Untitled Notes

Engineering Systems and Their Applications

Module 7: Selecting Engineering Systems Applications

Course Information

Institution: Letaba TVET College
Author: Machabaphala PT

1. Gear Trains

Definition

A gear train is defined as a combination of two or more gears used to transmit motion and power between machine parts.

Types of Gear Trains

Simple Gear Train: A basic arrangement of gears where the output shaft is driven by a single input shaft.
Compound Gear Train: Multiple gears are arranged in such a way that at least one gear drives another directly, involving more than one gear ratio.

Applications

Automotive Gearboxes: Used in vehicles to manage speed and torque.
Clocks and Watches: Helps in accurate time measurement by regulating movements.
Industrial Machinery: Essential for machines used in various manufacturing processes.
Conveyor Systems: Helps in the movement of materials from one location to another.

Advantages

High Efficiency: Provides effective power transmission with minimal energy loss.
Positive Drive (No Slipping): Ensures reliability as there is no slippage between the gears.
Precise Speed Control: Allows for accurate adjustments to speed settings.

Disadvantages

Can Be Noisy: Operation may produce sound due to gear interactions.
Requires Lubrication: Essential to maintain smooth operations and reduce wear.
Expensive to Manufacture: Higher production costs due to complexity.

Selection Criteria

Required Speed Ratio: Necessary gear ratios to achieve desired speeds.
Load Capacity: The amount of weight and force that the gear train must handle.
Space Availability: The physical space available for installation.
Maintenance Requirements: Ease of service and upkeep needed for optimal functionality.

Gears Calculations Recap

The speed ratio of two meshing gears is inversely proportional to the ratio of their teeth:
rac{T_A}{T_B} = rac{N_B}{N_A} = ext{Velocity Ratio}
Note: If the driven gear (Gear B) has more teeth than the driver gear (Gear A), it rotates more slowly (speed reduction). Conversely, if the driven gear has fewer teeth, it rotates faster (speed increase).

Formula for Gear Train Speed Calculation

Using the speed ratio formula:
$N_A imes T_A = N_B imes T_B$
  Where:
  - $N_A$ = speed of driver gear (rev/min)
  - $N_B$ = speed of driven gear (rev/min)
  - $T_A$ = number of teeth on driver gear
  - $T_B$ = number of teeth on driven gear

Example Problem 1

Given: Driver gear has 15 teeth and rotates at 400 rpm; driven gear has 45 teeth.
Calculate Speed of Driven Gear:
  1. Use the formula: $N_A imes T_A = N_B imes T_B$
  2. Substitute values: $(400)(15) = (45)N_B$
  3. Solve for $N_B$ :
  N_B = rac{6000}{45} = 133.3 ext{ rpm}

Practice Problems 1

Driver gear has 15 teeth and rotates at 900 rpm. It drives a gear with 45 teeth. Calculate the speed of the driven gear.
A motor gear with 25 teeth runs at 1200 rpm. It meshes with a machine gear of 50 teeth. Find the speed of the machine gear.
A gear with 30 teeth rotates at 800 rpm. It drives a larger gear with 90 teeth. Determine the speed of the larger gear.
A gear train has driver speed 500 rpm, teeth ratio 10:50. Find driven speed.
Calculate velocity ratio for gears with 12 and 36 teeth.

2. Belt Drives

Definition

A belt drive is a power transmission system using belts and pulleys to transfer power between shafts.

Types of Belt Drives

Flat Belt Drive: A simple belt running over pulleys.
V-Belt Drive: Features a trapezoidal cross-section for better surface contact.
Timing Belt Drive: Uses teeth to prevent slippage and to ensure precise timing of movements.

Applications

Fans and Blowers: Used to facilitate air movement in various devices.
Conveyor Systems: Essential for moving goods in industries.
Automotive Engines: Transmits power from the engine to other components.
Agricultural Machinery: Implements in farming for various tasks.

Advantages

Simple and Inexpensive: Easier to design and produce compared to other methods.
Absorbs Shock Loads: Can cushion sudden changes in load.
Quiet Operation: Operates with minimal noise relative to gears.

Disadvantages

Slippage May Occur: Can lead to loss of efficiency without constant tension.
Limited Power Transmission: Not suitable for all power requirements.
Requires Tension Adjustment: Periodic maintenance required to ensure optimal performance.

Selection Criteria

Power to be Transmitted: The amount of energy needed to be transferred.
Distance Between Shafts: The separation distance affects belt choice.
Speed Requirements: Desired output speed of the driven pulley.
Environmental Conditions: Conditions that may affect the performance of the belts.

Belt Drive Calculations

The formula for calculating speed in a belt drive is:
$N_A imes D_A = N_B imes D_B$
  Where:
  - $N_A$ = speed of driver pulley (rev/min)
  - $N_B$ = speed of driven pulley (rev/min)
  - $D_A$ = diameter of driver pulley
  - $D_B$ = diameter of driven pulley

Example Problem 1

Given: Driver pulley with a diameter of 100mm rotates at 450 rpm; driven pulley has a diameter of 150mm.
Calculate Speed of Driven Pulley:
  1. Using the formula: $N_A imes D_A = N_B imes D_B$
  2. Substitute values:
$(450)(100) = (150)N_B$
  3. Solve for $N_B$ :
  N_B = rac{45000}{150} = 300 ext{ rpm}

Practice Problems 2

A belt connects a driver pulley of diameter 0.40 m rotating at 800 rpm to a driven pulley of diameter 1.20 m. Determine the driven pulley speed.
A motor drives a pulley of diameter 250 mm at a speed of 1200 rpm. The belt connects this pulley to a larger pulley of diameter 750 mm. Find the speed of the larger pulley.
A driver pulley of diameter 0.20 m rotates at 1500 rpm. It drives a pulley of diameter 0.60 m. Calculate the speed of the driven pulley.
A motor pulley with diameter of 0.30 m runs at 1000 rpm. It drives a machine pulley of diameter 0.15 m. Find the speed of the machine pulley.

Power and Torque Transmitted by Rotating Pulley

The relation can be defined as:
  P = rac{2 ext{π}NT}{60}
  Where:
  - $P$ = power (W)
  - $N$ = speed (rev/min)
  - $T$ = torque (N·m)

Worked Example

Given: A pulley rotates at 1200 rpm transmitting a torque of 40 N·m. Find the power:
  1. Use the formula: $P = rac{2 ext{π} (1200)(40)}{60}$
  2. Calculating:
  P = rac{2 ext{π} imes 48000}{60} = rac{301592}{60} = 5026 ext{ W}

Practice Problems 3

A pulley runs at 900 rpm with torque 25 N·m. Calculate the power.
A pulley delivers 3 kW at 1500 rpm. Find the torque.

3. Chain Drives

Definition

A chain drive is a mechanism that uses a chain and sprockets to transmit motion and power between shafts.

Types of Chain Drives

Roller Chain: Commonly used due to flexibility and efficiency.
Silent Chain: Provides quieter operation than roller chains.
Leaf Chain: Utilized in various industrial applications based on load capacity.

Applications

Motorcycles and Bicycles: To transfer power from the pedals or engine to the wheels.
Conveyor Systems: Used in manufacturing for transporting goods.
Industrial Machines: Essential in machines that require precise movements.

Advantages

No Slippage: Offers reliable power transmission without loss of efficiency.
High Efficiency: Very effective in transferring power across various distances.
Suitable for Long Distances: Can be used over larger spans compared to other drives.

Disadvantages

Requires Lubrication: Regular maintenance is needed to ensure longevity.
Can Be Noisy: Often produces noise, especially under load conditions.
Needs Regular Maintenance: Requires periodic checks to maintain operational efficiency.

4. Brake Systems

Definition

Brake systems are mechanical devices designed to slow down or stop motion by converting kinetic energy into heat.

Types of Brake Systems

Disc Brakes: Comprising a rotor and caliper, utilizes friction to stop.
Drum Brakes: Uses a drum-shaped part that spins and slows down with friction.
Hydraulic Brakes: Employs hydraulic force to apply pressure to the braking system.
Pneumatic Brakes: Utilizes air pressure for operation in heavy applications.
Electromagnetic Brakes: Operates based on the principle of electromagnetism.

Applications

Vehicles: Critical in automobiles for safety and control.
Industrial Machines: Employed in manufacturing equipment.
Elevators: Ensures safe stopping and holding of loads.
Cranes: Provides motion control for lifting operations.

Advantages

Provides Safety: Essential for stopping operations under various conditions.
Controls Speed: Enables regulation of speed for better handling.
Reliable Stopping Mechanism: Offers consistent performance under normal conditions.

Disadvantages

Wear and Tear: Components may degrade over time with usage.
Heat Generation: Can generate excessive heat during prolonged use, possibly leading to fading.
Maintenance Required: Necessities for regular checks to ensure functionality.

Selection Criteria

Load and Speed: Understanding of the operational loads and speeds for effective braking.
Type of Application: Selection based on whether the environment is industrial, automotive, etc.
Heat Dissipation: Requirements for how the brake systems manage and dissipate heat generated during operation.
Safety Requirements: Essential considerations based on the consequences of brake failure for the application.