US2979793A - Cast iron - Google Patents

Description

April 18, 1961 R. 1.. WILSON ETAL 2,979,793

CAST IRON Filed May 8, 1958 2 Sheets-Sheet 1 INVENTORSI ROSSER L. WILSON FRANCKS B. HERUHY THOMAS J. WOOD Y. MW M E i-Pas- CAST IRON 2 Sheets-Sheet 2 Filed May 8, 1958 EMZ INVENTORS: ROSSER L. WI LQON FRANCIS B. HERUHY THOMAS J. WOOD BY:

Hi-F 5- United States Patent CAST IRON Rosser L. Wilson, Mahwah, Francis B. Herlihy, Hillsdale, and Thomas J. Wood, Ramsey, N..l., assignors to American Brake Shoe Company, New York, N.Y., a corporation of Delaware Filed May 8, 1958, Ser. No. 733,959

1 Claim. (Cl. 22-215) This invention relates to the production of cast iron castings and in particular to the production of cast iron brake shoes for railroad equipment and the like.

There are many instances where it is desirable to provide for selective hardening of a particular portion of an iron casting, and ms is particularly so in the instance of cast iron brake shoes of the kind mentioned above. Thus, as is well known in the art, cast iron brake shoes may be produced embodying varying degrees of hardness, which is to say, that one set of shoes for a particular equipment installation may desirably have exceptionally hard faces for engaging the wheel of the railroad car, Whereas under other cfrcumstances in a different type of installation it may be desired to have brake shoes with relatively softer faces. One reason for varying the hard- ,ness of the cast iron brake shoes in the foregoing manner is to account for different degrees of friction, and moreover it is often desired to have a relatively hard core in a cast iron brake shoe of the order of white iron surrounded by an envelope of softer gray iron, since so to do has particularly desirable effects on the thermal characteristics of the shoe.

The foregoing is explained in somewhat greater detail in US. Patent No. 2,370,279, and in this patent it is disclosed that such varying degrees of hardness in a cast iron body such as a cast iron brake shoe can be achieved by introducing tellurium into the mold in which the cast is to be poured, the tellurium serving to promote and stabilize the formation of iron carbide thereby accounting for the format on of a hard white iron section in the casting. This particular advantageous manner of stabilizing or promoting the formation of iron carbide was achievedby coating the reinforcements to be embodied in the cast iron shoe with what can be termed a liquid vehicle which included tellurium, and has proven eminently satisfactory, but we have now found that a greater degree of control and a greater degree of selectivity of hardening sections of a cast iron body can be achieved by having resort to a non-metallic strip-type carrier coated with powdered tellurium and suitably introducing the strip or tape thus coated into the mold in which the iron part is to be cast. Thus, in contrast to the liquid vehicle in which tellurium was carried in accordance with the aforesaid patent and which requ'red attention to the vehicle to assure uniform dispersion of tellurium therein, we have now found that such attention can be dispensed with [by furnishing nonmetallic strips coated with powdered tellurium dispersed in a dry binder adherent to the strip. Ths enables the concentration of tellurium to be accurately determined, and the strips can be stored and used 'at'any time without apprehension as to a uniform and stable concentration of tellurium. In other words, instead of having to rely upon a liquid vehicle containing tellurium wherein the tellurium is likely to settle after starting and must be brushed on to some kind of .an insert to be disposed withinthe mold at the time of pouringthe cast, we are able to eliminate these steps, and so Patented Apr. 18,

to do is one of the primary objects of the present invention. Additionally, it is an easy matter to support the tellurium coated strip with'n the mold by chaplets or like expendible supports without depending upon the presence of a solid member having a large surface area for receiving the tellurium in a liquid vehicle as in the aforesaid patent which is to become a partof the casting. In other words, we do not-need to rely upon the presence of'a member in the mold having a large surface area for carrying the tellurium, and hence cast iron parts can be hardened in accordance with the present invention in a facile and expeditious manner in various different ways by having'resort to high concentrations of tellurium on a small supporting area, and so -to do is another object of the present invention.

We have found-that there'is a degree of incompatibility involved between most expendible metal strips and tellurium, and moreover it is essential to use only a metal that will not vitiate against the desired action of tellurium. Thus, we have discovered that if a particular metallic foil is susceptible. to the adherence thereto of tellurium, such metal usually has the characteristic of undesirably promoting graphitization of cast iron which is the direct opposite effect-of tellurium. In accordance with the present invent on, tellurium is adhered to a non-metallic strip which, being. of an organic nature, disappears when the cast is poured without in any way affecting the formation .and stabilization of iron carbide promoted by tellurium on the strip, and this constitutes another object of the present 'invent'on.

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 .princ pIes 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 usedand structural changes may be made as desired by thosesk-illed in vtheart without departing from the present invention and the purview of the appended claim.

1n the drawings:

Fig. 1 is aside view, partly in elevation and partly in section, of .a typical-railroad .brakeshoe cast in accordance with the present invention;

Fig. 2 is a sectional view taken substantially on theline 2-2 of Fig. '1;

Fig. 3 is a sectional view, partly in elevation and partly in section, of a modified form of railroad brake shoe cast in accordance with the present invention;

Fig. 4 s a sectional view taken substantially on the line 44 of Fig. 3; V

Fig. 5 is a bottom plan view of a bundle of expanded metal reenforcing strips to be disposed in a mold for casting a railroad brake shoe and being taken substantially on the line 55 of Fig. 7;

Figs. 6 and 7 are side elevations of two bundles of expanded metal reenforcing strips, and showing different ways of associating the tellurium coated strip o'fthe present inventiontherewith;

Fig. 8 isa plan view of the coated side of a tellurium coated strip of thepresent invention; and

Fig. 9 is a sectional v.ew on a vastly enlarged scaleand taken substantially on the line 9-9 of Fig. 8.

Inaccordance with the present invention, wehave found that asectionof a cast iron body can be conveniently hardened to a white iron state by positioning within the mold in which such body is to be cast anon-metallicstrip coated with powdered tellurium in .a dry binder. Q'Ihe particular strip may of course take different forms since the only requirement is that the strip be non-graphitizing in respect of cast iron. Such a strip is afforded at a low cost by thermoplastics such as cellulose acetate, which, incidentally, can be easilycoated 'withabinder such as lacquer or'a liquid settable thermoplastic binder such as vinyl compounds, cellulose acetate, cellulose nitrate, ,or the like having dispersed therein powdered tellurium.

Hence, by mixing powdered tellurium in the binder and I applying the binder to the non-metallic strip or carrier and then drying the strip so coated, an adherent deposit of tellurium on the strip is obtained. The coating can be obtained in various degrees of thickness, and of course the tellurium concentration can be varied almost at will within practical ranges, whereby the effective tellurium concentration can 'be selected within a wide range.

As a specific example related to the production of a cast iron 'brake shoe, a flexiblecellulose acetate tape or band is fed through a coating machine so as to emit from I an aperture, and a lacquer binder containing the desired concentration of powdered tellurium is metered on to the strip at the aperture area, the thickness of the bindertellurium coating being controlled by the size of the aperture in accordance with well known strip coating techniques. After the cellulose acetate tape has thus been coated, the tape is then advanced through a drying oven to set the binder to a dry state causing the tellurium powders to be firmly adhered to the strip. The tape is then cut into convenient strip lengths.

The tellurium under the present circumstances is advantageously ball milled to approximately 200-300 mesh size, although the tellurium powders can be as fine as 600 mesh, and for cast iron brake shoes tellurium is added to the binder to produce a concentration of 0.00013 to 0.00800 weight percent on the total weight of the cast iron shoe depending upon the degree of hardness desired. The thickness of the coating consisting of binder and tellurium is not critical, but preferably the coating is as thin as possible. .The following is a specific example and represents the strip 10 shown in Figs. 6 to 9 which includes a cellulose acetate backing 10B and a coating of tellurium 10C in a binder:

Example 1.Tellurium coated strip While the above example represents a specific embodi- .ment of the tape of the present invention, various alternatives are possible insofar as the material for the tape 'is concerned, the kind and nature of the binder in which the tellurium is dispersed, and the tellurium concentration, tellurium concentration in the coating on the tape of course being selected on the basis of the extent ofhardening ,desired in a particular cast iron body. a

The tellurium coated strip may be introduced into the mold in which the cast iron part is to be cast in many difierent ways. Thus, as was mentioned,'the strip may .be supported by chaplets or associated with a mold insert. :Both methods will be described below in connection with the production of conventional cast iron brake shoes.

In Fig. 1 of the drawingthere is illustrated a conventional railroad brake shoe including a cast iron body B in which a reenforcement EM of the expanded metal type is embedded, the reenforcement EM consisting of a plurality of sheets of expanded metal.

Additionally, the shoe includes a ductile steel back S, and the shoe is cast to include so-called end stops E integral with the body B. A'center attaching lug L is provided on the back of the shoe mid-way between the ends of the shoe, and the .extending inwardly toward the center of the shoe.

. 4 article of commerce disclosed in various forms in many United States patents. The center attaching lug, the duetile steel back and the reenforcements EM are positioned in the mold in which the shoe is cast in a well known manner, and molten cast iron from the ladle is poured into the mold so that when the cast solidifies the reenforcements EM are embedded in the body of the shoe, and the back S and the center attaching lug L are firmly anchored to the body of the shoe. 7

Referring to Figs. 5, 6 and 7 of the drawings, there are illustrated bundles of expanded metal reenforcements,

EMl and EM2, and in accordance with one form of the invention a strip 10, Fig. 6, coated with tellurium powders in accordance with Example 1 above is related to the bundle of expanded metal reenforcing strips so as to be positioned in what will be the central section of the shoe tobe hardened. Thus, in Fig. 6, a strip 10 of the present invention is positioned in the middleof the bundle EMl of expanded metal reenforcement sheets or strips, in which instance the strip 10 will be substantially at the middle section ofthe body B of the shoe which will be hardened, thisbeing the unstippled or white iron area WA of the shoe shown in Figsnl and 2, surrounded by gray iron areas GAl. By changing the position of the tellurium coated strip in respect of the reenforcement bundle, as by locating the tellurium coated strip in contact with the lower-most one of the expanded metal sheets in the ,bundle EM2. of Fig. 7, the area of the 'body of the shoe to be hardened can be selectively determined. Thus, the tellurium coated tape 10 of Fig. 7 can be conveniently tied to the bundle EM2, and when the molten cast iron is poured about the bundle EM2 supported in the mold, a white iron section will be afforded adjacent the wearing face of the cast iron railroad brake shoe. As set forth above in connection with Example 1, one example of a cast iron'heat to .be used with the strip 10 is a heat known to produce a clear white chill of,%" to as determined by well known foundry procedures- It will be realized from the foregoing that by associating the tellurium coated plastic strip of the present invention with the bundle of reenforcements to be embedded in a cast iron railroad brake shoe, such represents a convenient mode of determining the section of the cast iron body to be hardened. This is, however, butone form of the invention, and as illustrative of another form of the invention and referringto Figs. 3 and 4, there is shown a railroad brake shoe identical to that described above except that the brake shoe in this instance does not include reenforcements. In this instance, it will be observed that the shoe of Figs. 3 and '4 has a white iron area WA2 '(the unstippled area) at the wearing face thereof and In achieving such hardening, a tellurium coated non-metallic 'plastic tape 10 of the present invention is conveniently 'first positioned or supported in the mold by expendible chaplets or the like, after which the mold is filled with a cast iron having'the known chill characteristic mentioned above. a

.form of commercial practice of the present invention wherein it is desirable to have a cast iron body having sections of different hardness varying from white iron as one extreme to gray iron as another extreme. It has lalso been explained that the tellurium coated plastic strip disclosed herein can .be conveniently handled in diflerent-ways insofar as positioning the saine within the mold is concerned, and the flexible nature of plastic enables the coated strip to be easily handled, configured,

vand manipulated. By coating a plastic tape or strip or equivalent flexible non-metallic material with tellurium d ispersed in a settable binder, a highly convenient mode shoe thus constructed and cast represents a well known of introducing tellurium'into the mold is attained, and

this is of particular importance inasmuch as the employees in the foundry will not be directly mixing or handling tellurium. Thus, the strips can be handled with tongs, and manufacture of the strips is carried out strictly as a mechanical operation including industrially safe-guarded dispersion of the telluriurn in the binder, automatic coating of the automatically fed tape, and drying and severing the tape into strips of predetermined length.

Hence, while we have illustrated and described preferred embodiments of our invention it is to be understood that these are capable of variation and modification, and we therefore do not wish to be limited to the precise details set forth, but desire to avail ourselves of such changes and alterations as fall within the purview of the following claim.

We claim:

A method of casting a cast iron railroad brake shoe of arcuate form to have sections of selectively difierent hardness characterized by white cast iron and gray cast iron and each of its own uniform hardness throughout and comprising, positioning elongated metal reinforcement of arcuate shape in spaced relation inward of the walls of the mold for casting the shoe, said reinforcement having in contact therewith a flexible strip of cellulose acetate thermoplastic material conforming to the arcuate shape of the reinforcement, said strip being non-graphitizing with respect to and thermally destructible by the molten cast iron to be poured and without efiect on the metallurgy of the cast shoe, said strip being sized to be of the length and Width of the section of the shoe to be hardened to white iron and by its position in the mold determining the area of the cast shoe to be hardened selectively to white iron, said strip having on one face thereof powdered tellurium bonded thereto by a thermoplastic binder in a dry state adhered directly to said strip, said binder being selected from the group consisting of vinyl compounds, cellulose acetate, and cellulose nitrate, said tellurium being dispersed uniformly throughout said binder and present in a concentration of about 0.00013 to 0.008 weight percent on the weight of the cast shoe, and thereafter pouring in the mold, having said reinforcement and strip, cast iron capable of forming gray iron" as aforesaid.

References Cited in the file of this patent UNITED STATES PATENTS 770,189 Schoellhorn Sept. 13, 1904 1,931,109 Ewing Oct. 17, 1933 1,941,672 Fahrenwald Jan. 2, 1934 2,250,483 Lorig July 29, 1941 2,370,225 Boegehold Feb. 27, 1945 2,370,279 Wilson Feb. 27, 1945 2,698,812 Schladitz Ian. 4, 1955 2,709,663 McLean et al. May 31, 1955

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