\n| Cake filtration<\/td>\n | Progressively finer<\/td>\n | Built-up cake layer on inlet<\/td>\n | Extended pour runs<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n The combination of all three mechanisms is what makes CFF filtration far more effective than simple mesh screens or fiberglass cloth filters for molten aluminum applications.<\/em><\/p>\n![\"\u0645\u0631\u0634\u062d\u0627\u062a](\"https:\/\/www.aluminiumceramicfiber.com\/wp-content\/uploads\/2021\/12\/Metal-Casting-Filters.jpg\") \u0645\u0631\u0634\u062d\u0627\u062a \u0627\u0644\u0631\u063a\u0648\u0629 \u0627\u0644\u062e\u0632\u0641\u064a\u0629 \u0641\u064a \u0645\u062c\u0627\u0644 \u0627\u0644\u062a\u0635\u0646\u064a\u0639<\/em><\/p><\/div>\n<\/span>What Are Ceramic Foam Filters Made Of?<\/span><\/h2>\nUnderstanding how ceramic foam filters are manufactured helps explain why quality varies between suppliers \u2014 and why that quality difference shows up in your casting results.<\/p>\n <\/span>How Are Ceramic Foam Filters Produced?<\/span><\/h3>\nThe production process follows these core steps:<\/p>\n \n- Foam template preparation<\/strong>\u00a0\u2014 open-cell polyurethane foam is cut to the desired filter shape and dimensions. The pore count (measured in pores per inch, or ppi) of this template determines the final filter pore size.<\/li>\n
- Ceramic slurry impregnation<\/strong>\u00a0\u2014 the foam is immersed in a ceramic slurry formulated from alumina, silicon carbide, zirconia, or blended compositions depending on the target application. The slurry coats every strut and cell wall of the foam uniformly.<\/li>\n
- Excess slurry removal<\/strong>\u00a0\u2014 the impregnated foam passes through rollers or a compressed air station to remove excess slurry, ensuring open pores are not blocked.<\/li>\n
- Drying<\/strong>\u00a0\u2014 controlled low-temperature drying removes moisture without cracking the green coating.<\/li>\n
- Baking and sintering<\/strong>\u00a0\u2014 the part is fired at temperatures between 1200 \u00b0C and 1600 \u00b0C. The polyurethane foam burns out completely, leaving behind a rigid ceramic replica of the original foam structure \u2014 an interconnected network of hollow ceramic struts with open porosity.<\/li>\n
- Quality inspection<\/strong>\u00a0\u2014 finished filters are tested for dimensions, weight, cold compressive strength, porosity uniformity, and permeability. Thermal shock testing \u2014 typically by pouring liquid aluminum through the filter placed in a gating system \u2014 verifies that the filter can withstand the sudden temperature rise to 700\u2013750 \u00b0C without cracking.<\/li>\n<\/ol>\n
After the pouring process, test filters are sectioned and examined under microscopy to confirm that impurity particles have been captured effectively throughout the filter depth, not just on the surface.<\/p>\n \n \n\n\n| Filter Composition<\/th>\n | Typical Service Temperature<\/th>\n | Best Suited For<\/th>\n | Relative Cost<\/th>\n<\/tr>\n<\/thead>\n | \n\n| Alumina (Al\u2082O\u2083) based<\/td>\n | Up to 1100 \u00b0C<\/td>\n | Aluminum alloy casting<\/td>\n | Low\u2013Medium<\/td>\n<\/tr>\n | \n| Silicon carbide (SiC) based<\/td>\n | Up to 1500 \u00b0C<\/td>\n | Aluminum, copper, iron<\/td>\n | \u0645\u062a\u0648\u0633\u0637<\/td>\n<\/tr>\n | \n| Zirconia (ZrO\u2082) based<\/td>\n | Up to 1700 \u00b0C<\/td>\n | Steel, superalloy casting<\/td>\n | \u0645\u0631\u062a\u0641\u0639<\/td>\n<\/tr>\n | \n| Alumina-SiC composite<\/td>\n | Up to 1300 \u00b0C<\/td>\n | Aluminum, specialty alloys<\/td>\n | \u0645\u062a\u0648\u0633\u0637<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n For standard aluminum foundry and casthouse operations, alumina-based ceramic foam filters offer the best balance of filtration performance, thermal resistance, and cost.<\/em><\/p>\n![\"\u0645\u0631\u0634\u062d\u0627\u062a](\"https:\/\/www.aluminiumceramicfiber.com\/wp-content\/uploads\/2020\/05\/Porous-Ceramic-Filter.jpg\") \u0645\u0631\u0634\u062d\u0627\u062a \u0627\u0644\u0631\u063a\u0648\u0629 \u0627\u0644\u062e\u0632\u0641\u064a\u0629 \u0641\u064a \u0645\u062c\u0627\u0644 \u0627\u0644\u062a\u0635\u0646\u064a\u0639<\/em><\/p><\/div>\n<\/span>What Pore Size Should You Choose for CFF Filtration?<\/span><\/h2>\nPore size \u2014 expressed as pores per inch (ppi) \u2014 is the single most important selection parameter for a ceramic foam filter. A higher ppi count means smaller pores and finer filtration, but also higher flow resistance.<\/p>\n Getting this tradeoff right matters. If the ppi is too coarse, fine inclusions pass through and end up in your casting. If the ppi is too fine, you get premature clogging, reduced pour rate, and risk of cold shuts or misruns \u2014 especially on thin-wall castings where metal fluidity is already marginal.<\/p>\n <\/span>Which PPI Grade Is Right for Your Application?<\/span><\/h3>\n\n \n\n\n| PPI Grade<\/th>\n | Approximate Pore Opening (mm)<\/th>\n | Typical Application<\/th>\n | Inclusion Removal Efficiency<\/th>\n<\/tr>\n<\/thead>\n | \n\n| 10 ppi<\/td>\n | 2.5 \u2013 3.0<\/td>\n | Rough castings, high flow rate required<\/td>\n | Moderate \u2014 large inclusions only<\/td>\n<\/tr>\n | \n| 20 ppi<\/td>\n | 1.5 \u2013 2.0<\/td>\n | General foundry castings, ingot production<\/td>\n | Good \u2014 removes most visible inclusions<\/td>\n<\/tr>\n | \n| 30 ppi<\/td>\n | 1.0 \u2013 1.5<\/td>\n | Quality castings, billet and slab production<\/td>\n | Very good \u2014 captures inclusions > 50 \u00b5m<\/td>\n<\/tr>\n | \n| 40 ppi<\/td>\n | 0.6 \u2013 1.0<\/td>\n | Aerospace, automotive critical parts<\/td>\n | Excellent \u2014 captures inclusions > 20 \u00b5m<\/td>\n<\/tr>\n | \n| 50\u201360 ppi<\/td>\n | 0.4 \u2013 0.6<\/td>\n | Ultra-clean metal for foil stock, can stock<\/td>\n | Maximum \u2014 finest practical filtration<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n Foundries running multiple product lines often stock two or three ppi grades and select based on the quality requirements of each specific casting order.<\/em><\/p>\nFor primary aluminum casthouses producing rolling ingot or extrusion billet, 30 ppi is the most common workhorse grade. Automotive structural castings increasingly call for 40 ppi or finer, driven by OEM specifications that set maximum allowable inclusion content per unit area of polished cross-section \u2014 standards you can find referenced in\u00a0Aluminum Association guidelines\u00a0and individual OEM casting specifications.<\/p>\n <\/span>How Does CFF Filtration Improve Casting Quality?<\/span><\/h2>\nThe practical benefits of effective CFF filtration show up across multiple quality metrics:<\/p>\n \n- \u062a\u0634\u0637\u064a\u0628 \u0627\u0644\u0633\u0637\u062d<\/strong>\u00a0\u2014 removing oxide skins and particle clusters eliminates the most common source of surface defects, pinholes, and roughness on machined surfaces.<\/li>\n
- \u0627\u0644\u062e\u0635\u0627\u0626\u0635 \u0627\u0644\u0645\u064a\u0643\u0627\u0646\u064a\u0643\u064a\u0629<\/strong>\u00a0\u2014 inclusions act as stress concentrators. Removing them improves tensile strength, fatigue life, and elongation \u2014 particularly important in safety-critical automotive and aerospace components.<\/li>\n
- \u0642\u0627\u0628\u0644\u064a\u0629 \u0627\u0644\u0645\u0639\u0627\u0644\u062c\u0629 \u0627\u0644\u0622\u0644\u064a\u0629<\/strong>\u00a0\u2014 hard oxide and spinel inclusions cause premature tool wear during CNC machining. Cleaner metal means longer tool life and lower machining costs.<\/li>\n
- Reduced porosity<\/strong>\u00a0\u2014 fine non-metallic particles serve as nucleation sites for dissolved hydrogen to form gas pores. Filtering them out works synergistically with degassing to minimize porosity.<\/li>\n
- Downstream process yield<\/strong>\u00a0\u2014 for products like aluminum foil, can body stock, and lithographic sheet, even tiny inclusions cause pinholes or surface streaks that result in rejected coils. CFF filtration at the casthouse is the primary line of defense.<\/li>\n<\/ul>\n
If your facility already uses\u00a0ceramic fiber-lined launders and transfer systems, integrating a properly sized CFF filter into the launder line is straightforward and delivers immediate, measurable quality improvements.<\/p>\n <\/span>Where Should You Place the CFF Filter in the Casting System?<\/span><\/h2>\nFilter placement affects both filtration efficiency and operational practicality. The two most common configurations are:<\/p>\n In-line filtration (casthouse\/continuous casting)<\/strong>\u00a0\u2014 the filter is housed in a dedicated filter box positioned in the launder between the degassing unit and the casting mold or trough. This is standard practice in DC (direct chill) casting of billet and slab. The filter box is typically preheated to 500\u2013600 \u00b0C before the cast begins to prevent thermal shock and premature metal freeze-off.<\/p>\nIn-gating system filtration (foundry\/gravity casting)<\/strong>\u00a0\u2014 the ceramic foam filter is placed directly in the runner system of the sand or permanent mold. Metal flows through the filter under the head pressure of the pouring basin. This approach is common in gravity die casting and sand casting of shaped aluminum parts.<\/p>\nEach approach has advantages. In-line casthouse filtration handles large metal volumes and can be combined with other melt treatment steps. Gating system filtration is simpler and cheaper but limited to smaller pour volumes. Many operations use both \u2014 coarse filtration at the casthouse, followed by a finer filter in the individual mold gating system for maximum cleanliness.<\/p>\n | | |
![\"Aluminum](\"https:\/\/www.aluminiumceramicfiber.com\/wp-content\/uploads\/2021\/07\/Aluminum-Melt-CFF-Filtration.jpg\")