Magazine September 2012

All the latest information from the textile world

Filter media in focus

In its 3/2010 the Online Newsletter already reported on the topics of filter production and filter technology. The great amount of interest shown at the ITMA ASIA in Shanghai has made it clear that felting needles for filter felts are continuing to capture the attention of the worldwide nonwovens industry. With Groz-Beckert you're optimally equipped for present as well as future requirements, as well as growth within a highly promising future market.

How filter media work

Ever more stringent demands made on the purity of air emitted to the environment are necessitating particle filtration systems which allow extremely low limiting values to be adhered to (particle size - PM 2.5 or smaller). Examples of these applications include power plants, cement factories, waste incineration plants, the chemical industry, carbon technology etc.

Selection and characteristics of felting needles

For optimum needling results, precise adjustment of the barb geometry to the fiber is extremely important. The thicker the fiber, the deeper the barb has to be.

Groz-Beckert provides felting needles for the most diverse fiber fineness.

Correct selection of the felting needle plays a decisive role here. Where preventing damage to the fibers is a key issue, the needles chosen should have features such as small barbs and a three-dimensional rounded shape (Groz-Beckert standard). When working with high-strength fibers, felting needles with a reduced number of barbs and a reinforced working part cross-section are used.

Tolerances in the 1/1000th mm range and absolutely even production ensure ultra-precise barb measurements - from one needle delivery to the next. This provides the absolute assurance of process reliability and reproduction accuracy for our customers, and consequently a consistently high standard of filter manufacturing quality.

Felting needles for special applications

As certain fibers such as glass fibers are highly abrasive, in this case the service life of the felting needle is of central importance. Here, needles are used which have been given a special coating such as partial chrome plating or GEBEDUR®.

To increase the tear strength and improve dimensional stability, backing materials known as support fabrics are often worked into the filtration medium (needled from both sides). Barbs with a minimal or even negative kick-up are designed to ensure the most careful possible treatment of the support fabric.

A special working part cross-section is also ideal for taking optimum care of the support fabric. The tear drop-shaped needle has only one edge with barbs and can be placed in a certain location relative to the direction of movement in line with specific type of gentle treatment required

Diversity among filter media

In ultra-fine filters, the finished filtration medium on the intake side is made of ultrafine or microfiber layers with a fineness of < 1 dtex. Here, needles should ideally be selected which have barb sizes of ≤ 0.04 mm.

Because of the high degree of chemical resistance and mechanical strength required, a large number of in some cases highly costly technical fibers are used to manufacture needled filter media, such as aramid, glass fiber, P 84, etc.

Different treatment finishes used for filter media

In order to guarantee that particle deposits are formed on the surface of the filter, which exert a positive effect on the actual filtration (e. g. surface filtration), after needling usually a "smoothing" process is carried out by means of calendering, the application of an ultra-fine fiber layer, or by coating with a material such as PTFE.

The unfiltered advantages

The benefits of needled felts:

  1. Cost-efficient manufacture
  2. High fiber retention rates
  3. Suitable for deformable and non-deformable gel-like particles
  4. Defined determination of pore sizes through targeted selection of needle fineness and barb size
  5. High elasticity compared to other textile constructs
  6. High flexibility in respect of width, thickness, volume, etc.
  7. High air permeability, large fiber surface
  8. Can be combined with other textile or non-textile surfaces

Groz-Beckert as your partner

The availability of a wide choice of suitable needles which vary in terms of their barb size, barb shape, working part fineness and working part cross-section allows Groz-Beckert to offer the ideal felting needle for all needled filter media. Improved wear properties due to special coatings ensure a consistent needling result during the manufacturing process. This helps our customers to manufacture with the utmost reproduction accuracy and process reliability and so assume and maintain a leading position in the marketplace.