Crushed spark plugs and car windscreens

[Bassnut (Fred)]

Today I was stunned by this connection.

Its not new, been a problem known from about 2003 apparently.

My Son tried to buy a spark plug today. Minors cant (along with paint spray cans). WTF !, below is the reason.

If you crush a spark plug, and casually toss the resulting white ceramic shards at a windscreen, it explosively destroys it .
Its become a huge problem with vandals and car thieves.

Apparently, spark plug ceramic is harder than glass, so on contact causes a small crack and a stress release that blows the window to bits.

There are many utube videos that show this effect, its stunning.

Who would have thought of trying this to start with .

Im guessing this would only occur with stressed glass, not game to test it.

Edit: http://en.wikipedia.org/wiki/Ninja_rocks

[Jen]

wow thats just crazy
http://www.youtube.com/watch?v=wUgsi9gQBeA

[koputai (Jason)]

"explosively destroys"? What about the glass being laminated to prevent this? Sounds like an urban legend to me.

Cheers,
Jason.

[Bassnut (Fred)]

Look at Jens post, duh.
Although ive seen other videos that destroy but just craze the glass, they are laminated I guess.

[renormalised (Carl)]

It's not an urban legend, Jason, it's a fact of physics. You're basically throwing sapphire at the glass (it's a ceramic of Al2O3, which is corundum=sapphire) and the tempered glass that they use in windscreens is tough but the high tension under which it's put when tempered makes it susceptible to shattering if it's cracked. Sapphire is much harder than glass (9 c.f 6.5 in hardness) and it only has to create a tiny crack in the glass...the tempering does the rest of the job.

[Barrykgerdes]

When I worked in the motor industry 50 years ago spark plugs wore out? at about 10000 miles. I haven't changed a spark plug in in any of my cars since 1985. I have checked them many times but not even bothered to clean them. Most of the reason is the technology improvement in insulators and the contacts. I don't wonder at the hardness of the ceramics.

Barry

[GrahamL]

Arn't all side and rear windows made of tempered glass so in the case of an accident they break easily into small pieces or can be broken without much effort to get people out ? I'm sure I've read of a couple small ball bearings being able to do this to .,,, so this means now spark plugs are are locked up with all the naughty paint behind bars ,, when will it end ?

Windscreens are all laminated these days afaik and would stay intact like there suposed to, mine did when a lump of concrete was chucked at it @ 100k.

[The_bluester (Paul)]

Yup. Hunting around now on sites like Snopes, but I can not see crushed spark plug insulator doing anything much to windscreen glass in a laminated screen anyway. Just not enough mass. Given that I have worn a couple of rocks the size of golf balls and larger at 100kmh in my time and come out without even a chip.

Have also seen firies showing the difference between breaking a side window (With a special impact tool they use for the job, I suspect it is an auto centre punch for sheet metal work but did not get a good look) On a standard window, one click and the window as diamonds in the seat. On a tinted window it made a bullseye chip after a couple of shots. On a laminated windscreen, thunk, thunk, thunk, thunk. That was it. They are designed to take some pretty huge forces in that direction (They are part of the structure of the car itself)

For a laminated screen anyway, it sounds like an urban legend to me.

Edit: Now looked at the youtube link posted by Jen. Side windows are tempered glass where windscreens are not (Not in Australia anyway, not sure when laminated glass became mandatory in new cars, but it would have been in the 80's)

Something like that happening is exactly why safety glass windscreens went the way of the dinosaur.

[marki]

Yep won't break the laminate, only the side and rear windows which are tempered. Still never seen a thief break in through the windscreen

Mark

[SkyViking (Rolf)]

Very very interesting. I had my car broken into a couple of years ago, while it was parked in the carport right outside the house.
The left side window was shattered to bits and now I know why I never heard a thing. They must have been using this trick.

[Ric]

I'd never heard of that until now, you live and learn.

I also never heard of that law where kids can't buy sparkplugs. As kids we were always buying them for our two stroke trail bikes. A sign of the times no doubt.

[multiweb (Marc)]

Originally Posted by Ric

As kids we were always buying them for our two stroke trail bikes. A sign of the times no doubt.

My brother and myself used to go and buy cigarettes for my Dad from the news agent around the corner when we were 7 or 8. No questions asked. Yeah, times change for sure.

[leon]

Hmmm, maybe you should have said nothing Fred, I would not have had a clue, but now am curious to see this happen, as I expect may others.


Not that I would be trying it.

Leon

[AstralTraveller (David)]

Originally Posted by leon

Hmmm, maybe you should have said nothing Fred, I would not have had a clue, but now am curious to see this happen, as I expect may others.


Not that I would be trying it.

Leon

I sort of agree but I'm also thinking, as a car owner, that fore-wrned is fore-armed - though I'm not sure what practical steps I can take.

[TrevorW]

tint you windows the film may stop the effect from happening or at least hold the glass together

[stephenb (Stephen)]

So, we have to put spark plugs in the category of "objects used for a purpose other than which they are designed for"? (including spray cans, balaclavas, baseball bats)