US3433293A - Mold for casting railroad car wheels - Google Patents

Description

March 18, 1969 F. w. PONZAR MOLD FOR CASTING RAILROAD CAR WHEELS I of 2 Sheet Filed Dec. 19, 1966 FIG] 0 WA Z N E O V P WW D E Du F BY we)? FIG.2

ATTORNEYS March 18, 1969 F. w. PONZAR MOLD FOR CASTING RAILROAD CAR WHEELS Sheet 3 of2 Filed Dec. 19. 1966 METAL ZONE AT FEED SLOT 48 HEAT SINK METAL NR m WP w D E R F ATTORNEYS United States Patent 3 Claims ABSTRACT OF THE DISCLOSURE A mold for casting a railroad wheel comprising a center core, a gate core reposing on the center core, and a float core resposing on the gate core; and so arranged and formed in relation to a riser opening in the mold as to facilitate completion of the hub opening of the wheel.

This invention relates to mold apparatus for producing railroad car wheels by foundry or casting procedures.

Railroad car wheels have been manufactured for many years from what is conventionally known as gray iron foundry techniques. These cast iron wheels were common in freight service until the railroads increased their operating speeds and loads to a point where the properties of cast iron were no longer satisfactory; and hence the use of steel became necessary. It was found, however, that merely substituting steel for cast iron would not produce satisfactory wheels, because certain basic differences between the two foundry practices revealed that practices which produced sound cast iron wheels were not suitable for steel. Some of these problems had their origin in the fact that molten steel is considerably less fluid than cast iron. Raising the pouring temperature of molten steel will improve its fluidity somewhat, but because of the relatively high shrinkage of steel, when it transforms from the liquid to solid state, higher pouring temperatures can cause unsoundness to develop in heavy sections in castings. Stated otherwise, it has been found that lower pouring temperatures tend to produce less porosity in steel castings.

Another factor which was encountered was the difficulty engendered by the geometry or configuration of the wheel. The conventional railroad car wheel is a disc-like body having a heavy hub section containing a cylindrical central aperture for receiving the axle, a relatively thin plate or web section and a relatively heavy rim or tread section. This shape, for practical considerations, requires that the location of the sprue or opening, whereby the molten metal is introduced into the mold cavity, should be coincidental with the rotational axis of the wheel and that the wheel shall be cast in a substantially horizontal plane. Some of the problems which arose when more or less conventional rammed sand mold techniques were attempted were porosity in the tread section, porosity in the hub zone and a severe washing of the mold cavity during the pouring operation which tended to produce surface and dimensional defects. The mold apparatus comprising this invention solves these problems, among others.

It is therefore a principal object of this invention to provide an improved mold for the manufacture of sound cast steel railroad car wheels, characterized 'by a center core, a gate core, and a float core assembled at the portion of the mold corresponding to the hub of the wheel and the riser opening through which molten metal is poured.

Briefly stated, and in accordance with one embodiment of this invention, a mold for casting such wheels is provided, including a gate core which prevents slag and other non-metallic material from entering the mold cavity, and which controls the rate at which the mold cavity is filled,

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thereby preventing washing, and which feeds molten metal to the heavy hub section during solidification to prevent porosity from developing.

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 a preferred embodiment of the present invention and the principles thereof and what is now considered to be the best 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 by 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 the present invention;

FIG. 2 is a fragmentary sectional view on an enlarged scale of a portion of FIG. 1;

FIG. 3 is a plan view of the gate core; and

FIG. 4 is a schematic view showing an intermediate stage in the cooling and solidification of the casting.

With reference to FIG. 1 of the drawing, the invention is disclosed as embodied in a rammed sand foundry mold 10 comprising a cope 12 and drag 14. Separating the cope and drag members is a chill member 16, for chilling the molten metal corresponding to the tread of the wheel. It will be understood that, as shown, the cope 12 and the drag 14 is preferably right circular cylinders, while the chill 16 is essentially a truncated right circular cone. These features are well known in the art, and are here described for purposes of understanding. In fact, the invention can be applied to the permanent car wheel mold disclosed in application Ser. No. 507,999, filed Nov. 12, 1965.

The mold cavity for casting the steel railroad car wheel is formed by the rammed sand or equivalent foundry refractory material in the cope and drag members, as shown at 20 and 21, and by the chill 16. That portion of the mold cavity within which the hub portion of the wheel is formed contains a refractory assembly 3 0, which may conveniently be referred to as a core; however, the functions performed by the core assembly go far beyond those presented by the usual foundry core, as will be shown presently.

The assembly of core 30 comprises a center core 32, a strainer or gate core 34 and a cover or float core 36. As shown in FIGS. 1 and 2, center core 32 is supported in a recess 38 in the rammed sand drag. It is composed of a solid, right circular cylindrical base portion 40 having a cup-shaped cavity 41 formed therein, opening at the top of the core member 32. The cavity 41 is defined by a vertical, annular wall 41W presenting an upper free edge 41E, FIG. 2. An external, annular shoulder 408 is formed in base 40, being of larger diameter than the wall 41W.

The exterior of the center core represents the hub opening of the wheel to be cast.

The strainer or gate core 34 is essentially a cup-shaped circular disc having a vertical rim portion 44 by means of which the core 34 is supported across the bottom of the pouring basin or riser cavity 46 in the cope, as shown in FIG. 1. The bottom wall 34W of core 34 is provided with a large central opening 48 and a plurality of smaller openings 50 adjacent rim 44, FIG. 3. The bottom wall 34W of the core 34 is provided with spaced fingers 34F each having a shoulder 348 at the underside, enabling the core to repose neatly on the upper edge 41E presented by the wall 41W of the center core 40.

The float core 36 is essentially a solid, circular plate provided with recessed shoulders 368 at the underside which rest upon the top surface of wall 34W of core 34, FIGS. 1 and 2, in such a manner as to completely expose opening 48 as well as the openings 50.

In use, the cope, drag, chill and core 3-0 are assembled together as shown. Clamping means, not shown, are provided to secure the cope 12 and chill 16 together and other clamping means (also not shown) are used to secure the cope and drag together. Molten steel is then poured into the opening 46, constituting a central riser, so that the initial contact of the stream of molten metal is upon the float core 36. The molten metal flows over the top of core 36 and down through openings 50. The pouring is continued at a rate such that the riser 46 is filled quickly and maintained substantially filled throughout the duration of the pouring operation. The weight and the velocity of the molten metal above the float core 36 holds it in place over opening 48 and the plurality of small openings 50 serve a metering and straining function which prevents slag and other relatively light impurities from entering the main mold cavity.

By thus restricting the rate at which the molten metal may enter the mold cavity, splashing and turbulence are vastly reduced and objectionable washing of the mold is avoided, thus contributing to an improved surface of the casting. Further, the interior of the mold cavity is filled at a constant, controlled or metered rate which is a desirable condition.

As the mold cavity is filled, the level of the molten metal approaches and ultimately reaches the feed opening 48, from whence it flows into and fills the cavity 41, which becomes a heat sink toward which contraction of the casting takes place. Eventually, molten metal fills cavity 41 and contacts the lower surface of the float core 36. Pouring is terminated. At this time, cover core 36, which is made from a refractory material which is lighter than the molten steel, floats free of core 34 and rises into opening 46, completely exposing opening 48. When core 36 reaches the surface of the molten steel in the sprue or riser 46, it serves the additional function of providing an insulating heat barrier and helps keep the molten steel below it, especially that in the heat sink 41, from losing heat too rapidly to the atmosphere.

On the other hand, the chill 16 promotes the rapid transfer of heat to the atmosphere and hence a directional solidification pattern is promoted which helps insure soundness in the tread and plate zones of the wheel casting and produces a desirable structure. Thus, solidification takes place first at the tread chill 1'6 and then progressively inwardly toward the hub. The last portion of the wheel to solidify in the hub zone where the core assembly 30 is located, and all of the shrinkage attendant with the final solidification occurs at that zone. However, the large volume of still molten metal in the pouring basic or riser area 46, as well as that in the reservoir 41, is available to feed through the large opening 48 and the openings 50' to supply molten steel to prevent shrinkage porosity in the hub zone. By these means, a thoroughly sound wheel is cast in which there is substantially no slag and in which all the shrinkage is confined to the riser which is later twisted E and discarded as hereinafter described.

After about fifty-five minutes of cooling, the general state of the casting, including the riser, is as shown schematically in FIG. 4. The metal in the zones corresponding to the feed slot 48 and gate openings is by no means completely solid at this time. The cope is lifted and twisted slightly. This separates the riser and the heat sink metal in the cavity 41, as well as the metal in zones 48 and 50, from what constitutes the hub of the wheel, generally along line SL, FIG. 4. The cope is replaced to keep the wheel casting hot. After about one hour, the cope is completely removed, and the casting is ready for shake-out.

Resultantly, upon separation of the casting front the center core 32 and the gate core 34, the hub opening is defined, and the metal in the cavity 41 is a mere slug or bob, already separated from the hub of the Wheel.

Hence, while I have illustrated and described a preferred embodiment of the present invention, it is to be understood that this is capable of variation and modification.

I claim:

1. In a mold for casting a railroad wheel having a hub opening: a circular center core the outer diameter of which represents the diameter of said hub opening; said center core having a cavity formed therein, bounded by an upstanding wall, and which opens at the top of the center core; a separate gate core reposing 0n the upper edge of said annular wall and having gate openings therein in communication with the portion of the mold cavity surrounding the exterior of said center core, said gate core presenting a feed slot through which molten metal may flow into said cavity; and a float core resting on the gate core and so dimensioned as to expose said gate openings and said feed slot.

2. A mold for casting railroad wheels comprising: a drag portion formed of a refractory mold material including a centrally located cylindrical center core which has an upwardly opening cup-shaped cavity therein; a. cope portion formed of a refractory mold material and being supported upon said drag portion, said cope portion having a centrally located riser opening within which is supported a gate core provided with a large central feed opening and a plurality of smaller apertures outwardly located of the central feed opening; and a float core formed of a refractory material having a lesser density than the metal to be cast resting upon said gate core and exposing said gate openings and exposing said central feed opening to said cavity.

3. The mold of claim 2 in which said large central feed opening is located above the cavity in said cylindrical core and said smaller apertures are located outwardly of said cylindrical core.

References Cited UNITED STATES PATENTS 106,243 8/ 1870 Wilmington 164356 5 1,025,438 5/1912 West 164356 1,281,946 10/1918 Griffin 249-56 2,835,007 5/1958 Hoefer 164353 I. SPENCER OVERHOLSER, Primary Examiner.

EUGENE MAR, Assistant Examiner.

U.S. c1. X.R.

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