Foam sealing with FIPFG processes

The industry standard for many sectors

From natural to synthetic sealing


Sonderhoff Serienfertigung Mischkopf

Mankind has been capable of sealing of joints and gaps for many centuries, e.g. when caulking ships’ planks. Beeswax, tree resin or tar was used.

The story of modern sealants starts with polymer chemistry in the 1930s and the development of synthetic plastics and sealants. And the history is still being written. Today a multitude of different materials and technologies is available for sealing components.

For modern industrial production, another crucial requirement has been set: the sealing process must ideally be fully automated. This automated sealing process for foam sealing is generally known as FIPFG sealing technology (Formed-in-Place Foam Gasket).

The chemistry makes it possible

Polymerising substances


The reaction substances in Sonderhoff products consist of a fluid to paste-like A-component (polyol) with varying molecular chain lengths for soft and hard foams and a hardener, the B-component (MDI). Sonderhoff polyurethane material systems are grouped under the brand name of FERMAPOR®. Silicone-based products bear the name of FERMASIL®.

A polymer is a material whose molecules are made up of chains of monomer units. The longer the molecule chains of the polyol (A-component), the more flexible the soft foam. Through a chemical reaction with water and the hardener (B-component) a cross-linked structure of molecule chains is formed. During this process, carbon dioxide is produced as a cleavage product, which is responsible in the low-pressure process for the foaming of the material. A soft foam seal is formed which cures at room temperature, without the use of a tempering furnace.


2-Component material systems

The A-component (polyol) determines the chemical and physical properties of the sealing foam. The B-component (isocyanate) initiates the chemical reaction and influences above all the reaction speed. That is why we speak of “2K” or 2-component material systems. The mixing ratio of A and B-components plays a vital role here.

Approximately 90% of Sonderhoff’s foam sealing systems are 2K PU material systems, which are developed with the use of polyurethane polyols. This substance is particularly versatile in its uses.

According to the choice of polyol and isocyanate, polyurethanes can have the widest variety of attributes. Depending on chain length and branching in the polyol, the mechanical properties can be positively influenced.

Silicone is used primarily if a high resistance to chemicals, solvents, very high temperatures and atmospheric influences is required.

Polyurethanschaum chemische Formel Aufschäumen PU PUR


Pot life and expansion time


Pot life

The duration of workability in a reactive substance is known as its pot life. In foam sealing it is the time spent mixing A with B-components in the mixing chamber before dispensing on to the part. Figuratively speaking it is the period in which the substances can still be taken out of the “pot” and processed. Usually the end of the pot life is signalled by a marked increase in viscosity, preventing further processing. The length of the pot life depends on the chemical properties of the components used and on the environmental conditions.

Thus giving the pot life of a substance only makes useful sense if the quantity, amount of mixing, surrounding climate (temperature and humidity) and vessel shape are also given.


Expansion time

The expansion time in the FIPFG process is the period after the pot life, in which the homogeneously mixed sealant mass of the particular material system used foams up into a seal.

With the chemical reaction between isocyanate and water in the polyol component, the propellant CO2, essential for foam production, is created as a cleavage product. Through the rise in temperature engendered by the (exothermic) reaction, the CO2 gas foams up the sealant mass.

At the end of the expansion time the propellant has done its job and can escape through the mixed-cell structure of the polyurethane foam.



The saving potential of foamed seals


With the FIPFG (Formed-In-Place Foam Gasket) process, much money can be saved in comparison with the manual insertion of pre-prepared seals. Especially where high production quantities are required and the parts can be provided with a traditional rubber seal only relatively labour-intensively (like EPDM or NBR), the direct foaming of a seal – the automated FIPFG process – offers clear advantages.

With the following example calculation the cost effect can be made clear in principle. Even if it represents a simplified overview, as a first estimate it can also be adapted to other applications.

In the following example an electronics box should be considered, production quantity 2,000,000 items per year, with a sealant length of 30 cm and a sealant thickness of 4 mm.

Calculation of the costs of a traditional manual sealing process

The essential costs are material and labour.

The material costs are calculated from the necessary sealing cord quantity (2,000,000 parts x 30 cm) and the material price (EPDM cord on roll 1,000 m for 300 €). Reckoned per unit, the material costs then runs to 0.09 € for each traditional seal.

The work time per sealing cord is often not exactly known. It is estimated from the number and hours of the necessary employees. In this example, 3 workers work in each of 2 shifts, 8 hours a day, 250 working days a year, to produce 2,000,000 parts – and even then have only 21 seconds’ time to mount a seal. The hourly wage is 20 €. From this arise labour costs of 240,000 € per year, or 0.12 € per part.

Through addition of the material and labour costs we arrive at a total price for manually inserted seals of 0.21 € per seal or 420,000 € per year.

Calculation of the costs by automated FIPFG process


To arrive at the labour costs we have to work out the cycle time for the foaming of a part. The cycle time can be roughly approximated from the estimated robot speed. The maximum robot speed is 58 m/min. As this value, however, is never achieved during application and as certain waiting and rinsing times have to be factored in, we can realistically expect that a part needs on average approx. 7 s to be sealed.

2 shifts x 250 days x 8 h x 3,600 s/h ÷ 7 s/part = approx. 2,000,000 parts

The machine is loaded and unloaded by a single employee per shift. This means labour costs of 0.04 € per part. For additionally incurred costs for energy, water, maintenance, waste disposal and material losses an extra cost of 10% is factored in, i.e. 0.01 €/part.

The sum of the individual seal costs comes to a total per seal of 0.11 €. This means for 2 million parts a year costs of 220,000 €.

Cost comparison EPDM v. FIPFG
Cost per seal Cost p.a.
per seal Cost p.a.
Material 0,09 180.000 0,01 20.000
Labour 0,12 240.000 0,04 160.000
Machine / / 0,05 100.000
Other / / 0,01 20.000
Total 0,21 420.000 0,11 300.000
Saving     0,10 120.000

Summary of the cost comparison

Comparing the costs of the above example calculation clearly shows the savings made possible by FIPFG.

At the same time, it is an idealised comparison. Costs for electricity, pressurised air, water, replacement parts, scrap parts etc. were only applied for FIPFG technology, and there only with a flat rate of 10%. In real life, every situation must be considered and compared.

In our experience, however, investment in a machine usually pays itself off after a year’s production of about 50,000 parts, and a cost comparison should be carried out.