by Bob Beranek

Recently we’ve seen an increase of original equipment (OE) glass purchases from dealerships. Why, because Advanced Driver Assistance Systems (ADAS) are being incorporated into new vehicles more often than not. This means auto glass companies that don’t recalibrate ADAS systems must depend on dealerships. By adding dealerships as a partner to complete auto glass services for their mutual customer, may mean the dealership will demand OE glass be obtained for the replacement to facilitate recalibrations.

What does that have to do with the title of this post? When OE glass is purchased from a dealer, it can sometimes come to auto glass shops pre-primed, especially if the vehicle is a new model or has just been manufactured for the new model year. This can pose a problem if the urethane adhesive you choose doesn’t allow use with unknown primers.

We all know technicians should never use a glass part with an unknown primer applied. If glass is delivered to your shop and the glass has a primer applied, it should be returned for a new part. The technician wouldn’t have a way of knowing how the glass was cleaned, primed, or prepared and what chemicals were used. You also wouldn’t know if the glass was cleaned properly and if the primer used was compatible with the primers the technician will use? None of these things are known and no one should assume the previous technician knew what they were doing when they prepped the part.

You may think, I’ll just clean it off, but will you, and can you? It may look clean and contaminant free when you’re done cleaning it, but is it really? If you use abrasives to remove any foreign materials some of the frit paint may be removed. The frit is a rough surface with peaks and valleys that are coated with chemicals that can’t be removed fully without removing a substantial amount of the frit paint. When frit paint is removed the frit is not as protective of the urethane as it was before. The adhesive will be more susceptible to ultraviolet light breakdown and reduction in mechanical bond.

So, what should we do to prep the pre-primed OE part? I asked that question to three of the top auto glass adhesive manufacturers’ in the industry. Unfortunately, each had a different answer, but none said you can’t prep an OE part properly with the right procedures. One of the top adhesive producers warned not all OE prepped glass was equal in terms of proper priming. OE’s make mistakes like everyone else. I’ve previously written about problems with priming that must be addressed if witnessed.

I urge all technicians and owners that read this article, to check with their adhesive representatives or check their adhesive instructions to verify the procedures in dealing with pre-primed OE parts. If your urethane of choice has neither a rep nor written instructions covering this issue, the only way you can be assured the primer on the OE part is compatible with the urethane used is to purchase the OE urethane kit with the OE glass part. Then follow the written instructions given to you by the OE adhesive company.

Last month I wrote an article on the terms used in the industry by auto glass professionals.  Today, I’m continuing it.

Plunge-cut – A plunge-cut has both a negative and positive connotation. It’s been seen negatively when it is used as a method of easing the use of a cold knife. The belief was that if you cut along the glass’s edge with a utility knife, the vertical cutting edge of the cold knife blade would be less of a drag on the tool, thus making it easier to pull. However, it would also score the floor of the pinchweld and cause oxidation to occur and undermine the urethane bead.

The positive connotation: it’s a technique to remove the flap of a “J” style moulding. Removing the extending flap makes it easier to remove the remaining portion of moulding and makes the cold knife cut smoother without hindrance. The trick is not to plunge the knife blade too deep where it contacts the pinchweld floor.

Gravity Stops – It’s the modern name for devices that support the bottom of the glass part and stops the glass from sliding off of the adhesive. Now, the OE manufacturers’ other means to support the glass while the adhesive cures that will do the job and not cause squeaking. The cowl panel is one method and additionally they use guide pins or hangers.

Guide Pins/Hangers – These are OE parts used by robotic machines that set the glass into place during assembly. You rarely see these parts used in the aftermarket, because they are usually located within about 8-12 inches from the top corner of the glass part and are held in place by double-sided tape or silicone adhesive. These guides serve two purposes: it helps the robot set the glass and keeps it in place until the urethane adhesive cures to its ultimate strength.

The above description does illustrate the use of guide pins in windshield mountings. However, there’s another use for guide pins when discussing other auto glass parts. Some side parts have a tilt-out style of mounting, like in quarter glasses and vents. These parts also use an extended “guide pin” that is threaded and used to attach the hinge to the vehicle frame. It’s also called a “T” bolt. These extended threaded bolts are usually a part of the hinge and helps the robot insert the part into the pre-drilled holes in the frame’s body. Then a nut is used to securely attach the part to the body.

“T” Bolt – “T” bolts are guide pins embedded into a plastic moulding around a glass parts’ edge. The extended bolts are used by robotic machines to set the glass part into place and to attach the glass part to the body.

Encapsulation – Encapsulation is a process where a glass part is placed into a mold and molten plastic is pumped into the mold to create a part where the glass and moulding become one.  Because the encapsulation is either PolyVinyl Chloride (PVC) or Reaction Injected Molded (RIM) plastic, the adhesives used to adhere the glass part to the body may need help to stick properly. That’s why the encapsulated parts are frequently equipped with “T” bolts embedded into the encapsulation or clips that hold the part in place until the adhesive cures.

My son Jay recently reported a problem with laminated door glasses breaking after installation. He said he noticed that the aftermarket parts were breaking at the mounting brackets, and that the glass itself seemed to be slightly out of bend. I hadn’t heard about this before, so I did some research with other technicians and found that this was a common problem.

The reason this intrigued me is that laminated door glasses are supposed to be constructed with two layers of heat-strengthened glass and lamination. Though “heat-strengthened” glass is not true tempered glass as defined by ANSI Z26.1, it is supposed to be heat-strengthened enough to withstand the abuse put upon it by the operation of the movable door frame and glass.

This raises a few questions. Did the aftermarket manufacturers reverse engineer the laminated-door glasses correctly? Did they recognize that the glass used for door-glass construction should be heat-strengthened and not just annealed glass? If they were aware of the necessity for the heat-strengthened glass construction, did they replicate the process and use the OE specifications or weaken it for a price point?

Here is the issue as I see it. The actual purpose for making door glasses laminated, rather than tempered, is murky. Was the change made for acoustical reasons to benefit the comfort of the occupants and the performance of voice-activated systems? Or are laminated parts safety devices that act as a backstop for the side impact airbags/curtains?

Depending on who you talk to at any given time, the answer changes. It is to the benefit of carmakers to consider glass as a performance feature, rather than a safety feature, to keep free of Federal regulation.  However, if you are a car salesperson, safety sells and, if a safety reason can be attached to the feature, it may close the sale.

Now let’s look into the minds of the ARG manufacturers. If the glass you produce is a performance feature, not driven by safety, and the cost of producing a part is prohibitive to the goal of reaching a price point, then why not laminate for acoustics but weaken the strength of the glass portion to meet that price objective? It makes perfect business sense.

Heat-strengthening glass is an expensive process. You must take the process steps of strengthening the glass (like tempering) but then add the additional step of lamination. Increasing the cost of a finished product that is naturally slower selling, like a door glass, may not make financial sense. Why not eliminate one of the processes that, in some assessments, are not necessary to the safety of the vehicle to meet the price point their customers demand?

In my opinion, the heat-strengthened auto glass parts serve both performance and safety purposes. If safety is even a small reason for its existence, it is my opinion that the product used in our service of auto glass repair and replacement must meet the specifications of the OE part. So, buyer beware. When buying ARG laminated side parts, think of the primary purpose of the part and act accordingly. I prefer to err on the side of caution.