The principle of filtration of molten aluminum and the choice of ceramic foam filters
The principle of filtration of molten aluminum and the choice of ceramic foam filters
The principle of filtration for molten aluminum
The characteristics of ceramic foam filter plate are similar to activated carbon, it has the characteristics of a multi-layer network multi-dimensional through-hole, and the connection between holes and holes. When filtering, the molten aluminum carries inclusions along the zigzag filter plate channel and the porous pore flow and the filter plate foam skeleton contact with the direct interception adsorption deposition and other effects, when the melt flows in the hole when the filter plate channel is curved, the melt flowing through the channel changes the flow direction, the inclusions collide with the hole wall and firmly adhere to the hole wall.
Use and selection of filter plates
A ceramic foam filter plate is installed in the filter box between the furnace mouth and the shunt plate, the filter box is made of "Chinese refractory No. 5" refractory material, it can pass through thousands of times of quenching and heat without cracking, has the advantages of high strength and high thermal insulation performance, and is currently the best material for making filter boxes, flow slots and so on. The closer the filter box is to the shunted disc, the better because it shortens the flow distance of the aluminum filtration and reduces or avoids the re-generation of oxides. The molten aluminum flows out of the furnace mouth through the filter box and then through the flow through to the human diversion disc. When the filter device starts, the drop before and after the melt filtration is about 50mm, and with the extension of the filtration time, the inclusions on the surface of the filter plate and the hole wall increase, the filter flow decreases, the gap between front and back increases, and by the end of casting, the drop increases to 60~120mm. The selection of the filter plate must be based on the flow of the molten aluminum, and secondly, the cleanliness of the melt, the maximum content of inclusions, and the total throughput of the melt should be considered (see Tables 1 and 2).
Table 1 Physical properties of foam ceramic filter plates
Thickness | 20-50mm |
holes number | 15-45 holes/inches(500-1770 holes/m) |
Hole inches | 80%-85% |
Bulk density | 0.359~0.45g/cm3 |
Air permeability | (1000~2000)×10-7 |
Compressive strength | 1300℃ 55 N/cm2 |
Fire resistance | >1800℃ |
Table 2 Typical flow characteristics of 25 mesh foam ceramic filter plates
Ceramic foam filter specification/mm | Volume /m3 | Maximum metal flow /kg*min-1 | Optimum flow range /kg*min-1 | Typical filtering volume /t |
178*178*50 | 0.0213 | 57.00 | 25-45 | 4.2 |
229*229*50 | 0.0378 | 118.00 | 35-102 | 6.9 |
305*305*50 | 0.0745 | 198.00 | 90-165 | 13.8 |
381*381*50 | 0.1220 | 325.80 | 130-265 | 23.2 |
432*432*50 | 0.1600 | 427.20 | 210-350 | 34.5 |
508*508*50 | 0.2270 | 606.60 | 280-465 | 43.7 |
585*585*50 | 0.3440 | 772.20 | 370-640 | 57.3 |
The filtration effect of the ceramic foam filter plate is mainly guaranteed by its size and porosity, the larger the pores of the filter plate, the better the passability, the greater the flow, but the worse the slag removal effect, for aluminum castings with strict requirements, a filter plate with small pores should be selected. If using a filter plate of 40-45 wells/inch (1770 wells/m).
