Page 146 - Analysis and Design of Machine Elements

Analysis and Design of Machine Elements
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Figure 6.5 Construction of a V-belt.
High strength cords
Outer fabric cover
Rubber

commonly manufactured using leather, fabric, rubber and synthetics, provide a quiet,
compact and resilient form of power transmission.
Figure 6.5 shows the construction of a typical V-belt. The outer fabric cover gives
a belt good durability. High strength cords, usually made from natural fibres, synthetic
strands or steel, are positioned at the pitch line of belt cross section to increase the tensile
strength of belts. These cords are embedded in firm rubber compounds that provide
flexibility for the belt to pass around sheaves [1]. Different sections are combined so
that a belt is constructed to meet specific design requirements.

6.2 Working Condition Analysis

6.2.1 Geometrical Relationships in Belt Drives
A typical open-belt drive with pulley or sheave diameters of D and D and centre dis-
2
1
tance a is showninFigure6.6.Fromthisfigure,wehavecontact angle on the small
1
pulley as
= − 2
1
where
D − D 1
2
≈ sin =
2a
Therefore, the contact angles in degrees are found to be:
∘ D − D 1 ∘
2
= 180 − × 57.3
1
a
∘ D − D 1 ∘
2
= 180 + × 57.3 (6.1)
2
a
Figure 6.6 Belt drive geometry.
θ
θ Slack side
a 2
a 1
D 1
ω 1 D 2
ω 2
Tight side

a