1. What is a Torque to Pretension Calculator?

Definition: This calculator determines the torque required to achieve a specific pretension force in a bolted joint.

Purpose: It helps engineers and technicians properly tighten bolts to achieve desired clamping forces in mechanical assemblies.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( T \) — Torque (Newton-meters)
• \( k \) — Friction factor (dimensionless)
• \( F \) — Pretension force (Newtons)
• \( d \) — Bolt diameter (meters)

Explanation: The torque needed is proportional to the desired clamping force, bolt diameter, and friction in the joint.

3. Importance of Torque-Pretension Calculation

Details: Proper torque calculation ensures bolt integrity, prevents loosening, and maintains joint strength while avoiding over-tightening.

4. Using the Calculator

Tips: Enter the friction factor (default 0.2), desired 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 (k) value?
A: For dry, unlubricated steel bolts, k ≈ 0.2. Lubricated bolts may have k ≈ 0.15-0.18.

Q2: How do I determine the required pretension force?
A: Pretension is typically 60-75% of the bolt's proof load, which depends on bolt grade and size.

Q3: Why does bolt diameter affect torque?
A: Larger diameter bolts have greater leverage, requiring more torque to achieve the same clamping force.

Q4: Does this account for thread friction?
A: Yes, the friction factor (k) includes both thread and bearing surface friction.

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