Fixing time & setup time
What is fixation time?
Two of the most important properties of structural adhesives and methyl methacrylate (MMA) adhesives without exception are "working time" or "set time" and "setting time" or "handling strength".
Working time / preparation time
The working or set-up time seems to be the easiest value to understand. It is the amount of time you have to apply the structural adhesive to the first substrate material and successfully bond the second substrate material. Effectively, the amount of time you have to work with the adhesive or that the bond is "ready". Pretty straightforward...
For moisture-curing adhesives, such as polyurethanes or silicones, this time starts as soon as the structural adhesive is exposed to air. For two-component adhesives, such as epoxies or MMA, this time starts when the adhesive and activator are mixed.
For both one- and two-component materials, this time is affected by temperature. Cooler temperatures result in longer set-up times, while warmer temperatures result in shorter set-up times. This is simply due to the nature of the chemical reactions, which are faster when heated. In the case of moisture-cured materials, the amount of water vapor in the air is also a factor. Slower in dry conditions, faster in humid situations.
Once we go beyond the working time of the material, we start talking about the handling and bonding time. Structural adhesive data sheets usually quote one or the other (or sometimes both). Plexus® brand MMAs always show a range of values for setting time.
Effectively, the handling time of an MMA adhesive is the amount of time after mixing of the two components until it is possible to generally "handle", i.e., move or gently manipulate an assembly. Of course, this depends on the size of the assembly. The handling time of, for example, the clamps of a molded composite part will be different from that of a large steel plate bonded to concrete. The handling time of your application will be unique to your process, your product and your adhesive.
Set time is generally a value that is defined when an adhesive has reached a certain tensile strength, or a percentage of its ultimate strength, or sometimes for a two-component material, when it has passed its exothermic peak (heat of reaction). As with handling time, the setting time for your application will depend on its specific characteristics.
Structural adhesive manufacturers often choose a definition of bonding time that they apply and note it on their data sheets. When selecting a structural adhesive, it is important that you are aware of the definition of the fixation time being used so that you can compare your options on a fair basis.
ITW Performance Polymers, manufacturer of the Plexus brand of adhesives, is the leader in the formulation of methacrylate adhesives and has always maintained the highest standards of quality and technical expertise. As such, Plexus' philosophy in reporting product data has always been to hold itself to a higher standard. That will not change. We will continue to lead the market: we will tell the story of our products in a way that helps our customer achieve the best result.
Do you have questions about opening/working time, handling time, bonding time or adhesion in general?