Elemen Mesin ( Belt calculation )
BELT DRIVES
Flat belts and V-belts:
It may be employed to transmit power from
one shaft to
another where it is not necessary to maintain an exact speed ratio between the
two shafts. Power losses due to slip and creep amount to from 3.0 to 5.0
percent for most belt drives. In the following discussion it will be assumed
that the shafts are parallel.
Belt design:
It involves either the proper belt
selection to transmit a required power or the determination of the power that
may be transmitted by a given flat belt or by one V-belt. In the first case,
the width of the bet is unknown, while in the
second case, the width is known. The belt
thickness is assumed for both cases.
The power transmitted by a
belt drive is a function of the belt tension and belt speed.
Power = (T1 –T2)v , W or = (T1 –T2)V/550 ,
hp
Where:
T1 = belt tension
in tight side, N
T2 = belt tension in loose side, N
V = belt speed, m/s
** The following formula for determining
the stress, σ2, for the flat belts applies when the thickness
of the belt is given but the width is unknown:
Where:
= maximum allowable stress, N/m2
= stress in the slack
side of the belt, N/m2
m¢
= mass of 1.0 meter
of belt 1.0 m2
in cross section , kg
f = coefficient of friction
between belt and pulley
a
= angle of wrap of belt on pulley, rad.
** The required cross-section area of the
flat belt for the case of the width unknown may be determined by:
Required area = 
** The required flat belt width b
is therefore:
B = area/thickness
The value of (T1 –T2)
may be determined from the horsepower requirement,
P = (T1 – T2)V, W
** The maximum tension in the tight side
of the belt depends on the allowable stress of the belt material. The allowable
tensile stress for leather belting is usually 2.0 to 3.45 MN/m2,
and the allowable stress for rubber belting will run from 1.0 to 1.7
MN/m2, depending on the quality of the material. Leather belting
can be obtained in various single ply thicknesses. Double and triple ply belts
are also available.
** The following formula for determining
the value of T2 for
both flat and V-belt applies when the width and thickness of the belt are
known:
Where:
m = b.t.p = mass of 1.0
meter of belt, kg/m
b = belt width, m, t = belt
thickness, m , p = belt density, kg/m3
q
= groove angle for the V-belt (q is 180° for a flat belt).
** The quantity mV2 is
due to centrifugal force, which tends to cause the belt to leave the pulley and
reduce the power that may be transmitted.
Angle of wrap:
The angles of wrap for an open belt may be
determined by:
The angles of wrap for a crossed belt
drive may be determined by:
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