INTERNATIONAL, CUSTOMER-ORIENTED AND INNOVATIVE

Freudenberg Sealing Technologies manufactures more than 5 billion seals annually. Customers in many industries rely on our expertise – from specific solutions and innovations for electric and hybrid vehicles, to the food industry with more than 6,000 seals per production line. Freudenberg Sealing Technologies can recall an impressive history of innovation dating back to the invention of the Simmerring®. Today, seals are high-tech components in their own right. Equipped with an encoder, they send data to the engine electronics. The gas-lubricated mechanical face seal LEVITEX® generates a cushion of air and thus functions nearly friction-free. Freudenberg Sealing Technology has a customer-oriented product portfolio that is available globally – from tailored special solutions to complete sealing packages.

But Freudenberg Sealing Technologies is not just the market and technology leader in the sealing field. We also combine the expertise of Dichtomatik and Corteco under one umbrella. Dichtomatik is a Freudenberg distribution services company active in the technical seals market. Corteco is also part of Freudenberg and specializes in the independent automotive aftermarket. Corteco offers replacement and service parts for sealing and vibration control technology as well as cabin air filters, among other products.

Simmerring

LEVITEX

The “Freudenberg Spirit” and the knowledge of how important our sealing know-how is across all industries are the guarantee for innovative and high-quality products. They may indeed be “invisible” – but they are always “essential”.

Freudenberg - NOK
Sealing Technologies

Freudenberg
Sealing Technologies

NOK - Freudenberg
Sealing Technologies

Freudenberg Sealing Technologies – locations worldwide

WHY SEALS?

Even back in ancient times, water was considered one of the costliest commodities. It was the job of engineers to find ways to transport the valuable liquid from its sources into the cities with minimal loss – often over hundreds of kilometers. The explosive growth of metropolises would have been inconceivable without a secure supply of water – after all, the daily per capita consumption around 100 A.D. was nearly three times what it is during the 21st century. Lead pipes in a casing of “Roman concrete” were mostly used in ancient Greek and Roman water lines. The efficient integration of these elements required special care. The sealing of the difficult-to-maintain pressure pipelines therefore required several layers of mortar.

SEALS FOR THE FUNCTIONING

OF VITAL SYSTEMS

More than 2,000 years ago, the Romans developed double-piston pressure pumps to bring water from deep wells to the surface, enabling a nearly continuous water flow. Intake openings, cylinders and parts of the riser pipes were made of oak. The valves of the hand pump were leather flaps. Wooden pistons moved in lead-lined cylinders. Leather piston seals were an ideal way to improve efficiency. With a displacement ranging between 0.5 and 1.3 liters, the pumps were able to transport water from depths of up to 16 meters – in amounts as high as 95 liters per minute.

Very early on, seals were needed to ensure that complex, vital systems operated reliably. Then as now, the basic task of a seal was to prevent or limit the undesired transfer of material from one space to another. Still, in a physical sense, there is no absolute impermeability. For example, within a few days, even the hydrogen atoms in a fuel cell vehicle’s carbon fiber tank penetrate its several-millimeter-thick walls. “Technical impermeability” is a question of definition – whether it relates to molecules, moisture, droplets or other criteria. The mechanical principle of the seal described here involves the compression of the sealing material so that its internal pores and the micro-gap between the seal and the parts or the medium to be sealed become so small that the contained material can no longer penetrate it. Sealing experts talk about a contact seal. Leather was especially well-suited as a sealing material due to its flexibility and was able to play an key role in seals for centuries.

But there is also the question of whether a material is suited for use in a seal long-term. This issue is primarily settled by the nature of the medium that it is supposed to seal off.

POLYMER MATERIALS
CHANGE THE WORLD

The development of elastomers began in the mid-19th century. In 1839, the American chemist, inventor and amateur researcher Charles Nelson Goodyear discovered how to make commercial rubber from its raw form. As is so often the case with ground-breaking discoveries, serendipity shaped the event. When Goodyear’s wife Clarissa came home one day earlier than usual, the researcher broke off a secret experiment prematurely – his wife had repeatedly demanded that he stop his experimenting and make money instead. So he hid a mixture of natural rubber and sulfur in his oven to save himself some aggravation. When he examined the mixture later, he realized that the resulting substance was extremely stable yet still flexible. Goodyear had accidentally discovered a process that he called “vulcanization,” opening the door to natural rubber’s use in industry. Goodyear was not a natural-born businessman and had planned to have the process patented in 1844. But by that point, others had claimed the patent for themselves and he failed to personally capitalize on his invention in any significant way.

Plastics made ever-greater inroads into everyday life in the 20th century in the form of linoleum and Bakelite and increasingly replaced materials that had been in use for centuries. The 20th century had already become the plastics century – a term that Munich chemist Ernst Richard Escales first coined in 1910. He even named a magazine that he founded “Plastics.” By the 1920s, Europe’s largest tannery could not escape a growing trend: Plastics were replacing leather in its usual applications.

Charles Nelson Goodyear

Rubber after vulcanization

It was only in the 20th century that plastics made inroads into everyday life. Bakelite was used in telephones into the 1960s.

FROM TANNERY TO

SEALING SPECIALIST

In 1929, Black Friday on the New York Stock Exchange was a difficult turning point for the Carl Freudenberg leather factory in Weinheim. Exports in particular collapsed; they previously represented 75 percent of its business. So its staff recalled one of its earlier ideas – making sealing collars out of leather scrap, which had no other use. Up until that time, the collars for their own machines were ordered from America at great expense and in poor quality. Engineer Walther Simmer – whose job was actually to further develop the tannery’s machines – was assigned to tackle the issue. After numerous attempts, he developed a collar ring made of chrome leather, which was embedded in a metal housing ring and pressed against the machine’s output shaft using a screw tension spring. It proved possible to achieve sufficient tightness and durability with the pressure. Simmer managed to build up a small production operation that made a profit right from the start. One aspect was crucial to the Simmerrings’success: The company was able to use its existing contacts with the auto industry and replace the felt seals that were employed to that point. In short order, the amount of leather scrap was no longer sufficient for the company’s sealing ring production, and leather had to be tanned specifically for the purpose of manufacturing them. With the emerging leather shortage in Germany in 1934, the material was on the brink of being replaced as a seal component.

Starting in 1934, intensive research on synthetic rubber production was undertaken – in part to replace leather as a sealing material. Rubber compounds for seal and vibration control applications were developed at the “main lab” in Weinheim. An elastomer replaced the leather in Simmerring collars in 1936. The development of the Carl Freudenberg leather factory into a market and technology leader in sealing technology was underway.

Photo: Freudenberg & Co. KG, Unternehmensarchiv

Thanks to its entrepreneurial vision, Freudenberg made the switch from a tannery to a sealing specialist and conglomerate at the right time – although the company continued to deal with leather until 2002.

THE PRINCIPLE OF POLARITY

In the selection of a sealing material, it is essential to know how materials react in the presence of media. Here the principle of polarity is crucial: If electrons are evenly distributed in larger groups of atoms so that their electrical behavior is outwardly neutral, the substances are described as nonpolar. Some examples are carbon, hydrogen and hydrocarbons such as oils and fuels. There are still other atoms such as nitrogen and oxygen that, compared to carbon and hydrogen, distribute electrons unevenly. Poles are formed due to this uneven distribution. Molecules that combine hydrogen and nitrogen, for example, have polar properties. The principle of polar and nonpolar characteristics can relate to small molecules such as water (very polar) and even large molecules, the so-called polymers, from which sealing materials are made.

There is a rule that applies to sealing technology: “Like dissolves like.” Polar materials only dissolve in other polar materials. Two polar substances, water and salt, form a new homogeneous solution when they are combined – they intermix with each other. On the other hand, polar water and nonpolar oil form a suspension. The two classes of substances do not intermix; a clear phase boundary continues to exist. Experts in sealing technology look for this boundary: Sealing materials are selected that exhibit a repellent property toward the medium. A situation where the sealing material and the medium display mutually opposing polarities is ideal.

Leather was in use as virtually the sole sealing material for a long time. The principle of polarity was still largely unknown. There were no known materials that were similarly flexible and robust. It was only with the development of elastomers that alternatives emerged for its applications.

MATERIALS

POLYMERS
AS SEALING MATERIALS

The job of a seal is to prevent the transfer of material from one space into another. In its simplest form, it is a “barrier wall”. This wall must press against the two counter-surfaces of the components in the installation space. That is why contact pressure is needed. Here a special feature of elastomers comes into play: They exhibit reset forces based on polymers’ molecular structure – a clumping into long chains of molecules. As soon as an elastomer is deformed, forces emerge to counter the deformation.

This exact quality makes elastomers an ideal option for seal compression. The effect of the reset forces is that the barrier wall remains continually pressed against the counter-surfaces. The elastomer flexibility even allows compensation for relatively small movements. The duration of the seal’s operating life depends on how long the reset forces are maintained – in the language of the trade, people talk about elastomers’ setting behavior. Even raw rubber has reset forces. But vulcanization greatly strengthens the effect. For example, if you press chewing gum that has already been chewed, its form changes. Its chains of molecules glide past one another and hardly reset at all. If you bounce a ball made of vulcanized material on the floor, it deforms. But thanks to the material’s strong reset forces, the ball strives to return to its original form and bounces back.

It is not just the mechanical effects, produced in the contact between the rubber and the surface, that are crucial for the seal’s functioning. There are other qualities that qualify them – or in some cases, don’t qualify them – for certain sealing tasks. The issue of polarity or nonpolarity is crucial. By selecting monomers and the way they link together, it is possible to selectively control a polymer’s characteristics – for example, by controlling the ratio in which polar and nonpolar molecules react with one another. Polarity is a key issue when it comes to the use of seals with particular media – whether polar or nonpolar. Yet another criterion – an elastomer’s heat and cold resistance – is addressed by selecting the right sealing material.

There are great differences here as well when it comes to the application and the suitability of the materials. It turns out that elastomers start to decompose at a specific (upper) temperature due to heat effects. Conversely, if the material is cooled down, a temperature range emerges for every elastomer. Below that range, it loses reset forces and develops cold brittleness. This boundary is known as the “glass transition temperature”. Based on these attributes, elastomers always have an upper and a lower application limit that can be shifted or expanded with certain mixing ratios. In addition, ambient temperatures and anticipated temperature peaks are always important criteria when selecting materials.

The molding of elastomers is always associated with a chemical reaction (cross-linking = vulcanization). At higher degrees of cross-linking, the glass transition point always shifts to higher temperatures until nearly all molecular movements are stopped by the rigid immobilization of the polymer chains – as is the case with hard rubber. At “normal” temperatures, it shows the same properties that other elastomers do below their freezing point. Then only very slight dislocations are possible even when there are exterior stresses.

THERMOPLASTIC ELASTOMERS

Thermoplastic elastomers (TPE) represent the second category of the most interesting material groups. From beyond their glass transition temperature to their melting point, they behave as elastomers do. But they can be processed thermoplastically at higher temperatures (>100 °C). In all TPEs, thanks to physical cross-linking across (partly) crystalline areas, a thermo-reversible structure with elastic properties results during the cooling-down phase. The result is that a slight advance beyond the softening temperature later would lead to an irreversible loss of the component’s geometry within the application. The “contorted yogurt container in a dishwasher” is a graphic example of this phenomenon.

NATURAL RUBBER

Thailand is the world’s top producer of natural rubber with an output of 3.1 million tons per year, followed by Indonesia, Malaysia, India, Vietnam and China. India and China, however, do not export natural rubber. They only cover their own needs.

In use for millennia, natural rubber is the best-known material. The Maya, Aztecs and other aboriginal peoples of the Americas were familiar with it. They especially used it in ritual acts, made solid rubber balls for their religious games and burned natural latex much as other cultures burned incense. The term caoutchouc is derived from a word for thickened sap in an Indian language that has not been reliably investigated to date, though the term has come down to us as caucho in Spanish (17th century). “Cao” presumably stands for tree and “ochu” for tears.

One rubber tree delivers about 100 grams of latex from each tapping process (three tappings at 33 grams each). A tree is tapped 150 days per year. This provides about 5 kg of latex annually. Over a lifetime of 25 to 30 years, one rubber tree thus produces about 130 kg of latex. The simplest form of vulcanized natural rubber is produced solely with the natural rubber itself plus sulfur and water. Since this mixture would slowly vulcanize even without heat, some ammonia is added – which keeps the latex mixture fluid due to its alkaline pH value and thus the mixture can be stored. Since it is free from harmful toxins, it is suitable for use as an adhesive for latex rubber, as a soluble paper glue or liquid latex for body painting.

A MULTIFACETED NATURAL PRODUCT

Due to its unparalleled, low inner friction and its adhesion, today’s car tires are still given a certain percentage of natural rubber. About 1.5 kg of natural rubber (NR) is needed for a car tire, and more than 10 times that quantity (16 kg) for a truck tire. Airplane tires are even completely free of synthetic rubber. It would generate so much inner friction that the tires would overheat to a dangerous level during landing.

Today, petrochemically manufactured synthetic rubber covers about 60 percent of the global demand for vulcanized rubber, displacing natural rubber. Compared to plant-based rubber, it stands out for its greater ability to resist environmental influences.

IN BRAZIL, NATURAL RUBBER’S MOTHERLAND, ONLY 111,000 TONS OF CAOUTCHOUC IS HARVESTED PER YEAR. THE FERTILITY OF

THE SOIL IN THE AMAZON REGION HAS DECLINED AND IS NO LONGER SUITED TO

THE CULTIVATION OF CROPS.