1] Belt material selection

(Leather, $\mathrm{E}=90 \mathrm{MPa}, \quad [\sigma]=7 \mathrm{MPa}, \sigma^{-1}=9$ to 10 $\mathrm{MPa}$ and $\rho = \frac{1400 \mathrm{kg}}{\mathrm{m}^{3}}$ and $\mu=0.25$

2] Belt section selection (as shown in the figure)

For given or assumed application determine service factor (SF) $\quad$ PSG-7.69

Based on design power $P_d = SF × P_m$ Select suitable belt section $\quad$ PSG-7.58

Draw belt cross section showing b (PSG-7.70) and B=width, T=thickness, cone angle $2\beta$.

Also, write recommended minimum pitch diameter of pulley $d_{1 min}$

Find the area of cross-section of the belt $A = T(B − T tanB)$

3] Pulley and Belt Geometry

Decide diameter of driver pulley $d_1$ using the reference of $d_{1 min}$

Find the diameter of driven pulley assuming slip of 1%

$\frac{d_{2}}{d_{1}(1-s / 100)}=\frac{n_{1}}{n_{2}}$ Find actual $n_{2}$ and actual velocity ratio $i=n_{1} / n_{2}$

Find $d_2$ and round off appropriately PSG 7.54

Assume initial centre distance as $C = d_2$

Arc of Contact = $180^{\circ}-\frac{d_{2}-d_{1}}{c} \times 60^{\circ}$ PSG-7.53

Length of belt

• Open Drive length $=2 C+\frac{\pi}{2}(D+d)+\frac{(D-d)^{2}}{4 C} \quad$ PSG-7.53

Find nominal pitch length for selected section PSG-7.60

Find exact center distance C after finding constants A and B PSG-7.61

4] Number of V-belts required ($n_b$) ($\sigma_{max}$ approach)

Belt Tensions $\frac{T_{1}}{T_{2}}=e^{\mu \theta} \csc \beta$

Belt Velocity $v=\frac{\pi d_{1} n_{1}}{60} m / s e c$

Using power $P=\left(T_{1}-T_{2}\right) \times v,$ determine belt tensions.

If life of belt is given then find $\sigma_{\text {max}}$ using life equation OR use $\sigma_{\max }=[\sigma]$

Maximum stress induced in the belt is given by,

$$\sigma_{\max }=\sigma_{t}+\sigma_{c}+\sigma_{b}$$

Where, $\sigma_{t}(\text { Tensile stress }) = {T_{1}} / A \times n_{b}$

$\quad$ $\sigma_{c}(\text {Stress due to centrifugal tension})=\rho v^{2}$

$\quad$ $\sigma_{b}(\text { Bending stress })=E b / r_{1}$

Determine the number of v belts $n_b$

5] Life of V Belt

Find the life of belt (H) in hours using the following equation

$$\sigma_{\max }^{m} \times \frac{v}{L} \times n_{p} \times H \times 3600=\left(\sigma^{-1}\right)^{m} \times 10^{7}$$

Where $n_p$ = number of pulleys and m constant = 8 to 9

ALTERNATIVELY

6] Number of Belts = $\frac{P \times F_{a}}{k w \times F_{e} \times F_{d}}$

• a) Motor Power

• b) Correction Factor according to service. ($F_a$) PSG-7.69

  Select according to industrial Service factor

• c) Power Capacity or Rating of V-Belt (as shown in the figure below)

  

• d) Correction Factor for length ($F_e$) PSG-7.58, 59 and 60

  Select according to the arc of the contact on the smaller pulley.

  Arc of contact $=180^{\circ}-60^{\circ} \frac{D-d}{c}$ PSG-7.68

  Select value from V-V or V Flat Belt.