Belt drives are the most widely used method of flexible power transmission. Improvements in materials and methods of manufacture have allowed the introduction of new belts with much broader application capabilities.

Belt drives basically fit into four types: flat,V,V-ribbed, and synchronous. Although each of these basic belt types are more suitable in specific application areas, most applications can be successfully designed with more than one type of belt.

Flat belts, one of the earliest forms of flexible power transmission, are generally more suited to high speed, low-horsepower applications. At low speeds and high loads, flat-belt drives usually become too large to be cost-effective.

V belts are the most commonly used today, and they are the only belts that can be used on variable pitch and variable speed drives. V-ribbed belts are described by some as guided flat belts. Their thinner cross section makes them suitable for operation on smaller diameters at higher speeds.

Synchronous (timing) belts are specifically designed as alternatives to roller chains and gears on drives, which require exact speed ratios and synchronization between the driver and driven machines. They are also widely used today in low-maintenance, energy-efficient applications.

Flat belts are still widely used for power transmission. Their thin, flexible cross section allows them to operate over small diameters and, in some cases, at very high speeds.

Many different sizes and constructions are available for a wide variety of uses. Flat belts are made either of fully molded or woven construction and may or may not have a tensile member.

One significant disadvantage of flat belts is that they depend entirely on friction in order to transmit power. Thus they require higher belt tension to do the same work, which results in higher shaft and bearing loads. The need for higher tension may cause more belt stretch, causing the belt to slip more easily than V belts.

The problems of high tension with flat belts led to the development of V belts. Unlike flat belts, which depend only on friction, V belts have deep V-shaped cross sections that wedge into the sheave groove to provide added horsepower capacity.

Because of the wedging action, V belts are highly stable and can operate at tensions considerably lower than those needed by flat belts.Thus,V-belt drives can be more compact and allow for smaller shafts and bearings.

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