The recent recall of airbags by some automakers has brought to the forefront the relationship between the airbag and windshield. This week I thought I would give you my opinion on this subject.
Some vehicles utilize the bonding and the strength of the windshield to help position the airbag after deployment. In other vehicles, the airbag deploys out the front of the dashboard so the windshield does not play as important a role. However, the majority of vehicles on the road today do rely on the windshield during airbag deployment in some way.
Fact: Safe Drive Away Time (SDAT) is defined as being met when the vehicle can pass Federal Motor Vehicle Safety Standards (FMVSS) 208 and 212. No. 208 is the passive restraint standard and 212 addresses windshield retention.
Question: How can urethane be strong enough to deliver SDAT when I know that it is not fully cured?
We know that urethane gains strength the longer it is exposed to humidity. The more humidity the urethane is exposed to, the faster it will cure. Modern urethanes have tensile strengths that exceed 700 psi, with some exceeding 1000 psi when fully cured. Tensile is the strength necessary to meet the FMVSS 208 & 212 requirements. In addition, there are other factors built into the chemistry of urethane adhesives that contribute to the initial strength of the adhesive.
The first generation of airbags exerted approximately 300 psi of force to the inside surface of the glass upon deployment. The new generation is significantly less than that. These facts put together give you the answer. Even with partial cure, the urethane is strong enough to withstand the pressures put upon it during airbag deployment. The only negative result will occur when you couple a poor application of materials with improper installation, which will cause the adhesives to perform improperly.
Adhesive companies and their chemists spend significant time and money testing their products. They know what sticks and what doesn’t. By following their instructions on safe drive away time to the letter, you will assure that your customers are safe.
“couple a poor application of materials with improper installation, which will cause the adhesives to perform improperly.”
^^ This. ^^
Good article, Bob.
**please delete previous comment – broken link**
However, respecting the SDAT will provide total serenity for the performing technician, as long as customer is not a nasty rusher. Procedures still rule and provide safety as they are strictly followed and routined.
My point of view.
Like you Bob, I am totally confident modern day polyurethanes, applied correctly, adequately meet load bearing requirements. My biggest concern is the correct preparation of bonding surfaces. I feel this is the Achilles heel of direct glazing.
What a GREAT topic as usual! I will temper my answer as we are trained by Ford/Carlite, GM, Chrysler, NGA and Icar on windshield installation. We don’t replace windshields, we just fix, or diagnose improper windshield installations by unqualified technicians, or fly by night guys who sell on cost only. In the last two weeks myself and my 20 guys have pushed out 35 windshields all due to poor installation. Usually short cut method. We also looked at 4 Ford F150’s that had the rear sliders replaced and all leaking due to poor placement of the butyl tape. We have also looked at 3 Cobalts all with the heat backlite wire trapped in the urethane and all missing the bottom moulding…There is talk about provincial legislation on licensing and training all glass installers in Ontario, Canada.
Hi John,
I’m glad there are guys like you out there in the field catching some of these poor installs!
I’m curious to know if you ever do any followup on these poor installs, as in find out who the installer was.
In regards to your comment about licensing and training for all glass installers I would love to see this come into effect here in Canada. British Columbia already requires every glass shop to have a glazier on staff. It would really help our industry if this were to happen.
I worked on the provincial steering committee for Auto Glass Technician in Ontario. I fought for it to have a mandatory exam and for it to be a compulsory trade. The national auto glass chains conspired together to vote down the exam and compulsory cerification. Auto Glass technician is a recognized trade in Ontario since the 90’s. howerever it’s voluntary.
If anyone is interested in taking up the fight for safety I am available to help.
Interesting comments from John, Would like to know if the separation was predominantly from the frame or from the glass. I know there is/was a big issue about new glass being contaminated with silicon from the mfg. process and technicians were not checking for it and therefore not using the correct cleaning procedure to ensure a clean glass surface.
My airbag deployed in my 2015 Nissan Versa and something caused the windshield to break because of some kind of impact from material that came from the dash or the airbag it self?