T–50
• Design with large pulleys with more teeth in mesh.
• Keep belts tight, and control tension closely.
• Design frame/shafting to be rigid under load.
• Use high quality machined pulleys to minimize radial runout and lateral wobble.
SECTION 10 BELT TENSIONING
10.1 What Is Proper Installation Tension
One of the benefits of small synchronous belt drives is lower belt pre-tensioning in comparison
to comparable V-belt drives, but proper installation tension is still important in achieving the best
possible drive performance. In general terms, belt pre-tensioning is needed for proper belt/pulley
meshing to prevent belt ratcheting under peak loading, to compensate for initial belt tension decay,
and to prestress the drive framework. The amount of installation tension that is actually needed is
influenced by the type of application as well as the system design. Some general examples of this
are as follows:
Motion Transfer Drives: Motion transfer drives, by definition, are required to carry extremely
light torque loads. In these applications, belt installation tension is needed only to cause the belt to
conform to and mesh properly with the pulleys. The amount of tension necessary for this is
referred to as the minimum tension (Tst). Minimum tensions, on a per span basis, are included in
Table 19, on page T-51. Some motion transfer drives carry very little torque, but have a need for
accurate registration requirements. These systems may require additional static (or installation)
tension in order to minimize registration error.
Normal Power Transmission Drives: Normal power transmission drives should be designed
in accordance with published torque ratings and a reasonable service factor (between 1.5 and 2.0).
In these applications, belt installation tension is needed to allow the belt to maintain a proper fit with
the pulleys while under load, and to prevent belt ratcheting under peak loads. For these drives,
proper installation tension can be determined using two different approaches. If torque loads are
known and well defined, and an accurate tension value is desired, Equation (10-1) or Equation
(10-2) should be used. If the torque loads are not as well defined, and a quick value is desired for
use as a starting point, values from Table 20 can be used. All static tension values are on a per
span basis.
0.812 DQ
Tst = –––––––– + mS2 (lb)
(10-1)
d
(For drives with a Service Factor of 1.3 or greater)
1.05 DQ
Tst = –––––––– + mS2 (lb)
(10-2)
d
(For drives with a Service Factor less than 1.3)
where:
Tst
= Static tension per span (lbs)
DQ = Driver design torque (lb•in)
d
= Driver pitch diameter (in)
S
= Belt speed/1000 (ft/min)
where Belt speed = (Driver pitch diameter x Driver rpm)/3.82
m
= Mass factor from Table 19
