SS diaphragms for pressure sensors 3

[cambria]

We are developing a small line of specialty pressure sensors. These are relatively small, and the diameters will be 2mm for one model, going up to 12mm for the largest. We are now at the tough part and thats designing a good diaphragm, and am looking for help. We can source the diaphragms or make them ourselves. Pressure ranges 0-15psi, 0-100psi, a very low pressure (1psi) and a high pressure unit. Temps will be nothing crazy: -20 to 150 C.

All sources, links, directions, suggestions, and warnings warmly welcomed.

dj

 

[EdStainless]

Most of the ones that I know of use a nickel alloys. This is done to address concerns about stress corrosion cracking and fatigue. Yes, the materials are expensive, but you aren't using much.

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Rust never sleeps
Neither should your protection

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[cambria]

Thanks Ed. No real cost issues at these dimensions. A question I would have on nickel alloys is their resistance to aggressive organic vapors: alcohols, hydrocarbons, etc. Its the one parameter I failed to list.

doug

 

[sreid]

I believe that many pressure transducers use Silicon diaphragms. This is probably mostly for electrical reasons (etched pizo resistive elements) but Silicon also has good chemical resistance and excelent fatigue resistance

 

[israelkk]

You could use gold plated nickel diaphragm or bellow. Look for the Servometer company

http://www.servometer.com/

may be they can help.

 

[cambria]

Yes, we could gold plate if need be. I think the key here is the physical design of the diaphragm to get a linear displacement in the center area of the diaphragm over the pressure range. It is quite an interesting problem, now we need to solve it! Thanks for the link on the Servo people, I'll take a look.

doug

 

[CoryPad]

Nickel will be immune to organics like alcohols, solvents, etc.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[cambria]

Sounds like Nickel is the one for chemical resistance. How does it compare in terms of elasticity etc to Stainless?

 

[CoryPad]

Almost identical: near 210 GPa.

 

[EdStainless]

Usually they are high Ni alloys, you see 625 used a lot.

These alloys are a little less stiff than stainless, but not bad. You can get tons of data from alloy producers such as Special Metals or Allegheny Ludlum.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[cambria]

I can plate in gold or rhodium, or not at all. It sounds like I can get away with a good nickel alloy and be good to go. These devices will be in action for typically 3 to 5 years in the agressive environment with steady but not incredible duty cycles. So no issues I assume with strain-hardening and long-term property changes, no stress-cracking. My next step is designing the "ripples" to get good linearity over the range without hysteresis. Any directions or links? The technology we have been working on shows very good results and I am hoping to field these sensors by the end of the year. Thanks for all of the input everyone. Again - any tips on designing the ripples in the diaphragm?

 

[sreid]

Flat and Corrugated Diaphragm Design Handbook

http://books.google.com/books?id=_7...G=Search&sa=X&oi=print&ct=result&cd=1#PPP1,M1

 

[cambria]

One of the most elaborate links I have ever seen! This looks like the answer! Great! Looks like Nickel alloy, and a book with perhaps the driest title in the world.

Thanks everyone, we are launched.

doug

 

[cambria]

FEEDBACK: I am now in possession of Flat Diaphragm Design Handbook. Ok, forget the title. That aside, the book is actually everything you would want to design pressure transducers. The materials section is good, and there are quite a few variations of design. It was a very good link. Thanks to all.