CA1071379A - Mold for casting nodularizing catalyst - Google Patents

Abstract

MOLD FOR CASTING NODULARIZING CATALYST
ABSTRACT OF THE DISCLOSURE
A metal mold is provided for casting a nodularizing catalyst in the form of a solid impervious and brittle block.
The mold includes a shallow pan, a cover extending across the peripheral wall of the pan to close the interior and a fluid connection for introducing a molten charge of nodularizing catalyst to the interior of the pan. The cover is provided with ribs arranged in grid pattern and facing into the pan and penetrating to no greater than 80%
of thickness of the cavity.

Description

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) : :
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.

- . ----- - , - - . . - . - . . - - -. - - ,. . . - .- - . - -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 - 3 - :

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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.

' . ~'. ' -' ' . . ~ ' :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 . ~ .

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 .. - . ~ - , ~1 0'7~379 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 .: .
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 ~ , .

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 - ' ' ~: , 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 ..
(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 -- 10 -- : : .

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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 '::
significant increase in yield.

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~ 7~L37~ l ~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 `

, :~
' -~7~3~9 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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Claims (4)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A metal mold for casting magnesium ferrosilicon or equivalent nodularizing catalysts, comprising:
(a) a metal drag defined as a shallow pan having a flak 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, said cope having ribs on the bottom thereof, which face the interior of said drag, the bottom and ribs of said cope constituting a mold surface in con-junction with the interior sides and bottom of said drag to define a cast body, said cope bottom being spaced from said drag when in the closed condition to define a sheet-like mold cavity having a width and length considerably greater than the thickness thereof, said ribs penetrating below said cope bottom no greater than 80% of the thickness of said cavity said ribs being arranged in a grid pattern with the module of said grid being generally equal to the thickness of said cavity, and (c) means defining a fluid connection for introducing a molten charge of nodularizing catalyst through the interior of said closed pan and cover.

2. The mold of claim 1, wherein ribs are formed on both the inner side of said cover and the inwardly-facing bottom of the pan, said ribs having tapered sides to define a slight taper to the extremities of each module of said sheet.

3. The mold of claim 1, wherein the ribs are spaced apart a distance no greater than the thickness of said cavity.

4. The mold of claim 1, wherein the spacing between the extremities of said ribs and the opposed bottom of said pan is no less than 80% of the total thickness of said cavity.