Focus Pinky..focus! (1 Viewer)

[Jay H]

Just pondering here at work (why am I here?) where nobody is in and just kind of killing time before those that are here head out to H**ters for lunch...
Say you have a glass door, how hot do you think it has to get outside and how cold does it have to be inside before the glass warps and shatters? Obviously outside the operational temps but say the heat gradually increases while the inside temp gradually cools, would the glass warp or shatter into thousands of pieces or just melt or what?
Just keeping the brain juices flowing on a mindless hot day by NYC...
Narf!
Jay

 

[Bill Catherall]

How was the glass formed? Was it rolled, poured...? Is it tempered? How thick is it? How pure is it?
But all that really doesn't matter because the glass won't warp or shatter. Assuming it's a solid piece then the only thing that would cause it to shatter would be stress from the frame holding the glass. It wouldn't shatter just from a heat differential. Sure, only one side of the glass is being heated, but the temperature of the glass will stay fairly uniform throughout. What difference there is from one side to the other is almost negligible. Certainly not enough to cause warping or shattering.
The only possible heat induced destruction for your glass panel (not taking into account any stress from the frame) is melting (actually softening, glass doesn't melt). Or if it were really hot outside you could throw some cold water on it and watch it shatter.

 

[Philip_G]

a differential from -40 outside to 75 inside won't shatter it

 

[Jay H]

Yeah, lets say the earth is heading to crash into the sun and outside the temperature is getting superhot, the closer you get to say melting stuff. Because the company I work likes to make it absolutely freezing in here, I'm just wondering if say the bodies working today, oblivious to the earth's impending doom, and because tomorrow is a holiday, many of the heat-producing bodies are out so it's even that much colder in here, say the A/C goes on overdrive and it just gets colder and colder. Due to a butterfly in China, the temps drop below 0°F and get colder and colder..

The glass would be standard door glass, not double paned, about perhaps 1/4" thick. Enough that I can put my hand on the glass and feel how hot it is outside, while I have two lab ESD coats on just to keep my blood from freezing in here.

Jay

 

[Dave Poehlman]

I thought I remember reading someplace or someone told me that glass in its "solid" form is still actually liquid. Apparently, windows were studied in ancient castles and buildings and it was found that the glass was thicker at the bottom of the pane than at the top due to the glass slowly pulling downwards over time.

Is there any truth to this or was someone just blowing smoke up my glass?

 

[Kyle Richardson]

Philip, I'm just sorry to hear that you know that as a fact by living in ND.

 

[Bill Catherall]

Enough that I can put my hand on the glass and feel how hot it is outside...

That's just the thing. The glass will be almost uniform in temperature. The glass is solid and conducts heat. That's how you can feel how hot it is outside through the glass. While one side of the glass is exposed to heat it obsorbes the heat from the sun through radiation (and some conduction/convection with the outside air). Inside the glass the heat is being evenly distributed by conduction. And the indoor side of the glass is radiating heat out to the cooler room (and some conduction/convection with the indoor air). The glass, being only 1/4" thick will remain fairly uniform throughout. The thicker the glass, the greater the temperature variation from one side to the other.

But temperature variation doesn't cause glass to warp and fracture. The hot part will just become really soft while the cool part remains ridged. Put a glass rod into a flame and watch the tip in the flame turn red hot and get soft. But the cool part in your hand stays ridged. There's a high temperature gradient from the hot part to the soft part, but there is no fracturing.

The only way to get glass to fracture through temperature changes is to heat or cool it rapidly. Pull that red hot glass out of the flame and plunge it into a glass of cold water and watch it break. Or pull a glass jar out of the refrigerator and drop it into boiling water (ask anybody who's done canning about that one).

 

[Charles J P]

The only thing that would shatter the glass would be a sudden change in temperature. Like if you heated it to 300 degrees F and then splashed a 5 gallon bucket of ice water on it or vice versa. It would not matter how cold it got because it would just freeze. It would not matter how hot it got up until the point it melted. The point Bill is trying to make is, if its 100 C outside and 0 C inside, the glass will be 50 degrees C, and glass most certainly would not shatter at 50 degrees C.

 

[Philip_G]

Philip, I'm just sorry to hear that you know that as a fact by living in ND.

lol. well my apartment has a large glass sliding door, and occasionally it gets down to -30 -40 ambient (not too often though) the cool thing is when the door ices up and you can't open it.
actually today I was contemplating the humidity up here in the summer, it's been so humid that if I go into the grocery store with my sunglasses off, when I leave they fog up
the winter here is a dry cold, so it's OK haha

 

[Paul_Fisher]

I've never heard of glass warping before.

Speaking of breaking glass, my fiance was cooking dinner a couple of months ago using a glass dish on the stove, and all of a sudden, "Bam!!", the dish blew up into 5 thousand pieces. It was scary. I was just thankful that no one got hurt.

 

[Keith Mickunas]

Dave, I think that's a myth, one that many people believe and I've heard several times. I read once that the truth to the glass being thicker at the bottom is that the process of making glass was worse back then, and they'd mount the thicker side down for some reason.

 

[Dave Poehlman]

Thanks Keith, I just found it:
An interesting site on glass.

 

[Charles J P]

Yeah, I had a glass pot explode on the stove too. Its scarry. Pyrex is oven, microwave, stove, dishwasher, etc. safe, but this wasnt Pyrex, it was just glass. It shattered and just blew the contents all over the room. We still found bits of glass until the day we moved out.

 

[BrianW]

The examples given of glass breaking as a result of temperature extremes (ice water thrown on panes of glass, etc.) don't really fit into the critera of the originally stated experiment. In these examples, the temperature differentials are across the surface of the glass, not through its thickness. If you throw ice water on a pane of hot glass, then the temperature differential exists between the middle (presumably where you threw the ice water) and the edges, not from one side of the pane to the other. This distance across the surface of a pane of glass is vast compared to its thickness, and even glass does not conduct heat quickly enough to prevent cold contraction (or heat expansion) from shattering the glass.

Perhaps a better question would be: For a particular kind of glass, what is the maximum thickness it could be and still endure a given temperature differential from one side to the other without cracking?

 

[Bill Catherall]

Perhaps a better question would be: For a particular kind of glass, what is the maximum thickness it could be and still endure a given temperature differential from one side to the other without cracking?

But glass doesn't crack due to a temperature differential. It cracks from rapid changes in temperature. The better question would be: For a particular kind and thickness of glass, what is the minimum rate of temperature change needed to cause it to crack.