U.S. patent application number 15/354677 was filed with the patent office on 2017-09-28 for sound attenuating baffle including a non-eroding liner sheet.
The applicant listed for this patent is VAW Systems Ltd.. Invention is credited to Emanuel Mouratidis.
Application Number | 20170276397 15/354677 |
Document ID | / |
Family ID | 59897838 |
Filed Date | 2017-09-28 |
United States Patent
Application |
20170276397 |
Kind Code |
A1 |
Mouratidis; Emanuel |
September 28, 2017 |
Sound Attenuating Baffle Including a Non-Eroding Liner Sheet
Abstract
A sound attenuating baffle device used in a duct receiving a
gaseous flow in a flow direction therethrough, includes a baffle
casing supported within the duct and a fibrous sound absorbing
material occupying the hollow interior of the baffle casing. One or
more perforated sheet members at least partially defines the
exterior of the baffle casing across which the gaseous flow of the
duct is arranged to be directed. A liner sheet of a non-eroding,
sound absorbing foam material is supported within the hollow
interior of the baffle casing against an interior surface of the
perforated sheet member(s) so as to span across each of the
perforations and prevent direct communication of the fibrous sound
absorbing material with the perforations to prevent erosion of the
fibrous sound absorbing material into the gaseous flow through the
duct.
Inventors: |
Mouratidis; Emanuel;
(Aurora, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VAW Systems Ltd. |
Winnipeg |
|
CA |
|
|
Family ID: |
59897838 |
Appl. No.: |
15/354677 |
Filed: |
November 17, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62312661 |
Mar 24, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F24F 2013/242 20130101;
F24F 13/08 20130101; F24F 13/02 20130101; F24F 13/24 20130101 |
International
Class: |
F24F 13/24 20060101
F24F013/24; F24F 13/02 20060101 F24F013/02; F24F 13/08 20060101
F24F013/08 |
Claims
1. A sound attenuating baffle device for use in a duct receiving a
gaseous flow in a flow direction therethrough, the baffle device
comprising: a baffle casing having a hollow interior and being
adapted to be supported within the duct such that the gaseous flow
is directed across an exterior of the baffle casing; the baffle
casing including at least one perforated sheet member having a
plurality of perforations therein which at least partially defines
the exterior of the baffle casing across which the gaseous flow of
the duct is arranged to be directed; a sound absorbing layer formed
of fibrous sound absorbing material occupying the hollow interior
of the baffle casing; and a liner sheet supported within the hollow
interior of the baffle casing against an interior surface of said
at least one perforated sheet member so as to span across each of
the perforations and prevent direct communication of the fibrous
sound absorbing material with the perforations; wherein the liner
sheet is formed of a non-eroding, sound absorbing material.
2. The baffle device according to claim 1 wherein the liner sheet
is formed of a sound absorbing foam material.
3. The baffle device according to claim 2 wherein a thickness of
the foam material in a direction perpendicular to said at least one
perforated sheet is between 0.125 and 2 inches.
4. The baffle device according to claim 2 wherein a thickness of
the foam material in a direction perpendicular to said at least one
perforated sheet which is less than 40% of a thickness of the sound
absorbing layer in a direction perpendicular to said at least one
perforated sheet.
5. The baffle device according to claim 2 wherein the sound
absorbing foam material comprises an open-cell foam.
6. The baffle device according to claim 2 wherein the sound
absorbing foam material comprises a closed-cell foam.
7. The baffle device according to claim 2 wherein the sound
absorbing foam material comprises a melamine resin.
8. The baffle device according to claim 2 wherein the sound
absorbing foam material comprises a thermoset polymer.
9. The baffle device according to claim 2 wherein the sound
absorbing foam material comprises polyethylene.
10. The baffle device according to claim 1 wherein the liner sheet
fully spans said at least one perforated sheet member.
11. The baffle device according to claim 1 wherein the fibrous
sound absorbing material is supported within the hollow interior of
the baffle casing under resilient compression and wherein the liner
sheet is supported against the interior surface of said at least
one perforated sheet member by the resilient compression of the
fibrous sound absorbing material.
12. The baffle device according to claim 1 wherein the baffle
casing includes at least one support flange overlapping at least a
portion of a perimeter edge of the liner sheet so as to retain the
liner against the interior surface of said at least one perforated
sheet member.
13. The baffle device according to claim 1 wherein the baffle
casing comprises two opposed faces having i) a length spanning in a
longitudinal direction between a leading end and a trailing end of
the baffle casing, ii) a width spanning in a lateral direction
between opposing sides of the baffle casing, and iii) a thickness
between the two opposed faces which is reduced in dimension
relative to the length and the width, the baffle casing being
adapted to be supported within the duct such that the longitudinal
direction is aligned with the flow direction; and wherein said at
least one perforated sheet member comprises two perforated sheet
members defining the two opposed faces of the baffle casing
respectively such that the liner sheet spans the interior surface
of each of the two opposed faces of the baffle casing.
14. A sound attenuating baffle device for use in a duct receiving a
gaseous flow in a flow direction therethrough, the baffle device
comprising: a baffle casing having a hollow interior and being
adapted to be supported within the duct such that the gaseous flow
is directed across an exterior of the baffle casing; the baffle
casing including at least one perforated sheet member having a
plurality of perforations therein which at least partially defines
the exterior of the baffle casing across which the gaseous flow of
the duct is arranged to be directed; a sound absorbing layer formed
of fibrous sound absorbing material occupying the hollow interior
of the baffle casing; and a liner sheet supported within the hollow
interior of the baffle casing against an interior surface of said
at least one perforated sheet member so as to span across each of
the perforations and prevent direct communication of the fibrous
sound absorbing material with the perforations; wherein the liner
sheet is a membrane of sound absorbing material.
15. A sound attenuating baffle device for use in a duct receiving a
gaseous flow in a flow direction therethrough, the baffle device
comprising: a baffle casing having a hollow interior and being
adapted to be supported within the duct such that the gaseous flow
is directed across an exterior of the baffle casing; the baffle
casing including at least one perforated sheet member having a
plurality of perforations therein which at least partially defines
the exterior of the baffle casing across which the gaseous flow of
the duct is arranged to be directed; a sound absorbing layer formed
of fibrous sound absorbing material occupying the hollow interior
of the baffle casing; and a liner sheet supported within the hollow
interior of the baffle casing against an interior surface of said
at least one perforated sheet member so as to span across each of
the perforations and prevent direct communication of the fibrous
sound absorbing material with the perforations; wherein the liner
sheet is formed of a sound absorbing foam material.
Description
[0001] This application claims the benefit under 35 U.S.C. 119(e)
of U.S. provisional application Ser. No. 62/312,661, filed Mar. 24,
2016.
FIELD OF THE INVENTION
[0002] The present invention relates to a sound attenuating baffle
intended to be mounted within the duct of an air distribution HVAC
system, a ventilation system, mounted directly to a fan or other
air movement system for either air or gas streams in which the
baffle is typically oriented in the flow direction through the
duct. More particularly the present invention relates to a sound
attenuating baffle the type including an outer baffle casing which
is at least partially perforated and which contains fibrous sound
absorbing material therein, and which is further provided with a
liner sheet against an interior surface of the perforations in the
outer baffle casing to prevent direct communication between the
fibrous sound absorbing material and the perforations so as to
prevent eroded fibrous sound absorbing material from being carried
by airflow externally of the baffle casing through the
perforations.
BACKGROUND
[0003] Silencers are used in air distribution HVAC systems,
ventilation systems and other air movement systems for either air
and gas streams. These products typically provide a duct section,
for mounting in a duct system or directly to a fan, which support
one or more baffle devices therein. Baffle devices are understood
herein to comprise any rectangular, circular or other shaped object
having a sound absorbing internal structure, typically using
fibrous acoustic media fill, that may include, but not be limited
to, fiberglass fiber, rock wool or natural cotton media. The media
fill material provides a dissipation of the sound energy as it
travels through the baffle device(s) of the silencer's duct
section.
[0004] Rectangular cross-sectional silencers typically employ sound
absorbing baffle devices in the form of rectangular sound absorbing
elements such as baffles or splitters within a rectangular
cross-sectional duct. Circular silencers may employ sound absorbing
baffle devices either in the form of rectangular baffles or
circular centerbody pods within circular cross-sectional duct.
Rectangular silencers may include one baffle or several parallel
baffles along the width of the duct or casing. The rectangular
baffles or circular center body pods may be uniform along the
casing length, or may be transitional where the inlet cross-section
is not equal to the outlet cross-section. Silencer attenuation may
be described as either a transmission loss (TL; dB) or an insertion
loss (IL, dB). TL is a measure of the sound power upstream versus
the sound power downstream from the silencer air opening(s). IL is
a measure of the change in the sound level at a defined point of
reception (e.g., outdoors, within a room, etc.) with and without
the silencer installed.
[0005] Silencers with rectangular shaped baffle devices or circular
centerbody baffle devices introduce aerodynamic losses due to the
nature of the silencer orientation and installation conditions,
resulting in blockage of the cross-sectional area, and aerodynamic
friction and dump losses. The net aerodynamic losses are quantified
as a total pressure drop or pressure resistance. Lower aerodynamic
losses are desirable for most systems, as lower energy would be
required to move a given volume or mass of air.
[0006] For systems that serve sensitive spaces (e.g., healthcare
facilities, laboratories, etc.) and/or silencers with relatively
high internal gap velocities (i.e., >4000 fpm), additional
measures are required in order to avoid unwanted media erosion.
[0007] For the current state of art, thin films, typically
Polyethylene or Polyvinyl materials at less than 0.08 inch thick,
are used in silencers to protect the media fill. The film liner is
positioned continuously between the media fill and the perforated
metal liner. This type of media fill protection is considered
advantageous towards human occupants, protection of the mechanical
equipment, or both.
[0008] Thin film liners are not acoustically porous and generally
do not provide any desirable absorptive properties. Thus, film
liners significantly degrade the silencer attenuation, as it
compares to a silencer internal geometry that applies media fill
only. In order to achieve higher levels of sound attenuation,
baffle device lengths and the quantity tend to increase
significantly, due to this degradation in performance related to
traditional film liners.
[0009] The present invention seeks to improve upon the construction
design and installation of baffle type silencers in a unique
fashion to improve the attenuation of the silencer in applications
where a liner protection is required.
SUMMARY OF THE INVENTION
[0010] According to one aspect of the invention there is provided a
sound attenuating baffle device for use in a duct receiving a
gaseous flow in a flow direction therethrough, the baffle device
comprising:
[0011] a baffle casing having a hollow interior and being adapted
to be supported within the duct such that the gaseous flow is
directed across an exterior of the baffle casing;
[0012] the baffle casing including at least one perforated sheet
member having a plurality of perforations therein which at least
partially defines the exterior of the baffle casing across which
the gaseous flow of the duct is arranged to be directed;
[0013] a sound absorbing layer formed of fibrous sound absorbing
material occupying the hollow interior of the baffle casing;
and
[0014] a liner sheet supported within the hollow interior of the
baffle casing against an interior surface of said at least one
perforated sheet member so as to span across each of the
perforations and prevent direct communication of the fibrous sound
absorbing material with the perforations;
[0015] wherein the liner sheet is formed of a non-eroding, sound
absorbing material.
[0016] Preferably, the liner sheet is formed of a sound absorbing
foam material.
[0017] The foam material liner sheet provides a more stable,
reliable and acoustically improved design for delivering protection
against fibrous media erosion. Acoustic foam material is
acoustically absorptive, with significantly higher noise reduction
coefficients (NRC) as compared to film liners. The foam, either
open cell or specially constructed closed cell material, has
self-supporting properties allowing for improved installation
quality and repeatability. When properly installed between the
media fill and the perforated liner, a foam liner with a thickness
greater than 0.125 inches offers improved acoustic performance with
the desired media protection against erosion or breakdown of the
silencer's absorptive media.
[0018] In preferred embodiments, a thickness of the foam material
in a direction perpendicular to said at least one perforated sheet
is between 0.125 and 2 inches so as to be less than 40% of a
thickness of the fibrous sound absorbing layer in a direction
perpendicular to said at least one perforated sheet.
[0019] The sound absorbing foam material may be either an open-cell
or closed-cell foam and may comprise a melamine resin and/or a
thermoset polymer, for example polyethylene.
[0020] Preferably the sound absorbing foam material continuously
and fully spans said at least one perforated sheet member.
[0021] When the fibrous sound absorbing material is supported
within the hollow interior of the baffle casing under resilient
compression, preferably the liner sheet is supported against the
interior surface of said at least one perforated sheet member by
the resilient compression of the fibrous sound absorbing
material.
[0022] The baffle casing may further include at least one support
flange overlapping at least a portion of a perimeter edge of the
liner sheet so as to retain the liner against the interior surface
of said at least one perforated sheet member.
[0023] When the baffle is suspended at an intermediate location
with the duct, in the instance of a full baffle, the baffle casing
comprises two opposed faces having i) a length spanning in a
longitudinal direction between a leading end and a trailing end of
the baffle casing, ii) a width spanning in a lateral direction
between opposing sides of the baffle casing, and iii) a thickness
between the two opposed faces which is reduced in dimension
relative to the length and the width, the baffle casing being
adapted to be supported within the duct such that the longitudinal
direction is aligned with the flow direction. In this instance said
at least one perforated sheet member consists of two perforated
sheet members defining the two opposed faces of the baffle casing
respectively such that the liner sheet spans the interior surface
of each of the two opposed faces of the baffle casing.
[0024] Alternatively, when the baffle device is a half-baffle
supported against a solid boundary wall of the duct, the baffle
casing may only comprise a single perforated sheet member across
which the gaseous flow is directed so that only a single liner
sheet fully spanning the single perforated sheet member is required
in this instance.
[0025] According to another aspect of the present invention there
is provided a sound attenuating baffle device for use in a duct
receiving a gaseous flow in a flow direction therethrough, the
baffle device comprising:
[0026] a baffle casing having a hollow interior and being adapted
to be supported within the duct such that the gaseous flow is
directed across an exterior of the baffle casing;
[0027] the baffle casing including at least one perforated sheet
member having a plurality of perforations therein which at least
partially defines the exterior of the baffle casing across which
the gaseous flow of the duct is arranged to be directed;
[0028] a sound absorbing layer formed of fibrous sound absorbing
material occupying the hollow interior of the baffle casing;
and
[0029] a liner sheet supported within the hollow interior of the
baffle casing against an interior surface of said at least one
perforated sheet member so as to span across each of the
perforations and prevent direct communication of the fibrous sound
absorbing material with the perforations;
[0030] wherein the liner sheet is a membrane of sound absorbing
material.
[0031] According to a further aspect of the present invention there
is provided a sound attenuating baffle device for use in a duct
receiving a gaseous flow in a flow direction therethrough, the
baffle device comprising:
[0032] a baffle casing having a hollow interior and being adapted
to be supported within the duct such that the gaseous flow is
directed across an exterior of the baffle casing;
[0033] the baffle casing including at least one perforated sheet
member having a plurality of perforations therein which at least
partially defines the exterior of the baffle casing across which
the gaseous flow of the duct is arranged to be directed;
[0034] a sound absorbing layer formed of fibrous sound absorbing
material occupying the hollow interior of the baffle casing;
and
[0035] a liner sheet supported within the hollow interior of the
baffle casing against an interior surface of said at least one
perforated sheet member so as to span across each of the
perforations and prevent direct communication of the fibrous sound
absorbing material with the perforations;
[0036] wherein the liner sheet is formed of a sound absorbing foam
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] One embodiment of the invention will now be described in
conjunction with the accompanying drawings in which:
[0038] FIG. 1 is a perspective view of an exemplary duct locating a
silencer comprising sound attenuating baffles according to the
present invention therein;
[0039] FIG. 2 is a schematic sectional view along the line 2-2 of
FIG. 1;
[0040] FIG. 3 is a schematic sectional view along the line 3-3 of
FIG. 2 of a plurality of baffles; and
[0041] FIG. 4 is a detailed sectional view along the line 3-3 of
FIG. 2 of a single intermediate baffle.
[0042] In the drawings like characters of reference indicate
corresponding parts in the different figures.
DETAILED DESCRIPTION
[0043] Referring to the accompanying figures there is illustrated a
sound attenuating baffle device generally indicated by reference
numeral 10. The device 10 is particularly suited for use in a
silencer apparatus for attenuating sound in a ducted flow. The duct
may be any suitable size or shape for receiving a flow of air or
gas therethrough in a flow direction of the duct in air
distribution HVAC systems, ventilation systems and other air
movement systems for either air and gas streams.
[0044] In the illustrated embodiment, the duct is a transitional
duct section 12 having a rectangular cross-section which tapers to
be reduced in cross-sectional area from an inlet end 14 to an
outlet end 16. In further embodiments however, the sound
attenuating baffle device 10 can be readily applied to any other
type of duct including duct sections with circular cross-sections,
a straight duct section, or an elbow duct section while still
achieving the benefits described herein. The flow direction through
the duct is understood herein to correspond to the direction that
air moves through the duct. In a straight or transitional duct, the
flow direction is typically linear from the inlet to the outlet end
of the duct; however, in an elbow duct, the flow direction is
understood to follow a generally curved path from the inlet to the
outlet of the duct.
[0045] The duct section 12 of the silencer apparatus is mounted
within a duct system or directly to a fan, and is comprised of one
or more baffle devices 10. In the illustrated embodiment, the
silencer apparatus mounted within the duct 12 comprises one
half-baffle device 10A mounted against one boundary wall of the
duct section 12 and two intermediate baffle devices 10B which are
mounted at respective intermediate locations within the duct
section. The baffle devices 10A and 10B are all generally parallel
and spaced apart from one another within the perimeter boundary of
the duct.
[0046] Each baffle device 10 extends in a lateral direction across
a full width of the duct between two opposing sides 18 of the
baffle. Each baffle also extends in a longitudinal direction
generally parallel to the flow through the duct from a leading end
20 of the baffle device to a trailing end 22. The baffle device is
generally uniform in shape in the lateral direction across the full
width. A thickness of the baffle device, measured perpendicularly
to both the lateral and longitudinal directions, tapers in the flow
direction so as to be reduced in overall thickness from the leading
end 20 to the trailing end 22.
[0047] Each baffle device includes an outer baffle casing 24 in the
form of a shell which defines the outer boundary of the baffle
device. The outer baffle casing 24 of the half baffle 10A is
approximately one half of the overall shape and size of each
intermediate baffle device 10B according to the illustrated
embodiment.
[0048] With regard to each intermediate baffle device 10B, the
outer baffle casing 24 includes a first cap 26 spanning laterally
across the full width of the baffle device at the leading end. The
first cap 26 is formed of sheet metal and is generally concave at
the outer side in the direction of the thickness of the baffle,
while extending generally linearly across the full width of the
baffle in the lateral direction with a uniform profile. The first
cap 26 is typically formed to be devoid of perforations so as to be
generally domed and aerodynamic in shape. In the illustrated
embodiment mounting flanges 28 are formed at opposing ends of the
first cap 26 for mounting two opposing side walls of the
surrounding duct, however in further embodiments various other
means may be used to support the baffle device relative to the
duct.
[0049] The outer baffle casing 24 further comprises two opposed
faces comprising perforated metal sheet members 30 which are
generally planar in shape for spanning the full width and
substantially the full length of the outer baffle casing. The
overall thickness of the baffle is defined by the distance between
the two opposed faces.
[0050] A second cap 32 is mounted between the perforated sheet
members 30 at the trailing end of the baffle device to span the
full width between opposing sides of the duct and to span the full
thickness between the opposing faces. The second cap 32 may be
planar in shape, oriented perpendicularly to the flow direction
through the duct. Mounting flanges 34 are also provided at opposing
ends of the second cap 32 for mounting to opposing side walls of
the duct according to the illustrated embodiment, however in
further embodiments various other means may be used to support the
baffle as noted above. The second cap 32 in the illustrated
embodiment is a solid panel.
[0051] The perforated sheet members 30 defining the two opposed
faces of each baffle device 10B are oriented generally in the flow
direction, however, the faces are sloped by a few degrees relative
to the flow direction such that the two opposed faces taper towards
one another to reduce the overall thickness therebetween in the
flow direction from the first cap 26 at the leading end to the
second cap 34 at the trailing end.
[0052] A hollow interior of the resulting outer baffle casing 24 is
filled with a sound absorbing material 36 which defines a sound
absorbing layer occupying most of the thickness of the outer baffle
casing. Sound absorbing materials suitable for use with the present
invention include lightweight, porous or loose fill materials such
as fibrous material including fiberglass, mineral wool, or natural
cotton media for example, which have the ability to dissipate sound
energy travelling therethrough.
[0053] The half baffle device 10A is similar to the intermediate
baffle devices 10B in that there is provided an outer baffle casing
124 which also forms the shell which defines the outer boundary of
the baffle device. The outer baffle casing 124 again includes a
first cap 126 spanning across the full width of the baffle device
at the leading end so as to spend the full thickness of the baffle
device. The first cap 126 is formed of sheet metal and is concave
at the outer side, but corresponds approximately to only half of
the profile of the first cap of the intermediate baffle devices.
Mounting flanges 128 are formed at opposing ends of the first cap
126 for mounting two opposing side walls of the surrounding duct
section.
[0054] The half baffle device 10A also includes a second cap 132
mounted at the trailing end of the baffle device to span the full
width between opposing sides of the duct and to extend the full
thickness of the baffle device the second cap 132 is oriented
generally perpendicularly to the flow direction through the duct
section.
[0055] The half baffle device 10A also includes a perforated metal
sheet member 130 which spans the full width of the duct section and
which extends substantially the full length of the outer baffle
casing 124 between the first cap 126 at the leading end and the
second cap 132 at the trailing end of the baffle device. The
overall thickness of the baffle is defined by the distance between
the perforated sheet member 130 and the adjacent boundary wall of
the duct section in the instance of the half baffle device.
[0056] The hollow interior of the resulting outer baffle casing 124
of the half baffle device 10A is also filled with a sound absorbing
material 136 which defines a sound absorbing layer occupying most
of the thickness of the outer baffle casing. As noted above, sound
absorbing materials suitable for use with the present invention
include lightweight, porous or loose fill materials such as fibrous
material including fiberglass, mineral wool, or natural cotton
media for example, which have the ability to dissipate sound energy
travelling therethrough.
[0057] In the instance of either a full baffle device 10B or a half
baffle device 10A the perforated metal sheet member 30 or 130
defines a substantial portion of the exterior of the baffle casing
which is oriented generally in the flow direction of the duct
section and across which the gaseous flow through the duct section
is directed in use. Each of the perforated sheet members includes a
plurality of perforations formed therein. The perforations in the
sheet members typically comprise the only openings in the overall
shell formed by the baffle casing. To prevent communication of the
fibrous sound absorbing material occupying the hollow interior of
each outer casing, a sound absorbing foam material liner sheet 150
is supported on the interior surface of each perforated sheet
member 30 and 130. The liner sheet 150 spans across each of the
perforations to prevent direct communication of the fibrous sound
absorbing material with the perforations.
[0058] In the illustrated embodiment each perforated sheet member
30 and 130 is provided with a single continuous liner sheet 150
which spans the full length and the full width of the sheet member
directly against the interior surface thereof. In further
embodiments the liner sheet 150 may be formed in sections which are
abutted with one another or joined at respective scenes by various
means, however careful attention is required to prevent any gaps at
the seams between adjacent sections of liner material which might
communicate with any perforation in the sheet member in this
instance.
[0059] The liner sheet 150 is formed of a foam material, either
open-cell or closed-cell. In the illustrated embodiment the foam
material is a melamine resin, thermoset polymer, for example
polyethylene. The liner sheet can be any membrane or sheet-like
material capable of forming a layer, devoid of any openings, and
which is non-eroding, and preferably non-fibrous, while remaining
sufficiently resilient to be more sound absorptive than
reflective.
[0060] Thickness of the foam material sheet in a direction which is
perpendicular to the perforated sheet member against which the foam
liner sheet is supported is in the range of 0.125 to 2 inches. The
thickness of the foam material is thus generally less than 40% of
an overall thickness of the fibrous material forming the sound
absorbing layer, and is preferably in the range of 5 to 10% of the
overall thickness of the fibrous material forming the sound
absorbing layer.
[0061] The fibrous sound absorbing material typically occupies the
remainder of the hollow interior of the outer baffle casing not
occupied by the foam liner sheet(s) 150 and is supported within the
hollow interior under resilient compression. The compression of the
fibrous sound absorbing material applies outward pressure to the
liner sheet 150 to support the sheet pressed against the interior
surface of the corresponding perforated sheet member 30 or 130
across substantially the full width and full length of the sheet
member.
[0062] To provide additional support at the perimeter edges of the
liner sheet 150, support flanges 152 may be mounted within the
interior of the baffle casing which overlap a portion of the liner
sheet adjacent to the perimeter edge such that the edge portion of
the liner sheet is retained between the support flange and the
perforated sheet member. The support flanges 152 may be part of
respective L-shaped or Z-shaped structural pieces mounted against
the interior surface of the perforated sheet members to extend
along respective ones of the perimeter edges of the liner
sheets.
[0063] Since various modifications can be made in my invention as
herein above described, it is intended that all matter contained in
the accompanying specification shall be interpreted as illustrative
only and not in a limiting sense.
* * * * *