Structure and material of ceramic filter

The research of ceramic filter mainly focuses on two aspects: one is the material of ceramic filter, including the manufacturing process and performance of ceramic filter; The second is the structure of the ceramic filter, including the shape of the filter, placement position, filtering mechanism and filtering effect.

The filter material should be selected according to the type of inclusions to be removed by filtration, and the creep resistance and thermal vibration resistance of the material should also be considered. A large number of experimental results show that material, porosity and inner surface roughness of ceramic filter affect the filtration effect. The structure of ceramic filter is determined by its material. According to the different material, ceramic filter can be divided into foam ceramic filter and particle ceramic filter.

Ceramic foam filters have an open volume of 75% to 90% and are usually classified by PPI per inch of line. For example, 10 PPI ceramic foam filter, its pore size is 1778 μm, the range is 584 ~ 3708 μm; The pore size of the 30 PPI ceramic foam filter is 711 μm, ranging from 229 μm to 1422 μm. The thickness of the ceramic foam filter is generally 25 mm. In the pouring system, there are upright and horizontal placement, and its structure is designed according to the specific situation of use.

Ceramic foam filter has been selected material NCL-MulLite, ZrO2, ZR-SiO4 and Al2O3. The use of Al2O3 foam ceramic, in the operation is not fragile, its thermal vibration cracking performance is good, at 1700℃ high temperature liquid metal flow, anti-creep deformation ability is strong. Because of the high porosity of the pores (75% to 90%) and the thin walls of the pores, the foam ceramic filter does not need to be preheated before coming into contact with the liquid metal.

The structure of the particle ceramic filter is a support plate with holes up and down, and the middle is a particle filler, on which a layer of active adsorption material is plated. The thickness of the support plate is generally 12 mm, and the hole diameter is 4.5 ~ 13 mm. MgO or Al2O3 is selected as filler for granular ceramic filter, and active adsorbent is selected according to the type of inclusions to be filtered. For the superalloy treated with rare earth metal, the rare earth metal is selected as the activator, and the waterproof problem should be solved when using calcium oxide particles.

CaO refractory is a good filler material for granular ceramic filters, which can not only rely on the principle of physical adsorption, but also can remove inclusions through chemical reactions. However, there are two reasons that limit its extensive application. First, it requires extremely high sintering temperatures (above 1800℃) to obtain the required density and mechanical strength. Second, it is easy to hydrate at room temperature and atmosphere.

The advantages of CaO refractoriness are high refractoriness, high alkalinity, good filterability of liquid steel and abundant resources. The way to improve the hydration resistance of CaO refractory for liquid steel filtration is to improve the sintering degree of CaO refractory, large crystal size, using ultra-high calcination or electromelting lime; A protective film is formed on the surface of CaO; Tar or organic resin film is soaked on Cao-fired products as an intermediate transition measure; The effect of adding a small amount of chemical additives in CaO is to reduce the sintering temperature of CaO, and to produce part of liquid phase in the sintered body at the later stage of sintering, so as to promote the growth of CaO grains.