Belt Materials and Construction
A timing belt has two main components – the cords that are molded inside it to carry the torque load and the plastic compound used to shape the teeth and cover the cord itself. Both are available in different materials for different types of belts. The end use of the belt is the major factor in determining what materials to use.
The cord is generally made from polyester, fiberglass, or Kevlar and does the work of transmitting the power in the drive system through the belt. It is wound perpendicular to the belt teeth so that it transmits the power applied to the belt in a linear way. The common example of belts that carry large loads are the serpentine belts used in automobile engines. Belts used in smaller drive systems such as York products go into don’t have anything approaching the loads in a car engine. But in both cases, elongation (stretch) of the belt is minimal. Especially in small drive applications, belt stretch is practically non existent since the cord materials are so strong in relation to the loads they are transmitting. Loads that are too high generally result not in cord breakage, but in the belt teeth jumping, or ‘cogging’ over the pulley teeth.
The plastic used in the molded belt is usually urethane, neoprane, or an engineered polymer with special properties. The plastic is injected into a mold that already contains the wound cord and has accurate tooth profiles cut into the mold. Each different belt length requires a different mold since the exact number of teeth on the finished belt must also be in the mold to produce a finished, continuous belt with no beginning or end. A mold produces a ‘sleeve’ that is often 18 to 36 inches wide with the desired number of teeth. Special slitting tools are used to very accurately trim the sleeve into the desired belt widths. Urethane is often used to produce belts for food processing when FDA requirements must be met. Urethane also can be colored or left in a clear or natural state, which means that any particles are less likely to be seen than those from black neoprene belts. Neoprene is generally the standard material for timing belts since it has good wear characteristics and very accurately holds the tooth profile from the mold. York PowerGrip GT2 neoprene belts include a nylon fabric facing to reduce wear. Special requirements for low dust/particle applications such as clean rooms, medical, or even office copiers can be met with engineered polymers. York’s TruMotion line of belts uses an EPDM polymer core with a nylon overcoating on all tooth wear surfaces to generate 78% less dust than neoprene while holding the tooth profile more accurately over thousands of hours of use than either neoprene or urethane belts.