Bolt Torque

on . Posted in Fastener

Bolt torque refers to the rotational force applied to a bolt or nut in order to tighten it.  It is a measure of how much twisting is applied to tighten (turn) the nut on a bolt.  It is a critical factor in ensuring that fasteners (such as bolts, screws, and nuts) are appropriately tightened to secure parts or components together.  Proper bolt torque is essential to maintain the integrity and safety of various structures and systems, ranging from mechanical assemblies to construction projects.

When tightening a bolt or nut, torque is applied using a torque wrench or other torque indicating tools.  The torque value is typically specified in units of force multiplied by distance and is based on factors such as the material properties of the fasteners and the parts being joined, as well as the intended level of clamping force.  When bolting flanges together or anything else for that matter, tightening the nut stretches the bolt adding pressure to the gasket.  The bolt are designed to stretch a bit acting like a spring.  Different factors can affect the torque like number of threads, oil, rust, type of material, etc.

Applying the correct torque ensures that the bolt generates the appropriate tension in the fastener and maintains a secure connection without risking over tightening or under tightening.  Over tightening can lead to bolt failure, material deformation, or other issues, while under tightening can result in inadequate clamping force and potential loosening of the connection.  Bolt torque is also influenced by various factors, including the type of thread used, lubrication, surface conditions, and the specific requirements of the application.  Engineering standards and guidelines often provide recommended torque values for specific scenarios to ensure reliable and safe connections.


Bolt Torque formula

\( T = k\;d\;p\;/\;12\)     (Bolt Torque)

\( k = T\;12\;/\;d\;p\)

\( d = T\;12\;/\;k\;p\)

\( p = T\;12\;/\;k\;d\)

Symbol English Metric
\( T \) = bolt torque \(lbf-ft\) \(N-m\)
\( k \) = torque coefficient \(dimensionless\) \(dimensionless\)
\( d \) = nominal diameter \(in\) \(mm\)
\( p \) = desired clamp load tension \(lbf\) \(N\)


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