1. What is Bolt Preload?

Bolt preload is the tension created in a bolt when it is tightened. This initial tension is critical as it creates clamping force that holds joint members together and prevents loosening under external loads.

2. How Does the Calculator Work?

The calculator uses the bolt preload formula:

Where:

• \( F \) — Bolt preload (N)
• \( T \) — Applied torque (Nm)
• \( K \) — Nut factor (dimensionless)
• \( d \) — Bolt diameter (m)

Explanation: The nut factor (K) accounts for friction in the threaded connection and typically ranges from 0.15 to 0.30 for most applications.

3. Importance of Bolt Preload Calculation

Details: Proper bolt preload is essential for joint integrity. Insufficient preload can lead to joint separation and bolt loosening, while excessive preload may cause bolt yielding or fracture.

4. Using the Calculator

Tips: Enter torque in Nm, nut factor as a decimal value, and diameter in meters. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical nut factor value?
A: For standard lubricated bolts, K is typically around 0.2. For dry or plated bolts, it may range from 0.15 to 0.30.

Q2: Why is preload important in bolted joints?
A: Proper preload ensures the joint remains tight under operating conditions, prevents leakage, and maintains structural integrity.

Q3: How accurate is the torque-preload relationship?
A: The relationship is approximate as only about 10-15% of applied torque actually creates bolt tension; the rest overcomes friction.

Q4: What affects the nut factor value?
A: Surface finish, lubrication, thread condition, and material combinations all influence the nut factor value.

Q5: When should direct tension measurement be used instead?
A: For critical applications, direct measurement methods (ultrasonic, strain gauges) provide more accurate preload determination.