The old saying is absolutely true...You do learn something new every day!
Last week I wrote a story about cleaning the new windows in our house. The story closed with a plug for GANA's window cleaning procedure. After all, I am in the glass industry, and GANA is the loudest and most knowledgeable voice in our industry. I have always, and still do believe, that if GANA's technical committee publishes a standard or procedure it is correct.
Here is what I learned...A gentleman named Gary Mauer sent a couple of replies to that post, with a couple of good questions. I thought back and did not ever remember coming in contact with Mr. Mauer. Who was he? I looked at his e-mail address on his note, www.window-cleaning.net and my learning for the day started.
This is an association of professional window cleaners. There was a lot of vendor info and a couple of technical papers. I read one on 'tempering debris' and why poorly cleaned and maintained tempering ovens can cause dust to be baked on the glass during tempering. When this glass is cleaned in the field these microscopic particles dislodge and these particles are the cause of the scratches, not the razor blade or paint scraper in the hand of the window cleaner.
The writer of the paper goes on to say that he disclaims scratches in any event on any tempered glass.
What a fascinating thought this is. I looked at our industry from the other side and found that we are not perfect. This truly was an "AHA" moment for me. Sure, I had customers want to remake glass because of problems, but that came from glass shops in my industry. I had never looked from the outside in.
I remember many times my tempering managers shut down one of our ovens for cleaning because of specks in the oven. I never thought of the results of not cleaning, as we always did clean. I imagine there are temperers who do not clean often enough and produce glass with embedded debris.
I don't agree with the web site that all scratches on tempered glass come from this problem, but it sure was interesting seeing the other side of the coin.
Mr. Mauer certainly did me a favor by taking the time to write his note. Thank you Gary Mauer for showing this old dog a new trick.
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1 comment:
Paul,
Thanks for the kind words.
>>>I don't agree with the web site that all scratches on tempered glass come from this problem...<<<
I wouldn't agree either, but I don't think that is quite what we're saying.
The typical heat treated glass scratch waiver does cover all scratches to heat treated glass, but the reality is that when only the heat treated glass is scratched - and not the nearby annealed glass - the most likely cause will be fabricating debris defects.
(Especially if only the roller side of tempered glass is scratched.)
The waiver typically covers all scratches on heat treated glass, because if the cleaner was still forced to provide forensic evidence of microscopic defects in every instance, the waiver would be moot.
As for fabricating debris defects; if you get a chance, read Ren Bartoe's 1999 article, "Maximizing Ceramic Furnace Roll Performance" published in US Glass and at Glass Performance Days '99 in Finland.
This is a link to the intro page at glassfiles.com
http://www.glassfiles.com/library/24/article176.htm
This article is available in the USGlass magazine archives, as well.
In this and other articles and seminars throughout the years, Mr Bartoe uses the word defect, stresses sound tempering practices including cleanliness and washer maintenance that keep the debris out of the furnace in the first place.
Bartoe points out that "Defects in tempered glass can usually be identified, isolated and resolved the use of optical microscopy, scanning electron microscopy and energy dispersive spectroscopy."
In other words, forensics can usually determine the real source of the problem.
And I would add that if poor quality heat treated glass is scratched during cleaning, we now have the ability to use optical microscopy to identify fabricating debris scratches by their unique characteristics.
This sure is an interesting topic, isn't it?
Thanks,
Gary Mauer
Window Cleaning Network
www.window-cleaning.net
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