US3460605A - Method for casting in a permanent mold a casting having thick and thin sections - Google Patents

Description

Aug. l2, 1969 n, H, BEETLE ETAL 3,460,605

METHOD FOR CASTING IN A PERMANENT MOLD A CASTING HAVING THICK AND THIN SECTIONS Original Filed Nov. 12, 1965 5 Sheets-Sheet l 63; :SSS Inventors 85 Robert 51. Beetle John B. Dabrzel/ B, auf/Dm .QH-orne@ 3 Sheets-Sheet 2 /IB l I THICK AND THIN SECTIONS R. H. BEETLE ET AL METHOD FOR CASTING IN A PERMANENT MOLD A CASTING HAVING Original Filed Nov. 12. 1965 zaT/////////'///////A Aug. l2, 1969 ewam Awww is ,m i H.. mwm l n im Allg. l2, 1969 R, H, BEETLE; ET AL 3,460,605

METHOD FOR CASTTNG IN A PERMANENT' MOLD A CASTING HAVING THICK AND THIN SECTIONS Original Filed Nov. 12. 1965 3 Sheets-Sheet 5 Invent-afs Robert H. Beetle John B. Dobne/ fl'i'torrze B Zdaiaa, mw( Dm v --United States Patent O U.S. Cl. 164-123 9 Claims ABSTRACT OF THE DISCLOSURE A method of casting metal in a permanent mold, the ultimate casting to have a thin section and a thicker section joined thereto, in which surfaces of the permanent mold material, defining the mold cavity for the thicker section of the casting, are exposed to chill at least a portion of the metal constituting the thicker section; whereas the permanent mold material is recessed and then lined with an insulating material to define the mold cavity for the thinner section of the casting.

This application is a division of application Ser. No. 507,999, tiled Nov. 12, 1965, now United States Patent No. 3,302,919, issued Feb. 7, 1967.

This invention relates to casting of metals, and more particularly to casting of metals into molds for receiving the cast metal.

The present invention is particularly directed to casting of metals into molds which are used repeatedly for a large number of castings, and hence the molds may be termed either semi-permanent or permanent molds, as contrasted with the sand mold which is expendible with each casting. Permanent molds made of metal with or without refractory lining have heretofore been employed, particularly with the casting of low temperature metals such as aluminum alloys, bronzes or magnesium alloys. However, metal molds, particularly when employed for casting metal such as steel poured at relatively high temperatures, are subject to becoming warped and cracker, which are presently limiting factors as to practices on a commercial scale.

A condition such as this in unacceptable when casting parts such as railroad car Wheels which must subscribe to rigid dimensional standards. Another deficiency of metal molds is that the metal walls of the mold lack the porosity to provide for escape of gases, resulting in defects caused by gas bubbles trapped at the interface between the mold wall and the casting, and even Within the casting.

Another material heretofore suggested for use as a permanent mold material is graphite. Graphite has a number of desirable characteristics recommending it as a mold material, among which characteristics are high resistance to thermal shock, resistance to warpage and ease of machinability. The graphite material has better resistance to Warpage than the metal mold and has a much higher thermal conductivity than sand enabling molten metal to solidify more rapidly than in a sand mold, thereby making possible faster production rates.

Faster production rates alford signiiicant reductions in the inventory of asks and storage of asks and may result in a greater yield from melting capability, which in some instances has heretofore been limited by the amount of time consumed for solidification of the metal in sand molds. Thus, sand is a poor heat conductor, and in the instance of castings such as railroad car wheels Where directional cooling is important, it sometimes requires an hour or more for solidification to become complete before ice a casting can be shaken out of the sand mold; whereas the same casting, if it could be cast in a graphite mold, could be removed from the mold in a shorter time period due to the greater ability of graphite to conduct heat.

While many of the foregoing properties of graphite as a mold material have been recognized, the prior art is signiiicantly lacking in a commercially acceptable technique employing graphite molds for the production of ingots or castings on a production basis without resorting to the use of special equipment for forcing the metal into the cavity formed in the graphite mold material.

One of the reasons for use of a pressure filling technique for graphite molds is to obtain a smooth and relatively fast ow of metal to fill the mold and thereby prevent the formation of laps, cold shuts, shot and other surface defects. Thus, the ability of graphite to conduct heat rapidly is not always an asset, since in castings with thin sections the graphite actually exerts undesirable chilling resulting in premature solidiication. Also, the castings are often designed to a specialized shape with large curves of continuing radii to facilitate rapid, non-turbulent flow of metal and to permit contraction of the hot casting without cracking or damage to the mold.

A problem with casting of sharp corners in permanent graphite molds is the inability to solidify metal in sharp corners and/or the inability of the hot casting to contract without restraint of the graphite. It is therefore an object of the invention to eliminate the foregoing limitaions by controlling the solidification of metal in a permanent mold formed partly of graphite to produce sound fine grain castings without resort to pressure filling techniques or special designs for the casting.

A further object of the invention is to control the solidification of metal in a mold by atfording selected portions of a graphite mold material with a facing or lining of a material having less thermal conductivity than that of the graphite.

Heretofore, known techniques tor casting high temperature ferrous metals or their alloys in graphite molds require considera-ble risering, hot tops or the like to feed the hot spots developed. The amount of metal needed for risers or hot tops decreases the 'yield from the metal poured, and additionally, the removal of risers adds to the cost of castings. Therefore, another object of the invention is to reduce substantially the metal loss in risers, hot tops or the like in permanent molds employing graphite.

Although the present invention can be employed to produce various shapes and sizes of castings and to produce ingots, bars, slabs or the like, one of the primary objects of the present invention, which is described in detail in the following specification, is to economically produce a high quality cast steel car wheels for railroad cars or the like in graphite molds. A railroad car wheel typically Weighs from 500 to 1000 pounds, and in operation is frequently subjected to large loads, severe dynamic stresses, and heavy wear conditions. Therefore, -a car wheel casting must be sound, particularly to assure safety against undue wear or fracture during use.

The present invention is directed to the use of graphite molds in a non-pressurized and top-pour casting process for railroad Wheels. Although it has heretofore been proposed in U.S. Patent Nos. 2,819,501 and 2,779,075 to produce railroad car wheels in a non-pressurized top pour casting process, to the best of our knowledge the process proposed in these patents has entailed resort to a pressure lling process in an eiort toward commercial practice. In the process described in the aforementioned patents, it has been found that the entering metal stream moves directly into contact with the graphite in the narrow-cross-sectional plate area of a car wheel mold and may result in laps, cold shuts, shots and other surface defects. The unprotected graphite at the plate and hub areas is severely eroded because the metal dropped from the ladle impinges directly against the graphite in these areas. Also, as the narrow cross-sectional plate of the casting solidies more rapidly than the larger cross-sectional wheel tread, this blocks feeding of metal from the hub and pouring gate to the tread. Hence, risers need be placed adjacent the tread to feed metal to the tread during solidification of the tread metal.

Under the process set forth in the aforementioned patents, the casting yield is reduced considerably by the amount of metal in the solid hub and in the plurality of risers located in a ring at the tread and plate areas of the mold. Risers interlock with .the casting and the mold, and thus a problem arises in the expense of detaching the `riseres from the casting and then removing the risers from the mold. The detaching of the risers from a casting often results in pads or areas on the wheel castings which should be ground off to prevent their detracting from the appearance of the casting. Accordingly, another object of the invention is to produce a railroad car wheel casting in a permanent graphite mold having controlled directional solidication of the metal by an insulating lining selectively applied to the graphite mold material to eliminate surface defects and the considerable amount of ri sering of prior art processes.

A more specific object of the present invention is to produce cast steel railway car wheels by a non-pressurized top pour of steel into a graphite block having the plate cavity areas thereof lined with an insulating material to afford directional solidification from the tread to a combined pouring gate and riser.

A more specific object of the present invention is to produce cast steel railway `car wheels by a non-pressurized top pour of `steel into a graphite block so configured and arranged as to present a mold wall of graphite at what corresponds to the tread of the wheel to effect a desired chill thereon, and inwardly thereof to present at what corresponds to the plate section of the wheel a mold cavity or wall defined by a ceramic insulating lining on the graphite block to prevent chilling of molten metal flowing through this thin or reduced section of the mold which is likely to result in shotting, spatter or lapped defects. This arrangement and configuration assures that molten metal fiowing through the thin plate section will flow rapidly outward to the tread portion of the mold cavity without occurrence of these defects as it ows through the reduced section of the mold cavity. The possibility of these defects has necessitated, in the prior art, resort to pressurized pouring of molten metal in an effort to overcome these defects at a graphite wall in a thin section of the mold that is in communication with an enlarged area outward thereof.

At the same time, the conliguration and arrangement referred to above as a characteristic feature of the present invention assures that the tread area of `the mold will be the rst to undergo a chill due to the graphite surfaces that are presented, resulting in the desired directional solidication that proceeds from the tread area rearward through the thin plate section and finally to what corresponds to the hub part of the wheel. These same advantages can, of course be realized in connection with other castings where molten metal is required to flow through a thin or narrowed-down part of the mold cavity outward to a larger section, and this consitutes a further object of the invention.

Another object of the invention is to cast new and Improved steel railway wheels.

Another object of the invention is to reduce the hot :ears and cracks in castings formed in graphite molds by ining the mold surfaces at the portion of the casting Jarticularly susceptible to hot tearing and cracking with t collapsible refractory material.

As mentioned above, the metal, dropping from the adle `and moving across the exposed graphite surface, :articularly at the hub and plate mold Walls, erodes the graphite surfaces. Therefore, a further object of the invention is to prevent erosion of a graphite mold cavity by lining areas subjected to erosion with a protective refractory, thereby achieving more castings before it is necessary to renew the mold cavity by machining.

Heretofore when casting complex shapes of castings in graphite moulds, the contraction of the casting during solidification in the mold exerted forces on the mold tending to crack or break the graphite mold material and to stress the casting adversely. Accordingly, a further object of the invention is to alleviate such stressing of the casting during contraction by providing a lining on the graphite, which lining collapses or yields when the casting contracts thereagainst. More specically, a further object of the invention is to afford collapsibility during contraction at the back of rim and ange fillets for wheel castings by means of a relatively thick and collapsible lining on a permanent mold material.

Another object of the invention is an improved car Wheel cast in a composite mold formed from graphite with a refractory lining at the plate cavity area.

Other and further objects of the present invention will be apparent from the following description and claims and are illustrated in the accompanying drawings which, by way of illustration, show preferred embodiments of the present invention and the principles thereof and what is now considered to be the lbest mode contemplated for applying these principles. Other embodiments of the invention embodying the same or equivalent principles may be used and structural changes may be made as desired fby those skilled in the art Without departing from the present invention.

In the drawings:

FIG. 1 is a sectional view of a mold constructed in accordance with one embodiment of the invention;

FIG. 2 is a plan view taken along the line 2 2 of FIG. l in the direction of the arrows;

FIG. 3 is an enlarged partial sectional view showing the lining of selected portions of the mold cavity with an insulating material;

FIG. 4 illustrates the use of a sweeping arm to apply an insulating coating to the drag mold section;

FIG. 5 illustrates the aligning of the cope section with a pattern;

FIG. 6 illustrates the injection of an insulating material in a cavity between the cope mold section and the pattern;

FIG. 7 illustrates the forming of a sand lining on the drag mold section of the embodiment of the invention of FIG. 8; and

FIG. 8 illustrates another embodiment of the invention employing a sand lining on the respective selected portions of the mold cavity.

Referring now to the drawings and more particularly to FIG. 1, there is illustrated in cross-section a moldcomprised of a top section or cope 10 formed from an annular block of graphite 11 disposed on a lower annular graphite block 12 of a mold section or drag 14. The blocks of graphite 11 and 12 are commercially available.

The cope 10 and drag 14 are clamped together lby suitably spaced clamps 16 extending between a cope flask or support element 20 and drag flask or support element 21. The clamps 16 hold the outer annular mating surfaces 23 and 24 of the graphite blocks 11 and 12, respectively, in fluid-tight contact during solidication of the molten metal entering the mold cavity through a combined gate-riser 2. The mold may be tipped or inclined, as viewed in FIG. 1, prior to pouring of the molten metal through the gate-riser 25; and after pouring the mold is returned to a level and generally horizontal position.

Graphite has the desirable characteristic of good thermal conductivity to chill the metal which affords a fine as-cast grain structure. Graphtie blocks are also known to be readily machinable to obtain the desired mold cavity. Graphite has good resistance to thermal shock and Warpage even for the high pouring temperatures required for steels. This is in contrast to metal molds which have less resistance to thermal cracking and warpage, particularly when casting steels therein.

An important aspect of the present invention is to control soliditication of the molten metal in a graphite :mold both as to the rate of solidication and as to the direction of solidification. For this purpose, selected areas of the cope and/ or drag are faced in an appreciable thickness With an insulating material to delay` solidification of the metal in contact with the insulating material.

In the illustrated embodiment of the invention, the insulating facings 30 and 31 are disposed opposite one another on selected surfaces of the respective cavities machined into the graphite blocks 11 and 12. The mold cavity, formed when the graphite blocks 11 and 12 are faced with the linings 30 and 31, is that of a railroad car wheel conforming to the AAR standards for railway car wheels, particularly those imade of cast steel having a carbon content of up to 1.2 percent. The present invention is not limited to railroad car wheels or to the carbon steels, buti s applicable to casting other metals such as but not restricted to high alloy steels, heat-resistant steels, stainless steel, malleable iron, manganese steel, abrasionresistant case iron, nickel and copper base alloys, low carbon alloy and carbon steels.

It will be seen from FIGS. 1 and 3 that after the insulating facings 30 and 31 are applied, the mold cavity or void has the configuration of a railroad car wheel having plate-forming surfaces 32 and 33, a front rim fillet surface 36, lback rim lillet surface 37, tapered annular surfaces 38 and 39, front rim surface 40, tread surface 41, flange surface 42, back of liange surface 43, front hub lillet surface 48, back of hub fillet surface 49 and back hub face 49A.

In the embodiment of the invention of FIGS. 1 and 3, the insulating facings 30 and 31 are of a ceramic material comprised of colloidal silica, citric acid, magnesium sulphate and kyanite, and the thickness of the facings 30 and 31 is varied to provide the proper rate of solidification of various areas of the casting, Precise thickness will vary depending upon wheel geometry and even ceramic composition. To this end, the coatings 30` and 31 may be of increasing thickness from the tread to the hub.

For example, the facings 30 and 31 are approximately 5/16 of an inch thick along the annular plate surfaces 32 and 33. The facings 3l) and 31 are feathered from to 1/32 of an inch thickness at the fro-nt rim fillet surface 36 on the cope block 11 and at the back rim illet surface 37 on the drag block 12. At the tread cavity S0, the graphite walls at the tapered surfaces 38 and 39 are preferably free of an insulating facing; but are coated with a conventional mold wash as are the graphite walls at the front rim face d0, tread 41, flange 42 and back of flange 43. At the hub fillets 48 and 49 the insulating facing is approximately B of an inch thick.

The relative thickness of the facings 30 and 31 at the hub iillets may be as much as Vs to 1/2 inch dimension at the front hub fillet 48 for some designs of wheels and for some of the ceramic coating materials employed; and the thickness for bonded said coating may be even considerably more, as explained hereinafter.

Thus, in contrast to a thin mold wash, it is contemplated that the insulating coating of the present invention can exceed the half-inch thickness and in some instances be one inch or more in thickness for sand-based facing materials. The mold may be described as a composite mold with molten metal at the tread and flange areas exposed directly to the graphite for a rapid transfer of heat, and with molten metal at the plate areas exposed to the refractory linings 36 and 31 for a less rapid transfer of heat.

The insulating linings 30 and 31 are non-permanent in the sense that they are replaced with a new lining for each of the separate castings formed in the mold. This is in contrast to the exposed (except for mold wash) graphite wall surfaces at the tread 50, which are renewed by machining, as explained hereinafter, only after a large number of castings. Thus, the mold is a composite mold in the sense that it has permanent blocks of graphite with non-permanent insulating linings 30 and 31 at selected areas.

A significant advantage afforded by the insulating linings 30 and 31 is that of controlled solidification of the molten metal as to time and as to direction from the large cross-section tread cavity 50 through the narrow cross-sectional plate cavity 51 to the large cross-sectional hub cavity t5 leading to the combined riser and gate cavity 25. That is, the molten metal is chilled by the mold wall of graphite at the tread of the wheel casting while the solidication of the molten metal within the plate cavity 51 is delayed by the linings 30 and 31 assuring liow of metal through the plate cavity without premature blocking of the plate cavity 51 by solidified metal that would interfere with proper feeding of the molten metal to the wheel tread from the molten metal at the hub gate and riser 25. Also, the linings 30 and 31 protect the graphite block at the hub and plate areas from being eroded by having the molten metal impinge onk the linings 30 and 31 rather than directly on the graphite surface.

A significant result achieved by directional solidiication from the respective insulating facings 30 and 31 is reduction of the number of risers to a single combined riser and gate 25. This single riser-gate 25 is in contrast to a ring of risers at the tread portions of the car wheel employed with prior art graphite molds in order to feed metal to the hot spots which could not be fed from the hub because of the rapid solidification of the metal within the narrow cross-sectional plate cavity. Thus, the present invention, by controlling the solidification of molten metal as above described, reduces the number of risers heretofore required.

The combined gate-riser 25 in graphite block 11 includes a cylindrical sleeve 56 with an open-center bore 57 fitted inside a cylindrical opening 59 machined at the center of the graphite block 11 of the cope 10. Preferably, the sleeve 56 is a one-piece core of sleeve shape with partial bell-shaped surface 57A, FIG. 1, formed on the bottom interior surface. In FIG. 3, the sleeve 56 is formed of two separate cores 58A and SSB joined to one another along an interface 58C. The lower surface of the hub core defines the front hub face 62 of the wheel casting. A plane of weakness exists between the metal in the riser and in the hub at the front hub face 62 rendering it easy to knock off the riser from the hub of the wheel casting. The sleeve 56 insulates the metal therein from the graphite at the bore 57 in the cope so that the molten metal in the sleeve 56 feeds in the manner of a riser after pouring of the metal therein.

The railroad car wheel has a hollow central hub for mounting on railway car axles. It is preferred that the car wheel have its hub cored. For this purpose, a solid hub core 66, FIG. l, is set into a recess 63 in the drag section and projects upward-ly slightly above the height of the front hub face surface 62. As best seen in FIG. 3, the core recess 63 includes a lower, annular wall 64 intersecting an inclined vertical wall 65. A core paste is used to secure the solid hub core 60 in the recess 63 against iioating free of the drag section 14 as the molten metal is enveloping the hub core 60. The hub core 60 may be an oil bonded sand core. Other suitable core materials may also be used and still fall within the purview of the present invention.

Although both the insulating linings and the graphite blocks are permeable materials and permit gases generated during pouring of the melt to move therethrough, it may be advantageous to accelerate venting of gas by forming vents 70 in the cope 10. Such venting of the gas may be at the elevated side of the cope 10, that is, the right-hand side of FIG. 1. Then, as the left hand and lower portion mold cavity, FIG. 1, is being filled, the gases continue to escape during filling of the cavity through the vent holes 71) disposed in a 180 arc on the right-hand portion y(FIG. 1) of the cope 10 in the area of the front rim face 40. lf deemed advisable, several vents 70, up to six in number, may be employed and equally spaced along the 180 arc.

The vent openings 70 if used are preferably formed by drilling a hole through the graphite block 11, filling the holes with an oil-bonded sand, and then driving a l/s inch wire through the oil-bonded sand to form a 1/e inch hole lined by sand. One of the vents 70 has a tapered steel plug in lieu of the sand lining so that if a casting does not readily release from the cope, the steel plug may be tapped with a hammer to exert a force on the top surface of the casting to knock the casting free of the cope 10.

In the example under consideration, the mold is preferably tilted at an angle up to 8 by the hydraulically operated plunger 75, FIG. 1. The mold is leveled almost immediately after filling. After three or four minutes have elapsed from the finish of pouring, the clamps 16 are loosened to permit contraction of the wheel casting after solidifcation particularly along the tapered back of the tread surfaces 38 and 39. These angles and times may vary tfrom the example given depending upon wheel geometry and the nature of the lining.

After an outer skin or envelope of solidified metal has formed to retain the inner and less solidified metal within the casting, the annular cope and drag surfaces 23 and 24- are no longer clamped in tight sealing engagement. It has been found that contraction of the tread of the casting wedges the cope upwardly a slight distance after the clamps 16 are removed. That is, the tapered surfaces 38 and 39 of the casting, contracting inwardly toward the center hub 45 during the solidiflcation of the wheel, lift the wheel and raise the cope 10. Releasing of the cope 10 for upward movement during contraction of the tread prevents hot tearing or cracking at the fillets 36 and 37. If desired, a mechanical force can be applied to lift at least a portion of the weight of the cope 10 from the casting during its contraction.

After an elapse of eight to ten minutes `from the time of pouring in the example under consideration, the cope `10 is lifted and the Iwheel casting detached therefrom. The wheel castings may then be transported to a soaking pit for temperature equalization, and thereafter subjected to heat treatment.

The handling of the cope and drag is facilitated by the flasks and 21 which include annular bands 80 and 81 disposed in contact with the outer peripheral surfaces 82 and 83 of the cope 10 and drag 14. The cope flask 20 has a top, inwardly directed flange 84 disposed to engage the top surface 85l of the cope. The top flange 84 is an annular member. Preferably, the peripheral surface 82 of the cope is machined to a shoulder at 88 and a series of spaced, segmental-shaped plates, three or four in number, extending beneath the annular shoulder 88, are secured by bolts 89 to outwardly turned annular flanges 90 on the lower portion of the band 80'. Thus, the segmental plates 88 extend inwardly toward the hub and are clamped against the shoulders 88. The cope 10 is adapted for convenient lifting and moving by connection to trunnions 92 secured to the cope flask 20 at the center of gravity of the cope to facilitate rotation thereof about the trunnions 92.

The drag flask is similar to the cope flask 20 and includes a bottom, annular flange 95 which is inwardly directed into engagement with the bottom surface 96 of lthe cope 10. Spaced rectangular plates 97 are secured by suitable fasteners 98 to outwardly directed annular flanges 99 integrally formed on the bands 81. The plates 97 extend inwardly toward the hub of the wheel and over a shoulder 100 machined in the peripheral surface 83 of the drag 14.

Suitable trunnions 101 are provided and attached to the cope flask 21 to permit the convenient handling of the block of graphite constituting the drag 14.

It will be appreciated that the shoulders 88 and 100 in the graphite blocks of the cope 10 and drag 14 are readily machined. After the mold cavity has been used repeatedly for a large number of castings, the surface of the mold cavity is refurbished by machining away proportional increments of approximately 1A inch along the generally horizontal mold cavity surfaces including the mating annular surfaces 23 and 24. The tapered and generally vertical surfaces at the hub and tread are not machined, as machining of the vertical surfaces would increase the diameter of the hub and the wheel. The graphite blocks are sufficiently thick to permit a plurality of machining operations to renew the casting cavity. During the refurbishing of the mold cavities, the flasks 20 and 21 need not be removed. A major problem of the aforementioned patented processes using graphite as a mold material has been erosion of the graphite by the molten metal, thereby necessitating renewal of the mold cavity by more frequent machining of the cavity that is desirable. With the present invention the linings 30 and 31 protect the graphite blocks at the hub and plate cavities where the metal is incoming from the ladle. This results in less erosion and less frequent machining to renew the mold cavity.

Other areas of the graphite mold are protected from mechanical abrasive wear by the linings 30 and 31 along the graphite surface at fillet 36 and 37 against which the contracting wheel casting would otherwise move during contraction of the solidifying wheel casting. Any mechanical breakage of the graphite at the tread risers during contraction of the wheel is avoided by the linings 30 and 31, the use of which eliminates the need for tread risers.

To form recesses in graphite blocks 11 and 12 for receiving the insulating layers 30 and 31, the cope 10 and drag 14 are each undercut by machining away a contour in the graphite block from that of the wheel contour.

The insulating linings 30 and 431 of ceramic adhere to the undercut graphite surfaces without any adhesive bonding agents or mechanical fasteners. It is thought that the graphite surface is sufficiently porous to receive the ceramic lining material which, as it sets, mechanically interlocks and keys itself to the graphite blocks. For other insulating materials, mechanical means, fasteners or adhesives may be employed to retain the linings in place.

One suitable method of applying the insulating lining 311 to the drag 12 is described hereinafter in conjunction with FIGS. 5 and 6. The drag 12 is provided with aligning apertures 121 in a pattern plate 122 of a pattern assembly 124. The pattern assembly 124 has secured thereto a centrally located Wheel pattern 12S having an upper surface 126 configured to the shape of a car wheel. The insulating material is placed on the pattern 125 and the drag 12 is brought into engagement with the pattern 125 along the annular flange face 43, FIG. 6, with suflicient force to squeeze and spread the ceramic material. Any excess ceramic material is squeezed outwardly and removed. Alternatively, the pattern 125 can be provided with internal ducts through which the facing material can be injected into the space between the plate surface 103 of the drag 12 and the surface 126 of the pattern 125. The ceramic facing 30 is allowed to gel and the drag 12 is lifted in its now attached insulating lining 30 from the surface of the pattern 125 which may be coated with a releasing or parting medium, if desired, to facilitate its release from the lining 30.

The cope 11 may also be disposed over a pattern similar to the pattern 125 for the drag, and the insulating material interposed between the pattern and the recess surface on the cope 11 to form the desired thickness of the facing 31 at the pre-selected recessed areas at the plate.

Another method of applying the insulating linings 30 and 31 is that of using a rotatable sweep 135, FIG. 4,

which includes a sweep arm 136 secured to a sleeve 137 journaled for rotation about a shaft 138. The shaft 138 is secured to a plug 140 seated in the core recess 63 of the drag 14. After applying a quantity of the insulating material to the surfaces 150 to be coated, the sweep arm 136 is revolved to rotate a sweep plate 142 to form the ceramic material between opposite ends 145 and 146 of the sweep plate 142. The curvature and recess surface 148 of the sweep plate 142 is such that sweeping of the plate 142 forms the ceramic slurry into the desired conguration and sweeps away the excess material, which may then be removed. In a similar manner, a suitable sweep for the cope 10 may be provided to deposit the refractory lining material over the plate surface in a coating of the desired thickness.

As will be brought out more fully hereinafter, sand may be used as the material for the linings 30 and 31. Additionally, a number of ceramic materials could be employed. By way of example, a ceramic coating material for the respective linings 30 and 31 is comprised of the following ingredients:

Colloidal silica (30% SiO2) cc-- 2160 Citric acid (one molar solution) cc -i 34 Kyanite (100 mesh x down) lbs-.. 16.5 Magnesium sulphate solution (600' gm./ 1000 cc.

H2O) cc-- 35 The above quantities are approximate figures and are varied slightly depending upon humidity, temperature and other environmental conditions which would affect gelling within a predetermined time.

The colloidal silica, citric acid and kyanite are mixed thoroughly, kyanite being added until the viscosity reaches approximately 82 Be. The sulphate solution is added and mixed well. The slurry is then ready for use. The amount of sulphate solution controls the time in which the mix gels. The more sulphate solution added, the quicker the setting time. When the slurry is applied to a warm mold, the heat from the mold causes the mix to set more quickly. A setting time of about minutes at room temperature produces a setting time of about 1 minute on a mold at 160 F., which is satisfactory for sweeping.

The initial gelling of the ceramic linings 30 and 31, which is in the form of a slurry when the lining is formed by the sweep method or by an injection method, is accelerated by the heat of the cope 10 and drag 14. On a production basis, the cope 10 and drag 14 will be at elevated temperatures because of the residual heat of previous casting operations. Where the cope 10 and drag 14 are being used initially, the cope and drag are preheated to approximately 150-180" F. to facilitate the gelling of the refractory ceramic linings 30 and 31.

After the linings 30 and 31 are gelled, the linings are cured. For example, the cope 10 and drag 14 may be brought to gether to form a complete mold and heated at a temperature and for a time sufficient to cure the linings, in an oven at about 400 F. for a period of several hours. Also, as much moisture as possible is driven otf the mold during this baking operation. Shortly before the mold is to receive the molten metal, the mold is removed from the oven, the vent holes (if used) are lined with sand, and the central opening is formed in the vent holes, the hub core 60 is pasted in position and the unlined areas of the mold cavity are sprayed with a mold wash made of a mixture of Zircon fluor, bentonite and water. The mold wash is sprayed or brushed onto form a very light layer of about 1&4 inch or less in thickness. The function of the mold wash is to protect the graphite surfaces. The mold is then closed with the cope 10 aligned on the drag 14 by the usual pins and holes on the respective ilasks and 31. Next the clamps 16 are applied and the mold is tilted by the tilting means 15.

Metal is poured into the mold through the central combined gate and riser means to till the entire mold cavity and the riser cavity 57 within a maximum pouring time of about 20 seconds. The pouring temperature and time of pour will depend upon the composition of the metal and the size and shape of the casting.

As soon as the mold is filled, the mold is leveled, that is, untilted. After a skin is formed on the metal, the clamps 16 are loosened to allow contraction of the wheel tread with the consequent lifting of the cope 10 relative to the car wheel casting. After the casting is cooled to a desired temperature, the cope 10 is lifted :and the wheel casting is separated therefrom. The riser having been knocked olf, the wheel casting is immersed in a soaking pit. The wheel casting is taken from the soaking pit and subjected to heat treatment.

The cope and drag have their casting cavities cleaned, particularly to remove any remaining portions of the linings 30 and 31 and the riser sleeve `56. The cope and drag are then ready to receive a new lining 30 and 31 and a new riser sleeve 56 for the next casting operation.

Another embodiment of the invention is illustrated in FIGS. 7 and 8, wherein the refractory linings 200l and 201 of sand are disposed on the plate areas of the graphite block 11 of the cope 10 and the graphite block 12 of the drag 14. The sand linings 200 and 201 function in the manner of the linings 30 and 31 to achieve the advantages of protecting the graphite plate surface against erosion and to afford directional solidiiication. As readily observed from contrasting the refractory linings 30 and 31 of FIG. 3 with the refractory linings 200 and 201 of FIG. 8, the particular thickness and shape of the refractory lining may be varied when changing the kind of refractory material used as a lining.

In these illustrated examples of the invention, the ceramic linings 30 and 31 are approximately @is of an inch thick along the annular plate surfaces 32 and 33, while the sand linings 200 and 201 are approximately 11/16 of an inch thick along annular plate surfaces 32 and 33 of the respective graphite blocks 11 and 12. The thickness of the sand linings 200 and 201 is increased to approximately 7s of an inch at the back of rim fillet 36. The sand lining at the back of iiange lillet 37 is approximately UAG of an inch thick. These relatively thick linings at the rim and flange fillets 36 and 37 are of significant importance in that they collapse with the contraction of the rim metal of the wheel thereby preventing hot cracks or hot tears in the wheel and prevent cracking or breaking of the graphite. That is, the sand linings 200 and 201 are thick and less rigid, that is, more yieldable than the graphite and are displaceable under pressure from the tapered surfaces 38 and 39 contracting after solidilication of the metal. Although the sand linings 200 and 201 collapse during contraction of the casting, it is also preferred vto release the clamps 16 holding the cope and drag sections together during contraction of the wheel rim.

It will be recalled that the ceramic linings `30 and 31 mechanically keyed themselves to the porous graphite surfaces such that additional fastening or locking means were not required. On the other hand, it has been found that the sand linings 200 and 201 do not self-bond or key themselves to the graphite blocks 11 and 12. For the purpose of locking the respective linings 200 and 201 to the respective graphite blocks 11 `and 12, each graphite block 11 and 12 is provided with a series of spaced holes 203, 204 and 205, which are drilled throughout the graphite blocks 11 and 12 and which extend from the respective linings 200 and 201 through to the outer surface of its respective graphite block 11 or 12. In practice, the holes 203, 204 and 205 are 3A of an inch in diameter and as many as nineteen such holes have been provided in each of the graphite blocks 11 and 12. Small screens 203A, 204A and 205A are disposed in their respective openings about of an inch from the graphite surfaces to block the sand from moving outwardly with the air through the screens 203A, 204A and 205A.

When the sand is set as by the residual heat of the mold or by heating in an oven, hardened plugs of sand of about 3%: inch in length are cured in the openings 203, 204 and 205 to lock mechanically the respective linings 200 and 201 to the graphite blocks 11 and 12, respectively. Additionally, it is to be noted that the holes 203, 204 and 205 function as vent holes to permit the escape of gas, thereby functioning to replace the vent holes 70 described in relationship to the embodiment of the invention illustrated in FIGS. l-3.

Additionally, the sand linings 200 and 201 are mechanically interlocked by portions 208 and 209 formed in annular grooves cut in the graphite blocks 11 and 12 adjacent the rim face and back o-f the flange face. The lining 201 is also anchored to the graphite block 12 by an annular portion 210 at the inner and lower end thereof adjacent the back hub surface 39 at which the graphite is exposed directly to the metal.

At the front hub llet 48, the sand lining 200 is increased appreciably in thickness to approximately 11/16 of an inch, and the sand lining 200 has an upper and annular sleeve or portion 212 extending considerably above the front hub face or plane 62. This additional annular sleeve 212 of sand lining affords additional insulation against rapid heat transfer to the graphite for the metal disposed in the combined gate-riser 25 above the hub face plane 62. The cores employed in the combined gate-riser 25 illustrated in FIG. 8 are preferred to the simple core sleeve 56 and the hub core 60l described hereinabove in conjunction with FIG. 1.

AS can best be understood from FIG. 8, the combined gate and riser means 25 includes a sleeve 213 similar to the sleeve 56 hereinabove described. Disposed beneath the riser sleeve 213 is a circular strainer core 214 which includes an annular tiange 214F which is secured by core paste to the sleeve 213 and to the annular portion 212 of the lining 200. The strainer core 214 is provided with a plurality of openings 214S through which the metal is free to flow into the hub cavity 45 about the hub core 216.

When the tread cavity 50, plate cavity 51 and hub cavity 45 are filled with molten metal, metal flows through spaces between the upper spaced legs 217 of the hub core 216 and flows into a central opening 214G in the strainer core 214 to lift and float a barrier core 219 resting on the strainer core 214. The central opening 214G in the strainer core 214 affords a large central opening for feeding molten metal from the riser sleeve 213 to the hub cavity 45 for the directional solidication proceeding from the tread cavity 50 wherein the molten metal is being chilled by the graphite at the rim surface 40, tread surface 41 and ange surface 43.

The apertures 2145 in the strainer core 214 are so dimensioned that the metal flowing therethrough, from a pool of metal disposed within the riser sleeve 213, flows at a constant controlled rate to gradually fill the mold cavity without unacceptable turbulence. As the level of the metal rises toward the underside of barrier core 219, the barrier core 219 ceases to function as a barrier across the central opening 214G and this large central opening 214G makes available the hot molten metal above the strainer core 214 for feeding into the hub zone to prevent shrink in the solidifying metal in the mold cavities.-

The strainer core 214 also creates a plane of weakness to permit the riser to be readily broken from the wheel hub along the front hub face or plane 62, FIG. 8.

The sand linings 200 and 201 thus constitute a refractory lining in the manner of the ceramic linings 30 and 31. Like the ceramic linings 30 and 31, the sand linings 200 and 201 are gas permeable. The sand mixtures for the linings 200 and 201 may be bonded by oil, resin bonded, or bonded by other materials.

The preferred manner of applying the linings 200` and 201 is described hereinafter in conjunction ywith the illustration of FIG. 7. The drag 14 is shown in FIG. 7 as mounted on a base plate B and an inverted pattern 223 is 12 aligned and secured in clamped relationship above the drag 14.

Aligning pins 221 extend downwardly from a pattern base plate 222 into apertures formed in the flask means 20 to align pattern 223 to have its axis centrally located coincident with the central axis of the drag 14. The pattern 223 has an outer rim portion 225 which tits tightly against the rim face 43 of the graphite block 12 to prevent the escape of sand outwardly from the pattern 223. The pattern 223 is suitably secured to the base plate 222 with a plurality of central apertures 228 aligned with apertures 229 in the base plate 222. The apertures 22S lead to the pattern face 230 which is spaced from the plate-forming surface 106 of the graphite block 12. Preferably, the sand is blown by a blast of air from a duct 235 through the apertures 229 in base plate 222 and through the aperture 228 in the pattern 223.

The incoming sand for forming the lining 201 is cornpacted in the cavity formed between the pattern face 230 and the graphite block 12. The air blast carrying the sand exits through openings 239 in the pattern 223. Strainer members 240 may be employed above the base plate 222 in aligned relationship with the openings 239 to permit the air to exit out of openings 239 while retaining the sand within the cavity between the graphite block 12 and pattern 223. The air also exits the apertures 203, 204 and 205 while filling the same with sand, which, after hardening serves as a mechanical lock for the lining 201.

A similar arrangement is provided for forming the sand lining 200 on the graphite block 11 constituting the cope. That is to say, a cope pattern generally similar to the drag pattern, illustrated in FIG. 7, is aligned with the sand blowing duct 235 to blow said through the openings in the cope pattern, which openings correspond to the openings 228 in the drag pattern 223.

The apparatus for blowing the sand lining does not constitute a part of the present invention and hence is not described in detail.

It is preferred that the sand linings 200 and 201 be made from known sand mixtures bonded by oil or sodium silicate; however, resin bonds or other bonding materials may be successfully employed.

Preferably, the interior surface 230 of the drag pattern 211 and the interior surface of the cope pattern (not shown) are smooth, and if desired may be lined with a release agent so that the pattern may be removed without causing the sand to be broken away from the graphite blocks 11 and 12.

The sand linings 200 and 201 have also been applied by using the sweep 135, FIG. 4, as hereinabove described in connection with the ceramic linings 30 and 31.

Additional light washes or sprays are preferably applied to the exposed graphite surfaces at the tread cavity 50, FIG. 8, and at the back hub face. If desired, a light wash may be applied to the sand linings 200 and 201 to provide an improved surface on the castings at the plate area thereof. The residual heat in the graphite blocks 11 and 12 dries the wash, core paste and sets the sand linings 200 and 201. Alternatively, the mold is baked for two or three hours at 425 F. to set the coatings 200 and mold. 201 and core paste, and to dry the wash and pre-heat the From the foregoing, it will be seen that the present invention affords a commercially feasible method and apparatus for producing sound castings in molds having graphite material with selected areas lined with an insulating material. This insulating lining protects the graphite against erosion and affords controlled directional solidification from the chill afforded by the exposed graphite.

The controlled solidication enables thinner cross-sectional areas to be cast in graphite molds while permitting significant increases in yield by reducing the amount of risering. The ability to cast thin cross-sectional plates for car wheels is a significant advantage for producing car wheels having a thinner plate section which, in some instances, is desirable.

As stated hereinabove, the present invention is not limited to the casting of steel. Typical steels for car wheels have carbon up to 1.20 percent, manganese 0.60 to 0.85 percent, phosphorous not over 0.05 percent, sulphur not over\0.05 percent, silicon not less than 0.15 percent, and the balance substantially pure iron except for special additive agents.

From the foregoing, it is seen that the refractory linings afford a number of advantages, such as protecting the graphite from erosion, that is, mechanical abrasion, either from the metal being poured from the ladle or from the hot casting moving against a graphite surface during contraction of the casting after solidification. Also, the linings afford significant protection to the graphite surfaces to protect them from rapid thermal gradients, particularly at the plate area of the mold, thereby affording a longer life between times of renewal of the graphite by machining.

As mentioned above, the present invention is not limited to the casting of Wheels; but it is to be pointed out that the present invention is as well not limited to the particular shapes of lwheels nor particular shapes of linings, set -forth in the specific examples described hereinbefore. It will be readily appreciated that wheels are cast in a number of different shapes having different thicknesses of plate and different thicknesses at the rim to constitute the familiar one-wear or multi-wear wheels. When casting multi-wear Wheels, the amount of metal disposed in the tread cavity 50 is increased appreciably from the amount of metal in the tread cavity 50 when a onewear wheel is being cast. With the changes between the different wheel designs, such as between one-wear or multi-wear wheels, the amount of lining may be changed not only as to thickness, but also as to shape of the lining. For instance, it is possible under the present invention to use the same cope 11 and drag 12 for one-wear wheels and multi-wear wheels by having the sand coating for the single wear wheels increased appreciably in thickness to occupy the space in which metal would be disposed when casting a multi-wear wheel. Another example of a different wheel design is that of the wheel designs preferred in some foreign countries wherein holes of a predetermined shape are formed in the plate section. By using suitable patterns, it will be appreciated that the respective linings in the plate areas can be so configured as to form cores to afford such holes or openings in the plate of these wheels.

In some instances, it is desirable to line the graphite at the back hub face 49, as illustrated in FIG. 3, and in other instances it is not desired to line the graphite at the back hub face 59, for example, as seen in FIG. 8. When the graphite at the back hub face 49 is unlined, the metal in the hub is solidified more rapidly, permitting the wheels to be removed more quickly from the mold than would be the case when the back hub face 49 is lined with a refractory lining. In the illustrated embodiment of the invention of FIG. 8, the wheel cast with the thick linings 200 and 201 solidifies and can be shaken out after 20 to 25 minutes because the hub face 49 is not lined other than by a thin mold Wash coating.

While the illustrated embodiments of the invention are described with unitary blocks 11 and 12 of graphite, it is to be understood that a plurality of pieces of graphite can be readily employed. `For instance, -when leaving the hub face 49 unlined, the hub face 49 may be an individual and separate graphite section from the remainder of the graphite drag block. Thus, the hub section can be readily replaced after erosion of the graphite at the hub face 49. Although the graphite blocks 11 and 12 significantly large with respect to the metal in the flasks 20, it is within the purview of the present invention to use a significant amount of metal in the permanent mold while using small pieces of graphite in the form of inserts. More specifically, the permament mold body may be formed mostly from cast iron with ring-like graphite inserts to afford the metal chill and with the refractory linings to aord the directional solidification. In this last described mold, the refractory linings and graphite protect the large body of cast iron `from the thermal gradients, heretofore the cause of warping and cracking of the surface of such permanent molds formed of cast iron.

Hence, -while we have illustrated and described preferred embodiments of our invention, it is to be understood that these are capable of vvariation and modification.

We claim:

1. In a method of casting a metal article in a cavity in a mold having permanent mold material to chill the metal cast therein, the steps of: affording a surface in the permanent mold material for chilling the molten metal by the permanent mold material, affording opposed recesses in the permanent mold material corresponding to substantially the entirety of a thin plate section and a thicker outer section of the article to be cast and which outer section terminates at the chill surface, lining the entirety of the opposed plate section recesses with an insulating material of less thermal-conductivity than the permanent mold material, and pouring molten metal into said mold cavity for movement past said lined portion of the mold cavity and then into chilling contact with the permanent mold material and reverse directional solidification from the chill past said lined portion.

2. A method according to claim 1 wherein the lining is also applied to the mold recesses Where the thin and thick sections merge.

3. A method according to claim 1l wherein the lining is yieldable, the cavity in said mold generally corresponding to the geometry of a railroad wheel having a central hub, an enlarged outer rim and tread and a thin plate joining the hub and rim at respective llet surfaces, the chilling surface of the mold corresponding at least to the tread 0f the wheel, the insulating lining extending to the portion of the recesses corresponding to the fillet Where the rim and plate are joined, whereby the insulating lining yields to the metal contracting thereagainst.

4. A method according to claim 3 wherein a riser opening is located at the hub section of the mold and through which molten metal is poured into the mold, said lining being present at all fillet areas of the mold cavity.

5. In a method of casting a wheel or other article of such cross-section as to have an enlarged first portion and a second thinner portion joined thereto, and wherein the metal for the casting to be poured through an opening, the steps comprising: forming a mold cavity in permanent mold material to present a thin portion conforming gene-rally to the geometry of said second thinner portion of the casting and to present an enlarged portion defined by surfaces of the permanent mold material conforming substantially precisely to said first portion of the casting, affording an opening in the mold in communication with the thin portion of the mold cavity and into which molten metal is to be introduced, lining the thin portion of the mold cavity in the permanent mold material corresponding to the thinner portion of the casting with an insulating refractory material of appreciable thickness to conform substantially precisely to the geometry of the thinner portion of the casting while excluding said lining from surfaces of the permanent mold material which conform to an enlarged portion of the casting, and pouring molten metal through said opening to fll said mold cavity resulting in solidification of metal therein directionally from said enlarged portion of the mold cavity to said opening through the thin part of the mold cavity.

6. A method according to claim 5 wherein the refractory lining is yieldable and terminates at the junction between the thin and enlarged mold cavities, whereby metal solidifying in the enlarged mold cavity contracts against the yieldable lining.

7. In a method of casting a steel wheel having a hub and a tread on a rim, and a plate interconnecting the hub and rim at an inner and an outer fillet, the steps of: forming a mold cavity in permanent mold material corresponding generally to the geometry of the hub and plate and llet portions of the wheel and to present surfaces of the permanent mold material conforming substantially precisely to the tread portion of the wheel, alording an opening in the mold, lining at least the outer llet portion of the mold cavity `with an insulating material to conform substantially precisely to the outer wheel fillet geometry While excluding said lining from the surfaces of the permanent mold material which conform to the tread of the wheel, pouring said steel through said opening to till said mold cavity and to solidify said metal directionally from said tread to said opening through said insulated portion.

8. A method according to claim 7 wherein the insulating lining covers substantially the entirety of the perma- 16 nent mold material corresponding to the plate of the wheel.

9. A method according to claim 7 conducted at ambient pressure and wherein the opening is a riser centrally located to feed the hub of the wheel.

References Cited UNITED STATES PATENTS 5/1912 West 164--356v 6/1963 Chandley 164-23 U.S. Cl. X.R. 164-127

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