So you want a fast adhesive. Many adhesives cure very quickly but often increasing the cure-speed of adhesives used can save companies from installing new production lines or adding shifts if demand for a production item increases. Understanding the factors that cause and affect cure allows production speed to be maximized.
Adhesives are generally specified to meet a precise production line speed. As production needs increase, it may be possible to increase the adhesive cure- speed. Following are some tips to cause the adhesive to cure faster than originally planned, without having to seek out a new fast-curing adhesive and go through the whole lengthy testing / specifying procedure!
Cyanoacrylates, or Instant Adhesives, cure when they react with the moisture on the bonding surfaces. Although cyanoacrylate adhesives are very fast adhesive, extremely dry parts will take longer to cure. Ensure there is optimum relative humidity of 40 – 60% and avoid over-applying the adhesive. Contrary to popular belief, an excessive amount of adhesive will decrease the cure speed. Less is more. If the cure is not fast enough, look for other reasons that are affecting cure speed. Cyanoacrylates also cure more rapidly in thin sections. Minimize the gap – the larger the gap, the longer it takes to cure. If even more speed is needed, chemical accelerators are available to further increase cure- speed.
Raising the temperature is the easiest way to speed up the cure of One Component Epoxies. The rule of thumb is that for every 8°C degrees raise in temperature; the cure time is halved. The maximum temperature will vary between products. Consult the technical data sheet for the product in use.
Tip: Keep in mind that the cure time is the length of time that the adhesive is at a specified temperature, not the amount of time in the oven. A large assembly may take a long time to heat up, thus increasing the total time in the oven before the adhesive itself gets to the required temperature. The speed of some applications can be increased by using induction curing instead of conventional ovens. The cure-speed of Two Component Epoxies can be increased by heating the components after assembly.
Tip: Ensure that the adhesive doesn’t flow out of the joint before it cures. If lowering the viscosity of the adhesive isn’t an issue, heat can be applied to the dispensing lines or valves during dispensing.
UV-Visible Adhesives cure on command they can be very fast adhesive – depending upon the lamp used. With the exception of deep- potting applications, increasing the intensity of the curing lamp will increase cure-speed. If a high-intensity lamp is already being used on a production line and still more speed is desired, add a second lamp which will double the total exposure time.
Tip: Ensure the bond line is the correct distance from the lamp. With some lamps, the closer the adhesive bond line is to the lamp, the higher the dosage. However, some lamps have focal points. If the focal point of the lamp is 2 inches, moving the bond line to 1 inch away from the lamp will reduce the intensity.
Safety Tip: Never adjust lamp height while the lamp is on. Always use UV protective goggles and avoid skin exposure to UV light.
In some cases, it may not be the cure-speed but the fixture-speed (or time to handling strength) that is the issue.
In these cases, the issue is not the adhesive cure time but the number of clamps available to secure the components while they cure. Depending on the design and handling strength required, cyanoacrylates can be used to fixture the components in place, avoiding the use of jigs or clamps.
In other situations, the challenge may be QC testing of final cured parts. Many adhesive types are considered fast adhesive as they set very quickly. However, full strength can increase in up to 24 hours. If the delay before QC testing is slowing down production, it is often possible to determine the minimum fresh cure strength required to ensure final (24 hour) strength.
Maxim
izing adhesive cure speed and minimizing bottlenecks increases the efficiency of production lines.
For further help and advice, please contact Permabond.
