Home Page T-11 The  tension  members  are  embedded  in  neoprene  or  polyurethane.    The  neoprene  teeth  are protected by a nylon fabric facing which makes them wear resistant. The contributions of the construction members of these belts are as follows: 1.   Tensile  Member  –  Provides  high  strength,  excellent  flex  life  and  high  resistance  to elongation. 2.   Neoprene Backing – Strong neoprene bonded to the tensile member for protection against grime, oil and moisture.  It also protects from frictional wear if idlers are used on the back of the belt. 3.   Neoprene  Teeth  –  Shear-resistant  neoprene  compound  is  molded  integrally  with  the neoprene  backing.    They  are  precisely  formed  and  accurately  spaced  to  assure  smooth meshing with the pulley grooves. 4.   Nylon  Facing  –  Tough  nylon  fabric  with  a  low  coefficient  of  friction  covers  the  wearing surfaces of the belt.  It protects the tooth surfaces and provides a durable wearing surface for long service. 6.1  Characteristics Of Reinforcing Fibers Polyester Tensile Strength 160,000 lbs/in² Elongation at break 14.0% Modulus (approx.) 2,000,000 lbs/in² One of the main advantages of polyester cord over higher tensile cords is the lower modulus of  polyester,  enabling  the  belt  to  rotate  smoothly  over  small  diameter  pulleys.    Also,  the  elastic properties of the material enable it to absorb shock and dampen vibration. In more and more equipment, stepping motors are being used.  Polyester belts have proven far superior to fiberglass or Kevlar reinforced belts in these applications. High-speed applications with small pulleys are best served by polyester belts under low load. Kevlar Tensile Strength 400,000 lbs/in² Elongation at break 2.5% Modulus 18,000,000 lbs/in² High  tensile  strength  and  low  elongation  make  this  material  very  suitable  for  timing  belt applications.  Kevlar has excellent shock resistance and high load capacity. Fiberglass Tensile Strength 350,000 lbs/in² Elongation at break 2.5 – 3.5% Modulus 10,000,000 lbs/in² The most important advantages are: 1.    High strength. 2.    Low elongation or stretch. 3.    Excellent dimensional stability. 4.    Excellent chemical resistance. 5.    Absence of creep, 100% elongation recovery. Disadvantages: 1.    High modulus (difficult to bend). 2.    Brittleness of glass.  Improper handling or installation can cause permanent damage. 3.    Poor shock resistance.  No shock absorbing quality when used in timing belts.