Stategies to prevent Galling in 6Al 4V Titanium

[EngTechUK]

Hi all,

My first question on Eng-tips!

I have a design element which calls for a displacement adjustment sliding interface between two Ti (6Al 4V) plates.

Once the plates have are in position, they are bolted tightly together such that the friction generated by the bolt clamping force prevents the plates from any further sliding.

My initial reaction to this design was that it was going to be incredibly susceptible to galling between the plates.

Would anyone have any suggestions to help mitigate this?

My first thoughts were either applying some Nitriding to one of the plates to increase hardness, or specifying some interstitial material between the plates (either a gasket like arrangement, or simple lubrication).

Thanks very much for any advice.

 

[monkeydog]

Yes, you are on the right track. What you put between the plates is really up to your design limitations and how large you plates are.

 

[EdStainless]

A solid interface layer will be the most durable and predictable solution.
If this will only be adjusted rarely and there is no risk of it slipping then a lubricant may be enough. But many lubes do not age well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[EngTechUK]

Thanks very much both - great to get some other opinions on this.

I was slightly concerned that the reduction in friction caused by any lubricant between the plates might necessitate a substantial increase in clamping force.

In your experience, would an interface material selected to increase friction be worth looking into? If so, would you have any suggestions?

 

[cap1a79]

I think you need to check friction coefficient when applying lubricant or nitriding.

In principle, Friction force = Normal force (shear force) * friction coefficient

The friction coefficient which should be updated by lubricant & nitriding shall be incorporated into friction force and the friction force shall demonstrate it is still within acceptable range of static friction zone.

In a few words, the friction force shall be in static friction zone that the facilities do not move.

Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[WKTaylor]

ETUK...

I am not particularly wild about flat Titanium plates slip-adjusted for linear position... then be simply bolted together and 'relying' on friction forces to keep them locked together. A jet I've worked-on had Ti-6Al-4V engine bay doors fastened to Ti-6Al-4V stiffeners/longerons and frames. Galling was definitely a problem: these doors had to be opened frequently and both of the mating surfaces, and the panel-fasteners, were wearing-out. Over the years galling had eroded the mating stiffener/longeron which was having a obvious material loss and superficial hardening/scoring effect... which effectively caused the panel fasteners to no-longer tighten properly.

This 'relatively permanent assembly' of Yours sounds like an ideal application for flat-parallel [identical] serrations on the mating faces of the two pieces... with a few drops of lubricant [oil, grease, etc] to prevent galling. Bolts/nuts squeeze the plates together [thru matching oval-cutouts... which locks the serrations together.

These 'flat-parallel serrations' look like mini-ridges running across the part-face, transverse to the linear-adjustment orientation direct. Often, these serrations look like threading on-edge [W or WO root radii and truncated 'peaks']. The finer the serrations the finer the extension-adjustment. The pieces are mechanically locked together using serrations. for various reasons serrations may run 90-degrees across faces... or an any angle down to 45-degrees... or rarely, even curved/arced patterns.

Just saying...



Regards, Wil Taylor

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[mighoser]

What temp are these plates exposed to? You could used a solid film lubricant filled polymer sheet/plate. Ketron HPV is a good material. You can go to plasma coatings (SiC or TiN) if you need temps over 500F. I believe Ti can be Ion Nitrided but isn't possible via liquid salt bath due to attack from the molten salt.

________________________________________
Mitsubishi Chemical Advanced Materials

http://www.mcam.com