Knitted wire construction permits production of filters in almost any material, density, thickness, or configuration

Air-bag slag filter for particle entrapment and heat transfer

NOTE: Density refers to the degree of compression given to the knitted mesh in the design and manufacture of a filter. It can also be described as the proportion of the amount of wire relative to the total volume of the unit after compression (usually expressed as a percentage of the volume of the unit). For example, a solid stainless steel wire filter with 50% of its area consisting of voids and interstices would create a unit of 50% density.

Filtering liquids or air in hostile environments—such as those subject to temperature extremes, high orders of shock/vibration, and caustic fuels or fumes—has posed problems for paper filter elements. These types of elements simply will not withstand these types of operating conditions.

Since paper filters are typically composed of organic materials, they are also subject to attack by the caustic byproducts of many industrial processes— such as those involving combustion. For example, corrosion often takes place when high-temperature lubricating oils are loaded with such acids. After extended use, the surface area of the paper filter becomes heavily loaded, resulting in filter weak spots. (If the pressure relief valve is not set low enough, and the pressure is allowed to remain at normal operating pressure [500 to 700 kPa], paper filter elements may tear, fracture, or even burst.)

Sintered metal filters—due to their granular construction—are also prone to fracture or disintegration when subjected to the stresses of high temperature and shock. Unless the fusion process involved in their construction is 100% complete, small particles may begin to break away. As a result, when installed on either rotating or reciprocating machinery, little particles of filter material very frequently detach and migrate to block the very devices the filter was designed to protect.

Metex knitted wire mesh liquid and air filters overcome the limitations and deficiencies of these and many other filtration methods. Where resistance to degradation, corrosion, mechanical, or thermal shock is desired—and where a resilient product is needed for proper cavity fit—Metex filters provide an economical, robust alternative. From cryogenic operating conditions up to temperatures of 650° C, knitted wire mesh filters maintain their integrity even when subjected to extremely high vibration and exposed to destructive gases such H₂, SO₄, and HNO₃.

Metex Knitted Mesh—A Superior Alternative to Paper or Sintered Metal

Knitted mesh consists of wires of various metals or strands of other materials that have been knitted into a mesh structure—creating a matrix of interlocking loops that can move freely in the same plane without distorting the mesh. (Each loop is actually free to move in three directions, and the finished metal knit permits two-way stretch.)

In addition, each loop acts as a small spring when subjected to compressive stress. Thus, filters of compressed knitted metal mesh yield when subject to the stresses of shock and vibration—yet, depending on the construction, can immediately recover to 90% of their original size when the force is removed.

Use of knitted mesh produces a “depth” or “three-dimensional” filter that provides an ideal tortuous-path-entrainment filtration effect. This is achieved by carefully balancing such variables as:

• Wire diameter
• Density and thickness of the pressed unit
• Configuration

Since there are literally thousands of voids resulting from the interstices of the overlapping wires, good filter efficiency accompanied by minimal pressure drop is maintained, despite knitted mesh’s high dirt-retention factor. And, since Metex knitted mesh filters are made from continuous lengths of wire interlocked with each other, particles can not break off to cause equipment damage or failure.

Knitted mesh filters are resilient enough to fit (or retrofit) into filter cavities of virtually any configuration and still retain a secure friction fit.

Metex knitted wire mesh may be used for liquid filtration and/or separation in the following industries:

Metex knitted wire mesh filters are used in the following applications:

Metex filtration-development engineers can help you determine the proper combination of wire diameter, compression density—which directly affect particle retention and dirt-holding capacity—and filter thickness that satisfy the requirements of each filter’s intended application.

The tables below list the particle-retention and dirt-holding capacities of typical units. (It should be noted that dirt-holding capacity is an important consideration only in applications where the filter will not be cleaned regularly.)

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