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Condition monitoring increases and maintains efficiency in paper production

Condition monitoring is an important subject for any industry. Yet not all condition monitoring measures are sufficiently applied to realistically 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. Yet 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 their 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. SAPPI managers answer some questions about the significance of condition monitoring in terms of sustained competitiveness.

How large is your annual paper output in tonnes, and what range of different products do you have?

Burkhard Köhn (Technical Manager): 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.

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

Burkhard 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 round the clock almost 365 days per year. It is therefore not possible to make up for any production lost during a machine failure.

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

Burkhard 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 metres 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.

What do you do to control the risk?

Burkhard Köhn: We realised 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 SKF online systems. You need to realise 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.

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

Burkhard Köhn: Our industry, like any other, suffers from very high and constantly increasing competitive pressure. 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.

No simple task. But what exactly do you do to make your plant more reliable in terms of operation?

Burkhard Köhn: Our plant is fitted with 385 sensors in different measuring positions. Our maintenance expert 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 (Foreman preventive maintenance): 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.

And what happens in the event of an alarm?

Burkhard Köhn: The limits are based on our 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.

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

Burkhard 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 recognise early enough when a component is not working as required. In other words: we can tell today how the machine will work tomorrow.

Hermann 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.

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

Burkhard Köhn: On the one hand, damage is to be recognised and evaluated, on the other hand, the bearing life must be optimised. 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 optimise our bearing choice in co-operation with SKF so that it fulfils the requirements of our operating conditions.

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

Burkhard Köhn: Yes, of course.

Hermann 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.

Can you quantify the results achieved by means of the condition monitoring programme?

Thomas Karger (Engineer, paper mill): 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.
Burkhard 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.

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

Richard 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 metres 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 programme.

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

Burkhard 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 optimise shortcomings. The SKF tools allow us to thoroughly analyse all bearings in our manufacturing facilities.
Article supplied by Minett Media

PICS - Burkhard Köhn, Technical Manager SAPPI Fine Paper Europe

Herman Huss - Foreman preventive maintenance wearing safety glasses

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." Richard Züfle, Maintenance Manager SAPPI Fine Paper Europe

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