Casting materials in the kiln head cover, grate cooler hot section and front kiln mouth of cement production lines are prone to bursting. The main reason is that during the kiln baking stage, the temperature in the kiln rises rapidly due to excessive heating, and the free water in the refractory castables material changes from liquid to gas in a short time, and forms a certain vapor pressure as the lining temperature rises. When the water vapor inside the lining cannot diffuse in time, it will cause an increase in pressure. When the water vapor pressure inside the lining loses balance, the castable will peel off, peel off or even burst. For the bursting problem of castables, refractory manufacturers in the cement industry generally add 0.1% to 0.3% organic fiber to prevent the occurrence of bursting. Organic fiber melts or burns at about 160℃ to form fine and evenly distributed long and narrow pores. Its formation increases the air permeability of the lining material, accelerates drainage, buffers water vapor pressure, and prevents the lining from bursting due to rapid temperature changes during the baking and kiln feeding stages. However, the use of organic fiber has problems such as difficult dispersion of castables, large additions, and strength impact.
5 suggestions for solving the bursting problem
01 Since all cement production enterprises have cross-operations such as equipment maintenance and refractory castables construction during the overhaul period, all departments must coordinate well and make good arrangements for the construction schedule of castables in various parts of the cement kiln. For castables in some parts that are difficult to bake (grate coolers, kiln head hoods and front kiln mouths), priority should be given to casting construction, and sufficient maintenance time should be reserved; at the same time, supervision of the construction unit should be done well, and the mixing, water addition, formwork support, and maintenance of the castables should be carried out strictly in accordance with the construction instructions.
02 When constructing the kiln head cover, it is best to leave exhaust holes. The specific drilling requirements are: spacing 300mm×300mm, and embedded with Ф5mm wooden strips, with a depth of half the castable.
03 After the kiln head cover pouring hole is closed, 8 vents should be retained and waterproofed. At the same time, in order to ensure that the refractory castable at the front kiln mouth does not burst during baking, it is best to use Ф3mm bamboo sticks to leave exhaust holes during construction, and the arrangement of exhaust holes is 100 per square meter.
04 For the medium and major repairs of cement kilns, before using the burner to spray oil to dry the kiln, some special parts (kiln head cover, grate cooler, front kiln mouth) are best baked with firewood, and the baking time is not less than 12 hours. At the same time, the heating speed should not be too fast during the kiln baking process. For low-cement series refractory castables, when the lining thickness is 200mm~400mm, the optimal heating speed is no more than 15℃ per hour, which can fully meet the needs of lining heating.
05 When there is no baking time for emergency repairs or accidental kiln shutdowns, phosphate-bonded refractory castables, such as PA-852 phosphate castables, can be used. This type of product has the advantage of being free of baking, and its strength increases with the rise in temperature. However, it should be pointed out that this type of product also has its own weaknesses, such as poor wear resistance and short service life. The bursting of castables is a complex issue, which is closely related to many factors, especially during winter construction. More attention should be paid.
In short, adding 0.1% to 0.3% of explosion-proof fiber to the castable can improve the explosion-proof performance of the product. For areas prone to castable bursts, such as the front kiln mouth, grate cooler, and kiln head cover, as long as the construction is reasonably arranged, the quality control of the construction link, the reserved exhaust holes, and the baking process are done well, the bursting of the refractory lining can be completely avoided.
