by Bob Beranek
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Keeping up with my theme of addressing the glossary of terms, this blog is dedicated to the most important term of all – frit. Why do I say it’s the most important? The answer – its importance to bonding glass to vehicle frames and the longevity of that bond.

The frit is the black paint band around the perimeter of an auto glass part. Though it does provide the appearance benefit of acting as a “moulding” substitute to cover the urethane bead, it also has a practical purpose.

For example:
• The black color protects the polyurethane adhesive from one of its biggest enemies, ultraviolet light. Ultraviolet light is found in sunlight and it attacks urethane by breaking it down to a “caulk like” black powder. This weakens the urethane and reduces its bonding strength.

• The application of the frit paint on the number four surface of the glass adds to its adherence by adding more surfaces to bond to through mechanical adhesion. The rougher the surface the more mechanical bonding can occur.

Back when frit wasn’t applied by the glass manufacturer and urethane was used to bond glass, we applied a “black-out” primer to serve the purpose of the frit. The black-out primer and large, wide chrome mouldings protected the urethane bead from ultraviolet light and the primer acted as the roughened surface for the mechanical bond. Then glass and vehicle manufacturers realized they could add more protection and better bonding by adding frit paint to the glass.

The frit allows for “exposed edge” glass parts, which contribute to eliminating mouldings. The frit also adds more of a mechanical bond, which strengthens the safety devices the glass contributes to, and it makes the car look good.

So, pay attention to that black paint called the frit. It is important. It is not just there to make the vehicle look good. It is there for safety purposes.

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.