricks that meet the technical conditions of semi-finished products in the kiln according to the structural characteristics of the kiln and the requirements of the thermal system when firing products. For tunnel kiln is also called loading (kiln) car.

1) According to different brick species, determine the height of the kiln and the method of loading. Usually, the kiln height of magnesia brick and first-class high alumina brick is 1~1.1m; silica brick is 1~1.7m; clay brick is between the two. Most of the brick loading methods are plain, silicon bricks are erected and clay bricks are side-mounted.

2) According to different brick types, determine the kiln loading ratio of general brick and special-shaped brick. The ratio of general special-shaped brick and general brick on the same kiln car is about 4: 6. At the same time, but also according to different brick type, to determine the different varieties of kiln parts. Generally, standard and ordinary bricks are installed in the lower part, special-shaped bricks are installed in the upper part, and some special-shaped bricks or brick blanks that are easy to crack during firing are packaged (bricks are packaged with bricks).

3) Under the premise of ensuring the quality of firing, increase the density of bricks (I. e., the amount of bricks per kiln car) to increase production and reduce fuel consumption.

The development of a reasonable kiln loading map is a prerequisite to ensure the quality of the kiln, but if the kiln loading operation is improper, it will also reduce the qualified rate of the shape of the fired products. Therefore, in the production of refractory materials, the basic requirement for the quality of the kiln is to ensure that the bricks are flat, stable and straight, and to avoid bonding between the bricks due to high temperature firing, and to reduce the distortion of the fired products. In order to achieve the above requirements, the kiln is usually filled with a layer of sand with a grain size of 0.5~3mm evenly between each layer of bricks. Products of different nature have different requirements for sand filling in kilns. Usually clay bricks and high alumina bricks use silica sand, bauxite chips, rice husk or rice husk ash. Silica brick uses waste silica brick sand or silica sand; Magnesia brick uses magnesia sand or chrome ore sand.

2. Firing

During the firing process, a series of physical-chemical reactions are carried out to make the brick compact, increase the strength, stabilize the volume, and ensure accurate dimensions. The whole firing process can be divided into three stages:

(1) The heating stage, that is, from the time when the product enters the kiln or ignites to the time when the maximum temperature of the product is reached. With the increase of temperature, to reach the liquid phase formation temperature and phase synthesis temperature, due to the diffusion of the liquid phase, flow, dissolved precipitation mass transfer process, particles in the liquid phase surface tension, further close to promote the green body densification, so that its strength increased, volume reduction, porosity decreased, green body sintering.

(2) The heat preservation stage at the highest firing temperature. The various reactions in the body tend to be complete and sufficient, the number of liquid phases increases, the crystal phase grows further, and the brick is densified. During the firing process of the product, not only the surface must reach the firing temperature, but also the interior of the product must also reach the firing temperature. This process of temperature homogenization is achieved by heat transfer, which requires a certain amount of time. It can be seen that the larger the product, the higher the density of the kiln, the longer the time. In addition, due to the uneven temperature of various parts in the kiln, a certain holding time is also required.

(3) The cooling stage is from the highest firing temperature to the kiln temperature. In this stage, the structural and chemical changes that the article undergoes at elevated temperatures are substantially fixed. At the beginning of this stage, some physical-chemical changes are also carried out in the products, such as the devitrification of the biological phase, the crystal transformation of some crystals, the solidification of the glass phase, and the generation of microcracks. The cooling system will affect the strength, thermal shock resistance and other physical properties of the product.

In order to reasonably carry out the firing of various refractory products, the firing system of each product should be determined in advance, including: the maximum temperature of firing; The heating rate at each stage; The holding time at the highest temperature; The cooling rate of the product under cooling; The nature of the atmosphere in the kiln in the above stages. The firing process of refractory products can be completed by two heating methods, that is, the product is fired at a lower temperature for a longer time, or the product is fired at a higher temperature for a shorter time. However, in fact, due to the slow heat transfer in the kiln and the unevenness of the heating of the product in the kiln, there is a limit to the rapid firing of refractory products.

The firing system of refractory products is not only related to the variety, shape and size of refractory products, but also closely related to the type of firing equipment. For example, a large-scale inverted flame kiln requires a slower heating rate and a longer holding time to ensure the uniformity of the brick temperature. Unsuitable firing system will increase the scrap rate and reduce the quality of products. The appropriate firing system is based on theoretical guidance and practical experience.

3. out of the kiln

Out of the kiln is the process of taking out the burnt products from the kiln after cooling, or unloading them from the kiln car. The operation of the kiln has a direct impact on the quality of the finished product. In the production of refractory materials, the kiln operation should generally pay attention to the following points:

(1) When taking and placing bricks, you should handle them with care to avoid product shape defects caused by careless operation out of the kiln.

(2) Products with different brick numbers should be stacked strictly separately, that is to say, products with different brick numbers cannot be placed on the same brick board when coming out of the kiln, otherwise, it is easy to cause confusion during the inspection and selection of finished products. Because the appearance of some different brick products can be exactly the same, but there is little difference in a certain size (several mm or more than a dozen mm), if they are mixed on a brick board, it is easy to mistake one of the brick products for waste during inspection, which will not only cause waste, but also affect the use.

(3) The tool bricks (frame bricks, drawing bricks, etc.) shall be arranged and stacked for continuous use during kiln loading.

(4) Pay attention to safe operation and labor protection during kiln and brick transportation.