40
4.5 ZRL tensioning
Calculation and setting of tension for
optibelt
ZRL-M open-ended
and
optibelt
ZRL-V joined endless timing belts
Correct tensioning is of special importance for the reliable and
efficient transmission of power. Proper tensioning of the stationary
belt will ensure that it will run at the correct tension.
● Insufficient tension coupled with high drive loads will lead to the
belt jumping teeth on the pulley and ultimately to belt breakage.
● Excessive tension under similar conditions will cause severe
wear, shearing of the belt teeth, excessive running noise and
bearing damage.
It is advisable therefore to calculate and set the static tension for
each drive individually using the formulae below. The tensioning
factor c
v
takes account of the loads combined in the overall service
factor c
2
.
Setting the static tension, Figure 3.1, page 28
One pulley of the drive only may be stationary when the static
tension is adjusted. The second pulley and the other pulleys of a
multiple pulley drive must be able to rotate freely.
1st method:
Controlled centre distance adjustment
Where timing belts are inaccessible tensioning can be carried out
by adjusting the drive centre distance by the calculated figure x
v
mean. Because of the low plastic stretch of the timing belts, this
method of tensioning is recommended mainly for two pulley drives
with very long centre distances.
2nd method:
Span deflection
The test force F
v
should be applied to the centre of the span length
L and perpendicular to it. The use of sharp-edged objects for
applying the force MUST be avoided to prevent belt kink. Correct
static tension is achieved when the deflection e
v
corresponds to the
calculated value.
When the drive system has more than the two pulleys shown in
Figure 3.1 page 24 the tension can be measured between any two
pulleys in the system provided the belt is in contact with these
pulleys with the same face (top or bottom). The only difference will
be e
v
which will change as a function of span length.
3rd method:
Measurement of static shaft load
Calculate static shaft load S
a
. Tension belt until the measured S
a
is
the same as the calculated S
a
.
By virtue of the zero stretch tension cord, the belt will
require no further tension checks after fitting.
* For i
=
1, see page 28 for the calculation of static shaft loading S
a
and of span length L.
Calculation of required tension, ZRL
Formulae
Tension factor c
v
Example, using the figures from pages 32 and 35
ZRL-M ZRL-V
c
v
= + 0.9 1.05 ≤ c
v
c
v
= + 0.9 = 1.4 c
v
= + 0.9 = 1.2
2.0 – 1
2
1.6 – 1
2
c
2
– 1
2
Tensioning
1st method
Tensioning distance x
v
x
v
=
for i = 1
x
v
=
x
v
= 2.4 mm
x
v
=
x
v
= 2.0 mm
1.4 · 0.001 · 6680
2.0 · 2
1.2 · 0.001 · 5360
1.6 · 2
2nd method
Test force F
v
and deflection e
v
for span length L
F
v
=
e
v
=
L= a
nom
for i = 1*
F
v
= = 15.0 N
e
v
= = 64.7 mm
L = 3235 mm
L
50
1.4 · 214.5
20
3235
50
F
v
= = 44.2 N
e
v
= = 49.6 mm
L = 2480 mm
1.2 · 736
20
2480
50
3rd method
S
a
= c
v
· S
n3
for i = 1*
S
a
= 1.4 · 214.5 = 300 N S
a
= 1.2 · 736 = 883 N
or
or
S
n3
, see earlier calculation,
also formulae on page 13
S
n3
, see earlier calculation,
also formulae on page 13
c
v
· 0.001 · L
wnom
c
2
· 2
c
v
· S
n3
20
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