management of process laboratory in mill environment by d k singhal chandpur enterprises ltd.,...

Management of Process Management of Process Laboratory in Mill EnvironmentLaboratory in Mill Environment

ByBy

D K SinghalD K Singhal

Chandpur Enterprises Ltd.,Chandpur Enterprises Ltd.,

Sargam Theatre, ChandpurSargam Theatre, [email protected]

[email protected]

www.paperonweb.comwww.paperonweb.com 22

What is Data?What is Data?

Improvement of product quality through Improvement of product quality through the use of statistical techniques.the use of statistical techniques.

Raw material for such techniques is DATARaw material for such techniques is DATA We get data from different testing and We get data from different testing and

evaluations.evaluations. For simplicity methods for standardization For simplicity methods for standardization

of techniques used are available.of techniques used are available.


Then, what is the problem?Then, what is the problem?

One may ask, “One can use equipments One may ask, “One can use equipments and instruments to check quality and instruments to check quality parameters and get the result. Then, why parameters and get the result. Then, why should we consider laboratory should we consider laboratory management as something different?”management as something different?”

Let us have a look at next example.Let us have a look at next example.


Hardness of WaterHardness of Water

In a mill, the chemists were checking total In a mill, the chemists were checking total hardness regularly. Once, when it was hardness regularly. Once, when it was required to check temporary hardness, the required to check temporary hardness, the chemist obtained negative result. chemist obtained negative result.

We know any hardness cannot be We know any hardness cannot be negative.negative.

They repeated the experiment, but the They repeated the experiment, but the result was same. Why?result was same. Why?


Hardness of WaterHardness of Water

Total Hardness (TH)= Temporary + PermanentTotal Hardness (TH)= Temporary + Permanent Temporary hardness is removed by BoilingTemporary hardness is removed by Boiling Permanent hardness cannot be removed by Permanent hardness cannot be removed by

boilingboiling so,so, Temp. Hardness Temp. Hardness

= TH of water - TH of boiled water= TH of water - TH of boiled water


Temporary HardnessTemporary Hardness

If we boil water, some of its content would If we boil water, some of its content would get evaporated.get evaporated.

If we forget to add water to make up volume, we may get wrong results.

The chemists were making the same mistake. They just forgot to add make up distilled water.


Another ExampleAnother Example


CD ProfileCD Profile

A chemist checks CD profile.A chemist checks CD profile. CD GSM Variation is often within acceptable CD GSM Variation is often within acceptable

range.range. Occasionally, whenever variation is higher than Occasionally, whenever variation is higher than

acceptable, papermaker objects that the chemist acceptable, papermaker objects that the chemist has made some mistake.has made some mistake.

On rechecking, many a times, variation is within On rechecking, many a times, variation is within acceptable limits. acceptable limits.


Why did it happen?Why did it happen?

Was the chemist careless?Was the chemist careless? Did he not checked CD variation properly?Did he not checked CD variation properly? Or did the papermaker force the chemist Or did the papermaker force the chemist

to alter the CD profile results reported to alter the CD profile results reported earlier?earlier?

Or there was something else that was Or there was something else that was creating unreliability?creating unreliability?


Sample CD Profiles in 1MinuteSample CD Profiles in 1MinuteBest & Worst CD Profiles

32.033.034.035.036.037.038.039.0

1 2 3 4 5 6 7 8 9 10 11 12

Best Profile Variation: 2 gsmWorst Profile Variation: 4 gsm

We may see that within one minute, profile varies significantly. In such a case getting any profile of the two above or in between is just a chance or luck.


Sample CD ProfilesSample CD Profiles

Range of GSM Obtained at Different Positions(Both profiles from the same roll, within 1 minute)

32.033.034.035.036.037.038.039.0

1 2 3 4 5 6 7 8 9 10 11 12

We may see that within one minute, average gsm varies significantly. In such a case getting any gsm in between the above two is just a chance or luck.


Average GSM as a Function of Time

34.0

34.5

35.0

35.5

36.0

36.5

37.0

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

Profile No. (1 Minute Plot)


CD ProfileCD Profile

We may see that something else (paper We may see that something else (paper machine approach flow, pulsations etc.) altered machine approach flow, pulsations etc.) altered the results every fraction of second.the results every fraction of second.

Hence, in this case reliability of laboratory data Hence, in this case reliability of laboratory data for CD profile is mainly governed by process, for CD profile is mainly governed by process, and not by sophisticated equipment or adoption and not by sophisticated equipment or adoption of some specific testing techniqueof some specific testing technique..


Breaking LengthBreaking Length

Breaking length is tested for every roll.Breaking length is tested for every roll. There are some variations roll to roll.There are some variations roll to roll. To confirm whether variations are To confirm whether variations are

governed by paper properties or testing governed by paper properties or testing error, several rolls were checked checking error, several rolls were checked checking breaking length at 5 positions, and breaking length at 5 positions, and average of these was compared with the average of these was compared with the reported data. reported data.


2400250026002700280029003000

1 3 5 7 9 11 13 15

Avg. Reported

Average of 5 samples in a roll.



We can see that there is a very high We can see that there is a very high fluctuation in reported data. fluctuation in reported data.

Similar to the case for basis weight, Similar to the case for basis weight, probably, something else is altering the probably, something else is altering the results.results.

To know this, each property from each To know this, each property from each machine has to be studied carefully in machine has to be studied carefully in detail.detail.



Unfortunately, test methods published by a Unfortunately, test methods published by a leading research institute in India, does leading research institute in India, does not explain not explain breaking length.breaking length.


BurstBurst

Sometimes, Burst Factor as tested in a Sometimes, Burst Factor as tested in a mill, may not be same as found in the mill, may not be same as found in the same mill some times later.same mill some times later.

Customer may complain having a paper of Customer may complain having a paper of lower BF, than that was actually produced lower BF, than that was actually produced in a mill.in a mill.


CobbCobb

In some grades, sizing is extremely In some grades, sizing is extremely important.important.

Most customers complain paper Most customers complain paper meltingmelting (wet rupture of paper when in contact with (wet rupture of paper when in contact with glue), without understanding what caused glue), without understanding what caused the problem.the problem.

Papers affinity to water is more at higher Papers affinity to water is more at higher water pH.water pH.


CobbCobb

Fortunately, mill can check Cobb; Unfortunately, Fortunately, mill can check Cobb; Unfortunately, many customers cannot.many customers cannot.

If glue is made of water of higher pH, customer If glue is made of water of higher pH, customer may face problem even though that paper was may face problem even though that paper was of same pH.of same pH.

The same paper (same Cobb value) cannot give The same paper (same Cobb value) cannot give same results on gluing in Rajasthan and West same results on gluing in Rajasthan and West Bengal where there is a significant variation in Bengal where there is a significant variation in atmospheric relative humidity.atmospheric relative humidity.


Cobb Values Reported Vs. Recheck

y = 0.8502x + 4.5161

2030405060

20 30 40 50

Reported Cobb

Rech

eck


Are There any Standards?Are There any Standards?

Yes! Standards do exist for almost all Yes! Standards do exist for almost all properties.properties.

These require sophisticated equipment, These require sophisticated equipment, techniques, operating conditions and techniques, operating conditions and manpower.manpower.

Some equipment are frequently calibrated Some equipment are frequently calibrated to give accurate results.to give accurate results.


So, What’s the Problem?So, What’s the Problem?


We may get wrong results due We may get wrong results due to:to:

Human carelessness.Human carelessness. Non-adherence to proper testing Non-adherence to proper testing

conditions.conditions. Alteration in sample/equipment.Alteration in sample/equipment. Process Fluctuations.Process Fluctuations.


What Can We Do?What Can We Do?

Improve testing methods or develop new Improve testing methods or develop new methods for testing in plants, so that such errors methods for testing in plants, so that such errors could be minimized.could be minimized.

Consider working environment equally important Consider working environment equally important as standard atmospheric conditions. So far, as standard atmospheric conditions. So far, testing methods standardization has been done testing methods standardization has been done only for laboratory testing, and not for plant only for laboratory testing, and not for plant conditions. conditions.

Ensure that chemists are able to do testing Ensure that chemists are able to do testing without stress.without stress.


What Can We Do?What Can We Do?

In case results seem unreliable, check out In case results seem unreliable, check out possible reasons instead of just rejecting a possible reasons instead of just rejecting a lot.lot.

Review test methods requiring Review test methods requiring unnecessary high parameters. unnecessary high parameters.


Some Details!Some Details!

Here, we’ll discuss some of the testing Here, we’ll discuss some of the testing along with the problems associated and along with the problems associated and how to get reasonably accurate and how to get reasonably accurate and repeatable data. repeatable data.


ConsistencyConsistency

Consistency is calculated as-Consistency is calculated as-

Weight of solidsWeight of solidsCy % = ----------------------- X 100 %Cy % = ----------------------- X 100 % Volume of slurryVolume of slurry

But, some error is possible while making But, some error is possible while making measurements. Let’s have an example-measurements. Let’s have an example-


Error in Consistency Error in Consistency MeasurementMeasurement

Let solids = 1.5 gm; Volume = 50 mlLet solids = 1.5 gm; Volume = 50 ml Error in weight = 0.001 gm (1 mg); Error in weight = 0.001 gm (1 mg); Error in volume = 1 ml Error in volume = 1 ml

(Do you expect to measure volume of a 3% consistency pulp sample with a (Do you expect to measure volume of a 3% consistency pulp sample with a better accuracy?)better accuracy?)

Cy. obtained Cy. obtained

MAX:= (1.5+0.001)*100/(50-1) = 3.063%MAX:= (1.5+0.001)*100/(50-1) = 3.063%

MIN:= (1.5-0.001)*100/(50+1) = 2.939%MIN:= (1.5-0.001)*100/(50+1) = 2.939% Difference = 0.124 percent pointsDifference = 0.124 percent points


Consistency Measurement Consistency Measurement

So, measurement in consistency may So, measurement in consistency may produce errors to the tune of produce errors to the tune of ++0.062%.0.062%.

Even if we take 100ml pulp slurry, we may Even if we take 100ml pulp slurry, we may get error of get error of ++0.03%. 0.03%.

This is fairly good for routine This is fairly good for routine measurements, but, for measurement of measurements, but, for measurement of °°SR and CSF, our standard test methods SR and CSF, our standard test methods require more accuracy.require more accuracy.


Consistency MeasurementConsistency Measurement

For Example, for CSF, the desired value is 0.3% For Example, for CSF, the desired value is 0.3% ++ 0.002%. 0.002%.

Above technique for consistency measurement is Above technique for consistency measurement is unsuitable for conducting CSF test.unsuitable for conducting CSF test.

So, So,


Error AnalysisError Analysis

Furthermore, was the pulp sample well Furthermore, was the pulp sample well mixed? Also, entrained air and ambient mixed? Also, entrained air and ambient temperature affect measurements. In case temperature affect measurements. In case mixing was not perfect, we cannot assume mixing was not perfect, we cannot assume that the sample of pulp was true that the sample of pulp was true representative of stock.representative of stock.

In other words, maintaining desired In other words, maintaining desired consistency conditions for CSF measurement consistency conditions for CSF measurement is virtuallyis virtually IMPOSSIBLE.IMPOSSIBLE.


What can we do?What can we do?

If the pulp sample taken is pre-diluted to If the pulp sample taken is pre-diluted to approximate target value for the desired approximate target value for the desired consistency, and consistency is checked from consistency, and consistency is checked from this sample, we may get reasonably good this sample, we may get reasonably good accuracy. accuracy.

Let us see how….Let us see how….


Slurry Preparation for CSFSlurry Preparation for CSF

Take pulp slurry.Take pulp slurry. Dilute to 0.3% (+) approximately.Dilute to 0.3% (+) approximately. Measure consistency accurately.Measure consistency accurately. Take calculated volume for CSF measurement.Take calculated volume for CSF measurement. Make up with water to 1000 ml.Make up with water to 1000 ml.


Error AnalysisError Analysis

Volume Taken = 1000ml, error = 1 mlVolume Taken = 1000ml, error = 1 ml Weight = 3gm (App.), error = 0.001gmWeight = 3gm (App.), error = 0.001gm Cy ObtainedCy Obtained

MAX = 3.001/999 = 0.3004%MAX = 3.001/999 = 0.3004% MIN = 2.999/1001 = 0.2997%MIN = 2.999/1001 = 0.2997%

So, error (So, error (++0.0003) is less than desired limit of 0.0003) is less than desired limit of ++0.002%0.002%

Now, we may get reasonably acceptable consistency Now, we may get reasonably acceptable consistency measurement.measurement.


GSM & ProfileGSM & Profile

Similar to above, we know that there is always some CD Similar to above, we know that there is always some CD profile variation.profile variation.

This means no single sample from a roll can be This means no single sample from a roll can be considered to be a true representative of paper GSM.considered to be a true representative of paper GSM.

Still, we are reporting GSM to one or even two decimal Still, we are reporting GSM to one or even two decimal point accuracy in most of our work, including research point accuracy in most of our work, including research papers.papers.


GSM & Profile: Mill PracticeGSM & Profile: Mill Practice

Errors due to carelessness in measurement, alteration of Errors due to carelessness in measurement, alteration of data are also possible in process laboratories. data are also possible in process laboratories.

To eliminate these, two CD profiles can be extracted To eliminate these, two CD profiles can be extracted from the roll, the one is used for testing and other is kept from the roll, the one is used for testing and other is kept for future cross check.for future cross check.

The cross checking is done the next day by a senior The cross checking is done the next day by a senior

chemist. chemist.



A significant variation between reported A significant variation between reported figure and cross check indicates the figure and cross check indicates the possibility of data manipulation. possibility of data manipulation.

In many cases, when this technique was In many cases, when this technique was implemented, chemists became cautious implemented, chemists became cautious and careful so the reporting improved.and careful so the reporting improved.



Later on, approach flow modifications Later on, approach flow modifications were made to ensure that there are no were made to ensure that there are no profile fluctuations.profile fluctuations.

This also helped reducing joints This also helped reducing joints significantly.significantly.


Roll JointsRoll Joints Always, the first target is to have nil or Always, the first target is to have nil or

minimal joints. minimal joints. Even if there is a joint, it must be marked Even if there is a joint, it must be marked

properly on the reel.properly on the reel.


Roll JointsRoll Joints Joint can often be ignored, and sometimes not possible Joint can often be ignored, and sometimes not possible

to detect when the roll sides are good.to detect when the roll sides are good.

To minimize such situation, flags are put after every joint To minimize such situation, flags are put after every joint or sample drawn from the pope reel.or sample drawn from the pope reel.

RED FLAG: ...... JOINTRED FLAG: ...... JOINT

GREEN FLAG:.. SAMPLEGREEN FLAG:.. SAMPLE

Unmarked joint or sample is reported by rewinder Unmarked joint or sample is reported by rewinder operator.operator.


BrightnessBrightness

For frequent calibration of the brightness tester, For frequent calibration of the brightness tester, it is suggested to have it is suggested to have Multi Level StandardsMulti Level Standards..

Frequent cross check with customer/ other mills Frequent cross check with customer/ other mills is often useful.is often useful.

In the next slides, mill wide multi level standards In the next slides, mill wide multi level standards are discussed. are discussed.


Brightness StandardsBrightness Standards

Typical Mills Multi Level Standards:Typical Mills Multi Level Standards: Primary Standard:Primary Standard:

Purchased from an ISO-9000 equipment supplier/calibrated by Purchased from an ISO-9000 equipment supplier/calibrated by some third party. Can be used maximum twice in a month for some third party. Can be used maximum twice in a month for calibration of secondary standard, and replaced every year.calibration of secondary standard, and replaced every year.

Secondary Standard:Secondary Standard:New blank plastic coated visiting cards calibrated by primary New blank plastic coated visiting cards calibrated by primary

standard for calibration of tertiary standard/equipment. Each can standard for calibration of tertiary standard/equipment. Each can

be used maximum of thrice only.be used maximum of thrice only.


Brightness StandardsBrightness Standards

Tertiary Standard:Tertiary Standard:To be used every time before testing.To be used every time before testing.

Made up of glazed ceramic tile.Made up of glazed ceramic tile.

To be replaced every month with a new one.To be replaced every month with a new one.


Tensile StrengthTensile Strength

To avoid fluctuation in readings as well as to save time in To avoid fluctuation in readings as well as to save time in pre-conditioning of the sample at standard conditions, pre-conditioning of the sample at standard conditions, the following approach may be used.the following approach may be used.

Conditioning of SampleConditioning of Sample

Heat in oven at 100-105 Heat in oven at 100-105 °°C, 2-4 min.C, 2-4 min.

Allow to cool for 2-4 min.Allow to cool for 2-4 min.

Continue testingContinue testing Results match closely with testing under standard Results match closely with testing under standard

conditions.conditions.


Burst StrengthBurst Strength

Preconditioning as for tensile can be done Preconditioning as for tensile can be done for Burst testing also.for Burst testing also.

Burst testing on a number of different Burst testing on a number of different samples in a roll, and average is taken samples in a roll, and average is taken discarding abnormal reading, if any. discarding abnormal reading, if any.

If there is a variation, by more than 8-10%, If there is a variation, by more than 8-10%, there is a need to study the machine itself there is a need to study the machine itself for the same.for the same.


CobbCobb

Cobb is highly sensitive to environmental Cobb is highly sensitive to environmental conditions (Temp., RH etc.)conditions (Temp., RH etc.)

Cobb is highly sensitive to water pH.Cobb is highly sensitive to water pH. Cobb is highly sensitive to paper condition, Cobb is highly sensitive to paper condition,

moisture, temperature, formation etc.moisture, temperature, formation etc.


CobbCobb

Oven treatment for 1 min. and cooling to 2 Oven treatment for 1 min. and cooling to 2 minutes before testing gives fairly good results minutes before testing gives fairly good results comparable to standard testing.comparable to standard testing.

Modification of Cobb targets depending on Modification of Cobb targets depending on probable date of dispatch, weather conditions, probable date of dispatch, weather conditions, location of customer, water properties in location of customer, water properties in customer area etc. can be consideredcustomer area etc. can be considered..


Cobb:Cobb:

On the basis of above, while cobb targets On the basis of above, while cobb targets were modified, it became possible to were modified, it became possible to reduce Rosin consumption for some reduce Rosin consumption for some customers.customers.

For some customers (qualities), For some customers (qualities), savings in rosin consumption savings in rosin consumption were to the order of 30-40%.were to the order of 30-40%.


Remember:Remember:

It is easy to maintain standard conditions It is easy to maintain standard conditions for testing in laboratory, but, customer may for testing in laboratory, but, customer may be using paper in extremely different be using paper in extremely different conditions.conditions.

Mill wise, testing methods should be Mill wise, testing methods should be flexible enough so that testing can be flexible enough so that testing can be done in short time before a huge quantity done in short time before a huge quantity is rejected. is rejected.


Can we-Can we-

Develop/modify testing methods for rapid Develop/modify testing methods for rapid in house testing?in house testing?

Minimize human errors to a minimum by Minimize human errors to a minimum by motivating our TESTING TEAM to be motivating our TESTING TEAM to be more attentive?more attentive?

Make our quality tests more flexible?Make our quality tests more flexible?


For better testing and quality of For better testing and quality of laboratory data, laboratory data,

we need.........we need.........


IInitiatives in nitiatives in

TTestingesting

EExcellencexcellence

inin

MManufacturing. anufacturing.


Thank You.Thank You.

management of process laboratory in mill environment by d k singhal chandpur enterprises ltd.,...

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