Viscosity: A measure of the resistance to flow of a liquid, sometimes measured
in terms of centipoise (cps). The higher the viscosity the thicker the liquid.
Hardness: The resistance of a material to permanent deformation. There are
many scales to measure the hardness, but the most common in the plastics industry
are Shore 'A' (softer materials) and Shore 'D' (for Harder materials).
How easy it is to flex a rubber is dependent upon both the hardness and on
the thickness. A soft material that is very thick may appear to be stiffer than
a hard material that is very thin. Think of glass fibers that you can easily bend in a
circle versus a window pane that will shatter if bent to far. Lowering the temperature
of a material not only decreases its flexibilty, but it also makes it more susceptible
to a brittle fracture. This is part of the reason the Challenger exploded shortly after take-off.
The O-ring, which is normally flexible at room temperature, was very weak and
brittle on the cold launch day.
Tensile strength: How much weight per unit area a material can withstand
at room temperature until it begins to permanently be defomred, often
measured in psi (pounds per square inch). A material with a tensile strength
of 5,000 psi means that a 1" x 1" square rod would be able to withstand
a 5,000 pound application before it would be permanently deformed. The tensile strength
usually decreases as the temperature is increased.
Pot life: Amount of time you have after you have mixed the two components until reaction
begins and the system begins to set.
Demold time: Amount of time after you first mix the two components and pour it into the
mold until it is stiff enough to remove from the mold. At this point, the part has not reached full
strength.
Cure time: Amount of time after first mix that the material has effectively achieved "full strength"
Filler: Materials that serve as thickening agents (cab-o-sil), act to take up space to reduce the
amount of resin used and make the part more light-weight (microballoons, fillite), or to achieve
a metallic appearance (bronze, brass, (aluminum, iron powders).
UV protection: Some clear plastic resins yellow over time when exposed to UV light. A special
additive that protects the plastic from yellowing is added to some systems, but usually drives the
cost up.
Transparent dye: A dye that will allow you to at a slight color to a clear system. Think about
putting a tiny amount of food coloring in a large glass container of water. Light can still be transmitted
through a system with transparent dye. This is the effect you can achieve in clear plastics systems with our product EP7701.
Opaque dye: A very concentrated pigment which acts to color a plastic system so that no light can travel through. Our selection of opaque dyes are named EP7702.
If you would like to learn more about the technical properties of plastics, check out some of the
links below:
The American Plastics Council gives a great overview of the plastics industry including the history, processing and chemistry of plastics.
The Society of the Plastics Industry is another good source for plastics specifics.
