Home Page
T-40
The following precautions should be taken when installing all timing belt drives:
1.
Timing belt installation should be a snug fit, neither too tight nor too loose. The positive grip
of the belt eliminates the need for high initial tension. Consequently, a belt, when installed
with a snug fit (that is, not too taut) assures longer life, less bearing wear and quieter
operation. Preloading (often the cause of premature failure) is not necessary.
When torque is unusually high, a loose belt may "jump teeth" on starting. In such a case, the
tension should be increased gradually, until satisfactory operation is attained. A good rule of
thumb for installation tension is as shown in Figure 20, and the corresponding tensioning
force is shown in Table 16, both shown in SECTION 10 BELT TENSIONING. For widths
other than shown, increase force proportionally to the belt width. Instrumentation for measuring
belt tension is available. Consult the product section of this catalog.
2.
Be sure that shafts are parallel and pulleys are in alignment. On a long center drive, it is
sometimes advisable to offset the driven pulley to compensate for the tendency of the belt to
run against one flange.
3.
On a long center drive, it is imperative that the belt sag is not large enough to permit teeth on
the slack side to engage the teeth on the tight side.
4.
It is important that the frame supporting the pulleys be rigid at all times. A nonrigid frame
causes variation in center distance and resulting belt slackness. This, in turn, can lead to
jumping of teeth – especially under starting load with shaft misalignment.
5.
Although belt tension requires little attention after initial installation, provision should be made
for some center distance adjustment for ease in installing and removing belts. Do not force
belt over flange of pulley.
6.
Idlers, either of the inside or outside type, are not recommended and should not be used
except for power takeoff or functional use. When an idler is necessary, it should be on the
slack side of the belt. Inside idlers must be grooved, unless their diameters are greater than
an equivalent 40-groove pulley. Flat idlers must not be crowned (use edge flanges). Idler
diameters must exceed the smallest diameter drive pulley. Idler arc of contact should be held
to a minimum.
In addition to the general guidelines enumerated previously, specific operating characteristics of
the drive must be taken into account. These may include the following:
9.1 Low Speed Operation
Synchronous drives are especially well suited for low speed, high torque applications. Their
positive driving nature prevents potential slippage associated with V-belt drives , and even allows
significantly greater torque carrying capability. Small pitch synchronous drives operating at speeds of
50 ft/min (0.25 m/s) or less are considered to be low speed. Care should be taken in the drive selection
process as stall and peak torques can sometimes be very high. While intermittent peak torques can
often be carried by synchronous drives without special considerations, high cyclic peak torque loading
should be carefully reviewed.
Proper belt installation tension and rigid drive bracketry and framework is essential in preventing
belt tooth jumping under peak torque loads. It is also helpful to design with more than the normal
minimum of 6 belt teeth in mesh to ensure adequate belt tooth shear strength.
Newer generation curvilinear systems like PowerGrip GT and PowerGrip HTD should be used in
low speed, high torque applications, as trapezoidal timing belts are more prone to tooth jumping, and
have significantly less load carrying capacity.
9.2 High Speed Operation
Synchronous belt drives are often used in high speed applications even though V-belt drives are
typically better suited. They are often used because of their positive driving characteristic (no creep or