1. What is a Preload Torque Calculator?

Definition: This calculator estimates the torque required to achieve a specific preload force in bolted joints based on friction factor and bolt diameter.

Purpose: It helps engineers and technicians determine the appropriate torque values for proper bolt tightening in mechanical assemblies.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( T \) — Torque (Nm)
• \( k \) — Friction factor (dimensionless)
• \( F \) — Pretension force (N)
• \( d \) — Bolt diameter (m)

Explanation: The torque is calculated by multiplying the friction factor with the desired preload force and bolt diameter.

3. Importance of Preload Torque Calculation

Details: Proper torque calculation ensures bolt joints have adequate clamping force without being over-tightened, preventing joint failure or bolt damage.

4. Using the Calculator

Tips: Enter the friction factor (default 0.2), pretension force in Newtons, and bolt diameter in meters. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical friction factor value?
A: For dry, unlubricated steel bolts, k is typically 0.2. Lubricated bolts may have k values of 0.15-0.18.

Q2: How do I determine the pretension force?
A: Pretension force is typically 70-90% of the bolt's proof load, which can be found in bolt specifications.

Q3: Why is bolt diameter important?
A: Torque requirements increase with bolt diameter as the lever arm effect grows.

Q4: Does this account for thread pitch?
A: No, this simplified formula assumes the friction factor accounts for thread friction effects.

Q5: How accurate is this calculation?
A: It provides a good estimate, but actual torque may vary ±25% due to surface conditions and lubrication.