Car manufacturers find the solution to adding more components into smaller spaces: nonwovens

28.06.2016
© A. Wilson
© Mann+Hummel

Automotive engine technology already includes many highly sensitive sensor technologies and as a result, the installation space for other components under the bonnet has been shrinking.

But at the same time, the demands on filter media for both performance and longer intervals between changes are increasing.

Nonwoven solutions to these complex issues are being provided by two key practices which have been developed over many years – the incorporation of nanofibre layers or coatings and the art of advanced pleating.

The Euro VI Standard for exhaust emissions which was introduced in the European Union at the beginning of 2014 means that a supply of clean air is now more important than ever for commercial vehicles and trucks – especially in industrial settings.

The Standard requires truck builders to cut the NOx (mono-nitrogen oxides) emissions of their vehicles by 77%, as well as particulate matter emissions by 66%. This is something of a tall order – especially on construction or mining sites where dusty or sooty air is a fact of life and trucks are used under very extreme conditions. Air filters are already essential in protecting the engines and their components from wear and malfunctions.

To comply with emissions levels, the truck manufacturers are increasingly installing more air flow meters in the vehicles, but these sensors only work properly when the engine intake air is free of pollutants. In order to protect them, highly-efficient protection against contamination by particle loading is essential. This is leading to the need for filter media separation efficiency of more than 99.95%.

“The air intake filter for an engine is complex,” explains Ivanka Poljak of leading heavy duty automotive filter specialist Mann+Hummel, based in Ludwigsberg, Germany. “First of all it removes particles from the ambient air to reduce engine wear – especially from cylinder heads, pistons and piston rings. It also protects sensitive measurement equipment such as air flow meters. The performance of an engine air filter is down to its ability to capture particles, which is directly related to the service life of the filter element, and by the filtration efficiency, which indicates the degree of particle separation of the ambient air.”

Filter suppliers are responding to the tighter regulations with highly efficient nanofibre coatings on their filter media.

These can be up to 300 times finer than the fibres employed in the nonwoven material and as a result, the surface on which dust particles can be deposited is much larger, making the filter much more efficient.


Technology

The technology for producing such nanofibre webs has improved significantly over the past few years as will be demonstrated by a number of exhibitors at the forthcoming INDEX™17 – the leading nonwovens show which takes place in Geneva, Switzerland, from April 4th-7th next year.

Nanofibre nonwoven-structured layers are ideal for creating composite materials with regular nonwovens and the most developed application for such materials is in air filtration.

While electrospinning was the first method for the production of such very fine submicron fibres to reach industrial production scale, it can have limitations. These are chiefly connected to the use of dangerous solvents, but also to relatively low productivity, which has motivated the development of alternatives in recent years.

The electrospinning process generally involves the formation of the nanofibres from a liquid polymer jet in a longitudinal electric field. The dominant mechanism is whipping elongation, occurring due to bending instability. Secondary splitting of the liquid polymer streams can also occur, but the final thinning process is elongation.

Some efforts to scale up the electrospinning technology have been based on a multiplication of the jets using multi-nozzle constructions, but in practice, the number of jets required to reach an economically acceptable rate of productivity is extremely high. This brings into play many challenges in respect of reliability, quality consistency and machine maintenance – especially cleaning.

Most of these problems have been solved with the advent of so-called ‘nozzle-less’ electrospinning, largely due to its mechanical simplicity. This process, however, is also more complex as a result of its spontaneous multi-jet nature.

In this system, a self-organisation of the jets occurs, and consequently the number and spacing of the jets is optimised, even if the technology variables – voltage, viscosity and surface tension of the solution – change. This leads to a significant improvement in process stability and a consistent quality of the nanofibre layers produced.

In its simplest realisation, a nozzle-less electrospinning head consists of a rotating drum dipped into a bath of liquid polymer. The thin layer of polymer is carried on the drum surface and exposed to a high voltage electric field. If the voltage exceeds the critical value, a number of electrospinning jets are generated. One of the main advantages of nozzle-less electrospinning is that the number and location of the jets is set up naturally in their optimal positions.

Several types of rotating electrodes for free liquid surface electrospinning for industrial machines have now been developed, but the drum type is still one of the most productive.

Significant improvements in nozzle-less technology have been made on the commercially-available systems which use stationary string electrodes supplied with polymer solution by a proprietary moving ‘painting’ head. This results in a notable decrease of solvent evaporation during the process, which has to be removed from the exhaust air released from the machine. The polymer solution concentration is also stable, enabling the system to typically run for more than 24 hours.


Pleating

A second important contributor to the efficiency of filter media is in pleating, which effectively provides the largest possible filtration surface in the smallest space.

Nonwoven filtration specialist Sandler, however, says that synthetic filter media developed to compete with glass fibre-based products can often lack the contour precision and pleat stability required to ensure long-term performance.

The company’s answer is its Sawscreen Pleat, which consists of two fine fibre meltblown nonwoven layers which are combined without the need for chemical binders and in which the fibres are highly aligned lengthwise. The result is a product that can easily withstand the high mechanical pressure applied in the pleating process and guarantee accurately shaped and extremely stable pleats which provide the widest surface area possible throughout the filter’s lifetime.

Sandler is one of many filter media specialists who will be exhibiting their advanced products at INDEX™17.

 

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