Glossary

Amine chemical terminology: NH2, different types used as curatives or catalysts
Angle of parallax make sure that the point of observation is correct or errors may occur.
Cheesiness cheesy-like feel of a casting
Combustible will burn
Curative substance used to react with the prepolymer to gel it
Diamine molecule with two amine (NH2) groups
Diisocyanate molecule with two isocyanate (NCO) groups
Dimer chemical reaction:  two isocyanate groups reacted together
Diol molecule with two hydroxyl (OH) groups on it
Flammable will burn
Flash point lowest temperature at which a substance gives off combustible vapour to produce a flash of fire if a small flame / spark is near
Gel irreversible solidification of substance; solid / reacted casting after curative is added
Glycol 1,2-ethanediol; a type of diol
Isocyanate molecule with an NCO- group on it
Inflammable same as flammable; will burn
MDI chemical name:  diphenylmethane diisocyanate.  There are many grades
Meniscus curved upper surface of a liquid at the sides where in contact with the mould / container. This curve will remain after gellation.  Measurements are read at the central flat portion.
Mix ratio the constant proportions in which the substances are mixed
MOCA/ MBCA amine curative:  4,4-methylene-bis orthochloroaniline
Plasticizer ingredient which can be added to urethane systems to modify systems but weakens the properties considerably; also used for flushing machinery or testing ratios
Polycaprolactone chemical term:  similar to polyester, but with better hydrolysis resistance
Polyester chemical term: high molecular weight substances containing the ester group –O-CO-
Polyether chemical term:  high molecular weight substances containing the ether group –O-
There are two types:  PPG (POPG) & PTMG (PTMEG)
PPG / POPG chemical term:  polypropylene glycol; low cost polyether
Pressure force applied to a surface, which is measured as force per unit area e.g. psi or bars or pascals or Kg per square meter
PTMEG / PTMG chemical term:  polytetramethylene ether glycol; high cost ether
Release agent silicone based substance / surfactant applied to mould to prevent sticking
Resin refers to blends and partially reacted urethanes, esters, ethers, isocyanates
Shore A/D measurements of hardness; shore A being the softer range, D the harder
Shot size size / weight of each dose of resin
Solvent liquid used to dissolve a substance; often used to clean machinery, often flammable
Stoichiometry the science of calculating the quantities of substances to be mixed together based on their reactivity
Substrate the object or surface one is casting on
Tear resistance force necessary to tear a sample of urethane. Test results may vary according to the method used.
Temperature the measurement of ‘hotness’ or ‘coldness’ of a substance
Tensile strength the breaking strength of a sample when subjected to tensile / stretching force which is measured in force per unit area
Vacuum the absence of air, usually in a sealed container
Vapour gaseous phase of a liquid
Viscosity The resistance of fluid to flow.
Wet spots parts on the surface of a casting that are ‘wet’ usually due to poor mixing



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