Using Ti/Cromo bolts on 6061/7075 Components

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Using Ti/Cromo bolts on 6061/7075 Components
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Posted: May 26, 2012 at 18:16 Quote
Just need to double-check something on this, because one of the users in here mentioned that if you use screws that are of a different metal than the component they are being screwed into, the inferior metal of the two begins to degrade in the presence of the superior one?!

Is this rubbish or true?

Surely this can't be true, otherwise companies like Profile etc wouldn't offer Ti bolts for their 6061 stems and the likes.

Posted: May 26, 2012 at 19:09 Quote
the word is Nobility. The more noble metal will live and the less will corrode. when you put 2 matals together they create electrolysis if they are far apart in the scale of nobility.

eg. copper touching steel, the copper will pit and degenerate. I havnt looked into it but Id wager that Ti and aluminum are close on the scale of nobility and that there would be no harm in them touching.

Ill leave it to you to investigate, but Im pretty sure youd be fine running ti bolts.
Salute

Posted: May 26, 2012 at 19:11 Quote
looked into it,

aluminim and titanium are pretty far apart on the scale and so the aluminum would lose ions to the titanium. this would take some time though and I still doubt it would be a real issue.

http://en.wikipedia.org/wiki/Galvanic_series

Posted: May 26, 2012 at 19:17 Quote
Cool thanks. Nice work.

I just took delivery of an Avalanche DHF 7.5 fork, and the condition it came in was absolutely appalling. The screws all looked about 50 years old, like they'd been salvaged from the titanic or something.

So I'm going to buy a whole new bunch of Ti screws..... But the fork is made of 6061 T6 Aluminium

I can't imagine this dissolving in the presence of Ti bolts though...

But I'll definitely read up on this; sounds very interesting in it's own right.

Posted: May 26, 2012 at 20:11 Quote
as a plumber i encounter this more than most would. the electrolosys is sped up in the presance of a substrate ( water ) so unless youre biking underwater it shouldnt be a problem.

Posted: May 26, 2012 at 20:26 Quote
You should see the state of some of these screws. There's this one screw which had sort of green rust all over the thread. Although, I don't think it's rust, it must be the Alu equivalent. But these bolts must be Cromo tho.... I don't get it. Green?! (Turquoise to be precise)

Posted: May 26, 2012 at 21:45 Quote
thats rust. oxidization to be precise. just like the statue of liberty, she is actually made from copper ( a gift to america from France ) but over time the copper oxidizes and forms that green scale, much like many church and cathedral roof tops. they start copper but over time they turn green. Salute

Posted: May 26, 2012 at 22:29 Quote
LOL so my screws are Copper?! Can't be....

Do they even make Alu screws? I can't imagine so. They gotta be Cromo screws for strength.

Posted: May 26, 2012 at 22:47 Quote
no theyre not copper, but what youre seeing is oxidization, which is rust.

Posted: May 28, 2012 at 13:02 Quote
roxovanos wrote:
Cool thanks. Nice work.

I just took delivery of an Avalanche DHF 7.5 fork, and the condition it came in was absolutely appalling. The screws all looked about 50 years old, like they'd been salvaged from the titanic or something.

So I'm going to buy a whole new bunch of Ti screws..... But the fork is made of 6061 T6 Aluminium

I can't imagine this dissolving in the presence of Ti bolts though...

But I'll definitely read up on this; sounds very interesting in it's own right.

a quick heads up about using titanium-alloy bolts in general

unless the component has been designed specifically with a bolt size and thread pitch to suit titanium-alloy bolts, I would not replace any "stressed" parts (handlebar clamp, stem clamp, fork clamp, crank bolt, etc.) with Ti

the reason is that the steel-alloys used for these bolts is actually stronger, and stiffer than the Ti-alloy bolts


what this means in reality is that you will get a different clamping mode using Ti bolts, than original steel bolts

titanium is a fantastic material, but its advantage is "strength to weight ratio" compared to heavier steel alloys



however, if using a "like for like" bolt replacement, steel is always stronger and stiffer

if you look at aerospace applications (fighter jets) for titanium-alloys, these are always designed from "ground up" with the properties of Ti in mind Wink



to give a "real world" example, I replaced the steel bolts in my Thomson X4 50mm stem with high-quality 6/4 rolled thread Ti (sourced from a Moto dealer)

what this did, was to make the handlebar feel flexible in the stem clamp, under high loads (cranking hard or pumping through jumps) and make alarming creaking noises! The bolts were fitted using torque wrench and ti-prep


switched back to the original steel, and the problem vanished, and the weight savings were minimal between steel and Ti


I will only use Ti bolts on non-stressed areas like shifter / brake lever clamp, derailleur cable pinch clamp, etc.

once of the nicest things about Ti bolts is they don't corrode (rust), but you need to be mindful of where you use them on your bike!

Posted: May 28, 2012 at 13:50 Quote
Do torque values need to be altered when replacing steel bolts with ti?

any thoughts on ti caliper mount kits?

Posted: May 28, 2012 at 13:54 Quote
ever get the chance to check out a ti frame ? you can hold the frame with your legs and literally flex the bike around with your arms. titanium is very strong and light but it is also very flexiblle so as heampsteadbandit has said I wouldnt really consider replacing steel bolts with ti a great option as the savings on weight are minimal. the flex i speak of is lateral flex and i am unsure weather this metal would dynamically stretch ( think side to side vs. pulling on it ) if it did it could potentially be dangerous in certain instances. What i can say for titanium is that it has replaced my femur and done quite well for me so far. Salute

Posted: May 28, 2012 at 13:58 Quote
tried a ti frame ages ago think it was an Orange, smooth ride but i prefer alu to steel frames! never mind tiEek

Posted: May 28, 2012 at 14:33 Quote
Nice post Hampstead. Yeah I would probably go for Steel bolts if the point in question relied on strength as a priority.

I don't get how your stem flexed with the Titanium bolts; that's pretty amazing...

Posted: May 29, 2012 at 12:59 Quote
iffoverload wrote:
Do torque values need to be altered when replacing steel bolts with ti?

any thoughts on ti caliper mount kits?

this is where it gets tricky

because Ti alloys are effectively more flexible for the same size as steel, you will find that the bolt itself will not provide the same resistance to flexure when loaded, despite the torque setting at the bolt head being the same (i.e. 5nm)

Ti can also give false torque readings because the Ti is somewhat "sticky" when the bolt is being tightened, this is why its essential to use loctite or Ti-Prep when installing Ti parts


Ti caliper mounting kits generally work well for XC and Trail riding, I have used Titanium-alloy bolts on Avid brakes (post mount and I.S.) for several seasons without any noticeable issues. these are typically torqued to 9-10nm and fitted with blue loctite threadlocker


I would avoid Ti caliper bolts for more abusive riding like FR and DH (where weight savings are less noticed) as riding speeds, braking forces are much higher, I have seen first hand Ti bolts on 203mm DH setups with the bolt head sheared clean off!

and also avoid for the largest 200mm / 203mm rotor sizes because the leverage placed on the brake bolts are dramatically increased over smaller rotor sizes (this is why large rotors have more "power" i.e. increased leverage) for the same amount of lever pull, I have been given figures of 400-500nm on a "hard stop"


something else to consider about buying any Ti bolt is the quality of the Ti Alloy in the bolt, and the quality of the manufacturing

some of the cheap Ti bolts on the market (Ebay,etc.) are suspect quality in terms of the Ti alloy itself, and the quality of the thread and bolt head manufacturing - I have seen cheap Ti bolts with "cut" threads, rolled thread are always preferable.

and also cheap bolts with poorly formed Torx or Allen heads that are prone to easy damage even when using quality tools to install.

SRAM offer some good quality Ti bolts for their Avid brakes, you pay a little more but the quality is evident when you inspect them carefully

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