Titanium, Aluminum Screws 1

[kelroy]

Anyone familiar with using Titanium screws or Aluminum screws in a military environment. Corrosion is not a big concern (should be in a sealed environement). They are not being used for major structural means -- just to fasten some electronics boards together w/ standoffs into an aluminum heatsink. I am scraping grams off my assy to meet wieght, and I am interested in halfing the wieght of my screws.

Loooking to have a buttonhead socket cap screw M3s.

Also any references for recommnended max torque, etc.?

 

[drawoh]

kelroy,

Have you called your suppliers yet? The last time I checked price and delivery on titanium screws, it was $11 Canadian per screw and two weeks. I forgot what kind of screw it was, either phillips pan head, or hex socket head cap screw.

The selection of head and socket styles will be limited.

Your machine design textbook should tell you how to work out torque.

JHG

 

[NickE]

ANTI-SIEZE is going to be essential!

Nick
I love materials science!

 

[kelroy]

I can deal w/ the price and lead time -- no I haven't checked, but that's in work. Yes, I'm worried about selection -- I need a specific head style to fit in my "box." I can do the calcs for torque -- I'm just lazy and like using handbooks and standards.

NickE -- well, I was planning on actually using loctite to assure they don't back out during high vibe levles....not sure how that works w/ Ti screws yet....

 

[CoryPad]

If you are going to use thread adhesive applied from a bottle prior to assembly, then that should provide enough lubrication to avoid adding another lubricant. You should analyze and test your joint for a proper torque specification. You can review this site (e.g. faq725-536) for tips on torque values.

For manufacturers, try:

Alcoa

http://www.alcoa.com/fastening_systems/aerospace/en/home.asp

Textron

http://www.textronfasteningsystems.com/aerospace/index.html

SPS Technologies

http://www.spstech.com/aero/

Regards,

Cory

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

 

[Kenneth]

To state the obvious: If adequate/appropriate for your application, aluminum socket head cap screws will be significantly cheaper (and lighter, and more readily available) than titanium fasteners.

 

[strokersix]

Sorry if this is too obvious but why not just use smaller screws? This has the advantage of whatever the screw goes into can also be smaller.

 

[kelroy]

Fine question strokersix. the governement has reuiqred a specific size for system bolts, so commonality is also paramount.

Worthy comment, Kenneth. When I run the torque calcs, I will certainly look at whether Aluminum will allow me to preload to the level I need to (it is a pretty high shock environment). These loads are lower compared to typical structural uses, but I'm not sure I'm willing to give up that much pre-load.

 

[MikeHalloran]

In a sealed environment, you don't need screws.

Use tubular standoffs with a shoulder, and upset the part that extends through the board.

The cheapest, lightest screw is the one that isn't there.



Mike Halloran
Pembroke Pines, FL, USA

 

[kelroy]

I'd like to hear more, Mike. By "upset" are you suggesting "flare" the end such that it captures the board? If so, that doesn't work for me, since I havew a stack of boards. However, I like any ideas w/o screws

 

[Kenneth]

http://www.aboveboardelectronics.com/raf/hardware/cbscbs.htm

?

 

[MikeHalloran]

The most common way to upset a tube is to flare the end. For stacked boards, that doesn't work, not by itself. But let's keep going a little.

Suppose you had a thin tube extending through all the boards. You could space the boards apart with slightly larger spacer tubes between the boards, and flare the ends of the central tube.

With some fairly serious tooling, you could space boards along a thinwalled tube by buckling its walls outward above
and below each board in turn. Sort of like the upset you see behind the panel for an installed rivnut.

OR, after positioning the stack and temporarily retain the boards in position, you could bulge the tube between the boards, e.g. with hydraulic pressure or an explosive cord. The boards would need to have substantial edge distance around the holes so the board would not split during the bulge process.

OR, you could carefully regulate the height and location of the components on each board, and just glue the tallest components to the bottom of the next board, with no standoffs at all.









Mike Halloran
Pembroke Pines, FL, USA

 

[NickE]

threaded rod,nylon/ptfe (temp dependant) spacers, two nylock nuts?

(Easy to assemble/disassemble, convienient, and Ti/Al threaded rod and nuts might be cheaper.)

 

[EdStainless]

I have seen the tube-over-tube system used. The spacer tubes are all flared to provide some bearing area. At the top a washer was put on the top board and then the inner tube was flared to hold it together.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

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