Filtration

Filtration refers to the separation of solid particles from liquids or gases using a permeable medium (filter). It is a fundamental process across many industries—from water treatment and chemical processing to pharmaceuticals and the food industry. Technical fabrics, especially wire and fiber meshes, often serve as the filtering medium in such processes. 

There are two main types of filtration: surface filtration and depth filtration. 

• Surface filtration: In surface filtration, as typically achieved by wire mesh, particles larger than the pores/openings are trapped on the filter’s surface, forming a so-called filter cake. Over time, this cake can even improve filtration efficiency by trapping finer particles, but it also increases flow resistance. Therefore, the cake must be periodically removed (by backflushing, scraping, etc.). 

• Depth filtration: In depth filtration (e.g., using nonwoven fabrics or sintered materials), particles penetrate into the porous medium and are retained inside. This allows for high particle-holding capacity, but eventually the medium becomes “saturated” and must be replaced or regenerated. 

Wire mesh typically functions as a surface filter with a defined mesh size that limits particle size. If particles smaller than the mesh opening need to be captured, a filter cake is deliberately allowed to form, which then acts as the filtering layer. Very fine filter fabrics (e.g., twill weave) can also directly capture particles in the low micrometer range. 

In practice, filtration systems are often designed as cartridges, bags, frames, etc., in which the fabrics are mounted. Examples include: 

• Filter presses: Filter cloths made from fabric are clamped into plates. 

• Cartridge filters: Long cylindrical screens (made from wire mesh or sintered metal) where filtration occurs from outside to inside. 

• Drum filters: Rotating cylinders covered with fabric that dip into a suspension; the cake builds up on the outside and is scraped off on the inside. 

• Bag filters: Sack-shaped filters made from textile fabric, where liquid seeps from inside to outside, leaving particles inside. 

Key filtration parameters include filter fineness (the smallest particle size retained, often given as nominal or absolute microns), flow rate (volume per time), and pressure drop (how much the flow is slowed). An optimized filter fabric has a high pore count for good flow but reliably retains the desired particles. 

GKD, as a fabric specialist, supplies filter media for filtration applications—such as multifilament fabrics, hybrid fabrics, or sintered laminates—to achieve specific properties. For example, sintering multiple layers of wire mesh can create depth filters that are robust and backwashable, which is a major advantage over disposable filter felts. 

Overall, filtration with fabrics is a clean, mechanical separation technique that requires relatively low energy (compared to processes like evaporation) and effectively removes particles. However, it has limits regarding fineness—ultrafine separations below 1 µm typically require membranes. Still, in the range of roughly 5 µm to several millimeters, fabric filters are often the best choice due to their reusability and high throughput.