Extremely lightweight CFRP clamping shaft: Custom solution for frequent roll changes in the packaging industry

How a core tube made of carbon fiber reinforced polymer (CFRP) reduces the shaft weight to such an extent that frequent manual roll changes remain within ergonomic occupational safety guidelines, without compromising stiffness and concentricity.

At a unwinding station in the packaging industry, the shaft is not moved once per shift, but many times: remove empty core, load full roll, lift shaft from storage, insert, align. With a steel shaft, depending on diameter and clamping length, this is a significant load with each pass, and with each repetition, the strain on the lumbar spine accumulates. This is precisely where a design decision becomes a matter of occupational safety.

A customer from the packaging industry approached IBD Wickeltechnik with this task: The clamping shaft needed to be so light that it could be handled by one person even with a high change frequency, without exceeding the permissible weight limits. A standard aluminum shaft was already at the upper limit of what was acceptable. What was needed was not fine-tuning, but a change of material.

The legal basis: What “too heavy” specifically means

The manual handling of loads in Germany is regulated by the Load Handling Ordinance (LasthandhabV), which implements EU Directive 90/269/EEC. Crucial for practical application: The ordinance does not specify a fixed maximum weight in kilograms, but rather requires a risk assessment that jointly evaluates weight, posture, gripping conditions, and especially frequency. Frequency, in particular, is the key lever: A load that is uncritical once becomes a risk with dozens of repetitions per shift.

The recognized assessment tool of the Federal Institute for Occupational Safety and Health (BAuA) is the Key Feature Method for Lifting, Holding, and Carrying (LMM-HHT). In it, two values act as de facto orientation limits: If men handle more than 25 kg or women more than 15 kg, the activity is considered so critical that it must be assessed separately. Practically, these values mark the threshold at which a shaft becomes unsuitable for repeated manual operation (for more in-depth information: DGUV Subject Area Physical Strain).

For particularly vulnerable groups, additional binding maximum weights apply: According to § 11 of the Maternity Protection Act (MuSchG), pregnant women may not regularly move loads exceeding 5 kg and occasionally not exceeding 10 kg without aids, while the Youth Employment Protection Act (§ 22 JArbSchG) limits activities beyond physical capacity. From a business perspective, this means: The lighter the shaft, the larger the pool of employees who can staff a station, and the less frequently the weight issue has to be solved by lifting aids or personnel selection.

Why not just aluminum?

Aluminum is the obvious step for weight reduction and is available in the standard program of the high-performance clamping shafts PSW-Z. However, with a long clamping length and bearing load, an aluminum core tube reaches a physical limit: the necessary bending stiffness and low deflection under a full roll require wall thickness, which is precisely the mass one wants to eliminate.

CFRP breaks this conflict of objectives through its specific stiffness, the ratio of elastic modulus to density (E/ρ), where carbon fiber is significantly superior to aluminum and steel. A CFRP core tube achieves the same bending stiffness at a fraction of the weight.

Only the core tube was made of CFRP. The mounting and bearing journals remain steel, as do the clamping journals, clamping elements, and filling valve from the proven modular system of the PSW-Z series. This is intentional: the mass of a clamping shaft is concentrated in the tube along its clamping length, while the highly stressed components at the ends contribute little to the weight but must transmit bearing, clamping, and drive forces, for which steel remains the right choice. Thus, the shaft retains the clamping principle and serviceability of the standard series and only shifts the handling weight downwards.

The direct comparison shows how significant the effect is: For a 3-inch clamping shaft (76 mm) with a 2 m clamping length, the CFRP core tube reduces the weight by approximately 20% compared to aluminum and approximately 60% compared to steel. What is remarkable is not so much the expected difference from steel, but the additional 20% compared to the already lightweight aluminum variant. Precisely this fifth is often the difference in practice between a shaft that scrapes the ergonomic threshold and one that remains comfortably below it.

Why CFRP pays off beyond just weight

The material premium for CFRP is real and not worthwhile for every application. Where it does pay off, it is rarely due to weight alone, but to properties that metal cannot simultaneously deliver constructively:

Lower deflection, better web geometry. A stiff, lightweight shaft sags less under a full roll. This equalizes web tension across the working width and reduces winding errors, especially with long clamping lengths.

Higher critical speed. The resonance speed depends on deflection, mass, and stiffness. The high specific stiffness of CFRP increases it, creating reserves for higher web speeds without instability.

Better damping, smoother running. CFRP has higher internal material damping than metal. Vibrations decay faster, and operation remains smooth even at high speeds. This protects bearings and improves the surface quality of the web.

Lower moment of inertia. Less rotating mass means: faster acceleration and braking, lower drive torque requirements, and less force during manual rotation, noticeable with frequent start-stop cycles.

Low thermal expansion. The low coefficient of thermal expansion keeps the shaft geometry stable across temperature fluctuations, an advantage wherever tightly tolerated web positions are required.

These effects are interconnected. A lighter, stiffer, and better-damped shaft is not just the sum of individual advantages, but allows for a different operating point of the system: faster, quieter, with less waste, and a permanently occupiable workstation.

Dipl.-Ing. Holger Brink, Managing Director and Technical Director at IBD Wickeltechnik:

“CFRP is not an end in itself and not the right answer for every shaft. Here, the task was clearly defined: frequent roll changes, one person, a tough weight target. Aluminum was at its limit, and that’s exactly when the carbon fiber core tube shows its strength. We retain our proven clamping and bearing modular system and only change material where it makes a decisive difference.”

Customer-specific shaft design as a core competence

The real value of this solution lies not in the material, but in the design. A clamping shaft is not a catalog part: core diameter, clamping length, bearing load, speed, drive connection, environment, and the required handling weight form a requirement profile that looks different from application to application.

The modular architecture of the IBD series is designed for this. Core tube material, clamping elements, and journals can be adapted without sacrificing the clamping principle or serviceability. Here, the material change to CFRP was the lever; in other projects, it was a movable shaft mechanism, an adapted clamping element configuration, or special bearings. Thinking of a Winding Shaft from the requirement profile rather than from the catalog, instead of over-dimensioning a standard shaft to fit, is the core of what IBD Wickeltechnik understands as customer-specific development.

Transferable to any weight-critical change station

The principle can be applied to virtually any unwinding or winding station where frequent manual changes are made and shaft weight becomes a bottleneck. Wherever a standard steel or aluminum shaft exceeds ergonomic limits, the CFRP core tube reduces weight without sacrificing stiffness, concentricity, or serviceability. The prerequisite is an honest assessment of the requirement profile, and that’s exactly where the design process begins.