Download Timing Belts: Selection, Maintenance, and Troubleshooting and more Lecture notes Technology in PDF only on Docsity! GatesFacts™ Technical Information Library Gates Compass™ Power Transmission CD-ROM version 1.2 The Gates Rubber Company Denver, Colorado USA ___________________________________________________________________________________________________________________________________ Page 1 Timing Belt Selection And Troubleshooting David E. Roos Maintenance Technology September 1989 Evenly spaced teeth on the bottom surface of synchronous or timing belts mesh with grooves on the pulleys for positive, no-slip transmission of power. Use of these belts has increased steadily since they were first developed and produced almost 40 years ago. Timing belts are versatile and dependable. They are replacing chain as a positive drive transmission because they are quieter, need no lubrication, and are capable of higher speeds than chain. In some applications, they are replacing gears. The teeth on the belt enter and leave the pulley grooves in a smooth, rolling manner, with low friction. Two other significant advantages leading to the increased use of timing belts involve lower maintenance and higher drive efficiency. Although drive maintenance is not totally eliminated, the positive tooth engagement and the high modulus tensile cords in these belts virtually eliminate retensioning. And the positive tooth engagement eliminates slip. Consequently, laboratory and field testing shows a 2 to 4 percent improvement in belt drive efficiency. Four basic parts make up the standard timing belt: • Tensile cord is the muscle of the belt, usually a high-tensile-strength fiber-glass cord that has a high resistance to elongation. • Backing protects the tensile member from oil, grease, moisture, and other adverse environmental conditions. • Teeth engage the grooves on the pulley. They are precisely formed and spaced and are made of a special high- modulus material. • Facing is usually made of fabric to act as a wear surface, protecting the teeth. The facing also helps keep frictional losses to a minimum. All four components are molded integrally to ensure that all work together as a unit . GatesFacts™ Technical Information Library Gates Compass™ Power Transmission CD-ROM version 1.2 The Gates Rubber Company Denver, Colorado USA ___________________________________________________________________________________________________________________________________ Page 2 Conventional trapezoidal-tooth timing belts come in several cross sections, which really relate to the pitch of the belt. Pitch is the distance in inches from center to center of the teeth. The six basic cross sections or pitches are listed: MXL = mini extra light 2/25 in. pitch XL = extra light 1/5 in. pitch L = light 3/8 in. pitch H = heavy 1/2 in. pitch XH = extra heavy 7/8 in. pitch XXH = double extra heavy 1 1/4 in. pitch Although the Rubber Manufacturers’ Association (RMA) standards identify six basic pitches, the smaller-pitch belts are generally used only on very lightly loaded drives. Curvilinear (round) tooth, tough high-torque-drive (HTD) belts also are available, but they are not yet part of the RMA standards. There are five basic cross sections or pitches. 3M 3 mm (0.118 in.) pitch 5M 5 mm (0.197 in.) pitch 8M 8 mm (0.315 in. ) pitch 14M 14 mm (0.551 in.) pitch 20M 20 mm (0.787 in.) pitch The most recent development in high-capacity, curvilinear-style synchronous belts, the Poly Chain GT developed by the Gates Rubber Company has a tooth profile similar to that of other high-performance synchronous belts. However, its pressure angle, tooth depth, and materials (polyurethane and Kevlar) were optimized to maximize load/life capacity and other important drive characteristics (such as anti-ratcheting). These improved performance characteristics can result in more compact drive packages, or greater capacity from existing drive packages, or improved drive economies.
