Sintered fiber filter
Sintered fiber filters are provided that can afford high particle capture efficiency and/or low pressure drop during operation, and are useful in applications such as semiconductor processing. The shape of at least a portion of the individual fibers (e.g., metal fibers) used to make the filter have a three-dimensional aspect, which allows for a low packing density and high porosity filtration media. Certain filters have a cylindrical or tube-like shape with tapered ends of higher density. Methods of making such filters, for example, using axial pressing, are also described.
1. A method of making a sintered fiber filter element, the method comprising:
(a) providing a mold having a cylindrical cavity with an end closure at one end of the cylindrical cavity, and a fill cap at another end of the cylindrical cavity, wherein the fill cap is removable to provide an open end, and a core rod movably sealed in said end closure and extending coaxially within said cavity;
(b) orienting said mold vertically with said open end disposed upwardly;
(c) introducing fiber and liquid into said cavity through said open end substantially radially evenly about said core rod;
(d) creating a pressure differential in the mold to expel liquid from the mold;
(e) applying pressure to said mold and thereby to said fiber in said cavity, whereby said fiber coheres to form a substantially tube-shaped structure;
(f) removing said substantially tube-shaped structure from said mold;
(g) sintering said substantially tube-shaped structure to obtain a porous tube-shaped sintered filter element having a first end and a second end; and
(h) densifying the ends of said porous tube-shaped sintered filter element.
2. The method of claim 1 , wherein densifying the ends of said porous tube-shaped sintered filter element includes rotating said porous tube-shaped sintered filter element while applying a roller burnisher tool to the ends of said porous tube-shaped sintered filter element.
3. The method of claim 1 , wherein densifying the ends of said porous tube-shaped sintered filter element includes rotating said porous tube-shaped sintered filter element while applying a tool to at least one end of said porous tube-shaped sintered filter element, and wherein the tool is designed to provide a gradual transition from a center portion of the filter element to an end of the porous tube-shaped sintered filter element.
4. The method of claim 1 , wherein the fiber includes metal fiber.
5. The method of claim 4 , wherein the metal includes stainless steel.
6. The method of claim 1 , wherein the liquid includes water.
7. The method of claim 1 , wherein the end closure is removable.
8. The method of claim 1 , further comprising attaching a vacuum line to the mold, and opening the vacuum line while introducing fiber and liquid to the cavity.
9. The method of claim 1 , further comprising drying said tube-shaped structure before sintering said tube-shaped structure.
10. The method of claim 1 , further comprising welding an end of said porous tube-shaped sintered filter element to an end cap.
11. The method of claim 1 , further comprising welding an end of said porous tube-shaped sintered filter element to a filter end fitting or housing.
12. The method of claim 1 , further comprising applying pressure to the porous tube-shaped sintered filter element to control the density, shape, or length of the structure.
13. The method of claim 1 , further comprising vibrating the mold.
14. The method of claim 1 , wherein creating a pressure differential in the mold to expel liquid from the mold comprises applying a vacuum to the mold.
15. The method of claim 1 , wherein creating a pressure differential in the mold to expel liquid from the mold comprises supplying pressurized gas to the open end of the cavity.