\nChemical compatibility<\/td>\n Good with water and many oils; limited with strong oxidizers, hot acids<\/td>\n check supplier chemical guide.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\nKey point: datasheet numbers vary between suppliers; the values above represent commonly seen ranges and should be validated for any critical process.<\/p>\n
4. Why choose 20 PPI \u2014 performance tradeoffs and where it fits<\/h2>\n 20 PPI sits at a practical midpoint: it is coarser than fine foams (30\u201360 PPI) and finer than very coarse media (5\u201310 PPI). The tradeoff can be summarized:<\/p>\n
\n\nPermeability:<\/strong> 20 PPI allows higher face velocity and lower initial pressure drop than higher-PPI media because the pore openings are larger. This keeps pumps and blowers from seeing excessive head loss in prefiltering stages.<\/p>\n<\/li>\n\nParticle capture:<\/strong> It captures coarse-to-medium particulates effectively (e.g., sand, weld splatter, larger oxide films). For true sub-micron capture, 20 PPI is not sufficient by itself; a multi-stage filter with finer media downstream is required.<\/p>\n<\/li>\n\nClogging and maintenance:<\/strong> Coarser foams resist rapid surface sealing and therefore last longer between cleanings in many real-world systems. Forum and field reports often prefer 20\u201330 PPI for systems where clogging would otherwise create operational issues.<\/p>\n<\/li>\n<\/ul>\nIn molten aluminium filtration, engineers must choose between polymer foam (not used in contact with molten metal) and ceramic foam filters. A 20 PPI ceramic filter is commonly used for general casting where a balance of filtration efficiency and permeability is required. For high-integrity aerospace castings, higher PPI ceramics (30\u201360) may be specified.<\/p>\nZirconia Ceramic Foam Filter<\/figcaption><\/figure>\n5. Typical industrial and commercial applications<\/h2>\nA. Foundry and aluminium casting<\/h3>\n Alumina-based ceramic foam filters with 20 PPI are widely used in aluminium casting to reduce oxide inclusions and turbulence-induced defects while balancing melt flow. They are often placed in the gate or runner to smooth flow and trap slag. Choose ceramic CFFs if you will expose the filter to molten metal.<\/p>\n
B. HVAC and air prefiltration<\/h3>\n 20 PPI reticulated foam works well as a reusable prefilter in HVAC units, removing coarse dust and debris without choking the system. Many off-the-shelf replacement foams are sold in 20 PPI for consumer and light-commercial filters.<\/p>\n
C. Aquarium and pond filtration<\/h3>\n Many aquarium filter cartridges and models use 20 PPI rated foam as the coarse layer in multistage cartridges; it captures larger particulates and protects biological media downstream. Manufacturer parts lists commonly denote 20 PPI for coarse replacement pads.<\/p>\n
D. Liquid polishing and industrial process filtration<\/h3>\n 20 PPI foams serve as intake strainers, splash guards and gross-particle arrestors in chemical baths, cooling loop strainers and other industrial liquid systems.<\/p>\n
6. Design and sizing recommendations<\/h2>\n Designing a filtration stage with 20 PPI foam requires attention to face velocity (vf), thickness (t), and available surface area (A). The goal is to keep the pressure drop across the foam within acceptable limits while giving sufficient residence time and surface area for particle capture.<\/p>\n
Quick sizing rules of thumb<\/h3>\n\n\nFace velocity (air):<\/strong> Keep vf for disposable prefilters under 2.5\u20133.0 m\/s for conservative performance; higher vf increases pressure drop and wear.<\/p>\n<\/li>\n\nFace velocity (liquid):<\/strong> Depends on viscosity and particle load; start with 0.1\u20130.5 m\/s for polishing stages and adjust by pilot tests.<\/p>\n<\/li>\n\nThickness:<\/strong> Typical foam thicknesses range from 6 mm to 50 mm. Thicker foam increases dust holding but raises initial pressure drop.<\/p>\n<\/li>\n\nRedundancy:<\/strong> For higher dirt loads, use layers: coarse 20 PPI upstream, then 30\u201360 PPI or depth media downstream. This staging protects finer media and extends maintenance intervals.<\/p>\n<\/li>\n<\/ul>\nExample calculation (air prefilter)<\/h3>\n Given air flow Q = 1,000 m\u00b3\/h and desired face velocity vf = 2 m\/s, required area A = Q \/ vf = (1000\/3600) \/ 2 \u2248 0.139 m\u00b2. Select a panel of standard size with equal or larger free area to maintain the design velocity.<\/p>\n
Always bench-test actual pressure drop vs flow with a production sample before finalizing fan and duct specifications. Manufacturer flow curves and ASTM-based testing are essential.<\/p>\nWorkers are making ceramic foam filter plates<\/figcaption><\/figure>\n7. Installation, handling and maintenance best practices<\/h2>\n\n\nCutting and shaping:<\/strong> Use sharp blades and a straightedge. Bonding to frames is typically done with spray contact adhesives compatible with PU.<\/p>\n<\/li>\n\nOrientation:<\/strong> Install foams so that the primary loading face receives the coarse feed to avoid pushing particulates into downstream stages.<\/p>\n<\/li>\n\nCleaning:<\/strong> For reusable foams, cleaning includes compressed-air back-blow (air systems), washing with low-pressure water or detergent (liquid systems), or gentle brushing. Avoid high-pressure washing that can tear the reticulated skeleton.<\/p>\n<\/li>\n\nReplacement intervals:<\/strong> Dependent on loading; typical service ranges from weeks to months. See the replacement table below for common guidance.<\/p>\n<\/li>\n\nStorage:<\/strong> Keep packaged in dry, ventilated storage away from direct sunlight and ozone sources; store flat to avoid permanent deformation.<\/p>\n<\/li>\n<\/ul>\n8. Testing, quality control and acceptance criteria<\/h2>\n To accept a production batch, request the supplier provide:<\/p>\n
\n\nPPI count verification (visual sampling).<\/p>\n<\/li>\n
\nDensity and tensile\/elongation test reports (ASTM D3574 or equivalent).<\/p>\n<\/li>\n
\nAir or liquid flow vs pressure drop curves at standard thicknesses.<\/p>\n<\/li>\n
\nChemical compatibility worksheet for the expected fluids and cleaning agents.<\/p>\n<\/li>\n
\nCertificate of origin and manufacturing date for traceability.<\/p>\n<\/li>\n<\/ol>\n
Common QC tests include cell-count, volumetric air flow, compression set and tear strength. Representative datasheets for 20 PPI foams list these parameters; request sample test coupons for in-house validation.<\/p>\nAlumina Ceramic Filters for Molten Aluminum Filtration<\/figcaption><\/figure>\n9. Common problems and troubleshooting<\/h2>\n\n\nRapid pressure rise:<\/strong> Usually caused by undersized surface area or unexpected particle loads. Remedy by upsizing area or adding a coarse prefilter.<\/p>\n<\/li>\n\nFoam breakdown (crumbing):<\/strong> May result from chemical incompatibility or excessive temperature exposure. Switch to a more chemical-resistant polymer or change cleaning chemistry.<\/p>\n<\/li>\n\nChanneling or bypass:<\/strong> Poor sealing at frames allows untreated fluid to bypass the foam. Use gasketing or adhesive retention frames.<\/p>\n<\/li>\n\nMelt contamination in casting (ceramic case):<\/strong> If inclusions persist after adding a 20 PPI ceramic, consider a higher PPI ceramic or a two-stage ceramic arrangement (coarse + fine) and re-evaluate melt handling upstream.<\/p>\n<\/li>\n<\/ul>\n10. Environmental, safety and compatibility notes<\/h2>\n\n\nPolyurethane foam<\/strong> is combustible; when used in air systems comply with local fire codes and consider fire-retardant variants where required.<\/p>\n<\/li>\n\nDisposal:<\/strong> Spent polymer foam is usually non-hazardous solid waste but check for adsorbed hazardous constituents (e.g., oils or heavy metals) before disposal.<\/p>\n<\/li>\n\nCeramic foams<\/strong> used for molten metal are brittle; handle with care. Spent ceramic filters may be considered industrial waste and often require separate handling.<\/p>\n<\/li>\n<\/ul>\n11. Product selection checklist (quick procurement form)<\/h2>\n\n
\n
\n\n\nItem to confirm<\/th>\n Requirement \/ note<\/th>\n<\/tr>\n<\/thead>\n \n\nIntended medium<\/td>\n Air, water, oil, molten metal (ceramic)<\/td>\n<\/tr>\n \nExpected particle size distribution<\/td>\n Confirm D50 and largest particles<\/td>\n<\/tr>\n \nFlow rate and face velocity<\/td>\n Provide Q and design vf<\/td>\n<\/tr>\n \nTemperature exposure<\/td>\n Operating and cleaning temperatures<\/td>\n<\/tr>\n \nChemical exposure<\/td>\n List chemicals the foam will contact<\/td>\n<\/tr>\n \nThickness and panel size<\/td>\n Standard sizes or custom cuts<\/td>\n<\/tr>\n \nCertification needed<\/td>\n RoHS, REACH, UL (for flame retardance)<\/td>\n<\/tr>\n \nReplacement cadence<\/td>\n Estimate to size spare inventory<\/td>\n<\/tr>\n \nSupplier QC docs<\/td>\n PPI report, ASTM tests, COA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n12. Tables<\/h2>\nTable A: Quick specification snapshot<\/h3>\n\n
\n
\n\n\nParameter<\/th>\n Typical 20 PPI reticulated PU foam<\/th>\n<\/tr>\n<\/thead>\n \n\nCell count<\/td>\n 20 \u00b15 PPI<\/td>\n<\/tr>\n \nDensity<\/td>\n 1.3\u20131.6 PCF<\/td>\n<\/tr>\n \nThickness options<\/td>\n 6 mm, 12 mm, 25 mm, 50 mm (custom)<\/td>\n<\/tr>\n \nMax continuous temp<\/td>\n ~80\u2013100 \u00b0C (polyurethane)<\/td>\n<\/tr>\n \nCommon color<\/td>\n Charcoal\/black<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\nTable B. PPI vs common application (selection map)<\/h3>\n\n
\n
\n\n\nPPI<\/th>\n Typical use cases<\/th>\n<\/tr>\n<\/thead>\n \n\n5\u201310<\/td>\n Heavy debris straining, coarse liquid intake<\/td>\n<\/tr>\n \n20 (this article)<\/td>\n General prefiltration, HVAC prefilter, aquarium coarse pad, foundry medium-grade ceramic filters (alumina CFF) for castings.<\/td>\n<\/tr>\n \n30\u201360<\/td>\n Fine polishing, biological media support, high-integrity castings (ceramic 30\u201360 PPI).<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\nTable C. Recommended replacement \/ service intervals (typical)<\/h3>\n\n
\n
\n\n\nEnvironment<\/th>\n Condition<\/th>\n Replace \/ clean<\/th>\n<\/tr>\n<\/thead>\n \n\nAquarium, moderate bioload<\/td>\n weekly cleaning; replace every 6\u201312 months<\/td>\n Clean weekly, replace annually<\/td>\n<\/tr>\n \nHVAC prefilter, light dust<\/td>\n monthly visual checks<\/td>\n Replace 3\u20136 months<\/td>\n<\/tr>\n \nIndustrial liquid with heavy solids<\/td>\n weekly or based on \u0394P alarm<\/td>\n Clean weekly; replace when integrity lost<\/td>\n<\/tr>\n \nCasting ceramic filter<\/td>\n single-use (molten metal)<\/td>\n Replace after each pour<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
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