The main function of the ceramic foam filters use is to prevent the inclusions in the molten metal from entering the casting platform and eliminate the inclusion defects. In recent years, with the rapid development of car manufacturers, the output of car castings has been increasing year by year. The role of ceramic foam filters has been paid more and more attention, and the amount of use has been increasing year by year.
There are three types of filters commonly used in casting production:
- Glass fiber filter: made of high temperature resistant glass fiber and resin, it can filter out the inclusions larger than the mesh, the effect is general, the price is cheap, and the manufacturing process is simple.
- Straight-hole ceramic filter: it is pressed or extruded from ceramic material, the filtering effect is worse than fiber filter, but not as good as foam ceramic filter.
- Foam ceramic filter: It came out in 1978. It was first used in non-ferrous alloys. Since 1985, it has been used in cast aluminum and cast steel. Its production process uses foam plastic as the skeleton, coated with ceramic slurry, and fired at high temperature. It Has a good filtering effect.
The filtering effect of the ceramic foam filter benefits from its comprehensive effects:
- Mechanical filtration: inclusions larger than the filter mesh are blocked.
- Filter cake function: During the flow of aluminum water, larger inclusions are continuously blocked, and they continue to accumulate. At the same time, the channels for the flow of molten metal are gradually reduced, blocking smaller inclusions.
- Adsorption: The inclusions have a greater affinity with ceramic materials. In the complex filter channel of the filter, the molten metal has a large contact area with the filter, and the inclusions are easily adsorbed on the channel wall.
- Rectification effect: during pouring, after the high-speed flowing molten metal passes through the filter, the flow rate decreases, and the turbulent flow tends to laminar flow, reducing the splashing of the molten metal and reducing the generation of oxidized slag; allowing sufficient time for inclusions float and stay in the filter box.
Reasonable Use of Foam Ceramic Filters
Through experiments, in order to effectively eliminate the inclusion defects when formulating the casting process plan, according to the process characteristics and importance of the casting, the foam ceramic filter was placed before casting, and good economic benefits were obtained. There are strict requirements on the quality of the filter itself, and its normal temperature strength, high temperature impact resistance and dimensional accuracy should meet the requirements of use. Proper room temperature strength can overcome the problems of damage and slag falling during transportation; if the filter has poor thermal shock resistance or low fire resistance, the filter will burst and break during the casting process, and it will not The effect of filtration will instead form more inclusions rushing into the casting platform; the dimensional accuracy of the filter is also important, and it will be damaged when the size is too large, and the size is too small to be used or the filtering effect is poor.