Home Page T-41 slip), and because they require minimal maintenance (don't stretch significantly).  A significant drawback of  high  speed  synchronous  drives  is  drive  noise.    High  speed  synchronous  drives  will  nearly  always produce more noise than V-belt drives.  Small pitch synchronous drives operating at speeds in excess of 1300 ft/min (6.6 m/s) are considered to be high speed. Special consideration should be given to high speed drive designs, as a number of factors can significantly influence belt performance.  Cord fatigue and belt tooth wear are the two most significant factors  that  must  be  controlled  to  ensure  success.    Moderate  pulley  diameters  should  be  used  to reduce the rate of cord flex fatigue.  Designing with a smaller pitch belt will often provide better cord flex fatigue characteristics than a larger pitch belt.  PowerGrip GT is especially well suited for high speed  drives  because  of  its  excellent  belt  tooth  entry/exit  characteristics.    Smooth  interaction between  the  belt  tooth  and  pulley  groove  minimizes  wear  and  noise.    Belt  installation  tension  is especially critical with high speed drives.  Low belt tension allows the belt to ride out of the driven pulley, resulting in rapid belt tooth and pulley groove wear. 9.3   Smooth Running Some  ultrasensitive  applications  require  the  belt  drive  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  pulley diameters,  and  instead  choosing  moderate  sizes.    The  dimensional  accuracy  of  the  pulleys  also influences  tooth  meshing  quality.    Additionally,  the  installation  tension  has  an  impact  on  meshing quality.    PowerGrip  GT  drives  mesh  very  cleanly,  resulting  in  the  smoothest  possible  operation. Vibration  resulting  from  high  tensile  modulus  can  be  a  function  of  pulley  quality.    Radial  run  out causes belt tension variation with each pulley revolution.  V-belt pulleys 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. 9.4   Drive Noise Drive  noise  evaluation  in  any  belt  drive  system  should  be  approached  with  care.    There  are many potential sources of noise in a system, including vibration from related components, bearings, and resonance and amplification through framework and panels. Synchronous belt drives typically produce more noise than V-belt drives.  Noise results from the process of belt tooth meshing and physical contact with the pulleys.  The sound pressure level generally increases as operating speed and belt width increase, and as pulley diameter decreases. Drives designed on moderate pulley sizes without excessive capacity (over designed) are generally the quietest.  PowerGrip GT drives have been found to be significantly quieter than other systems due to their improved meshing characteristic (see Figure 9, page T-9).  Polyurethane belts generally produce more noise than neoprene belts.  Proper belt installation tension is also very important in minimizing  drive  noise.    The  belt  should  be  tensioned  at  a  level  that  allows  it  to  run  with  as  little meshing interference as possible. Drive alignment also has a significant effect on drive noise.  Special attention should be given to  minimizing  angular  misalignment  (shaft  parallelism).    This  assures  that  belt  teeth  are  loaded uniformly  and  minimizes  side  tracking  forces  against  the  flanges.    Parallel  misalignment  (pulley offset) is not as critical of a concern as long as the belt is not trapped or pinched between opposite