1. What is Preload Calculation?

Preload calculation determines the axial force applied to a fastener using the formula F = T / (K × D), where F is the preload force, T is the applied torque, K is the nut factor (coefficient), and D is the nominal diameter of the fastener.

2. How Does the Calculator Work?

The calculator uses the preload formula:

Where:

• \( F \) — Preload force (N)
• \( T \) — Applied torque (Nm)
• \( K \) — Nut factor/dimensionless coefficient
• \( D \) — Nominal diameter (m)

Explanation: This formula calculates the axial force generated in a bolt when a specific torque is applied, considering the friction coefficient and bolt diameter.

3. Importance of Preload Calculation

Details: Accurate preload calculation is crucial for proper bolt tensioning, joint integrity, and preventing failures in mechanical assemblies. Proper preload ensures bolts remain tight under operating conditions.

4. Using the Calculator

Tips: Enter torque in Nm, coefficient (typically 0.15-0.25 for steel fasteners), and diameter in meters. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range for the K coefficient?
A: For steel fasteners, K typically ranges from 0.15 to 0.25, but can vary based on surface finish, lubrication, and material.

Q2: Why is preload important in bolted joints?
A: Proper preload prevents joint separation, reduces fatigue failure, and maintains clamping force under external loads.

Q3: How does lubrication affect the K coefficient?
A: Lubrication reduces friction, which decreases the K value, resulting in higher preload for the same applied torque.

Q4: What units should be used for diameter?
A: Diameter should be in meters to maintain consistency with torque in Nm and force in Newtons.

Q5: Are there limitations to this calculation?
A: This formula provides an estimate. Actual preload can vary due to friction variations, surface conditions, and measurement accuracy.