Filter nonwoven refers to a porous flat filter medium used to separate particles from gases or liquids. Filter nonwovens consist of randomly oriented or deliberately oriented fibres that are bonded mechanically, thermally or chemically. Filtration takes place via the fibre structure of the nonwoven and not through defined hole structures.
Filter nonwovens are used in industry for air filtration, liquid filtration, dust separation, process filtration and to protect machines, equipment and products. Typical fields of application include the automotive industry, mechanical engineering, ventilation and air conditioning technology, electrical engineering and process engineering.
Technical properties and fundamentals
Structure of filter nonwoven
A filter nonwoven consists of a large number of fine fibres that form a three-dimensional pore network.
The fibres can be:
- continuous or cut
- randomly or layer-wise oriented
- mechanically needle-punched
- thermally consolidated
- chemically bonded
The structure determines permeability, separation efficiency, pressure drop and service life.
Functional principle of filtration
The filtration effect of a filter nonwoven is based on several physical mechanisms:
- Sieving effect for coarse particles
- Inertial separation at higher flow velocities
- Diffusion separation for very fine particles
- Adhesion on fibre surfaces
In practice, these mechanisms act simultaneously. Filter nonwovens are therefore depth filters and not pure surface filters.
Porosity and air permeability
Porosity describes the proportion of voids in the filter nonwoven. High porosity enables low pressure drops but reduces separation efficiency. Low porosity increases separation efficiency but leads to higher flow resistance.
The design is always a compromise between filter performance and energy demand.
Materials for filter nonwoven
Synthetic fibres
Synthetic filter nonwovens frequently consist of polymer fibres.
Typical properties:
- Good chemical resistance
- Low moisture absorption
- Definable fibre geometry
- Good reproducibility
The exact suitability depends on the specific polymer.
Glass fibre nonwoven
Glass fibre nonwoven is used where high temperature resistance or fine separation grades are required.
Typical properties:
- High temperature resistance
- Very fine fibre structures possible
- High separation efficiency
- Mechanically sensitive
Glass fibre nonwoven is frequently used in high-performance and fine-dust filters.
Natural fibre nonwoven
Natural fibres are used in special applications.
Typical properties:
- Limited temperature and media resistance
- Biological degradability possible
- Variable material properties
Industrial use is strongly application-dependent.
Filter classes and performance characteristics
Separation efficiency
Separation efficiency describes the percentage of retained particles. It depends on:
- Particle size
- Flow velocity
- Nonwoven structure
Filter nonwovens are designed for specific particle sizes depending on the application.
Pressure drop
Pressure drop is the resistance that the filter nonwoven exerts on the flowing medium. A high pressure drop increases the energy demand of the system.
The pressure drop rises with increasing loading of the filter nonwoven.
Dust holding capacity
Dust holding capacity describes how much particle mass a filter nonwoven can absorb before the pressure drop rises to impermissible levels.
Filter nonwovens with a depth structure have a higher dust holding capacity than pure surface filters.
Applications and fields of use
Filter nonwovens are used in numerous industrial applications:
- Air and indoor air filtration
- Industrial extraction systems
- Ventilation and air conditioning systems
- Cabin air filters
- Liquid filtration
- Process air purification
In electrical engineering, filter nonwovens frequently serve to protect sensitive components from dust and particles.
Design considerations for filter nonwoven
Flow guidance
Uniform incoming flow is decisive for filter performance. Uneven flow leads to local overload and shortened service life.
Mechanical fixation
Filter nonwovens must be mechanically fixed without damaging the fibre structure. Pleating, clamping or frame constructions are common.
Maintenance and replacement
Filter nonwovens are wear parts. Service life depends on particle load, medium and operating conditions. Regular monitoring of the pressure drop is required.
Distinction from other filter media
Filter nonwovens differ from woven fabrics, screens and membranes through their depth filtration. Membrane filters have defined pore sizes, whereas filter nonwovens exhibit a statistical pore system.
The choice of filter medium depends on particle size, medium and operating conditions.
Limits of filter nonwoven
Filter nonwovens are subject to physical and material limits:
- Limited temperature resistance
- Mechanical sensitivity at high pressures
- Dependency on the medium
- Ageing and contamination
Not every filter nonwoven is suitable for continuous operation or aggressive media.
GOBA Takeaway
Filter nonwoven is a versatile and technically established filter medium for gas and liquid filtration. The filtration effect arises from the depth structure of the nonwoven and the combination of several separation mechanisms.
Selecting a suitable filter nonwoven requires an exact analysis of particle size, medium, flow conditions and service life requirements. A blanket assessment is not possible. Function, energy efficiency and maintenance effort must be considered together.