PolyChain® GT Timing Belts - Walther Flender

Walther Flender Gruppe
PolyChain ® GT Timing Belts PAGE 15
Belt tension
The Poly Chain® timing belt needs a certain tension during operation
to maintain reliable engagement of the teeth also under
intermittent loads and temporary overloads. Unnecessarily high
initial tension reduces the service life of the drive system, increases
wear on the bearings and the teeth, and also increases the noise
level. Insufficient tension can prevent the belt teeth from meshing
properly in the pulley teeth, which can even cause the belt to
skip in case of an overload. Depending on the application and the
particular dynamic peak loads, the belt tension can deviate from
the calculated initial tension, so that the calculation provided here
should be used only as a recommendation for standard applications.
This applies especially to drive systems with extreme impact
and pulse loads; in this case, please contact us.
Calculation of the static initial load
F St = K · P + m · v 2
v
F St [N] = Static initial tension
P [kW] = Installed motor power output
v [m/s] = Belt speed
m = Factor for weight per metre, see table
K = Constant for compensating for
impact loads
K = 600 max. initial tension for compensating for pulse loads
Pitch Belt width (mm) m Y
8 mm 12 0.057 80
21 0.098 140
36 0.167 240
62 0.290 413
14 mm 20 0.158 245
37 0.291 454
68 0.536 834
90 0.711 1103
125 0.986 1530
Table: Calculation factors for belt tension
If the transmission capacity is significantly higher than the calculated
capacity of the belt, the calculations can result in incorrect
belt tensions. In this case, please use the minimum initial tensions
specified in the following table:
Pitch Belt width (mm)
8 mm
14 mm
Min. F st
Values (N)
12 125
21 220
36 375
62 645
20 530
37 980
68 1800
90 2380
125 3310
Table: Minimum initial tension of PolyChain® timing belts
Checking the belt tension
Two methods can be used for checking the belt tension:
1. Frequency measurement and 2. Test load method
1. Frequency measurement
A precise method for pre-setting the correct belt tension is to
measure the frequency with the WF Tension Meter (Figure 1) or
the Gates-Sonic Tension Meter (Figure 2). With a sensing head
that is held above the installed belt it is possible to measure the
frequency at the pre-tensioned belt in order to achieve the optimum
belt tension.
The calculated oscillation frequency f [Hz] depends on the freely
oscillating span length L [m], the static initial tension load FSt [N]
and the weight per meter m [kg/m] of the belt and corresponds
to the relationship
f = 1 · √ F St
2 · L m
For a detailed description of the instruments and detailed calculation
documentation, please contact our application engineers.
2. Test load method
Calculation of deflection
S = √A2 – [ dwG – d 2
wk ]
2
S : Span length for test force measurement (mm)
d : Deflection (mm)
dwk : Pitch diameter of the small pulley (mm)
dwG : Pitch diameter of the large pulley (mm)
FP : Test force (N)
A : Centre distance of axes (mm); separate tables are available
for the calculation and will be provided on request.
If the span tension is set correctly, the deflection is
d ~ 1 / 100 · S
Calculation of test force
Figure 1:
WF Tension Meter
S
d
FP
Figure 2:
Gates Sonic Tension
Meter 507C
F St + S · Y F P : Test force (N)
F P = l w F St : Static initial tension
25 l w : Pitch length (mm)
Y : Constant (see table)
Adjusting the initial tension
For the calculated test force, the deflection should be ca. 1/100 of
the span length [mm] of the test force measurement. It may be
necessary to correct the belt tension.