Note: Descriptions are shown in the official language in which they were submitted.
109~s~,
SP~CIFIC~TIO~
Field of the Invention
This invention relates to ~eat-resistant, thermally-
rigidi~ed structural articles, and to methods for producing
such articles. More particularly, the invention is directed
to rigid, sturdy, sintered ceramic, high surface-to-weight
structural components having as an essential part thereof
closely-spaced, longitudinally-extending ducts of small cross-
section, and to methods of forming such articles.
While a presently preferred embodiment of the inven-
; tion will be described as a catalyst support for use in
automotive pollution control systems, the ceramic articles of
this invention have other uses, such as catalyst supports in
other systems, as heat exchange materials, as heat storage
elements, and as heat insulating materials.
Background of the Invention
; The need for strong, thermally-stable catalyst
supports for use in automobile exhaust pollution control
systems has led to intensive research and development efforts
by numerous companies. Pollution control reactors must with-
stand normal operating temperatures as high as 200QF. In
addition, they must operate efficiently with gas temperatures,
; pressures, compositions, and velocities that fluctuate rapidly
over wide ranges, and they must withstand the mechanical
shocks and vi~rations of vehicle operation.
.~
The task of finding substrates that will stand up to
these severe operating requirements has been formidable.
The size and weight criteria imposed by the auto
industry require a catalyst support having a high surface area
per unit of volume. While monolithic ceramic materials are a
good choice for such catalyst supports based on costs, strength,
-2-
--' iO930Sl
and thermal stability, ~ ~ajor dra~back to the use of ceramic
materials has been the development o~ a suitable process fo~
fabricating a high strength, high surface area monolithic
product at a reasonable cost.
Brief Description of the Invention
The invention provides a process of preparing ceramic
articles having a honeycomb structure. Pulverized ceramic
material is thoroughly admixed with a binder, and a plastic-
izing agent to form an extrudable admixture that is shape-
retaining and self-supporting, and that will flow under
pressure. A longitudinally continuous bar of admixture is
then forced through a transversely enclosed forming zone.
Initial shearing forces are applied to the admixture in the
forming zone to form the bar of admixture into a plurality of
discrete ribbons. Duct-forming shearing forces are applied on
each of the discrete ribbons within the forming zone by flow-
~ng outside portions of the ribbons at the upstream ends of a
plurality~ of~ spaced, ~l~ongitudinaly-extending
members positioned within the forming zone to divert outside
portions of each of the ribbons and thus form a webbed
member containing a plurality of longitudinally-extending
ducts as the ribbons flow together about the spaced members.
The webbed member is cut into articles of discrete length, and
the duct-containing articles are subsequently dried and ~ired.
Preferably, the transverse cross-section of the
admixture flowing through the forming zone is reduced during
passage through the forming zone so that the cross-sectional
area of the webs of the webbed member is about 65%-99%, and
optimall~ about 75%, o the sum of the cross-sectional area of
t~e di~crete ribbons in a plane perpendicular to the flow
direction of the admixture in the forming zone.
~'
., ~
10930Sl
It is also pxe~erred that the for~ing zone be less
than about 1 inch lon~ and t~at the duct~forming shearing
forces be exerted on the admixture durtng the last 0.090-0.15
in~ of the passage of the admixture through the forming zone.
It is further preferred that the articles of discrete
length be fired to their maturing temperature while shielded
from direct radiant heat from the heating source at a rate of
temperature increase of no more than about 100C/hour, and
that the rate of temperature increase during firing be no more
than about 50C/hour as the articles are heated from about
1080 to 1400C.
The invention also provides useful ceramic articles
comprising a plurality of webs, with a plurality of parallel
circular ducts that are separated by the webs extending across
the article to provide for fluid flow through the article.
A majority of the parallel circular ducts are surrounded by
six other circular ducts with the axes of the six surrounding
ducts being spaced an approximately equal distance from the
axis of the circular duct they surround. The number of ducts
per square inch of article surface in a plane transverse of the
parallel axes of said ducts i9 at least 100 to provide a high
surface area per weight ratio. Such an article has a trans-
verse compressive strength of at least about 5~ of its long-
itudinal compressive strength.
The process of this invention lends itself to the
production of ceramic articles on a high volume low cost basis,
and makes possible t~e production of catalyst supports that
~re attractlve f~r use in automotive exhaust systems. The
process can produce ceramic articles having a uniform cross-
section and contalning a large number of small, closely-
spaced, longitudinally-extending ducts.
~93~51
The raw materials used in making ceramic articles
in accordance with the invention are relatively in-
expensive, and are readily available in large quantities.
Both of these factors are important considerations with
respect to a high volume market, such as for use in
automotive pollution control systems.
Thus, in accordance with the present teachings, a
catalyst support is provided for use in pollution control
systems which comprise a fired cordierite article which
has a plurality of parallel circular ducts separated
by webs with the ducts extending across the article to
provide for fluid flow through the article, the majority
of the parallel circular ducts are surrounded by six
other circular ducts with the axes of the six surrounding
ducts being spaced at approximately equal distance from
the axis of the circuIar duct they surround. The number
of ducts per square inch of article surface in a plane
transvers of the parallel axes of the ducts is at least
100, with the article having a longitudinal compressive
strength of about 5000 psi and a transverse compressive
strength of between about 400-700 psi.
The presently preferred embodiment of the invention,
in which longitudinally-extending circular ducts are
hexagonally-packed, provides transverse compressive
strengths that are significantly superior to that
attained by any other known monolithic ceramic article
of comparable surface area/volume ratio. 5pecifically,
transverse compressive strengths of between about 400-700
psi are attained for cordierite articles. All prior
--5--
1093051
art attempts at producing closely packed ducts in
cordierite articles have produced articles that exhibit
a transverse strength of about 50 psi along one trans-
verse axis. Surprisingly, the fired, hexagonally-
packed ceramic articles feel resilient to the touch
when compressive force is applied to them.
Brief Description of the Drawlngs
Of the drawings:
FIG. 1 is a sectional view of an extrusion apparatus
for practicing the process of this invention;
FIG. 2 is a plan view of the downstream face of a
die plate member for forming a square celled ceramic
article in accordance with the invention;
FIG. 3 is an elevation view of the die plate member
of FIG. 2;
FIG. 4 is an enlarged fragmentary plan view of the
downstream face of the die plate member illustrated in
FI&. 1
FIG. 5 is an enlarged fragmentary end view of one
embodiment of the ceramic article of this invention;
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1,
1~9305~
FIG~ 6 is a phase dia~ram illustratin~ the general
types o~ ceramlc material produced by various ~gO A1203 -
SiO2 raw material ratios;
FI~. 7 is an elevation of a hollow mill cutting tool
used in ~orming the die mem~er illustrated in FIGS. 1 and 4;
and
FIG. 8 is a view of the hollow mill cutting tool of
FIG. 7 in which the tool has been rotated 90 in a cloc~wise
direction about its axis with respect to its position in FIG. 7.
Detailed Description of Preferred
Emb_diments of the Invention
In accordance with the invention, a process of
preparing monolithic ceramic articles having a honeycomb
strueture is provided in whieh pulverized ceramic material is
thoroughly admixed with a binder and water to form an extrud-
able admixture that is shape-retaining and self-supporting,
and will flow under pressure.
A variety of known sinterable eeramic materials that
can be made plastic (i.e. that will flow under pressure upon
the addition o~ a plasticizing agent) àre suitable for use in
the process of this invention.
The term "plasticizable eeramic composition" as
used in the speeifieation and elaims means an inorganic
substanee or substanees in the erystalline or amorphous state
whieh ean be caused to flow under pressure, but is not fluid,
and that is shape-retaining and evidenees substantially no flow
characteristics when non-supported. For example, refractory
eompositions, sueh as magnesium silieates, magnesia, zireonia,
zireonium silicate, eordierite, eorundum, aluminum silieates,
aluminum titanate, lithium aluminum silieate and siliea or a
eombination of such materials are all suitable for the present
purpose.
--6--
1093051
A refractory composition which consists of cordierite
when sintered is particularly suitable for making catalyst
support articles which requtre lo~ thermal expansion and high
thermal shock res~stance. FIG. 6 is a triangular phase
diagram that illustrates the well-known MgO A12O3 SiO2
ratios which can be used to produce cordierite. However, the
method of the invention is not dependent on the sinterable
ceramic material selected, and hence the material which has
the most suitable properties for the conditions of its use
can be selected.
It is desirable that the ceramic material be
pulverized to an average particle size sufficiently small to
insure easy passage of the mix through the forming zone
(the die plate of the extruder) used in accordance with the
invention. Preferably, the ceramic material will all pass
a 200 mesh screen and optimally it is all -325 mesh material.
In forming the ceramic composition, it is desirable
to mix the dry ingredients thoroughly before addition of water
or other liquid-containing materials to promote plasticity of
the mixture. Generally, a mixing time of about 5 minutes for
the dry materials is sufficient. However, if extremely fine
particle materials are utilized, (all -325 mesh) longer mixin~
times of up to 10 minutes may be necessary to insure good
dispersion.
After dry mixing, the required amount of water or
other liquid to promote plasticity is added to the batch.
Thorough blending of the liquid and solid ingredients is
necessary to impart extrusion consistency to the batch and to
insure a well-formed, cross-sectional shape for the article.
The wet blending times generally range between 5 and 10
minutes and can be performed in less than 2 minutes. In
general, when the ceramic material includes a clay of high
10930Sl
pla~ticity, from 10 to 20 parts b~ weight of water per hundred
parts by wei~ht of clay are utilized.
Water, the preferred wettin~ media, should desirably
be water at a constant pH, preferably 7Ø Di-ffer~nces in the
pH of the water can affect the surface activity and workability
of the clays and other ingredients used. Thus, the use of
water of varying pH may introduce variables in the processing
characteristics of the admixture.
Plasticizing agents which can be utilized lnclude
wa~, gum, and colloidal magnesium aluminum silicate.
Desirably, a binder is included in the admixture to
impart coherence and strength to the formed article. The
binder can be an inorganic binder or an organic binder.
Suitable inorganic binders include colloidal magnesium
aluminum silicate and sodium silicate. Suitable organic
binders include methylcellulose, polyvinyl alcohol, paraffin
and gum arabic. The binder preferably comprises about 0.5 to
2.0% by weight of the total solids in the admixture.
A surface active agent, such as sodium ligno-
sulfonate solution, or "Darvan C"* solution, sold by R. T.Vanderbilt Co., is an optional ingredient. The purpose of the
surface active agent, if used, is to aid in the dispersion of
the ingredients in the extrusion mixture.
A longitudinally continuous bar of admixture prepared
as described above is forced through a transversely enclosed
forming zone, such as is provided by a conventional ram-type
extruder. Initial shearing forces are applied to the admixture
in the forming zone to for~ the bar of admixture into a
plurality of discrete ri~b~ns. Preferably, these initial
shearing forces are applied by forcing the bar of admixture at
a linear speed of between about 5 and 200 inches of product
per minute through the upstream face of a forming die
* Trademark -8-
1093051
having the cross~section i:llustrated in F~GS~ 1 and 4 to
produce ~ plurality of r~bbons having a circular cross--section.
Duct~forming shearing forces are exerted on each of
the discrete ribbons within the forming zone be forcing outside
portions (portions at the outside of the cross-section of each
discrete ribbon) of the ribbons at the upstream ends of a
plurality of spaced, longitudinally-extending members that are
positioned within the forming zone. The longitudinally- -
extending members divert outside portions of each of the
ribbons and thus form a webbed member containing a plurality
of longitudinally-extending ducts as the ribbons flow together
about the longitudinally-spaced members.
FIG. 1 illustrates an embodiment of an apparatus for
carrying out the process of this invention. It is presently
preferred to extrude horizontally, and to deposit the extrudate
on a conveying means that moves away from the die plate at
about the same rate of speed that the material passes through
the die plate.
With reference to FIG. 1, a die plate member gener-
ally 10 is illustrated that includes a plurality of circularpassages 12 on its upstream face and plurality of cylindrical
pins 14 on its downstream face. The relative alignment and
spacing of passages 12 and pins 14 is illustrated in FIG. 4.
As illustrated in FIG. 1, the die plate member 10
is held by a retainer ring 18 against a nozzle member 20
that is welded to barrel member 22 of the extruder.
As illustrated in FIGS. 1 and 4, the plate member 10
has an upstream ~ace comprising a plurality of closely spaced,
longitudinally~extending passages 12 which permit flow of
material through the upstream face of plate member 10 in
the form of a plurality of discrete ribbons. The downstream
face of plate member 10 is formed by a plurality of transversely
_9_
10930Sl
spaced cylindxical pins 14. Each of the pins has a closed
circular perimeter in a plane transverse of the direction of
the material flow through plate member 10, and extends long-
itudinally of the flow direction~ Each pin 14 is
separated from other pins by an interconnected recessed area 26.
The cross-section of recessed area 26 is selected to have the
desired cross-section of the product being formed by extrusion
through the die and is uniform throughout the length of pins 14.
Passages 12 terminate at the upstream end of recessed
area 26 with the axes of passages 12 aligned generally parallel
to the flow direction of material through plate member 10.
This flow direction is preferably transverse of the upstream
face of plate member 10. Passages 12 terminate at a plurality
of spaced locations, with a pair of pins 14 blocking a portion
of the cross-section of each of passages 12 to force the
material being extruded to fill the entire volume of the
recessed area 26 between the upstream end of the recessed
area and the exit face of plate member 10. As used in this
specification and the claims, the term "exit face" or "down-
stream face" of the plate member refers to the plane extend-
ing through the downstream end of the spaced members (pins 14).The term "upstream face" or "inlet face" of plate membex 10
refers to the plane of the other face of plate member 10,
which was a flat planar surface prior to removal of material
to form passages 12.
Preferably, and as illustrated in FIGS. 1 and 4,
passages 12 are cylindrical, and pins 14 are cylinders. In
the illustrated embodiment, a pair of cylindrical pins 14
extend into the flow path of the material out the exit end
of all passages 12 except those at the perimeter of plate
member 10 where only a single pin extends into the flow path
of the peripheral passages. Thus, a pair of pins extends into
--10--
1093051
the flow path of a majority of c~lindrical passages 12.
As best illus-t~ated in FI`~. 4~ spaced cylindrical
passages 12 terminate at locations that are spaced about the
periphery of the upstream end of each of pins 14. This
spacing permits discharge of material from passages 12 at a
plurality of locations about the periphery of each pin 1~ and
helps insure that the desired intricate cross section of the
articles can be achieved during only a short length of flow
through the downstream portion of the plate member.
Preferably, and as illustrated in the embodiment of
FIGS. 1 and 4, any given cylindrical pin 14 is surrounded by
six other cylindrical pins 14, except for pins located adjacent
the perimeter of plate member 10. Each of the six cylindrical
pins spaced about a given pin 14 has its axis spaced approx-
imately an equal distance from the axis of the given cylind-
rical pin.
The resulting product formed by extruding pastpins 14 spaced as above produces hexagonal packing of the
longitudinally-extending ducts as illustrated in FIG. 5. This
arrangement permits forming an extremely high number of small
diameter ducts 15 per square inch of extruded article 17 and
enhances the strength properties of the extruded article and
particularly the resistance to transversely applied compress-
ive forces. The article 17 illustrated in FIG. 5 has a smooth
cylindrical longitudinal wall. surface 19 that is desirable for
some applications, such as in automotive emission control
systems.
It is possible to utilize over 100 pins per square
inch of downstream face of plate member 10 and thus provide
over 100 ducts per square inch. Indeed, dies having pin
densities of over 190 per square inch have been made and used
to successfully extrude uniform ceramic articles that have
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~093051
over 200 ducts per s~ua~e inch after firin~.
As illustrated in FIGS. 1 and 4, the passages 12
extend transversely o~ the upstream face of plate member 10
and are aligned with the direction of flow to permit flow of
material through the upstream face with a minimum of pressure
drop. It is also preferred that the ratio of the cross-
sectional area of the recessed area 26 to the combined cross-
sectional area of passages 12 be between 0.65 and 1.0, with
optimum results for extruding ceramic mixes presently being
achieved with a ratio of about 0.75.
In the extrusion of ceramic material, it has also
been found desirable to make the length of pins 14 from about
0.090-0.15 inches. If the length of pins 14 is less than
0.090 in., it has been found that it is difficult to achieve
~inished articles having uniform cross sections. If the
length of pins 14 is more than 0.15 in., excess extrusion
pressures must be used to counteract the increased frictional
resistance of a plastic ceramic mix in prolonged contact
with pins 14.
The desirable length of passages 12 is similarly
determined by (a) the need to achieve uniform flow across
each passage before material reaches recessed area 22 and (b)
the need to minimize frictional resistance of the die plate
member to material flowing therethrough. Generally, the
length of passages I2 can vary from 0.100 to 0.500 in. with
about 0.250 in. being presently preferred.
The die plate 10 is desirably formed of hot rolled,
low-carbon steel for ease of machining. ~he crystal direction
of the steel should be aligned with the direction of milling
so that it is not necessary to drill or mill across the
crystallographlc axis. Preferably, the die plate member is
coated prior to use with electroless nickel to a thickness of
-12-
lOg30Sl
0.002 in. Equally satisfactory results have been obtained
using dies machined ~ro~ solid plastic.
As best illustrated in FIG. 4, a presently preferred
alignment of the passages and pins for purposes of ease of
fabrication, and for ensuring uniform distribution of the
material about pins 14, is provided by aligning the axes of
pins 14 and passages 12 in a plurality of parallel planes.
The repeating sequence along a given plane, such as depicted
by center line 28 in FIG. 4, comprises: (1) pin, (2) passage,
(3) pin. The axis of a passage is spaced about midway along
plane 28 between the adjacent axes of the pins. The axes of
individual pins in plane 30 adjacent to given plane 28, are
(a) offset horizontally with respect to FIG. 4, from the
position of the axes of the pins in plane 26, and (b) are
approximately vertically aligned with the axes of passages
28 in plane 26.
FIGS. 2 and 3 disclose another embodiment of a die
that can be used in accordance with the process of this
invention. This embodiment is designed for extruding ceramic
articles having a plurality of longitudinally-extending
rectangular ducts.
The die of FIGS. 2 and 3 comprises an integral plate
member, generally 40, having an upstream face comprising a
plurality of spaced circular passages 42 which permit flow of
material through the upstream face of plate member 40. The
downstream face of plate member 40 is formed by a plurality of
transversely spaced rectangular pins 44 preferably having a
square cross-section. Each of the pins has a closed rect-
angular perimeter in a plane transverse of the direction of
the material flo~ through plate member 40, and extends long-
itudinally of the flow direction. Each pin 44 is separated
from other pins by an interconnected recessed area 46 that has
the desired cross-section of the product being formed by
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10930Sl
extrusion through the die.
Passages 42 terminate lon~itudinally at the upstreamend 48 of recessed area 46 with the longitudinal axis of each
passage 42 aligned ~enerally parallel to the flow direction of
material through plate member 10.
Passages 42 terminate at a plurality of laterally-
spaced locations, with four of pins 44 blocking a portion of
the cross-section of each of other than the peripheral
passages 42. The presence of four pins 44 exerts duct-
forming shearing forces on the material being extruded through
each passage and causes the material to flow transversely tofill the entire volume of recessed area 46 between upstream
end 48 and the exit face of plate member 40. Preferably,
and as illustrated in FIGS. 2 and 3, pins 44 are rectangular
solids having a square cross-section in a plane transverse
of the flow direction, hollow passages 42 have a circular
cross-section, and pins 44 and passages 42 are of constant
cross-section along their length.
As illustrated in the embodiments of FIGS. 1 and 4,
and 2 and 3, it is preferred that the exit ends of the passage
be in a common plane, and that the inlet end of the recessed
area and the upstream end of the pins lie in the same common
plane.
With reference to the process followed by the appar-
atus of FIG. 1, a batch of thoroughly mixed plastic, ceramic
material is transferred to the interior of barrel member 22.Preferably, the interior of the extruder is exhausted by
~acuum to remove all air from the admixture prior to beginning
the extrusion operation. Ram 24 is used to force material
through plate member 1~ and form a length of material contain-
lng a plurality of longitudinally-extending ducts at closely
spaced intervals across the cross-section of the extrudate.
-14-
1093051
Generally, the pressure at the upstream face of dieplate lQ during extrusion will be from 100 3000 psi depending
on the plasticity of the mix being extruded.
The webbed extrudate is cut into articles of discrete
length, preferably by a very fine diameter wire, such as a
steel or tungsten wire of about 0.002 inch diameter. The use
of a cutting wire has been found to be far superior to use of
a knife as a cutting means, as a knife generally causes tear-
ing of the duct walls, and thus blocks easy passage of fluid
through the resulting article. Generally, it is desirable to
use the finest wire available which will withstand the stress
involved in the cutting operation.
The duct-containing web members cut to discrete
lengths as described above are dried, preferably at room
temperatures for a minimum of 8 hours. A slow drying step is
necessary to avoid cracking. It is desirable to keep the
ends of the articles open to access by a drying fluid, and to
loosely cover the longitudinally-extending surface or surfaces
of the article to promote drying of interior ducts of the
article at about the same rate as the exterior surface of the
article. Desirably, the cut lengths are allowed to air dry at
room temperatures for a minimum of 8 hours. The articles can
then be placed in a forced air oven and heated from room
temperature to about 110C over a 4-hour period and held at
110C for a minimum of 1 hour. The above-described drying
procedure is desirable to avoid cracking of the cut length of
ceramic article.
In accordance with the invention, the dried shapes
are fired;`in either a ~as or electrically-heated kiln. The
shapes are desirably placed on their side and supported on a
layer of high-purity silica sand. Care should be taken to
insure that shapes are shielded from direct heat from the
-15-
109~05~
heating source~ This can be accomplished by using muffle
plates. In general ! it is desirable to conduct the heatiny
schedule ~ith the following criteria in mind: ~1) decomposition
and dehydration of various clay, talc, and binder components;
(2) formation of intermediate microstructural phases; and (3)
formation of final microstructural phases. A typical heating
schedule is described in the examples below.
In the embodiment of the ceramic article of this
invention illustrated in FIG. 5, longitudinally-extending
circular ducts 15 extend the length of cylindrical article 17.
Such an article 17 formed of cordierite has a longitudinal
compressive strength of about 5000 psi and a transverse
compressive strength along any axis transverse of the long-
itudinal axis of the article of between about 400-700 psi.
Generally, transverse compressive strength varies from about
8 to 14% of the longitudinal compressive strength of the fired
ceramic articles.
The ratio of transverse compressive strength to
longitudinal compressive strength is considerably higher than
achieved by prior art high surface area ceramic articles. For
example, a cordierite article containing rectangular, long-
itudinal ducts displays a low transverse compressive strength
of about 50 psi along a trans~erse axis that splits the 90
inte~section of a pair of duct walls.
The articles of the present invention can be fabri-
cated to have a geometric surface area of over 50 sq. in. per
cubic inch of space taken up by the exterior of the article.
For example, for a cylindrical article, over 40 sq. in. of
internal duct surface can be provided per cubic inch of volume
required to emplace the cylindrical article as measured by
Volume = ~r21 where ~ is 3.1417, r is the radius of the cylindr-
ical article and 1 is the length of the cylindrical article.
- 16 - `
~9~51
EXAMPL~S 1-10
The following exam~les illust~ate compositions
extruded successfully ~n operations in accordance with the
disclosure of this invention. In the examples and throughout
the specification, all parts and percentages of ingredients
are calculated by weight unless otherwise specified. Unless
otherwise stated, all screen sizes are U.S. Standard.
In these examples, ceramic articles are formed from
ten different batches of ingredients as listed below. Each
batch is blended by first mixing the dry ingredients about 5
minutes in a paddle mixer to uniformly disper~se these ingred-
ients. Subsequently, water, aqueous solution, or liquid
binder, used singly or in combination is added to the batch
to promote plasticity. Thorough blending imparts extrusion
consistency to the batch and thus ensures a well-formed shape.
Wet blending times in a paddle mixer vary from about 5 to
about 10 minutes.
Example 1
~; 325 grams Georgia kaolin (-325 mesh)
175 grams prochlorite talc (-325 mesh)
100 ml of 3.8% sodium ligno-sulfonate solution
35 ml of 12.5% polyvinyl alcohol solution
Example 2
325 grams Georgia kaolin (-325 mesh)
175 grams prochlorite talc (-325 mesh)
145 ml of 3.8% Darvan "C"* solution
(R.T. Vanderbilt Co~)
Example 3
1925 grams Georgia kaolin (-325 mesh)
3 350 grams ball clay (-325 mesh)
1225 grams prochlorite talc ~-325 mesh)
745 ml 3.8% sodium ligno-sulfonate solution
430 ml 9.1% polyvinyl alcohol solution
* Trademark -17`}
1093051
Example 4
1925 ~rams Georgia kaolin (:-325 mesh)
350 grams ball clay (;325 mesh)
1225 grams prochlorite talc (-325 mesh)
1350 ml of 2% methylcellulose solution
Example 5
1736 grams Georgia kaolin (-325 mesh)
315 grams ball clay :(-325 mesh)
1099 grams prochlorite talc (-325 mesh)
350 grams zirconium silicate (-200 mesh)
24.5 grams dry methylcellulose powder
1050 ml distilled water
Example 6
1736 grams Georgia kaolin (-325 mesh)
315 grams ball clay (-325 mesh)
1099 grams prochlorite talc (-325 mesh)
350 grams calcined clay (-100+200 mesh)
24.5 grams dry methylcellulose powder
: 1100 ml distilled water
Example 7
: 2625 grams Georgia kaolin (ground to -325 mesh)
350 grams ball clay (-325 mesh)
350 grams prochlorite talc (-325 mesh)
175 grams magnesium carbonate (-325 mesh
Reagent Grade)
~ 35 grams methylcellulose powder
:~ : : 1485 ml distilled water
Ex-ample 8
~; 1350 grams Georgia kaolin (-325 mesh)
600 grams ball clay (-325 mesh)
1050 grams prochlorite talc (-325 mesh)
900 grams zirconium silicate (-200 mesh)
-18-
10~3051
~8.25 grams coll~dal magnesium aluminum
si:l~cate (R- T~ Vandexbilt Co.)
90Q ml d~st~lled water
. . .
E'xample'9
892S grams'zirconium silicate (-200 mesh)
1050 grams ball clay (-325 mesh)
525 grams Georgia kaolin (-325 mesh)
210 grams Vee Gum-T
1440 ml distilled water
'Example' 10
850 grams -200 mesh A12O3 (Tabular)
130 grams -325 mesh ball clay
20 grams colloidal magnesium aluminum silicate
130 ml distilled water
The following materials used in the Examples have
the following analysis:
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~09305~
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1093051
The thoroughIy mixed batch is transfexred to the
mater~al cylinder of an extruder as schematically illustrated
in FIG. 1. The admixed compositions are subjected to a vacuum
in the extruder to remove air therefrom and are extruded
through a 3 in. diameter die having the arrangement of passages
12 and pins 14 illustrated in FIGS. 1 and 4. Extrusion speed
for the various batchesis varied between about 10 and 100
inches of product per minute depending on the extrusion force
required to force the material through the die and properly
form a continuous web structure. The pressure at the upstream
face of the die varies from 300-3000 psi depending on the
plasticity of the mixture being extruded.
The extruded material is cut into the desired
cylindrical lengths of about 48 inches using a 0.002 inch
diameter tungsten wire. The cut lengths are allowed to dry at
room temperature for about 8 hours with the cylindrical surface
loosely wrapped with porous paper or plastic film. The lengths
are then unwrapped, cut into shorter lengths, and placed in a
forced air oven and heated from room temperature to 110C
over a four-hour period and held at 110C for a minimum of
1 hour.
The drled shapes are fired ln a gas fired kiln.
The shapes are first placed on their side and are supported on
a layer of high-purity silica sand. Care is taken to ensure
that the shapes are shielded from direct heat from the heating
source. This is accomplished by using muffle plates. A
typical heating schedule is as follows:
-22-
.
1093051
H~ATING SCH~D~hE
Q to 400C at 100C/Hr
30 min. at 400C
400C to 490C at 90C/Hr
1 Hr at 490 C
490 to 590C at 90C/Hr
1 Hr at 590C
590 to 620C at 60C/Hr
1 Hr at 620C
620 to 780C at 90C/Hr
30 min. at 780C
780 to 980C at 100C/Hr
30 min. at 980C
9~0 to 1080C at 100C/Hr
~; ~15 1 Hr at 1080C
1080 to 1180C at 50C/Hr
30:Min. at 1180C
: 1180 to 1300C at 50C/Hr
2 Hr at 1300C
20~ COOL
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-23-
-
~Q93051
The fired articles haye the hexagonally packed duct
arrangement of FI~. 5. The cord~erite articles of Examples
1-8, and 10, exhibit a longitudinal compressive strength of
about 5000 psi and a transverse compressive strength that
varies from about 400 to 700 psi, and exhiblt about 15-18%
water absorption after firing.
Example 11
In this Example, 1400 grams Georgia kaolin; 400
grams of Victoria clay; and 1400 grams talc, each having the
original analysis listed above and then screened to remove
+100 mesh material; and 800 grams of fused cordierite (-200
mesh) are dry blended in a paddle mixer for five minutes.
Subsequently, 60 grams of Vee Gum-T (a colloidal magnesium
aluminum silicate, sold by R. T. Vanderbilt Co.), and 1040 ml
of distilled water are added and the mixture is blended for
5 more minutes in a paddle mixer.
The thoroughly mixed batch is transferred to the
barrel of an extruder as schematically illustrated in FIG. 1.
The admixed composition is subjected to a vacuum in the
extruder to remove air therefrom and is extruded through a
5 in. diameter die having the arrangement of passages 12 and
pins 14 illustrated in FIGS. 1 and 4. The die has a thic~ness
of about 0.250 and the pins are about 0.125 in. long. The
pins are densely packed, abaut 154 pins per square inch of
downstream face of the die. Extrusion speed for the batch is
abaut 36 inches of product per minute. The pressure at the
upstream face of the ~ie is about 200 psi.
The extruded material is cut into cylindrical
shapes having a length of about 7 inches using a 0.002 inch
diameter tungsten wire. The cylindrical shapes are allowed to
dry at room temperature for about 8 hours with the cylindrical
-24-
iO9305~
wall surface loosely wrapped with paper o~ pl~stic sheet.
The lengths are then placed in a forced air oven and heated
~rom room temperature to 110C over a four-hour period and held
at 110C for 1 hour.
The dried shapes are fired in a gas fired kiln. The
shapes are first placed on their side and are supported on a
layer of high-purity silica sand. Care is taken to ensure that
the shapes are shielded from direct heat from the heating source.
This is accomplished by using muffle plates. The heating
schedule is the same as described in Examples 1-10.
The resulting fired cordierite articles have a
longitudinal compressive strength of about 5000 psi and a
transverse compressive strength of about 500 psi.
FIGS. 7 and 8 illustrate an embodiment of a hollow
mill cutting tool that is particularly adapted for forming
cylindrical pins, such as pins 14 illustrated in FIGS. 1 and 4.
In general, the cutting tool forms a cylindrical pin by
removing material that ~ies adjacent the cylindrical surface of
the pins.
The cutting tools of FIGS. 7 and 8 include a
generally cylindrical member 50 that terminates in a tip
portion 52 that has a toroidal eross-section. The axis of tip
portion 52 is aligned with the axis of eylindrieal member
generally 50.
Tip portion 52 includes a pair of forward helical
surfaees 54 that each terminate at their forward end in a
eutting edge 56. Cutting edges 56 extend across the thiekness
of the toroidal eross-section of tip member 52. Eaeh forward
helical surface extends rearwardly along a cylindrical path
from cutting edge 56 at an angle as illustrated in FIG. 7 of
from 9 to 11 with a plane trans~erse of the longitudinal axis
of cylindrical member, generally 50. The angle ~ , as
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109~051
illustrated in FIG. 7 is important to obtaining good cuttingaction from the cutting tool, which as viewed in FIG. 7 is ro-
tated in a clockwise direction during cutting operations. As
illustrated in FIG. 7, the angle ~ is defined as the angle
between a plane transverse of the longitudinal axis of cylind-
r~cal member generally 50, and the angle at which forward
helical surface 54 extends rearwardly along a cylindrical path
from cutting edge 56. If the angle ~ is less than 9, very
little cutting action is obtained. If the angle ~ is over
11, the strength of the cutting tool is reduced near the
cutting edges. Preferably, the angle ~ is 10.
A plurality of back helical surfaces 58 are provided
with each back helical surface 58 connected to one forward
helical surface 54 preferably with a smoothly-curved portion
connecting these two helical surfaces. Each back helical
surface adjacent its rearward end, and at approximately a
longitudinal distance from cutting edge 56 that corresponds to
the desired length of the cylindrical pin being machined, is
inclined at an angle ~ as illustrated in FIG. 8 of at least
55 to a plane parallel to the axis of cylindrical member 50,
with a presently preferred angle /~ being 55. It is important
that back helical surface be inclined at an angle of at least
55 to insure the presence of clearance for discharge of
displaced material away from the cutting tool during cutting
operations.
A plurality o~ generally longitudinally-extending
surfaces 60 are provided, with one of the longitudinally-
extending surfaces connected at one end to one of the forward
helical surfaces 54 to form a cutting edge 56. The other end
of each longitudinally-extending surface 60 is connected to the
rear end of an adjacent back helical surface 58.
- 26 -
