Metso Paper Analysis Lab - Overview
What is causing the MD streaks in your paper? Why can’t you get rid of calender barring? Why do you get uneven rolls from your winder? Do you have other chronic problems you just can’t seem to solve? Wouldn’t it be awful to replace your headbox and still have MD streaks because the problem is in your stock approach flow system? There is a way to answer these questions by testing the paper you produce.
Examples for the articles in this series are drawn from the Metso Paper Analysis Lab, located in Norcross, GA, USA. Tests were performed using instruments such as the TAPIO Analyzer and the Metso Automation PaperLab PlusTM.
Accurately tracing quality disturbances
High-resolution off-line measurements are useful for understanding paper quality variation and machine diagnostics. They utilize high-resolution data collection, variable aperture sizes for different information, same-point measurement of all properties, true MD and CD profiles, and long MD samples. They yield the frequencies of periodic disturbances. Various parts of the process have their unique natural frequency areas. Therefore, quality disturbances may be traced back to their origins with surprisingly good accuracy.
Testing an MD roll from near the front of the machine, an MD roll from near the back of the machine and a set of consecutive CD strips yields a complete picture of the variation in paper.
Alignment is crucial for measurement comparison
In high-resolution off-line testing, the sensors are software-aligned to measure exactly the same points on the paper for every property measured. This is important in determining the source of the variability. If a disturbance is apparent in every property measured, it is probably from the stock-approach-flow system. If a disturbance is apparent in caliper but not in basis weight, it occurs after the web is formed. If a disturbance is apparent in basis weight and ash content but not in fiber grammage, it comes from filler or coating application.
True MD and CD profiles
Testing the rolls yields true MD data that is used to find random and periodic MD disturbances from the stock-approach-flow system, and press, dryer and calender rolls. With thin papers, such as LWC and newsprint, more than 5000 meters (3 miles) of paper may be tested to get long-term data. Shorter portions of the roll are tested at slower speeds to get short-term data.
To obtain true CD profiles, a stack of about thirty strips is cut off of a full-width reel. They are taped end-to-end consecutively, cut to a uniform width, and rolled onto a core. Usually twenty are actually tested. Looking at a graph containing all twenty individual profiles yields information about the paper. In basis weight, S-shaped curves that go in opposite directions in consecutive strips often indicate a MD disturbance moving through the header. In caliper, S-shaped curves going in opposite directions in consecutive strips often indicate vibration in a press, dryer, or calender roll. Profile ends going opposite ways indicate that the ends of a roll are vibrating in opposite phase.
Why go to an outside laboratory?
The Metso Paper Analysis Lab gives new insight into your machine's performance. We work personally with you to meet your objectives and to create value for your organization:
- By identifying specific sources of variation in your sheets
- By comparing your sheets to results from our global database
- By confirming the accuracy of your on-line sensors
- By diagnosing sources of problems to improve machine performance
Using the Metso Paper Analysis Lab allows you to expand the scope of your own mill testing and analysis without having to invest in advanced testing tools. For more information on the Metso Paper Analysis Lab, contact your Metso Paper service representative.
Catch us next week for the second article in this series. We will demonstrate how off-line testing lab measurements helped to identify winder roll throw-out problems at a North American paper mill.
