Sunday, November 14, 2010

Quality Assurance in Siding Manufacture

Before, during, and after it is manufactured, CertainTeed siding
is tested against a set of manufacturing and product specifications.
These specs define the minimums, maximums, and
tolerances that a raw material or sample of a finished product
must meet to satisfy either our standards, ASTM International
requirements, Vinyl Siding Institute (VSI) recommendations,
or local and national building codes. While some of these
tests don’t appear to directly relate to the conditions siding
is exposed to during installation and use, they all contribute
to the quality and durability of the final product.
Raw Material Testing
Each lot of raw material that comes into our plants is
thoroughly examined and approved as part of an ongoing
quality assurance plan. CertainTeed quality assurance verifies
that our suppliers maintain consistently high standards and that
minor variations in materials do not affect the appearance or
quality of our siding. While the raw data that these tests generate
are of little value to you or your customers, we mention them
because it’s worth noting that top quality siding and accessories
can be produced only from the highest quality raw materials.
Below are just a sampling of the raw material properties that
are tested on a regular basis.
Product Testing
Finished products are also subjected to a series of tests to
evaluate how well they meet specifications. The first tests occur
during the manufacturing process. The materials that go into
each product are continually scrutinized manually and by
computer. Computer evaluation systems adjust mixes, line
speeds, and other process variables to ensure optimal
finished quality. Blending operators check resin and all
micro-ingredients for weight even as they draw samples
for quality assurance testing.
Product quality is also verified at the extruder and injection
molding equipment. In addition to equipment checks,
operators verify:
• panel width
• warp
• bow
• panel weight
• gloss
• panel projection
• butt angle
• nail slots
• weep holes
• color
• embossing
(panel thickness)
CertainTeed Vinyl Siding Master Craftsman Education & Development Program
7. Quality Assurance
In this chapter you’ll read about CertainTeed’s
Quality Assurance:
• Raw materials testing
• Product testing
• Testing physical properties
flow time
trace elements
melt viscosity
percent moisture
particle size
oil absorption
congealing point
percent free fatty acid
Izod impact
needle penetration
percent insolubles
specific gravity
resistance (ohms)
refractive index
percent ash
percent stearic acid
Extruder attendants visually and physically check:
• locking mechanisms
• panel squareness
• warp
• bow
• length
The final product check includes:
• factory codes
• labels
• number of panels per box
• number of boxes per pallet
Together, these tests make up our CertaVision™ quality control.
We test and retest our products to maintain our high standards.
Physical Property Testing
Siding gets some of its appearance and much of its installation
properties from its shape, known in the industry as “profile.” As
you read earlier, the sheet that emerges from the extruder is still
pliable but chemically stable. It is at this point that the highly
trained operators at the plants begin testing for important
physical properties of, first, the vinyl sheet, then the finished
• Length and width: Siding that is not uniformly sized cannot
be installed properly, even by the best of applicators.
Inconsistent width produces uneven courses, especially on
adjacent walls or around doors and windows. For this reason,
all CertainTeed siding is held to close tolerances, closer than
the +/-0.250 in. (length) and +/-0.062 in. (width) required
by the ASTM.
• Thickness: There is some relationship between the thickness
of a panel and its ability to bounce back when it is struck by
hail, baseballs, and other objects that crash into it. Also,
siding that is too thin or is not uniform in thickness is
unforgiving and may buckle (oil can) during installation.
Because of variations in grain and patterning, thickness varies
across the length of all siding, but the ASTM requires a
nominal (average) minimum thickness of .035 in. for vinyl
siding, though many styles and embossing patterns yield
thicker siding.
• Weight: Each CertainTeed siding has its own weight
specification. Wall thickness and panel projection determine
the weight of siding. For example, a .044 in. exposure with a
3/4 in. panel projection will weigh more than a similar panel
with a 1/2 in. panel projection. Other panel components can
affect weight. CertainTeed’s CertiLock,™ which is featured on
Monogram™ siding, has 35 percent more vinyl than
competitive locks. Thus, they are heavier panels.
• Bow: Panels must be straight to be installed and perform
properly. CertainTeed’s carefully designed panel profile and
rigorous quality control ensure uniformly straight panels.
• Gloss: Gloss must be uniform because gloss that is blotchy
reflects light unevenly, giving the appearance of color variation
or a checkerboard effect. Also, uneven and inconsistent gloss
will weather inconsistently. To prevent this, gloss level is
checked at several points on a panel every hour during the
manufacturing process with a gloss meter. It indicates the
relative reflectance of the sample on a scale of 0 to 100.
The standard (ASTM D3679) requires readings of at least
three points on the sample; the three readings must not vary
more than +/-10 percent to be considered a surface with a
uniform gloss. This gloss control process ensures consistently
low gloss from panel to panel, carton to carton, in all
CertainTeed siding.
• Fading and weathering: Everything that is exposed to the
weather fades, so normal fading can be expected for
all siding. However, CertainTeed siding weathers consistently
and retains its beauty because every style and color undergoes
accelerated weathering tests in our laboratories as well as at
least two years of accelerated outdoor testing in such places
as hot, dry Arizona; hot, humid Florida; and the temperate
industrial air of Michigan. Six-inch-long samples are hung
outdoors, facing south, at a 45° angle and at an angle representative
of normal installation requirements for at least two
years. At the end of the test, the material must be free of any
visual surface defects such as peeling, chipping, cracking,
flaking, or excessive weathering due to manufacturing
This test is also used to evaluate chalking on painted surfaces.
The tester transfers chalk from an exposed weathered surface
to a piece of black test fabric. The quantity of chalky material
is visually compared to photographic reference standards of
increasingly chalky standards.
CertainTeed Vinyl Siding Master Craftsman Education & Development Program
• Expansion and contraction: As outside temperatures change,
all polymer siding expands and contracts. Laboratory tests
have shown that a 12-ft. length of PVC, a thermoplastic,
will expand and contract as much as 1/2 inch over
temperature swings of 100° F. However, when it is
installed correctly, the normal expansion and contraction
of CertainTeed vinyl and Cedar Impressions® siding are not
visible to the homeowner. When vinyl siding is free to “float” on
the wall, it retains its profile and fit as it expands and contracts.
And even though its installation procedure calls for Cedar
Impressions® polypropylene siding to be hard nailed to a solid
substrate through the round hole in the nail hem, Cedar
Impressions® expands and contracts equally on both sides of the
nail, thus preserving its appearance on the wall.
In the laboratory, siding is tested for expansion and
contraction (its coefficient of linear expansion) by alternately
exposing it to hot and cold environments and measuring the
changes in length throughout the test. The coefficient of linear
expansion is the change in length per degree of temperature
change. This number is used to calculate the amount of space
that should be left during installation to accommodate
contraction and expansion between the panel and channel.
• Impact: The ability of siding to resist impact is measured in a
Gardner impact test (ASTM D4226). From a specified height,
a test instrument drops an 8-lb. weight with a rounded tip
onto an area of siding. When the siding fails, it will either
crack, split, or tear (ductile failure), or it will shatter (brittle
failure). Thick, high quality siding with good elasticity is likely
to suffer only ductile failure.
Our field experience shows that CertainTeed siding far
exceeds the minimum impact resistance rating for
ductile break.
• Surface Distortion (oil canning): In the ASTM test for
surface distortion (D3679), three 6-ft. pieces of siding are
installed on a frame. The middle course is gradually heated to
120° F and then visually inspected for bulges, waves, or
ripples. The ASTM specifies that no distortion be present at
120° F; CertainTeed siding shows no distortion at 120° F. To
take heat build-up into consideration, darker colors are
heated to 130° F without distortion.
CertainTeed Vinyl Siding Master Craftsman Education & Development Program
• CertainTeed siding is tested against a set of manufacturing
and product specifications.
• Raw materials are tested before and during the manufacturing
process. These tests ensure batch-to-batch quality
and consistency.
• As the product moves through the manufacturing process,
the vinyl sheets are tested to ensure that they meet
manufacturing specifications like width, thickness, and
weight; color and gloss; the height and angle of the panel
projection; and warp, bow, and squareness.
• Finished product is also tested for physical properties: fading
and weathering, expansion and contraction, impact resistance
and surface distortion. These tests ensure that every
CertainTeed siding panel performs as promised.
• The molds used to create our Cedar Impressions siding are
created and regularly inspected by our in-house tool shop.

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