Condition monitoring increases and maintains efficiency in paper production

At SAPPI GmbH in Germany, condition monitoring has been far from an unknown quantity for a number of years. Thanks to comprehensive condition monitoring, everything is going according to plan.

Condition monitoring is an important subject for any industry. Yet not all condition monitoring measures are sufficiently applied to really have all machines and equipment under control. This is partly due to the fact that some companies have financial limitations for wide-scale condition monitoring. But in the long run, the financial loss after a system failure is significantly higher than the investment required for an online condition monitoring system.

Even if it does not appear so at first sight, Ehingen, a small town on the Danube in the German province of Swabia, is a Mecca of papermaking. SAPPI Fine Paper Europe established one of its seven European manufacturing works here. As early as the start of the 1990s, SAPPI implemented the first condition monitoring measures and quickly discovered that monitoring of equipment is essential for competitive and profitable operation. In this question-and-answer article, SAPPI managers answer some questions about the significance of condition monitoring in terms of sustained competitiveness.
The interview subjects are Burkhard Köhn, technical manager; Hermann Huss, foreman of preventive maintenance; Richard Züfle, maintenance manager; and Thomas Karger, paper mill engineer.

Question: SAPPI Fine Paper Europe is one of the largest papermaking companies. How large is your annual paper output in tonnes, and what range of different products do you have?

Burkhard Köhn: In the Ehingen factory alone, we produce around 250,000 tonnes of paper per year. SAPPI Fine Paper Europe, as a whole, has an annual output of more than 2.7 million tonnes. Our wood free coated paper is mainly used for the preparation of high-gloss brochures for industrial advertising, artistic print calendars and art portfolios.

Question: What is the significance of the time factor in manufacture and supply to your customers?

Köhn: We supply mainly to wholesalers who all have high expectations in terms of quality and delivery reliability. But the time factor is particularly decisive if the machine fails. We manufacture around the clock almost 365 days per year. It is, therefore, not possible to make up for any production lost during a machine failure.

Question: What are the main problems that you face with your type of equipment?

Köhn: I do not know about the situation in other industries, but our equipment has a large number of potential problem areas. The equipment is 200 meters long and full of control and drive systems, with a large number of bearings and gears. There is the risk of a component failure almost everywhere.

Question: What do you do to control the risk?

Köhn: We realized early on that condition monitoring of equipment parts at risk is the decisive factor in safeguarding reliable functioning. Initially, we used offline measuring systems, but we gradually changed over to online systems. You need to realize that a failure of the equipment costs us 10,000 euros  per hour. It is, therefore, logical that our ultimate goal is to prevent unnecessary machine failures.

Question: Does this imply that the operational reliability of the plant is the essential factor for sustained competitiveness?

Köhn: Our industry, like any other, suffers from very high and constantly increasing competitive pressure, but we rise to this challenge. It is true that condition monitoring plays a decisive role. The millions that we spend are a clear indication of the importance we attach to maintenance. One thing is clear: If the plant is down for longer than it is running, you need not wonder about your position in comparison with your competitors. You will always be behind them.

Question: That is no simple task. But what exactly do you do to make your plant more reliable in terms of operation?

Köhn: Our plant is fitted with 385 sensors in different measuring positions. Our foreman of preventive maintenance, Mr. Huss, can retrieve data from all these sensors on his computer. If a value exceeds a set limit, an alarm is triggered.

Hermann Huss: The alarm clearly identifies in which position on the production line the operating conditions of a rolling bearing have changed so that I can respond immediately.

Question: And what happens in the event of an alarm?

Köhn: The limits are based on our many years of experience and are set in such a way that an alarm does not always indicate a failure. Live measurements allow us to instead determine whether the damage on the rolling bearing remains constant or if the bearing condition is deteriorating. This allows us to calculate when we need to change the bearing or if the bearing can be operated until the next scheduled maintenance date with the application of additional lubricant.

Question: Does condition monitoring also help if a bearing needs to be changed?

Köhn: The fact is that if one of our cylinders is not rotating, the plant is down. But thanks to our safety precautions and condition monitoring devices, we have the situation under control and can recognize early enough when a component is not working as required. In other words, we can tell today how the machine will work tomorrow.

Huss: I completely agree with Mr. Köhn, yet there is always an element of risk that something could break. But even then, we are at an advantage. Based on the parameters measured, we can see which component is in the red. They allow us to say exactly why the plant is down and where the defective bearing is located. Without condition monitoring, it would be difficult to find the one failed bearing. In our plant, a planned bearing change takes between two to four hours; without condition monitoring, it might well take eight hours.

Question: What other knowledge do you derive from the measurements taken as part of condition monitoring?

Köhn: On the one hand, damage is to be recognized and evaluated; on the other hand, the bearing life must be optimized. If we have been using a bearing for several years, it can be assumed that a defect is a normal failure. However, if a new bearing would fail, a damage analysis must be carried out. This would be the only way to determine the cause and optimize our bearing choice in cooperation with SKF so that it fulfills the requirements of our operating conditions.

Question: Which SKF tools and devices do you use?

Köhn: Online systems, Microlog data loggers for manual measurements on the routes, vibration sensors fitted to the measuring positions and the evaluation software which allows us to view the data in detail and analyze it.

Question: Does this mean that you can evaluate and assess any component of your plant at any given point in time?

Richard Züfle (maintenance manager): Precisely. The decisive factor is that we can respond to changes quickly and in a systematic manner. It is not only our task to monitor the plant, but to ensure that it only needs to be shut down every six weeks for scheduled maintenance. It is our responsibility to maintain this cycle and prevent additional shutdowns in between.

Question: When you call it a day, is your mind more at ease thanks to condition monitoring?

Köhn: Yes, of course.
Huss: No, not always, as I am familiar with the measuring data and know which components are presently at the limit of their service life. But it is generally very comforting to know when everything is “in the green” in the truest sense of the phrase.

Question: Can you quantify the results achieved by means of the condition monitoring program?

Thomas Karger (paper mill engineer): In the time since we started our offline and online measurements, we have successfully identified exactly 1,000 instances of damage. Successfully, of course, means that we detected and diagnosed the damage before the plant failed. The experience and know-how gained from these cases over the years advance our knowledge base, even if many instances of damage are different.
Köhn: If you want a figure to quantify our success, I would point to the regular maintenance intervals. Whereas in 1991 we had to stop the plant every other week, today the interval between two maintenance downtimes is six weeks. It would not have been possible to extend these intervals without condition monitoring.

Question: What is the next step you intend to take in order to safeguard the future of SAPPI in terms of plant reliability?

Züfle: Due to the ever-increasing requirements, there is still a risk for us as far as gearboxes are concerned. Our increased production speed of 1,120 meters per minute will take the gearbox to its limits more quickly than planned. In order to achieve better control and reliability in planning, our next step will be to include this area in the condition monitoring program.

Question: Briefly, how would you define why condition monitoring is necessary for SAPPI Ehingen GmbH?

Köhn: It is very clear – our objective is to be state of the art in our plant and equipment so that we can identify and optimize shortcomings. The (condition monitoring) tools allow us to thoroughly analyze all bearings in our manufacturing facilities.