Tire Pyrolysis (vid worth watching)

[ChrisCo]

Shamelessly stolen from NWW. Worth your time to watch it if you're new to fabbin' junk...

YouTube- Wheels of Fire Training Video

[Gabriul]

I don't understand how it can ignite the tire...?? Wouldn't this be the same as stepping on the brakes?? What causes the tire to ignite??

[nwx]

Wow..

[Racinkid13]

Passed that link around to a few friends. Interesting.

[Gabriul]

So, after researching pyrolysis last night untill 1...

I still don't understand how radiant heat from the rim (from a short burst of welding) can cause the chain of destruction that causes the tire to explode. If the rims exterior only heats up 5 degrees...how does it ignite the organic rubber?

I could understand if the electrical field got into the steel belts, internal combustion, boom.

But, to me it seems like the brake drums on big rigs would heat up the tires more than that 3 second burst of welding.

[nwx]

What makes you think the the outside of the rim only heats by 5 degrees after a short bit of welding (6500°) link to Lincon
I referenced arc welding as that was the example given. Rims are a thin material and it would conduct the heat over a greater area. I'll bet the heat at the tire raises substantially more than 5 degrees.
Very interesting deal regardless. Scary how the chain reaction occurs in the minutes following the welding and the end result is so violent.

[Gabriul]

6500 at the weld area, dissipated over that large of an area of the rim.

Anyway, the air temp stayed down at 68 or so degrees for 3 minutes. Only in the last few seconds does the air temp rise.

I'm just still very confused. Thats all.

I for sure am not arguing that its a problem, just trying to get a grasp on how the chain reaction starts. Once started, I know where it can go!!

[ChrisCo]

From Page 5 of this PDF:

Pyrolysis is defined as the irreversible chemical decomposition of a material under the sole action of heat.

In the case of a tire, degradation of the rubber takes place. This phenomenon occurs:

• when the temperature inside the tire reaches 185°C
• in the absence of oxygen (inflation with nitrogen does not eliminate the phenomenon of pyrolysis)
• in a few seconds.

The next page notes that it can start as low as 100°C. That's only about 212°F. That's really not all that hot, considerign that steel starts turning yellow hot around 420°F. Steel doesn't even start changing color yet at just 212°F.

I'd heard about welding on tires causing them to explode, but I hadn't ever heard the details of it before now. Very interesting, to say the least.

[Gabriul]

Yes yes, I read up on the process...and I understand the process.

However, i still am having trouble with the heat and cooling of a rim that is that large.... I might have to go weld on a rim WITHOUT A TIRE and see how warm the edges get.

[leftcoaster]

wow good info.. I didnt know this could happen.