How do we avoid

bouncing in flexographic printing?

Scroll down

Carbon-fiber-reinforced plastics (CFRP) are currently used in a wide variety of industrial applications. However, to tap into the various design opportunities offered by this material, specific expertise is required.

In the following article, we will provide an insight into the basic influential factors which must be taken into account when developing and carrying out calculations for CFRP tubes for rollers, adapters and air cylinders. We will also take a look at vibration problems during the printing process and why INOMETA is playing a leading role in this respect.

CFRP – a material with a wide spectrum

The view that CFRP is only ever used in very high-end applications is still currently widespread, even amongst engineers. However, this statement has been outdated for some time now and is based on experiences from the early days. Due to its broad spectrum of properties, this versatile material has succeeded in conquering numerous other market sectors and fields of application. In recent years, particularly in the printing industry but also in the paper and film production industries, there has been a noticeably rapid increase in the components produced using CFRP compared with conventional metallic materials.

INOMETA, as an established manufacturer of metal rollers, had already identified the huge potential of CFRP as a material for use in roller construction more than 30 years ago.
Both then and now, we have succeeded in recruiting the best development engineers to carry out intensive research into potential fields of application and to continue to drive lightweight design forward.

This allowed INOMETA to build up an immense knowledge of this miracle material at an early stage, a knowledge that still exists today.

CFRP precision rollers

Using CFRP requires a radical change in mindset, as there is probably no other material  that can be so individually tailored to the respective applications in modern construction and development as CFRP can.
In the past, in order to use a conventional roller tube, it was sufficient to know whether it was made of steel or aluminium. With the help of standard applicable tables, the engineer could determine the exact characteristics of the metal material used. When using CFRP in tube manufacturing, this generic information is no longer adequate, as the engineering constants of this composite material are much more complex than the customary empirical values used by an engineer.

The composite materials consist of a great many individual carbon fibers. The diameter of each individual fiber is approx.5-10 µm and is therefore much lower than the diameter of a human hair at 50-70 µm.
In addition, carbon fibers exhibit significantly better physical properties in the longitudinal direction than isotropic metallic materials. However, in the transverse direction, these values are much worse (isotropy represents material uniformity in all directions when subjected to loads).

In order to offset the limitations of the characteristics in a transverse direction, our engineers used the filament winding process when manufacturing CFRP tubes from the very outset. In the process, the carbon fibers are deposited in different layers as fiber bundles with different angles and embedded in a suitable plastic. The rigidity and also the strength of composite material created in this manner are directly related to the type and orientation of the carbon fibers. Our engineers no longer have to work in line with universally applicable guide values and are therefore free to adjust the rigidity and strength of the material in terms of length, circumference and direction of thrust. For each new case of application in construction, individual geometry and load bearing designs and calculations are carried out for the respective INOMETA roller tube on a case by case basis.

This means that highly qualified lightweight design specialists are particularly required, because when CFRP is used, detailed consideration of process-related cause variables – which can lead to the deformation of the roller tube – can determine whether the desired application is successful or not.
For every industrial application, there are different static and dynamic load conditions. They have a significant influence on the potential quality of the material to be produced and inevitably lead to deformations in rollers, printing bridge adapters and air cylinders. Experiences gleaned from cross-industry cases of application now offer the highest degree of technical knowledge, meaning that our customers benefit from the development and production of lightweight solutions and therefore achieve significant competitive advantages.

Vibration effects and bouncing in the printing machine

All printers fear resonance effects or bouncing, which can lead to loss of speed and quality in their printing machines. When researching the causes, we often encounter natural frequency, which causes objects to vibrate when they are triggered through impact from a blow, for example.

Resonance excitation often takes place in printing machines and particularly in flexographic printing units. When different roller speeds and print images interact with hard leading edges, this causes part of the printing unit to vibrate. As a minimum consequence, print quality is reduced, but often complete print failures occur. If this persists, it may even lead to damage to the printing system.

In a printing unit with numerous rotating components, calculating the multitude of natural forms is a complex task. Individually, but also simultaneously, so-called bending, torsional and ovalization vibrations can occur, which deform the cylindrical bodies again and again and in the worst case scenario lead to high oscillation amplitudes.
The standard measure to reduce these amplitudes is generally a reduction in web speed, as this is the only way to reliably ensure that the printing machine is removed from the range of damaging vibration excitation.
Printers therefore face the challenge of diminished productivity every time the printing speed is reduced, whilst every increase in printing speed means reduced quality.

In collaboration with printing machine manufacturers, the experts at INOMETA have carried out extensive modal analyses of the printing units and continue to do so. With the help of this vibration analysis, natural frequency, natural form and the corresponding damping value can be determined for printing cylinders, air cylinders, Anilox rollers and chamber blades.
The results of the modal analysis show that various components’ natural frequencies are stimulated, depending on the web speed and print image.

Due to these results, right from the development and construction phase, the INOMETA INOflex^® program was designed to damp the vibrations that occur throughout the entire system as well as the associated energy on a linear basis.
In addition to the bridge adapters, the patented damping technology for air cylinders in flexographic printing units is a notable result of the research and development works at INOMETA. Here, in addition to the already excellent damping properties of CFRP as a material, the vibration damping of the entire product has been successfully enhanced using a damping technology contained in the product itself.

Numerous independent printing tests carried out by machine manufacturers and print shop operators confirm the functionality of INOflex^® products and play a major role in the optimization of the entire production process in flexographic printing. Thanks to the mutually compatible INOflex^® program, print shops now have the opportunity to fully exploit machine performance and to minimize disruptive influences such as bouncing.

Find out more about the INOflex^® product range

With the INOflex^® product family – a system solution for flexographic printing – INOMETA offers a comprehensive portfolio of lightweight products for use in printing units and other areas of flexographic printing machines. As a specialist in rotating printing unit components, INOMETA develops and produces components that are designed to work perfectly together, including anilox rollers and anilox sleeves, CFRP bridge adapters with hydraulic or pneumatic clamping systems and CFRP air cylinders. INOMETA is also a specialist in the production of web-guiding rollers and winding cores.

Contact us and we will be glad to advise you!

We look forward to receiving your enquiries and subsequently contacting you, in order to discuss our solutions with you

Enquire now