Mullite castables production process

Mullite refractory castables production process

Mullite refractory castables have good flow properties, spalling resistance and heat preservation properties, suitable for use in high temperature parts of the heating furnace. Fireramo summarizes the production and formulation process of common mullite castables for you to improve the service life of the furnace body, reduce the thermal conductivity of the heating furnace body and increase the heat rate.

Synthesis process of mullite refractory castables

In order to reduce the production cost of lightweight aggregate in mullite castables, refractory castables manufacters choose low-iron gangue and high alumina bauxite after iron removal treatment as the main raw materials to introduce Al2O3 and SiO2, and the synthesized part adopts raw materials. The mixing of the raw materials is carried out by high stirring mills, which provide sufficient mixing while grinding finely. The grinding rate of the high stirring mill is about three times that of an ordinary ball mill, and it is easy to grind the above mixture to below 800 mesh.

The main mineral constituent of gangue is kaolinite, which can partially restore plasticity and viscosity under the condition of sufficient grinding. In order to make progress in increasing the strength of raw blanks, 2%~3% of montmorillonitic clay can be added during the grinding process.

The ground slurry is partially dewatered and mixed with organic matter such as sawdust, small balls of polystyrene foam, and also low ash anthracite and bituminous coal. It is then extruded and molded into blanks using a brick extruder, or it can be manually pounded or poured into shape.

The wet blanks after molding are dried in the drying kiln using the exhaust gas of the calcining kiln, and natural drying can also be used where available. The dried blanks are calcined at 1550℃×20h in a coal-fired inverted flame kiln.

The inverted flame kiln adopts the new structure of multiple heat exchangers, lightweight lining and heat insulation layer, which breaks through the difficulty of burning high temperature in coal-fired inverted flame kiln, and at the same time, it has a lower energy consumption than the traditional inverted flame kiln by one-third. Coupled with the use of a large number of billet raw materials in the gangue at the same time, in addition to adding a large number of organic matter as a pore-making agent, both in the billet calcination process can play a role in internal combustion heating, the whole system has a high energy utilization rate.

The calcined blanks are crushed and sorted immediately, the coarse and fine particles larger than 500um are used as coarse and fine aggregates for castables, the fine powder smaller than 500um is finely ground by vibration mill to less than 43um, and part of it is sold as high-purity mullite fine powder, and part of it is used as the fine powder of castables to formulate castables.

Mullite refractory castables preparation process

The calcined lightweight mullite aggregate blank is crushed into particles of ≤1cm, and divided into 3mm~10mm, 0.5mm~3mm and part of it as coarse aggregate and fine aggregate of heat-insulating refractory castables respectively.

In order to control the bulk density of the end products of the castables, some 0.5mm~2.85mm sawdust or expanded perlite can be used instead of fine aggregate. Less than 0.5mm part of light weight mullite powder is finely ground to ≤43um by vibration mill, partly used as the fine part of castable material to produce castable material, partly used as high-purity mullite fine powder for sale.

In order to reduce the line shrinkage of the castables in the process of high temperature use, it is necessary to add part of the blue crystal stone as an expansion agent. Bluecrystal is added in the form of ≤74um fine powder. In order to improve the high temperature resistance of mullite insulating refractory castables, pure calcium aluminate cement with w(Al2O3)>80% of Al2O3 content is used to ensure sufficient strength of the castables, so that the content of CaO in the system can be reduced by one-third as compared with that of the ordinary high alumina cement.

In order to promote the sintering of the castables and widen the sintering temperature range, it is also necessary to add a small amount of SiO2 and Al2O3 powder. The amount of Al2O3 micro-powder added in addition to the added SiO2 micro-powder partially converted to mullite, but also need to be enough to react with the decomposition of the blue crystal stone when heated out of the SiO2 to form mullite.
 
In order to reduce the drying shrinkage of the castable and increase the strength after drying, it is also necessary to add a small amount of high water reducing agent. As the allocation of mullite insulating castables must follow the principle of close packing of particles, the addition of blue crystalline stone and SiO2 micropowder and Al2O3 micropowder will inevitably reduce the amount of mullite fine powder.

Mullite refractory castables production process

Artificial picking: the purchased low (particle size of 10 ~ 30cm, Al2O3 content of 50% ~ 60%) first by artificial picking for points, according to the products are processed.

Crushing: In order to facilitate the follow-up, it is necessary to feed the bauxite after picking to the jaw crusher for crushing, and the particle size after crushing is less than 10mm.

Mixing: the crushed bauxite particles are transported to the sand mixer, and the purchased quartz powder and alumina powder are put into the sand mixer at the ratio of 37%:55%:8% (bauxite: quartz powder: alumina powder), and water is added for stirring and mixing, and the mixing time of the sand is about 15min. the sand mixing time is about 15 min.

Molding: The material after sand mixing is transported by conveyor belt to the hydraulic vibration press for blanking and molding. Hydraulic vibration press is a new type of press, using the principle of vibration pressure to press the bulk material into shape, in the upper hydraulic cylinder pressure at the same time eccentric vibration, in order to get high density, uniform structure of the blank. This type of hydraulic machine blank rate of 1 block / min.

Sintering: the molded blanks are manually transported to the sintering kiln for yarding and sintering, the sintering temperature is about 1600 ℃, and the sintering time of each kiln is about 48 h. The sintered materials can be cooled down to room temperature after 48 h for subsequent picking. The sintering in this project adopts energy-saving tandem sintering kiln, and the fuel is natural gas.

Secondary picking: the finished products after sintering are picked manually, categorized according to quality and transferred to the finished product warehouse.

  Mullite refractory castables are suitable for the working lining or thermal insulation lining of many kinds of flame furnaces and other industrial kilns to realize high temperature energy saving. After learning the production process of mullite refractory castables, we will understand it better and be more skillful in using it.