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Gypsum Board Core Structure by
Computed X-ray Tomography
Introduced
October 2004
The gypsum board industry is very competitive,
each company trying to provide better quality products at lower cost. Gypsum
companies are responding to these market pressures by reducing board and
liner weights. With the increase in fuel costs, efforts have redoubled to
reduce energy consumption in drying the board. Reducing board weight and
gauging water require the addition of more foam to the mix as well as ensuring
that the internal structure of the board is well “engineered” to satisfy
the market requirements and meet the required product specifications. The
cost savings available for those that are proficient at reducing board
weights and energy consumption are significant, amounting to $5-10 million
dollars per year for a modern high speed plant.
Efforts to optimize the process and product
have been hindered by the ability to quantitatively measure the properties
of the core structure in a manner that allows correlation with product
performance. A common technique using scanning electron micrographs of polished
epoxy filled samples is very expensive and time consuming, and yields only an
analysis of a single two dimensional surface.
Innogyps Inc. has developed a new technique for
the analysis of gypsum board using high resolution CT Scan (Computed
Tomography). This technique gives a full three dimensional structure of the
core yielding both high resolution images and quantitative measurements of
the gypsum core. There is no need to pre-treat the samples in any way, just
cut and mount for analysis. The technique is non-destructive so further
analysis can be performed on the exact same sample used for CT Scan
analysis. The practical resolution is about 20 microns (nominal), making it
very straightforward to obtain a bubble size distribution of a typical
gypsum board core. A typical analysis will determine the size and position
in the sample of about 200,000 bubbles. Higher resolution scans are
possible to investigate specific features if desired.
A typical analysis yields the following
results:
Qualitative
Images
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Images in XY, YZ, or XZ planes at 20 micron
intervals between “slices”.
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Movies showing a “fly through” of the sample
along any axis (usually XZ or XY)
Quantitative
Analysis
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A density profile of the gypsum core along any
axis, for example giving the density and thickness for higher density
layers adjacent to the liners. This is similar to bone scan measurements
for osteoporosis.
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An analysis of the total void content of the
board structure, or for any particular volume in space. We typically
analyze the regions within 1 mm of each liner, as well as the top and
bottom halves of the core excluding these regions (4 regions in total).
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The bubble size distribution for the entire
sample, or for any particular volume in space. We typically analyze the 4
regions just described above.
We have analyzed three gypsum board samples
that compete in the same market and compared the results described above.
In addition to these CT Scan tests we also analyzed the boards for core
gypsum content, nail pull resistance and breaking strength (ASTM C36). The
intent was to determine if there was any obvious correlation between
product performance and core structure. The fact that none of the boards
tested passed the nail pull test suggests that some optimization of core
structure would be of value.
Typical images for the three board samples are
given below.
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Sample A
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Sample B
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Sample C
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XZ cross section
of each board sample
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Although there is work ongoing to further
develop the capabilities of this new analysis technique, we have determined
that it is mature enough to offer this as a service for those who would
like to use it to optimize their products and processes. A report has been
written that discusses the basics of how the measurements were performed,
along with the results obtained. This report is 18 pages in length with the
full results for the three commercial samples each segmented into four
regions. The report is accompanied by a QuickTime movie for each sample
showing the core structure in the XZ plane.
Please
contact us for report pricing and availability.
RESEARCH SERVICE – Gypsum Board Core Characterization by Computed Tomography
The gypsum board
industry is highly competitive with excess capacity, similar products and a
very price sensitive market. As a result, quality improvement and cost
control are of paramount importance. The manufacturing process is
constantly tuned to give a satisfactory product at the lowest possible
cost. In recent years, this has meant lower board weights, lower liner
weights and efforts to reduce energy costs. This has resulted in a move to
optimize the gypsum board core structure to get the most out of the raw
materials used to make the product. Today, gypsum board often has a finely
tuned core structure with densified layers or coatings at the liner/core
interface and foam structures that are carefully managed. Optimizing this
process has proven difficult due to a lack of quantitative data.
Innogyps Inc. has
studied board macroscopic physical performance as a function of microscopic
gypsum core matrix structure leading to a better understanding of the
fundamentals involved.
Using high resolution
Computed X-ray Tomography (CT) we are able to determine full three
dimensional density representations of the core yielding both qualitative
high resolution images and quantitative measurements. The practical
resolution of this analysis is approximately 20 microns. Typical calculated
results include: density profile comparisons in any plane, total voidspace
analysis and bubble size distribution. Corresponding ASTM physical test
results are also often determined for scanned samples.
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Assigned
voids in a gypsum board core |
3D
Isosurface of bubble voidspace
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Please
contact us for more information.
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