Metallic Membrane Filters Making More of Filter Efficiency

Author / Editor: Dirk Stoecker; Lalit Vashishta / Dominik Stephan

Sintered metal filter elements have been successfully used in different applications for years. Asymmetric metallic membrane elements have various advantages over standard sintered metal filter cartridges. Here’s an overview of how the overall performance of these filters has been improved.

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Typical installation of metallic membrane filter: Sinter connected design between solid and porous body
Typical installation of metallic membrane filter: Sinter connected design between solid and porous body
(Picture: Diva Envitec)

Structures formed by sintering of metal powders into a ‘solid’ component always contain some porosity. These interconnected pores are the most useful in the field of ‘porous metals’. Metal powders for manufacturing of porous parts are selected according to their application. The most commonly used powders are bronze, stainless steel, nickel-based super alloys and titanium.

These porous sintered elements have a stable shape even at high pressures, good mechanical strength under permanent loads, impact loading or under pressure peaks. Another attribute is high temperature strength, i.e., some metals can operate up to 1,000°C, and demonstrate thermal shock resistance. It is also chemically stable against acids and (alkaline) detergents.

Generally, metallic filter materials are weldable and easy to machine. However, welding on porous media should be avoided to reduce corrosion risk and thermal stress. Additional aspects in favor of highly porous powder metal products are emphasized by increasingly more restrictive environmental legislation requesting recycling or cleansing instead of producing waste. These advantages are of growing importance for selecting competitive technical products.

The Limits Of a Filtration Technologies

Like all other technologies and products, sinter metal filters also have their limits. Therefore the research is ongoing to eliminate these weak points. This has led to the development of the ‘seamless metallic membrane’, which has no welding seams on porous media. It is a surface filter that has improved the back pulsing performance.

Furthermore, it has improved permeability in comparison to standard sintered metals filter media and has a defined particle retention in the lower micron range. Its applications can also be extended to the areas of micro filtration using the powder metallurgy approach.

Asymmetric Designed Sintered Filter Elements

Because of their unique properties, metal filter composite structures are extensively applied in a multitude of different applications. Besides the well-known advantages of stainless steel filter cartridges, the wall thickness of 2-3 mm – necessary for the self-supporting system – causes a high pressure drop. The wall thickness has to provide sufficient mechanical strength but is not absolutely necessary for particle retention. The separation of particles takes place on the surface of the filter material and in the first tenths of a millimeter of the wall thickness. The other requirements from a filter element are high flow rate and good back flushing performance.

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