Drallfrei: Micro-helices and the risk of fluid loss

aprile 09, 2025

Have you ever wondered why some seals fail even when the component seems perfectly machined?
The Drallfrei phenomenon could be the hidden cause.

What does Drallfrei mean?

"Drallfrei" literally means "without a helix" and refers to the need to eliminate invisible micro-helices from the surface of shafts, hubs and gears.
These microscopic traces, caused by processes such as grinding or hard turning, act like a screw, dragging lubricant or contaminants along the axis of the component.

Even a slight surface directionality can seriously compromise the dynamic seal.

Why Drallfrei is so important?

Ignoring the Drallfrei problem can lead to significant damage to rotating systems.
The loss of lubricant reduces the effectiveness of the lubrication, causing friction and overheating.
Contamination, on the other hand, can introduce abrasive agents that damage internal components and even cause the system to fail.

An apparently invisible anomaly can therefore result in high maintenance costs, plant downtime and loss of operational efficiency.

Where does Drallfrei occur?

The risk of Drallfrei concerns all components with dynamic sealing.
Rotating shafts that use oil seals, hubs with seals, gearboxes, pumps and electric motors are particularly vulnerable.
In these applications, even a small imperfection can compromise the functionality of the seal.

How to check Drallfrei

Empirical method: the wire test

A practical and quick method to check Drallfrei consists of using a 0.25 mm braided wire and a weight of 100 g.
The wire is placed on the rotating surface at a speed of 20 meters per minute.
If after 30 seconds the wire moves by more than 1 millimeter, it means that the surface is not compliant.
It is essential to repeat the test by reversing the direction of rotation to obtain a valid result.

Analytical methods: advanced tools

When the application requires a more precise check, analytical tools are used.
Waviness Analyzers allow you to measure directional roughness with very high repeatability.
Three-dimensional profiles create a detailed mapping of the surface, while 3D optical microscopes analyze the orientation of the tracks with extreme precision.

Even using advanced tools, a functional validation is always necessary in addition to simple numerical measurement.

Compliance with the Drallfrei condition is not an aesthetic detail but a fundamental technical requirement.
Ensuring surfaces free of micro-helices means protecting the functionality of the seals, reducing the risk of failure and improving operational efficiency.

👉 Do you want to guarantee perfectly Drallfrei surfaces in your rotating components?
Contact us, our experts will help you improve the reliability and durability of your systems.

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