Belt Drives And Vibration

Some ultra-sensitive applications require belt drives to operate with as little vibration as possible, as vibration sometimes has an effect on the system operation or finished manufactured product. In these cases, the characteristics and properties of all appropriate belt drive products should be reviewed. The final drive system selection should be based upon the most critical design requirements, and may require some compromise.

Vibration is not generally considered to be a problem with synchronous belt drives. Low levels of vibration typically result from the process of tooth meshing and/or as a result of their high tensile modulus properties. Vibration resulting from tooth meshing is a normal characteristic of synchronous belt drives, and cannot be completely eliminated. It can be minimized by avoiding small sprocket diameters, and instead choosing moderate sizes. The dimensional accuracy of the sprockets also influences tooth meshing quality. Additionally, the installation tension has an impact on meshing quality.

PowerGrip® GT®2 drives mesh very cleanly, resulting in the smoothest possible operation. Vibration resulting from high tensile modulus can be a function of sprocket quality. Radial run out causes belt tension variation with each sprocket revolution. V-belt sheaves are also manufactured with some radial run out, but V-belts have a lower tensile modulus resulting in less belt tension variation. The high tensile modulus found in synchronous belts is necessary to maintain proper pitch under load.

PowerBand® Joined V-Belts

PowerBand V-belts are multiple Gates V-belts that are joined with a single backing. PowerBand V-belts provide the following advantages (compared to single V-belts):

• They are more latterly rigid, making them more stable on drives with pulsating or heavy shock loads. This makes them less likely to flip over or jump off a drive.
• The single belt design promotes uniform loading.

PowerBand V-belts can carry the same load as an equivalent number of single V-belts. For more information on the Gates family of PowerBands belts, visit http://www.gates.com/brochure.cfm?brochure=2921&location_id=3102

CenterTrack

Gates Carbon Drive has just released its newest innovation; CenterTrack. The new system from Carbon Drive (the branch of Gates responsible for replacing roller chain on bicycles with a specially designed Poly Chain belt) is a leap forward in bicycle drive technology. The feature that separates this drive from the previous drive is the flange that runs down the center of the sprocket. This makes the system lighter, and narrower, while still maintaining the benefits of a belt drive such as its debris shedding capability, smoothness, lack of stretch, and cleanliness. Because the sprockets can be narrower, the drive can be integrated on frames and internally geared hubs where previously it would not fit, opening up even more options for the consumer. The belt itself only changes by receiving a small slit cut through the teeth of the belt. This doesn't affect the performance of the belt, because great care is taken to keep the slit from reaching the carbon cords inside the belt. For more information, and for images, check out the Gates Carbon Drive Blog site at: http://blog.carbondrivesystems.com/?p=740

How Adjustable Are You?

When designing a belt drive, one important feature you always need to keep in the back of your mind is how you will be applying tension to the belt. If you have two fixed shafts, you will need an idler assembly. If your center distance is adjustable, you will need to know how much adjustment you have. Fixed center distance without adjustment or idlers have worked in the past, but success stories are rare and this type of belt drive set-up is not recommended.

Anytime a Gates Engineer designs a belt drive for you, you will get a theoretical center distance and also an install/take-up range. What do these mean you ask?

• An installation distance is the center distance we recommend your shafts be able to achieve in order for proper installation without issues. If you don't have the available installation distance for your belt during the installation process than your belt will seem like it's too short for the center distance you measured. This can lead to forcing the belt onto the pulleys which can be damaging for the belt and pulleys.
• A take up distance is the center distance we recommend your shafts be able to achieve in order to maintain proper tension on the belt throughout the life of the belt. If you don't have the available take up distance then your belt can become loose which can lead to premature failures.

Each belt line has a different installation and take-up range because they all have different length and stretching properties. If you don't know what your belts installation and take-up range is than you can use one of Gate's drive design programs (DesignFlex or Design IQ) to calculate it, or you can calculate it yourself by looking up the equations in the appropriate Gates Drive Design Manual. Gate's drive design programs and drive design manuals are available on the website at www.gates.com/drivedesign.