Threaded holes in Titanium

Under what sort of condition will this part have to work? Will it be subject to being taken apart for maintenance? These two things will give us the vital info required.

Conditions; Aircraft assembly. Some fasteners will see working temperatures from +400^o F to -65^o F. Most fasteners will need to be removed and replaced often for inspection purposes until a maintenance schedule has been determined.

That's a tough one have you given N.A.S.A any thought. They must deal with these thing on a regular basis. With those temps not many materials will survive. This is out of my league.

Careful! Aircraft have to be assembled so that certain critical parts do not shake loose or even disassemble while the plane is in flight. The best source of reference would be aircraft manufacturers' existing maintenance procedures.

It concerns me that a person is designing parts for an aircraft that does not already know the information you seek on this site. If you are not an engineer in your designated field, what are you doing in design work in such a mission-critical operation? Is this for a personal aircraft, built in your garage? If so, there are still lots of rules and regs to meet in your design.Not just for your safety, but for other people, in the air, and on the ground. You are not likely to find all the info you need on line,so please consult a qualified engineer in the field. HTRN

Hi J,

They make anti-sieze compounds (a paste that is just painted on the threads prior to fastening) for SS parts; why not Ti? I haven't Googled this yet, but if I find anything , I'll let you know.

Mike

Hi Again JB,

Maybe this would do the trick:

Product Description
Anti-Seize Assembly Lubricant. Prevents cold-welding, galling, and seizing of metal to metal contact parts, especially those subject to extreme pressures and moist conditions such as bolt threads, seatposts, pedals, bottom brackets, etc. For all metals, but essential when attaching reactive metals like titanium, aluminum, and specialty alloys and magnesium. Available in a 6.5cc Sachet 3-Pack or 8oz Brush-Top Can. Prevents cold welding, galling and seizing of threaded parts. Excellent for use on parts subjected to extreme pressures and moist conditions. Use on all metals; aluminum, titanium, carbon steel, magnesium.

http://www.amazon.com/Finish-Line-Anti-Seize-Assembly-Brush/dp/B000FPQE3M

Hope this helps,

Mike

You can get copper loaded grease and graphite loaded grease Also Molyslip but they will not survive at +400 deg C.

Yes, but 400ºC is a lot hotter than 400ºF!

Mike

Ok so I goofed on C versus F. 400F is still plenty warm. 218.666666666666 C

Scoundrel in deed just for that I will keep you guessing.

Oh yes and:

Identify thyself, scoundrel!!

Mike

What aircraft are you working on? Because if you are asking us a question like this I want to be sure not to get on that airplane!

I wouldn't worry about this aricraft... I would worry about the ones out there that no one asked this question. I would worry if the mechanic just stripped out the threads and didn't fix it because there wasn't enough time or the part was to expensive to replace. The extreme temperatures are what raise the suspicions.

Now you're really scaring me! But I agree that would be worse.

You did not say how thick the titanium was ? the depth of the thread has a great bearing regarding thread distortion etc, and as to whether to use inserts or not ,if you did use inserts stainless would be an obvious choice.

Also if you use an anti-galling paste you have to take care of how much torque is used in the tightening procedure what are your mechanical requirements? There are special self locking heads available if you need to go that route

We use a 1-1/2 times dia. rule of thumb on the material. Measuring from the center of the fastener out. For example: 1/4" dia. fastener will have a minimum of a 1/4" thick wall of stock, all around the fastener.

Using an anti-galling paste is a secondary preventative. Also, threads can be coated with Molybdenum Disulfide or something like it.

Just having this discussion helps me think through this. I'm hoping that someone has had experience in this and will let me know the outcome.

Thanks, you have some good thoughts on the matter.

Talk to technicians. They will know what works and what doesn't. That is the MOST important thing that very few design engineers do. All the school and design experience in the world doesn't compare to what the guy taking it apart learns on a practical level.

There must be someone at your company that understands how to deal with this, it it something that all aircraft manufacturers must deal with.

If you go with inserts, talk to the vendor in detail. Emhart Helicoil, a division of Black&Decker makes very high quality aerospace inserts (http://www.emhart.com/products/helicoil.asp). I use them on satellites, but those don't get repeatedly taken apart. Helicoils do have limited lifespans, particularly locking ones and coated ones.

Look up NASA and Mil Spec standards as well.

You are right about asking a technician, however, there is not one here that has any experience with this.

I am communicating with the people that make the Helicoils. They will get back with me soon, I hope. I think that they will suggest to use them because that is what they would want, sell more inserts. Its also like the coating companies that sell coatings, this is their business. I just want to get more information to base my decision on.

Thanks for your input.

If it's to be taken apart repeatedly, studs have been used in race engines so the threads in the block don't get worn. For light weight, maybe even " gun" drill the studs. We used gun drilled axles ( a hole bored through the center of the shaft) in drag race cars. They were actually stronger than solid shafts, more surface area, with increased strength you could use a smaller diameter.

Thanks for your suggestions.