U.S. patent application number 10/462724 was filed with the patent office on 2003-11-06 for refractory lined ducts and coating for use therewith.
Invention is credited to Davis, Matthew S., Davis, Victor M..
Application Number | 20030205284 10/462724 |
Document ID | / |
Family ID | 26955421 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030205284 |
Kind Code |
A1 |
Davis, Victor M. ; et
al. |
November 6, 2003 |
Refractory lined ducts and coating for use therewith
Abstract
The present invention is directed to ceramic fiber insulation
and related products and methods. A coating that is capable of
being brushed and/or sprayed lightly as a liquid onto vacuum-formed
ceramic fiber insulation for use at high temperatures is also
provided.
Inventors: |
Davis, Victor M.;
(Parkersburg, WV) ; Davis, Matthew S.;
(Washington, WV) |
Correspondence
Address: |
HELLER EHRMAN WHITE & MCAULIFFE LLP
1666 K STREET,NW
SUITE 300
WASHINGTON
DC
20006
US
|
Family ID: |
26955421 |
Appl. No.: |
10/462724 |
Filed: |
June 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10462724 |
Jun 17, 2003 |
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09909979 |
Jul 23, 2001 |
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6596120 |
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60272302 |
Mar 2, 2001 |
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Current U.S.
Class: |
138/145 ;
138/146 |
Current CPC
Class: |
C04B 41/009 20130101;
C04B 28/24 20130101; C04B 28/24 20130101; C04B 41/009 20130101;
C04B 41/5089 20130101; C04B 41/009 20130101; C04B 41/85 20130101;
C04B 41/009 20130101; C04B 28/24 20130101; C04B 2111/00482
20130101; Y10T 428/13 20150115; C04B 41/009 20130101; C04B 14/06
20130101; C04B 28/24 20130101; C04B 41/5035 20130101; C04B 14/06
20130101; C04B 30/02 20130101; C04B 14/4625 20130101; C04B 41/5035
20130101; C04B 30/02 20130101; C04B 35/10 20130101; C04B 35/18
20130101; C04B 14/324 20130101; C04B 14/321 20130101; C04B 14/4656
20130101; C04B 41/5035 20130101; C04B 41/507 20130101; C04B 41/5071
20130101; C04B 14/06 20130101; C04B 41/5059 20130101; C04B 14/30
20130101; F16L 59/143 20130101; C04B 28/24 20130101; C04B 41/5089
20130101; C04B 41/5089 20130101; Y10T 428/1314 20150115; Y10T
428/1393 20150115; C04B 41/5089 20130101; C04B 41/009 20130101;
F16L 58/14 20130101; F16L 59/147 20130101 |
Class at
Publication: |
138/145 ;
138/146 |
International
Class: |
F16L 009/14 |
Claims
We claim:
1. A method of increasing fire resistance, erosion resistance, and
corrosion resistance of a duct lined with a vacuum-formed ceramic
fiber lining comprising treating said ceramic fiber lining with a
coating, wherein said coating renders said duct capable of being
used at temperatures from about 2300.degree. F. to about
3000.degree. F.
2. A method according to claim 1, wherein said coating comprises a
mixture of: silicon dioxide power; collodial silicon dioxide;
water; and an emissivity agent.
3. A method according to claim 1, wherein said coating comprises a
mixture of: silicon dioxide power in an amount of from about 23.0
to about 44.0 wt %; collodial silicon dioxide in an amount from
about 25.0 to about 45.0 wt %; water in an amount from about 19.0
to about 39.0 wt %; and an emissivity agent selected from the group
consisitng of silicon hexaboride, silicon tetraaboride, silicon
carbide, molybdenum disilicide, tungsten disilicide and zirconium
diboride.
4. A ceramic fiber lined duct comprising a vacuum-formed ceramic
fiber liner that has been treated with a coating affixed to a metal
jacket.
5. A vacuum-formed ceramic fiber lined duct according to claim 4,
wherein said coaling comprises a mixture of: silicon dioxide power;
collodial silicon dioxide; water; and an emissivity agent.
6. A vacuum-formed ceramic fiber lined duct according to claim 4,
wherein said coating comprises a mixture of: silicon dioxide power
in an amount of from about 23.0 to about 44.0 wt %; collodial
silicon dioxide in an amount from about 25.0 to about 45.0 wt %;
water in an amount from about 19.0 to about 39.0 wt %; and an
emissivity agent selected from the group consisitng of silicon hex
aboride, silicon tetraaboride, silicon carbide, molybdenum
disilicide, tungsten disilicide and zirconium diboride.
7. A method of making refractory lined ducts having an elongated,
structurally supporting tube and a ceramic fiber liner carried on
an interior wall of the duct comprising: a) forming a sleeve and
binder materials on a structurally supportive die in a hydrated
state by vacuum-forming wherein said sleeve has an external wall of
a configuration that is geometrically and dimensionally
complemental to the interior wall of the supporting duct to form an
interference fit therewith effective in mechanically retaining said
sleeve and duct in fixed interengagement; b) inserting the sleeve,
while in a hydrated state and on the die, coaxially into the
supporting tube and after insertion, removing the die from the
sleeve; and c) drying the sleeve while said sleeve is maintained in
fixed position within the supporting tube to remove substantially
all liquid resulting in solidification of the sleeve in a
frictionally and adhesively retained relationship with the
supporting tube.
8. A method according to claim 7, wherein said sleeve is formed
from a slurry of a material selected from the group consisting of
mineral wool, graphite felt, ceramic fiber, and mixtures
thereof.
9. A method according to claim 8, wherein said slurry further
comprises a material selected from the group consisting of
plasticizing agents, de-wetting agents, and mixtures thereof.
10. A method according to claim 7, further comprising treating said
sleeve with a coating, wherein said coating comprises a mixture of:
silicon dioxide power; collodial silicon dioxide; water; and an
emissivity agent.
11. A method according to claim 7, wherein said coating comprises a
mixture of: silicon dioxide power in an amount of from about 23.0
to about 44.0 wt %; collodial silicon dioxide in an amount from
about 25.0 to about 45.0 wt %; water in an amount from about 19.0
to about 39.0 wt %; and an emissivity agent selected from the group
consisitng of silicon hexaboride, silicon tetraaboride, silicon
carbide, molybdenum disilicide, tungsten disilicide and zirconium
diboride.
12. A method according to claim 7, wherein said sleeve is dried
with microwave energy.
13. A method according to claim 7, further comprising combining
said duct with one or more of said ducts so as to make one complete
duct.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to ceramic fiber
insulation, and more particularly to methods and coatings for use
with the same.
[0003] 2. Description of Related Art
[0004] In many industrial applications it is necessary that
conduits or ducts be provided for interconnection of various types
of apparatus which require the routing of hot atmospheres or gases
of many chemical compositions from one component to another. In
most of these environments, the hot gases exhibit not only
corrosive characteristics which will adversely affect conventional
metallic conduits, but are also caused to flow at relatively high
velocities. The relatively high gas flow velocity frequently
encountered results in further adverse effects of frictional
wearing and erosion of the interior of metallic ducts or other
types of ductwork including but not limited to the increased
likelihood of chemical corrosion. The relatively high temperatures
also have a substantial adverse effect on the metal conduit such as
decreasing structural strength and presenting a safety hazard to
workers who may need to be in close proximity.
[0005] One technique heretofore utilized to meet the requirements
of this highly adverse operational environment has been to line
metallic or steel ducts with a castable refractory material. A
disadvantage of the ducts having the castable refractory liner is
that such refractories are not thermally efficient and as a
consequence, the metal ducts which are lined with such materials
must be made so as to develop greater structural strength to
support the weight of the castable refractory that is required in
most cases to meet the operational requirements.
[0006] There has also been an attempt to form ducts capable of
withstanding the operational requirements of transmission of hot
gases by lining metal conduits with a soft ceramic fiber material.
The soft ceramic fiber material, as its name implies, does not
exhibit the desired resistance characteristics to erosion by the
relatively high gas velocities that are encountered. In an effort
to meet the erosion effect, there have been attempts to also coat
the interior surface of these liners with a layer of suitable
material to attempt to rigidify the interior surface layers. These
attempts have also not proven to be sufficiently successful as the
rigidifying surface material will eventually crack and peel off and
expose soft ceramic fibers to the point where the liners will erode
and eventually become unusable, thus requiring replacement.
[0007] Another disadvantage of either the castable refractory
liners or the soft ceramic fiber lining is the technique of
obtaining the attachment or positioning of the liner within the
metal conduit. The usual techniques require first securing of
anchors to the interior of the metal duct. The refractory material
is then either mechanically secured or it is formed directly onto
those anchors such as by spraying or molding. Similarly, the soft
ceramic fiber linings have been applied to the interior of the
metal conduits by use of anchors which are first secured to the
interior of the metal conduit.
[0008] Another attempt to meet the problems has been the formation
of a vacuum cast sleeve or liner which is then subsequently
assembled with a metal duct. This technique is not particularly
advantageous in that it requires assembly at the operational site
where the duct will be utilized. This technique increases the cost
of installation.
[0009] In order to meet fire codes in terms of fireproof and fire
resistance protection, insulation products must either have
substantial mass or be endothermic in nature. Therefore, many
insulation products must be treated or fabricated in such a way so
as to give them such properties. Many endothermic materials are
known. However, there are still problems associated with such
materials and it would be desirable to have a material that is
advantageous in terms of its end use properties and its ease of
manufacture.
SUMMARY OF THE INVENTION
[0010] In accordance with these and other objectives, the present
invention is directed to ceramic fiber insulation and related
products and methods. The present invention further is directed to
a ceramic coating that is capable of being brushed and/or sprayed
lightly as a liquid onto vacuum-formed ceramic fiber insulation for
use at high temperatures.
[0011] In a preferred embodiment, the instant invention provides a
method for making refractory linings and insulation products
wherein a ceramic fiber sleeve is positioned in and retained
without the need for expansion joints and, in most applications,
without utilization of mechanical attachment anchors, however the
instant invention also contemplates the use of expansion joints and
anchors as well. Preferred embodiments of the instant invention
also provide ceramic fiber linings capable of handling gases of
relatively high temperatures.
[0012] The instant invention also provides a ceramic fiber lined
duct comprising a vacuum-formed ceramic fiber liner that has been
treated with a coating affixed to a metal jacket.
[0013] In another preferred embodiment, the instant invention
provides a method of making a duct capable of handling gases of
relatively high temperatures and also having fire resistant,
erosion resistant, and corrosion resistant properties fabricated by
first forming a ceramic fiber sleeve and, while the sleeve is in a
wet or hydrated state, positioning the sleeve within a metal tube
and thereafter subjecting the assembly to a drying operation to
remove moisture from the ceramic fiber sleeve. This method results
in the sleeve and metal tube being mechanically and adhesively
secured together into assembled relationship.
[0014] In another preferred embodiment, the instant invention
provides a method of vacuum-forming a ceramic fiber insulation or
lining conforming to the size and shape of a particular fitting or
commercial healing component and positioning it within a metal
jacket similarly to a ceramic fiber sleeve within a metal tube.
[0015] In another preferred embodiments the instant invention
provides a "clamshell" method for making ceramic fiber-lined
metal-jacketed fittings or ducts of complex shapes which cannot be
made with a single vacuum-forming operation. This involves forming
sections or half sections of such a fitting or duct and combining
them so as to make one complete fitting.
[0016] In another preferred embodiment, the instant invention
provides a method for making refractory linings and insulation
products wherein materials such as, but not limited to, mineral
wool and/or graphite felt can be used in place of or in addition to
ceramic fiber within the metal jacket of a duct, fitting or
commercial heating component.
[0017] The instant invention also provides a refractory lining
comprising a vacuum-formed ceramic fiber liner that has been
treated with a coating. In a preferred embodiment, the instant
invention provides a method of increasing fire resistance, thermal
resistance, erosion resistance, and corrosion resistance of a
vacuum-formed ceramic fiber lining comprising treating said ceramic
fiber lining with a coating on a surface of said ceramic fiber
insulation, wherein said coating renders said duct capable of being
used at temperatures from about 2300.degree. F. to about
3000.degree. F.
[0018] In addition to the above applications, the coating's fire
resistance, as opposed to merely beat resistance, as well as the
coating's erosion resistant and corrosion resistant properties,
make the present coating a desirable coating for vacuum-formed
ceramic fiber products. In ibis case, as in the above applications,
the coating would preferably be brushed and/or sprayed lightly onto
the hot face of ceramic fiber insulation, whether or not the
insulation contains an outer steel jacket.
[0019] Additional objects, features and advantages of the invention
will be set forth in the description which follows, and in part,
will be obvious from the description, or may be learned by practice
of the invention. The objects, features and advantages of the
invention may be realized and obtained by means of the
instrumentalities and combination particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate a presently
preferred embodiment of the invention, and, together with the
general description given above and the detailed description of the
preferred embodiment given below, serve to explain the principles
of the invention.
[0021] FIG. 1 is an elevational view of a duct formed in accordance
with the method of this invention with portions of the elements
removed for clarity of illustration.
[0022] FIG. 2 is an elevational view of a ceramic fiber sleeve
formed by a vacuum process onto a die.
[0023] FIG. 3 is a diagrammatic illustration of the process of
assembly of the ceramic sleeve in a wet form into a metal tube.
[0024] FIG. 4 is an elevational view of a section of conduit formed
in accordance with the method of this invention and having multiple
refractory liners.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0025] In a preferred embodiment, the present invention relates to
high-temperature vacuum-formed ceramic fiber insulation, as well as
to a coating which can be applied to ceramic fiber products so as
to make them more resistant to erosion and corrosion caused by
extreme velocity in high-temperature airflow within ductwork and by
particulate matter in that airflow. The invention further relates
to improvements in refractory liners for ducts or conduits, and
particularly to ducts or conduits having a ceramic fiber liner
functioning as a refractory to accommodate the corrosive and
abrasive characteristics of hot gases designed to be routed through
such conduits or ducts. It further relates in particular to a
method for making of a duct having a refractory liner of ceramic
fiber.
[0026] As used herein a duct is a metallic enclosed vessel or
conveyance including, but not limited to, a pipe, tube, or
channel.
[0027] Suitable high emissivity coatings are disclosed, for
example, in U.S. Pat. No. 5,296,288, the content of which is
incorporated herein by reference in its entirety. For example, a
coating of the instant invention generally comprises a mixture of:
silicon oxides such as silicon dioxide powder and colloidal silicon
dioxide; water, preferably de-ionized; one or more emissivity
agents; and optional organic elements as additives to extend shelf
life.
[0028] An emissivity agent is an agent which radiates heat into the
duct and away from the lining. Typical emissivity agents of the
instant invention include, but are not limited to polyborides such
as silicon hexaboride or silicon tetraaboride, silicon carbide,
molybdenum disilicide, tungsten disilicide and zirconium
diboride.
[0029] In one preferred embodiment the coating comprises a mixture
of silicon dioxide power in an amount of from about 23.0 to about
44.0 wt %; collodial silicon dioxide in an amount from about 25.0
to about 45.0 wt %, water in an amount from about 19.0 to about
39.0 wt %, and an emissivity agent preferably is in the form of a
powder. The protective coating can have a solids content of from
about 40 to about 60 wt %.
[0030] The present coating is especially resistant to hostile
environmental conditions, such as air velocity, temperature,
acidity, water vapor or steam, etc. The coating is suitable for
withstanding the same temperature range as the ceramic fiber lining
itself, for example about 2300.degree. F. to about 3000.degree.
F.
[0031] The protective coating can easily be prepared, for example,
by preparing a slurry of the components of the coating, and then
ball milling the slurry to provide a uniform solid dispersion which
is then further mixed together. It has unexpectedly been found that
the coating according to the present invention is highly resistant
to fire. Accordingly, in a preferred embodiment, the instant
invention provides a vacuum-formed ceramic fiber insulation or
liner treated with a coating of the present invention. In this way,
the treated ceramic fiber insulation or liner is resistant to
erosion caused by air velocity, to particulate matter in such an
air stream, to corrosion caused by acid, moisture, fire and extreme
heat.
[0032] The instant coating may be applied to a ceramic fiber lining
or insulation by any method commonly employed in the art, such as
brushing or spraying.
[0033] The present coating is particularly advantageous for use
with: (1) ductwork that is adapted for high velocity airstreams,
(2) ductwork that is used for airstreams having particulate matter;
(3) ductwork that regularly is exposed to airstreams having an
acidic content therein and/or (4) ductwork that accepts airstreams
having a high moisture content.
[0034] Because of its inherent fire and heat resistant properties,
the present coating may also be used for high-temperature
applications such as those at or above about 2300.degree. F. Often
it may be cost-effective to apply the coating as a heat barrier,
thereby permitting a reduction of the wall thickness of the
insulating ceramic fiber. In the case of steel-jacketed ceramic
fiber products such as Danser Inc.'s commercially available
VACUDUCT.RTM. product, the coating's heat barrier may also permit a
reduction in the diameter and amount of the steel necessary to
enclose the insulating layer of ceramic fiber. For example, the
thickness could be reduced by about 5-50%.
[0035] Particularly challenging duct environments may require two
applications of the coating. First a dilute application, for
example, from about 10% to about 90% strength, and more preferably
from about 10% to about 15% strength) may be applied so as to
maximize absorption into the relatively porous density of
vacuum-formed ceramic fiber, which may be approximately 17 lbs./cu.
fi. This dilute application can then advantageously be followed by
a full-strength application to maximize the impervious nature of
the barrier to air velocity, particulate matter, acid, moisture and
heat.
[0036] The instant coating is suitably applied to materials, such
as refractory liners or refractory liners with passive fire
resistance due to its high emissivity. The present coating's high
emissivity qualities are greatly advantageous over prior
endothermic materials. Coated ceramic fiber insulation according to
the present invention is generally capable of meeting appropriate
ASTM, NFPA and UL fire prevention standards.
[0037] A coating composition for coating the interior of ceramic
materials such as ceramic fiber-lined ducts of the present
invention act to direct thermal energy toward a load in the duct
wherein the duct reaches a temperature of above about 1100.degree.
C., thereby increasing the thermal efficiency and also the fire
resistance of the interior of the ductwork.
[0038] In a preferred embodiment, the instant invention provides
high-temperature vacuum-formed ceramic fiber insulation for
ductwork. U.S. Pat. No. 5,078,822, the content of which is
incorporated herein by reference in its entirety, discloses a
refractory lined duct, fitting, or component having a sheet metal
outer jacket or "skin" lined on the inside with a ceramic fiber
matrix bonded with binder materials forming a refractory lining of
predetermined shape, thickness, and thermal characteristics. This
duct's refractory lining is held in fixed, retained relationship
with the exterior sheet metal jacket solely by frictional and
adhesive forces inherent in the art of the invention.
[0039] A method for making the duct, fitting, or component includes
the steps of vacuum-forming a refractory inner lining, conforming
to the shape of the sheet metal outer jacket, from a slurry of
ceramic fibers and binder materials onto a forming die, inserting
the ceramic fiber lining while in a hydrated state into the sheet
metal supporting jacket or casing of complementary shape and size
such that adjacent surfaces of the jacket and sleeve are in
contacting engagement, and then drying the assembly to remove the
water resulting in the formation of a hard, solid-structure
refractory liner that is fixed in the tube solely through
frictional and adhesive forces inherent in the art of the
invention. A modified duct, or fitting, formed by the same
methodology includes a composite refractory liner formed from a
plurality of tubular liners that each have their own respective
structural, physical and thermal characteristics.
[0040] The present invention further provides refractory lined
ducts, fittings or components having sheet metal jackets or casings
lined with a ceramic fiber matrix bonded with binder material
forming refractory liners of predetermined thickness and thermal
characteristics. For example, liner thicknesses range preferably
from about 1 to about 8 inches and more preferably from about 2 to
about four inches with thermal characteristics when dry of a low
density insulation which is also low in thermal conductivity and
highly resistant to thermal shock. The duct has the refractory
liner held in fixed, retained relationship with its outer metal
jacket solely by frictional forces and adhesive bonding by the
binder material. A modified duct or fitting formed by the same
methods includes a composite refractory liner formed from a
plurality of tubular liners that each have their own respective
structural, physical and thermal characteristics. It is also
possible to render such materials erosion resistant, corrosion
resistant, and fire resistant or even fireproof by applying a
coating such as corrosion resistant coatings and/or coatings of the
instant invention.
[0041] In accordance with this invention, there are also provided
methods for making the instant refractory lined ducts, fittings or
components. In a preferred embodiment, a ceramic fiber inner lining
is positioned in and retained within a metal jacket or casing. In
accordance with this preferred embodiment, a duct capable of
handling gases of relatively high temperatures, for example,
2300.degree. F. and also having corrosive properties, is fabricated
by first forming of a ceramic fiber inner lining and, while the
lining is in a wet or hydrated state, positioning the lining within
the metal jacket and thereafter subjecting the assembly to a drying
operation to remove moisture from the ceramic fiber lining. This
method results in the lining and metal jacket being mechanically
and adhesively secured together into an assembled relationship.
[0042] The ceramic fiber lining can be formed, for example, by
well-known operations for vacuum-forming of such articles through
placement and forming of the ceramic fibers onto a forming die. The
ceramic fibers are formed in a layer on the die to form a fiber
lining having an outside diameter or shape that is at least equal
to, if not slightly larger than the interior diameter or chamber of
the metal jacket or casing into which the lining is to be placed.
While in a wet condition, the die-supported fiber lining is
inserted into the metal jacket and the die is removed either at a
point in lime where the ceramic fiber lining is partially inserted
within the jacket or when it is fully inserted. After the die is
removed from the ceramic fiber lining, the assembled metal jacket
and ceramic lining are placed in an oven wherein the elevated
temperature of the oven and airflow is sufficient to effect
evaporation of the water from the ceramic fiber lining.
[0043] Preferably, a method for making the instant duct, fitting,
or component comprises the steps of vacuum-forming a refractory
inner lining from a slurry of ceramic fibers and binder materials
onto a forming die, inserting the ceramic fiber lining while in a
hydrated state into the sheet metal supporting jacket or casing of
complementary shape and size such that adjacent surfaces of the
jacket and sleeve are in contacting engagement and then drying the
assembly to remove the water resulting in forming of a hard, solid
structure refractory liner that is fixed in the tube solely through
frictional and adhesive forces inherent in the art of the
invention.
[0044] The ceramic fiber lining is of a size such that when it has
been dried, it will mechanically engage with the interior surface
of the metal jacket and be at least partially retained therein
through frictional and adhesive forces resisting relative axial
displacement. The instant invention is particularly suited for
predetermined shapes, configurations and sizes of metal jacketed
ceramic fiber lined ducts, fittings or components in sizes, for
example, ranging from an inner diameter of two inches to an outer
diameter of eight feet.
[0045] In accordance with another aspect of this invention, a
conduit assembly or fitting having multiple ceramic fiber liners is
provided through sequential formation and insertion of two or more
ceramic fiber liners into a metal jacket or casing. This aspect of
the invention enables a ceramic fiber liner adapted to lower
temperature applications to be first placed within the conduit and
then a second ceramic fiber liner adapted for higher temperature
applications inserted and secured in a similar manner.
[0046] In a preferred embodiment, the invention provides a method
of making refractory lined ducts having an elongated, structurally
supporting tube and a ceramic liner carried on an interior wall of
the duct comprising forming a sleeve of ceramic fiber and binder
materials on a structurally supportive die in a hydrated state by
vacuum-forming wherein said sleeve has an external wall of a
configuration that is geometrically and dimensionally complemental
to the interior wall of the supporting duct to form an interference
fit therewith effective in mechanically retaining said sleeve and
duct in fixed interengagement; inserting the sleeve, while in a
hydrated state and on the die, coaxially into the supporting tube
and after insertion, removing the die from the sleeve; and drying
the sleeve while said sleeve is maintained in fixed position within
the supporting tube to remove substantially all liquid resulting in
solidification of the sleeve in a frictionally and adhesively
retained relationship with the supporting tube.
[0047] A preferred embodiment is illustrated in FIG. 1, wherein a
refractory lined duct 10 embodying this invention and formed in
accordance with the method is shown with portions broken away for
clarity of illustration. The duct 10 includes a structurally
supporting tube 11 and a refractory liner 12. The tube 11 is formed
from a suitable material for the particular installation and may
most commonly be formed of sheet steel. The size of the duct 10 is
also dependent upon the particular installation for which the duct
is designed as is the diameter. As an example, duct embodying this
invention may have a nominal diameter in the range of about 2 to
about 100 inches, more preferably about 8 to about 50 inches with
the liner itself having a thickness of the order of 3 inches. Duct
of this type frequently is required in installations where there
are large volumes of gaseous materials that must be transported
from one location to another, and accordingly, large-size ducts are
preferred to reduce velocities while maintaining sufficient
capacity to handle the volume of gas.
[0048] The supporting tube 11 which is indicated to be fabricated
of sheet steel may be of a type that is formed by spiral winding
techniques of elongated strips of steel with the adjacent edges
being mechanically interlocked. FIG. 1 does not illustrate
specifics of detail of the structure of the tube 11 as that does
not form a part of the invention and is dependent upon a particular
design. However, the tubes 11 are generally provided with end
flanges 13 which provide a means for mechanically interconnecting a
number of such ducts in serial alignment. These flanges are
generally drilled to accommodate fastening bolts. Again, the
technique of interconnecting adjacent duct in end-to-end
relationship is a matter of mechanical design and is of a type
selected to be appropriate for a particular installation and the
details are not a part of this invention.
[0049] In accordance with this invention, the refractory liner 12
is retained in position within the interior of the supporting tube
11 through a combination of frictional and adhesive forces as
between the contacting wall surfaces of the liner and the tube. As
can be seen in FIG. 1, the liner 12 has an inner wall surface 14
which is termed "The Hot Face" and an outer wall surface 15 which
is termed "The Cold Face". One of the functions of the refractory
liner 12 is to provide thermal insulation and thus have a
characteristically low thermal conductivity such that the cold face
will not exceed predetermined temperatures for a particular
application. This is advantageous to reduce the mechanical stresses
that must be accommodated by the supporting tube 11 as well as
enhancing safety in the environment as it concerns workers who must
operate in the processing installation in which such duct may be
installed.
[0050] In accordance with this invention, the refractory liner 12
is formed from ceramic fibers which are held in a matrix by
suitable binders. The ceramic fibers that are particularly useful
for a refractory liner of this type and for high-temperature
installations comprise a combination of alumina-silica fibers and
aluminum oxide fibers. These fibers which are of small
cross-sectional shape are held in a matrix by means of binders
which may include combinations of colloidal silica binders and
cationic starch binders. These materials are mixed in a slurry
composition which, through a vacuum-forming process, can be
fabricated into a tubular shape such as the illustrative refractory
liner, or into virtually any shape complementary to an outer steel
jacket or casing. The specific materials, their proportions in the
composition, are known in the art and the specifics are not deemed
of importance to the invention other than to note that the
materials are selected in accordance with known techniques to form
a refractory which will have the desired thermal and structural
characteristics.
[0051] In another preferred embodiment, the instant invention
provides for the addition of a plasticizing agent in the ceramic
slurry mix to reduce brittleness of individual ceramic fibers in
the finished product thereby reducing erosion and thermal shock of
the finished product when it is in operation.
[0052] In another preferred embodiment, the instant invention
provides for the addition of a de-wetting agent in the ceramic
slurry mix to accelerate drying of the finished product after it
has been removed from the die.
[0053] Vacuum-forming of a tubular liner such as that which is
illustrated is conventionally accomplished by vacuum-forming
techniques with the ceramic fibers and binder being collected on an
elongated tubular die. This forming technique is diagrammatically
illustrated in FIG. 2 where an elongated die 16 is shown with a
quantity of the ceramic fibers and binder collected on its exterior
and thus forming an elongated tube. In the initial forming stages,
the ceramic fiber and binder matrix is in a highly hydrated state,
although it will be sufficiently compacted with the binder material
functioning to adhesively secure the fibers in a structurally
self-supporting shape. The refractory liner at this stage can be
handled and moved for performance of other operations to complete
its fabrication. Such tubular refractories are utilized in other
applications than that of the invention and, for such purposes, the
article subsequent to the initial vacuum-forming operation is
subjected to a drying operation such as by placing the article in a
conventional oven and circulating air for evaporation of the
moisture which is predominantly water. In another preferred
embodiment, the lining, subsequent to the initial vacuum-forming
operation, is subjected to a drying operation in a microwave oven
wherein penetrating microwave energy and airflow are sufficient for
evaporation of moisture. In either type of drying environment the
temperatures and drying times are dependent upon the particular
characteristics of the fiber lining as to its physical size and
moisture content. The article as thus formed in accordance with
prior art practices is a structurally solid article that can be
mechanically placed and secured in specific installations.
[0054] However, in accordance with the method of invention for
forming the duct embodying this invention, the tubular refractory
liner 12 while in a wet hydrated state is first positioned within
the interior of the supporting tube 11 prior to being subjected to
a drying operation. Depending upon the state or degree of hydration
of the liner, it may be advantageous to dry the liner to an extent
where it will have adequate structural integrity to enable its
assembly with the tube. To form a duct 10 embodying this invention,
the refractory liner 12 is formed with an exterior diameter that is
at least equal to or advantageously slightly larger than the inside
diameter of the supporting tube 11. For example, in the case of a
supporting tube 11 having a diameter in the range of about 2 to
abut 100 inches, more preferably about 8 to about 50 inches, the
exterior diameter of the liner 12 as fabricated by the
vacuum-forming process may be one-fourth inch larger to better
assure that there will be a mechanical engagement as between the
liner and tube to result in the desired frictional forces for
retaining the liner within the tube. Assembly of a vacuum-formed
liner with the tube 11 is diagrammatically illustrated in FIG. 3.
While the refractory liner 12 is in a hydrated state and still
retained on the forming die 16, it can be easily lifted and slid
axially into the upper open end of the tube 11. The tube 11 would
be supported on a transporting plate or other carrier device and
the liner 12 as it slides down into the tube 11 would also come to
rest on that supporting plate. As the liner 12 is slid into the
tube, excess refractory material may be skinned or shaved off from
the exterior surfaces or realigned onto the surface forming a
continuous contacting surface engagement with the interior of the
supporting tube 11. A refractory liner in a hydrated state does not
have a smooth surface as the material has a tendency to flow to a
certain degree and this is illustrated in FIG. 2 by the rough
surface conformation. When the liner is at least partially inserted
within the tube, the forming die 16 may be removed. This may be
accomplished by mechanical rotation of the die which will break the
surfaces loose and enable the die to be withdrawn. Once the die has
been withdrawn, the hydrated liner will continue sliding down into
the tube until it comes to rest on the bottom supporting plate.
[0055] Once the hydrated liner is fully positioned within the tube,
the assembly may then be subjected to a drying procedure. This
drying procedure follows that previously described in connection
with forming of refractory articles of a more conventional nature.
Such a procedure as indicated comprises placing the article into an
oven which is at a sufficiently elevated temperature, or utilizes
microwave energy, so as to cause evaporation of the water in the
liner. Air is circulated around the articles to aid in removal of
the water vapor and thereby hasten the drying process. A drying
apparatus is not shown as such is well-known in the art as are the
operating techniques as to temperature and airflow. The operation
does continue until the water is evaporated at which time the
refractory material is fully solidified. This process also
completes forming of the inter-fit of the liner to the interior of
the tube to result in generation of frictional and adhesive forces
which prevent the removal of the liner from the supporting tube.
Thus, in accordance with this invention, a duct 10 having a
refractory liner is provided which does not require the use of any
other mechanical means for securing the refractory liner within the
interior of the tube.
[0056] A modified duct 20 also fabricated in accordance with the
method of this invention and thus embodying the advantageous
structural arrangement is shown in FIG. 4. This duct also includes
a structurally supporting tube 21 and a refractory liner designated
generally by the numeral 22. However, in this modification, the
liner 22 comprises a plurality of tubular refractory liners with
two ceramic fiber liners 23 and 24 shown which are disposed in
coaxial relationship to each other and to the supporting tube 21.
Utilizing two liners 23 and 24 to form a composite refractory liner
22 permits each of the liners to be fabricated from different
combinations of materials. By appropriately proportioning the types
of ceramic fibers that are selected and the binder materials, it is
possible for a liner of predetermined thickness to be formed having
different physical and thermal characteristics. One objective of
this is that the inner liner 23 of such a composite structure may
advantageously be formed from ceramic fiber materials and binders
such that it will have relatively less thermal shrinkage at high
temperatures. The second liner 24 may then be formed from the
ceramic fiber materials and binders with the resulting liner having
a characteristically higher shrinkage at high temperatures. This
dual liner construction thus permits a lower fabricating cost as
the inner liner having a relatively lower thermal shrinkage is
relatively more expensive as compared to the outer liner.
[0057] Other factors may also be considered in a combination of two
liners to achieve particular physical and thermal objectives. For
example, in another preferred embodiment, the instant invention
provides a method for making refractory linings and insulation
products wherein materials such as, but not limited to, mineral
wool and/or graphite felt can be used in place of or in addition to
ceramic fiber within the metal jacket of a duct, fitting or
commercial heating component.
[0058] Assembly of the dual liners 23 and 24 with the supporting
tube may be effected in substantially the same manner as described
with respect to the assembly shown in FIG. 3. A first liner 24 is
placed within the supporting tube 21 with its die then being
removed. A second or innermost liner 23 may then be similarly
placed within the outer liner in the same manner and its respective
forming die then removed. The assembled liners and supporting tube
may then be subjected to an appropriate drying procedure to remove
the water. With the water being removed, the two liners then
maintain their respective coaxial aligned positions through
frictional and adhesive forces as is the assembly retained within
the supporting tube. It will be understood that the dimensions
given for the illustrative duct are for purposes of example and
that the duct may be fabricated in any desired size and
configuration. It will also be understood that the illustrative
dimensional thickness of the refractory liner is also for purposes
of example and its thickness may be varied depending upon the
particular installation in which the duct will be placed. Also, the
specific ceramic fiber materials and binders will be selected on
the basis of the structural and thermal characteristics desired for
the particular duct
[0059] In the present invention, there is also provided
high-temperature vacuum-formed ceramic fiber insulation, as well as
a coating used for passive fire protection applications such as in
commercial construction, manufactured products, transportation, and
industrial construction market segments. These materials can be
used, for example, to control the spread of flames and to limit an
increase in temperature in order to prevent or contain the outbreak
of fire. Potential applications include fireproof storage cabinets
and safes, hazardous material storage and transportation
containers, ventilation and grease ducts, electrical and
telecommunication conduits, and cable trays.
[0060] It will be readily apparent that a novel and particularly
advantageous refractory duct, fitting or industrial heating
component is provided by this invention. It will also be readily
apparent that the method of its fabrication results in economy of
assembly and produces a unitary structure wherein the refractory
liner and supporting metal jacket are retained in mechanical
inter-engagement.
[0061] Additional advantages, features and modifications will
readily occur to those skilled in the art. Therefore, the invention
in its broader aspects is not limited to the specific details, and
representative devices, shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined bye the
appended claims and their equivalents.
[0062] As used herein and in the following claims, articles such as
"the", "a" and "an" can connote the singular or plural.
[0063] All documents referred to herein are specifically
incorporated herein by reference in their entireties.
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