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Filter Foam (continued)
Filter foam is the ideal material for applications where porosity, surface area and low-density are integral for success. In addition to fabricating filter foam products to custom designed specifications, New England Foam stocks filter foam in bun, roll and sheet forms, in porosities ranging from 10 PPI or pores per inch (coarse) to 100 PPI (fine) and those colors most requested: charcoal (black) & white. Additional porosities and colors are available upon request, as well as Underwriters Labratory (UL) compliant filter foam.
Filter Foam's Cell Structure
Filter foam operates as a depth-loading filter, as opposed to a surface-loading filter, essentially trapping dust particles within its cells. The cell structure of filter foam is remarkable in that each cell has a dodecahedron shape (12 sided), the cell’s walls or “struts” are comprised entirely of organic polymers (polyurethane, polyether, polyester) and the empty space or “windows,” between each strut, comprise 95% - 98% of the filter foam’s mass. The size, shape and distribution of cells within filter foam can be manipulated during manufacture to provide precisely the desired porosity level, measured in PPI or pores per inch.
Polyester Filter Foam vs. Polyether Filter Foam
In applications where the filter foam will come into contact with a liquid-based solution, the filter foam should be manufactured with polyether-based polyols. In applications where the filter foam will come into contact with gases, such as oxygen, nitrogen and/or carbon dioxide, the filter foam should be manufactured with polyester-based polyols.
Manufacturing Filter Foam
Filter foam can be manufactured using a thermal process where a preformed block of conventional polyurethane foam undergoes the removal of space from between each cell wall or “strut.” Penetrating the internal structure of the filter foam with a combustible gas, such as hydrogen, and then igniting the gas in a controlled explosion accomplishes the removal of the thin layer of foam between each cell's membrane. The result is freshly manufactured filter foam that is perfectly porous and ready for further fabrication. It is during this manufacturing process that flame retardant additives can be introduced to the filter foam to meet various fire code standards.
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