Allen Engineering Corporation MSP470A, Manual

Page: 57 / 120

053257 - 01/2014
SECTION 3
SERVICE
Page 3-17
Because of the high performance capabilities of PowerGrip belts, it is pos-
sible to design drives that have significantly greater load than are neces-
sary to carry the actual design load. Consequently, Formula 14 can pro-
vide Tst values less than are necessary for the belt to operate properly,
resulting in poor belt performance and reduced service life. If a more
appropriately sized drive cannot be designed, minimum recommended Tst
values are provided in Table 10 to assure that the belts function properly
when lightly loaded.
Always use the greater T
st
value; i.e., from T
st
Formula 14 or Table 10.
NOTE: When applying static belt tension values directly, multiply the
required base static installation tension (T
st
) calculated in Formula 14 by
the following factors:
For New Belts:
Minimum Static Tension = Base Static Tension X 1.1
Maximum Static Tension = Base Static Tension X 1.2
For Used Belts:
Minimum Static Tension = Base Static Tension X 0.8
Maximum Static Tension = Base Static Tension X 0.9
STEP 2: Calculate the minimum and maximum
recommended deflection forces.
A. Measure the span length of your drive (see sketch).
B. New belt minimum recommended force:
Formula 15
deflection force, Min
.
C. New belt maximum recommended force:
Formula 16
deflection force, Max.
Where:
T
st
= Base Static tension, lbf
t = span length, inches
L = belt pitch length, inches
Y= constant from Table 10
USED BELT NOTE: For re-installation of a used belt, a recommended ten-
sion of 0.8 T
st
to 0.9 T
st
value should be used in calcu-
lating the deflection forces, instead of the
1.1 T
st
to 1.2 T
st
shown for new belts.
STEP 3: Applying the tension.
Force deflection tension method
A.
At the center of the span (t) apply a force perpendicular to the span large
enough to deflect the belt on the drive 1/64 inch per inch of span length
from its normal position. One sprocket should be free to rotate. Be sure
the force is applied evenly across the entire belt width. If the belt is a
wide synchronous belt, place a piece of steel or angle iron across the
belt width and deflect the entire width of the belt evenly.
B. Compare this deflection force with the range of forces calculated in
Step 2.
1. If it is less than the minimum recommended deflection force, the
belt should be tightened.
2. If it is greater than the maximum recommended deflection force,
the belt should be loosened.
Span vibration tension method
The Sonic Tension Meter detects the vibration frequency in the belt span,
and converts that measurement into the actual static tension in the belt.
To use the Sonic Tension Meter, begin by entering the belt unit weight,
belt width, and the span length. To measure the span vibration, press the
“Measure” button on the meter, tap the belt span, and hold the micro-
phone approximately 1/4” away from the back of the belt. The Sonic
Tension Meter will display the static tension, and can also display the span
vibration frequency.
The belt unit weights for use with the Gates Sonic Tension Meter are
shown in the following table.
Belt Product Family
Belt Cross
section
Adjusted Belt Weight
(grams/meter)
Poly Chain GT2
8mm 4.7
14mm 7.9
Belt Tensioning - cont’d
The following are the parameters for belt
tensioning on the MSP470.
Drive Shaft Poly Chain Belt:
Pen Tester Sonic Tester
15-16 Lbs New 904 to 986 N
11-13 Lbs Used 657 to 740 N
Engine Shaft Poly Chain Belt:
Pen Tester Sonic Tester
14-15 Lbs New 894 to 975 N
11-12 Lbs Used 650 to 731 N