The process of firing refractory bricks includes three process

 The process of firing refractory bricks includes three processes

1. Kiln installation

The so-called kiln loading refers to the operation 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 the products are fired. For the tunnel kiln, it is also called loading (kiln) car.

1) Determine the kiln installation height and kiln installation method according to different brick types. Usually, the kiln height of magnesia bricks and first-class high-alumina bricks is 1-1.1m; that of silica bricks is 1-1.7m; and that of clay bricks is between the two. Most of the bricks are installed flat, the silica bricks are installed vertically and the clay bricks are installed sideways.

2) According to different brick types, determine the kiln loading ratio of ordinary bricks and special-shaped bricks. Generally, the ratio of special-shaped bricks and ordinary bricks on the same kiln car is about 4:6. At the same time, it is necessary to determine the kiln installation positions of different varieties according to different brick types. Generally, the standard and ordinary bricks are installed in the lower part, and the special-shaped bricks are installed in the upper part, and some special-shaped bricks or adobes that are easy to crack when fired are packaged (bricks wrapped in bricks).

3) On the premise of ensuring the quality of firing, increase the density of bricks (that is, the amount of bricks per unit kiln car) to increase production and reduce fuel consumption.

Making a reasonable kiln installation plan is the premise to ensure the quality of the kiln installation, but if the kiln installation operation is improper, the qualified rate of the appearance of the fired product will be reduced. Therefore, in the production of refractory materials, the basic requirements for the quality of the kiln are to ensure that the brick stack is flat, stable and straight, to avoid bonding between the bricks due to high temperature firing, and to reduce the distortion of the fired products. In order to meet the above requirements, a layer of sand filling with a particle size of 0.5-3mm is usually evenly sprinkled between each layer of bricks when the kiln is installed. Products with different properties have different requirements for kiln filling sand. Usually, clay bricks and high alumina bricks use silica sand, bauxite chips, rice husk or rice husk ash; silica bricks use waste silica brick sand or silica sand; Magnesia bricks use magnesia or chrome ore.

2. Firing

The adobe undergoes a series of physical-chemical reactions during the firing process, making the adobe compact, increasing its strength, stabilizing its volume, and ensuring 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 is ignited to the time when the product reaches the highest temperature for firing. As the temperature increases, the liquid phase formation temperature and the phase synthesis temperature are reached. Due to the diffusion, flow, dissolution, precipitation, and mass transfer process of the liquid phase, the particles are further approached by the surface tension of the liquid phase to promote the densification of the green body. The strength is increased, the volume is reduced, the porosity is reduced, and the green body is sintered.

(2) The heat preservation stage at the highest firing temperature. Various reactions in the green body tend to be complete and sufficient, the amount of liquid phase increases, the crystalline phase grows further, and the brick body reaches densification. In 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 temperature homogenization process is achieved by heat transfer, which requires a certain amount of time. It can be seen that the larger the product and the higher the kiln density, the longer this time will be. In addition, due to the uneven temperature of various parts in the kiln, a certain holding time is also required.

(3) The cooling stage refers to the period from the highest firing temperature to the kiln exit temperature. During this stage, the structural and chemical changes that the article undergoes at high temperatures are essentially fixed. At the beginning of this stage, some physical-chemical changes are still going on in the product, such as the crystallization of the physical phase, the crystal transformation of some crystals, the solidification of the glass phase, and the generation of microcracks. The cooling system will affect the physical properties of the product such as strength and thermal shock resistance.

In order to reasonably fire 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; product cooling The lower cooling rate; 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 products are fired at a lower temperature for a longer time, or at a higher temperature for a shorter time. But in fact, due to the slow heat transfer in the kiln and the uneven heating of the products in the kiln, there is a limit to the use of fast firing 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 downdraft kiln requires a slower heating rate and a longer holding time to ensure the uniformity of the brick temperature. An unsuitable firing system will increase the reject rate and reduce the quality of the product. The proper firing system is based on theoretical guidance and practical experience.

3. Out of the kiln

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

(1) When taking and placing bricks, handle them with care to avoid appearance defects of the product due to careless operation out of the kiln.

(2) Products of different brick numbers should be stacked strictly separately, that is to say, products of different brick numbers cannot be placed on the same brick board when they leave the kiln, otherwise, it is easy to cause confusion when checking and selecting finished products. Because the appearance of some products with different brick numbers 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 distinguish them when checking. The product of one of the brick numbers is mistaken as a waste product, which will not only cause waste, but also affect the use.

(3) Tool bricks (frame bricks, drawn bricks, etc.) should be arranged and stacked for continued use during kiln installation.

(4) Pay attention to safe operation and labor protection when leaving the kiln and transporting bricks.

We Changxing Refractory Material Co.,LTD is professional manufacturer and supplier of refractory materials for more than 30 years. Our high quality refractory products are good sold to many countries say South Africa, Bangladesh, Indonesia, Malaysia, etc.  

Article Source:The process of firing refractory bricks includes three process
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