Disk Spring for thermal effects compensation 5

[eli28]

Hello,

I have an Ultem 1000 Flange that has to be connected to a Titanium container with a screw made of steel.
I am presenting only a portion of the bolted joint for simplification:

First of all I have to point out that my preload is limited by the ULTEM 1000 and hence it's only preloaded to 2450N.
I was looking for a solution to 2 problems:
1. Preload decrease due to exposure to cold temperature (del_T=-25 celcius degrees).
2. Preload decrease due to the (unknown) ULTEM creep in compression.

As a result I thought that adding a "spring" element with a moderate stiffness may compensate the deflections with only quite small load decrease. So I decided (as a result of limited space) to try to use (for the first time) Disc Spring for this purpose, as described in the picture above.

I have some questions regarding this design:
1. Is there a problem of stacking 10 Disks in parallel?
I couldn't find an adequate standard Disk Spring (for a #10 bolt) that may give me such forces.
It's important to point out that I have a limitation of maximum outer diameter (of the Disk Spring) of 12 mm that isn't seen in the picture above, and that's why I can't use a massive disk spring.
2. Is there another elegant solution I didn't think of and that is preferable?
3. Just to make sure I have no mistake - is the ULTEM 1000 surface will have a reaction force that is equal to the bolt axial load (that is equal to the equivalent spring force exerted by the induced deflection)? I read somewhere that as a result of internal friction between the disks the ULTEM 1000 experiences a lower force than the exerted force (of the bolt), but when I drew a Force Body Diagram I found out that for an equilibrium the reaction in the ULTEM surface has to be equal to the bolt axial force.

I am looking forward to your good advice!

Have a nice day

 

[itsmoked]

Hi eli28;

I was working in the little town of Scotts Valley in the Silicon Valley outskirts. There was a company across the street from mine called StressTel. As far as I know they were the inventors of the stress based bolt torquing hand-tools. It seems a decade or so ago they where bought by another company Krautkramer then Krautkramer and all its acquisitions were slurped up by Waygate Technologies. Waygate just looks like a tech suck-up company.

Meanwhile. The company who's brochure I linked above 'Dakota Ultrasonics' has sprung up about a sling-shot's distance from where StressTel was but is in much nicer digs. I suspect this is a case of bought-out employees rolling an advanced and updated version of whatever StressTel was selling and going back in business. Personally I'd go with Dakota as the current tech leader in the subject matter and also the company selling the product is the company actually building the product so you can contact The People rather than a company who buys the product from someone else.

Besides. My dog liked walking around their building - their lawn and the deer that were frequently standing on it.
[URL unfurl="true"]https://dakotaultrasonics.com/[/url]

Keith Cress
kcress -

http://www.flaminsystems.com

 

[eli28]

desertfox, the external load for each bolt is estimated to be 1500N.

 

[eli28]

Thanks (itsmoked) for replying and explaining your choice

 

[desertfox]

Hi eli28

Is the external load compressive on the clamped joint or tensile?
My only other comment depending how you preload the screw is that if you use a ordinary torque wrench then the tolerance for torque error is +/- 25% however if you use a device like itsmoked suggested the error should be a lot less.
I mention the error tolerance because I think 25% could cause the Ultem material to yield if it goes in the wrong direction.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[eli28]

Hey, the loads are in both directions.
It means the joint experiences tensile and compressive force.
About the tolerance in preload when using the traditional torque meter - I am also worried about it and I am sure the suggested solution given above is excellent.
Now is the difficult part - convincing the project managers to buy it.