PolyChain® GT Timing Belts - Walther Flender

Walther Flender Gruppe
PolyChain ® GT Timing Belts PAGE 23
Calculation & formulas
Calculation
General
The basis for determining the timing belt dimensions is a calculation
method that takes the following influences into account:
* Power
* Torques
* Speed
* Duty cycle of the drive system
* Operating characteristics
* Number of meshing teeth
* Transmission ratio
* Centre distance of axes
All data concerning the transmitted torque, the speed and the
length of a PolyChain® timing belt relates to the pitch line, which
is assumed to be centre of the tensile member. The pitch line is
precisely defined and is identical to the pitch diameter on the timing
belt pulley. Half the difference in diameter between the pitch
diameter and outer diameter is equal to the size of the belt tooth
root to the centre of the tensile body.
Project data sheet
During the design and the later dimensioning of a drive system,
you should remember that optimum use of the transmission
capacity, long service life and high efficiency are possible only if
the actual operating conditions are known, so that critical conditions
can already be taken into account during the design stage.
The project data sheet on page 44 is provided to help you with
this task.
Preliminary selection
Use the diagram on page 5 to make a preliminary selection of the
suitable belt pitch.
Belt width
Taking into account the inherent load of the timing belt, it is
always a good idea to select a belt width that is smaller than the
diameter of the smallest timing belt pulley. A wider timing belt, if
mounted incorrectly, is more likely to cause varying edge tensions,
which can prevent optimum running of the belt. In borderline
cases, it is often better to select a larger pitch instead of a wider
belt. If this is not possible, we recommend a belt pitch in 2 parallel
running belt segments (of the same length), to reduce the
transverse rigidity of the belt in combination with the small pulley
diameters.
Pulley diameter
Use pulleys with the largest diameters possible! This makes optimal
use of the power output range of the belt at high peripheral
speeds. Pulleys with larger diameters have less bending stress and
the belt does not have to be as wide.
Safety factors
The table on page 25 shows load factors that include the drive
characteristics of various machine types as an increased safety
factor.
In addition to these safety factors, it can be extremely important
to include starting and stopping processes together with the corresponding
mass effects of the respective drive system as a design
criterion for the safety considerations. Especially during stopping
or locking processes, mass effect can cause inertia forces that are
far above the maximum permissible tangential loads of the belts
listed in the power output tables (pages 17 and 20).
The use of suitable regulators (e.g. a soft start ramp controller for
starting and stopping) or the use of suitable overload protection
can greatly reduce the mass effect to optimize fail-safe operation.
Abbreviations
a
a
A
b
b R
B
B W
C spez
d B
d a
d w
d wk
d wg
e
F a
F b
F B
F H
F P
F R
F t
F U
F V
F zul
g
h S
h t
i
l w
l t
M
m
m L
m R
m ges
m Z
m Z, red
n
n MOT
P
P B
P N
S Bruch
S G
S 1
S 2
S 3
S 4
S 5
S 6
S 7
t
v
z
z e
z g
z k
Temperature expansion coefficient
Acceleration
Centre distance of axes
Braking deceleration
Belt width
Pulley width
Flexural fatigue
Specific spring constant
Bore diameter
Outer diameter
Pitch diameter
Pitch diameter of small pulley
Pitch diameter of large pulley
Stretching
Acceleration force
Braking force
Driving force, calculated
Lifting force
Test load for belt tension
Friction force
Span tension
Tangential load
Initial tension
Maximum permissible tangential load
Acceleration of gravity
Belt thickness
Tooth height
Transmission ratio
Pitch length
Taut side
Torque
Mass
Mass of load
Mass of belt
Total weight
Mass of timing belt pulley
Reduced mass of timing belt pulley
Speed
Motor speed
Power output
Calculated power output
Rated power output
Security against fracture
Total application factor
Load factor
Tooth mesh factor
Transmission allowance
Bending factor
Special application factor
Belt length factor
Belt width factor
Pitch
Speed
Number of belt pulleys
Number of meshing teeth
Number of teeth, large pulley
Number of teeth, small pulley
1/K
m/s 2
mm
m/s 2
mm
mm
1/s
N
mm
mm
mm
mm
mm
%
N
N
N
N
N
N
N
N
N
N
m/s 2
mm
mm
mm
mm
Nm
kg
kg
kg
kg
kg
kg
l/min
l/min
kW
kW
kW
m/s
(The formula collection applies to all timing belt catalogs;
therefore, it is possible that not all abbreviations occur in
this catalog).