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explain automotive glass tempering to me.

Discussion in 'The Okie Corral' started by BEER, Jun 15, 2012.

  1. BEER

    BEER bad example

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    this is probably one of those things that's just too simple for me to see.

    if auto glass is tempered to break into tiny squarish pieces when it shatters how is it possible to get long curving cracks all the way across? i know the embedded film keeps it together until it tears and then it blows apart, but shouldn't the cracks form in jagged angular lines?
     
  2. Arquebus12

    Arquebus12 Non-broccophobe CLM

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    The windshields are laminates... they're the ones that spiderweb but remain intact for the most part. The individual panes are held together by the laminate bond, and actually resist the cracking in the first place.

    Side windows are non-laminates, and break up into cubes when struck. That's the heat treating coming into play, which pre-stresses the pane.
     

  3. janice6

    janice6 Silver Member

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    There are two types of "Safety Glass".

    One is the laminate used in front windshields that has a polymer bonded between two pieces of glass. This is to prevent gaping holes of sharp glass slicing up the front seat passengers/driver especially in front end collisions.

    Early days of cars had plate glass in the windshield and many persons were cut so severely they bled to death, after putting their head through the windshield..

    The second is "Tempered Glass" which is manufactured so that when it breaks it shatters into many tiny pieces, instantly. This is used mainly in the automobile side glass. Doors and such.
     
  4. BEER

    BEER bad example

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    ooooh, ok. that's it then, i was confusing the difference between windshields and the other glass. i just realized that i've never seen a windshield blow apart like the side windows, and i've never seen a side window crack like a windshield.

    see i knew it was something simple. got it now. thanks.
     
  5. HandyMan Hugh

    HandyMan Hugh NRA Life Member

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    IIRC (from visiting the Corning Glassworks) tempered glass is made by first shaping and making whatever holes are necessary, and then heating it to a specific temperature. At that point puffs of cooler air are aimed at the glass. this causes the outside of the glass to shrink while the inside cools more slowly. This sets strains in the glass. There is a LOT of pent up energy in this "tempered" glass. If the glass breaks, it releases the energy and granulates into dull edged particles.

    I've seen that happen up close. It's fast! When Mandalay built my motorhome, they put a retaining screw too close to the moving part of the bedroom window. ONE time I was a little too vigirous when closing the window, and the INSIDE pane of glass hit that screw. It made a kind of hissy-crackle noise as the whole pane granulated outward from the point of impact. There was no stopping it. It was done in less than 1.5 seconds. Fortunately the window frame held the broken glass in place so that we could duct tape it.