Screw joints as the basis for modern industrial assembly

Screw joints play a central role in industrial assembly. Whether in the construction of machines, the assembly of vehicles, or the manufacture of technical devices, they offer a flexible way of connecting parts to each other with safety. One major advantage is that classic screw joints can be loosened again, which is why special attention is paid to them in the context of the modern circular economy.

We would like to discuss the different types of screw connections, present application areas and challenges, and provide best practices for optimal screw assembly.

Different types of screw joints

Screw joints can be divided into several categories depending on their mechanical function:

Materially bonded connections: With this type of screw locking, adhesives or sealants fill the spaces in the thread to hold the screw in place. The result is a permanent connection that cannot be easily loosened
Form-fit connections: Here, the geometric shape or special design of the connecting elements provides a holder, such as with tongue and groove systems.
Force-fit connections: This group includes the classic screw connection, which is held together through friction and preload force.

Within the screw joints, there are variants with nuts, direct screwed connections or special solutions for specific requirements, such as flow-hole forming connections with one-sided accessibility.

When is which screwed connection suitable?

Choosing the right screwed connection is essential and depends on several factors:

Material properties: Metals, for example, require different screws than plastics.
Load: Dynamic loads, such as vibrations or positioning of screwdrivers, place higher demands on the screw.
Environmental conditions: Corrosion protection plays a role when screws are exposed to moisture or chemical substances.
Screwdriving class: Must a certain screwdriving class be achieved or must VDI guidelines be adhered to?
Recycling: If recycling management and disassembly are an issue, the detachability of the screw connection must be clarified in advance.

Precise matching of application and connection technology is crucial for efficient and safe production processes.

What needs to be considered with screw joints?

A screwed connection usually consists of several elements - the screw itself, possibly a nut and a washer. The right combination of these components is elementary.

With automated screw assembly, care must be taken to minimize the quantity of elements and thus the effort required for automation. Screw-in connections are ideal here. In terms of technical cleanliness, pocket holes in which the dirt remains trapped are advantageous.

The technical parameters are just as important:

Preload force: The correct preload force (clamping force) ensures that the screwed joints do not move towards or away from each other.
Torque / angle: Correctly set, the torque and angle ensure that the connection is neither too loose nor too tight.
Friction: The friction between the parts depends on the materials used and has a significant influence on power transmission.

International standards and norms provide reliable orientation for the calculation and design of screw joints (VDI/VDE 2230).

Why can screwed connections come loose?

Despite their reliability, screwed connections are not error free. Common causes of loosening are

Mechanical loads: Vibrations and changing loads can reduce the preload force and thus lead to automatic loosening.
Assembly errors: Incorrect friction coefficients through incorrectly tightened torque or insufficient cleaning of the threads reduce the preload force and can weaken the connection.

Countermeasures such as the insert of tooth washers or adhesives reduce the risk. It is also important to select the correct assembly parameters and use a suitable screwdriver.

8 best practices for the assembly of screw joints

The design and assembly of screw joints requires care and precision. The following best practices provide a solid basis for a safe and durable connection:

Cleaning the contact surfaces: Before installation, the screw, nut and threaded hole must be free of dirt, grease or rust.
Use of suitable tools: Only calibrated and suitable tools, such as torque wrenches, guarantee correct assembly. Controlled screwdriving systems, where the angle and depth can also be monitored, offer even greater reliability. Process data documentation offers additional precision and safety.
Observe the installation parameters: The prescribed tightening torque according to the manufacturer's specification is decisive for the preload force and should be strictly observed.
Use of locking elements: For dynamic loads, tooth washers or thread adhesives can provide additional holder.
Check material compatibility: The screw and part must be compatible in terms of material hardness, corrosion protection and thermal expansion.
Tighten in stages: For several screws, for example on flanges, we recommend crosswise, step-by-step tightening to ensure even pressure.
The right tightening method: Depending on the area of application and the required preload force of the screw connections, Fasten to torque and/or Fasten to angle offer various advantages.
Assembly documentation: Proper documentation of the parameters used ensures traceability and quality assurance.

Maintenance and inspection

Regular verification is crucial for the reliability of screw joints. Inspection and maintenance of screwdriving tools at regular intervals is therefore essential. This is the only way to ensure that the screw connection can withstand the operating loads. Sheet 3 of the VDI/VDE 2645 guideline also describes procedures for process capability tests (PFU) for further torques of screw connections with preload force and provides support in assessing the tightening process as a whole.

Outlook on industrial screw joints

Screw connections are and will remain an indispensable part of industrial assembly. Their versatility, reliability and adaptability make them a key solution in almost every industry. Through the right choice, assembly and maintenance, they can develop their maximum performance - and thus make production processes safer and more efficient.

With digitalization and automation, innovative solutions are also finding their way into screwdriving technology. Smart tools enable the monitoring and documentation of assembly processes in real time. At the same time, the focus on the circular economy and sustainability is becoming ever greater - from reusable screws to resource-saving production and disassembly processes.

Screw joints - a foundation of modern industrial assembly