Estimated reading time: 5 minutes

A secure bolted connec­tion is the founda­tion of numerous assembly processes in various industries.

Ensuring consis­t­ently high quality and safety is one of the main challenges in every company.

If the bolted connec­tion fails on a compo­nent, the conse­quences can be severe, especi­ally if it has been produced on a large scale.

This is why preven­tive error analyses, such as compre­hen­sive quality assurance, are an integral part of produc­tion planning.

The founda­tion for quality manage­ment of any kind is always a precise under­stan­ding of the requi­re­ments for each bolt that is used.

What is a Bolt Connection?

The term ‘bolt connec­tion’ defines the process during which at least two compon­ents are merged using a bolt.

A bolted connec­tion is also typically charac­te­rized by the fact that it can be undone without damage.

Appro­pria­tely chosen for the material and correctly executed, a bolted connec­tion can be undone repea­tedly without the risk of material damage.

Often this is an important factor when it comes to the repair or modifi­ca­tion of machi­nery, especi­ally since the modula­rity of produc­tion machines is incre­asing conti­nu­ally.
The opera­ting principle of a bolted connec­tion is based on the genera­tion of a tensile force in the thread, which is created by tightening with an appro­priate tool (e.g., nutrunner, EC nutrunner).

A secure connec­tion of the compon­ents is ensured by the combi­na­tion of clamping force and preload force.

The correct torque

Since it is diffi­cult to deter­mine the clamping force, usually the torque is measured to check if the bolted connec­tion meets the assembly requirements.

Proper Instal­la­tion Matters! — Important Aspects of Bolt Connections

The purpose of bolted connec­tions is to unite two or more elements so that they behave as one whole.

A classic day-to-day example is the attach­ment of wheels to a vehicle.

Effective Bolted Connections: Attaching a wheel to a car

Attaching a wheel to a car appears to require a relatively simple bolted connec­tion.

However, this impres­sion is decep­tive because the attached tires must withstand signi­fi­cant mecha­nical stresses daily to trans­port the driver from A to B safely.

The poten­tial conse­quences of an insuf­fi­ci­ently tightened bolted connec­tion can be deadly in this case.

Basically, the follo­wing applies: All forces and external influences acting on bolted compon­ents, such as tempe­ra­ture changes, can cause elastic and / or plastic defor­ma­tions and thus movement between indivi­dual parts.

Thus, the most important aspect of a high-strength bolt connec­tion is ensuring the correct preload force, which provides the neces­sary clamping force to keep the connected compon­ents securely together and prevent relative movement.

This is why precise torque appli­ca­tion during instal­la­tion is of utmost importance.

Of Course, bolted connec­tions can also be found on a large scale.

A steel bolted moment connec­tion is a struc­tural joint used to connect steel beams and columns.

It is designed to resist rotational forces and provide stabi­lity in building structures.

Another example are slip-critical bolt connec­tions that are commonly used in struc­tures subjected to tension, shear or bending loads.

What is slip-critical bolt connection?

A slip-critical bolt connec­tion is a type of fastening method, where bolts are tightened to a speci­fied tension to create friction between the connected surfaces to prevent relative movement under load.

This method is employed when building bridges and high-rise buildings.

Bolting Basics: Ensuring Safety and Stability

Secure Connec­tion

A bolted connec­tion is considered secure only if the combi­na­tion of all loads does not lead to self-loosening.

To ensure a certain level of safety, there are guide­lines and standards that focus on various aspects of bolt technology.

These European and German standards are among those commonly used in enginee­ring and related industries:

  • ISO 5393
  • DIN 1319
  • VDI 2230

Another standard is provided by the American Insti­tute of Steel Construc­tion (AISC).

Diffe­rent Standards

While European standards use the metric system, AISC prima­rily employs English units like inches and pounds.

It also supports the Inter­na­tional System of Units (SI), however it is really important to pay close atten­tion to deviations.

The main objec­tive of standar­diza­tion is the precise defini­tion of the influen­cing factors and minimum requi­re­ments for the bolt techno­logy being used.

Additio­nally the testing and calibra­tion of tools are also subject to specific standards.

Beyond Tightening: Decisive Factors that Affect Bolt Connections

Each bolted connec­tion has specific charac­te­ristics that can be influenced by various factors.

Utili­zing an Ishikawa diagram (also known as cause-and-effect diagram) is one possi­bi­lity to illus­trate those influences. 

These 5 crucial factors can influence the quality of a bolted connec­tion significantly:

PersonnelChoice of the wrong tool leads to an insecure bolted connection
MaterialsQuality varia­tions in material composition
Equip­mentMalfunc­tions that are not immedia­tely detected
Environ­mentDesta­bi­liza­tion of the bolted connec­tion by external influences, such as cold or heat
MethodsAssembly method and material do not match

For businesses, the human element remains the most signi­fi­cant factor in the success of produc­tion processes.

Regar­ding bolted connec­tions, proper training can consider­ably reduce errors and even reveal oppor­tu­ni­ties for enhan­cing quality or cutting costs.

That’s why ongoing, job-specific training focused on work processes and tool utiliza­tion is vital.

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