What is torque, and how is it measured?

Short Answer:

Torque is a measure of the rotational force applied to an object, such as a bolt or a motor shaft. It is the twisting force that causes rotation, and it depends on the amount of force and the distance from the point of rotation. Torque is usually measured in Newton-meters (Nm) or pound-feet (lb-ft).

Torque is measured using devices called torque sensors or torque wrenches, depending on the application. These devices detect the force applied at a certain distance and convert it into an electrical or mechanical reading. Torque measurement is important in engines, machines, robotics, and quality control.

Detailed Explanation:

Torque and its measurement

Torque is a key concept in mechanical and electrical engineering, especially in systems involving rotating parts. It represents the turning or twisting force applied to an object around an axis. Understanding and measuring torque is essential in applications like motor control, automotive systems, machinery, and manufacturing.

What is torque?

Torque is defined as the product of force and the distance from the axis of rotation. Mathematically:

Torque (T)=Force (F)×Distance (r)\text{Torque (T)} = \text{Force (F)} \times \text{Distance (r)}Torque (T)=Force (F)×Distance (r)

  • Force (F): The linear force applied (in Newtons).
  • Distance (r): The perpendicular distance from the axis of rotation (in meters).

If you use a wrench to turn a bolt, the farther you apply force from the bolt, the greater the torque you generate.

Units of torque:

  • SI unit: Newton-meter (Nm)
  • Imperial unit: Pound-foot (lb-ft)

How is torque measured?

There are different methods and tools to measure torque, depending on whether it is static (not rotating) or dynamic (while rotating).

1. Torque Wrench (Manual Method):

  • A torque wrench is a hand tool used to apply a specific amount of torque.
  • It has a built-in scale or indicator to show how much torque is being applied.
  • Used mostly in automotive and mechanical assembly.

Example: Tightening car wheel nuts to a specific torque value.

2. Torque Sensor or Transducer (Electronic Method):

  • Used for real-time torque measurement, especially in motors and machines.
  • Converts the applied torque into an electrical signal using strain gauges or magnetic sensors.
  • The sensor is placed between the driving and driven shaft.
  • The signal is processed and displayed as a torque value.

Types:

  • Rotary torque sensor: Measures torque in rotating shafts.
  • Reaction torque sensor: Measures torque in non-rotating applications.

3. Strain Gauge Method:

  • A strain gauge is bonded to a shaft.
  • As torque is applied, the shaft twists slightly, causing the strain gauge to stretch.
  • The change in resistance of the gauge is measured and converted to torque.

Application: In test benches and laboratory measurements.

4. Magnetoelastic Torque Sensor:

  • Uses the change in magnetic properties of a material under stress.
  • A magnetic sensor detects changes as torque is applied to the shaft.
  • Non-contact and highly durable.

Used in: Automotive and aerospace applications.

5. Hydraulic or Pneumatic Torque Tools:

  • Used in heavy-duty applications like pipeline or turbine assembly.
  • Use fluid pressure to apply and measure torque.
  • Include pressure gauges to correlate with torque values.

Importance of torque measurement:

  • Engine testing: To measure power output and efficiency.
  • Machine safety: Prevent overloading of shafts and couplings.
  • Manufacturing quality: Ensures correct tightness of bolts and parts.
  • Robotics and automation: Controls movement and force applied.
Conclusion:

Torque is the force that causes an object to rotate around an axis. It is calculated by multiplying force with distance from the pivot point. Torque can be measured using torque wrenches, sensors, or strain gauges. Accurate torque measurement is essential in engineering for performance, safety, and quality control in various rotating systems and machines.