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The main processes of various refractory products (burned bricks or non-fired bricks, tar-bonded bricks, fused cast bricks or amorphous refractory materials) are as follows (the specific production methods vary with the variety) ):
(1) Raw material calcination: Most of the refractory raw materials are calcined before brick making. This is because their weight and volume change under the action of high temperature. If the whole raw material is used, the volume of the brick will change greatly, and even a large amount of deformation and cracking waste will appear. The calcination temperature of clay and high alumina bauxite is generally 1350~1550 °C, and the weight loss is about 15%; the calcination temperature of magnesite and dolomite is generally 1650-1850 °C, and the weight loss is about 50%. The calcining equipment mainly has a shaft kiln and a rotary kiln.
(2) Raw material processing: mainly includes the sorting, crushing and crushing, fine grinding and screening of raw materials. Picking is the selection of mixed debris, raw materials, unburned fuel blocks and lumps to ensure the quality of the raw materials. Grinding and sieving is to prepare the bulk material into pellets having a certain particle size composition for furnishing.
(3) Preparation of mud: mainly includes processes such as batching, mixing, and trapping. The ingredients are compounded according to the weight of each material and the appropriate proportion of the particle composition to ensure the compactness of the body after molding and the performance of the product meet the requirements. The mixing process is to make the components in the mud material evenly distributed after mixing. The trapping material is a process in which the mixed mud material is stored for a certain period of time under certain temperature and humidity conditions to improve the forming performance of the mud material. With the improvement of the production technology level, the production of most refractory products has eliminated the trapping process.
(4) Billet forming: By means of external force (pressure), the loose mud is obtained into a shape, size and as dense as possible. The compactness of the brick determines the density of the finished product. The molding methods generally include: grouting method, plastic method, semi-dry method (including dry method), melt casting method, and isostatic pressing method. Usually more than half dry machine press molding. The main equipment for press forming is various types of friction brick presses, lever presses, rotary brick presses and high pressure hydraulic presses. For large and specific products, vibration molding, air hammer tamping or manual ramming can be used.
(5) Finished product firing: The semi-finished product after molding is generally dried and then fired. The moisture entering the kiln brick is too high and it is easy to crack. After drying, the strength of the brick is greatly improved, which can reduce the damage rate during transportation and kiln. A series of physicochemical changes are produced during the firing process. Under the action of high temperature, the density and strength of the green body are increased, and a high temperature stable crystal phase is formed, and a volume change is generated. According to the characteristics of the product, a reasonable firing system should be developed. It is generally divided into four stages, namely preheating, firing, holding and cooling. The firing equipment has a downdraft kiln and a tunnel kiln. At present, the tunnel kiln is the main one, but for the refractory products with small production volume or special shape, the downdraft kiln still has certain use value.
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