Home Page T-44 ground.  Standard rubber synchronous belts do not meet this requirement, but can be manufactured in a static conductive construction on a made-to-order basis.  Normal belt wear resulting from long term operation or environmental contamination can influence belt conductivity properties. In  sensitive  applications,  rubber  synchronous  belts  are  preferred  over  urethane  belts  since urethane belting cannot be produced in a conductive construction. 9.7   Belt Tracking Lateral tracking characteristics of synchronous belts is a common area of inquiry.  While it is normal  for  a  belt  to  favor  one  side  of  the  pulleys  while  running,  it  is  abnormal  for  a  belt  to  exert significant  force  against  a  flange  resulting  in  belt  edge  wear  and  potential  flange  failure.    Belt tracking is influenced by several factors.  In order of significance, discussion about these factors is as follows: Tensile  Cord  Twist:    Tensile  cords  are  formed  into  a  single  twist  configuration  during  their manufacture.    Synchronous  belts  made  with  only  single  twist  tensile  cords  track  laterally  with  a significant force.  To neutralize this tracking force, tensile cords are produced in right and left hand twist  (or  "S"  and  "Z"  twist)  configurations.    Belts  made  with  "S"  twist  tensile  cords  track  in  the opposite  direction  to  those  built  with  "Z"  twist  cord.    Belts  made  with  alternating  "S"  and  "Z"  twist tensile cords track with minimal lateral force because the tracking characteristics of the two cords offset each other.  The content of "S" and "Z" twist tensile cords varies slightly with every belt that is produced.  As a result, every belt has an unprecedented tendency to track in either one direction or the other.  When an application requires a belt to track in one specific direction only, a single twist construction is used.  See Figures 16 & 17, previously shown, on pages T-12 and T-13. Angular  Misalignment:    Angular  misalignment,  or  shaft  nonparallelism,  cause  synchronous belts  to  track  laterally.    The  angle  of  misalignment  influences  the  magnitude  and  direction  of  the tracking  force.    Synchronous  belts  tend  to  track  "downhill"  to  a  state  of  lower  tension  or  shorter center distance. Belt  Width:    The  potential  magnitude  of  belt  tracking  force  is  directly  related  to  belt  width. Wide belts tend to track with more force than narrow belts. Pulley  Diameter:    Belt  operating  on  small  pulley  diameters  can  tend  to  generate  higher tracking forces than on large diameters.  This is particularly true as the belt width approaches the pulley diameter.  Drives with pulley diameters less than the belt width are not generally recommended because belt tracking forces can become excessive. Belt Length:  Because of the way tensile cords are applied on to the belt molds, short belts can  tend  to  exhibit  higher  tracking  forces  than  long  belts.    The  helix  angle  of  the  tensile  cord decreases with increasing belt length. Gravity:    In  drive  applications  with  vertical  shafts,  gravity  pulls  the  belt  downward.    The magnitude  of  this  force  is  minimal  with  small  pitch  synchronous  belts.    Sag  in  long  belt  spans should be avoided by applying adequate belt installation tension. Torque  Loads:    Sometimes,  while  in  operation,  a  synchronous  belt  will  move  laterally  from side  to  side  on  the  pulleys  rather  than  operating  in  a  consistent  position.    While  not  generally considered  to  be  a  significant  concern,  one  explanation  for  this  is  varying  torque  loads  within  the drive.  Synchronous belts sometimes track differently with changing loads.  There are many potential reasons for this; the primary cause is related to tensile cord distortion while under pressure against the  pulleys.    Variation  in  belt  tensile  loads  can  also  cause  changes  in  framework  deflection,  and