Note: Descriptions are shown in the official language in which they were submitted.
1a~7~1L379
The present invention is directed to a mold ~or
forming a nodularizing catalyst for use in nodulari2ing
iron. This application is a di~ision of copending Canadian
application Serial No. 254~177 filed June 7, 1976.
The ability to nodularize cast iron was signifi- ¦
cantly advanced some 30 years ago when it became known that
magnesium, rare earth metals, calcium or their alloys
(hereinafter referred to as the alloy), will reliably
condition a molten iron charge to form nodular graphite
upon solidification. Since that time, the art has moved
progressively from (a) adding the alloy to the molten iron
charge in the ladle by such methods as plunging, immersion
or the sandwi~ch technique, to (b) adding the alloy to the
molten charge in a stream immediately before entering the
mold, and finally to (c) adding the alloy into a portion
of the gating system within the mold. - ~
The earliest use of adding the alloy to a portion ~i
of the gating system in the mold was developed particularIy
with respect to inoculation, a form of cast iron and nodular '~
iron conditioning which not only heralded the way but
proved that total nodularization can be carried out
within the mold. All of the in-the-mold techniques have
possessed one common characteristic, namely: the alloy
has been introduced in a particulate or powdered form or
a compact made of these. The particulate alloy was (1)
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introduced in measured scoops spilled into a reaction
chamber defined in a sand~mold or (2) the alloy was
premolded in particulate form within a ~oam suspension ~ i~
- defining the gating system, or (3) a precompacted or
extruded shape of particulate magnesium alloy was placed
in the gating system contacting only one supporting surface.
The latter has only been conceptually brought forth; it -
has not been used in a practical manner to date.
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1071379
This progression of technology has resulted in a
more matched use of magnesium or other nodulariziny agent
with the needs of the specific casting, it has eliminated ~:
fading effects associated with the use of the alloy, ¦:
eliminated flare and other environmental problems, and
has aided in reducing costs. Nonetheless, there still
remains the likelihood of (a) defects in the casting
resulting from undissolved or nonuniformly mixed
particulate nodularizing agent which has floated or has
been carried into the cavity, (b) variable segregation of
the alloy or a variable solubility rate causing a metal~
lurgical variation in the casting, (c) unnecessary waste
resulting from expansion of the volume of the gating system
to accommodate the particulate matter, (d) the inability
to closely target the minimum amount of magnesium to
obtain complete or partial nodularization, (e) slag
defects in the casting resulting from the greater surface
oxidation of the selected nodularizing agent used in
particulate form, ~f) the lnability to remove the alloy
from unpoured molds, thus deteriorating the molding
properties of the sand mixture in said unpoured molds.
Even if the nodularizing agent was used in a very ~ -
; elemental.cast form, prior to its being ground and sized
into a particulate or powder form, such cast form would . .:
not achieve the objec:ts of this inventicn because ~a) it .
is not in a condition which will fit the variety of sizes
and quantities required of different cast.ing applications ~
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- without special tail~oring a specific such application, ~b)
the cast form usually is not made and therefore cannot be
later converted to an angular form which may be required for
a ~redeterminod solution rate, and (o) the cast ~orm
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~L~7~L379 t
~enerally has not been able to be made in thjcknesses greater
- than 1.25 inches without encountering significant segregation
within the interior o~ the cast form.
The invention of the parent application referred to
above and out of which this application is divided is directed
to the provision of nodularizing catalysts in modular form
suitable for manual breakage into any desired block con-
figuration and thereby facilitate the neeas of a variety of
different casting applications without the necessity for
tailoring the specific nodularizing agents for each individual
application. The present invention is directed to a mold for
use in forming such modular form nodularizing catalyst.
In a~ccordance with the present invention, there is
provided a metal mold for casting magnesium ferrosilicon or
equivalent nodularizing catalysts, comprising: (a) a metal
drag defined as a shallow pan having a flat interior bottom
and a peripheral wall; (b) a metal cope defined as a cover
effective to extend across the peripheral wall of said drag
and thereby close the interior, the cope having ribs on the
bottom thereof, which face the interior of the drag, the
bottom and ribs of the cope constituting a mold surface in
conjunction with the interior sides and bottom of the drag
to define a cast body, the cope bottom being spaced from the
drag when in the closed condition to define a sheet-like
mold cavity havlng a width and length considerably greater
than the thickness thereof, the ribs penetrating below the
cope bottom no greater than 80~ of the thickness of the
cavity, the ribs being arranged in a grid pattern with the
- module o~ the grid being generally equal to the thickness of
the cavi~y; and (c~ means defining a fluid connection for
introducing a molten charge of nodularizing catalyst through
the interior of the closed pan and cover.
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:107~3'79
The i.nvention is described further, by way of
illustration, with reference to che accompanying drawings,
in which:
Figure 1 is a sectional elevational view of a mold
useful for producing the nodularizing catalyst and con-
structed in accordance with one embodiment of this
invention;
Figure 2 is a plan view of the mold construction
shown in Figure l;
Figure 3 is a sectional elevational view, sub-
stantially schematic for a mold system for making cast iron
utilizing a precast nodularizing catalyst produced in the
mold of Figures 1 and 2; and
Figure 4 is a plan view of the mold system of
Figure 3
As shown in Figures 1 and 2, a preferred construc-
: tion of a mold provided in accordance with this invention is
comprised of a shallow pan-like molding base (drag 10) and :
a flat cover (cope 11) adapted to fit so as to close off the~ -
interior of the pan. The cope and drag are each constituted
of metal and have a sufficient thickness to provide a pre- .
determined rate of cooling for the molten catalyst charge to `:
be introduced into the covered mold. The interior 20 of the
- . drag is defined by a generally flat bottom surface 13 and a
continuous upright peripheral surface 14. The surface 14 may
: have a slight taper to accommodate stripping of the mold from
the drag, preferably in the range of 3 to 8. The cope has a ~:
flat interior surface 15 substantially parallel to the bottom
surface 13 of the drag when the cover i9 in the closed con-
` 30 dition, as shown in Figure 1. The interior surface 15 is
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interrupted by a pIurality of depending ribs 16 which are
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~L~7~379
arranged in a predetermined ~attern as best illustrated in
Figur~ 2. The ribs each have slanted sides 16b meeting at an
apex 16a, the apex penetrates or projects into the interiox
of the cavity defined by the drag to a distance roughly
half the depth defined by the cavity in the closed condition.
The projection or penetrating distance 18 of each of the
ribs is designed to imprint a perforation or groove line
into the resulting cast nodulariæing ca-talyst sheet so that
the sheet product may be broken into a desired number of
modules cons~ituting said pattern. The module i5 determined
by the spacing between the ribs in either direction of the
cast product. The module is preferentially selected to have
a dimension which is generally square. The module is designed
to accommodate the smallest or minimum casting charge with
which the nodularizing catalyst is to be used. As a practical
application, the distance 19 between the apices 16a of ribs,
taken in one direction, is about 2 inches. The thickness of
~ height 17 of the cast product is preferentially in the range
; of 0.5 to 4.0 inches, this being considerably greater than
the thickness range capable of being cast by the prior art
techniques without encountering signi~icant segregation in
the interior of the cast product.
A fluid gating means 21 may be provided, such as
by defining a mouth in the cover through which a molten
chaxge of the nodularizing catalyst may be pour~d. The
nodularizing catalyst is essentially comprised of a nodu-
larizing element selected from the group consisting of
magnesium, cerium, calcium and rare earth metals, the
selected element being alloyed with iron and silicon in a
homogeneous form substantially devoid of segregation and
oxides on the interior thereo~. The oxides are substantially
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eliminated by maintaining the product in the as-cast form
since -t~e ~Qvered mold system therefore elimina-tes contact
with oxygenUduring the solidification process and there is
no crushing involved.
The as-cast product is thus formed of a solid im-
pervious brittle body comprised of an iron and silicon base
alloyed with a suitable element to effect nodularization.
Preferably, such width is about 9 feet and the length is
approximately 18 feet, whereas the thickness varies prefer-
entially from 0.5 to 4.0 inches~ The as-cast sheet or pro-
duct has premolded perforations along at least one surface
thereof as shown in Figure 2. In certain applications, the
depending ribs may project from both the interior of the
cover and from the interior of the bottom drag or pan. Thus~
- the spacing from the apices of opposed ribs will reduce the
smallest thickness of the as-cast product. With the ribs
defining perforations in both surfaces of the as-cast product,
and the ribs also containing slanted sides 16b, as shown in ~ ;
Figure 1, the module (to be manually stripped or broken off
from the sheet product~ will have tapered upper and lower
sides which facilitates control of the solution rate in
certain instances where a variable flow rate is encountered
during the molding or pouring operation.
When the catalyst is particularly comprised of
magnesium ferrosilicon, such molding technique as disclosed
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herein will provide less than 0.20~ by weight impurities
within the interior of the as-cast sheet and the magnesium
may generally be concentrated in the range of between S to
15% ~y weight.
As shown in Figures 3 and 4, the mold system A
comprises particularly a cope 110 and a drag 111 meeting
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379
along a partin~ surface 112 which extends horizontally through
first walls defining the cavity A-2. The gating system
employs second walls defining a conventional downsprue 113
with a basin 114, the hasin having a cross-section greater
than the downsprue or horizontal runner 115 tthe horizontal
runner 115 leads to the molding cavity A-2). The gating
system may contain risers, skimmers, dams and other devices
which are not shown here.
~he recess B has second walls comprised of side
walls 116 and bottom wall 117 which define a space set into
and along the lowar wall 115a of the horiæontal runner, The
cro~s-sectional area of recess B as viewed generally parallel
to surface 115a (or transverse to line 118 which is normal
to the extent of the surface 115a) is substantially the same
throughout each elevation of the block. The side walls 116
may be given a slight taper (such as 3-5% which is equivalent . ,
to the draft angle of a conventional sand mold) to reduce the
cross-sectional area at the bottom of the recess and thus
accommodate an increase in dwell time of the trailing end of
the charge flow which occurs particularly with gating systems
experiencing a large variation in iron flow rate during the
entire pour cycleO
In order to achieve minimum 80% by weight nodularity
in the casting, the exact volume of recess B must be obtained
substantially empirically, but as a rough rule it is designed
in conformity with the ~ollowing relationship:
V(in ) = K x W
M :
where K = constant
~ W = weight of the metal poured into the mold
M~= % Mg in MgFeSi alloy
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1~71379
K = 0.265 for average casting sections 1/4" to 1.5"
= 0.275 for average casting sectlons 1.5" to 4"
The weight is that of -the molten cast iron charye. This
relationship is significant since it demonstrates that the
reduced volume required with this invention is opposed to
- that required for the prior art; the volume relationship is ¦.
typically at least twice as much to accommodate particulate I .:
. material and maintain an equivalent solution rate with all
other :Eactors being equal. In many applications, the block
form will occupy about 80~ of the volume of the recess wherein 1,
the.powder form occupies typically a maximum of 55~. The
height 120 of the runner 115 can be as little as 0.25", but
the height 121 of the recess should be no greater than 10 ; . :
times the dimension at 120. This ~imensional limitation
cannot be achieved when using a particùlate agent..
The nodularizing agent is formed as an impervious
mass or block C snugl~ fitting into recess B; side walls 123
and bottom wall 124 respectively mate with side walls 116
and bottom wall 117 of the recess. The mating relationship
is such that molten cast iron cannot conveniently flow alony
the sides of the block other than the upper exposed sur~ace
125. Some penetration may be experienced in some applica-
tions along the sides of the block due to small tolerance
variations, but this quickly freezes during conditioning and
the flow avoidslthis area. The upper surface is configured
to be substantially parallel and slightly below the surace
115a of the runner (such as 0.~5" or less inches; with
particulate material the distance 149 must be at least
0.75"). Thus, molten cast iron will be encouraged to in-
timately contact surface 125 o~ the block since it will dropand undergo a dip in its flow across the block; this will
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7~379
prevent molten metal from gliding swiftly in a streamlined
manner with large portions there~f never contacting the block.
Both because the block is solid and the flow is drawn down
to the block out of the normal runner flow, there will be
little or no tendency for dragging particles of undissolved
agent into the casting cavity. The agent will not move
until reacted with the flow, this is also assured by reducing
5 to 10% the cross-sectional area of the runner exiting from
the recess in comparison to the cross-sectional area of the
runner leading to the recess.
- The block is pxeferably constituted of magnesium
ferrosilicon alloy such as is conventionally used in the
production of nodular iron, but other agents may be selected
from the group consisting of cerium, yttrium, other rare
earths, calcium, and their alloys and such selected agent
may be combined in a desired concentration with other
elements compatible with cast iron to form a binary or
more complex conditioning alloy. Examples of other elements
are iron, silicon, carbon, nickel, etc.
The nodularizing agent is preferably formed as a
substantially homogeneous substance such as by casting
into chill molds. For makiny magnesium f~rrosilicon, a
quantity o* quartzite (silica) is reduced and melted in the
presence of carbon and iron to a molten ferrosilicon alloy
in an electric carbon and iron to a molten ferrosilicon~
alloy in an electric furnace, to which is added magnesium
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(5-15~ by weight) and generally rare earth metals and
calcium. The molten nodularizing alloy is poured into -
~ closed chill molds to define modules or precisely measured
blocks with predetermined dimensions. The interior of each ;~
block will be substantially free of oxides; and will generally
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~L~'7~3'7~
have far less total MgO/poun~ of alloy as a result of Par
less surface are~ per pound than particulate alloy forms.
This is important because one of the advantages herein is
an increase in solution rate and greater economy of alloy
use during nodularization due to more free magnesium avail-
able within the alloy. Thus, less contact time of the molten
charge is required to pick up the required amount of magnesium
to facili~ate nodularization. One possible explanation ~or
- this is concerned with a physical barrier. IP MgO were
present, such as about each particle of a powdered agent
lwhether in loose or compacted form), this MgO does not
take part in the nodularization of cast iron but contaminates
the iron charge as a slag or dross impurity. This is gener-
ally prevente~ from entering the casting cavity by enlarging
the runner and the gating volume so as to allow it to float
out of tne metal. Another possible explanation for this may
be grounded in heat transfer. The heat of the molten cast
iron must first be used to remove the outer sheIl of re-
fractory-like oxide before heat can operate on the agent
itself. This increase in heat will require that the molten
runner flow be 2 to 3 inches higher for a typical casting
application and will limit mold design, reducing casting
yield,! and increase the possibility of a non-uniorm nodu-
larized casting. Variations in surface oxidation during
crushing, handling and storage oP particulate nodularizing
alloy forms increase this problem. With these two factors,
the total volume of the runner or gating system can how be
made smaller~ the risers, downsprues, and runners can be
reduced as much as 25% in some cases (the recess or reaction
chamber can be reduced by as much as 60%), thus rendering a
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significant increase in yield.
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~he block, since it is made as a direct chill
cas-ting has minimum alloy segregation and results in a
uniformly con`ditioned molten iron. Alloy segregation may
occur in two ways with respect to powdered agents: (a) when
maae as a powder, such as 6 x 20 mesh, the finer particles
will settle out toward the bottom of the bulk shipment
during transportation to the site of use; (b) all finer
particles will, immediately on crushing~ form an MgO coating
which is an impurity and may constitute a significant volume
of the powder. The latter shows up as slag in the system
and, if excessive, will move to the final casting as a
deect. Only by reducing the exposed surface area of the
agent can this be improved.
The solid character of the agent is advantageous
also because it allows a consistently accurate predetermined
weight of agent, free from operator discretion or errors of
calculation. The block eliminates migration of the agent
into the casting cavlty in an undissolved form; the latter
may occur with a powdered or granular agent as drag-through
by the molten metal flow (see Figure 3) or as blow~out
(or off) when the open drag is cleaned off by air jets prior
to mold closure while the agent is in place. With respect
to the latter, high air flows can now be used during the
blow-off step without risk of contamination or loss of agent.
Moreover, the typical alloy addition operation can now be
manually handled by one or two men as opposed to two or
three men using the techniques of the prior art. Automation
of the addition system is also considerably simplified with
the block material.
The design of the cross-sectional arqa of the
block is critical to achieving a uniform solution rate, the `
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latter being unattainable by the prior art. The cross-
sectional area determines the exposed interface with the
molten cast iron since the sides and bottom and interior of
the block are not exposed to molten iron flow. Thus, as the
each successive section of the block dissolves, a new cross-
section becomes progressively exposed. This interface area
should be substantially constant throughout the entire period
of conditioning although it has been found necessary to
deviate somewhat when using a casting technique experienc-
ing a wide variation in ferrostatic pressure head and con-
sequently molten iron flow rate over the block during
condi-tioning. The former can be achieved by making the
block with a uniform cross-section throughout, the latter can
be achievea by incorporating a taper into the side walls of
the block so that the bottom cross-sectional area will be
less. The taper can be about 5 to 15. A wide variation
of ferrostatic pressure will occux in vertical shell mold
casting techniques where a tall object is to be cast. The
weight of the molten iron in the filling cavity will counter
the weight of the iron in gating system causing a decrease
in pour rate near the trailing end of conditioning which in
turn increases the molten iron dwell tlme and thus the amount
of heat being transferred to the agent in the recess. By
slightly reducing the exposed interface area at the trailing
end of the pour commensurate with the change in molten iron -
flow rate, a constant solution rate can be assured.
Although the block is preferably illustrated in
Figures 3 and 4 as recessed in a wall of the horizontal
runner with a mold system~ it can be recessed in a wall of
runner system used as an exterior stream treatment device
for conditioning the molten iron prior to it being intro-
duced to the mold~
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