Are You Losing Sleep Over Poor Basis Weight Control - PowerPoint PPT Presentation

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Are You Losing Sleep Over Poor Basis Weight Control

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    1. Are You Losing Sleep Over Poor Basis Weight Control

    3. GSM: 110-132 Profile Variation:3 & 4 in roll #9 & 10 It increased to 8 in roll #11 GSM reduced suddenly in Roll#12 by 4 gsm Bottom average range is 118.34-120, but, average profile variation is 6.21GSM: 110-132 Profile Variation:3 & 4 in roll #9 & 10 It increased to 8 in roll #11 GSM reduced suddenly in Roll#12 by 4 gsm Bottom average range is 118.34-120, but, average profile variation is 6.21

    4. Mill Issues: 110-132gsm individual samples 3-11 gsm profile variation GSM control in 114-128 Averaged profile- 118.34-120 Average profile variation- 6.21 Poor machine runnability Lack of operator confidence over gsm checked 29 rolls Profile Var. 6.21 Average GSM 119 Whether it is a system problem? Or operator problem? A single position MD profiling can help. 29 rolls Profile Var. 6.21 Average GSM 119 Whether it is a system problem? Or operator problem? A single position MD profiling can help.

    5. Average GSM In the graph, we can see that there is a significant fluctuation in average profile variation (114-128gsm).

    6. May we ask? Were the operators careless? Was there so high a stock consistency variation?

    7. Profile Summary: Here, we may see that the out of 24 rolls studied, the section wise average does not vary much (118.3-120gsm)

    8. In fact, such a stable averaged profile (Green) suggests the absence of any CD problem in machine. Typically, disturbed average profile can be due to various reasons such as localized wire and felt choking, head box slice unevenness, drying constraints etc.

    9. Another Profile Report Let us study the another profile study, consisting of 45 profiles. For simplicity, instead of giving a lot of data, preliminary profile analysis is presented in form of a graph.

    10. Profile Variation: * Best: 2.0gsm * Worst: 4.0gsm

    11. Range of GSM Obtained at Different Positions:

    12. Average GSM as a Function of Time

    13. What is so special in these profiles?

    14. Time is Short. All these profiles have been taken from a SINGLE roll, one after another. For a machine speed of 200mpm, and roll diameter of nearly 1M, this can be said that these profiles are one second apart from each other. Thus, 45 profile means nearly 45 seconds of production. If, basis weight can vary between 34.0 to 36.5 within a short span of 45 seconds, how can we expect to control the same?

    15. Scanner Malfunctioning The most important aspect about such a case is that the basis weight scanners installed for DCS & QCS systems seem to malfunction. You may take a sample which could be 34.0gsm or 36.5gsm, and most probably the DCS system would be displaying some other basis weight on its console. In such a case, most papermakers will say that the scanner is giving wrong results. So, if you are not satisfied with your scanner, please read ahead.

    16. Single Position MD Profiling: Single position MD profiling is a technique, in which data are obtained for basis weight profile in machine direction, and plotted against time. Any specific pattern indicates the possible source of the problem, which can be considered for rectification. Since, data are taken only for a small time of paper manufactured, sometimes, it may be required to repeat the same.

    17. Single Position MD Profiling

    18. A Typical Single Position MD Profile:

    19. Issues: Different zones of stable gsm These zones exist for a small time duration of say 30-50 seconds. Had the operator taken sample 30-50 seconds earlier or later, what gsm value he would have observed? For a two minute MD plot (gsm range 122-132 in the plot), to achieve 120 gsm, should the operator reduce gsm by 2 or by 12? Fluctuations within stable zones 127 to 132 gsm in first stable zone. What should the operator do when he checks that the sample is of 127 gsm or 132 gsm? Why does it happen? If you are calibrating your scanner, which value you would choose for sample? Lets see what is happening in approach flow equipments.If you are calibrating your scanner, which value you would choose for sample? Lets see what is happening in approach flow equipments.

    20. Approach Flow:

    21. Inlet Consistency Changes? Yes, it keeps on changing due to various reasons e.g. Pump speed variations due to voltage, frequency etc. Presence of entrained air through pump glands etc. Centricleaner pit level and consistency variations As a result, profile gets disturbed.

    22. Centricleaner Consistency Change

    23. Pressure Screen Consistency Change

    24. Taper Manifold

    25. Effects: Fluctuating CD profile >>>disturbed short term MD profile Loss of confidence for the sample taken No action deadband increases Poor basis weight control

    26. Effects: In most of such cases DCS & QCS systems malfunction as scanners do not seem to sense correct basis weight.

    27. Reasons: Fan Pump Pulsations: RPM: 1500, vanes: 6, Speed: 200mpm Pulse to pulse difference: 200/(1500*6) i.e. 0.02 m So, for such a case, on lower speeds, fan pump pulsation cant harm you; but if the speed itself is fluctuating.? Similarly, effect of other equipments e.g pressure screen, holey rolls etc. can be considered.

    28. Fan Pump Speed: Speed of approach flow equipments vary due to voltage and frequency variations. Servo voltage stabilizer is able to control voltage to a maximum of 2.5% only. Frequency variations, (2%) remain uncontrolled. Net effect: 4.5% (i.e.fan pump speed may vary by 75rpm if running at full speed) Installation of VFD will be helpful in eliminating this problem.

    29. Holey Roll: Unfortunately, these run at much less speeds say 10-15rpm, and may result in pulsations at after 15-20m distance. The one minute MD profile is able to reveal if a particular holey roll is bend or misaligned.

    30. Checking for Holey Roll Related Problems: For the same, at least three 2 minute MD profiles are taken, one each at NDE, center and DE. Higher fluctuation amplitude at center indicates bend holey roll. Higher fluctuation amplitude at any end indicates the possibility of bearing off-center at that end. After the problem has been identified and rectified, it is recommended to verify the results.

    31. Entrained Air: Creates disturbance! Irregularly. Problem worsens if there are dead pockets. Much more severe in improperly designed pipings. Often serious on light gsm paper, when the speed is higher. Analog (bourdon Tube) gauges do not reflect pressure fluctuations.Digital pressure gauges with large diameter transmitters do help. Profile unstability Analysis A higher value at stock entry side indicates possibility of entrained air. More joints from this side.

    32. Manifold: Octopus header can be used to avoid CD profile fluctuations related problems in place of taper manifold.

    33. Typical Inferences: A bend/misaligned holey roll Entrained air in approach flow systems Inadequate inlet pressure at pressure screen inlet Centricleaner pit level and consistency fluctuations

    34. Typical Actions Taken: Installation of a new closed centricleaner Installation of VFDs for all approach flow pumps Provision of air venting lines at different piping locations Correct alignment of holey roll.

    35. Typical Results: For a yankee machine(No consistency regulator, no DCS)- Average basis weight for 24 hours varied between 48.2-49.4gsm; Individual samples between 47.4-50.2gsm Average basis weight for 72 hours varied between 54.7-57.0gsm; Individual samples between 54.0-57.8gsm

    36. Extra Benefits: For a yankee machine(No consistency regulator, no DCS)- Machine joints reduced from 150 to 50-60 per month Increase in machine speed by 3-5% Increase in yield Reduction in chemicals consumption Power savings Overall ..3 months payback only.

    37. How to begin? If you are not satisfied with the basis weight control you are having, just follow the following steps-

    38. Single Position MD Profile Collect data on single position in machine direction at drive end, non-drive end and at centre. Make sure that the data are being taken from such a roll of paper that no process change had been done prior to at least 10 minutes before producing that roll.

    39. Plot a Graph Make a graph plotting time at X axis, and basis weight at Y axis. Identify any repeated pattern. If hills and valleys are repeated, compute their frequency. Now, isolate the equipment in the machine the frequency of which matches with the plot. This is your first culprit.

    40. Repeat: Having rectified the problem of earlier identified culprit, repeat single position MD profiling, and possibly you may find another pattern. Very soon, you would be observing a better basis weight control.

    41. Thank you.