heel2toe

iTrader: (41)

Is that a fact? I thought it was the exact opposite? Why is it when people are Tig welding AL they will often times preheat the metal with an oxy torch prior to welding so it doesnt burn through? I thought thats bc AL heats up slower and it pulls the heat out so quickly?

Now Im even more confused

LetsGetThisDone

iTrader: (1)

Heat exchangers aren't trying to block heat, they're trying to dissipate it. My thinking on these shields was that I was trying to block heat from reaching the balljoint boots.

heel2toe

iTrader: (41)

Do you really think there is going to be a temperate differential on the 2 sides of the heat shield? The gold foil will act to reflect the heat sure but I dont see a shield blocking the heat on one side such that the other side is cool. I guess the idea is that its absorbing the heat instead of allowing it to pass through to the BJ? But in that case it the SS is absorbing the heat and not dissipating it then wont that now no longer be shielded as it will start to radiate the heat to the BJ?

kaj

iTrader: (60)

Aluminim radiators are usually due to weight savings from what I'm told. The old copper ones are better, but heavy. Copper is closer to Al than SS on the therm conductivity scale, FWIW.
I was told Al top hats on brake rotors transfer less heat to hub assys.
I'm no an engineer nor chemist, so I'd have to research it.
I sometimes confuse Specific Heat Capacity with conductivity LOL

heel2toe

iTrader: (41)

Yes, I agree 100% with that last statement. But can you really block the heat? Once the SS absorbs the heat whats stopping it from radiating to the boot?

I dont wanna go completely off topic but how to the Ti brake shields work? Its almost like then ned to absorb and then dissipate immediately so the pistons dont get hot which in turn doesnt boil the fluid.

LetsGetThisDone

iTrader: (1)

Damnit, I'm all wrong...HAHA. Aluminum has a higher specific heat than stainless steel. WTF...lol

LetsGetThisDone

iTrader: (1)

Looks like if I ever start ballin again I'm gonna order a sheet of Ti from McMaster-Carr and redo these heat shields...

kaj

iTrader: (60)

That's where I looked first...then settled on Al. LOL

I'm not even sure if my nibbler would cut Ti......?

V.8MR

iTrader: (6)

The issue is heat radiation. Not conduction or convection.

There will be no physical contact to the rotor and the shield so no conduction, convection is a non issue due to the airflow.

So as far as radiation, we are blocking infrared light. As I read, you can think of radiated heat like a heat lamp. The radiated heat is not affected by air etc. Its "light" if you will. So realistically, either material will work in this regard. SS has less conductivity of heat thus the heat will not pass through it. Temp differential on the heated side vs non heated side where as aluminum will efficiently transfer the heat from 1 side to the other(which is why its good for radiators and heat sinks).


But I'm no engineer haha so I could be dead wrong

kaj

iTrader: (60)

so it's a wash and we can go with what's cheapest. woohoo



Thinking about it.....
​Steel makes sense, though. Our cars have steel heat shields everywhere. As mentioned above, aluminum is good for drawing in and dissipating heat, which Is different than blocking it. The parts aren't touching, so no heat sink needed.
Space in between = block heat. Not trying to reduce it. I.E. Exaust heat shield.
Parts touching = absorb and radiate heat to reduce it. I.E. Radiator.

Right? LOL

V.8MR

iTrader: (6)

3 ways to move heat

Radiated: Think infrared light.
Convection: Heating surrounding air and thus anything the air contacts.
Conduction: Similar to electrical conduction, requires physical contact.

kaj

iTrader: (60)

Correct. I'm referring to the efficiency of different metals in protecting against those methods.

V.8MR

iTrader: (6)

The only one which would be able to melt the ball-joint boot is radiated in this case.

A good analogy is when sitting around a camp fire. You raise your hand to shield your face from the radiating heat of the fire. It doesn't matter what your hand is made of so long as it blocks infrared from passing through it. Just need to block the "light" from the source.

The other 2 methods don't come into play. The shield makes no contact with the rotor for conductive heat. And there is ample air flow to prevent convection in any meaningful sense.

heel2toe

iTrader: (41)

Lol no #evoguru for you!

So I was thinking about this last night and had a similar thought about how OEM uses steel for almost all of the heatshields. Lets think about the actual brake rotor heat shield as it seems to be the best comparison. Yes that is steel but why did they use steel vs any other material? You cant definitely say they did that because it works the best. Maybe it is more durable which was important? We know that to be true relative to Aluminum. Maybe it had to do with costs? Maybe steel is just easier to work with? There are a lot of reasons why they may have choose steel vs AL in those situations.

But to say its a wash doesnt seem like an acceptable answer in my mind. One must be better than the other for one reason or another.

Yes, agreed, well we can add induction to the mix as well but both induction and conduction are not how the ehat is being transferred in this case.

I think the heat is being transferred via convection but we may disagree on that too

And this once again is the million dollar question. What is a better material for blocking the heat? Remember in this scenario there is no physical contact. The more I think about it the more it seems using heat reflective tape seems to make the most sense. But that is not the question.

So lets break this down. Same shape size distance exposed to the same heat source we agree that the AL will take longer to heat up vs SS. The AL will also cool down much quicker relative to the SS. However Im not sure cooling down faster even matters if you think about it as were looking for heat protection during operation. So who cares how quickly it cools down; it's irrelevant.

If AL heats up slower than so far I'd say it's in the lead here. However its not that simple because while it may take longer to heat up thats only giving you a said window of extra protection which is good but isnt the whole story. So what happens once they are both at the same temperature? Its the AL or the SS transferring the energy to the boots at the same rate now? I think since the SS will hold the heat it wont transfer as much to the boot. So now Im thinking that SS might actually be preferred

But at the same time if its holding the heat vs dissipating it into the air then itsnt it now radiating that heat all around it thus heating up the boot?

Im still extremely confused here. I always thought for these heat shields AL was the preferred choice but never thought much of it. Now that Im trying to break it down Im beyond confused and seems the more I know the more I realize that I don't know.

nollij

iTrader: (21)

Preheat aluminum to make it require less initial amps from the welder to get the weld to puddle/penetrate. Otherwise, you sit there trying to get the weld to puddle up while all you are doing is heating up your material and your welding machine is crying at you and your tungsten is balling up.

Aluminum radiates heat throughout the metal very well compared to other metals. You weld aluminum and you are heating the entire piece. You weld steel and the heat stays near the Heat Affected Zone (relatively).

If you want a heat shield, Titanium is best followed by steels. Aluminum and copper do not make good heat shields.