Battery systems

Battery: Gasket Comparison

Solid rubber delivers unparalleled benefits in battery sealing solutions

Andreas Proksch
Jul 2, 2024

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Mobility

 

Manufacturers must decide between foam gaskets and solid rubber seals for battery housing seals, considering factors like performance, durability, installation complexity, and production schedules in the mobility sector.

For sealing system critical battery housings, manufacturers have multiple technologies and challenges to factor into the decision making process. Seal integrity, performance and durability must be closely scrutinised, alongside the process of installation itself and the pressure it puts on production schedules. The foam gasket, which is often applied by hand or robotically as part of a Cure-in-Place (CIP) process, is one of the most common solutions across the mobility sector. But how does this technology compare to the solid rubber alternative? Here, we compare and contrast to see where the advantages clearly stand out. 

Advanced materials

Foam gaskets are produced using materials such as polyurethane or silicone that are filled with air bubbles. They create a very soft seal when the battery housing is closed. The gaskets are usually flat or semi-circular in appearance, and are either placed directly onto the part itself or produced separately with an accompanying adhesion tape. Their performance within a battery housing requires an application at a width of 20-26mm at a compression rate of 50% on average.

For a more robust level of performance, solid rubber gaskets made out of EPDM or silicone deliver a superior result. This is because their composition is free of air bubbles. From a compression perspective, a rate of only 20% on average is required at a seal width of 6mm. Cost savings can be achieved as a result of decreased seal height and the required width of the pack frame, as the material thickness of the housing can be reduced.

Streamlining processes

It can take two to three people up to 10 minutes per housing to apply a foam gasket. In countries such as China this is common. Multiple sections are assembled individually to complete the gasket. The gasket must be transferred manually, a separate liner added, and the separate sections fixed with an adhesive. Inconsistencies in quality are often experienced when using this time consuming process.

CIP solutions, although they apply the foam seal robotically, require a curing process of 12-24 hours to complete the sealing process with parts stored in a separate area. This adds significantly to the production timeframe and increases the required space which results in higher overall cost of the process itself. CIP in China is used primarily for controller boxes, whereas the manual foam gasket is generally used for battery housings.

To achieve higher sealing tolerances within smaller spaces is one of the core challenges for manufacturers. This is where a sealing solutions partner with the ability to influence the design process and the material composition itself can add significant value. Operators often have to cut foam gaskets to size and assemble them in many sections by hand. A solid rubber solution can be tailor-made to highly specific designs and tolerances and vulcanized to the battery cover in advance automatically. The gasket is completely bonded to the surface, meaning assembly is a single process.

Manually applied foam gaskets can take 20 minutes to vulcanize, while solid rubber takes just 3-5 minutes. Further cost savings can be made as there is no requirement for post curing, foaming, die cutting, glue or liners. Line robots can also grip, transfer, loosen and tighten the solid rubber solution automatically.

Tailor-made functionality

The need to reopen battery housings for maintenance or even recycling purposes increases as e-mobility solutions become more widespread. For foam gaskets, including those applied by CIP methods, once the housing is opened the gasket can only be reused a very limited number times before the seal is compromised. Further delays and costs can also be experienced as the cleaning process is complex and certain elements of the gasket may still need to be replaced.

Solid rubber gaskets are far more durable and are able to be opened and resealed many times following a simple cleaning process. After the useful lifecycle of the battery, this gasket type can be removed simply by placing it into the appropriate recycling process. Whilst foam and CIP applications are effective while the housing remains closed throughout its operational life, solid rubber is better where reopening and reuse is required, for example when performing maintenance tasks involving fuses.

Functionality levels are higher when working with solid rubber gaskets from a specialist supplier. It is possible to influence the design to achieve maximum performance with the least amount of material used through the co-engineering process. A customer’s unique specifications can be incorporated including material selection and testing, ensuring all parameters are taken into consideration. The efficacy of the final gasket components will also become the responsibility of the supplier – decreasing the risk for the customer further.

Fast transition, fast return on investment

To transition to solid rubber gasket solutions can be undertaken very quickly. The sampling and testing process of the gasket is managed in-house. In China the process can be changed and operational within a 3-6 month timeframe. Additionally, the return on investment is also achieved very quickly. For example, an investment of CN ¥500,000 (€65k) can be recouped after just 75,000 parts assembled. From that point onwards, the cost savings from the material reduction and significant process improvements add directly to the customer’s bottom line.

There is little downside to making the transition to solid rubber gasket technology. The process of making the change is fast and efficient and the material ensures that battery housing sealing solutions are future-proofed as e-mobility applications increase. Finally, the return on investment can be seen in as little as 75,000 parts assembled, making the decision to move forward as appealing as the solution itself.

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