Below are some useful terms and definitions related to Fenner Precision's timing belts:
Abrasion Resistance - Ability of polyurethane to withstand mechanical action (such as rubbing, scraping, etc.)
Additives - Materials combined with prepolymer and curative to modify the properties of the urethane. Examples are plasticizers, fillers, and stabilizers.
Backing Thickness - The distance from the cord support (in flighted belts) or the tooth root (no flight belts) to the backside of the belt.
Bashore Resilience - An ASTM test for the rebound characteristics of the elastomer. High bashore resilience generally implies low heat buildup in the urethane when used at high speeds under loads.
Catalyst - The ingredient in polyurethane which initiates a chemical reaction or increases the rate of chemical reaction.
Coefficient of Friction (COF) - The ratio of the force required to move an object across a surface to the weight of the object.
Colorants - Dyes or pigments that provide color to polyurethane.
Compression Set - The characteristic of an elastomer to return to its original state after deforming forces are removed.
Creep - Slow continued growth or lengthening of a material under a constant load.
Denier - The weight in grams per 9,000 meters of a particular reinforcement.
Density - Weight per unit volume of a substance.
Driven Pulley - The load-bearing pulley in the system that is directly powered by the belt.
Driver Pulley - The pulley in the system that supplies power directly to the belt.
DurometeR - The hardness of the final elastomer, or the gauge used to measure hardness.
Elastic Limit - The maximum stress to which a test specimen may be subjected and still return to its original length upon release of the load.
Elasticity - The property whereby a solid material changes its shape and size under the action of opposing forces, but recovers its original configurations when the forces are removed.
Elastomer - A natural or synthetic material which exhibits rubber-like properties of high flexibility.
Endotherm - Heat absorbed in a chemical reaction.
Exotherm - Heat given off in a chemical reaction.
Hysteresis - A loss of energy due to successive deformation and relaxation.
Modulus - The slope of the line on a stressstrain curve. The slope is the ratio of stress to strain.
Polyester - A chemical building block (DIOL) reacted with diisocyanate to produce prepolymers. The polyester provides good solvent resistance and good mechanical properties in the final elastomer.
Polyether - A chemical building block (DIOL) used in place of polyester in some prepolymers. The polyether provides outstanding resilience and hydrolytic stability.
Polymer - A material, of either synthetic or natural origin, made of many repeating molecules.
Polyurethane (Urethane Elastomer) - A synthetic rubber made by reacting diisocyanate with polyhydroxy-terminated compounds.
Prepolymer - The liquid that is reacted with curative to form the final polyurethane polymer.
Pulley Runout - The total deviation of a surface when rotated about an axis.
RMA - Rubber Manufacturers Association SLIP Occurs when the torque load in the system exceeds the frictional force provided by tension in a flat belt or Fenatrak belt.
Strain - The elongation of a specimen under load measured as a percentage of the original length.
Stress - The load per unit of original crosssectional area.
Synchronous Drive - A power transmission mechanism with zero slip between the input and output.
Synthetic - Not of natural origin; prepared or made artificially; "man-made."
TDI (Toluene Diisocyanate or Tolyene Diisocyanate) - A chemical building block reacted in excess with polyester or polyether to produce prepolymers.
Tear Resistance - Opposition of a material to a force acting to initiate and then propagate a failure at the edge of a test specimen.
Tear Strength (Split Strength) - A measure of tear resistance.
Tenacity - Break strength per unit of linear density.
Tensile Strength - The maximum tensile stress sustained by the specimen before failure in a tensile test.
Tension - A force tending to produce elongation or extension.
Thermoplastic - A urethane which can be repeatedly softened or melted and which will harden to a new shape when cooled.
Thermoset - A urethane which cures using heat (or catalyst). The material is chemically crosslinked and cannot be reprocessed. Thermosets, unlike thermoplastics, can be used at elevated temperatures.
Total Indicator Reading (T.I.R.) - The value derived (high to low reading) by a dial indicator.
Viscosity - Measure of the torque produced on a constant-speed, rotating spindle, in a liquid medium. Usually designated in centipoise.
Yield Point - A point on the stress-strain curve at which there is a sudden increase in strain without a corresponding increase in stress.
