What is bolt preload force?

Bolt preload (also called clamping force or initial tension) is the tensile force induced in a bolt during tightening. It creates the clamping force that holds the joint together and is essential for joint integrity, preventing loosening and fatigue failure.

What utilization factor should I use?

Typical utilization factors (η) are 0.7 to 0.9 of the yield strength. For controlled tightening (torque wrench), 0.7–0.75 is common. For precision methods (stretch measurement, hydraulic tensioner), 0.85–0.9 can be used. Never exceed 0.9 for static applications.

How is bolt preload related to torque?

The approximate relationship is T = K × d × F, where K is the nut factor (typically 0.2 for dry steel, 0.15 for lubricated), d is the nominal bolt diameter, and F is the preload force. This is an approximation with ±25% uncertainty.

Why is preload important in bolted joints?

Preload is critical because it: (1) prevents joint separation under external loads, (2) reduces bolt fatigue by minimizing load fluctuations, (3) creates friction that resists shear loads, (4) prevents bolt loosening from vibration, and (5) provides gasket seating force in sealed joints.

What happens if bolt preload is too high?

Excessive preload can cause bolt yield or fracture during tightening, thread stripping, gasket crushing, flange distortion, or joint member damage. This is why utilization factors are used to keep preload safely below the yield point.

मुक्त अभियांत्रिकी साधन

बोल्ट पूर्वलोड बल कॅलक्युलेटर

उपयोगिता गुणांक, यील्ड स्ट्रेंथ आणि तन्य तनाव क्षेत्रावरून मेट्रिक बोल्टमधील असेंब्ली प्रीलोड बल मोजा. F = η × Rp × As.

ISO 898-1 VDI 2230 M3 – M64

बोल्ट आकार

प्रॉपर्टी क्लास

उपयोगिता गुणांक η (%)

नट गुणांक K (टॉर्क अंदाजासाठी)

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असेंब्ली प्रीलोड बल (F)

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अंदाजित घट्ट करण्याचा टॉर्क

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यील्ड लोड (100%)

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तन्य तनाव क्षेत्र

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उपयोगिता

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प्रीलोड बल

असेंब्ली प्रीलोड बल हे घट्ट करतानाचे लक्ष्य बोल्ट ताण असते:

η — उपयोगिता गुणांक (साधारणतः 0.7–0.9)
R_p — प्रूफ / यील्ड स्ट्रेंथ (MPa)
A_s — तन्य ताण क्षेत्र (mm²)

टॉर्क अंदाज

अंदाजे घट्ट करण्याचा टॉर्क (संक्षिप्त समीकरण):

K — नट गुणांक (घर्षणावर अवलंबून, साधारणतः 0.15–0.20)
d — नाममात्र बोल्ट व्यास (mm)

व्यावहारिक उदाहरण

उदाहरण — M10 × 8.8 @ 70%

Given: M10, वर्ग 8.8 (Rp = 640 MPa), As = 58.0 mm², η = 70%

F = 0.70 × 640 × 58.0 = 25,984 N ≈ 26.0 kN

T = 0.20 × 10 × 25,984 / 1000 = 52.0 N·m

⚠️ Note: टॉर्क-आधारित घट्ट करणे ±25% अनिश्चिततेसह येते. महत्त्वाच्या जोडांसाठी, अधिक अचूकतेसाठी स्ट्रेच मापन किंवा हायड्रॉलिक टेन्शनिंग वापरा.

Bolt Preload Force Calculator | ISO 898-1 | Free Online Tool

Published by admin on फेब्रुवारी 15, 2026 फेब्रुवारी 15, 2026

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