Adhesive used for Windshield Mounting

Even with a higher viscosity sealant the windshield may shift. How much will depend on cure time. If you make the sealant more viscous and reduce the cure time you will also reduce the green strength or working time. May make difficult to align the windshield. Once placed will be difficult to move unless you have equipment that can place it exactly where you want it. Even then with out some means of support it may shift until the sealant cures. We use an almost pure silicone sealant a hot melt which has green strength time of 15 minutes. Once the glass is placed it is very difficult to move. In aligning it we break some glass. About 2 to 3% but were talking about a small product a window sash. Which is easier to pull from a production line and go to the next. Would be a little hard I would think in an automobile assembly line. Even with this sealant the manufacture recommend setting blocks to keep the glass from shifting. Its cure time is 24 hours.

Thanks for that info.

So this means we need to have gravity stoppers and it is not preferrable to go for high viscosity adhesives. This brings some more curiousity in me. What does Green strength means? Will higher viscosity lead to curing rapidly? Will rapid curing decrese green strength? Please help me with these doubts.

Green strength is the resistance the sealant has to mechanical movement before it set up and starts to cure.

I see two pieces of tape at the top about two inches wide by 6 inches long, half on the windshield and half on the car's roof in many "on-site" repairs done around here. That seems to hold things in place till cure is sufficient.

Not an endorsement of 3M.

Thanks a lot Lynlunch.

But that is some thing you do for aftermarket purpose and it is basically also done so as to align the Windshield in area available maintaining the OEM specified gap between BIW and windshield. I am much more concerned with production related technique used by them.( i.e what is being done at time of on going production of Cars ).

Sorry.

I didn't understand that you were, apparently a manufacturer of automobiles.

I think that you can find an adhesive that will keep the windshield in place during assembly.

I cannot tell you how to do that, except to say call your present supplier of adhesive.

This is done on replacement glass to keep the trim on glass hard rubber the opportunity to stay in place as the adhesive cures, or in the old days to keep the trim on clips from coming off until the older butyl tape adhesive bond settled into place.

Bob

I have toured a GM plant before they closed it down and the adhesive was applied and the windshield set in place immediately. They never used gravity stops. I can only deduce the adhesive was a rapid cure type.

I was working in a GM dealership in the 70s. Around that time they were switching to a urethane window bonding tape. It was about 1/2" by 1/2", and was rolled around a plastic coated paper. We would wipe the recessed area the windshield set into, let it dry, and lay out the tape with no gaps, and no overlapping. One quick wipe of the sealing area of the glass, and then just lay it into the tape. Very little movement was possible, but some movement could be accomplished id constant pressure was used. I thought butyl was used before the urethane. Same install procedure. I do have a roll of windshield tape if you want some information from it.