US1915157A - Car-wheel - Google Patents

Description

I June 20, l1933. Av. FAHRENWALD 119155157 CAR WHEEL Filed July 6, 1929 Vla o ze A 9,/ QQ" Ligoaigbot;

- the periphery Patented June 20, 1933' A UNITED STATES PATENT OFFICE FAHRENWALD, oF CHICAGO,` ILLINoTs, AssIGNoR rro SOUTHERN WHEEL COMPANY, or NEW YORK, N. Y., A coRPoRA'rIoN oF GEORGIA CAR-WHEEL Application med my e, 1929. serial No. 376,354.

This invention relates to car wheels and has for its object theprovision of a new, cheapened and improved wheel for railway rolling stock. Such wheels have long been made by casting iron into a mold of the proper shape, of the mold consisting of a massive iron ring called a Chiller, which Causes this exterior portion of the casting to become solidified very rapidly. The composition employed for the purpose 1s what I call an unstable iron nixture, namely one which produces grey cast-iron when cast in a sand.

mold, or white-iron when cast against a chiller. A composition often used for car wheels is carbon 3.25% to 3.50%, silicon .60% to .90% 'and the balance iron. In such anmixturethe Carbon is at least largely held in s0- lution when the Ametal is melted, but the presence of silicon tends to precipitate that carbon in the form of graphite at and imme` diately below the temperature of solidification. The res'ult is that when suchpa mixture is poured in a sand mold the resultant slow' cooling Causes the` graphite to become separated out in the form of innumerable minute .graphite platesl or flakes which almost completely interrupt the metal phase, so that the latter, although it consists of an iron which would ordinarily be tough and ductile, exhibits the well known weakness and brittleness'of cast-iron. The samematerial when cast in a chilled mold,'produces a casting, the fracture of which is white, like silver but very crystalline,'the carbon being retained in combinaton with the iron in the form of a car- A' bide known as cementite. FeSC. Such K tremely hardland resi ant to Wear, and the quick chilling is steel matrix due to" ass-like brittleness the making of car wheels, all the mold excepting the tread portion hasheretofore customarily been made of sand, but the tread portion has been formed by a massive iron ring known as a Chiller, thus producmg a wheel having a body of grey cast-iron and a tread of chilled white-iron, the chilled condition ordinarily extending into the metal aldistance of from one-half to one inch depending upon the composition of the metal. 'Due to the sudden cooling and .the consequent contraction of the periphery of the wheel during the time that the hub remains not only hot but almost molten, very severe stresses are set up, as a consequence of which it is customaryto remove the Chiller at the earliest possible moment, to lift the wheel from themold, and to transfer it while still red hot to a slow cooling device where it can be annealed for a period of one or more days. According to contemporary practice no `fuel is em'- ployed in this annealing operation, the wheels being merely deposited in piles of six oreight in` thermally insulated pits where they Cool gradually by reason of theirrmutually high temperature; and care has been taken not to introduce or maintain. them at an unduly high temperature lest the treads be softened, while at thesame time introducing them into the pits at a temperature above the critical range, which for this composition is about 1325o -Fahrenheit. jWith this in View a.A

temperature changes (caused principallyby the friction of the brakes) sometimes Causes these Wheels to fail by breakage of the plates. With the constantly increasing weights-and speeds of trains and the consequent vigorous application of the brakes the strain upon the car Wheels is Constantly increasing and has nowreached a point which is upon the bor-` derline of the ability-of grey iron wheels to stand. l

Even a very small improvement in the Wheel yas regards toughness would add a valuable factor of safety, but many years of research by metallurgists all over the world have failed to produce any treatment whereby grey iron castings can be rendered tough or.ductile. On the other hand the only alternative heretofore known has been to use steel wheels which While suiiciently tough and ductile, are so expensive in the first cost chilled'tread; the provision of a method of' casting and heat-treating a cast-iron carwheel which shall render the plate tough a'nd ductile without substantially softening the tread and without substantial increase 4in cost; the provision of a method of heat-treating carfwheels which shall im rove the quality of the product while fitting in conveniently with present established manufacturing .technique and facilities; while further objects and advantages of the invent-ion will become apparent as the description proceeds.

In the drawing accompanying and forming a part of this application I haveillus'- trated certainapparatus and certain process steps explanatory of my improvements. Fig. 1 is a vertical, sectional view through one form of mold containing my :improvements and ready/for the reception/ of the molten metal; Fig. 2 is -a horizontalsectional view corresponding to the broken line 2 2 of Fig. 1; Fig. 3 is a perspective view of one of the chiller blocks sometimes used in one of the grooves; Fig. 4^ is a graph showing the relation between tensile strength, temperature, and time of treatment for a specimen comJ position of chill cast-iron; Fig. 5 is a graph illustrating approximately the rate ofhheatv joined to a comparatively massive hub 2 by4 ing ofthe different parts of a wheel havlng the section shown in Fig. 1, when introduced at 1150 Fahrenheit into an atmos- Aphelge of 1850" Fahrenheit; Fig. 6 and Fig. 7*' illustrate an optional method of additional-l ly chilling the tread Vduring the heat-treat-v ment; Fig. 8 is a sectional view through a special form of heat-treating furnace whereby portions of the wheel can be heated se-v lectrvely for the purpose in view; and Fig. 9 is a horizontal sectional view corresponding to the line 9 9 of Fig. 8.-

A car-wheel ordinarilycomprises a coml paratively massive rim 1 termed the tread a compara-tively thin web '3 ordinarily termed the p late. This-plate is generally `dishgd more or less as shown in Figs. l and 5 although its .specific contour is relatively unimportant provided that thel hub and tread preserve their requisite standard relatlonship. 'According to the present invention all parts of the wheel outside of the hub are cast from an unstable iron mixture under chilling conditions, not only the tread for purposes of hardness and wear-resistance, but also the plate for a reason to be later described.

referably, for purpose of the present invention the hub is cast without chilling, at least interior-ly. One lmode of accomplishing this result is by the employment of a mold constructed as shown in Figs. 1 and 2, wherein the drag'consists of a single massive metal block 5 excepting for an annular portion 6 located adjacent to the outwardly and downwardly sloping shoulder presented by the inner rear face of theltread, this portion being made yielding by the use of sand' or better still of baked core-composition, inset in a groove 7 provided for the purpose. Resting on the marginal portion of this drag in a position fixed by dowel pins 8 is the treadchiller usually employed. Resting in turn on this tread-Chiller is the cope element 10, here also consisting of a massive piece of cast-iron excepting for a portion immediately inside the forward shoulder of the tread which also is made yielding by the use of sand, or preferably, of baked core-material 11 received ina groove 12. Formed at the center of the drag is a print 13 for the lower portion of the hub core 14.- whose upper end 1s receivedbetween suitable fingers '15 projecting inwardly around the lower endV of the pouring hole 16. Suitable recesses 17 are formed in theperipheries of these members to enable quick handling since it is important to remove the cope and chiller at the earliest possible moment after pouring to reduce the danger that the wheel will draw apart upon contraction. It is for this reason that the cru'shable portions 6 and 11 are introduced, namely to allow a trifle more latitude in the time of opening the mold. Excepting for this I would prefer to make the ent-ire mold of metal; and in any event it is permissible, atleast as regards the portion 11, to employ a plurality of tapering metal chiller-blocks 18 sufficient in size to exert a chilling effect,

but separated from each other and from the inner wall of the groove by crushable material. The core 14, however, is preferably made of ordinary baked-core-materials, and I preferably form it 'with an enlarged lower end 19 as shown in Fig. 1 defining the end face of the hub as well as the`bore, so that the molten iron entering through the pouring hole may fall thereon instead of on the metal surface of the mold on which it might have a local eroding influence. y

The composition which I prefer to employ is what I term an unstable iron mixture, namely one which will cast gray in a sand mold and white under chilling conditions. Examples of such mixtures are as follows:

' A l B t C Carbon per cent 3.25 to 3.50 2.75 to 3.10 2.50 to 2.75 Silicon prr cent .90 to .60 1.25 to .90 1.30 to 1.00 Iron BalancV Balance Balance Phosphorus per cent .60 .60. .60 Sulphur per cem .20 .20 .20 Manganese-.. per cent 1.00 1.00 1.00

I prefer mixture B, although the -others can be used. All` of them will cast grey in a sand-mold and white to a considerable depth when chilled. lVhen poured into the mold shown in the drawing the web should become chilled all the'way through. If not it should either bemade thinner or the percentage of silicon should be decreased. The tread also` becomes thoroughly chilled, but the huh, due partly to the presence of' the lsand core and 'partly to the local heating due to the flow of the molten iron therepast, willordinarily turn out gray at least interiorly. The cope and the tread-Chiller are lifted off at the earliest possible moment in order to metal appears to have sufficient tenacity to tions of the last two ingredients depen avoid cracking, despite having been made of a very weak and brittle mixture.

After cooling, as described, the wheel is next introduced into a kfurnace having an atmosphere temperature of about 18500 Fahrenheit where it is left fora sufficient period of time to enable the cementite content of the plate to become more or less decomposed, but without substantially decomposing and hence softening the cementite of the tread. Fig. 4 of my drawing shows the relation of toughness to time of treatment at different temperatures for compositions of the type I have described when cast against Chillers. The liberation of the combined carbon is substantially complete in portions of the casting which are maintained at a temperature of' 18000 Fahrenheit for evei less than an hour,

' although in an equal length of time the decomposition is little more than commenced in portions which are maintained at 16500 Fahrenheit'. Maximum toughness is exhibitedby portions which are maintained about four hours at 17000 Fahrenheit. The toughness developed in twenty minutes at 18000 Fahrenheit is higher than that developed in an hour at that temperature. f The effect of this heat treatment is toproduce a steel-like matrix having nodular masses submerged therein consisting partly ,of cementite and partly of graphite, the procporing upon the time and-temperature of treatment.

Indeed with over-treatment the combined i carbon is mostly driven out of the matrixmetal also, leaving the same substantially in the ferrite condition, butwith shorter treatment the matrix-metal can be made to consist almost wholly ofpearlite, which is known,

to exhibit a high degree of strength and toughness. Accordingly the best results .from the standpoint of mere tensile strength arel obtained at a point short of complete breaking down of the cementite or liberation of combined carbon.- However the operating requirements in the case of car-wheels are'not such as to demand the maximum -obtainable toughness, since a condition 'wh1ch sometimes limits the life of a gray iron car-wheel is the thermal expansion and contraction of its tread which sets up strains in the plate which the latter being totally devoid of ductility is unable to bear, despite the fact that the actual amount of expansion and contraction is very smal-l. Hence even a small accesslon of ductility is enough to satisfy the essential requirements.

Accordingly in order to obtain the requisite strength in the plate, while retaining the requisite hardness in the tread, it is necessary merely to subject the plate to a temperaturetime-condition which shall produce a partial liberation of the cmbinedcarbon therein* While maintaining the tread below that timetemperature condition; and owing tol the marked effect of temperature on time of treatment this is not at all ditlicult to do.

When a car-Wheel is introduced'into a heated furnace, 'thethin parts, namely the plate and the flange, become heated'substantially more rapidly than the moremassive parts such as the hub and tread. For example the heatingcurve for the plate follows approximately the curve A in Fig. 5, the tread follows curve B and thev hub followscurve C. If Y the wheel be subjected to a furnace temperav ture of 18500 Fahrenheit for approximately thirty minutes, it will be seen that the plate portion will be maintained at a temperature above'16500 Fahrenheit for approximately twenty minutes,` and above 18000 for approximately fifteen minutes which is enough to afford a measurable degree of toughness; the tread will have been above 16500 Fahrenheit iio for about only ten minutes and above 17000 only about live minutes so that it will have received only a very small amount of decomposition.- The hub will scarcelyhave risen above 16500 Fahrenheit, so that unless this secure an adequate toughness of the plate without softening of the tread.

It will be understood that special or additional expedients may be employed to shield the tread, or keep it cool, or delay its heating. This is' more frequently necessary with wheels having a lighter tread-section and is seldom necessary with those of heavy tread, although occasionally of advantage in that connection also. Thus in Fig. 6 I have shown a massive metal ring surrounding and overlapping the tread portion so as to protect the same from the furnace heat, and by its own comparatively slow increase of temperature to protect the' tread against softening. Any degree of massivenesscan be employed as can well be under'stood. In Fig. 6 the fiange as well as the tread is protected. However,

it is possible by reversal'of the position as shown in Fig. 7 to expose the flange as Well as the plate While holding back the tread.

In Fig. 8 I have shown a muiile' type of furnace arranged for the treatment of individual Wheels. The bottom part of the muffle consists of a circular support 2l of refractory material adapted to receive the wheel flange and hollowed out as shown at 22 to space it from the hub. Resting on the support 2loutside of the flange 1s the rim portion 23 of the removable top 24, here shown as lined with refractory material 25. The rim portion is spaced slightly from the tread of the wheel, and is formed with an annular circumferential air-duct 26 communicating with numerous get apertures 27 which discharge against the ace of the tread. The top member 1s also formed with an annular gasduct 28 Whichcommunicates with the interior.

of the combustion chambel` 29` by numerous apertures 30 opening just above the tread.

The air entering through the duct 26 both serves to keep the tread cool and to effect the combustion of the fuel which heats the remainder of the wheel; the hot combustion products pass through the hub bore and out through discharge openings 3l in the base part, whence they are conveyedto a suitable stack (not shown) by conduit 32. With this type of furnace it is possible to chill the hub' as well as the tread since the hub can in this way be heated sufficiently to decompose its cementite constituent. v

It is also possible with this kind 4of a furnace to emplty a composition containing less carbon an /or less silicon, which casts White in a sand mold. I do not 'advocate this procedure since this type of 'white-iron is not decomposed so readily as the chill-cast unstable white-iron, and does not exhibitsuch a markedvariation in rate of decomposition with comparatively small changes in tem-- perature. Furthermore when the Aentire Wheel is cast in White iron, it is necessary to produce a considerable decomposition of the 05 same before 'it is possible to effect the necesproducing initial gray iron.

sary machining of the hub. However, While it is not so profitable a course as that rst described, still it is one that with care and time and careful manipulation can be successfully followed.

I have also used other alloying constituents, such as are customarily called hardeners and softeners, and While I do not advocate them, I desire to point out that if one'desires or if they be found accidentally in the scrap iron portion of the melt, they can be used if any one desires with the same manner and with the same limitations as in other castiron work. Such hardeners as chromium,A vanadium, manganese, or molybdenumrender the cementite more diiicult to break down and increase the time and temperature required. They also tend to neutralize the effect of the silicon and to enable more silicon to be used (and also more carbon) without l Such softeners as nickel, copper, or'aluminum may reduce the amount of silicon (or carbon) permissible or reduce the time or temperature of treatment.

It will be remembered that in the casting of iron the depth of the chill can be quite definitely foretold from the composition employed, so that the skilledfoundryman can produce a melt which shall give a one half inch chill, an inch chill, etc. according to requirements. This means that if the articleis one halfinch or one inch in thickness next to the Chiller it will show aywhite iron structure throughout, while if it be thicker than that it Willexhibit a White iron condinecessary to render the plate portion white l to a sufficient depth to--yield' the degree of toughness desired. Iprefer to chill it clear through, but it is often suiicient for practical purposes to chill only part way. Either of the formulas A or B above will do this and will also produce a suitably chilled coni dition on the surface ofthe tread though the interior of the tread will ordinarily exhibit a gray core of flake graphite. This is no disvlia car-wheel, although it may be possibly unii' form in chemical composition, exhibits at different points the physical and microscopic structures indicated in Fig. 6, namely a hard surface around the periphery of the tread indicated at 4.0, a gray iron core inside the tread and hub, indicated at 41, and a plate of tough iron indicated at 42, this also extending intothe flange at 42a and constituting at least in part a layer covering the gray iron although this may be thinner at theA points 42 when the mold was made crushable. I do not instance the presence of a gray iron core inside the tread as an advantage to my product since it is undoubtedly weaker than an equivalent amount of tough iron would be, but mention it as likely to be present, in any event and as not specially injurious since the factor of safety of this portion of the rim has heretofore been superior to that of the hub.

iron containing less than 1.30% of silicon and having its plate and tread portionssubstantially devoid of primary graphite, said tread being also substantially devoid of secondary graphite and said plate exhibiting a substantial proportion of its carbon in the form of secondary graphite occurring in the form of rounded nodules.

In testimony whereof I hereunto affix my signature.

FRANK A. FAIIRENWALD.

By the word tough as employed herein I mean such a quality as enables deformation by plastic liow such as is encountered in bending past the elastic limit without breaking even to a considerable degree of permanent deformation. Ordinary cast-iron ,exhibits substantially none of this quality.

It should be remembered, however, that in any part where it is desired to obtain toughness, primary graphite should not be allowedto appear, thatvis to say the cooling rate andthe composition employed must be so chosen as to produce white iron in the portions which are to be modied by the heattreatment. In other respects than this one', many changes can be made within the scope of my invention and I do not limit myself in any wise except as specifically recited in my several claims, which I desire may be construed broadlyl each limitations contained in other claims.

Having thus described my invention what I claim is:

1. A one-piece cast-iron car-wheel havlng an integral plate connecting its hub and tread, said plate consisting of cast-iron in which substantially all the uncombined carbon occurs in nodular form and the wearing surface of said tread consisting of cast-iron in which substantially all the carbon exists in combined form.

2. A one-piece car-wheel wherein the tread and plate are cast from a molten iron mixture having a similar chemical composition throughout -characterized by the wearing surface of the tread exhibiting primarily cementite in a steel-like matrix and the plate exhibiting nodules of secondary graphite in a steel-like matrix, and wherein not'more 'than a substantially negligible proportion of graphite occurs 1n primary flakeform.

3. A one-piece car-wheel having a chilled white iron tread, a gray iron hub and a tough plate, the wheel being cast from a molten iron mixture having a similar chemical composition throughout.

4. A one-piece car-wheel made of castindependently of

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