U.S. patent number 3,804,701 [Application Number 05/385,994] was granted by the patent office on 1974-04-16 for insulating compositions and structures formed therefrom for use in hot topping comprising fibrous wollastonite.
This patent grant is currently assigned to Oglebay Norton Company. Invention is credited to James A. Bognar.
United States Patent |
3,804,701 |
Bognar |
April 16, 1974 |
INSULATING COMPOSITIONS AND STRUCTURES FORMED THEREFROM FOR USE IN
HOT TOPPING COMPRISING FIBROUS WOLLASTONITE
Abstract
Insulating compositions and hot topping structures formed
therefrom comprising from about 5 to about 95 wt. % fibrous
Wollastonite; at least about 3 wt. % of a second fibrous material
which may be inorganic, organic, or a mixture of both; from 0 to
about 90 wt. % of an inorganic particulate filler; and from about 2
to about 8 wt. % of an inorganic or organic binder.
Inventors: |
Bognar; James A. (North
Olmsted, OH) |
Assignee: |
Oglebay Norton Company (County
of Cuyahoga, OH)
|
Family
ID: |
23523723 |
Appl.
No.: |
05/385,994 |
Filed: |
August 6, 1973 |
Current U.S.
Class: |
428/66.3;
106/38.3; 428/220; 428/526; 524/35; 106/38.22; 106/38.27; 428/177;
428/436; 524/9 |
Current CPC
Class: |
C04B
14/46 (20130101); C04B 14/465 (20130101); B22D
7/10 (20130101); C04B 35/22 (20130101); Y10T
428/24653 (20150115); Y10T 428/31949 (20150401); Y10T
428/31627 (20150401); Y10T 428/214 (20150115) |
Current International
Class: |
C04B
14/38 (20060101); B22D 7/10 (20060101); C04B
35/16 (20060101); C04B 35/22 (20060101); B22D
7/00 (20060101); C04B 14/46 (20060101); B28b
007/36 (); B32b 019/02 (); C08g 051/18 () |
Field of
Search: |
;260/17.2,38,39SB
;106/38.27,38.22,38.3,17.3 ;161/165,168 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Chem. Abst. 71:116153X; Schutt, "Non-Flaking Crack Resistant
Coating For Rocket and Refractory Uses." .
Chem. Abst. 73:38148Z, Anzalone, "Wollastonite-Mineralizer-Silica
Refractories-Arc Furnace Roofs." .
Chem. Abst. 75:132557v, Alexenco, "Ceramics for Wall
Coverings.".
|
Primary Examiner: Short; William H.
Assistant Examiner: Woodberry; Edward
Claims
1. An insulating composition for use in hot topping comprising, on
a dry basis, from about 5 to about 95 wt. % fibrous Wollastonite;
at least about 3 wt. % of a second fibrous material selected from
the group consisting of inorganic fibrous materials, organic
fibrous materials and mixtures thereof, said inorganic fibrous
material being present in an amount within the range of 0 to about
20 wt. % and said organic fibrous material being present in an
amount within the range of 0 to about 8 wt. %; an inorganic
particulate filler present in an amount within the range of 0 to
about 90 wt. %; and from about 2 to about 8 wt. % of a binder
selected from the
2. The composition defined in claim 1 wherein said second fibrous
material
3. The composition defined in claim 1 wherein said second fibrous
material
4. The composition defined in claim 1 wherein said inorganic
particulate
5. The composition defined in claim 1 wherein said binder comprises
a
6. An insulating composition for use in hot topping comprising, on
a dry basis, about 8 wt. % fibrous Wollastonite, about 4 wt. %
second inorganic fibrous material, about 3 wt. % cellulosic pulp,
about 80 wt. % powdered
7. An insulating composition for use in hot topping comprising, on
a dry basis, about 94 wt. % fibrous Wollastonite, about 1 wt. %
second inorganic fibrous material, about 2.5 wt. % cellulosic
fiber, and about 2.5 wt. %
8. An insulating structure for use in hot topping defined by a body
having a thickness within the range of about one-half inch to about
13/4 inch, at least in part formed of a composition comprising, on
a dry basis, from about 5 to about 95 wt. % fibrous Wollastonite;
at least about 3 wt. % of a second fibrous material selected from
the group consisting of inorganic fibrous materials, organic
fibrous materials and mixtures thereof, said inorganic fibrous
material being present in an amount within the range of 0 to about
20 wt. % and said organic fibrous material being present in an
amount within the range of 0 to about 8 wt. %; an inorganic
particulate filler present in an amount within the range of 0 to
about 90 wt. %; and from about 2 to about 8 wt. % of a binder
selected from the group
9. The insulating structure defined in claim 8 wherein said body is
formed entirely from said composition, said structure having a
thickness within
10. The insulating structure defined in claim 9 in the shape of a
board.
11. The insulating structure of claim 9 in the shape of a curved
board.
14. The insulating structure defined in claim 9 wherein said
composition comprises, on a dry basis, about 8 wt. % fibrous
Wollastonite, about 4 wt. % second inorganic fibrous material,
about 3 wt. % cellulosic fiber, about 80 wt. % powdered
Wollastonite and about 5 wt. % phenol-formaldehyde resin binder.
Description
BACKGROUND OF THE INVENTION
This invention relates to the hot topping art and more particularly
to insulating compositions and structures formed therefrom for use
in hot topping.
As is well known in the art, the principal use of hot tops is in
the manufacture of steel ingots. Conventionally, hot tops are
either superimposed upon, or are inserted into the top of the ingot
mold and act as reservoirs to feed molten metal to the ingot mold
during the process of ingot formation.
As molten steel cools and solidifies, it shrinks. The cooling
occurs more rapidly near the peripheral walls of the ingot mold
than in the center of the ingot. Accordingly, a shrinkage cavity
tends to form vertically through the center of the body of metal in
the ingot mold, as the molten metal in the center feeds itself
downwardly and outwardly in response to the lessening volume of
cooler metal near the periphery.
Impurities as well as certain formulated ingredients in the steel
composition tend to migrate toward the ever-decreasing pool of
molten metal, resulting in a segregation of these impurities and
formulated ingredients in the last metal to solidify. This portion
is unusable and must be discarded, reducing the volume of sound
metal which can be obtained from the ingot.
By superimposing or inserting a hot top in the ingot mold or by
insulating the top portion of the mold to form an in-the-mold hot
top, the effect is one of minimizing or eliminating the shrinkage
cavity in the body of the ingot by maintaining a reservoir of
molten steel in the hot top which feeds the ingot. This permits
recovery of a higher percentage of sound metal from the metal
forming the ingot.
To insure that the hot top serves its function of feeding molten
metal to the ingot mold as the metal in the latter solidifies, the
interior surfaces of the hot top are provided with a lining of
highly insulative material which slows the transfer of heat out of
the molten metal. Since the ingot mold is not insulated, its
contents will cool before the contents of the hot top do. The
present invention is addressed to providing improved insulating
compositions and structures formed therefrom for use in hot
topping.
The insulating compositions and structures of the present invention
are particularly useful in connection with so-called "reusable" hot
tops. These comprise outer shells of cast iron or the like formed
integrally with or separately from the ingot mold, and an
insulating lining which is replaceable. The replaceable lining is
generally formed from at least one, but frequently a plurality of
self-supporting panels or boards which will generally range from
about one-half inch to not more than about 11/4 inch in thickness.
The shape of the panels or boards will conform generally to the
surface configuration of the hot top, and accordingly, may be flat
or curved. In some instances, the board is formed of a plurality of
connected sections of flat or curved elements which may be folded
to form two or more sides of the lining.
In addition to the replaceable panels or boards, many hot tops in
use today are provided with a replaceable bottom ring or gasket. By
convention the structure is referred to as a "bottom ring" when
associated with in-the-mold hot tops, and a "gasket" when
associated with superimposed hot tops. The bottom ring or gasket,
which may be from one-half to 13/4 inches thick, is disposed at the
bottom of a hot top and forms a seal between the hot top casting
and the ingot wall to prevent molten metal leakage between the
juncture; protects the hot top casting from molten metal; seals off
molten metal leakage behind the insulating liner; and supports the
lower edges of the replaceable panels or boards.
While the insulating composition forming a bottom ring may be the
same as that forming the panels or boards, it is generally
preferred that a gasket be formed of a composition which is softer,
less dense, and more resilient than that forming the boards or
panels. A softer and more resilient gasket forms a better seal with
the bottom edges of the panels or boards, and between the hot top
and ingot mold.
In addition to possessing a low coefficient of thermal
conductivity, compositions useful in forming panels, boards and
bottom rings for hot tops preferably possess no more than nominal
quantities of water and decomposable organic constituents, and
should be relatively free of materials which will adversely affect
the quality of the steel being manufactured. The panels should be
light weight to facilitate handling.
The compositions of the present invention fall within the foregoing
criteria and in addition, permit the formation of structures which
have a wide variety of densities, ranging from about 30 lbs. per
cubic foot to about 60 lbs. per cubic foot. Moreover, the
compositions have proven to be suitable replacements for insulating
compositions employing silica and asbestos.
It is therefore an object of the present invention to provide
improved insulating compositions for use in hot topping.
A further object of the invention is to provide improved hot
topping structures, such as panels, boards, and bottom rings and
gaskets formed of improved insulating compositions.
Another object of the invention is to provide insulating
compositions for use in hot topping which have very good thermal
insulating properties, are relatively free of water, and contain
only nominal quantities of decomposable organic materials.
Yet another object of the invention is to provide insulating
compositions which can be formed without the use of asbestos or
silica.
A further object of the invention is to provide improved hot
topping structures having densities within the range of about 30 to
about 60 lbs./ft..sup.3.
These and other objects and advantages of the invention will become
apparent from the following detailed discussion, including the best
mode presently contemplated for practicing the invention.
In accordance with one aspect of the present invention, there is
provided a composition comprising, on a dry basis, from about 5 to
about 95 wt. % fibrous Wollastonite; at least about 3 wt. % of a
second fibrous material selected from the group consisting of
inorganic fibrous materials (i.e., other than fibrous
Wollastonite), organic fibrous materials and mixtures thereof, the
inorganic fibrous material being present in an amount within the
range of 0 to about 20 wt. % and the organic fibrous material being
present in an amount within the range of 0 to about 8 wt. %; an
inorganic particulate filler present in an amount within the range
of 0 to about 90 wt. %; and from about 2 to about 8 wt. % of a
binder selected from the group consisting of inorganic or organic
binders.
Wollastonite is a naturally occurring calcium metasilicate. It is
the only pure white mineral available commercially which is wholly
fibrous. Fiber lengths average thirteen to fifteen times the
diameter. The properties of Wollastonite are as follows:
Chemical Formula CaSiO.sub.3 Molecular Weight 116 Crystaline
Structure acicular Specific Gravity 2.9 Coefficient of Expansion
(mm/.degree.C) 6.5 .times. 10.sup.6 Refractive Index 1.63
Transition Point 1200 (to pseudo-Wollastonite, .degree.C) Melting
point (.degree.C) 1540 Solubility in H.sub.2 O (gm/100 cc) 0.0095
Hardness (Mohs' scale) 4.5 Color Brilliant White Weight (lbs./solid
gallon) 24.2 Bulking Value (Gal./lb.) 0.0413 pH (10% slurry) 9.9
Moisture Content (per cent) 0.5
Wollastonite is also available in powder form, and as such can be
used as the inorganic particulate filler ingredient of the
composition as described more fully hereinafter.
Consistent with the function of fibrous materials, fibrous
Wollastonite serves to provide high green strength for hot topping
structures formed from compositions containing the same.
Compositions of the present invention should also contain, in
addition to the fibrous Wollastonite, at least about 3 wt. % of a
second fibrous material selected from the group consisting of
inorganic fibrous materials, organic fibrous materials and mixtures
thereof. This second fibrous material tends to enhance the green
strength of the compositions since these fibers are generally
longer than Wollastonite fibers. Suitable inorganic materials
serving this function include rock wool, slag wool, glass fiber and
the like. Cellulosic fiber, e.g. finely divided paper or paper
fiber, is the least expensive and most readily available organic
fiber, although other synthetic organic fibrous materials may also
be used.
While it is not necessary to use more than about 3 wt. % of a
second fibrous material, under certain circumstances it may be
desirable to use higher amounts. However, it has been found in
general that where an inorganic fibrous material is employed, its
concentration should not exceed about 20 wt. %, and where an
organic fibrous material is employed, its concentration should not
exceed about 8 wt. %.
As the inorganic particulate filler material which may be present
in an amount within the range of 0 to about 90 wt. %, use may be
made of a wide variety of conventional materials such as the
diatomaceous earths, perlite, burnt rice hulls, olivine, kyanite,
mullite, fly ash and the like. A preferred inorganic particulate
filler material is powdered Wollastonite, due to its relative
purity, low water content and essential freedom from uncombined
silica.
Both fibrous and powdered Wollastonite are available from Interpace
Corporation. The fibrous grade Wollastonite is sold under the
designation F-1, and powdered Wollastonite under a variety of
designations, the most preferred of which is C-6. This powdered
Wollastonite comprises almost 90% minus 200 mesh (74 micron)
particles by wet sieve analysis.
The preferred binder is a phenol-formaldehyde resin, although other
organic, e.g. urea-formaldehyde resins, and inorganic, e.g. sodium
silicate, binders may also be used.
Compositions of the present invention may be prepared by adding the
fibrous ingredients, e.g. the fibrous Wollastonite and second
fibrous material to water with adequate stirring to uniformly
disperse the fibrous materials in the water. Thereafter, the
inorganic particulate material and the binder are added with
stirring until uniformly dispersed.
The slurry is then placed in a suitable mold dimensioned to the
shape of the desired hot topping structure, e.g. a panel, board,
wrap-up liner, or gasket.
The mold preferably is a filtering-type mold having foraminous
surfaces. If desired, the rate of dewatering can be increased by
applying vacuum, pressure, or both to the mold and its contents.
The compositions of the present invention have proved particularly
suitable for forming with a pressure differential dewatering
technique in a filtering-type mold.
Where dimensional stability is important, the molded structure
should be at least partially dried within the mold.
It has been found that for most purposes, adequate dimensional
stability is achieved by partially drying the structure in the mold
and then removing the structure from the mold and free-drying it.
Where a very high level of dimensional stability is required, the
structure may be completely dried while in the mold.
EXAMPLE I
A 52% uniform slurry of, by weight, water, 1.22% of rock wool,
18.3% of a 5% aqueous dispersion of pulp stock, 2.52% of F-1
fibrous Wollastonite, 24.43% of C-6 Wollastonite powder and 1.53%
of phenol-formaldehyde resin was made by stirring to produce
uniform dispersment.
The composition was then poured into molds, dewatered and dried.
The resulting composition had a density of about 55 lbs. per cubic
foot. On a dried basis, this produced a composition in the
following proportions:
Fibrous Wollastonite 8 wt. % Rock Wool 4 wt. % Paper Fiber 3 wt. %
Powdered Wollastonite 80 wt. % Resin Binder 5 wt. %
EXAMPLE II
A lower density product was prepared in a manner similar to that
described in Example I, the ingredients being present in the
proportions indicated below (dry basis):
Fibrous Wollastonite 94 wt. % Paper Fiber 2.5 wt. % Glass Fiber 1
wt. % Resin Binder 2.5 wt. %
This composition produced a structure which was much softer than
that produced from the composition of Example I, and which had a
density of about 31 lbs. per cubic foot. This composition was
deemed to be more useful in the manufacture of gaskets than panels
or boards, while the denser composition of Example I was deemed to
be more useful in the manufacture of panels or boards.
EXAMPLE III
An intermediate density product was prepared in a manner similar to
that described in Example I, the ingredients being present in the
proportions indicated below (dry basis):
Fibrous Wollastonite 20 wt. % Glass Wool 8 wt. % Perlite 3.5 wt. %
Powdered Wollastonite 65 wt. % Resin Binder 3.5 wt. %
This composition provided a structure having a density of about 42
lbs./ft..sup.3, using inorganic fibrous materials exclusively.
EXAMPLE IV
Another intermediate density product was prepared in a manner
similar to that described in Example I, the ingredients being
present in the proportions indicated below (dry basis):
Fibrous Wollastonite 30 wt. % Paper Fiber 6 wt. % Powdered
Wollastonite 60 wt. % Resin Binder 4 wt. %
This composition provided a structure having a density of about 43
lbs./ft..sup.3, using a second fibrous material consisting of
organic fibers.
The compositions of Examples III and IV produced insulating panels
exhibiting a high degree of impact resistance and an ability to
undergo moderate bending without breaking.
Although the compositions of the present invention permit the
exclusion of asbestos and silica, it will be appreciated that the
invention may be practiced with the inclusion of these
ingredients.
* * * * *