PAPER INDUSTRY WEB (PIW)

WOUND ROLL TESTERS

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1. Backtenders' Helper
2. Wit-Wot Roll Analyzer
3. Roll Density Analyzer
4. Cameron Strain Test
5. Torque Wrench Tester
6. J-Line Test
7. Beloit Rho Meter
8. Schmidt Hammer Tester
9. Smith Needle Tester
10. PAROtest Tester

There are several reasons why a ROLL PRODUCER may want to test the roll structure of shipping rolls (or jumbo reels): To determine the cause of specific roll defects such as crepe wrinkles or corrugations. As an aid to establishing the winding criteria of a newly installed winder or major rebuild of a winder or reel. As a quality control tool to check rolls before they are shipped to an end user.

A CONVERTER may want to check shipping rolls received from a roll producer: To determine how specific roll irregularities effect the efficiency of their machine. To supply creditable data to enable the roll producer to understand and resolve his concerns.

A major consideration of roll testing is the time and cost involved. Some testers are costly in themselves, some testers are automatic and can be used on the machine in real time such as a roll density analyzer. Others can be labor intensive and destructive such as the Cameron Strain Test or "J" Line testing. The more popular testers are the handhold units such as the Beloit Rho Meter, the Schmidt Hammer and Smith Needle.

Still another consideration, when choosing the type of tester to use is the ability of the tester to profile the roll diameter (MD) or across the winder face (CD). Testers like the Gap test, the J-line, the roll analyzer and the Smith needle are suited for testing profiles from the core to the OD but are not effective in cross winder direction. Conversely, The Beloit Rho Meter and the Schmidt Hammer are effective in the cross winder direction but not suitable for diameter profiling.

Regardless of the type of tester used, sampling size will have a great impact on the results of testing (and cost). Sound testing results rely on the statistical data and the data interpretation. The results of this testing will not only effect the winding process but can be useful in making changes in the paper machine process to eliminate root causes of some of the defects generated during the winding, shipping and converting processes.

There are many causes of poor shipping roll quality including the many properties of paper. Some of those paper properties have a great impact on the roll structure. Unfortunately, many of the paper properties can not be changed due to economic or equipment considerations. This paper limits the discussion to tools used to test roll structure-the roll hardness and roll profile of the shipping roll.

As background to this discussion, for those not experienced in wound roll structure, it may be useful to review Wound Roll Structure and TNT The Tools of the Winding Trade, two papers previously posted in this series.

THE BACKTENDER'S HELPER

The most basic tool used for roll testing is "the backtenders helper," a simple short length of stick used to manually strike the roll surface to judge the hardness and profile by the sound and "feel" of the stick impacting the roll surface. This is not a safe practice while machines are running and the absence of a means to quantify the test limits the value of the backtenders stick to a subjective determination of roll structure.

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WIT-WOT TESTING.

The WIT-WOT tester is a valuable tool in analyzing roll structure and results in very precise and complete measurements. The roll being tested is unwound in a single drum winder, load cells are used to measure the wound-in (WIT) and wound out tension (WOT). This type of testing is costly. The WIT-WOT machine is a laboratory unit and the testing involves cost to ship rolls to and from a remote location as well as the cost to use the laboratory facilities. Although this testing is considered very useful the use of the WIT-WOT is generally reserved for very specific defects that elude the normal testing routines described below.

The WIT WOT is also useful when evaluating paper property or equipment changes from stock prep through the winding processes.

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DENSITY ANALYZER

The density analyzer uses encoders to measure web footage and roll revolutions. The diameter of the winding roll is measured using the ratio of the pulses of the encoders. The pulses from the encoders are counted over a time interval and sent to the computer for calculation. The density analyzer is an automated system for measuring roll structure, used in both portable and online winder applications. This system is the basis for many winder TNT control systems.

Many winder builders offer a service to temporarily fit up a portable density analyzer to monitor a winder over a period of time. A continuing printout will permit evaluation of the roll structure off the winder. This service is also useful when studying reel or supercalender wind-up conditions. It should be remembered that a roll analyzer can only measure roll structure by diameter and not across the winder face (CD). Regardless of this limitation, the density analyzer is a very valuable tool for monitoring wound roll structure.

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THE CAMERON STRAIN TEST

The Cameron Strain Test is an interesting and useful tool to measure roll structure. This test was originated by The Cameron Machine Company and although Cameron referred to it as the Cameron Strain Test it is more commonly known as the "gap test."

The gap test in summary: With the roll resting on the floor, loose outer wraps are removed to expose a uniform, clean outer wrap. The outer wrap is slit across the face. The gap that results is measured and applied to a formula to establish wound in tension or wound in stress. The accuracy of the test is dependent on the care taken by the person doing the test, the number of consecutive wraps tested, the number of tests across the roll face and axially through the roll.

Cameron described the test procedure in the early 60s as follows:

• First, measure the circumference of the roll.
• Next, with the roll resting on the floor, slit the outer ply with a sharp knife or razor blade, using care to slit only through a single layer of paper.
• With the palm of the hands, draw the severed sheet together as close as possible without introducing additional tension, and carefully measure the gap.
• Then apply the formula A to determine residual stain or formula B to calculate wound-in tension in PLI.
  

(A) Residual strain = (Gap/(PI*diam))*100

(B) PLI = (Gap/(PI*diam)) * Caliper * Modulus of elasticity

The procedure hasn't changed since the above description appeared in TAPPI Standards. Experience indicates that using multiple layer testing and increased number of incidences of gap measuring across the face of the roll as roll width increases, result in improved statistical results.

Many labs and paper mills use the gap test frequently for roll structure analysis. The only tools needed are a tape measure, a magnifying glass with graduations to .0005", a calculator and marker pen.

For a more detail discussion, review The Cameron Gap Test and The Cameron Gap Test Gap 2, two papers previously published in this series.

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TORQUE WRENCH

A simple but effective tool for measuring the tightness of a roll at the core is a common torque wrench. By fitting up the torque wrench to a core adapter, the amount of torque required to slip the core can be measured. An example of it's use is checking rolls that have a tendency to telescope during the unwind process. After testing and statistical analysis determines the torque level considered acceptable, shipping rolls can be checked before shipment to the converter.

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J-LINE TESTING

J-line testing is a means to check the internal slipping inside a roll during winding (or unwinding). The test is simple and low cost and will indicate the magnitude of layer to layer slippage in the roll. The procedure: The winder is stopped, a straight is line is scribed from core to OD. The winder is restarted and again stopped after a time interval. The magnitude of J-line deformation indicates the amount of layer to layer slippage in the roll. This test is useful for determining the tendency for a sheet to crepe wrinkle. If conditions are right, generally speaking, the greater the magnitude of layer to layer slippage the greater the tendency to crepe. When the J-line is scribed on an unwinding roll, the amount of J line deformation is an indication of the internal gearing in the unwinding roll.

 The greater the deformation the more likelihood that defects can occur during the unwinding process-particularly close to the core. The J-line tests outlined, can be repeated after making process changes to reduce slipping/and or gearing to determine if the changes were effective in reducing layer to layer slippage.

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BELOIT RHO METER

The Beloit Rho Meter, like the backtender's stick, is an impact tester-but the similarity stops there. The Rho Meter measures the peak deceleration of a hammer striking the roll surface. The built-in scale permits quantifying the test results. The results of testing using the Beloit Rho Meter and other hand held testers like the Schmidt Hammer are dependent on the care and skills of the user. Measurements must be taken in equal spacing across the roll face and tangent to the radius of the roll.

The Rho Meter and Schmidt Hammer can be used to check the profile from core to OD by doing destructive testing similar to the procedure used in Gap testing.

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SCHMIDT HAMMER

The Schmidt Hammer is another impact tester measuring the rebound of a plunger striking the roll surface. The use of the Schmidt Hammer in many ways is similar to that of the Rho Meter. The Schmidt Tester, in addition to having a built-in scale is also available with a paper tape print-out that gives an instant picture and a permanent record of the cross roll hardness profile.

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SMITH NEEDLE

The Smith Needle tester is another hand held tester uniquely different from the previous testers described. The Smith tester measures the amount of force necessary to penetrate a needle between the wraps of a wound roll. Like the previous 3 testers, the Smith needle has a built in scale to quantify the results. In some cases, the Smith needle can be considered a destructive test. Unusual care should be used to minimize edge damage of the rolls being tested.

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PAROTEST

PAROtest: Measuring Principle: The test is initiated by launching a spring loaded body against the test surface. The impact and rebound velocities are compared resulting in a instantaneous numerical hardness value. The tester is portable, easy to implement and extremely accurate. Digital Display and inherent data memory help make the PAROtester as easy to interpret as it is to operate. Accuracy to .5% - non contact measurement results in very little wear or maintenance. The information gathered by the instrument is down-loadable to a PC via an RS-232 output. A portable printer is available for immediate documentation of test results.

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Luigi Bagnato-Paper Industry Web

REFERENCE PAPER RECOMMENDATION

In the need for brevity, this paper is limited in the amount of detail regarding the use of testers and the requirement for sound use and statistical sampling. For those interested in detailed information on roll testing, a paper by David R. Roisum, titled "ROLL QUALITY MEASUREMENT" is highly recommended. A reprint is available in the TAPPI PROCEEDINGS, 1988 Finishing & Converting Conference. A copy can probably be obtained by contacting TAPPI Press. 

CREDITS

References:
G. Erikson, C. Lydig, P. Komulainen, J. Viglund, - Measurement of Paper Roll Density During Winding
J. David Pfeiffer, - Internal Pressures in a Wound Roll of Paper,
J. David Pfeiffer, - Wound-off Tension Measurement in Paper Rolls
Kenneth G. Frye, - Winding Variables and Their Effect on Roll Hardness and Roll Quality
Al Hadlock, - The Principles of Winding
David Roisum , - Roll Quality Measurements