|Scrapers & Fabricating Debris Issues - Revised 1/17/07|
Window cleaners: This article will help you and your customers
understand the problems presented by fabricating debris on some heat treated
glass, and why you need to have a fabricating debris damage liability waiver
signed before you scrape tempered glass.
This update contains several clarifications, including the statement that "The incidence of fabricating debris is greatly minimized when temperers adhere to all recommended maintenance procedures for washers, rollers and other tempering equipment."
Print copies and show it to builders. Help them realize why they should insist on quality tempered glass - that can be scraped - and why they need to sign your waiver.
encouraged to manage fabricating debris as a manufacturing defect on
some of the tempered glass they are getting, and address this issue with
their suppliers. We've been urging fabricators to test their own glass for this problem
IWCA Seminar on Fabricating
Debris Awareness - 2007
Dan Fields, a highly regarded
expert on the subject, presented a seminar called "Fabricating Debris
Awareness" February 2007 at the IWCA Convention.
IWCA Seminar on Glass
Fabrication & Processes - 2005
Click here for Gary Mauer's article about the tour & seminar
The day after a tour of the local Arch
Aluminum & Glass
tempering facility - during their 2005 convention in Orlando - the IWCA
recorded a very interesting discussion about how hard these fabricators worked
to produce better quality tempered glass for their customers.
This seminar was recorded by IWCA - but no longer sold
Partnering with the Glass Fabricating Industry
International Glass Review is no longer in publication - links to articles are no longer active.
|This 2002 International Glass Review
article by the leading supplier of furnace rollers points out they offer
"free seminars to customers focusing on roller properties, cleaning and
maintenance procedures, roller refurbishing and regrinding options and
precautions, the effects of the plant environment and fabricating practices
on tempered glass."
They also offer laboratory analysis as a free service to their clients, to properly identify "glass surface conditions or markings".
At one point, this article says, "Most often the conditions that appear on glass surfaces during the heat treating process are related to foreign materials that have been mechanically impinged into the glass or that has damage the glass as it passes over the rollers. "
An illustrated article from the
2001 International Glass Review entitled,
This article also discusses issues
related to tempered glass quality from the perspective of the roller
manufacturer, and advocates good housekeeping and good fabricating practices. At one point, this article says, "Glass dust and debris deposited on the furnace rollers can be picked up by the glass."
There are several color photos.
Temper Temper Article in
Glass Magazine (broken links)
Managing the Problems Inherent in Tempered Glass; By: Regina R. Johnson
|This 1998 US Glass Magazine article says in part that "particles such as glass fines from the cutting edging process and handling smudges that are not washed off the surface of glass before tempering will bake on to the surface, causing blemishes..... described throughout the industry by various names, including "orange peel," "heat prickling," "seeds," "bubbles," or just plain "garbage" that was not washed off prior to the glass entering the tempering furnace. During normal window cleaning after building construction, the pimples can be scraped off and the dragged across the glass surface, causing scratches"|
6/99 Maximizing Ceramic Furnace Roll Performance
(find this link on Resources page.)
By Renald D Bartoe, Frederick Caillaud, Dr. John Dodsworth and Jerry Osele
|The authors of this 1999 US Glass Magazine article identify glass fines and other surface deposits as defects. The article underlines the importance of plant cleanliness, roller & furnace cleanliness and maintenance, dust control, and states that "Effective use of the glass washer is critical to every tempering operation. The glass should be washed just prior to tempering... The glass washer must be operating properly with the detergents, brushes and rinse water at the manufacturer's recommended settings. Maintenance of the glass washer is equally important to ensure the glass is clean and without residue or debris that will be carried into the furnace... "|
Bulletins by GANA - (Glass Association of North America)
Procedures for Cleaning Architectural Glass Products
Glass Association of North America
bulletin is often interpreted as a "ban" on scrapers.
clearly does not condone or recommend scrapers, and scraping is not
considered a "normal cleaning procedure" by
This bulletin claims that "widespread" use
of scrapers will "often" damage glass.
Treated Glass Surfaces are Different
Glass Association of North America
to the presence of fabricating debris as a "surface condition"
- agrees that fabricating debris may be present on some tempered glass, and also
scraping can result in damage, "if any microscopic particles have adhered to the surface".
It does not, however, address the variable presence of fabricating debris. On most tempered glass, one side is fine, and the other side may or may not have fabricating debris. There is no explanation for why that occurs, or what is being done about it.
The truth is that proper maintenance in the tempering plant yields a better tempered glass surface - but this GANA bulletin doesn't mention that.
There is also the
suggestion that ASTM standards allow the presence of fabricating debris, which suggests that builders have no choice but to accept tempered
glass. However, the ASTM C 1036 standard contains disclaimers which seem to contradict
that - and clearly,
the ASTM standard does not actually state that detectable fabricating debris is
A window cleaner's view would probably be that most of those "millions upon millions of square feet of glass" have in fact felt a scraper - with no ill effect, because there was no fabricating debris problem. Scraper use among window cleaners is widespread - nearly universal. Window cleaning scrapers are offered by every major squeegee manufacturer, and sold by every major window cleaning supply house.
6 second audio clip - recorded by Gary Mauer
You can often detect
fabricating debris on
tempered glass by running a scraper lightly
over the surface. However, hearing this sound does not prove the glass
will be scratched. (Some fabricating debris won't budge.)
A microphone was attached to a scraper..... the scraper was placed on a piece of tempered glass, pushed a short way, then lifted and placed on a nearby piece of tempered glass which was loaded with fabricating debris and pushed again - lightly, so as not to scratch the glass.
The smooth surface that you hear first would have been the top side when that particular piece of glass was tempered, and the rough surface you hear next was the bottom - the side that was touching rollers when that particular piece of glass passed through the tempering oven.
The tinkling sound you hear is little glass fines and other fabricating debris. This is the "tinkle test".... If you've never heard this before, you'll be impressed - or maybe you'll think we faked it.
Caution - Fabricating debris is variable, and this is a more extreme example. It won't always sound this bad, and you cannot count on feeling or hearing this surface defect while you are working - particularly on a messy construction site. It is also important to realize that hearing this sound does not prove the glass will be scratched. (Some fabricating debris won't budge.)
Mohs Hardness scale at About.com
This and other Mohs hardness scale web pages rank glass and blades at about the same hardness. Unfortunately, most Mohs hardness scale web pages are written by and for gemologists. Those which do mention glass and blades are similar in hardness tend to mention the fact only in passing.