Thermal conductivity calculation ?? for comparing thermal interface materials

washer ) when mounting TO-247 to distribute the pressure.

I recall 'discovering' Belleville washers about 13 yrs ago.

Trouble is - I've never found a stockist who understands their application in electronics. I've never seen any data that helps make a selection.

Graham

electronics. I've never seen any data that helps make a

Neither have I. The app notes always just list "Belleville washer" with no data on diameter or spring pressure. I guess there just isn't enough of a difference between the different ones that are available?

I whipped out my trusty McMaster-Carr catalog and they have Belleville washers with serrations on top and bottom (for socket-head cap screws only), top only, and non-serrated. Interestingly, the top/bottom serrated ones are the least expensive? I thought the plain ones would have been.

Since I'm using pads (which will compress), I'm ordering a bunch of the #6 top-serrated ones along with some washers that are fatter (a bit) than the washers.

John

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Let's try that again.... Since I'm using pads (which will compress), I'm ordering a bunch of the #6 top-serrated Belleville washers along with some large flat washers.

I *believe* that's the recommeded setup...have to check the mounting app note again.

John

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electronics. I've never seen any data that helps make a

Well, you have to hire an engineer to figure out complicated stuff like that.

John

in electronics. I've never seen any data that helps make a

Machinery's Handbook doesn't have design data on them- they say it would take too many formulas and dozens of curves for the constants.

Nice the way you can put them in 'series' or 'parallel' to make up different forces/deflections.

in electronics. I've never seen any data that helps make a

I did get some data on them faxed to me - before I had internet access - probably before you'd have found that data on the web too. I can't really remember now what conclusion I came to.

In the end I used single coil spring washers.

Graham

in electronics. I've never seen any data that helps make a

I just looked them up, and was kind of surprised to find that belleville washers are much simpler of a design than I thought - it's just an ordinary, round, flat washer that's not flat, but kind of, um, banked - like the sides of a very wide, not very tall cone.

I was thinking of those things that look like half of the little cymbals on a tambourine, that they use under nailheads to post bills on telephone poles, and stuff like that - the closest McMaster-Carr has is "Finishing Washer", but that's not it either.

But I didn't see anything (at McM-C) like those little cymbal-shaped thingies.

Anybody know what I'm talking about?

Thanks, Rich

I had a much more complex curve (profile) in my mind for the washer too. Perhaps they used to be made that way until someone realized that they could get most of its performance with a much simpler washer shape (i.e., less expensive)?

John

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Belleville washers have been around :) a LONG time. I recently did a bit of research into springs (read as: found an excuse to buy more engineering books) and found this gem:

Mechanical Springs, A.M. Wahl, Penton 1944. see Ch. XIV - Initially coned disk (belleville) springs....

Cheers Terry

A very long time. Any hint as to why they are called "Belleville" springs?

My copy of "Mechanical Design of Machines" (copyright 1939-1965) gives equations for the force/deflection and maximum stresses at the edges, but notes they have been unable to confirm with measurements, and are inferring the stress levels (perhaps 180,000 psi) based on endurance life tests.

Best regards, Spehro Pefhany

Found this while looking for the proper way to use them. From the Adolf Schnorr GmbH + Co. KG "Handbook for Disc Springs":

"Although the disc spring has found a wider application during the last few decades, it is still an old established machine component. The original inventor is not known, but more than 130 years ago (on 26.12.1861 to be precise) Julien Francois Belleville of Dunkirk was granted French Patent Number 52399 for a spring design which already contained the principle of the disc spring. The importance this invention achieved is un known, but the fact that even today France and the Anglo Saxon countries still speak of ?Belleville Springs? infers a broad dissemination of this or similar springs. Today this tends to denote a disc spring of inferior quality, which still reflects the not always satisfactory design and function of springs at that time. This is no wonder considering that in the last century neither the theoretical conditions for calculations nor the necessary materials for manufacture were available. Not until 1917 did Fr. Dubois develop the theory on which the calculation of the disc spring is based in his dissertation ?The Strength of the Conical Shell? [1] at the ETH in Zurich. However, it still took several decades until this was adopted in practice. For a long time disc springs continued to be calculated ? if at all ? in accordance with the theory of the flat perforated plate. Then in 1936 two Americans, Almen and László, published a simplified method of calculation which allowed a quick and practically correct method for calculating disc springs"

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I come to add to your choices, try:

Crikey mate, just google for belleville washers and learn what you want to know.

Please tell me Phil, where do you get pre-punched thin mica now days?

Did that after my post. Still couldn't find a LOT of the info I needed though. Many, many of the manufacturers don't agree on some of the most basic things, like how far to "set" the washers (50% of height, 75%, fully set. etc.). Very frustrating.

Sometimes it's just better to ask for a recommendation from those who use the darn things.

John

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Thanks Joseph, they have a couple with very impressive specs.

John

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Ok, i was a bit rough. If you want thermal conductivity - fully set. If you want vibration resistance 75%. if you want to allow the part some room to move without busting something 50%. Easy, once you ask yourself how it might behave under various tightenings.