Amir Yazdani and Andreas Proksch explore how Datwyler's new folding gasket addresses the challenges of existing technology
Safety and efficiency are core points of focus for today’s battery system developers. Batteries for new mobility solutions present new challenges compared to those used in internal combustion engines (ICE). Issues such as thermal runaway and corrosions of battery components could lead to situations that endanger the occupants or significantly reduce the battery lifecycle. Proper sealing of the battery within its housing is essential for mitigating these risks, as the seal is the first line of defence against unwanted negative influences. The battery must be correctly sealed to avoid ingress relating to dust and moisture. Electrical conductivity of the seal must also be considered for electrical grounding of the cover.
The incumbent gaskets, mostly based on adhesives and silicone elastomers, are common for sealing battery housings, as are form in place (FIP) solutions, which are injected onto the housing and left to cure. Both present challenges in terms of handling during installation, positioning on the tray, efficacy after curing and the ability to facilitate both on-going maintenance and end-of-life recyclability. As a result, Datwyler has engineered an innovative solution—the foldable gasket—which delivers a sealing solution for battery packs that overcomes all of these issues. The solution combines advanced elastomer materials with thin metal plates, foldable at points and stiff as a whole, which can be specified and placed at intervals according to unique part geometries, allowing for precise mounting either manually or robotically.
Figure 1. Working principle of Datwyler’s foldable gasket
Challenges and solutions
Normally, for the battery housing and its associated seals, the tolerances are very restrictive and must comply with IP6x or equivalent ingress protection parameters. Any gaps will not be accepted, therefore when designing the metal insert, Datwyler can control the dimensions precisely with minimal margin for error. Engineers use the elastic properties of Datwyler’s rubber material, which is very precise, to fulfil the requirements within the parameters required at certain heights. Unlike FIP gaskets, there is no beginning or an end section, where you have to ensure that there is no small channel to protect against the effects of corrosion.
The precise and reliable installation of the foldable gasket is key, as battery manufacturers are making higher density battery systems and their housings are becoming more complex and diverse. These more complex designs need a more precise gasket to ensure the seal integrity is not compromised and the metal element of the solution ensures this is the case. The metal is usually the same as that used for the housing itself and the surface is anodised and treated to ensure a strong bond with the elastomer component. The result is a sealing solution that delivers enhanced durability and also electrical conductivity, meaning electricity can transfer easily from the upper cover to the lower casing via the gasket, which avoids corrosion as a consequence of electricity build-up. Standalone pure rubber and FIP solutions do not have this ability.
Figure 2. Explosion view of a battery with a foldable gasket (in blue)
Finally, electromagnetic interference (EMI)—which can affect components such as sensors or critical control units—can also be mitigated via EMI shielding materials, which can be used to formulate the rubber element of the foldable gasket.
Simulation delivers optimised outcomes
Numerical simulation of the sealing performance of foldable gaskets is a core element in the entire design process. Such simulations allow the understanding of the accurate mechanical and thermal behavior of the seal under extreme conditions, ensuring the effectiveness and reliability of the seal in various critical situations. This effort begins with a two-dimensional finite element model, in which the variations of the sealing pressure along the seal lips are evaluated (see figure 1). Once the contact pressure and area at the seal meet the requirements for the specific defined performance, the simulation effort continues with conducting a three-dimensional finite element modelling in order to evaluate the amount of pre-stress at the bolts required to keep the foldable gasket in place. This pre-stress also guarantees the desired electrical conductivity between the housing parts.
Finally, The last step focuses on the simulation of the entire battery housing connected with the foldable gasket, so that the seal integrity along the entire seal lip is ensured. These sets of simulation tasks facilitate the optimisation process during the design of the gasket with the outcome being optimised geometrical dimensions, material properties and mounting forces.
(a)
(b) Figure 3. The results of a two-dimensional simulation of a four-lip foldable gasket design: (a) the maximum principal strain within the gasket; (b) the variation of contact pressure at the boundary of the seal
Sustainability built in
Battery makers are also considering the possibility of opening the battery pack several times over its lifetime for inspection and maintenance. The foldable gasket makes this possible. If an FIP gasket is used, one side of the gasket is permanently adhered onto the housing. This means when the gasket is opened it cannot be removed. The foldable gasket can be removed and easily replaced as there is no adhesive between the gasket and the housing. The fastening solution uses general self-piercing rivets or M5/M6 screws for ease of opening. This also enables easier disassembly with zero damage of the sealing gasket when inspection or maintenance is needed, or when the battery reaches the end of its useful lifespan.
From an Ecodesign perspective, the design principles of the foldable gasket mean that, from initial transportation, handling and installation to effective application, maintenance and ultimately recycling, battery manufacturers experience the benefits of an outstanding sealing solution.
About the authors: Dr Amir Yazdani is Advanced Technology Development Manager at Datwyler. Andreas Proksch is Product Manager Electrification at Datwyler
Keyword: Foldable gasket tackles battery pack sealing headaches