Nowadays, various types of refractory castables have been widely used in industrial furnaces, such as refractory clay castables and low-cement castables. These materials prolong the service life of various industrial furnaces and gradually make traditional ordinary castables gradually Neglected. This paper describes the process characteristics, ratio and preparation process of phosphate castables, as well as applications in industrial furnaces.
Process characteristics of phosphate castables
The phosphate castable is prepared by mixing clay clinker or bauxite clinker as aggregate, using industrial phosphoric acid as a binder and high alumina cement as a coagulant. It has the characteristics of high strength, high refractoriness and high thermal shock stability. The design requirements are met by changing the Al2O3 content of its raw materials. The temperature range is between 1450 and 1600 ° C, which is a castable with a relatively high temperature.
Ratio of phosphate castables
The ratio of ingredients should be appropriate, especially the performance of the admixture should be mastered. Phosphoric acid should meet the requirements of phosphoric acid. The concentration of industrial phosphoric acid in the market is usually 80~%85%. It is usually diluted to 40%~42.5% when used on the construction site. When diluting, the concentrated phosphoric acid should be slowly poured into the water and stirred while pouring. It is strictly forbidden to pour water into phosphoric acid. In order to prevent acid splashes from injuring people. The high alumina cement used as a coagulant shall be numbered for 425# and shall comply with the regulations for high alumina cement.
Preparation and stirring process of phosphate castable
In the industrial furnace maintenance, according to the size of the workload, manual or mechanical mixing of the ingredients can be used, but the overall process requirements are the same, the refractory raw materials are fully stirred and mixed, then 50%~60% of the required amount of phosphoric acid is added to In the mixed dry material, the first stirring is carried out, but the coagulant is not added. After mixing, the material should be trapped. According to the season, the time of trapping is 24~48h, and the material after the trapping should be carried out before pouring. The second agitation, at this time to add a coagulant high alumina cement, stir evenly and then add the remaining phosphoric acid, continue to stir for 3 to 4 minutes.
Pouring construction of phosphate castable
For the construction of any castable, the formwork is required. According to the different construction parts of the industrial furnace, there are usually flat formwork and curved arch formwork, which are divided into steel mold and wooden mold according to the material. The size of the template should be accurate, the support should be firm, and the displacement should be prevented when the castable is sputtered. On the side of the contact between the template and the castable, a layer of kraft paper or plastic cloth is applied to eliminate the pockmark when demolding.
When the castable is poured, the vibrating rod is usually vibrated. The vibration time is returned to the surface of the castable. If the vibration time is too long, the cast material will be stratified internally, resulting in a decrease in the strength of the castable; the vibrating time is too short, and the inside thereof Will not be dense.
Maintenance and baking characteristics of phosphate castables
Phosphate castables tend to absorb moisture and deliquesce when exposed to a humid atmosphere, which will reduce their compressive strength. They should be cured in a dry environment. The curing temperature should be 20~50°C. If the ambient temperature is low, it should be dried at low temperature. grilled.
Phosphate castables add a certain amount of water during the preparation process, and need to be dehydrated multiple times at different temperatures to produce crystal form conversion and polymerization. Therefore, baking before the lining is used is necessary, and baking can also The castable lining reaches a certain sintering strength. If it is improperly baked, it will cause damage to the castable lining, causing cracks, peeling and the like. A scientific oven curve should be established based on the size of the castable construction area and the thickness of the castable. For the whole lining, the kiln with phosphate castable construction is used. Usually, the oven time is within 7~10d, and the temperature is maintained at the three temperature points of 150, 350 and 650 °C for a certain period of time, and the other time can be raised. For parts with a small construction area, it can be baked to above 350 °C. At this time, the free water and crystal water in the castable can be basically eliminated, and then can be carried out according to the conditions of the refractory brick lining oven.
(1) After years of use, it shows that the phosphate castable has the characteristics of flaking resistance, air scouring and abrasion resistance, and the service life of some key parts of the industrial furnace is longer than that of ordinary refractory bricks.
(2) In the complex structure of the industrial kiln, the phosphate castable is used instead of the refractory brick masonry, which eliminates the cumbersome operation of grinding bricks and brick cutting, has the advantages of simple and convenient construction, saving construction period, etc., and overcomes the processing due to processing. The harmful dust generated by refractory bricks can harm the workers' body and prevent and reduce the incidence of occupational diseases.
(3) The physical and chemical indicators used to prepare the raw materials of phosphate castables should meet the standard requirements. The amount of binder and coagulant must be strictly controlled. At the same time, the time for the first time after stirring is sufficient, only the above requirements can be met. In order to produce a qualified phosphate castable.