Power Transmission
GT-profile involute tooth form are normally used. For very
I
compact drives, a 5mm pitch belt with an extremely rigid carbon tensile member is recommended. Belts with small pitches, such as 2mm and 3mm, are used for low-power applications that involve high-precision positioning, measurement, machining or engraving.
Selecting a minimal width to reduce noise level
The use of several narrow belts on one belt pulley, as opposed to one wide belt, has proven particularly effective in minimising transmission noise. The width of the individual belts used in these kinds of drives is typically between 12mm and 30mm and these are suitable for rotational speeds up to 10,000rpm, with an 8mm pitch belt system.
Setting the correct preload
This is important because, in the case of high-speed synchronous belt drives, the preload influences service life, heat generation, noise levels and the reliability of the components. The preload also has a significant impact on the stiffness of the system. As such, as early as during the planning stage of dimensioning a belt drive, it is necessary to bear in mind the stiffness and preload of the belts. The preload of the belts decreases at first due to post-installation run-in behaviour, but then remains constant after run-in for the rest of the service life of the machine, if the correct belts have been selected. Therefore, drives with synchronous belts can be expected to be maintenance free for the entire duration of their service life. This can be tens
ncreasingly, synchronous belt drives are being used instead of simple transmissions and chains, which are not designed for higher speeds, and are loud and require frequent maintenance.
of thousands of operating hours depending on dimensioning and wear to the drive components. For slow-
running drives with a high torque, ranging from a
few revolutions per minute to 1,000rpm, a belt pitch of 14mm provides the best solution. Spindles or tables can be rotated using endless belts, usually with carbon tensile members that deliver the correct level of stiffness within the minimum package size. Systems for automatically changing tools and work
pieces can utilise open-ended synchronous belts or flat belts made of elastomer or polyurethane materials, the end of which are clamped in place using profiled clamping plates. Depending on the mass of the object to be moved, belt drives can be used at acceleration and deceleration rates up to 60m/s2
. To ensure that belt drives reliably and sustainably
perform their function, they must be resistant to ambient conditions. Belts in machine tools often come into contact with aggressive liquids, or at the very least oil vapours. For such applications, HSN/HNBR elastomer belts or polyurethane belts are most suitable. Although polyurethane v-belts are resistant to aggressive ambient conditions, if oil enters the grooves of the v-belt pulley, there is a risk of slippage. The compact construction of machine tools results
in poor heat dissipation. For temperatures of up to 100°C, polychloroprene belts are the best option, and for temperatures of up to 130°C, HSN/HNBR belts, special polyurethane belt models and standard Quad Power III belts made of an EPDM compound are most suitable. A well designed and installed belt drive can last
many thousands of hours on a variety of applications within a machine tool platform. When deciding on the right solution for a specific
project or application, it pays to get some expert advice. Gates is known globally as a leading manufacturer of power transmission belts and fluid power products. Its highly engineered products are critical components that are used in diverse industrial and automotive applications. The company offers a complete portfolio product and service solutions for both replacement and first-fit applications across its targeted end markets. l
For more information ✔ at
www.engineerlive.com/ede Poly Chain belt on a milling machine.
David Clark is a senior engineer at Gates PT, in Dumfries, Scotland.
www.gates.com/europe/industrial
www.engineerlive.com 43
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