Brochure

88
®
where:
L = Pitch Length of Belt
C = Center Distance
D = Datum or Pitch Diameter of Large Sheave
d = Datum or Pitch Diameter of Small Sheave
DrivenSpeedVariations
All V-Belt Drives will vary slightly from the speeds shown in the Drive
Selection Tables. These variations are due to different motor speeds
depending on load, changing frequencies (on A.C. Motors) or voltage
(on D.C. Motors), varying tensions and resulting slip, and allowable
manufacturing tolerances in belts and sheaves. Also, actual sheave
pitch diameters and actual belt pitch lines have been changed slightly
over the years by all manufacturers but catalog data has not been
changed to reflect this.
The drive selection tables are still very usable and ratios still can be
calculated from published sheave pitch or datum diameters since the
variations are small and historically have caused very few problems
through out the vast range of V-Belt Drive applications. A good rule of
thumb is to design a belt drive based on ±3% speed variation.
In the few instances where very close speed tolerances are required,
contact Application Engineering for assistance or use the Browning
Edge
Selection Program.
Speed-Up,Quarter-Turn,andV-FlatDrives
These drives occur infrequently and should be referred to Browning
for special design considerations.
Belt Section Selection Chart
Table No. 1
DatumSystem
In December, 1987, RMA/MPTA adopted Standard IP20-1988. This
standard supersedes IP20-1977 and affected the A, B, C, and D belts
and sheaves. Those products in this catalog are in accordance with
IP20-1988 which incorporates the Datum Diameter System.
The Datum System specifies the Datum Diameter as the effective
diameter for determining the pitch length of the belt for center distance
calculation. In this catalog, Datum Diameter (D.D.) is now listed for the
A, B, C, and D sheaves and is equal to the old Pitch Diameter (P.D.)
shown in previous catalogs.
BeltVelocity
Belt velocity is not needed for calculation of drives, as the horsepower
ratings shown are based on the rpm of the sheave. If belt velocity is
desired for any reason, use the formula:
BeltVelocityinFeetperMinute(rpm)=
D.D.orP.D.ofSheave×.2618×SpeedofSheave(rpm)
Cast Iron Sheaves must not be used beyond 6500 fpm belt speed.
Since the majority of stock sheaves are made of cast iron, we list no
ratings above 6500 fpm.
Some types of belts lose ratings before they reach 6500 fpm and other
types continue to increase beyond 6500 fpm. The Basic Rating Tables
and the Drive Selection Tables reflect these variations.
Special Balance
Functionally, speeds up to 6500 fpm are acceptable; however, in ap-
plications where vibration requirements are critical, special balancing
(usually dynamic) for speeds above 5000 fpm may be considered.
Factors to be considered for special balance requirements are: rigidity
of drive mounting, whether noise created by a level of vibration would
be prohibitive, etc. Many drives are in service running at speeds up
to 6500 FPM without special balancing.
Center Distance and Belt Length
The belt lengths listed in the Drive Selection Tables can be interpo-
lated for belt size, center distance and "F" factor from the shortest to
the longest shown.
Interpolation
For every inch of belt length difference there is approximately 1/2 inch
center distance change. All belt numbers reflect a relation if it is pitch
length, outside length or inside length. An A26 belt is 2" longer than
an A24 belt; a B105 belt is 15" longer than a B90 belt; a 3V335 belt is
8.5" longer than a 3V250 belt, etc.
Interpolation example:
If an A128 belt gives 50.0" C.D. with 1.12 "F" factor and an A96 gives
34.0 C.D. with 1.05 "F" factor, then an A112 belt gives 42.0 C.D. with
1.09 "F" factor.
If a 5V1200 belt gives 83.1" C.D. with 1.07 "F" factor and a 5V1600
gives 63.1 C.D. with 1.03 "F" factor, then a 5V1800 belt gives 73.1
C.D. with 1.05 "F" factor.
Center distance and belt lengths determined by interpolation are usu-
ally close enough as all drives should provide for take-up as indicated
on page 85. If closer calculation is necessary for any reason use the
following formula:
(D – d)
2
L = 2C + 1.57 (D + d) +
4C
Gripbelt
®
DriveEngineeringData
hp Belt Section
1/2 A AX
3/4 A AX
1 A AX
1 1/2 A AX
2 A AX
3 AX A BX
5 BX AX B A
7 1/2 BX B 5VX 3VX
10 5VX,BX B 3VX AX
15 5VX,BX B 3VX AX
20 5VX BX B 3VX
25 5VX BX B 3VX
30 5VX BX B 3VX
40 5VX,5V BX B
50 5VX,5V BX B CX
60 5VX,5V BX B CX
75 5VX,5V CX BX C
100 5VX,5V CX C
125 5VX,5V CX C
150 5VX,5V CX C
200 5VX,5V CX
250 5VX,5V CX
The best drive will usually be found by using Belt Section from the first column. If,
for any reason, such as sheave shortage, this drive is not suitable, go to the next
column.
"AX" drives are found in the "A" Drive Selection Tables; "BX" in the "B" Tables, etc.