Freeze Plugs in 6AL-4V Titanium 1

[USACompositeGuy]

Does anyone have any references for installing freeze plugs in Titanium?

The SRMs cover installation of freeze plugs and bushings in aluminum however I can’t find anything that provides this same level of guidance in titanium.

I have reviewed this thread:

http://www.eng-tips.com/viewthread.cfm?qid=285324

wktaylor gives a good reply to a similar topic, but I can’t find anything to give to the mechanics as an installation procedure.

If anyone has any info on the installation and analysis of freeze plugs in titanium please point me in the right direction.

 

[WKTaylor]

USA Composite Guy...

Freeze-Fit Ti plugs in any material, especially titanium are a rarity. Mostly because titanium alloys have the lowest coefficient of expansion [and contraction]. Hence recieve the smallest benefit of shrinkage even with deep cryo cooling [LN2]. All my charts show CRES-STEEL-ALUMINUM-BRONZE plugs [or bushes] in ALUMINUM-STEEL-CRES structure. I couldn't find info for straight shank Ti-plugs in Ti-structure.

HOWEVER...

Working on F-15s in the 1990s we installed tapered plugs in tapered holes [Ti-Ti]. These plugs were MF Taper-Loks: heads with shanks were pressed into tapered holes [threads and excess shank then milled-off]. Tapered hoes were drilled with tapered drills used for TL installation. Plugs could be in single layers only; or thru the stack-up. See SAE AIR809 Metal Dimensional Change with Temperature for actual values.

Another approach is to electron-beam weld a patch/plug in position [special processes and vacuum EB welding required].

Also...

A very successful emerging technology for "patching" holes in titanium is to taper-drill the hole, then friction-weld-install a matching tapered-plug of the same alloy, in the hole. IE: spin-up the plug, then ram it into the tapered hole until it friction-welds itself [full-length] in position. Ensure hole/plug are metallurgically clean; and that the areas is free of moisture [dry inert gas, both sides works best and provides rate controled cooling]. After installation, simply machine both sides flush. The area can obtain static and fatigue capability approaching the undrilled base alloy. Hole can be re-drilled/reamed for BP fastening.


Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[A380istoobig]

If you have access to it, have a look at Boeing Drawing 65C38131, Freeze Plug MRB Repair Installation Procedure.

 

[WKTaylor]

A380istoobig..

I have seen that drawing You referenced. It is helpful for liaison engineers but requires training/caution to use it properly: too many variables are left un-explained.

The titanium bushings and associated holes tolerances listed are not specific to base alloy they are being installed in. The drawing neede a matrix as to bushing type, VS structural alloy/temper, VS recommended interference.

I would be especially careful with high interference bushings installed in SCC prone alloys... specifically in orientations where SCC is a screaming problem.

Regards, Wil Taylor

Trust Me! I'm an engineer!

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

Unfortunately, in science what You 'believe' is irrelevant – "Orion"

 

[A380istoobig]

Mr Taylor,

I agree with you. The original post was looking for a good installation refenence (which that drawing is). The actual use of the drawing would require the appropriate level of approval (FAA 8110-3, FAA 8100-9 etc). The approval would require the analysis and cautions you mention above.