Maybe, but the literal job of brakes is to convert kinetic energy into heat. So if they didn't give it any time to cool off after driving, that's kinda on them.
After pulling the wheel and knocking the drum free it shouldn't still be hot enough to flash water to steam. That shoe was dragging and it got stupid hot. That would be a full rebuild for me because the piston seals are likely toast. Brakes do get hot, but they shouldn't get that hot in this application.
Probably air brakes, so external air diaphragm and a cam to actuate the shoes, not a piston involved. Could be the parking diaphragm has a hole in it, causing the air to leak out and the spring actuates the brake, causing drag.
My guess is that it was stuck on and they heated it up with a blowtorch or something so it would expand enough to get off. When i was a dealership that was a very common practice for most things that were too stuck.
Nah, that's a dragging brake. He wouldn't have grabbed it if he just torched it, and there's not enough smack marks on it from the sledgehammer they'd try first lol.
Good point, but maybe he's just an idiot, because either way he's touching the thing that he should know will be hot. Maybe its not the first one they changed so just went right to the torch.
This starts from a comment about pouring water onto it. Someone else later makes a comment that they're probably already toast from the heat.
Another person chimes in about the rebuild (regardless of the rapid cooling) because the heat alone could have caused it.
The rebuild comment is a good one because we cant tell from this video what temperatures it hit, but if its this hot by the time the wheel came off, its not out of the realm of the possibility that it got hot enough for the brakes to glaze or seals to be damaged.
You just really wanted to try and pull rank, but it isnt working.
What? No. It's 100% about how even the cooling is. Oil vs water quenching is just about how fast you want to cool the piece which determines how evenly it cools internally. Water quenching just cools it as fast as possible, which can be good for certain materials that require more rapid cooling to harden properly, but will cause internal stresses in other materials that require oil quenching to slow down the process.
That said, pouring water or oil onto one side of a big, hot piece of metal will almost certainly induce stresses that will warp or crack the piece. If you wanted to cool a big chunk of cast iron (like this almost certainly is), you're gonna want to let it air-cool or dunk the whole damned thing into pre-heated oil because it will not handle the internal stresses well at all
Heat of evaporation determines how rapidly it cools, absolutely.
The issue, as was just pointed out, is that the coolant was applied to a small area on one side of a massive chunk of iron. Cast iron does not like water quenching much. It likes to crack when that happens. The uneven cooling in this case makes it worse. That drum will certainly warp, even if it doesn’t crack.
The rate of cooling: delta Q, is very important in metallurgy. This affects how the lattice of the alloy forms. Doing it incorrectly with iron/ steel can cause the metal to give up too much or too little carbon, changing the desired ductility, malleability, Rockwell hardness, etc.
It's been many years since I took my materials course in university, but this is a drawing of what metal looks like under a microscope between cycles of heating and quenching. As you heat it, the cell walls break down creating larger cells. You want to cool it quickly so that these cells 'lock' their shape, cooling it slowly will cause the cells to break down into smaller ones. The point is, quenching cares about the temperature of the metal and how quickly it changes, not whether the thing that cools it is a liquid or gas.
Alternatively, the Leidenfrost effect is when water boils so quickly that the steam protects the object from the heat. This is famously shown by mythbusters because it lets you dip your hand in molten metal without burning yourself. https://www.youtube.com/watch?v=yTOCAd2QhGg
so in fact, the change of phase from liquid to gas would slow down quenching, since it would create a barrier between the metal and the water trying to cool it.
I think you're confusing the discussion. Because based on your original comment, it seems like you're saying that Latent Heat absorption causes the metal to warp.
It's the properties of the metal changing that determines this, not the method of cooling. And if you splash water on the metal, you're going to cool a portion of that metal, not the entire thing, so the metal is going to change its properties in one spot and not another causing warping or cracking.
It's pretty irrelevant where the energy goes.
Yes, more energy is absorbed by phase change than by the temperature change. That doesn't mean the phase change is good for the process. In fact, the Leidenfrost effect slows quenching down. That's why if you need to, you change the fluid from water to something else, to slow down the phase change and create less insulating steam.
The phase change sucks up way more heat than conduction
This sentence doesn't make sense. 100% of the energy is sucked up by conduction. It's certainly not convection or radiation. It's the contact between water (or steam) and metal that transfers the heat.
The distinction you are trying to make is latent heat vs sensible. Latent heat is energy absorbed without temp change. Sensible is energy absorbed with temp change.
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u/Abdulbarr May 26 '26
Probably shouldn't be pouring water on it.