What electric isolator material?

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Discussion Overview

The discussion revolves around selecting an appropriate material for an electric isolator that is rigid, durable, and capable of withstanding a wide temperature range. The context includes considerations for mechanical stress, drilling capabilities, and application in battery pack construction.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Andy seeks a material that is stiff, durable, and can withstand temperatures from -40°C to +80°C, while being able to be drilled and pressed without cracking.
  • One participant suggests high toughness ceramics like Si3N4 or SiAlON, noting their difficulty in machining and potential overkill for the application.
  • Another participant proposes using a composite material, mentioning the importance of loading direction and suggesting laminate configurations to manage stress.
  • Andy clarifies that the isolators will be pressed together in a battery pack configuration, with stainless threaded rods compressing the assembly.
  • Suggestions include acrylic, though Andy expresses uncertainty about its stress tolerance, and Hylam is mentioned as a potential option from another forum.
  • One participant recommends fiberglass materials like G10/G11 for their insulating properties.
  • Another participant raises the idea of using HDPE as a possible material.
  • A more unconventional suggestion is made to consider wood as a primitive option for the isolator material.
  • There is a mention of epoxy combined with glass fiber, highlighting the potential for isotropic properties and avoiding delamination.

Areas of Agreement / Disagreement

Participants present multiple competing views on suitable materials, with no consensus reached on a single best option. Various suggestions reflect differing priorities regarding mechanical properties, ease of machining, and application-specific requirements.

Contextual Notes

The discussion includes considerations of mechanical stress, temperature resilience, and the feasibility of machining different materials, which may not be fully resolved or agreed upon.

Andy Haard
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Hi all
I need some suggestions on what material to use, hope you guys can help me.
It needs to be an electric isolator, as rigid and stiff as possible without being brittle.
I must be able to drill holes into it and put some pressure on it without it cracking and it needs to be as durable in -40 C as in +80C. I will use it in bars 8mm thick by 15mm wide and in length of about 180mm
/Andy
 
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Is it held in tension or compression?
What scale of production are you looking at?

You have a couple of options, really.

a High Toughness Ceramic - it may be overkill as they are most useful at very high temperatures, but Si3N4 or SiAlON might work. Drilling holes in it would be difficult, could you put the holes in in the die stage? Stabilised zirconia, i.e Ceria or Yttria Stablised Zirconia (YSZ) has excellent toughness, but again the ceramic-aspect of it means it is difficult to machine.

A composite may work, if the load is along a single axis. Again, the loading direction matters. You could just use a laminate at 0/60/120 degree layers or 0/45/90 to spread out the load in the plane. you can get pretty cheap pre-preg matting and cut it into shape.

It depends on the specifics of the part really. Was this any help at all?
 


Thanks streeters, they will be pressed together, the 15mm sides against each other, 75 of them. Between each pair will be two thin alu tabs. It is not for series production.
It is for building battery packs for these cells:
http://blog.evtv.me/store/proddetail.php?prod=123
The idea is to have two stainless threaded rods running though all 75 isolators with bolts at each end and compress it all together. It is to go into a car so it must be able to handle vibrations and temperature.
Would be nice if I could use acrylic but I'm not sure it will stand the stress.
Over on mechanicaldesignforum, Hylam was suggested.
/Andy
 


Why not use some fiber glass like G10/G11? You will need to isolate your tie rods through the Al parts.
 


That's an excellent suggestion Mquack! I'll look into that :-)
 


What about HDPE?
 


At the risk of sounding primitive, how about wood?
 


You can buy rods and plates of epoxy +glass fibre. The fibre can even be unwoven short whiskers, if you want isotropic properties (which starts with: no delamination...)
 

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