IP-6x rated sealing
Within the electric vehicle (EV) and battery pack manufacturing industries, we are frequently asked for material solutions to seal enclosures, typically to IP-6x7 or IP-68 rating of some level. This post seeks to address the various options available to the design engineer.
Those options are quite numerous and can be narrowed down with some very basic selection criteria. Gaskets in some shape or form have been around forever. Technology-wise, there isn’t much new today for EV designers, but the application of sealing in automotive applications isn't new and remains pertinent for today's EV designers. It is useful to understand the basics and hone in quickly on the right type of gasket for your specific application.
What is IP-6x rating?
IP stands for Ingress Protection; 6x is protection from dust ingress, and finally the x is the level of protection from moisture ingress. IP-67 is dust tight protection from water immersion less than a meter in depth for at least 30 minutes. IP-68 is the same except that it allows for the manufacturer to specify immersion conditions greater than a meter for specific lengths of time. Lately, we are being asked about IP-69K which specifies protection against hot, high-pressure water jets. IP-69 is often a requirement in the pharmaceutical/medical industries with 69K more specific to road vehicles. The good news is that with proper material selection and gasket application, it isn’t difficult to meet these conditions. Especially for those of us who are used to sealing against hot oil, gasoline, transmission fluid, anti-freeze and the like!
Does the enclosure need to be resealable?
If yes, we point in two possible directions – Cure in Place Gaskets (CIPG) or die-cut gaskets, and we eliminate Form in Place Gaskets (FIPG) as an option. The most cost-effective solution, primarily because of eliminated waste and process efficiencies, is CIPG. However, this type of gasketing requires some up-front capital expense for dispensing equipment and is best suited for high volume applications. Therefore, CIPG may not be appropriate for a start-up. Another option is die-cut gasketing. The up-front capital expense is typically very low but the downside is the piece price for these manufactured gaskets, and the labor to install them, is typically higher. Even so, the wide variety of options both in materials and in design make die-cut gaskets a very attractive option for resealable enclosures.
Design consideration for these gaskets should be given to compression set to ensure proper functionality after repeated opening/closing cycles.
If the enclosure doesn’t need to be resealable, die-cut gaskets can still be employed bringing the many benefits discussed in this article. It also allows FIPG to be considered as an option. By far the most cost-effective gasket for large volume applications, FIPG is widely used in automotive applications today. Again, this type of gasketing is best suited for more high-volume applications, or small complex gaskets that are difficult to assemble with a pre-molded gasket.
***Quick note about molded or extruded gaskets – these types of gaskets are very ubiquitous and very cost-effective. Hisco doesn’t participate in this subset of gasketing and while many of the material considerations discussed here are useful to down-select the composition of molded or extruded gaskets, we won’t address them explicitly.***
Other Design Considerations:
Chemical resistance is an important consideration when designing a new seal. Various resources are available on-line to verify the type of elastomer that should be used based on chemical exposure, such as: Rubber Eastomer Chemical Resistance Guide
What is the operating temperature of the seal?
There is a wide range of elastomeric materials available based on short-term and long-term temperature exposure. Typically, seals expected to perform at temperatures higher than 150C continuous usually recommend silicone. The moderate temperature exposure of EPDM, CR, or nitrile is usually acceptable.
Cellular vs Solid Elastomers
Design considerations for selection of cellular vs. solid elastomers are based on seal loading (psi). Typically, molded/extruded seals require solid elastomeric materials.
Compression Force Deflection (or Shore Hardness)
Most elastomers are available in various durometers (or hardness) based on seal loads (psi). Shore A hardness applies to solid elastomers, whereas cellular elastomers are classified by Shore 00, CFD (compression force deflection), or ILD (indention load deflection). The proper scale is almost always specified by the material manufacturer.
Compression Set (or Recovery)
Compression set is a measurement of the elastomer’s ability to recover to its original thickness following long-term compression of the seal. Compression set properties are applied mostly to cellular materials, whereas solid elastomers are usually classified by recovery. Both classifications are essentially the same and is listed as a percentage, such as 3%. Using the standard ASTM D3575 for foam and D395-18 for rubbers test for compression set, a 3% value means that the sealing material recovered to within 97% of its original thickness. This is a very important value when considering whether the design will require a resealable or permanent seal of the enclosure.
Closed-Cell vs Open Cell Elastomers
High-performance, open-cell elastomers are sometimes included in the design when the sealing material will require a re-closable enclosure gasket such as an access panel or door. Open cell elastomers can provide a very effective seal when compressed to 40-50% of its original thickness and moderate water exposure is above grade. Any direct contact with constant water pressure will almost always require a closed-cell cellular or solid elastomer. References to material testing such as NEMA and UL can assist with making the right design selection. Classification of cellular elastomers as open cell or closed cell is based on material testing for water absorption (by weight). Classification of open-cell materials is based on water absorption above 5% of the original weight.
Re-Sealable or Permanent Enclosures
Design consideration should be given to the frequency of opening the enclosure. Frequent opening and closing of the enclosure will require an elastomer with improved compression set (or recovery) properties. Both open-cell and closed-cell materials are available with low compression set properties. Permanent seal closures can utilize closed cell cellular or solid elastomers, especially where the gasket will be replaced during servicing of the component.
Additional factors need to be considered when designing a proper sealing material, including resistance to flame, UV, ozone, abrasion and the product life cycle. Please inquire with Precision Converting for further references to material selection.