Volume 12, Issue 2 - March/April 2010
Ask the Doctor
Curing Under Pressure
One of the fundamental rules to achieving a structurally sound, long-lasting
and visually superior windshield repair comes at the very end of the process.
This also is when you can ruin what would have been a perfect repair.
under pressure compromises both the mechanical and chemical bond
Curing Under Pressure
Curing under pressure has several benefits, as follows:
• It creates a mechanical bond to the PVB, so it does not separate upon curing or over time, creating an unsightly repair.
• Curing under pressure increases both the mechanical and chemical bond to the glass because the pressure keeps the resin in place while it cures.
• It compensates for shrinkage. The rule of thumb to address adhesive shrinkage is to overfill, and the only way to overfill a stone break is to cure under pressure. Shrinkage is caused by the tight-knit structure of the free-radical double-bonding; the UV cure being exothermic, a chemical reaction that releases heat; and surface tension caused by the wetting of the glass and not the PVB. Shrinkage causes the cross linkage to be stressed instead of relaxed, creating residual stress within the structure. Relaxed cross linkage gives the repair more elasticity to expand and contract without crosslinks snapping/breaking, creating a better bond and preventing deterioration. Slow cure also controls shrinkage, as too fast of a cure increases shrinkage and stress.
• Curing under pressure improves the cohesive strength, which is the internal bond of the resin, to itself by allowing more monomers to join with other molecules to form polymers. This is needed to bridge and fill any void/gap in the break, legs and bullseye.
In summary, do not remove your tool before you cure. Curing with your repair tool in the pressure mode forces the resin to stay put while curing, instead of shrinking and pulling off of the PVB
Richard Campfield is the founder and president of Ultra Bond Inc. in Grand Junction, Colo. Mr. Campfield’s opinions are solely his own and not necessarily those of this magazine.
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