Your Windshield is Not Just a “Wind-Shield” Any More – Part 2 of 2
What is automotive grade urethane?
Automotive Grade Urethane is a unique product. It needs to be strong and flexible, bond to smooth and rough surfaces, withstand adverse weather conditions and still be workable.
Automotive urethane strength is measured in two ways; tensile and lap shear.
Tensile strength is measured by pounds per square inch (PSI) of force necessary to pull apart two hard surfaces until the bond fails. If you adhere your coffee cup to the kitchen table and pull it vertically off the surface, the strength needed to separate it from the table would be called tensile strength. Automotive urethane usually has more than 1000 psi of tensile strength.
Lap shear strength is also measured by pounds psi until failure. However, to test lap shear strength, objects are pulled in a diagonal fashion. If you were to pull the same coffee cup off the table diagonally, the strength needed to separate it from the table would be lap shear strength. Automotive urethane has more than 500 psi of lap shear strength. This is especially important in automotive collisions where a roll-over occurs. Strong lap shear strengths are important as they add to the structural strength of the vehicle.
Just as strength is important, flexibility is also important. Urethane must have flexibility to allow for vehicle body movement. Your vehicle is not completely rigid. It bends and flexes with the roadway. The glass, however, is rigid. If the adhesive is too rigid, the glass would break every time you drive over a rough road surface.
One unusual thing about urethane is the way is drys. Unlike paint or other adhesive products, urethane takes moisture that’s present in the air (humidity) and uses it to cure the product to it’s strong, rubber-like consistency.
What happens if the humidity is low?
In some areas of the country humidity levels are very low. An example of this might be Arizona or in the Northern states where cold air in the winter turns humidity to snow. Low humidity slows down the cure rate of urethane adhesive. So it stands to reason that moisture must be added to promote faster cure.
In most cases, simply adding water after the installation will give the urethane enough moisture to begin the cure. However, in the situation where mobile service is offered in low moisture locations, the answer may not be as simple. Warm air holds more moisture than cold air. In cold dry climates, it may be necessary for the installation to take place under controlled conditions, such as a heated garage or repair facility.
Are there automotive adhesives that don’t need moisture to cure?
Yes! There are currently new adhesives on the market that require no moisture for cure, but they do need some warmth for the curing process. These products are usually a little more expensive than urethane, but the quick release of the vehicle may sometimes be worth the costs.
How can I help ensure my family’s safety?
– Insist that a strong automotive grade adhesive be used to bond the glass.
– Don’t let the glass be installed on corroded metal.
– Follow to the letter the directions given by your technician.
– Drive the vehicle only when the adhesive has fully cured.
– Always were seat belts and insist that all passengers wear them too.
Speedy always strives to be aware of the lastest urethane technology to provide our clients the safest auto glass and windshield installation as possible.
*Information provided by CASPA