Torque

The rotational force (moment of force) that tends to cause rotation about an axis, measured in Newton-meters (Nm) or pound-feet (lb-ft). Torque is the rotational equivalent of linear force and is the parameter that determines the capacity of power transmission components: shafts (shear stress τ = 16T/πd³), couplings, gearboxes, and belt/chain drives. Relationships: T = P / ω, where P is power (watts) and ω is angular velocity (rad/s). Practical formulas: T(Nm) = 9,549 × P(kW) / n(RPM), or T(lb-ft) = 5,252 × P(HP) / n(RPM). In speed reduction: a 3:1 gear or belt ratio reduces output speed to 1/3 of input while (ideally) tripling output torque, minus efficiency losses. Starting torque is critical for belt drive design: motor starting torque can be 150-300% of rated torque (NEMA Design B), and the drive must handle these peaks without belt slip. Per ISO 1081 and ARPM for belt drive torque calculations. For bolt tightening: torque wrenches apply specified torque to achieve target bolt preload. For coupling selection: service torque = rated torque × service factor. Unit conversion: 1 Nm = 0.738 lb-ft, 1 lb-ft = 1.356 Nm.

What you need to know

The rotational force (moment of force) that tends to cause rotation about an axis, measured in Newton-meters (Nm) or pound-feet (lb-ft).

Torque is the rotational equivalent of linear force and is the parameter that determines the capacity of power transmission components: shafts (shear stress τ = 16T/πd³), couplings, gearboxes, and belt/chain drives.

Relationships: T = P / ω, where P is power (watts) and ω is angular velocity (rad/s).

Practical formulas: T(Nm) = 9,549 × P(kW) / n(RPM), or T(lb-ft) = 5,252 × P(HP) / n(RPM).

In speed reduction: a 3:1 gear or belt ratio reduces output speed to 1/3 of input while (ideally) tripling output torque, minus efficiency losses.

Full definition

Torque is a fundamental concept in mechanical engineering that describes the rotational force applied to an object around an axis. It is quantified in Newton-meters (Nm) or pound-feet (lb-ft) and is crucial for understanding the performance and capability of various power transmission components such as shafts, couplings, gearboxes, and belt or chain drives. The relationship between torque (T), power (P), and angular velocity (ω) is defined by the formula T = P / ω, highlighting how torque is a function of both power output and the speed of rotation. For practical applications, engineers often utilize the formulas T(Nm) = 9,549 × P(kW) / n(RPM) and T(lb-ft) = 5,252 × P(HP) / n(RPM) to calculate the required torque in specific mechanical systems.

In power transmission systems, torque plays a critical role in determining the efficiency and performance of the drive mechanisms. For example, when dealing with gear or belt ratios, a 3:1 reduction will decrease the output speed to one-third of the input speed while ideally tripling the output torque, although this is subject to efficiency losses in real-world applications. Additionally, the starting torque is a significant factor in belt drive design, as the motor's starting torque may range from 150% to 300% of its rated torque, particularly under NEMA Design B specifications. This necessitates careful consideration in the design phase to ensure that the drive can accommodate these peak torque demands without slipping.

Moreover, torque is not only applicable in rotational machinery but is also essential in other applications such as bolt tightening. Here, torque wrenches are used to apply a specified torque to achieve the desired bolt preload, which is critical for the integrity and safety of mechanical assemblies. Coupling selection further incorporates torque considerations, where the service torque is calculated as the rated torque multiplied by a service factor, ensuring that the coupling can handle the operational loads effectively. Understanding these relationships and calculations is vital for engineers involved in the design and maintenance of mechanical systems, ensuring reliability and performance across various applications.

What you need to know

What you need to know: Torque is measured in Newton-meters (Nm) or pound-feet (lb-ft), critical for power transmission components.

The relationship T = P / ω explains how torque is influenced by power and angular velocity.

Starting torque can be 150-300% of rated torque; designs must accommodate these peaks to prevent belt slip.

For gear ratios, a 3:1 reduction decreases speed to 1/3 of input while ideally tripling output torque.

Service torque for couplings is calculated as rated torque multiplied by the service factor to ensure reliability.

Industrial applications

1In conveyor systems, the correct torque calculation ensures reliable movement without slip.

2In automotive applications, torque specifications are critical for engine performance and component longevity.

3For industrial machinery, ensuring the right torque allows for optimal operation of gearboxes and drives.

4In construction, torque wrenches are used to ensure proper fastening of bolts, maintaining structural integrity.

5In robotics, torque calculations are essential for motor selection to achieve desired movements.

Common mistakes

✕Underestimating starting torque requirements can lead to system failures and inefficiencies.

✕Neglecting efficiency losses in gear ratios may result in inadequate torque output.

✕Incorrect torque application in bolting can lead to joint failures or excessive wear.

✕Failing to account for service factors during coupling selection can compromise system reliability.

Torque

What you need to know

Full definition

What you need to know

Formula

Industrial applications

Common mistakes

Pro tip

Technical standards

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Applicable standards

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