# Web course - tightening, fastening and assembly

Welcome to the Atlas Copco web course - tightening technique and find out why tightening technique is so important!

## Lesson 2

### Video 1 - Why do we monitor angle? (9:10)

• Hard joint and soft joint

• Angle limit

## If this course was interesting to you, we also invite you to download the dedicated pocket guide

• Tightening Technique - Pocket Guide - Lesson 2.pdf 4.1 MB, PDF

## Tightening technique glossary

Clamping force - Compressive force that the bolt exerts on the joint materials, also called clampload

- Tension force that is generated in the bolt

- Applied force in the same direction as the axis of the bolts

- Applied force to the joint that is perpendicular to the bolts

Friction
- Resistant force to materials moving against each other

Torque
- Resistant force to materials moving against each other

Prevailing torque
- The amount of torque required to run down a screw or bolt, typically associated with a lock-nut or thread forming screw

Residual torque
- The amount of torque remaining in the joint after tightening

Static breakaway torque
- The amount of torque remaining in the joint after tightening

Relaxation - A loss of clampload in a joint after tightening

Embedment
- A cause of relaxation attributed to high surface pressure in hard surfaces, most apparent in hard joint with multiple hard layers Relaxation associated with embedment typically stabilizes quickly (less than 0.2 seconds)

Creep
- A cause of relaxation attributed to soft materials under high pressure that slowly flow material away from the joint. Can take longer periods of time than embedment losses

Stress
- Force per unit area e.g. Newtons per square millimeter or pounds per square inch

Strain
- Change in length compared to original length

Elastic area
- The region of the angle-torque curve in which the material returns to the undeformed state when applied forces are removed

Plastic area
- The area in which the material deforms permanently

Yield point
- The point separating the elastic from the plastic area

Snug
- The point at which the components of a bolted joint are contacted together and torque starts to build

Hard joint
- The plates and material between the nut and bolt bearing surfaces have a high stiffness. Usually defined as hard if the bolt is tightened to its full torque and it rotates through an angle of 30 degrees or less after it has been tightened to snug

Soft joint
- The plates and material between the nut and bolt bearing surfaces have a low stiffness. This usually has to be tightened by two or more complete turns, after it has been torqued to snug