Note: Descriptions are shown in the official language in which they were submitted.
~32~
File
8803
TITLE~ Making a ~aphole
BACKGROUND OF THE INVENTION
This invention concerns a method of making a preformed
taphole and a refractory composition for use therein.
Tapholes are openings, usually round, in the wall of a
melting furnace such as a BOF furnace or other metal melting
furnace through which molten metal and/or slag can be poured
when the furnace i~ tilted or when a plug or other closing
device in the ~aphole is removed. Tapholes are generally made
o~ refractory material which is compatlble with the refractory
material used in lining the furnace or other molten metal
container.
As the steel or other molten metal pours through the
taphole, it causes wear on the re~ractory making up the
taphole. ~enerally, the refractory making up the taphole
wears much faster than the refractory making up the furnace
lining and therefore the taphole has to be replaced on a
20 regular basis during the life of the lining.
While it is possible ko repair the taphole in place, for
example by gunning refractory around a form placed in the old
taphole (which has become enlarged by wear), such repair is
les~ than totally satisfactory. Since such repairs have to be
made on a hot furnace (it not being economical to cool the
furnace down to make the repair), the refractory forming the
repaired taphole is of lesser strength and density, due to the
increased amount oP water required to gun refractory material,
and hence will last for an even shorter time, than a taphole
30 formed by meth~ds such as casting or pressing, methods which
result in greater density and strength but which cannot be
used to repair a hot furnace.
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Accordingly, it has become the practice to preform
refractory tapholes and then place them in tha furnace to be
repaired, the preformed taphole being held in place by, for
example, refractory material gunned around it.
Generally, such preformed tapholes are made by forming
suitable refractory material, for example by casting, about a
hollow metal pipe used as a form. In the first few seconds
that molten metal flows through the taphole so formed, it
washes away the metal and thereafter the refractory channels
the metal flow.
This invention is concerned with a method of making an
improved preformed taphole and particularly with a refractory
composition useful in making such an improved taphole.
SUMMARY OF THE INVENTION
According to this invention, an improved preformed
taphole can be made by the method comprising (1) selecting a
metal pipe of the desired length and diameter, (2) admixing
(a~ from 1% to 8% of a water soluble binder, (b) from O.l~ to
2% of metal fibers, (c) and 0 5~ to 5% of graphite with (d)
20 refractory grain making up the balance of the admixture, all
percentages being by weight and based on the total weight of
the admixture, ~3) adding sufficient tempering liquid to the
admixture to make a formable refractory mass, (4) forming the
tempered admixture about khe outer sur~ace of the metal pipe,
and (5) drying the so-formed refractory mass to mak~ a
preformed taphole.
BRIEF DESCRIPTION OF THE DRAWING
The drawing is a perspective view of a preformecl taphole
which can be made by the method o~ this invention.
DETAILED DESCRIPTION OF THE INVENTION
The pipe used as a ~orm about which to mold the
refractory can be of any metal, for exampl~ aluminum, but
u ~
generally will be of iron or steel. Commonly steel pipe is
used. The diameter o the pipe will be chosPn to conform to
the size of taphole desired by the customer ~e.g., a
steelmaker) and the length also will be chosen to fit the
particular furnace in which the taphole is to be used.
Generally, the steel pipe will be longer than the refractory
wall thickness of the furnace. The wall thickness of the
steel pipe is not critical, for example it can be from 1/8
inch to 1/4 inch; generally the steel pipe will be the
thinnest which can be used in the forming process and which
can be shipped and handled without deforming.
The aggregate used ln the refractory surrounding the pipe
should be compatible with the refractory making up the lining
into which the taphole is to be place. Generally, this will
be a basic lining such as periclase or periclase/chrome. A
particularly preferred aggregate is high purity periclase,
i.e., one containing 95% or more MgO. The aggregate will be
sized, as is well known in the industry~ to provide maximum
packed density.
The water soluble bond can be any such material or
combination of materials compatible with the aggregate and
able to provide a strong bond in the composition. Such bonds
are well known in the refractory art; a particularly preferred
one is shown in the example below.
The metal fibers may be any such; preferably they will
have a length of from 1 to 3 cm and a diameter of 0.2 to 0.6
mm. Usually the fibers will be steel and most preferably
stainless steel. A variety o~ such metal fibers are
commercially available.
The graphite used may be any of various commercially
available graphites but a preferred graphite is the type
known, from its morphology, as flake graphite~ It will
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pre~erably be of a size so that at least 90% of it is larger
than 0.05 mm.
In ~orming the taphole, the requisite amounts of
re~ractory aggregate, bond, fibers, and graphite will be
admixed in a suitable mixer, for example a Hobart epicyclic
mixer, as is well known in this art. A tempering liquid,
usually water but other liquids such as alcohol might be used
in particular cases, is then added to the admixture. The
amount of tempering liquid will depend on the ~orming method
to be used. A pxeferred forming method is casting and this
will generally require from about 3 ~ to about 8 ~ water,
based on the weight of dr~ ingredients. For pres~ing, on the
other hand, a much smaller amounk, perhaps about 2% water,
will be used.
The tempered refractory admixture is then placed about
the metal pipe. As mentioned, placement by casting the
re~ractory about the metal pipe as the inner form, and using a
removable sleeve, for example a split steel pipe, as the outer
form, is a preferred forming m~thod~ The thickness of the
20 refractory may be, ~or example, from 3/4 inch (2 cm) to 2
inches (5.1 cm)O
The refractory will be placed completely about the
circum~erence of the metal pipe, but will generally not extend
to both ends of the pipe. In some cases, it may be terminated
short of each end of the pipe, as shown in the drawing,
wherein the preformed taphole is indicated generally by the
numeral 11, the metal pipe by 12, and the re~ractory by 13.
The reason for the pipe to extend beyond the refractory is to
provide means to handle the pre~ormed taphole without damaging
30 the re~ractory and also to prevent damage due to inadvertent
hitting o~ the taphole against the furnace or other structure.
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The formed taphole will then be dried or otherwise cured
(depending on the type of bond used) before being shipped to
the customer, who will install it i~ his ~urnace or other
device.
EXAMPLE
A taphole was made according to this invention by
admixing 97.9 parts by weight sized periclase grain with 0.8
part aluminum sulfate, 0.7 part boric acidl 0.6 part citric
aoid, 0.5 part F-310 stainless steel fibers 3/4 inch (19 mm)
10 long, and 1.0 part natural flake graphite.
The periclase had the following typical chemical
analysis: 0.8 % CaO, 0.3 % sio2, 0.2 % Fe2O3, 0.05 % A12O3,
less than 0.02 % B2O3, and ~by difference) 98.6 % MgO, and was
sized so that all passed a 3 mesh screen (i.e., was finer than
6.7 mm) and 22 % passed a 100 mesh screen (i.e., was finer
than 0.15 mm).
The aluminum sulfate~ boric acid, and citric acid were
the commercially available materials described in detail in US
Patent 3,~79,208.
The dry ingredients were mixed in an epicyclic Hobart
mixer for 1 minute and then 5 % water (based on the weight of
dry ingredients) added and the mixing continued ~or a further
4 minutes.
The admixture was then cast about a 6 inch (15 cm)
diameter steel pipe 5 ~eet (1.5 m~ long and having a wall
thickness of 3/16 inch (5 mm). A steel form of 7.5 inches tl9
cm) inner diameter was placed concentrically about the metal
pipe and the refractory admixture cast between the two using
vibratisn to obtain maximum density.
The taphole thus formed was stripped of the outer form
after setting at ambient tempsrature over night and then was
heated on a preset schedule to a temperature of 600 F (315
1 ~2 ~ `3
C) over a period of 30 hours be~ore being shipped to the
customer.
Pre~vrmed tapholes made according to this invention were
installed in BOF furnaces in a steelmaking plant. In the
newest furnace, the tapholes made according to this invenkion
had an average life o~ 48.6 heats, and in the oldest furnace
an average life o~ 32.3 heats. This compares ko an average
life for prior art preformed tapholes not containing the
combination of graphite and metal fibers of 33 heats in the
newest ~urnace and 22.5 heats in the oldest ~urnace.
While the reasons ~or the superior per~ormance o~
tapholes made with the combination of metal ~ibers and
graphite is not fully understood, and it is not desired to be
bound to any particular theory, it is believed that the
graphite prevents slag penetration into the refractory,
allowing the metal fibers to perform their strengthening and
reinforcing function for a longer time.
In the specification and claims, percentages and parts
are by weight unless otherwise indicated. Mesh sizes referred
20 to herein are Tyler standard screen sized which are defined in
Chemical Engineers' Handbook, John S. Perry, Editor-in-Chief,
Third Editlon, 1950, published by McGraw Hill Book Company, at
page 963. Analyses of mineral components are reported in the
usual manner, expressed as simple oxides, e.g. MgO and SiO
although the components may actually be present in various
combinations, e.g. as a maynesium silicate.
