Bolt Preload Torque Calculator

How Bolt Preload and Preload Torque are Calculated

Bolt preload is a critical factor in ensuring the stability and integrity of bolted joints. It refers to the axial force applied to a bolt when tightening it, which creates a clamping force between the joint components. This clamping force is essential for maintaining the joint's integrity by preventing relative motion between the components.

Calculation Formula for Bolt Preload:

The bolt preload P can be calculated using the following formula:

P = (1 / FoS) * (σ_y * (π * D² / 4)) - F

Where:

• P: Bolt preload
• FoS: Factor of Safety
• σ_y: Yield Strength of Bolt Material
• D: Bolt Diameter
• F: External Load

How Preload Torque is Calculated:

Once the bolt preload P is determined, the preload torque T can be calculated using the following formula:

T = P * D * K

Where:

• T: Preload Torque
• P: Bolt preload
• D: Bolt Diameter
• K: Torque Coefficient for the Type of Bolt

Material Yield Strengths (MPa):

Torque Coefficients for Types of Bolts: