Tempered IGU glass flatness spec
tdbaugha
| Posted in General Questions on
Hello,
Can anyone tell me what the glass flatness spec is for cardinal glass, specifically tempered? I’m looking at you Oberon. I’m seeing ASTM C 1048. 1/32” per foot plus 1/32”. So maximum out flatness spec in 6’ of glass would be 0.219”. Am I reading this correctly?
Thanks
Tory
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are you asking because it tempered naturally looks wavy/distorted? this can be really apparent as size goes up.
i can't answer your question but i have a ~75x83" sliding door and 2 36x84 windows with tempered glass from cardinal and its so distorted looking when viewed from the outside :\
my 24x36 window with tempered on the outside looks pretty flat from the outside, while 36x60 starts to look a little "off".
I think the spec is not cumulative. I bought 8 ~6x3 foot cardinal tempered IGUS and they had no such deviation.
Hopefully, any glass produced with have no bow or distortion, that's always the goal.
Same question as cs55, are you looking for a specification for glass distortion, or for bow, or something else?
The 1/32" +1/32" is a Cardinal spec for glass bow and does not relate to glass distortion. The ASTM 1048 has a chart for allowable bow that does match the 1/32" spec for some thicknesses and sizes but not all.
People are generally surprised to find out that there is no industry spec for tempered glass distortion because it's so subjective. What might be absolutely unacceptable to one person might be perfectly fine to someone else. Unless something has changed in the recent past, no one has come up with a method of quantifying what's acceptable and what's not.
The most common type of tempered glass distortion is known as roll-wave, and roll-wave can be measured and quantified depending on the measurements and whatever the manufacturer allows. Tempering lines that are equipped to measure roll-wave will have a laser measuring system installed at the end of the line that will give the operator both a numerical and a visual display of glass flatness. Roll-wave distortion is measured and displayed in millidiopters and the system can be set up to alert in any glass coming down the line that isn't within parameters.
Cardinal has in the neighborhood of about 60 tempering lines throughout the system and they range from - no longer state-of-the-art and are likely planned for replacement - to absolutely top-of-the-line brand new furnaces. Flat and distortion-free tempered glass used to be as much about the skill of the operator as well as the quality of the equipment, but the newer furnaces are so automated that operator skill is no longer what it used to be.
And after all that I realized I didn't answer your original question.....yes, a 6' sheet of tempered glass has an allowable bow spec of 7/32" or .219" using the 1/32" + 1/32" rule . You did read it right.
does speccing thicker tempered glass alleviate any of the typical problems?
Yep, that's one of the main reasons why thicker glass is required for larger sizes
Think of shower doors or glass walls and doors in shopping centers or offices. Not much of any bow in those, although visible distortion can be pretty bad some times in commercial tempered glass windows walls.
welp, live and learn
the larger windows met all of the requirements for safety glass and the doors a door..
did 7mm laminated for interior and tempered exterior. i didnt specify a size and i guess i got the thinnest possible. the dang glass flexes when i tap on it. weirds me out even if its normal.
while the laminated has a nice solid thud to it, doesnt move and doesnt look distorted.
for a 48x60 window did laminated inside and out, no distortion on it either. much nicer. minus the $ and weight.
A quick read of the ASTM spec shows that you're probably fairly close, but the allowable tolerance varies based on the size of the pane AND the thickness of the glass (reference pages 4 and 5 here: https://elitesafetyglass.com/wp-content/uploads/2021/04/ASTM-C1048-Standard-Specification-for-Heat-Treated-Flat-Glass.pdf)
9.4.1 says there won't be more than 1/16" of "localized warp" in any 12 inch span.
11.6 is probably most pertinent here, and it describes a method to place the pane horizontally (for the thicknesses likely to be used in a window of this size), then to use that "alternate method" and read from Table 2 on page 5, which says for a pane with edge dimension range of 71-83 inches, maximum bow and warp should not exceed 0.24".
I'd take that to mean a TOTAL (note plus or minus, due to the measurement methodology) of just shy of a quarter of an inch over the entirety of the pane, and not more than 1/16" in any 12" span (per 9.4.1 mentioned earlier).
Any manufacturer that claims to meet this ASTM standard should have similar specifications for their glass.
Bill
Thanks for everyone’s input and information. I ended up buying my windows from Europe. Some of which are fairly large triple pane IGU’s (50 - 65 sqft) and the big units are almost perfectly flat. There are some medium sized units that are bowed, but within the European spec EN 12150 which is 3mm/m. They are like 2.4 and 2.8mm per meter and I was disappointed to learn that this is normal. Then I have a swing door that’s giving me fits. Its glass is bowed 3.7mm / m. I brought this up with the importer and am waiting to hear back about replacement or if I’m SOL. Here’s a handy article about glass tolerances: https://www.glastroesch.com/fileadmin/user_upload/Service/Fachwissen/Toleranzhandbuch/Sanco_Toleranzenhandbuch_EN_02_2022.pdf
So basically I was trying to see if this is normal here in the states and it sounds like it is.
For what it’s worth, 2 years ago I was looking into other products which used IGU’s from garibaldi in Vancouver. The salesmen said their internal flatness spec is 1/2 the industry standard. I didn’t think much of it at the time because I thought glass was flat anyways! lol.
Sorry to hear that you have to deal with those issues. Quality specifications are like codes - the minimum requirement - not something to shoot for.
At the same time, I would probably take the comment from the garibaldi rep with a grain of salt.
You probably already did this, but if you haven't try converting 3mm/m into fraction-inches per foot and compare result with 1/32" spec.
Yeah it’s essentially the same. The astm spec is 1/32” per foot plus 1/32”. So there’s more tolerance in the astm spec over short distances, and lesser over long distances.
What I find interesting is the fact that the big pieces are nearly perfectly flat while the small ones are bowed. It’s like you mentioned, probably the best equipment and operators run large tempering pieces. The small pieces probably don’t get as much care. Hopefully the mfg replaces the IGU.
Are those specs for tempered glass or IGU's?
I cannot imagine the IGUs would vary that much, you would not be able to build a window
Hell it would be hard to build an igu with metal spacers that varies that much
Tempered glass. Annealed has different specs I believe. But individual pieces of tempered glass are used to assemble an IGU.
The specs in the standard are worst case. This is a pass/fail type of system here, so worse than the standard specifies and the product fails, and doesn't meet the standard. ANYTHING as good or better than the specs in the standard passes. I think most stuff is quite a bit better than it says in that standard document, just going by observation and no actual measurements on my part. I don't normally put metal straight edges against window glass after all :-)
I think you'll find that the glass is generally much better than that standard says it could be, but you'll not get anyone to guarantee anything better than the standard's specified tolerances.
Bill
Yeah some pieces are bowed but surprisingly within tolerance. One is out of spec that I have found so far.
Aluminum is softer than glass so I was in the clear!
Update: turns out 90% of the bow in the glass was caused by the sun. I went to the project early today before the sun heated the glass and it was almost perfectly flat. These hermetically sealed IGU’s cause the glass to bow out due to the expanding gas trapped inside. You don’t see that as dramatically with North American windows since they have breather tubes. Learned something new today.
This issue comes up with people installing windows at high altitudes too. I think it's Alpen that specifically talks about this, which makes sense since they're outside of Denver.
Bill