Field Services part 2: Finite Element Analysis improves equipment reliability
During the design process, an engineer must determine that the assembly will stand up structurally to loads it is being asked to support; and then some. Preferably, they need this information before manufacture to ensure that time and money is not wasted building something that will inevitably fail. And once the machinery is performing in the field, having a good system to predict failures becomes invaluable; and will make life much less stressful. Finite Element Analysis addresses both of these issues.
What is Finite Element Analysis?
Finite Element Analysis (FEA) was first introduced around 1943 as a way to study vibration using a complex mathematical model. Basically, if you know enough about the structure, and all the elements that make up the structure, you can build a three dimensional model and apply stress to it. The way your model responds will guide you in designing for better reliability.
The problem, in the 1940s at least, was lack of numerical processing speed. Today, computers are so powerful that FEA is a standard part of any serious machinery manufacture.
Metso performs FEA on new designs of many different types of equipment, from papermaking to minerals processing. However, one of the more interesting applications for FEA is on pre-existing equipment. Metso can accurately model the machinery in question - we can predict failure points, help to forestall failure and prolong machinery lifetime.
How does Finite Element Analysis work?
The first step in FEA is to construct a 3D model using many nodes which are connected in a mesh. Typically in areas that see high stress levels more nodes are added.
The mesh is then provided with information about the material and structural properties that relate to load, vibration and stress levels. It may help to think of this mesh of nodes as a spider web, whereby any movement or stress at one point in the web can affect a web location far away from the point of stress.
After the model is prepared, several types of analysis may begin. Structural analysis can simulate pushing the model beyond its elastic limits to determine what deformation occurs. Vibrational analysis will look at random vibration, as well as the affect of impacts (such as cranes colliding with framework, or parent reels descending too quickly to rails), and how this relates to the resonant frequency and failure. Fatigue analysis will examine the potential for cracks and corresponding failure points in the structure.
When is Finite Element Analysis appropriate?
There are many cases where FEA is warranted. Some examples from Metso customers are: studying the existing corrosion on a particular machine section, and predicting future corrosion expansion; determination in advance of the effects of a desired nip load increase on the machine framework; discovery of the natural frequency of the machine and its main sections; and applying a new design to existing machinery to help prolong life or improve production.
Case Study: FEA used to solve vibration problem
A Canadian paper mill employed Metso to perform a machine audit. High vibration occurring at the dyer section prevented operation at high speeds. The machine was thus limited to 4018 fpm (1225 m/min). Metso’s audit engineers identified a main frame resonance with a peak amplitude occurring near 4477 fpm (1365 m/min).
Dryer section modeled with Finite Element Analysis, showing expected deformation at target frequency of 3.52 Hz.
Metso performed the FEA and determined that reinforcements were needed. The FEA measurements, engineering, manufacturing and installation of reinforcements occurred during four shutdowns. As a result, the vibration amplitudes were reduced to normal levels, allowing a speed increase to 4290 fpm (1308 m/min).
Dryer section after installation of reinforcements as determined by Finite Element Analysis
The mill’s production gain after reinforcement was $3,250,000 per year. They also achieved significantly better paper quality. In addition, mill personnel were surprised to find that the calender section and winder sections now ran much better. Their project payback time for the Metso machine audit, FEA analysis, design work and installation of reinforcements was only a few months.
Why choose Metso to perform Finite Element Analysis?
The paper machine is a constantly stressed structure. Weld joints are subject to fluctuating loads. Failure due to fatigue is common and plays a dominant role in the machine's lifetime. Metso has successfully used state-of-the-art FEA software for many mills to evaluate high stress areas to increase reliability, enhance performance and maximize fatigue life. Our specialized expertise in the proper application of computer-aided tools is supported by lab testing and empirical data gathered over the years on our equipment in the field.
As an original equipment manufacturer, Metso already has the drawings for hundreds of paper, board and tissue machines - whether they were originally built by Valmet, Metso, Beloit or other manufacturer now part of Metso Corporation. This drawing availability, combined with our engineer's experience both in FEA and onsite support of paper making equipment, uniquely qualifies us to know when and how to best apply FEA techniques to support your process.
So far in the field service article series, we reviewed short circulation studies and finite element analysis. In future field service articles we will examine other helpful Metso services such as troubleshooting and machine analysis, and provide example case studies of what can and has been achieved. Contact your Metso representative to learn how Metso's application of Finite Element Analysis on your machine line may greatly assist your maintenance and rebuild project planning.
