11.1 State TWO advantages of a belt drive system compared to a chain drive system - NSC Mechanical Technology Fitting and Machining - Question 11 - 2018 - Paper 1

To calculate the fluid pressure, we use the formula:

$P = \frac{F}{A}$
where:

• $F = 120$ N (force applied)
• $A = \frac{\pi d^2}{4}$ (cross-sectional area) with $d = 0.032$ m (diameter of the plunger).

Calculating the area: $A = \frac{\pi (0.032)^2}{4} \approx 0.0008 \ m^2$
Then, $P = \frac{120}{0.0008} \approx 150000 \ Pa = 0.15 \ MPa$

We start with the pressure calculated above and calculate the area needed to exert the maximum force:

$P = \frac{F}{A} \implies A = \frac{F}{P}$
Substituting the values:

• $F = 18000$ N (18 kN)
• $P = 150000$ Pa (pressure from above)

Calculating the area: $A = \frac{18000}{150000} \approx 0.12 \ m^2$
Now we can find the diameter using the area: $A = \frac{\pi d^2}{4} \implies d = 2 \sqrt{\frac{A}{\pi}}$
Substituting the area: $d = 2 \sqrt{\frac{0.12}{\pi}} \approx 0.39 \ m \approx 390.88 \ mm$

The symbol for a one-way spring-loaded valve typically consists of a circle with a line indicating the flow direction and a spring symbol at the opposite end. This should be sketched according to standard hydraulic symbols.

The rotation frequency of the driver pulley can be calculated using the formula:

$N_{DR} D_{DR} = N_{DN} D_{DN}$
Given:

• $N_{DN} = 80$ r/min
• $D_{DN} = 240$ mm
• $D_{DR} = 75$ mm

We calculate: $N_{DR} = \frac{N_{DN} D_{DN}}{D_{DR}} = \frac{80 \times 240}{75} \approx 256 \ r/min$

The rotation frequency of the output shaft, considering gear ratios, follows:

• Input speed = 3000 r/min
• Gear A has 20 teeth, Gear B has 35 teeth:

Using the gear ratio: $N_{A} = N_{O} \frac{T_{B}}{T_{A}}$
Letting $T_{A} = 20$ and $T_{B} = 35$: $N_{O} = 3000 \frac{35}{20} \approx 5250 \ r/min$
To convert this to revolutions per second, divide by 60: $\frac{5250}{60} \approx 87.5 \ r/s$

The gear ratio can be calculated using the formula:

$\text{Gear Ratio} = \frac{\text{Number of teeth on driven gears}}{\text{Number of teeth on driver gears}}$
From the information:

• Teeth on Gear B = 35
• Teeth on Gear A = 20 Thus, $\text{Gear Ratio} = \frac{35}{20} = 1.75:1$

Work done can be calculated using the formula:

$W = F \times d$
Where:

• $F = 250$ N
• $d = 15$ m

Calculating: $W = 250 \times 15 = 3750 \ J$