Statiscal Analysis of the Tensile Stregth of Paper
1. TENSILE STRENGTH OF PAPER
Travis Drew – Sarah McLean – Mady Fewster
RYERSON UNIVERSITY
GRA 534 – SECTION 01
Instructor: Martin Habekost
December 7th
, 2015
Word Count: 1602
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Table of Contents
Theory...........................................................................................................................................................2
What are we testing?................................................................................................................................2
Definitions.................................................................................................................................................2
Equations ..................................................................................................................................................2
What is the theory behind the test?.........................................................................................................2
What is your expected outcome?.............................................................................................................2
Educational gains ......................................................................................................................................3
Practical Applications................................................................................................................................3
Results & Interpretation ...............................................................................................................................4
Equipment Used........................................................................................................................................4
Materials Tested .......................................................................................................................................4
Test Procedure..........................................................................................................................................4
Results.......................................................................................................................................................5
Grain Long vs. Grain Short ....................................................................................................................5
Control Limits – Tensile Strength..........................................................................................................6
Control Limits – Elongation...................................................................................................................7
Discussion..................................................................................................................................................8
Recommendations....................................................................................................................................9
Runability ..............................................................................................................................................9
End Use ...............................................................................................................................................10
Appendix .................................................................................................................................................11
References ..................................................................................................................................................12
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Theory
What are we testing?
This test will analyze the elongation properties and tensile strength of a paper substrate.
The Tensile Strength Tester was used to measure the amount of stress 30 strips of both grain
long and grain short paper could withstand before breaking. The Tester measured the weight
load that was applied to the paper before it ripped, and also measured the elongation of each
paper strip. We observed the relationship between the grain direction of the paper, and its
tendency to tear. After conducting the test, the measure of central tendency, the lower control
limit, and the upper control limit were calculated for both sets of paper strips.
Definitions
Central tendency: The mean or average (Lund Research, 2013)
Lower control limit (LCL): The bottom limit that indicates the lowest level of quality
acceptable for a product or service (WebFinance, 2015)
Tensile strength: The force required to pull a material to the point where it breaks
(Janalta Interactive Inc., 2015)
Upper control limit (UCL): The value that indicates the highest level of quality
acceptable for a product or service (WebFinance, 2015)
Equations
LCL = mean - (3)(sample standard deviation)
UCL = mean + (3)(sample standard deviation)
What is the theory behind the test?
Grain direction is the main factor that will determine how much stress a paper strip can
take before tearing. When paper feeds throughout a printing press, tension is applied at
different points to ensure proper register and correct printing. The grain of the paper has a
large influence on how easily the paper will break as it travels through the press. Grain long
paper is able to endure more force than grain short. Because of this, grain short paper will tear
easier than grain long. The grain direction of the paper and the amount of tension that is
endured by the paper strips will be determinants in the papers’ strength and ability to
withstand tension.
What is your expected outcome?
We predict that the grain long paper strips will have the highest tensile strength, while
the grain short paper strips will have the greater elongation measurement. Since the paper
fibers are longest in the grain direction, paper moving through the press along the grain will be
able to sustain a higher amount of tension than paper being pulled against the grain (Larracey,
2013). When paper moves through the press with the grain direction, it ensures the paper does
not stretch, and ensures the stability of the paper is not compromised (Bann, 2007). Since
paper fibers grow in width rather than length, the paper substrate will become weaker as the
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fibers separate and elongate (Stromberg, 2005). This is why we predict the grain short paper
will have a smaller tensile strength and a longer elongation.
Educational gains
After conducting and completing this test, a greater understanding of the importance of
what grain direction the paper should run through the press and the amount of tension a paper
substrate can withstand before breaking will be obtained. Since paper tension is very important
in the printing process, it is crucial to understand the amount of stress it can take without
breaking. With tensile strength, other issues such as mis-register, dot gain, and mottle can
occur (Stromberg, 2005). Understanding the tensile properties of a substrate will save the
printing company time and money, as it will reduce downtime and spoilage. Since a substrate
can stretch under stress on a press, it is important to understand the fiber properties of the
substrate to accommodate or prevent elongation from occurring on press.
Practical Applications
The main practical application for this test is the web tension that is applied to the
substrate during the press run. It is important that there is sufficient tension applied to the web
to ensure printing issues such as slurring or doubling do not occur due to insufficient tension. In
addition, too much tension on a web can occur, which will cause the paper to stretch, and tear.
The tension must be understood and controlled by the press operator to ensure minimum
downtime and spoilage, which will cost the business time and money, and will cause delays in
the workflow.
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Results & Interpretation
Equipment Used
Thwing-Albert Instrument Company - QC 2 Electronic Tensile Strength Tester (Model #: 19154)
Materials Tested
Paper: Colonial Glowhite Bond 15M
Test Procedure
1. Select a paper to test, uncoated or coated.
2. Determine the grain direction of the paper.
3. Cut the paper into 30 strips in the grain ling direction and 30 strips in the grain short
direction.
3.1. Strip dimensions = 1 inch wide, 8 inches long
3.2. You should have 60 strips in total
4. Test the 30 grain long strips and record the tensile strength and elongation values.
5. Test the 30 grain short strips and record the tensile strength and elongation values.
6. Input your results into excel and calculate the following values for all 4 sets of data (GL
Tensile Strength, GS Tensile Strength, GL Elongation, and GS Elongation)
6.1. Mean
6.2. Standard Deviation
6.3. Upper Control Limit (UCL)
6.4. Lower Control Limit (LCL)
7. Using a chart, compare the tensile strength and elongation between the grain directions.
8. Using the mean, UCL, and LCL create a line chart and plot the values.
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Discussion
Our results indicate in figure 1.0 that paper shows more tensile strength when strained
in the same direction as the grain. The grain long strips consistently demonstrated a higher
tensile strength than the grain short strips as they were being pulled apart in the same direction
as the grain. With regards to elongation, we found that paper experiences the most amount of
elongation when it is being pulled or stressed in the opposite direction of its grain. Our results
shown in figure 1.1 clearly show that the grain short paper demonstrated more elongation as
the grain was running opposite to the direction the paper was being pulled.
These results were expected as it is generally understood that paper is stronger along its
grain direction. According to Cindy Thai and Rute Tupe, “the longer fibres tend to distribute the
stress over more fibres and bond, while short fibres allow the stress to be concentrated in a
smaller area.” (Thai & Tupe, 2011). This is the why paper is stronger in its grain direction.
The reason we saw more elongation going against the grain is because paper fibers tend
to expand along their width dimension. Paper fibres long strands and will break when pulled
apart. They will however expand in their width dimension causing them to stretch. This occurs
both when the paper is stressed against the grain and over time as the moisture content
changes. (Cowie, 2013)
The statistical analysis shows that paper being stressed along its grain direction deviates
from the average more than paper being stressed against its grain. The UCL and LCL for our
grain long paper shown in figure 2.0 was 45.60 and 16.09 while the UCL and LCL for the grain
short paper (figure 2.1) was 19.95 and 9.38 for tensile strength showing that paper breaking
against its grain has a more consistent breaking point. Elongation was the only factor with
values outside of the control limits, below are the new control limits after removing those
samples.
0.00
0.50
1.00
1.50
2.00
2.50
3.00
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
Elongation(mm)
Strip
Elongation Grain Long (causes removed)
Elongation (mm) Average UCL LCLFigure 4.0
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As you can see after removing the outlying values the control limits are much tighter
representing less deviation from the average elongation. Comparing grain long and grain short
we can see that there is more deviation when the paper is being pulled against the grain which
makes sense as we already know that paper fibres will stretch more along their width
dimension.
**raw data tables in appendix
Recommendations
Runability
The main issue that this instrumentation looks at is the pressure that paper is put under
while in a web offset environment. When a web of paper is fed through a web-offset press it is
under constant pressure (Web Offset Printing, n.d.). This test looks at the relationship between
feeding paper grain long, grain short and the effect of the elongation and load placed on the
paper.
Runability is affected due to the stress placed on paper while it is running through the press.
This can cause issues from web breaks to image quality. Therefore it is important to always be
cognizant of the grain direction, load and the quality of the paper that you are using on press
(Grain Direction and Folding of Paper, 2014). These issues can not only affect the end product,
but it can completely increase costs and stall a job. An issue such as a web break can cause
severe issues on press if it is not caught right away. Therefore it is very important to ensure that
when you are working on a web offset press that you pay attention to how much pressure the
paper is put under.
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829
Elongation(mm)
Strip
Elongation Grain Short (causes removed)
Elongation (mm) Average UCL LCL
Figure 4.1
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End Use
End-Use can also be affected through the tensile strength of paper. Although not as big
of a factor, it is important to understand how to print your product so that when the consumer
receives it, the print is durable and a quality good. This is extremely important with goods that
may be put under more pressure. Take children’s books for example, these books get thrown,
pulled, chewed and they are still expected to stay in one piece. So as a print producer, you need
to ensure proper quality and the correct paper choice to ensure quality that lasts.
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References
Ammann, L. (2015). Measures of Dispersion. UT Dallas. Retrieved from
https://www.utdallas.edu/~ammann/stat3355/node10.html
Bann, David. The All New Print Production Handbook. New York, NY: Watson-Guptill, 2007.
Cowie, B. (2013, October 11). Grain direction…the long and short of it. The paper Mill Store
Blog. Retrieved from http://blog.thepapermillstore.com/grain-directionthe-long-short/
Grain Direction and Folding of Paper. (2014). Retrieved December 7, 2015, from
http://www.printing.org/page/9837
Janalta Interactive Inc. (2015). What is Tensile Strength? - Definition from Corrosionpedia.
Retrieved December 4, 2015, from
https://www.corrosionpedia.com/definition/1072/tensile-strength
Lund Research. (2013). Measures of Central Tendency. Retrieved December 4, 2015, from
https://statistics.laerd.com/statistical-guides/measures-central-tendency-mean-mode-
median.php
Printing Process Explained - Web Offset Printing. (n.d.). Retrieved December 6, 2015, from
http://dynodan.com/printing-process-explained/web-offset-printing/
Stromberg, M. (2005). Paper dimensional stability in sheet-fed offset printing. Retrieved
December 4, 2015, from http://du.diva-
portal.org/smash/get/diva2:517895/FULLTEXT01.pdf
Thai, C., & Tupe, R. (2011, May 12). For your print information: Folding and paper strength.
Graphic Arts Magazine. Retrieved from
http://graphicartsmag.com/articles/2011/05/for-your-print-information-folding-and-
paper-strength/
