The way we look at it, this is a physical property that can be controlled to your benefit. Instead of being subjected to variations in temperature and the resulting changes in viscosity, find the optimum viscosity and lock in the temperature.
Different materials react differently but the materials we work with most consistently, (sealant, adhesive, paint and ink), can undergo dramatic swings in viscosity with the normal temperature variations we see from season to season or even from morning to afternoon.
Many of the materials we work with can double in viscosity with a 15° F decrease in temperature. This also means that the viscosity can be cut in half with a 15° F increase in temperature. Here in the Midwest, it’s not uncommon to see 30° F swings just from morning to afternoon.
The diagram below is a graphic representation of testing we did dispensing a bead of hem flange sealer. While robotic systems can repeat the gun path, speed, angle and distance to the part, flow rate, and total volume of sealer on every dispense cycle, they can’t compensate for the viscosity variations resulting from the ambient temperature swings that occur from morning-to-evening and season-to-season. Shown here, temperature-based viscosity variations directly affect the shape of the bead being dispensed.
You can see the change in width of each bead on the left, and the bead height on the right. Because each bead is comprised of the same volume of sealer, the change in width is offset by a change in height – the wider beads are also flatter. This is often referred to as “spread” or “slump” and can significantly compromise the function of the bead.
As production moves from the colder morning to the warmer afternoon, without adjustments it is common to see spread out or splashing causing rework or scrap. In paint, the juggling act between solvent additions and other process adjustments increases the likelihood of defects and produces inconsistent finish quality.
So how much does temperature variation affect your process?
Probably more than you thought.
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