Rule of Thumb for EMI Shielding of Plastic Parts in E-Mobility

 

In this rule of thumb post, we discuss the use of metal fibers, carbon fibers and glass fibers in plastics compounds to increase the EMI shielding effectiveness.

In another post, I showed already the importance of EMI shielding for new e-mobility applications and polymer material selection.

Key questions for new plastic compounds are:

1)    How high is the additive level to fulfill the set requirements? In our case, how much steel, carbon, glass fiber is needed to reach a sufficient shielding effectiveness according CISPR 25 (A1 and A2 level)

2)    What is the impact of the compound modification on the processing equipment and what is the impact on the allover properties such as mechanical, thermal and chemical properties?

Finding answers to the above questions, the research institute Fraunhofer LBF conducted a study [1]. They investigated PA 6.6 base resin pellets loaded with 10% stainless steel fibers, 20% carbon fibers, and 30% long glass fiber and compared them to the unreinforced PA 6.6 pellets. The test conducted was a DKI platelet wear testing method. With this method it is possible to find out the impact of the different compounds on the production processing equipment such as injection moulding machines.

Results

The study showed that the 10% stainless steel fiber PA 6.6 compound resulted in approximately the same EMI shielding performance as the 20% carbon fiber PA 6.6 compound. Furthermore, the stainless steel fiber compound results in a much lower wear and tear of the equipment, compared to the other compounds, especially carbon fiber.

Table 1 shows the amount of stainless steel fibers needed to achieve a certain EMI shielding level [1]. 

Table 1: amount of stainless steel fibers needed to achieve a certain EMI shielding level [1]. 

Figure 1 shows the filler addition needed to achieve a certain EMI shielding level [1].

Figure 1: filler addition needed to achieve a certain EMI shielding level [1].

Conclusions

Plastic compounds modified with stainless steel fibers are an effective alternative to carbon fiber loaded compounds since a low filler load is needed resulting in lower wear and tear of moulding equipment and keeping the allover properties in balance.

Thanks for reading and #findoutaboutplastics

Herwig

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Literature

[1] https://www.bekaert.com/-/media/Files/Download-Files/BFT/White-papers/Whitepaper-4--Shielding-EN.pdf?la=en