Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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1 - CBP~-7084
ACOUSTICAL CEILING BOARD
Background of the Invention
Field of ~he Invention
The invention is directed to a ceiling board
and, more particularly, a ceiling board that has an
acoustical prooerty wi~hout the conventional pin punched
perforations normally provided in acoustical ceiling
board.
Description of the Prior Art
It is old to produce ceiling panels with
grooves in their face as shown in U.S. Design Patent il~.
23~,573 of January 27, 1976 to Goldman and Design Pat-
ent No. 249,367 of Sep-tember 12, 1978 to Reese.
In addition, U. S. Patent No. 3,470,977 of Oct-
ober 7, 1969 to Shannon shows an acoustical panel
having short slits cut into the front face of the
panel. Furthermore, it is known in the marketplace
that there are a number o~ ceiling boards which
have heavily 3cored surfaces~ However, it
:!~ is noted that of the prior art known to the inventor
herein, none of the scored building products that exist
or have existed in the past are capable of securing a
desireA acoustical rating without the utilization of
acoustical pin punched oerforations which tend to
2~ aesthetically detract from the decorative effect o~ a
grooved board having plain linear geometric patterns.
Summarv of the Inventlon
The invention is directed to an acoustical
ceiling board comprising a mineral fiber board structure
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having a porosity such that the board will have an air
flow resistance of approximately 1220 cgs rayls or less,
according to a modified test method using the Leonar~
Air Flo~ Apparatus described in the article by R. W.
Leonard appearing in The Journal of the Acoustical
Society of America; Volume No. 17, page 240, 1946, so as
to achieve a 0.50-0.55 NRC rating, when tested according
to ASTM C423-77, Sound Absorption of Acoustical
Materials in Reverberation Rooms. A decorative pattern
is placeA on one surface of the board, and this pattern
is a number of grooves cut in the surface of the board.
The grooves are provided with side walls perpendicular
to the plane of the board. The side walls of the
grooves, and therefore, the grooves are of such a number
and size as to provide at least about 50 square inches
of side wall area per 1 square foot of board surface.
Brief Description of the Drawing
~ The figure of the drawing is a cross-sectional
view of a ceiling board embodying the invention herein.
Description of the Preferred Embodiment
As shown in the drawing, the acoustical
ceiling board 2 is made of a mineral fiber structure
which is approxim~ately 3/4 of a inch thick. On the
face of the ceiling board as shown in the drawing there
is provided a decorative pattern on this surface of the
board. The pattern is a number of grooves cut in the
surface of the board, and the grooves extend in a
parallel relationship from one side of the board to the
other. These grooves 9 are formed with side walls 6
which are perpendicular to the plane 8 of the ceiling
board. In the embodiment shown in the drawing, the
grooves are 1/8 of an inch deep and are 1/~ of an inch
wide and are spaced 3/8 of an inch apart. The grooves _~
in the drawing are such that the side wall area of the
pattern shown is such that there is formed 50 square
inches of side wall area per square foot of board
surface. The ceiling board is provided with a paint
coat which is normally sprayed on the ceiling board.
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The paint coat(s) woulA be applied to the raised areas
10 and the ~epressed areas 12 which are either in or
parallel to the plane of the ceiling board. These areas
are not capable of functioning as efficient sound
absorbing surfaces. The painting of the surface of the
board provides these flat areas with a smooth untextured
surface. Since the grooves are cut in the ceiling
board, the side walls of the ceiling board do not'have a
smooth surface and are somewhat open in nature, and this
open structure is not plugged by the paint coat applied
to the board. In addition, the nature of the board is
such, hecause it is made on a fourdrinier, it has less
air flow resistance measured across the board and it has
greater air flow resistance measured through the board5 or perpendicular to the surface ~.
rrhe invention herein is a unique acoustical
ceiling product in that both the decorative appearance
of the panel and its acoustical properties are produced
bv cutting a series of grooves in the board surface.
The c~ttin~ Process is called a "rilling" process
wherein a series of cutters cut the grooves in the
board. Whereas the surface of most conventional ceiling
boards are perforated with pins or fissuring dies, for
acoustical purposes, the product herein achieves its
desired acoustical properties by rilling. While in many
conventional ceiling products the board perforations are
necessary for sound absorption and are sometimes
decorative, there are certain products where the
perforation detracts from the appearance. In those
instances, where perforations are not desirable, the
ceiling board manufacturer may try to disguise ~he
perforations by covering the board surfaces with an
acoustically transparent material, such as a fabric or
thin film, or by positioning the perforations so that
they blend in with an embossed or printed decorative
surface pattern. In the invented product herein is
desired a plain linear geometric pattern on a untextured
surface, and here the perforations would compete with
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the visual objective of the ceiling. A conventional
board formulation for a ceiling produc~ would be as
listed below~
Ingredients Percent by Weight
5 mineral fiber 73-84%
organic fiber 5-4%
starch 7-6%
clay 15-5%
The above provides the basic ingredients of a
mineral wool fiber board and the approximate range in
which these products appear. In many cases, the mineral
fiber ingredient is composed of virgin mineral fiber and
"broke," which is scrap processed ceiling board being
recycled back into a new ceiling board. ~roke, in
particular, has fine particulate matter in it and this
fine particulate matter will affect the board's
porosity. Listed below are two board structures
referred to as Formula 1 and Formula 2. Both boards
have the same material composition as that set out above
for board formulation. However, in Formula 2 r 27 .5
percent of the ingredients provided is provided by
broke. In Formula 1, broke amounts to only 20.0 percent
of the ingredients provided, and such broke was
processed to remove dust particles and, therefore,
Formula 1 has less fine particulate matter. Considering
the two products described above, their acoustical
ratings are as follows:
Cgs RaylsNRC (4 Freq. Avg.)
-
-
Formula 1 1220 0.54
Formula 2 2280 0.42
Sound absorption is dependent on the porosityof the board formulation and on the amount of surface
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area exposed to the sound source. When comparin~ a
perforated pattern to a rilled pattern, both products
have vertical surfaces which will affect the acoustical
rating and the horizontal surfaces of both patterns will
have minimal affect upon the acoustical rating. The
porosity of the board must give an air flow resistance
(AFR~ of approximately 1220 cgs rayls or less. As can
be seen in the above Formula 1 - Formula 2 examples,
when a product has the 1220 cgs rayls rating, it will
get the 0.54 NRC rating which is an acceptable rating to
permit one to call their product an acoustical product.
When the air flow resistance increases as in Formula 2,
the NRC rating goes down and the product shown in
Formula 2 is not considered an effective acoustical
product.
While many conventional mineral fiber board
formulations, when perforated in a normal manner, will
provide an NRC in the 0.55-0.65 range, these products
were found to produce an essentially non-acoustical
product when rilled only. Conseguently, the rilling
I alone does not contribute to the desired acoustical
rating. lt is the rilling with the desired amount of
open vertical surface plus a certain air flow resistance
for the board that gives the desired combination to
produce acoustical rilled ceiling board.
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