low thermal conductivity material

[renniks]

I,m looking for materials that have a low thermal conductivity rate in the operating temp range of 100F to 300F, that has machining properties, and or the strength of mild steel, aluminum or that will withstand a linear pull of 40.0lb of force using external threads of 5/8-12 UN in a oily enviroment.

Here's a description: the part to be made will be attached with the 5/8 tread to aluminum engine with temps range of 100- 260F I'm trying to keep a eletrical part attached to otherside from absorbing the temp of the engine and keep the eletrical parts as close to outside ambient temp. The distance from the engine to electrical part is 1/2inch 2 inches diameter and the distance cannot be changed, the material will be between the engine and eletronics.

Material can either be cnc machined, molded, molded with insert for strength, cast. I,m looking for all options of methods of manufacturing.


Thanks Scott

 

[FEMdude]

How about some heat resistant reinforced plastic, like:

http://www.matweb.com/search/DataSheet.aspx?MatID=48569

 

[RPstress]

It might narrow down choices a bit if you could tell us what sort of conductivity you're after. Also, quantities and hence price. Any info about shock loading and minimum temperature might also help.

A glass filled engineering thermoplastic may well be suitable (like the 30% glass PBT that FEMdude found), or maybe an unfilled advanced engineering thermoplastic such as PEEK if a glass filled conductivity is too high. Most of these are happy in oil.

If reinforced, the axial thread shear strength may not be typical of the bulk material shear strength. It depends on fibre size and distribution. Icotec (

http://www.icotec.biz

or

http://www.icotec.ch)

make composite fasteners which can (probably) easily handle the forces you've got; at RT their 5 mm dia. glass fasteners can take over 2000 N (>400#), and 5.8" is 15 mm! Strength at temperature is harder to come by, but it should be ok at 260 F even at 5 mm.

Icotec fasteners aren't cheap, but they do work well.

NB: you say you'd like a material about as strong as ally (say, 6061 => 30-40 ksi) or steel (maybe 30-60 ksi). However, you almost certainly won't need that strength level to take the tension load you've given on a 5/8 fastener. To achieve these sorts of steel/ally strengths in plastic you'll need reinforcement, which will reduce machineability and will increase thermal conductivity. On the other hand, without glass the cheaper engineering thermoplastics won't have an adequate heat distortion temperature. Also, beware of thermoplastics' high CTE (even when glass reinforced). To get a low CTE out of an engineering thermoplastic you'd typically use carbon reinforcement; that puts the thermal conductivity up more than glass does, though it might still be adequately low.

NNB: Another potential drawback to a reinforced thermoplastic is low stiffness. Look at that PBT with 30% glass: A bit over 1 Msi, 1/10th that of Al.

Non-thermoplastic options get a bit thin on the ground, unless anyone knows different. Some ceramics might be suitable. It depends a lot on toughness requirements and just how low the thermal conductivity needs to be (most things conduct rather better than plastic).

 

[sreid]

Search McMaster Carr

http://www.mcmaster.com

for G-10/FR4

This is Epoxy fiberglass, 285 deg F. Can and is often machined.