Some insights of basis weight control by process optimization, approach flow minor modifications and similar actions.

1. Engineering Aspects of
Basis Weight Control
By:
D K Singhal
Chandpur Enterprises Ltd.
Chandpur-246725

2. Problem:
How do you control basis weight?
Basis weight valve
Stock flow to fan pump
Machine chest consistency control

3. Problem:
What are modern techniques for basis
weight control?
Automatic machine chest consistency
control
Scanner controlling basis weight valve
Having a DCS/QCS system

4. Is it Really a Problem?
Maintaining correct basis weight is the
duty of machine operator.
If he is careless, we can have good
scanners, DCS/QCS systems.
Why should we waste our precious time
discussing such small things?

5. Yes!
Yes! It IS a genuine problem.
Please do spare a few minutes now.

6. Problem:
In fact, basis weight variation is a
common problem in all the mills.
Some mills manage to get the best
results out of their system.
Let us have a look at various points that
are the possible sources for poor basis
weight control.

7. Possible Sources for Poor
Control
Machine Chest
Centricleaner
Pressure Screen
Approach Flow Piping
Approach Flow Pumps
Head Box Manifold
Distributor-Rectifier Rolls
Electricity Supply System

8. Machine Chest
Machine chest consistency plays its own
role.
Too high a consistency results in fiber
flocculation as well as air entrapment in
pulp which creates a lot of problems in the
approach flow area.
In case consistency is too low, pulp fibers
tend to settle down resulting in changing in
SRBox consistency over a period of time.

9. Centricleaner
In the conventional centricleaners,
pulp enters from one side, it goes to
centricleaner bottles, and then leaves
through accept of these bottles.
Final accept is also at the same side.
This results in slow response of inlet
consistency change as shown in next
slide.

10. Centricleaner Consistency Change

11. Pressure Screen
Similarly, pressure screen is also a
huge vessel resulting in a similar
response as that by centricleaner.
The only difference is that the outlet
consistency plot will look a little
smooth when compared to that with
plot of centricleaner.

12. Approach Flow Piping
Approach flow piping may create
problems if not properly designed.
For example, let us consider line from
S R Box to fan pump. An oversized
line results in too slow pulp speed
vertically downwards.
This results in plug flow where pulp
flows in form of a plug. (Remember:
pulp is not an ideal liquid)

13. Approach Flow Piping
During the plug flow, plug like structure is
developed in pipeline. These plugs are
intermittent in nature as a combination
separate plugs one after another.
When it happens, we get intermittent pulses
of consistency fluctuation after the fan
pump.
This results in basis weight fluctuation.

14. Approach Flow Piping
On the other hand, if the pulp velocity
is too high (i.e. pipeline is undersized),
pulp starts to show erratic behavior.
In such a case any change in basis
weight valve opening may not reflect
proportional change in stock flow and
hence basis weight.

15. Approach Flow Pumps
All the pumps used in approach flow
should be of low pulsation type.
Pressure pulses travel at a speed
much higher than that of pulp (almost
equal to the speed of sound) and
create fluctuation in basis weight.

16. Approach Flow Pumps
Pumps must be regularly checked for
gland leakage etc.
Leaking glands are often the easiest
entry point for entrained air.
This entrained air creates
unpredictable fluctuations in basis
weight.

17. Head Box Manifold
As discussed earlier, most of the
machine direction changes, be these
due to consistency change, or due to
any other reason, or the desired
change in basis weight valve, enter
the manifold where these are
converted to cross direction changes
as indicated in nest slide.

18. Taper Manifold
Stock Entry
Time increases

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

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

21. Distributor-Rectifier Rolls
Distributor rectifier rolls (commonly
known as holey rolls) could be a major
reason for basis weight fluctuation.
In most of the cases, the head box
manufacturer gives very good rolls,
but with time, some rolls get bend,
misaligned or due to journal wear out,
bearing related problems, the
problems start appearing.

22. Distributor-Rectifier Rolls
Time series analysis (plotting machine
direction basis weight at a single CD
position against time) is an effective
tool to predict holey roll related
problems.

23. 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 by repeating the measurements.

24. A typical 45 second profile:
35.50
35.30
35.10
34.90
34.70
34.50
34.30
34.10
33.90
33.70
33.50
1
9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193

25. 35.50
35.30
A 45 second profile:
35.10
34.90
34.70
34.50
34.30
34.10
33.90
33.70
33.50
1
9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129 137 145 153 161 169 177 185 193
Such a profile can reveal a lot of
information.
The trend line (red color) indicates different
high basis weight pulses. These are
indicated by vertical lines in the plot. These
correlate to revolutions of holey roll.
There are minor pulses also in the graph,
which might be due to pulsations caused by
holes or something else.

26. 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 often able to reveal if a particular holey
roll is bend or misaligned.
Single Position MD Prof ile
140.0
Possibily due to testing error .
135.0
Stable
130.0
Stable
Stable
125.0
16
9
11
8
16
6
11
5
16
3
11
2
16
0
9
1
7
6
6
1
4
6
3
1
1
6
1
120.0

27. Typical Inferences:
A bend/misaligned holey roll
To high holey roll speed
If the fluctuation is not of the same
magnitude after each holey roll
revolution, there is a possibility of
loose chain/ chain sprocket driving the
holey roll.

28. Typical Solution:
In one instance, while checking approximately
200 samples during the machine run of one
minute, the fluctuation in basis weight was
found to be within + 0.5gsm.
On the basis of the same, holey roll speed was
reduced from 22 rpm to 11 rpm.
The fluctuation immediately reduced to
+0.23gsm.
Well, in many cases, repair or replacement of
holey roll becomes a must to get good basis
weight control.

29. Electricity Supply System
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 of 1440 rpm)
One may very well understand the effect of such level
of uncontrollable speed variation of fan pump and
other approach flow equipments on basis weight.

30. Fan Pump Speed:
Installation of VFD will be helpful in
eliminating this problem.
So far, most of the VFD installations
are aimed towards energy
conservation, but in approach flow
area, the improved process control is
greatest advantage of VFD.

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. Let us now have a look at typical
basis weight profile…..

33. RollNo. #1
#2
#3
#4
#5
#6
#7
#8
#9
Var
Avg.
1 115.0 115.0 119.0 119.0 120.0 119.0 120.0 120.0 119.0
5.0 118.4
2 112.0 112.0 116.0 116.0 119.0 118.0 115.0 116.0 116.0
7.0 115.6
3 120.0 122.0 121.0 120.0 122.0 120.0 119.0 120.0 123.0
4.0 120.8
4 117.0 119.0 114.0 117.0 115.0 116.0 118.0 118.0 119.0
5.0 117.0
5 112.0 116.0 114.0 118.0 112.0 114.0 114.0 115.0 116.0
6.0 114.6
6 116.0 118.0 114.0 115.0 112.0 116.0 118.0 120.0 118.0
8.0 116.3
7 118.0 118.0 114.0 114.0 115.0 120.0 120.0 120.0 117.0
6.0 117.3
8 120.0 122.0 118.0 119.0 120.0 120.0 119.0 119.0 120.0
4.0 119.7
9 122.0 123.0 123.0 121.0 120.0 122.0 121.0 122.0 122.0
3.0 121.8
10 122.0 120.0 119.0 122.0 119.0 123.0 121.0 121.0 122.0
4.0 121.0
11 118.0 120.0 116.0 118.0 124.0 123.0 122.0 121.0 119.0
8.0 120.1
12 120.0 118.0 116.0 116.0 115.0 114.0 113.0 115.0 116.0
7.0 115.9
13 115.0 115.0 114.0 118.0 116.0 117.0 115.0 120.0 122.0
8.0 116.9
14 117.0 115.0 114.0 118.0 117.0 119.0 117.0 122.0 123.0
9.0 118.0
15 110.0 111.0 111.0 117.0 115.0 117.0 117.0 115.0 113.0
7.0 114.0
16 121.0 124.0 131.0 131.0 131.0 132.0 130.0 126.0 128.0 11.0 128.2
17 126.0 126.0 120.0 125.0 124.0 124.0 121.0 122.0 125.0
6.0 123.7
18 122.0 119.0 117.0 118.0 117.0 120.0 121.0 118.0 120.0
5.0 119.1
19 126.0 126.0 125.0 120.0 123.0 125.0 126.0 124.0 130.0 10.0 125.0
20 120.0 122.0 123.0 121.0 118.0 118.0 122.0 124.0 125.0
7.0 121.4
21 115.0 117.0 116.0 115.0 116.0 118.0 117.0 117.0 115.0
3.0 116.2
22 115.0 115.0 118.0 120.0 120.0 119.0 118.0 119.0 121.0
6.0 118.3
23 125.0 120.0 120.0 120.0 121.0 123.0 121.0 123.0 123.0
5.0 121.8
24 118.0 119.0 120.0 122.0 123.0 122.0 118.0 117.0 118.0
6.0 119.7
25 118.0 120.0 122.0 121.0 120.0 119.0 117.0 119.0 120.0
5.0 119.6
26 122.0 115.0 116.0 118.0 117.0 118.0 118.0 116.0 117.0
7.0 117.4
27 122.0 124.0 128.0 126.0 124.0 125.0 122.0 124.0 125.0
6.0 124.4
28 113.0 114.0 118.0 115.0 116.0 117.0 114.0 112.0 112.0
6.0 114.6
29 118.0 118.0 115.0 121.0 118.0 116.0 115.0 116.0 116.0
6.0 117.0
Min
110.0 111.0 111.0 114.0 112.0 114.0 113.0 112.0 112.0
3.0 114.0
Max
126.0 126.0 131.0 131.0 131.0 132.0 130.0 126.0 130.0 11.0 128.2
Avg.
118.45 118.72 118.34 119.34 118.93 119.79 118.93 119.34 120.00 6.21 119.10
Range
16
15
20
17
19
18
17
14
18
8 14.222

34. 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

35. Best & Worst Profiles
135.0
130.0
125.0
120.0
115.0
110.0
105.0
1
2
3
4
5
Best
6
Worst
7
8
9

36. Who is to blame?
•Is it a problem of poor designed
approach flow?
•Is it a problem of Head Box?
•Is it due to carelessness of the
operators?

37. Average GSM
130.0
128.0
126.0
124.0
122.0
120.0
118.0
116.0
114.0
112.0
110.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
In the graph, we can see that there is
a significant fluctuation in average
profile variation (114-128gsm).

38. Now, may we ask?
Were the operators careless?
Was there so high a stock consistency
variation?
Or, there was something else
responsible for the problem?

39. Let us try something…
Out of the available 24 consequent
profiles, we take average at different
positions. Similarly, position wise
minimum and maximum values can
be found out.
The values are plotted as in next
figure.

40. Profile Summary:
135.0
130.0
125.0
120.0
115.0
110.0
105.0
1
2
3
4
Min
5
Max
6
7
8
9
Avg.
Here, we may see that the out of 24 rolls
studied, the section wise average does not
vary much (118.3-120gsm)

41. 135.0
130.0
125.0
120.0
115.0
110.0
105.0
1
2
3
4
Min
5
Max
6
7
Avg.
In fact, such a stable averaged profile (Green)
suggests the absence of any CD problem in
machine. Typically, disturbed average profile
can also be due to various reasons such as
localized wire and felt choking, head box slice
unevenness, drying constraints etc.
All of such factors force machine operators to
disturb CD profile so that they are able to
maintain CD moisture profile in acceptable
range.
8
9

42. Another Profile Report
Let us study the another profile study,
consisting of 45 profiles.
All of these profiles were drawn from a
single roll.
These profiles are taken within 1
minute of production.
For simplicity, instead of giving a lot of
data, preliminary profile analysis is
presented in form of a graph.

43. Profile Variation:
* Best:
* Worst:
2.0gsm
4.0gsm
Best & Worst CD Profiles
39
38
37
36
35
34
33
32
1
2
3
4
5
6
7
8
9
10 11 12

44. Best & Worst CD Profiles
Profile Variation:
39
38
37
36
35
34
33
32
1
2
3
4
5
6
7
8
9
10 11 12
Here, we may see an interesting pattern.
Out of the 45 profiles taken from a single
roll, we may get CD variations of 2.0 and
4.0.
So, how much CD variation we are
getting is depending on our luck. Within
a span of one minute, we may get a
profile variation of 2.0 or 4.0 gsm.

45. Range of GSM Obtained at
Different Positions:
40
38
36
34
32
1
2
3
4
5
6
7
8
9
10 11 12

46. Range of GSM Obtained at
Different Positions:
40
38
36
34
32
1
2
3
4
5
6
7
8
9 10 11 12
Here again the situation is same.
As clear, there is a variation of 2 gsm at
any individual position.
Obviously, if the operators are drawing
sample at any instance, there is always a
possibility of 2gsm inaccuracy in
measurement, no matter however
accurate is the measuring system.

47. Average GSM as a Function
of Time
37
36.5
36
35.5
35
34.5
34
1
5
9 13 17 21 25 29 33 37 41 45

48. Average GSM as a Function
of Time (after modification)
45.4
45.3
45.2
45.1
45
44.9
44.8
44.7
44.6
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

49. Average GSM as a Function
of Time
37
36.5
36
35.5
35
34.5
34
1
5
9 13 17 21 25 29 33 37 41 45
Here we can see that the average gsm is
fluctuating significantly.
Suppose the desired basis weight is 36,
and operator is getting anything as
above, the problem appears should he
alter basis weight valve opening or
ignore the difference?
You decide!

50. What is so special in these
profiles?
Best & Worst CD Profiles
Range of GSM Obtained at Different Positions
39
38
37
36
35
34
33
32
40
38
36
34
32
1
2
3
4
5
6
7
8
9
10 11 12
Average GSM as a Function of Time
37
36.5
36
35.5
35
34.5
34
1
5
9 13 17 21 25 29 33 37 41 45
1
2
3
4
5
6
7
8
9
10 11 12

51. 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 fluctuate between 34.0
to 36.5 within a short span of 45 seconds,
how can we expect to control the same?

52. 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.

53. Scanner Malfunctioning…
Look at the following 1 minute gsm
plot.
51.50
51.00
50.50
50.00
49.50
49.00
48.50
48.00
1
21 41 61 81 101 121 141 161 181 201 221 241 261 281

54. Scanner Malfunctioning…
51.50
51.00
50.50
50.00
49.50
49.00
48.50
48.00
1
21 41 61 81 101 121 141 161 181 201 221 241 261 281
In this plot if canner is indicating 50
gsm and your sample is 49.5 gsm you
may say that scanner is indicating
basis weight higher by 0.5 gsm.
But, if your sample is 50.5 gsm?

55. Scanner Malfunctioning…
Scanners work on a scientific principle of
radioactive rays penetration properties of
cellulose fibers.
A calibration problem may result in over or
under reporting of basis weight, and this can be
corrected easily.
But, in case there is a fluctuation in basis
weight as seen earlier, one may doubt that the
scanner is not functioning well.

56. Advantages of Such
Analysis:
It is possible to analyze different
reasons and their contribution to
existing basis weight variation
problem.
Common inferences that can be
drawn by such study are..

57. 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

58. In House Troubleshooting:
Single position MD profiling has been
found a very good technique for such
problems.
The following slides indicate how you
may use this technique to solve basis
weight related problems in your plant.

59. 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.

60. Single Position MD Profiling
Cutter
12 11 10 9
8
7
5
6 5
4
3 ….
Unwind
# A 2 minute profile can be used to reveal much information.
# For a longer duration, 10th or 20th alternate samples can
also be used.

61. Another Typical Single
Position MD Profile:
140.0
Possibily due to testing error.
135.0
Stable
130.0
Stable
Stable
125.0
120.0
1
18
35
52 69
86 103 120 137 154 171 188

62. Issues:
Different zones of relatively stable gsm
Single Position MD Profile
140.0
Possibily due to testing error.
135.0
130.0
Stable
Stable
Stable
125.0
1
16
31
46
61
76
91
106
121
136
151
166
181
196
120.0
• 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 122132 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?

63. A Typical Approach Flow:
Often, the conventional approach flow
system looks perfect, as below…

64. Seems a perfect system!
Ideally, if inlet consistency is fixed,
basis weight should remain fixed.
But, if the consistency is changing at
different points, basis weight
fluctuation cannot be controlled.
But, the inlet consistency to head box
keeps on changing.

65. Inlet Consistency Changes!
How?
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.

66. Effects:
In most of such cases DCS & QCS systems
malfunction as scanners do not seem to
sense correct basis weight.
Single Position MD Profile
140.0
Possibily due to testing error.
135.0
130.0
Stable
Stable
Stable
125.0
1
16
31
46
61
76
91
106
121
136
151
166
181
196
120.0

67. 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 can’t harm you; but if the speed itself
is fluctuating….?
Similarly, effect of other equipments e.g
pressure screen, holey rolls etc. can be
considered.
At higher machine speeds fan pump pulsations
create significant problems.

68. 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

69. 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.

70. 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
Reduction in CD profile variation by more
than 50% after such studies were made and
suitable actions were taken.

71. Extra Benefits:
For a yankee machine(No consistency regulator, no DCS)Machine joints reduced to just 25-30% of
earlier
Increase in machine speed by 3-5%

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

73. Single Position MD Profile
Collect data on single position in machine
direction at drive end, non-drive end and at
centre.
Ensure 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. Also, the basis
weight control should be running in manual
control mode.

74. Plot a Graph
Make a graph plotting time at ‘X’ axis,
and basis weight at ‘Y’ axis. Such
study is known as Time Series
Analysis in mathematics.
Identify any repeated pattern. If hills
and valleys are repeated, compute
their frequency.

75. Analyze
Now, look at the equipment in the
machine the frequency of which
matches with the plot. This is going to
be your first enemy. Do the needful to
minimize the problem it is creating.

76. Correct
Take corrective action to solve the
problem identified. Once the problem
is solved the variations from such
section are reduced.

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

78. Finally….
You will be getting better basis weight
control.
Please do not forget to share your experiences
with others. I’d really like to have your email
containing your achievements in my inbox.

79. Average GSM as a Function
of Time (after modification)
37
36.5
36
35.5
35
34.5
34
1
5
9 13 17 21 25 29 33 37 41 45
45.4
45.3
45.2
45.1
45
44.9
44.8
44.7
44.6
1 2 3 4 5 6 7 8 9 101112131415161718192021222324

81. Thank you.
D K Singhal
deveshksinghal@gmail.com