Glossary of Technical Terms
Density is mass divided by volume. We conduct these tests at 25°C so that the density measurement in grammes per cubic centimetre (gcm3) is also equal to the specific gravity.
Hardness is a material’s resistance to deformation. This test is conducted with a Durometer utilising the D scale. A Durometer forces a metal point into the material and provides a numerical reading which corresponds to the resistance at the point. The results of a hardness test are important for comparative purposes and determining the degree of cure.
Mix ratio is the target ratio of resin to hardener required to achieve published properties and may be different by weight and volume due to the differing densities of the resin and hardener.
Every resin/hardener combination has an optimal target and acceptable range. Please note that the target is often not in the middle of the acceptable range.
Achieving the correct mix ratio can be simplified by using PRO-SET® Dispensing Equipment.
Pot life is the amount of time a mixture of resin and hardener has at a workable viscosity while in the mixing container. Pot life is determined using 150 g and 500 g samples in a standardised container at 22°C, 25°C and 29°C. Both mass and ambient temperature affect the rate at which an epoxy system will cure. Pot life should only be used for comparative purposes when evaluating an epoxy system’s cure time.
The thix index (or shear thinning index) is a ratio determined by viscosity measurements taken at 10 and 100 RPM. The low speed reflects how epoxy will flow undisturbed. The high speed measurement indicates how well it will flow when shear force is applied as is often the case during processing.
Viscosity is a fluid’s resistance to a shear force and can be thought of as how easily a fluid flows. A rotational viscometer is used to measure viscosity. A spindle rotates in the epoxy to measure its resistance. A thicker fluid will give the spindle more resistance, indicating a higher viscosity. Since temperature will affect the viscosity, we provide data points at different temperatures as well as graphs that provide viscosity data over a wide range of temperatures.
Manufacturing process and processing temperature are important considerations when determining the required mixed epoxy viscosity. Infusion processes often require very low viscosity to enable good flow, whereas a wet lay-up may require a higher viscosity allowing thorough fabric wet-out yet preventing drain out.
Working time is the amount of time the viscosity of the epoxy remains low enough to be processed. It is determined using a gel timer which employs a spindle travelling through an 3.2mm thick volume of liquid epoxy. Working time is the amount of time the spindle can travel through the epoxy without leaving an indent in the curing epoxy.