Highly efficient drive technology in the new coating section of Mayr-Melnhof Gernsbach GmbH.

Since September 2020, the board manufacturer Mayr-Melnhof has been operating a new coating section with state-of-the-art drive technology at its mill in Gernsbach. The new and more powerful coating section is driven gearless with synchronous machines.


The project goal

On the KM2, the Baden-Württemberg board manufacturer produces coated board with a grammage of 250-500 g/m². One objective of the rebuild project was to improve the board and the surface quality. For this purpose, the coating capacity as well as the drying capacity of the coating section has to be increased. Among other things, additional coating aggregates and more infrared dryers should be installed. To create the necessary space, the coating section itself has to be extended.

The high demands on the drive system of this section were therefore additionally overlaid by a significantly increased temperature and a particularly tight installation space. Together with the increasingly important energy balance of the entire drive system, a compact and highly effective solution has to be found. The drive system has to be particularly effective and dynamic, but also low-maintenance and durable.



The choice of the new drive

s an initial solution for the drive of the new coating section, Mayr-Melnhof checked the drive using standard asynchronous motors. With this type of drive, the power of the motor is transmitted to the respective drive or guide rolls via preliminary gears and cardan shafts.

However, asynchronous motors are usually equipped with air cooling, which is unsuitable for these hot ambient conditions. To protect the motors from the heat in the new coating section, the asynchronous motors would have had to be located at a large distance from the machine frame, which would have been extremely space-intensive. In addition, the wear of mechanical components (e.g. the pre-gearboxes) increases the maintenance expense. The installation space requirements and efficiency of this drive system are also not up to date. All in all, the project goal was not readily achievable with standard asynchronous motors. Standard asynchronous motors were therefore ruled out as the drive type for this project.


The new drive

The hot ambient conditions and the limited installation space finally led to a solution from AS Drives & Services GmbH (hereafter AS Drives).


AS Drives took over the engineering of the new drive concept and relied on the self-developed direct drives. The synchronous drive FlexoDirect® offers a maximum of efficiency on smallest installation space. Due to the high-power density, all FlexoDirect® for the paper industry are tempered with water. The closed circuit is thus detached from the ambient temperature and can easily withstand any environmental influences that may occur. Operation directly inside the coating section could be implemented without any problems. In contrast to air cooling, the FlexoDirect® is thus also ideal for use in dusty and hot areas. The cooling medium usually has temperatures around 60°C. All drives are manufactured in insulation class H, so that sufficient thermal reserve is always available. This means that the FlexoDirect® can also be operated directly under the hood in dryer groups and at thermally demanding drive positions in coating parts.


The cooling medium used for temperature control (e.g. water) is provided by a central temperature control unit from AS, the Cooliflex®, in a closed circuit. The customer only has to dissipate the energy on the secondary side. The allocation of the cooling medium to the motors is taken over by the intelligent flow controllers FlexoFlow® Water. This ensures that the system provides the perfect amount of water safely and with low maintenance. All this happens fully automatically during operation.

In order to be able to drive the guide rolls without additional shafts or frame parts, the FlexoDirect® motors are plugged directly onto the journal of the guide roll. The reaction torques that occur are dissipated by a play-free torque arm.

FlexoDirect® motors in the foot version are used in the draw press and Varibar area. Mounted on a console, they drive the rolls via cardan shaft. All other mechanical drive components such as pre-gears etc. are omitted, so that no additional losses occur, no gearbox maintenance is required and a very compact design can be realized. Despite its high performance, the FlexoDirect® fits perfectly into the available installation space.

A total of 32 FlexoDirect® motors were installed in the new coating section. The rated torques range from 100 Nm for the guide rolls to 2100 Nm for the other drive points.

Mayr-Melnhof commissioned Kühne+Vogel Prozessautomatisierung Antriebstechnik GmbH (K+V) with the electrical part of the multi-motor drive. AS Drives and K+V have had a strategic partnership in the field of drive technology in the paper industry since 2013. The WebDrive®/Paper/FD module library developed by K+V is optimized for the high-performance control of FlexoDirect® motors. This ensured seamless integration of all new drives into the customer’s existing stock system of the remaining board machine, as well as into the existing PCS7 process control system.

Further rebuild measures

In addition to the drive-side equipment of the coating section, AS Drives also equipped the guide roll bearings of the coating section with a fully automatic oil lubrication system. Here, the intelligent flow controllers FlexoFlow® are used for monitoring the oil. In this version, the FlexoFlow® regulates the oil flow rate fully automatically. All new oil flow controllers were integrated into the existing circulating oil lubrication system. AS Drives took over the installation including the complete piping.

An additional feed cylinder was to be installed upstream of the dryer section. Here, too, AS Drives was able to convince with the FlexoDirect® drive. Despite the tight space conditions, the direct motor could be installed without any effort. From engineering, de-installation of the old piping, delivery and installation of the brackets to the installation of the entire drive and lubrication technology including installation management, everything was carried out by AS Drives.


Situation after the rebuild

Comment of Mr. Spissinger (Project Manager at Mayr-Melnhof Gernsbach GmbH)

We are extremely satisfied with the new drive and lubrication technology and with the entire implementation on the part of AS Drives and its project partner K+V.

Due to the space conditions and the high temperatures, the project could only be realized in this form by using the FlexoDirect®. The motors also reduce the maintenance effort enormously, the spare parts inventory has decreased drastically. Where previously a large number of belts, gears, mechanical components, etc. had to be kept in stock, a few compact spare motors are now sufficient. The control quality of each individual motor enables precise control of all drive points. Since the FlexoDirect® does not require any intermediate gearboxes or any other mechanical components, the complete drive train has a very good efficiency of approx. 97%. When selecting the motors, we already made sure that they were designed for future speed increases of the machine.

Before the modernization of the oil lubrication system, we only had a simple, manual oil flow control without any monitoring capability. As far as the new flow controllers are concerned, we are highly satisfied. All flow values, both those of the cooling water flow and the oil flow, can now be fully and conveniently monitored from the control room. And we also have a full overview of the current values on site at the registers. Both at the flow controllers themselves we can see what is going on at a glance, and on the touch panels. The adjustment of all flow controllers is fully automatic, which makes our work much easier.

The next step for the future is to integrate the remaining lubrication points (e.g. cylinder bearings and dry group gearboxes) into the new lubrication technology. These are also to benefit from the new flow controllers. All preparations have already been made.