…and there is not just one type of seal either!
The majority of MANN+HUMMEL’s products revolve around filtration, and be they air, oil or fuel filters, they all have one thing in common: they must lock the outside world out of the filtration process in order to provide optimal performance, which requires the use of a variety of materials, geometric shapes and specifications. Despite all serving to perform the same end goal, sealing elements, too, can differ greatly. They ensure that a medium (such as oil or fuel) that has already been filtered does not come back into contact with the contaminated fluid, or guarantee that none of the medium inadvertently leaks out, preventing fuel from running onto a road, for example.
How is a seal chosen?
For every elastomer put to use by MANN+HUMMEL, there is a customer with a different set of specific requirements for the materials. What oil resistance properties are required? How should it respond to environmental influences, such as ozone? And how much may the sealing swell?
For each sealing application, the importance of each of the various factors becomes lesser or greater. Amongst others, these requirements include factors like mechanical properties – such as tensile strength and elongation at break – and heat resistance. The latter is often particularly important, as seals must ensure that they maintain a certain level of elasticity even at high temperatures. In an oil filter, for example, temperatures can range between 80 and 120 degrees centigrade – or even higher. A further vital property is an elastomer’s flexibility at low temperatures, referred to as the ‘glass-transition temperature’ in technical circles. Seals can become brittle if temperatures are too low, possibly causing them not to function. Swelling also plays a major role in the selection of a sealing material, as seals – much like sponges – absorb the fluids they come into contact with. This usually causes a certain degree of swelling, however the expansion must remain within a specific threshold so as not to restrict the functionality of the material.
For all of these reasons, it is particularly important that the right sealing materials for each project are obtained from our various suppliers, each of whom have their own formula, production processes and outflows for their sealing materials. Our task is to select the supplier who has the best ‘recipe’ for our customers’ ‘tastes’. With this in mind, here at the MANN+HUMMEL materials department we take care to line up all of the available properties with the desired requirements in order to find the perfect product for our customers. Furthermore, we also test the elastomers prior to their installation, ensuring that the materials meet all requirements.
A ‘recipe’ for success – no matter the requirements
In many cases, changes can be made to the basic formulation for the production of elastomers that will allow them to meet specific requirements, yet there are some properties which stand in contrast to one another. For example, a choice must be made between the material’s polymer chains being densely cross-linked, creating a high degree of strength, and fewer branch points being connected, making the material extremely flexible and malleable. It is only rarely possible to optimise both of these properties simultaneously, chiefly through switching to a higher material class (which commonly incurs higher costs), and while additives such as plasticisers, antioxidants and heat stabilisers can improve properties without changing the material class, major changes to the basic properties are impossible. This why prioritising requirements is always so important: is heat resistance more important than elasticity or cold resistance?
A look to the future
In future, changes to the amount of space under car bonnets and the use of alternative fuels will, in turn, change the requirements placed on elastomers. Personally, I believe that the most significant changes will come about as a result of the key concept ‘motor efficiency’. More and more combustion engines are now operating in a higher temperature range to increase efficiency, which optimises CO2 emissions. What this ultimately means for sealing materials in engine compartments is that being able to withstand high temperatures is becoming a significantly more common requirement, while low-temperature requirements remain unchanged. Rather than simply being suitable for temperatures ranging between -40 and 100°C, the material must be able to withstand anything between -40 and 150°C or even as high as 180°C. But to go higher, faster and farther is not possible without increasing costs – after all, the higher grade the material, the more functions it can serve.