SACA - Smart Automation Certification Alliance Mechanical Power Transmission Questions and Answers 1 — Questions and Answers
Question 1: A motor operates at 1800 RPM and is connected to a simple gearbox. The drive gear on the motor shaft has 20 teeth, and the driven gear on the output shaft has 80 teeth. What is the approximate output speed of the gearbox?
- 450 RPM (Correct answer)
- 1800 RPM
- 7200 RPM
- 900 RPM
Correct answer: 450 RPM
The gear ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the drive gear (80 / 20 = 4). This results in a 4:1 speed reduction. The input speed (1800 RPM) is then divided by the gear ratio (4) to determine the output speed (1800 / 4 = 450 RPM).
Question 2: Which of the following is a primary advantage of using a synchronous (timing) belt drive system compared to a standard V-belt drive?
- Greater ability to absorb shock loads
- Lower operational noise at all speeds
- Positive, slip-proof engagement for precise positioning (Correct answer)
- Less expensive and more readily available sprockets
Correct answer: Positive, slip-proof engagement for precise positioning
The key advantage of a synchronous belt is that its teeth mesh with the grooves of the sprockets, creating a positive engagement that prevents slipping. This is crucial for applications that require precise timing and position control, which V-belts cannot guarantee as they rely on friction and can slip under load.
Question 3: What is the primary function of a flexible shaft coupling, such as a jaw or grid coupling, in a mechanical power transmission system?
- To provide a perfectly rigid connection with zero backlash
- To significantly increase the torque transmitted between shafts
- To act as a mechanical fuse that fails during an overload
- To accommodate for minor parallel and angular misalignment between shafts (Correct answer)
Correct answer: To accommodate for minor parallel and angular misalignment between shafts
Flexible couplings are specifically designed to connect two shafts while allowing for small amounts of misalignment (angular, parallel, or axial). This prevents premature wear and failure of connected components like bearings, which would be subjected to high stress if a rigid coupling were used with misaligned shafts.
Question 4: During a routine inspection, a technician notes a loud, high-pitched grinding noise originating from a pillow block bearing on a conveyor line. The noise increases with the speed of the conveyor. Which of the following is the most likely cause?
- Improper V-belt tension
- A loose shaft key
- Contamination or lack of lubrication in the bearing (Correct answer)
- Motor soft foot
Correct answer: Contamination or lack of lubrication in the bearing
Grinding, whining, or squealing noises that change with rotational speed are classic symptoms of a failing rolling-element bearing. This typically indicates a lack of lubrication, contamination with foreign particles, or physical damage to the bearing's internal components.
Question 5: When performing preventative maintenance on a roller chain drive, which of the following are the two most critical parameters to check and adjust to ensure maximum operational life?
- Sprocket material hardness and color
- Chain lubrication and proper tension (Correct answer)
- Ambient air temperature and humidity
- Direction of chain travel and motor voltage
Correct answer: Chain lubrication and proper tension
Proper lubrication is essential for reducing friction and wear between the pins, bushings, and rollers of the chain. Correct tension is also critical; a chain that is too tight causes excessive bearing load, while a chain that is too loose can whip, jump teeth, and wear rapidly.
Question 6: A V-belt drive is configured to transmit power from a small, high-speed motor pulley to a large driven pulley on a low-speed, high-load industrial mixer. Which of the following correctly describes the change in speed and torque at the driven shaft?
- Speed is increased and torque is decreased
- Speed is decreased and torque is decreased
- Speed is decreased and torque is increased (Correct answer)
- Speed is increased and torque is increased
Correct answer: Speed is decreased and torque is increased
In a mechanical drive system, power is a function of both speed and torque. When a drive system reduces speed by transmitting power from a small pulley to a large pulley, there is a proportional increase in torque (assuming minimal efficiency losses). This allows a smaller motor to drive a high-load application at a slower, more controlled speed.
SACA - Smart Automation Certification Alliance Mechanical Power Transmission Questions and Answers 1
A motor operates at 1800 RPM and is connected to a simple gearbox.
The drive gear on the motor shaft has 20 teeth, and the driven gear on the output shaft has 80 teeth.
What is the approximate output speed of the gearbox?