Metallic filter media
Metallic filter media
Metallic media offers obvious advantages in terms of mechanical strength, temperature resistance, wet strength and chemical resistance. In addition, metallic media means that the facility could be cleaned by a percussive shockwave or reverse flow of gas through them which, to some degree, would dislodge the previously collected solids. The finer the thickness of the filter medium section, the more likely the filter medium is to give up its solids. The greater the thickness, then the more likely it is that the medium will retain its solids within the depth of the medium, leading to permanent blinding.
Three main types of industrially common metal media are typically used – sintered metal powder, sintered metal fibre and sintered woven wire mesh. In addition to these, composite structures of mesh/fibre and powder/mesh are also available. Sintered woven mesh is generally considered to be suitable for filtration applications of less than 10 microns and not generally suitable for HEPA protection.
Sintered metal powder filters are manufactured from sieved metal powder. The particles can be irregular or spherical in nature and typically in the size range 1–100 microns. The powder is laid out as a flat sheet or loaded in a mould and pressed prior to sintering. The resultant porous media has a 30–50% porosity and is very mechanically robust.
The low porosity results in low permeability and the manufacturing methodology limits geometry to largely plain cylindrical filters, in-turn resulting in large footprints when compared to existing fibrous technology. Development has seen the use of a fine membrane surface layer on a course structure enabling increased efficiency and improved permeability characteristics.
Sintered metal fibre media is a randomly laid (nonwoven) matrix of sintered metal fibres as shown in Figure 2.
Sintered metal fibre media possess many of the positive attributes of the traditional microglass fibre media including randomly laid nonwoven fine fibres, which enable high efficiency filtration at the fine submicronic particle range. Coupled with high porosity and thus high permeability, and its ability to be pleated, this makes it possible to reduce the size of the whole system compared with alternative materials.
Attributes including its robust thermal stability, chemical and radiation resistance, suitability for use at high temperatures, high mechanical strength, low pressure loss and ability to be pleated, make it possible to use the media in special process HEPA applications, as well as providing HEPA protection.