Perfect Seals and Bonds

Sonderhoff Oliver Voelker

By Adrian Wilson, European Correspondent

Sonderhoff is the specialist in ensuring that filter housings are perfectly aligned with their housings, for maximum results.

Whether in vacuum cleaners, cars or the air conditioning systems of industrial plants, the principle behind every air filter is basically the same – contaminated air is taken in at one side and the clean, filtered air flows out of the other.

To ensure this process is maximized, however, filters must be well bonded and ensure a perfect seal. To ensure this, Cologne, Germany-based Sonderhoff provides mixing and dosing machines, as well as material systems for sealing and bonding of filters in different applications.

At the recent Filtech 2016 exhibition in Cologne, the Sonderhoff group of companies showcased its expertise and products in the field of filter applications.

Sonderhoff Chemicals delivers a wide range of two-component foam gaskets, adhesives and potting compounds, to leading manufacturers of filter systems, covering the application areas from vacuum cleaner filters to air filters for clean room quality.

For this broad spectrum of filters, the dispensing machines of Sonderhoff Engineering are employed for the automatic application of foam sealing or adhesive potting systems. So called ‘formed in-place’ (foam) gasket dosing technology is well established in the filter industry. The two-component reaction materials on the filter parts cure at room temperature and can be further processed quickly.

During Filtech 2016, Sonderhoff demonstrated how accurately the mixing head of its Smart-M dispensing cell moves along the contour of the filter frame, while dosing a special gel-like potting compound from the Fermadur product family precisely into the frame groove. The quality requirements are very high for the potting gel used for sealing filter frames in air conditioning systems of hospitals and for chip manufacturing in clean rooms.

“The filter frame built into an air conditioning installation is mounted on a frame counterpart with a circumferential edge,” explained Sonderhoff Technical Director Oliver Völker (pictured) at the exhibition. “The frame edge exploits the tongue and groove principle to then hermetically seal the potting gel in the filter seat, so that all the air goes through the filter and air pollution cannot pass the filter.”


Not only is the proper selection of raw materials decisive for a consistently high quality in sealing, gluing and potting of filters, but also the safety and accuracy of the production plant, which has to ensure a precise application process of the material to the parts. This is where the low-pressure mixing and dosing systems from Sonderhoff Engineering excel.

The design of the Smart-M dispensing cell is modular and can be adapted to different production concepts. Subsequent modifications can easily be realized with little planning. Due to the small outside dimensions of 1,200 x 1,700 x 2,400mm (width x depth x height) the cell has a minimal footprint. The three-axis linear robot scans parts with a traversing range of up to 500 x 600 mm (width x depth) and up to a part height of 250mm. In doing so, the mixing head of the dispensing cell is positioned with a repeat accuracy of +/- 0.05mm above the part. As a result, the sealing material can be applied through the mixing head dosing nozzle directly onto the part precisely to its contour or in a groove by. A maximum acceleration of 5 m/s² in the part radii is possible with the Sonderhoff linear robot.

At the Sonderhoff booth in Cologne the feeding of parts to the dispensing cell was demonstrated with a rotary indexing table with a 180° partitioning for an insertion and a work position turning within 1.5 seconds. For this semi-automatic part feeding, the access of the insertion area at the cell is secured by a light grid. Alternatively, the parts are fed manually through the cell front, by a worktop or fully automatic via a transfer belt running through the cell.

Low-Emission foam gaskets

Fermapor K31 polyurethane foam seal systems from Sonderhoff are used for the sealing of air filters in cars, to ensure a leak-free seat of the filter on the air intake passage. No unfiltered air can flow past the filter into the car interior. In order to significantly reduce the load on the air with VOCs (volatile organic compounds) in the passenger compartment, Fermapor low-emission polyurethane foam seal systems are used for the tight sealing of filter housings in the car. They comply with the strict limit requirements of nearly all vehicle manufacturers. Sonderhoff, for instance, fulfills the Daimler specification DBL 5452-13, which specifies emissions a target value of 100 micrograms for VOC and 250 micrograms for the fogging behavior per gram of polyurethane. Too many VOCs in the air often result in fogging. Soot, dust and/or aerosol particles in the air thereby move from warm to colder zones where they are deposited. This can lead to condensation on the windshield or inside car headlights.

Another product characteristic of Fermapor 31 polyurethane-based sealing systems is the antimicrobial sealing that prevents microorganisms and molds contaminating the sealings of air filters used for air conditioning systems.

Antimicrobial foam gaskets

The Institute for Air Hygiene (ILH Berlin) has tested Fermapor K31-A-9020-17F and K31-A-9308-5-VP5-F foam seals, as well as the potting product, Fermadur-A-196- 4F, with regard to their resistance to fungi and bacteria according to DIN EN ISO 846 (the evaluation of the action of microorganisms on plastics). They are developed by Sonderhoff specifically for the sealing or potting of filters used in air conditioning systems. The test results show that the sealing and potting material does not serve as a nutrient source for microorganisms. Special additives in the material formulation of Fermapor K31 antimicrobial foam seals effectively protect the sealings of climate-technical components for air distribution, such as ventilation grilles, air filter, nebulizer and access locks, against attack by harmful microorganisms.

Heating, ventilation and air conditioning (HVAC) manufacturers demand special requirements for their sealings in order to meet the hygiene requirements for HVAC systems according to VDI 6022 – and especially for the sealing and bonding of air filters. In particular, the air filters of these plants, which improve the climatic conditions of interiors, are often the cause of contamination of indoor air. The accumulation of microorganisms on air filters is often the cause of potent allergy risks when such contaminated air is inhaled by humans and animals. Especially at increasing temperatures, the concentration of microorganisms significantly increases and the fungal spores develop a higher vitality. Such conditions are a fertile breeding ground for germs which can cause infections in humans.

Air conditioning systems need to be serviced regularly in order to work properly and ensure a good indoor climate. Here, among other things, the leakage-free seat of air filters is checked which is provided by perfect foam sealings and in optimal cases with an antimicrobial protection.