McLaren Wheel Nuts

[marcush.]

I have seen ti hubs before ..and as with aluminium Ti is not Ti .....the sparse info we have been able to drag to the surface are not going to shed light into this.

One things for sure - these systems are all fragile and show how you can get it all completely wrong in the development of a subsystem.

It´s not just material pairings ,coatings ,treatments ,it´s not just cad and calculating ,it´s not even only manufacturing tolerances , you need to understand where you can take risks and where you need to play a bit on the safe side.

mclaren is one of the teams that has shown more than once they are a bit too sure about where to draw that line -experiencing a fair amount of hub/nut related issues over the last years.

Same for Mercedes
Same for RedBull

No ways a cross thread is possible.
The problem is galling seizing with surface imperfections /foreign objects or maybe even friction welding with those high speed guns?

[xpensive]

I have seen ti hubs before ..and as with aluminium Ti is not Ti .....the sparse info we have been able to drag to the surface are not going to shed light into this.
...
The problem is galling seizing with surface imperfections /foreign objects or maybe even friction welding with those high speed guns?

It's probably Ti Gr.5 (800+ MPa yield) in the hub and Al 7000-something in the nut, none of those are very forgiving in terms of elongation, which might be a scary combo if lubrication is less than perfect.

Friction weld - I think you could have a point there marcush?

[marcush.]

the problem is .you will not stop the wheelgun do the do ...the paioli has a opening torque of over 2000NM and rpm of 14K (!)rpm

with that thread diameter that´s around 35 m/s I have calculated in the back of my head. but that´s not accounting for the incredible acceleration when the nut is broken loose and the wheel nut is accelerated to that speed -disengaging from the threads after only 4 to 6 turns... so not even 1 tenth of a second of duration from breaking loose to having the nut off the hub..
Is this enough time to start friction weld? ..I have the feeling it´s something different ..

[xpensive]

14 kRpm, holy crap, that's 1460 rad/s, what's that diameter anyway, 40 mm means 30 m/s?

Even with a liquid lubricant, resistance will be very high due to the viscous forces at 30 m/s with a thick gel/paste, which could result in xtreme local temperatures in the thread. On top of that there's the impact-load when bottoming out...ouch!

Aluminium will behave very strange at higher temperatures, full melt at 600C, and a babbitt coat will go away at 230.

Something's very wrong here, perhaps not friction-weld but local surface damage due to overheating?

[PlatinumZealot]

-convection- free or forced ?
You are releasing a huge amount of energy when doing a hot pitstop -but your claim the brakes are relying on forced convection is simply not valid when the car is stationary.I would estimate the worst case scenario is the pit stop which is not working as planned ...eg the standstill is taking longer than planned and temperatures sore ...

and :Material mismatch is sometimes very surprising...but Ti is known for this .so you don´t even try without coating ,the coating will help the surface but local stress may still move the material beneath globally and expose uncoated base or dig into the other component.

As a sideline wheelnuts look just awful after a few mounting dismaounting actions ,and all teams use big gobs of monting compounds -with solid particles- to provide a non galling protection- It all is a bit fishy ,at least for me-

I did not make any claim that forced convection is the only mechanism so don't put any words in my mouth. It's obvious that both mechanisms are acting.

When the car is at a standstill in ZERO wind it is free convection that is happening - as the natural buoyancy of the hot air rises.
While the car is moving it is forced convection. If there is also any wind it is also forced convection.


Anyway. Did you see that after the jammed wheel-nut was finally removed after a couple tries it got red hot? It was glowing like a lava stone. Now, this was due to the raw friction involved removing a cross threaded nut. It was plastically deformed - litterally wrung like plastic till the temperatures reached near melting point to remove it.

Just saying that a small temperature change whether 100*C or 200*C is not going to jam the nuts, seeing that the guys removed it even after it got red hot.

In fact nuts are usually easier to remove at elevated temperatures. My BMW has copper locking nuts on the exhaust. I changed them to stainless steel, and lo and behold the steel nuts fell off after a few days of driving. They just loosend up all by them selves and fell off. The studs were 8.8 steel.

With aluminum you would expect it to actually expand more than titanium on heating.



Here is a table of thermal expansion. You can see the thermal expansion coefficients of Ti, Al, Stainless steel etc.

http://cp.literature.agilent.com/litweb ... -90143.pdf

[hardingfv32]

I have both F1 front axle and rear axles. The front axle and all the nuts are non-magnetic. The rear axle is magnetic. The nut does not file like any aluminum I have ever worked with, but some of that could be the surface treatment.

All these materials and surface treatments have been around for many years. The issues and limitations should be well known. I would doubt that the material are becoming inferior to the past.

What is the top goal of all this pitstop activity: to reduce the length of the pitstop. What is one of the few areas that can be improved: the time required to remove and install the wheel nut. I say they are pushing the tolerance of the material surfaces with their race to install the nut faster.

Brian

[xpensive]

...
In fact nuts are usually easier to remove at elevated temperatures. My BMW has copper locking nuts on the exhaust. I changed them to stainless steel, and lo and behold the steel nuts fell off after a few days of driving. They just loosend up all by them selves and fell off. The studs were 8.8 steel.
...

I think most mechanical engineers are aware of the difference in thermal xpansion between metals, the funny thing is that austenitic stainless steel like 18.8 or 304/316 has almost xactly the same thermal xpansion coefficient as copper.

Thermal conductivity however is vastly different, with copper conveying heat 26 times better than 18.8/304/316.

[marcush.]

the copper nuts are usually self locking items ..look from above and you see them distorted a bit ...then stainless is not stainless it´s like AL -it could be pure 99% al the equal of chewing gum paper or something like 7068 ...

as X has put it stainless is conveying heat unbelieveably bad...you have to adapt to this when starting working with it as you touch your welded work and it still is sooo hot...a vast difference to steel fabrications ..let alone alumium.

But i think we should hook in about the word cross threading ...I think this is just an impossible thing with those threads.It will engage and find its way..What is happening is galling or ripping of the first thread when the wheel is not engaged onto the pegs and the nut is torqued before all thread is fully engaged.
This will start a self locking action and increase the friction dramatically.

[strad]

What is happening is galling or ripping of the first thread when the wheel is not engaged onto the pegs and the nut is torqued before all thread is fully engaged.
This will start a self locking action and increase the friction dramatically

Correct..but it is because it is or is trying to cross thread. Higbee aside I think a coarser thread could be the answer. Perhaps that's the crux right there,,That they or the supplier changed the threading on them. Is there a mismatch...SAE vs Metric?
Also I have long wondered.. In LeMans cars in particular but F1 as well you can hear (when the pits are quiet) the impact gun hammer away til the nut comes free. In NASCAR they tune the guns to tighten/torque the nuts just enough with the purpose being that the gun doesn't take as long to undo an over tightened nut.
It seems to me that these days in F1 they may have gone from high torque guns to a high speed gun..Perhaps so fast that it creates too much heat simply from spinning the nut that fast as has been said, without lube. Plus when it slams home at those RPMs it could distort the thread.
Perhaps some molybdenum coating?

[xpensive]

...
Correct..but it is because it is or is trying to cross thread. Higbee aside I think a coarser thread could be the answer. Perhaps that's the crux right there,,That they or the supplier changed the threading on them. Is there a mismatch...SAE vs Metric?
Also I have long wondered..
...

I believe the thread is carefully specified by McLaren in this case and once you've seen one of those nuts, there was images of a Super Aguri nut on another nut-thread some time ago, I think you will agree that cross-threading is practically impossible.

I agree with marcush that the speed and impact of that gun is the culprit, in combination with Ti vs Al in the thread, that doesn't sound right to me anyway.

But why do you want a Ti hub in the first place, weight savings is one thing, but could it also have something to do with heat transfer, where Ti alloy has a thermal conductivity of some 6 W/m*K, while carbon steel is almost 10 times that?

Edit: On the F2012 thread there are comparative images between Ferrari and McLaren wheel-nut threads, like day and nite,
having seen that I can very much understand McLaren's problems, looks like a regular m-thread, doesn't it?

[marcush.]

also something to ask yourself:

you may be used to changing wheelnuts but what about the hub thread? how deep are you going into inspection after Q3 ,when you have already performed at least 4 times do undo cyles....

One faulty nut-and your hub has an issue creeping up potentially..with parc ferme ruling it seems entirely possible teams just have not enough access to be 100% sure these things are in check.

Mercedes had issues right at the start of the race before introducing their current system,right?



what´s goimng on with debris trapped into the thread system at the speed and impact ? I think weak(ened) base materials (due to temp) are not a good idea ..

[xpensive]

Personally, I believe that image on the Ferrari F2012-thread closes the case, what an odd thread design for a wheel-nut?

[strad]

I believe the thread is carefully specified by McLaren in this case

Look at the picture...It's a standard thread.

[xpensive]

I believe the thread is carefully specified by McLaren in this case

Look at the picture...It's a standard thread.

I think that's what I concluded a few posts ago, remarkable, you might be right on the money with cross-threading strad.

[Crucial_Xtreme]

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