Specification

This is a continuation-in-part patent applica¬ tion of pending U. S. patent application of Harold M. . Bowman, Serial No. 78,447 filed September 24, 1979, which 5 is a continuation-in-part of U. S. patent application

Serial No. 3,093 filed January 15, 1979, which in turn is a continuation-in-part patent application of Serial No. 669,650 filed June 24, 1976 (now abandoned), which ^' in turn is a continuation-in-part patent application of. Serial No. 10 600,060, filed July 29, 1975 (now abandoned).

This invention*relates to ingot molds and more particularly to reusable or recycleable ingot molds of improved construction and functionability. Certain of the embodiments show sectional ingot molds formed of a plur- it> ality of individual and completely separate side wall sec¬ tions, which when assembled, define a mold cavity, with means to connect or couple the side wall sections together to provide automatic compensation for expansion and re¬ traction of the mold side wall sections when molten metal 0 is poured into the ingot mold ana during the resultant heating and subsequent cooling thereof. During the pour¬ ing operation of molten metal into the mold and the for- tuation of the ingot, the connecting or coupling means allow for expeditious and controlled expansion of the 5 mold sections, with respect to one another, while aiding in sealing the respective moid sections from leakage of

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rαolten metal during the pouring and subsequent solidifi¬ cation of the ingot in the mold. At least certain of the coupling means includes disc spring means operable for pre¬ loading to a predetermined extent. In certain embodiments, 5 the molds are of generally one-piece construction, but having openable and closeable junctures therein providing for the aforementioned automatic expansion and contrac¬ tion of the mold during pouring of the ingot, the solidi¬ fication thereof and subsequent cooling. A novel method 0 for th* production of ingots is also disclosed. Background of the Invention

Sectional ingot molds are known in the prior art. U. S. patent 496,736 issued May 2 , 1893 to C. Hodgson and ϋ. S. patent 1,224,277 issued May 1, 1917 to F. Clarke, 5 are examples of prior art sectional mold constructions.

U. S. patents 354,742 issued December 21, 1886 to J. Sabold and British patent 13446 of A.D. 1900 in the name of Stephen Appleby, et al and entitled "Improvements in or Connected with Ingot Molds", disclose sectional mold ar- 0 rangements embodying means for relieving stress on the fastening bolts thereof due to the expansion of the molten metal. However, such prior. rt sectional molds have not alway been satisfactory, d e at least m part to often¬ times leakage of molten metal occurring between the mold 5 sections during the pouring of the molten metal into the mold cavity and subsequent solidification of the metal, or due to the complexity and/or costs of such arrangements.

H. S. Lee and Amos E. Chaf e in U. S- patent 1,584,954 issued Hay 18, 1 2 identified Perr.-anent iuold r _^ r Distortion and its mpted control by using thermally responsive insert cle.-r.ents to effect control of a perma¬ nent mold lea.-cing rtoiten rcitil aion tne parting line and to avert distortion or a bowing a ti of the mold by

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placing higher or lower coefficient of expansion metals in position in the mold to resist the inward or outward move¬ ment of the mold thus directly effecting the casting being formed and produced by the permanent mold. 5 U. S. patent 158,696 to Foster et al discloses a sectional mold in conjunction with spring-loaded bolts to provide for lateral expansion of the mold sections relative to one another during the expansive force of the molten metal poured into the mold. 10 In the aforementioned pending U. S. Serial os.

3,093 and 78,447 of applicant, there is disclosed section¬ al ingot molds having fastener means for connecting mold wall sections together to form a mold cavity, and provid¬ ing for automatic compensation, including a delayed faster 15 rate of expansion for reducing stresses, and also includ¬ ing memory, to allow for expansion and retraction of the mold assembly sections when' molten metal is poured- into- the ingot mold and during the subsequent cooling of the ingot, while aiding in sealing the mold sections from 20 leakage of molten metal during the pouring and subsequent cooling of the ingot in the mold. The prior art cited in said U. S. pending applications is incorporated herein by reference.

In British patent 1,380,720, published January 25 15, 1975 there is disclosed a sectional ingot mold having separate corner members adapted to mate into concave recesses in the mold wall sections for attempting to re¬ lieve the stress resulting from the temperature gradient existing across the side wail sections_upon pouring of ->v_. molten metal into the rr.olα. ~_ extending around the wall sections serves to hold the latter in assembled re¬ lation in one embo iment, ana coilea spring strips at the mold corners exerting constant force are utilized in

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another embodiment.

British patent 1,464,075 published February 9, 1977 discloses a liquid cooled chill-casting sectional mold which includes split clamping rings holding the mold 5 parts together, with Belleville type disc spring means acting on the extremities of the split clamps, for press¬ ing the extremities toward one another. However, there are no teachings concerning pre-loading or what such pre¬ loading should accomplish.

10 British patent 1,240,893 published July 28,

1971 discloses a slab mold having a bottom wall movabile upwardly relative to the side walls of the mold at a rate which will exert a pressure on the metal equal or greater than the ferrostatic pressure, thereby attempting

15 to prevent a rupture of the skin of a solidifying slab and escape of molten metal from the slab's interior. None of the prior art molds, in applicants* opinion, is optimumly operable when exposed to thermal., elastic and ferrostatic stresses resulting from the pour-

20 ing of molten metal into a sectional mold in the formation of ingots, such as for instance steel ingots, in the man¬ ner of applicants' arrangement. Summary of the Invention

The present invention provides novel ingot mold

__ constructions wherein the mold is provided with juncture means affording stress relief thereto during the ingot forming operation, while effectively aiding in maintaining the mold in condition to prevent metal leakage therefrom during the pouring operation and suosequent cooling of

_, ^tne ingot, and providing fs r the proauction of an ingot having an ingot skin with sufficient structural integrity to support the molten interior of the poured ingot, and a

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-£ ^• - mold which can be recycled for use in ingot production in a faster manner as compared to heretofore used one- piece ingot mold structures. In this respect, the coupl¬ ing means coacting with the openable and closeable junct- ures of the side wall portions defining the mold cavity comprises adjustable spring means which are preloaded a predetermined extent prior to the molten metal pouring operation. In certain embodiments, the mold is formed of a plurality of separate side wall sections defining at least the side periphery of the mold cavity, while in other embodiments, the mold walls are of a generally ^• one-piece affair having juncture sections or slit port¬ ions which are openable and closeable during the casting or molding process for releasing stresses in the mold. The- aforementioned spring means preferably comprises Bellevil¬ le type springs.

Accordingly, an object of the invention is to provide an ingot mold with openable and closeable junct¬ ure means therein, with coupling means to at least inital- ly hold the junctures closed to form a mold cavity for pouring molten metal thereinto; the coupling means in conjunction with the junctures provides for automatic compensation for expansion and retraction of the mold, when molten metal is poured into the mold, and during subsequent cooling of the ingot, with resulting action of relatively quicker heat dissipation from the mold.

A still further object of the invention is to provide a mold in accordance with the above which aids in relieving "as cast" stress surface cracks in the pro- duced ingot, and metal leakage from the resulting ingot during the formation thereof.

A still further object of the invention is to

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provide an ingot mold which has laterally projecting flanged sections on the mold at openable and closeable junctures therein, adapted for receiving means coupling the mold juncture sections together into an integral and an 5 initially closed mold defining an ingot mold cavity, and with said coupling means possessing memory and automati¬ cally compensating for expansion and retraction of the mold assembly during the ingot forming operation in the mold assembly, and resultant heating and subsequent cool-

10 ing and solidification of the formed ingot, and wherein at least certain of the coupling means includes adjust¬ able spring coupling means adapted to preload to prede¬ termined extent the mold junctures in closed condition prior to the pouring operation on the mold, and prevent—

15 ing leakage of molten metal at the mold junctures and providing for formation of an ingot skin having suffi¬ cient structure integrity to support the molten interior of the poured ingot, while providing for predetermined

20 release of stresses due to the thermal moments in the mold sections.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, wherein:

~-r Brief Description of the Drawings

FIGURE 1 is a perspective view of a sectional ingot mold constructed in accordance with an embodiment of the invention;

FIGURE 2 is an enlarge . sectional view taken

^ϋ generally along the plane of line 2-2 of FIG. 1, looking in the directions of the arro _* s;

FIGURE 2A is a side elevational view of one of the Belleville spring elements of FIG. 2;

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FIGURE 3 is an enlarged sectional view taken generally along the plane of line 3-3 of Fig.l;

FIGURE 4 is a perspective view of another em¬ bodiment of a sectional ingot mold embodying the invention; FIGURE 5 is a perspective view of one side wall section of the FIG. 4 mold, looking at the interior of the side vail section;

FIGURE 6 is a perspective view of the side wall section of FIG. 5, looking at the opposite or exterior side thereof;

FIGURE 7 is a perspective view of another em¬ bodiment of ingot mold generally referred to as a one- piece mold structure, and embodying the invention, and having multiple areas of vertical, separable juncture . surfaces;

FIGURE 8 is a perspective view of a further em¬ bodiment of ingot mold, embodying the invention, and being of the type generally referred to as a one-piece mold structure, and having a single area of vertical, separ-. able juncture surfaces extending for the full height of the mold;

FIGURE 9 is a vertical view of a one dimensional Heat Transfer model used in connection with the explana¬ tion concerning heat transfer analysis for the determina- tion of the desired preload on the fastener means for the mold sections;

FIGURE 9A is a sectional view taken along the plane of line 9A-9A of FIG.9;

FIGURE 10 is a finite difference grid for the heat transfer model illustrated in FIGS.9, 9A;

FIGURE 11 is a radial temperature profile graph

^β AD OR ^{T OMPI}

of the heat transfer model of mold shown in FIGS . 9 and 9A, for specific times from the commencement of the pour, and illustrating the effect of separation of the ingot from the interior surface of the mold when the ingot skin 5 possesses sufficient structural integrity to support the molten interior of the poured ingot;

FIGURE 12 illustrates a plot of the temperature of the interior surface of the mold wall, illustrated in FIGS. 9, 9A for the instances of "no contact resistance" 0 as compared "with contact resistance", or in other words with an air gap in existence ^' between the ingot skin and the mold wall interior surface;

FIGURE 13 is a perspective diagrammatic view showing for illustrative purposes the free thermal bend-

3_5 ing that occurs upon the heating of one side of a uniform thickness plate section;

FIGURE 14 is a graph of the thermal expansion co¬ efficient pC and the modulus of elasticity E in conjunc¬ tion with temperature, and particularly for Class 20 cast

2o iron, which represents a typical material from which the molds of the invention may be found;

FIGURE 15 is an approxiamte temperature profile in a mold wall of a typical ingot mold embodying the in¬ vention;

_5 FIGURE 16 is a diagrammatic perspective view showing free thermal bending that could occur in a sec¬ tional ingot mold of the general type illustrated in the drawings when molten metal is poured into the mold's in¬ terior, thereby causing heating of the latter;

_ _> 0 FIGURES 17 and 17A illustrate a ^" simple plate model useful in estimating the necessary clamping forces for maintaining the flanged juncture surfaces of the mold

in generally abutting condition until completion of the filling of the mold cavity and during predetermined ingot solidification for the elastic analysis;

FIGURE 18 illustrates a force displacement curve 5 for the preloading of the adjustable fastener means to achieve an adequate clamping force from the adjustable fastener means to keep the mold closed furing the pour¬ ing and the formation of an ingot skin having sufficient structural integrity to support the molten interior of the 10 ingot;

FIGURE 19 is a transverse sectional view of one of the larger Belleville springs utilized in certain of the adjustable fastener means embodied in the ingot mold of the invention; 15 FIGURE 20 is a transverse sectional view of one of the smaller Belleville springs utilized in the adjust¬ able fastener means embodied in the ingot mold of the in¬ vention;

FIGURE 21 is an illustration of the force dis- 20 placement curves of the larger Belleville springs of FIG. 19, both with and without the flats on the top inside and bottom outside corners; FIG.19 illustrates the 3elleville spring with the aforementioned "flats";

FIGURE 22 is a generally diagrammatic elevation- 25 al view of the top disc spring fastener arrangement shown in FIGS. 1 and 3, and showing dimensional relationships in a particular ingot mold assembly;

FIGURE 23 is a view similar to FIG. 22 but il¬ lustrating the middle disc spring fastener assembly of _, _υ FIGS. 1 and 2 for particular ingot mold assembly;

FIGURE 24 is a view similar to FIGS. 22 and 23 but illustrating the lower αisc spring fastener assembly of FIG. 1.

FIGURE 25 illustrates another e oodiment of an

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ingot mold assembly generally similar to that of FIGURE 1 except that no clip fastener means are utilized in the assembly.

Description of Preferred Embodiments Referring now again to the drawings and parti¬ cularly to FIGURES 1, 2, 2A, and 3 there is illustrated an ingot mold 10. Such ingot mold in the embodiment illustrated, comprises separate but generally identical mold sections 12, 14, 16 and 18 coupled together. Each of sections 12, 14, 16 and 18 may have transverse rib sections 20,20a, 20b on the exterior thereof, and generally wave-like or sinuous-like interior surfaces 22. Surfaces 22 are adapted to aid in stress relief in the ingot as cast; and aid in reducing external skin cracks in the ingot, as well as aiding in preventing leakage of molten metal from the interior of the newly poured ingot or from the mold assembly cavity.

The side ends of each mold section 12, 14, 16 and 18 is provided with laterally projecting flanges or lugs 26, 26a. Each of the lugs or flanges 26, 26a is adapted for abutting engagement as at 27 with the con¬ fronting flange or lug of the adjacent mold section, to define the ingot mold cavity 28. Flanges or lugs 26, 26a preferably extend the full height of the respective mold section, as illustrated, and embody vertically spaced sections 30 of reduced size or thickness for a purpose to be hereinafter set forth. While the interior surface of each mold section is illustrated as having a wave-like or sinuous configuration, such interior surface can be generally smooth surfaced.

As illustrated, the mold 10 may be open from vertical end to end thereof, and curing pouring of an

L

ingot, may be set for instance in a sand area or pref¬ erably on. a metal base plate or "stool" (not shown) for furnishing the bottom for the mold. The mold sections may be formed of any suitable material, but aforementioned Class 20 gray cast iron, or blast furnace iron may be utilized ^' . It will be seen that in the event of breakage or the wearing out of one mold section, that another section can be readily substituted for the broken or worn out section, so that the entire mold does not have to be replaced. Moreover, the sectional construction with the coupling or fastener means 34, provides for expan¬ sion and contraction of the mold sections during heating and cooling, and eliminates stresses and strains found in one-piece or unitary molds, and as will be hereinafter described in detail.

Lugs or projections 32 may be provided at the upper end portion of certain of the mold sections of the respective mold, such as for instance mold sections 14 and 18, and are adapted for lifting purposes so that once the ingot has adequately solidified, the mold can be raised as for instance by a crane or the like, utilizing a lift chain about the lugs 32, and then shaken, to shake or slide the ingot out of the mold. If the mold is of open bottom construction, the ingot is adapted to slide out of the bottom of the mold. If it turns out that the solidified ingot cannot be dislodged from the mold, then a hydraulic pusher ram may be used, or of course the mold sections could be opened after sufficient cooling, by loosening of the coupling means 34 holding the mold sections together to separate the mold sections and pro¬ vide for removal of the i o .

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Mold sections 12, 14, 16 and 18 of the FIG. 1 mold may be generally similar to the ingot mold sections illustrated in FIGS. 31-39 inclusive of applicant's afore¬ mentioned copending patent application Serial No. 78,447, and reference may be made thereto and the associated des¬ cription therefor for a more detailed discussion of the structural arrangement of such mold sections.

The aforementioned coupling or fastener means 34 in this FIG.1 ingot mold embodiment has been illustrat- ed as including clip members 44 of generally C-shaped configuration inplan (FIGURE 1) which coact with or between the adjacent flange portions 26, 26a for clamping the mold sections together into an integral mold assembly. Each clip 44 is formed of metal and comprises a body portion 46, and arm portions 47 projecting laterally from said body portion in generally converging relation with respect to one another, with the- arm portions being adapted to clasp the adjacent flange or lug of the mold section therebetween in coupling relation. Body portion 46 of each clip is preferably pro¬ vided with a generally concave interior surface 50 adapt¬ ed to face in spaced relation the confronting end faces 52 of the adjacent flanges of the mold assembly. The clips are inserted into the aforementioned reduced size section 30 of the flanges, with the arm portions being readily received in encompassing relation to the reduced size flange sections 30 and then the clips are moved or driven vertically into tight coacting relation with the tapered pockets or cam surfaces 54 on the wider portions oδ the flanges, for clamping the mold sections tightly together at the clip locations. The vertical gripping faces of the clips are tapered for facilitating their

movement from the reduced size sections 30 of the flanges into tight camming coaction with the cam means 54 on the wider portions of the σoacting flanges. Reference may be made particularly to FIGS. 27 to 30 of the aforementio ed 5 copending application Serial No. 78,447 for a more det¬ ailed discussion of the clips 44 and- their coaction with the cam pockets on the ^' mold section, and such disclosure is incorporated? herein by reference.

The clips 44 may be formed of stabilized aus- 10 tenitic stainless steel. A suitable type of stainless steel material for use for the clips is that known as ^* RA-330 stainless, purchaseable from Rolled Alloys, Inc. of Detroit, Michigan and described in its present bulletin identified as No. 107. Stabilized austenitic stainless 15 is characterized by having a relatively high nickel content, with the stainless steel material having rela¬ tively low rates of thermal conductivity as compared, to, for instance, carbon steels, and possessing elasticity to return back to its original condition after it has 20 been heated up to a relatively high temperature (e.g. 220 ^β F) . Reference may be made to a orementioned Serial No. 3,093 and 78, 447 for a detailed discussion of suit¬ able clip structure and such is incorporated herein by reference. In other words, this material has "memory" ,5 which causes it to return to substantially its original condition after cooling thereof.

"Memory" as used herein, and in the hereafter set forth claims, means the ability of the fastener means material of the mold assembly to return to substantially _, ₀ its original preheated size condition and to retain its important physical properties, after undergoing thermal stress and other stress (e.g. ferrostatic stress) at

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temperature to which the fastener means is subjected upon the pouring of molten metal into the mold cavity to form an ingot, and the resultant heating and subsequent cooling thereof. It is well known in the ingot mold art to have "big ended" molds wherein one end of the mold is of a larger cross sectional area as compared to the other end thereof, and it is common practice to pour ingot molds with either the "big end" up or the "big end" down. Also "bottle top" ingot molds, "open bottom" ingot molds,

"closed bottom" ingot molds, and "plug bottom" ingot molds arewell.known in the art, with such molds having various cross-sections of "flat sided", "cambered", "rippled", "corrugated" and/or "fluted" interior surface configur- ations, each traversing partially or completely the length of the mold side wall. Moreover, the use of "hot tops" are well known in-the ingot mold art, in order to aid in preventing piping and the like in a produced ingot. The inventions of the present application may be useable in conjunction with any or all of the above prior art structures. A typical chemical analysis of aforementioned blast furnace iron for producing the mold side wall sec¬ tions 12, 14, 16, and 18 luay be as follows:

Ran e Phosphates .15% to .25%

Sulphur .025% to .045%

Silicone 1.15% to 1.45%

Magnesium .30% to.50%

Carbon 3.5% to 4.5% In accordance with the present invention, there is provided adjacent both the upper and lower ends of the vertically oriented mold asseiribly 10 as well as intermediate

n* ⁴ -

such upper and lower ends, another form of fastener coup¬ ling means 34, for releasably holding the mold sections together. In the embodiment illustrated such fastener means comprises disc spring fastener assembly 56 coacting between adjacent mold sections (e.g. 12 and 18) at the upper end of the mold assembly, a disc spring fastener assembly 56a, coacting between the adjacent mold sections just below the approximate middle of the mold assembly, and a disc spring fastener assembly 56b coacting between the adjacent mold sections in the vicinity of the lower end of the mold assembly.

Each fastener assembly 56 (FIG. 3) comprises a bolt 58 threaded as at 58a preferably at both ends thereof, with such bolt extending through aligned openings 60 in the adjacent flanges 26 and 26a of adjacent mold sec¬ tions. A threaded nut 62 coacts with the respective threaded -end of the bolt 58, and solid ^" flat washer merα- bers 64, 64a provide a flat abutment surface for the disc springs 66, 66a of the fastener assembly. The springs 66, 66a are preferably Belleville-type disc springs and are preferably stacked in the manner illustrated in FIGURE 3.

The bottom spring assembly 56b for the ingot mold is generally identical to the assembly 56 illustrated in FIGURE 3, except that it also includes an assembly of disc springs on the other end of the bolt, and as is clearly shown in FIGURE 1 of the drawings. The bolt 58 in assembly 58b is thus longer as compared to the bolt in assembly 56. The bolts 58 are preferably high strength steel bolts (identified in the trade as B7 bolts) the particulars of which V-άll be hereinafter discussed in greater detail. In the assemblies 56, 56b, the bolts are preferably thr^eded at both ends thereof as illustrated

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and coact with a respective nut.

In the intermediate fastener assembly 56a illus¬ trated in FIGS. 1 and 2, the bolt 58* is headed as at 70 with the associated nut 62 coacting with the threaded end of the bolt. As can be best seen in the enlarged, sectional view of the Belleville springs illustrated in FIGURES 19 and 20, the exterior corners of the springs, are preferably "broken" or flattened as at 72, while the interior corners which coact with an adjacent spring are likewise preferably "broken" or flattened as at 72a, which improves the transmission of force from one spring to the adjacent spring, as will be hereinafter discussed in greater detail. Spring assemblies 56, 56a, 56b are adapted for preloading to predetermined extent prior to pouring of the ingot for maintaining the juncture surfaces of the mold sections in generally abutting condition until completion of the filling Qf the mold cavity to a predetermined extent with molten metal and the for¬ mation of an ingot skin on the poured ingot having suf- ficient structural integrity to support the molten in¬ terior of the poured ingot.

Referring now to FIGURE 4 there is illustrated a sectional ingot mold comprised of only two mold side wall sections instead of the four sections illustrated in FIG- URE 1. Such mold sections 12', IS* are joined to one another along generally vertically extending juncture sur¬ faces 27 in a similar manner as in the first described embodiment and the pair of mold sections are maintained in assembled relationship by fastener clips 44 and spring fastener assemblies of 56, 56a and 56b in a generally similar manner as in the first described embodiment. In this embodiment, each of the mold sections 12', 18* also

includes a vertically extending openable juncture or slit 27' adjacent top and bottom ends of the respective mold section , with such openable juncture surfaces 27' including flange segments 26' 26a' .with each adjacent pair of flange segments coacting with a respective fastener assembly 56, 56b in a generally similar manner as for the full length juncture surfaces 27 of the assem¬ bled mold. The preloading of the spring fastener assem¬ blies in the mold assembly of FIGURE 4 is generally the same as aforedescribed in conjunctionwith the first described embodiment of mold assembly _*

FIGURE 5 illustrates a view from the interior of one of the mold sections 12* or 18', showing the openable juncture surfaces 27' thereof extending from both the bottom and top extremities of the respective mold section 12' or 18 ', and FIGURE 6 illustrates one of the mold sections 12' or 18' without the fastener coupling means associated therewith.

FIGURE 7 is a view generally similar to FIGURE 4 except that the mold is continuous (non-separable) in its central section (having no openable juncture surfaces in the central portion) while the openable juncture sur¬ faces 27' are located adjacent the upper and lower extremi¬ ties thereof with associated flange segments in four oppos- ing locations on both the top and bottom portions of the mold. Such openable junctures or slits operate-.in a gen¬ eral manner as those identified at 27' in the FIGURE 4 embodiment. Fastener spring assemblies 56, 56b coact with the respective adjacent flange segments, and are preloaded in a similar manner as those in conjunction with the prior described FIG. 4 e.nDodiment, and control the opening of the juncture surfaces 27' of the mold at the

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top and bottom portions thereof, to aid in relieving stresses in the mold in the manner aforediscussed.

FIGURE 8 discloses a further embodiment of mold having a single, vertically extending juncture surface 27 5 therein, and with such single openable juncture surface . being held in predetermined closed condition by the clips 44 and spring fastener assemblies 56, 56a and 56b and are adapted to operate-in a generally similar manner as those aforedescribed in conjunction with the first described

10 embodiment of FIG. 1.

A feature of the sectional ingot mold with cfoupl- ing of fastener means 34, capable of being preloaded to a predetermined amount while providing for expansion and contraction of the mold wall sections after molten metal

15 has been poured into the ingot mold cavity, is seen oc- . curing during the initial pouring of molten metal into the ingot mold cavity, when the resulting initial impact ^• force or dynamic load acting against the mold walls is transferred through the mold wall sections and is part-

20 ially absorbed by the fastener or coupling means. This reaction of the coupling or fastener means to partially absorb the impact energy force or dynamic load is a result of the preloaded fastener means being flexible enough to allow sufficient deflection to partially absorb

__ the said dynamic load and thus relieve the impact stres¬ ses normally associated with molten metal being poured into an ingot mold cavity, yet maintaining sufficient stiffness to impose a predetermined preload, capable of forcing the mold wall sections together to maintain the

_ _u juncture surfaces in a generally abutting condition until completion of the filling of the mold cavity a predeter¬ mined extent with molten metal.

OM

Fig. 25 illustrates an embodiment of an ingot mold assembly generally similar to that of FIGURE 1 except that no clips are utilized in the mold assembly, and the spring fastener assemblies 56, 56a and 56b coact- ing between the mold sections along the separable junctures thereof are the only coupling means utilized for holding the mold sections 12, 14, 16, and 18 together into an integral unit.

The following design analysis to determine the desired preloading of the spring fastener assemblies 56, 56a, and 56b is based on an ingot mold assembly of the general FIGURE 25 arrangement. The added clip fasteners of for instance the FIGURE 1 arrangement provide an ad¬ ded degree of safety to the respective mold assembly in which clip fasteners are also utilized in conjunction with the aforementioned spring fastener assemblies 56, 56a and 56b.

The design analysis of the segmented mold shown for instance in FIGURE 25 (or in FIGURE 1) involves three disciplines: heat transfer, thermal stresses and elastic displacements. While each discipline requires a model on which an analysis is based, the numerical results from each model provide Qaca for other steps in the analysis and can be interpreted to establish the per- formance of the mold.

Heat Transfer Analysis — The heat transfer analysis is based on a model of two concentric cylinders, a solid cylinder contained within a cylindrical sleeve, as shown for instance in FIGURES 9, 9 ^* . The sizes of the cylinders are scaled to generally n.atch the volumes of an actual ingot: and moid. Ti.c inside solid cylinαer represents the ingot whic.. is assumed to be initially at

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the pour temperature. The outside cylinder represents the ingot mold which is assumed to be initially at ambient temperature. The heat transfer analysis is based on a model of the inner cylinder solidifying from the melt and raising the temperature of the outside culinder. The governing equation is based on the thermal diffusion from the hot ingot

where

C-. — heat capacity

^* 7S = thermal conductivity

^• 4fc = thermal diffusivity with the following initial conditions at t = 0

7 ^* *7 *< . < £ -£ (molten ingot)

f - f & _O ~G < ζ ^" < ^0 (mold at ambient) and the following boundary conditions for all time

ZmmZ symmetry at the center and

__^ ^C ' J - θ~( 7 ^* — T ^* ) radiation of the outside

<-ssC /> _* g ₀ surface to the surrounding these equations apply until the ingot separates from the mold. For t t* the ingot has pulled away from the mold at «*^— _< £ and the heat flux across the small gap takes place by radiation.

mold ingot mold

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The aforementioned model is complicated by three elements which must be included in the analysis in order to provide realistic predictions of the temperatures. a) The material properties are functions of the temperatures. b) The interface between the ingot and the mold provides a resistance to heat transfer c) The mold transfers heat to its surroundings by radiation and convection. Referring now to FIGURE 10 of the drawings, *

C - position η - time

_T_ %- L.n 1+_tL . u.ά 7 <-, 7

An exact closed form analytic solution could not be found for this problem so one of the classical approximate solu¬ tion methods was applied. An array of uniformly distrib¬ uted points was defined, as shown in FIGURE 10. An un¬ known temperature was identified for each point and the spatial derivatives expressed in terms of finite dif- ferences between adjacent points. A solution is then found for each point in the domain for each increment in time. This solution method known in the literature as a Finite Difference Scheme was programmed for the computer. Typical data input to run the heat transfer model includes the following parameters for the mold and ingot material ° = 490 lbs/ft ³

SA ⁷

< = 0.9 emissivity

✓ _# —8 Btu

Is = Stephan Boltzmann Constant = 0.1718*10 hr-ft ² (°R) ⁴

and with € _Λ = 2.28 ft « 10.5 in 7^ - 2815 ^β F = 30 ^β F (winter experiment)

The following Table I shows the results for two successive time increments t = approximately 60 and t = approximately 65.9 from commencement of the entry of molten metal into the mold. It is interesting to note that the outside of the mold is just beginning to experi¬ ence an increase of temperature in spite of the fact that the interface between the molten metal and the interior surface of the mold has already increased to almost 1000 ^β F.

TABLE I - TWO TYPICAL SUCCESSIVE TEMPERATURE PROFILE _S THROUGH THE INGOT AND MOLD.

The heat emitted by the solidification of the ingot will continue to transfer into the mold through a model of simple conductivity moving these two elements closer to thermodynamic equilibrium. As this happens the ingot tends to shrink because of the volumetric changes on solidification and the reduction of temperature. At the same time the mold tends to grow and distort due to the nonuniform rise in temperature. When the solidified skin of the ingot develops sufficient structural integri- ty to support the ferrostatic head of the molten ingot core, a gap between the ingot and the mold develops. ^* Thereafter the heat flux is impeded because the air gap produces a resistance to the path. Heat transmission across the gap then takes place by radiation rather than by conduction.

FIGURE 11 shows the temperature profile through the ingot and mold wall for various fixed times ( 0.9-23 min, 1.85 min, 4.61 min, 9.22 min ...} For this particu¬ lar set of data an air gap develops between the ingot and the mold after approximately 4.61 minutes from the commence¬ ment of the pour- The temperature profiles are smooth continuous curves through the ingot mold interface for times up to 4.61 minutes. Thereafter a discontinuity of the temperature profile develops because of the air gap. The temperature of the outside of the ingot increases because it is "upstream" to the resistance while the tem¬ perature of the inside of the mold decreases because it is "downstream" and heat input is reduce -

FIGURE 12 shows a plot of the temperature of the inside mold wall for -the cases of "no contact resistance" and "with contact resistance" (i.e. with air gap). The case of "with contact resistance" is based on a radiation

heat transfer model and may exaggerate somewhat the resistance. These two models probably bound the true . solution and provide a reasonable guideline for the tem¬ perature profiles. The program is therefore capable of 5 estimating the temperature distribution in both the ingot and the mold for each time increment for the mold and ingot characteristics specified in the input.

Thermal Stress Analysis — The thermal stress analysis is based on a model of a flat plate subjected to 10 a thermal gradient through the thickness which is assumed to be uniformly distributed over the plan form, as shown in FIGURE 13. The thermal gradients are determined from the finite difference analysis and used to determine the thermal thrust Ai d M _r thermal moment.

^' "r-J ^«e 2 ^ψ( 2 ⁾ *% -Z ^£r 3 ⁷ l &

It is important to recognize that thermal expan¬ sion coefficient -**-> and the modulus of elasticity E are functions of temperature- FIGURE 14 is a plot of these two :0 parameters for Class 20 cast iron, a material with proper¬ ties similar to the typical mold-material which may be blast furnace iron. Included also is a plot of the ^d ^^£ ^* ~ product for the temperature range of 70"F to 1600°F. It is interesting to note that the ' ^ product is approximate- 5 ly constant at a value of 100 for 500 ^β F to 1600 ^β F. This observation serves as the basis for approximating the thermal thrusts and moments as

Values for the thermal thrust ^-a d the thermal moment _* .can be approximated by one of two methods based on the temperature profiles generated by the heat transfer analysis. 5 Integral of a_ Continuous Function — In the first scheme, an analytic function is fitted to the computer generated temperature profile for the mold wall. FIGURE 15 is a plot of the temperature profiles for the mold wall for several samples. These profiles were approximated by 0 two continuous functions

A parabola

and a constant

For the time increments, shown in FIGURE 11, the thermal 0 moments were calculated according to this approximation as t (minutes) Mr Kin-lb/in)

0.923 -566,000

1.850 -730,000

4.61 -842,000

25 The thermal thrusts /.were not estiωte since they do not contribute to the therπ^.1 bending distortions.

Discrete Sum — Alternatively the thermal mom¬ ents can be calculated using the temperatures at the dis¬ crete finite difference grid points and the discrete slice ^3.1 _' ^τhis calculation was programmed for the computer and coupled to the heat transfer program to provide esti¬ mates of - for each time increment.

Using these estimates for the thermal moments, the free thermal distortions of each mold section is esti¬ mated. For this analysis, the plate (i.e. mold sections) are assumed to be free to displace, and because of the sym¬ metry of the loading the plate deforms into the shape ^* of a spherical segment, as shown in FIGURE 16.

3 Mr s - \

*^ ~~ -7Z~ ^" 7* * ^• "*** ^" y ^ox the midsurface

The stresses are as followsr

For the case where the mold section is free to displace and form this spherical shape.

The displaced shape maintains the center of the mold sections in contact with one another and displaces the edges and corners away from the ingot. For a one-piece mold composed of four flat mold sections or plates inte¬ grally attached at the corners, the restraining of the free displacement of each plate in^to spherical sectors pro¬ duces exaggerated stresses at the adjoining corners. Since the mold of the invention is segmented at the corners, cor¬ ner stresses in the FIG. 16 mold assembly do not develop.

However, the mold must be connected at the cor¬ ners by some fastener means to contain the molten ingot. For this case, a conservative estimate of the stresses

can be determined by assuming that the fastener means and edge restraint are sufficient to remove the thermal moments but not the thermal thrusts.

Elastic Displacement Analysis — The elastic displacement analysis is based on an elastic plate stif¬ fened with two ribs on the vertical edge as illustrated for instance in the mold sections of FIGS- 25 or 9. The plates are restrained in the free displacement to a spherical sector by the spring fastener assemblies used to keep the mold walls together. ^' The attachments have to be designed to keep the mold segments together and ^* aid in preventing leakage of the molten ingot, or cracking of the solidified skin of a cooling ingot.

For the case of extremely large molds, i.e., particularly tall heights (e.g. 100 inch tall mold assembly with the transverse interior dimension of the mold cavity being between approximately 28-32 inches) the free thermal expansion tends to dominate. The mold will tend to spring open during the early stages of the pour because oi the accumulated thermal displacements of the spherical shape over the large span. These molds tend to leak at the seam lines unless an adequate load is available to restrain the displacements. In this situation an elastic attachment capable of preloading to .significant levels is desirable. Thus, this arrangement will be dominated by the thermal- elastic consideration with the ferrostatic loads playing a minor role. Since the ingot solidifies from the bottom to the top, and the top is the last portion of the ingot to be poured, the following criterion for the design of the mold segment clamping forces can be established.

Top Clan-o — ϊne preload in the spring clamps 56 at the top of the mold should be sufficient to prevent leakage of freshly poured material

at the end of the pour, mainely at approximately 120 seconds for a 100 inch tall mold having an approximate 30 inch interior diameter. Bottom clamps — The preload in the spring clamps 56b at the bottom of the mold should be suffi¬ cient to support the skin of a partially solid¬ ified ingot until such time as the ingot skin has cooled and developed enough structural in¬ tegrity to support the molten interior. Central clamps — The preload in any of the gen¬ erally intermediately located spring clamps 56a can be used to assist the lower clamps in sup-- porting the ferrostatic head.

FIGURES 17, 17A present the simple plate model used to estimate the desired clamping forces. The pri¬ mary bend.ing deformation can be calculated from the dis¬ placement equation of a centrally loaded uniform beam by equating this displacement to the free thermal displace¬ ments.

u exe E -* -</ '%, y • Substituting F * 1.414 (P. + P ) and approximating P = P leads to the following equation for

Substituting the following dimensions for the 100" ingot mold 2-f the following approximate ex¬ pression for the bolt force can be determined.

P = 0.306 Ά_. Using this formula, the forces necessary to keep the ...old closed during the ingot soli iric cion are estimated as follows:

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time &in./lb/in P in Pounds

0.923 -566000 173,000

1.85 -730000 223,000

4.61 -842000 257,600 Therefore a clamping force of approximately 257,600 pounds is required to keep the top of the sectional mold closed for approximately the first five minutes from com¬ mencement of the pour. Small amounts of separation of the outermost lateral edges of the flanges 26, 26a on the mold segments tend to occur.

Furthermore, ^' the clamping force at the bottom of the mold should be slightly larger than the clamping force at the top. This will insure that the first separation of the juncture flange surface 27 will occur at the top where faster stabilization of the ingot skin occurs. The clamping forces (or preload) for each fastener assembly were thus conservatively set at 300,000 pounds. For the case under discussion 3" diameter high strength aircraft quality bolts (B7) were selected for use in the spring fastening assemblies.

The bolts 58 which supply such a clamping force to keep the mold sections closed during the pour and the early stages of solidification must then allow the mold segments to bend due to the thermal moments. Therefore the bolts are elastically interfaced with the mold by means of the disc springs of the assemblies to allow the thermal distortions.

The force displacement curve of FIGURE 18 indi¬ cates the curve for the preloading necessary to achieve a clamping force adequate to keep the mold closed during the pour. Thereafter the mola opens until the springs of the fastener assemblies reach their maximum stroke and the

associated bolts 58 restrain the mold walls from further thermal displacements.

Belleville Washers — Considering the limita¬ tions of space and the structural demands of extremely highloads, Belleville Washers are preferred for the spring fastener assemblies. Using the equation for the stress analysis of Belleville Washers, a computer program was prepared and the washers shown in FIGURES 19 and 20 were designed. The corresponding force-displacement plots for the 12" diameter washers is shown in FIGURE 21. A similar curve is obtained for the 7.0" or smaller diameter washers.

When two Belleville Washers are nested together, the force required to achieve a given ^' displacement add together. When two Belleville Washers are stacked in oppo- sition, the resulting displacements add. The two washer designs were selected so that small washers would require approximately 100,000 pounds to flatten each washer. At the same time the large washers would require approximate¬ ly 75,000 pounds to flatten each washer. Bystaking advan- tage of the possible stacking sequences and friction, it becomes possible to stack sequences of the washers to pro¬ vide the desired clamping forces and still permit a maxi¬ mum travel after the molα sections commence to separate. FIGURES 22, 23, and 24 indicate the stacking sequences of both the large and small washers for respectively the top, middle and bottom fastener clamps. The preload force values are measured by inserting a feeler gage between the Belleville Washer and the adjacent bearing plate (e.g. 64a). For each of the stacking sequences illustrated, the desir- ed clamping force is achieved by preloading each Bellevil¬ le Washer supported bolt 58 to approximately half of its capacity.

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It will be understood therefore that the mold spring fastener assemblies must- be sized to provide sup¬ port for the adjacent mold section walls during the solidi¬ fication process of the ingot. 5 The spring supporting the bolts of the fastener assemblies must be sized to provide enough displacement freedom to minimize the restrained thermal stresses.

The preload on the spring fastener assemblies connecting the mold segments must be sized in conjunction

10 with the associated clip fasteners 44, to keep the mold segments together and prevent leakage at the flange junc¬ ture surface while the interface between the ingot and the interior of the mold is molten.

The mold assembly illustrated in FIGURE 25 is

15 approximately 100 inches tall (about 8 1/3 feet) with the wall thickness of the mold sections being approximate¬ ly 10.5 inches, and with the inside transverse or cross dimension of the mold cavity being approximately 28 inches at the top of the mold and approximately 32 inches at

20 the bottom of the mold. Thus the cavity, in the embodi¬ ments illustrated is tapered outwardly in a downward direction. The temperature of the metal poured into the mold for formation of the ingot may be in the order of 2800°F. The height of molten metal to which the mold is

^ poured is generally determined by the desired weight of the produced ingot, as determined by the orders given to the production mill. However conventionally, metal is poured to within approximately six inches of the top of an ingot mold of the aforementioned 100 inch mold cavity

_Ju height.

From the foregoiny di≤ccs-=ion and accompanying, drawings , it will be seen tnat the invention provides an

»v>» -

ingot mold provided with means affording stress ^' relief thereto for the ingot pouring operation, while maint¬ aining the mold in condition to aid in preventing metal leakage therefrom during the ingot pouring operation and 5 subsequent cooling of the ingot, and providing mold wall support for the ingot until its skin has sufficient struc¬ tural integrity to support the molten interior of the in¬ got, and a mold which can be recycled for use in a faster manner as compared to heretofore utilized solid or one- 10 piece type ingot molds. In certain embodiments, the mold is formed of a plurality of completely separate and indi¬ vidual side wall sections defining at least the side periphery of a mold cavity, together with coupling means connecting the wall sections together. The coupling means 15 provide for expansion and contraction of the mold sec¬ tions relative to one another during the pouring of molten metal into the mold, and the resultant heating and sub¬ sequent cooling thereof. At least certain of such coup¬ ling means comprises adjustable spring means able to be 20 preloaded a predetermined extent prior to the pouring operation, and thus providing for predetermined preload¬ ing of the openable and closeable junctures between the mold sections. In other embodiments, the mold may be of a generally one-piece affair, but having side wall sec- 5 tions with junctures openaole and closeable, together with the aforementioned coupling means, including pre- loadable spring means, for automatic compensation for expansion and contraction of the_mold during ^' the pour¬ ing and ingot producing cycles tnereof in a manner to _ - provide stress relief to the mold. A novel nietnod for pro¬ duction of rt.etal ingots is dlso disclosed.

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