1. What is Preload Calculation?

Preload calculation determines the axial force applied to a bolt when tightened with a specific torque. It's essential for ensuring proper clamping force in bolted joints, which affects the integrity and safety of mechanical assemblies.

2. How Does the Calculator Work?

The calculator uses the preload formula:

Where:

• \( PL \) — Preload (kN)
• \( T \) — Torque (N·m)
• \( K \) — Nut factor (unitless)
• \( D \) — Diameter (mm)

Explanation: The formula calculates the axial force (preload) generated in a bolt when a specific torque is applied, considering the nut factor and bolt diameter.

3. Importance of Preload Calculation

Details: Proper preload ensures bolted joints maintain clamping force under operating conditions, preventing joint failure, leakage, or loosening due to vibration and thermal cycling.

4. Using the Calculator

Tips: Enter torque in N·m, nut factor (typically 0.15-0.25 for lubricated bolts), and diameter in mm. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the nut factor (K)?
A: The nut factor is a dimensionless coefficient that accounts for friction in the threaded connection. It varies based on lubrication, surface finish, and thread condition.

Q2: Why is preload important in bolted joints?
A: Proper preload ensures the joint remains tight under operating loads, prevents fatigue failure, and maintains seal integrity in pressurized systems.

Q3: How accurate is the torque-preload relationship?
A: Accuracy is typically ±25% due to variations in friction. For critical applications, direct tension indicating methods or ultrasonic measurement are recommended.

Q4: What are typical nut factor values?
A: For clean, dry threads: 0.20-0.22; For lubricated threads: 0.15-0.18; For plated threads: 0.18-0.25.

Q5: When should I use this calculation?
A: Use during design phase to determine appropriate torque values, or during assembly to verify that applied torque will produce the desired preload.