by Bob Beranek
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I have been involved in some discussions recently concerning value-added accessories on automobiles, and specifically automotive glass as it pertains to safety and/or performance. Anyone who knows me would say that I usually fall on the side of safety over performance. However, it is not as black and white as it might seem. As a matter of fact, most of the items that have been added to the modern automobile represent a little bit of increased safety and a little bit of increased performance—blurred lines.

The fact is that safety items are government regulated and performance items are not. If a car company has a choice of labeling a value-added item a “safety” device or a “performance” device it would weigh the profit advantage of each and come up with a decision that benefits the bottom line. If an accessory improves safety, that value will be there regardless as to how it is labeled, but by calling the add-on a performance feature, car companies can avoid regulation and possible liability.

What does this mean? It means that if a value-added item can be labeled as both safety and performance, it will be labeled as performance.

I alluded to this phenomenon a few weeks ago when I wrote about laminated door glasses. I questioned back then whether a laminated door glass was a safety device or a performance feature. The National Highway Traffic and Safety Administration (NHTSA) saw the same blurred lines and backed away. Since then, I have been asked numerous questions about other items added to the modern day vehicles such as Heads-Up-Display (HUD), rain sensors and special urethanes. For the next few posts I will voice my thoughts on the matter and try to clear up the blurred lines of safety versus performance.

Special Adhesives

Let’s start this off with a material we are familiar with but are unsure how it should be labeled—special urethane. By special urethane I mean high modulus and low-conductive. Are these safety products or performance products?

If you ask the vehicle manufacturers, high modulus urethane is used for solidifying the body and boosting the performance characteristics of the driving experience. High modulus urethanes are stiffer when cured so when it is paired with other performance characteristics of the body assembly, it makes the unibody vehicle stiffer and improves handling on the roadway. So it is definitely a performance feature, right?

Now ask the collision experts. If a vehicle is involved in a collision with all of the body panels assembled properly, the crash dynamics are predictable and meet the safety standards put upon the manufacturer. However, if the panels are repaired differently than the engineers dictate, the result could be significantly different and possibly dangerous. The windshield and all the stationary bonded glass parts are structural panels that must be assembled properly for the vehicle to be safe in a collision. If stationary parts are installed in the aftermarket using regular modulus adhesives when the manufacturer assembled the vehicle using high modulus, could performance in a collision be compromised? This sounds like a safety issue, doesn’t it?

Let’s look at another example. These days we see many more vehicles with aluminum bodies, with windshields that are installed with low-conductive urethane at the factory. If you ask vehicle manufacturers, low-conductive urethane is used to limit the interference of electrical systems like an antenna or defogger. This makes some sense because regular urethane is primarily carbon black that conducts electricity. Therefore, if it is used in bonding a glass part to a vehicle where it has contact with electrical components, it could interfere with electrical performance. Low conductive urethane is then a performance material, right?

Now ask a mechanical engineer. When two dissimilar metals come in contact with each other the result is what is called galvanic corrosion. If regular urethane, which is primarily carbon black, is applied to an aluminum vehicle body, the possibility of two dissimilar metals (carbon black to aluminum) coming in contact is higher than normal. This may cause corrosion which causes deterioration of the vehicle body, undermining the bond of the glass to the vehicle body. If this vehicle is involved in a collision, the windshield or other bonded stationary parts would not perform according to design, potentially putting the occupants in danger. This sounds like a safety issue, doesn’t it?

Blurred lines are everywhere in our industry. I suggest we use our heads and think it out. If we do, we cannot go wrong. Err on the side of safety and your sleep will always be restful.