Ask The Doctor
pros who know
Thermal Cycling Resin Testing
by Richard Campfield
Field tests of windshield repair resins are much more accurate than lab
tests. The problem with field tests is that it takes one year in a four-season
climate using an un-garaged vehicle to get a read on the resin’s performance
in the real world. The Repair of Laminated Automotive Glass Standard (ROLAGS™)
Resistance to Thermal Cycling test is a custom-made windshield repair
resin test that mimics the field test, but can be done in one day.
In the late 1980s, I started a mobile service windshield repair business
in Southern California. I repaired damage that others could not. I did
not have a problem with filling these breaks and cracks completely and
made them look great. I thought everything was just fine. Then something
happened that rarely happens in South California. We got a frost. An ice-scraper
is not something you have in your vehicle living in that climate. Everyone
had to use their defroster not just those without ice scrapers.
For two weeks my phone rang off the hook. The calls weren’t for new business;
they were warranty calls and I gave a money-back guarantee. I was about
to close the business and quit, but I liked what I was doing so instead,
I set out to fix the resin problem.
The first thing I did was to stop doing repairs off the bottom of the
windshield because all of the warranty calls were breaks and cracks that
were on the bottom of the windshield near the defroster. Then I began
my quest to fix the resin problem.
“For cracks and stone breaks, my
requirement is a one-year field test on the boom of the windshield with
the ungaraged vehicle.”
It took a few years to fix the resin problem and I did so by field testing.
I found out that the resin’s lab test scores did not determine the resin’s
field performance. In fact some of the resins with the highest lab scores
were the ones that did the worst. So, going back to what I thought was
a disaster in Southern California actually led to my requirement for resins.
For cracks and stone breaks, my requirement is a one-year field test on
the boom of the windshield with and un-garaged vehicle. Living in Colorado
now is good for that as winter nights can get to zero degrees and summer
can get to 100 degrees. The hardest thermal stress on a resin is going
from cold to hot and has to do with the contraction and then expansion
of the glass molecules.
The ROLAGS Product Performance Subcommittee has developed a resin test
that duplicates the field test, but the ROLAGS test can be done in one
day, costs less than $100, only requires a heat gun, freezer, thermometer
and a meat cooking thermometer. (For more information, see the draft of
the updated ROLAGS Standard, available on www.rolags.com.
To the left are photographs of a resin that failed the test.
The ROLAGS test simulates the use of the defroster on an ungaraged cold
Richard Campfield is the founder and president of Ultra Bond Inc.
in Grand Junction, Colo.
© Copyright 2012 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.