US3311403A - Car wheel - Google Patents

Description

March 1967 R. H. BEETLE ETAL CAR WHEEL Filed June 3, 1965 INCREASED PLATE ANGLE s 4 m o Inverdors T o GN A R D OLD V -W. PREFERRED DESIGN Robert :H. Beet le m 2% i W x A; E

United States Patent 3,311,403 CAR WHEEL Robert H. Beetle, Mountain Lakes, N.J., and Arthur W. Farrell, Tallman, N.Y., assignors to Abex Corporation, a corporation of Delaware Filed June 3, 1965, Ser. No. 460,995 4 Claims. (Cl. 295-27) This invention relates to railroad wheels and more particularly to a geometrical shape for railroad wheels,

Developments in the railroad industry have necessitated some wheels carrying much greater loads without increases in the wheel diameter. Both operating and car design factors have also placed greater mechanical loadings laterally on the wheel. In order to design this section of the wheel which connects the tread and the hub, commonly called the plate or web, it has been necessary to consider both the effects of these mechanical forces vertically and laterally as well as the complex stress situation developed in the wheel by thermal action due to braking on the tread. When the plate sections are designed to meet the mechanical aspects of service, they tend to be too rigid for the optimum resistance due to stress build-up to thermal action.

The present invention is directed to reducing the danger of fractures of railroad wheels and particularly to reducing the danger of fractures of railroad wheels by the rapid propagation of thermal cracks rupturing and fracturing the railroad wheels into separate parts, which is commonly known as explosive fracture of the wheel. Thermal cracking on the tread of the wheel is generally the result of braking abuse and is more a result of the material than of the wheel design. Thermal cracking, however, which can result from such braking abuse must be detected so that the wheel can be removed from service before explosive fracture. It is thus most important to have the wheel design which does not foster rapid propagation of the thermal crack so that fracture might occur before a wheel is inspected and removed from service. In addition to the mechanical factors that are involved in the propagation of the thermal crack into the wheel, there is an important stress condition which is thought to result from the plastic flow of metal during severe frictional heating of the tread of the wheel by prolonged application of the brake shoes directly against the tread of the wheel. When the metal in the tread of the wheel which has been subjected to plastic fiow during heating, has an opportunity to cool down, tensile stresses can build up circumferentially in the tread area, Such high tensile stress can cause rapid propagation of the thermal crack and result in an explosive racture of the wheel. The thermal cracks grow larger with repetitive high-temperature frictional heating, or upon the application of the subsequent hightensile stresses until a sudden propagation of the thermal crack occurs. The thermal crack propagates during the explosive fracture in various directions for different wheels, through the rim, plate, hub, or circumferentially about the plate.

It has been shown previously that thin plate sections which tend to be flexible will minimize the plastic flow of the tread during prolonged application of the brake shoe and thus also minimize the build-up of tensile stresses in the tread area upon subsequent cooling. The handicap with the thin-plate solution to the problem lies not only in the possibilities of mechanical or fatigue type fracture in the plate due to external forces on the wheel, but also the possibilities of fatigue in sections of the plate due to the thermal action on the tread. The solution to this problem appeared to be an increased plate thickness which would have to be designed in a manner to provide adequate protection against the growth of thermal cracks.

Accordingly, an object of the present invention is a new and improved railroad wheel geometry, which has strikingly improved characteristics against wheel fracture. A more specific object of the present invention is a railroad wheel having increased resistance to the growth of thermal cracks when subjected to prolonged or repetitive braking.

A specific object of the invention is a cast steel railroad wheel having a plate angle which imparts improved characteristics to the railroad wheel against the rapid propagation of thermal cracks causing explosive fracture of the wheel.

Other and further object 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 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 and the purview of the appended claims.

In the drawings:

FIG. 1 is a sectional view of a railroad wheel having the geometry of the preferred embodiment of the invention; and

FIG. 2 is a graph showing test results of the new wheel geometry and wheel geometries of the prior art.

The present invention is adapted to be employed with various sizes of wheels including the usual 33, 34 and 36 inch wheels, as well as larger and smaller wheels employed for special purposes. Additionally, it has been found that the present invention is applicable to wheels having different rim thicknesses and commonly designated as one wear, two wear, and multiple wear wheels. The present invention affords significantly increased resistance to explosive fracture from thermal cracks for railway car wheels which have their rims toughened by a quenching operation as well as those car wheels that do not have toughened rims.

The wheel W, illustrated in FIG. 1 in solid lines, has a hub H, an annular bore B in the hub H for receiving the car axle, an annular rim portion R, and a plate portion P extending from the hub H to the rim portion R. The rim portion R has a conventional flange F extending upwardly and at one edge from an annular tread surface T on the outer surface of the rim R. The section of the car wheel illustrated in solid lines in FIG. 1 is constructed in accordance with the preferred embodiment of the invention. The superimposed phantom outline of another car wheel is that of one well known form of prior art wheel. Difierent configurations of car wheels fall within the purview of the present invention and the configurations illustrated herein are for the purpose of aiding in description of the discovery of the present invention.

Underlying the present invention and as an important aspect thereof is the purpose of inhibiting wheel failures particularly due to thermal cracks and the propagation of thermal cracks by making a relatively small change in the angle of the plate with respect to its inclination between the rim R and the hub H. It has been discovered that a relatively small change in the angle of the plate P from that of known prior wheel shapes results in surprisingly significant increases in resistance to explosive fracture of wheels undergoing drag brake testing. As seen in FIG. 1, the wheel W (in solid lines) has a center line CL for its plate section P. The center line CL intersects the bore B of the hub H at an included angle of approximately 77.5 More specifically, the included angle is preferably measured at the intersection of the center line of the plate extended to intersect the center line or axis of the bore B in the hub. Typical of the cast steel wheels of the known prior art is the design geometry indicated in dotted or phantom lines which has a dotted center line CL which center line CL makes an included angle of approximately 81 at the intersection with the bore B of the hub H. The slight change of plate angle, exemplified as 3 /z, results in a surprisingly greater resistance to explosive fracture of the car wheels under simulated prolonged braking applications common-1y referred to as drag brake tests.

Referring now to FIG. 2, the significant change of plate angle from the approximate 81 of the prior art type of wheel to the 77.5 plate angle is shown in the form of bar graphs of actual test results of drag testing of a number of car wheels. The shaded bar, FIG. 2, for car wheels of the 77.5 plate angle design show a surprisingly and significantly greater number of drag brake applications before fracture of the car wheels shown in the unshaded bar. Insofar as feasible under experimental conditions, the only difference between the wheels tested was that the change of the plate angle from 81 for old design wheels to approximately 77.5 plate angle for new design of the car wheels.

The car wheels tested were of differential metallurgical compositions and a very marked increase in resistance to fracture was noted in each of the various metallurgical compositions. All of the car wheels tested were made of cast steel having a ladle analysis approved for cast steel car wheels by the Association of American Railroads. The cast steel for the wheels may have a carbon content of .60-l.20 percent. Also, the dimensions and tolerances of the car wheels tested met the design requirements for AAR cast steel freight car wheels wherein among the dimensions specified are the length L, FIG. 1, of the tread, the width of the hub, the distances R and R of the ends of the hub from the flange side of the wheel. It will be appreciated that other countries use different standards from those of the American Association of Railroads. For instance, in some European countries, the steel wheels have a carbon content of less than .60 percent. However, the principles of the present invention may be applied to these lower carbon wheels and still fall within the purview of the present invention.

Considerable testing has also been done with decreasing the plate angle from 81 of the prior art design down to a plate angle of approximately 72. It has been found that further reductions in plate angle from approximately 77.5 to 72 affords about the same results as obtained with the approximate 77.5 plate angle. That is to say, the decreasing of the plate angle was not found to give the same degree of increased benefit when further reducing the plate angle after reaching the approximately 77.5 plate angle. Thus, the reduction of the included plate angle from various stages from 77.5 down to 72, was not found to markedly increase the resistance to explosive fractures which resulted upon initial change from 81 to approximately 77.5 or 78 at which plate angle the surprising results are increased so significantly from the results of wheels having plate angles of 81 or thereabouts.

As the graph indicates, an average number of 17 drag cycles were endured by the wheels having the 81 plate angle before an explosive fracture resulted. Another group of wheels of same metallurgical composition and of the same geometrical construction except for the reduction 'on the plate angle to approximately 77.5 were found to experience an average of about 70 drag cycles before fracture.

The fracture of the car wheels was the result of rapid propagation of cracks from a milled slot S, FIG. 1, milled in the tread of the ear wheel. These milled slots S simulated a large thermal crack in the tread T of the car wheel. The milled slot had a depth 'of approximately of an inch, 21 Width of & of an inch and a length of 2 inches. The bottom of the slot S was arcuate in configuration and was milled with a cutter having a radius R of 1 /8 inches.

From the foregoing, it will be seen that the slot S was a quite severe notch or slot and hence simulated a large and severe thermal crack. Thus, the number of drag cycles endured by each of the car wheels is to be taken as a relative number, which number would be increased considerably for slots or for thermal cracks 'of a smaller size.

The drag test conditions were performed on a test stand wherein the car wheel was mounted on an axle and rotated at approximately 45 mph. and the brake shoes were applied with at least 3,000 pounds of pressure. The brake shoes were applied for 50 seconds and then were released for 10 seconds during each minute of a 30 minute braking period. Thus, the brakes were being applied for 25 minutes out of each 30 minute braking period. After a 30 minute brake period, the car wheel was permitted to air cool for 15 minutes and then was water cooled for 12 minutes. After water cooling for 12 minutes, the car wheel was inspected for a period taking not more than 13 minutes which period included the time for changing brake shoes, if necessary. The next braking period of 30 minutes was then instituted to start a new drag brake cycle.

The drag cycles listed on FIG. 2, indicate the number of drag cycles to which each car Wheel was subjected before failure and each drag cycle lasted for 70 minutes and included the following: 30 minutes of 50 seconds of continuous brake application followed by 10 seconds of brake release; air cooling for 15 minutes; water cooling for 12 minutes; and inspection for 13 minutes.

Referring again to design of the car wheels illustrated in FIG. 1, it is seen that the thickness of the plate section for the phantom line wheel and the solid line wheel are maintained at approximately the same thickness. However, the positions of the rim fillets 20 for the 77.5 wheel are shifted slightly from the position of the rim fillets 20a for the 81 plate angle wheel. The changing of position of the rim fillets and hub fillets is primarily for the purpose of blending of the fillets between the rim R and the plate P. On the other hand, the position of the hub fillets 25 for 77.5 plate angle Wheel are moved significantly rightward, in FIG. 1, from the position of the hub fillets 25a for the 81 plate angle wheel. The change of plate angle primarily results in the shifting of the point of connection of the plate section P to hub H whereas the plate section P joins the rim R at approximately the same position.

Thus, in the preferred embodiment of the present invention, the plate joins the rim R at a fairly centralized location on the rim T and this location is generally disposed beneath the portion of the rim which is adjacent the flange F and which bears most directly on the railroad rail.

The center line for wheels having generally parallel and fiat portions adjacent the center of the plate section, as in the illustration of FIG. 1, is preferably determined by drawing a line through a pair of midpoints, such as MP and MP1, at the center of thickness of the plate section. The plate angle is determined by extending the center line to intersect the hub to define an included angle therewith. For car wheels wherein the outer plate surfaces are more generally curving throughout their plate sections, the plate angle is measured by a line drawn tangent to the curved center line extended to the bore of the hub to make an included angle with the hub.

From the foregoing, it will be evident that the present invention greatly inhibits fracture of car wheels from explosive fractures resulting from thermal cracks by a slight decrease in the plate angle of the car wheel to approximately 78 and not less than 72.

The preferred embodiment has a plate angle of approximately 77.5 it is observed that a plate angle of 78 affords good results. The defining of the upper limit as approximately 78 includes within its purview the angle of 78 and any additional fractions of a degree beyond 78.

Hence, while preferred embodiments of the invention have been described and illustrated, it is to be understood that they 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 claims.

We claim:

1. In a railway Wheel having a geometry affording a relatively high resistance to fracture by rapid propagation of thermal cracks, a hub portion having an axially extending bore therethrough, an outer rim portion, and a plate portion extending between said hub portion and said rim portion for joining said hub portion to said rim portion, said plate portion having a center line through the cross-section thereof when projected to said hub portion intersecting the center line through said bore of said hub portion at an angle not greater than about approximately 78 and not less than 72.

2. A wheel according to claim 1 in which said angle is approximately 78.

3. In a cast steel railway wheel having a relatively high resistance to rapid propagation of thermal cracks when subjected to severe braking conditions, a hub portion having an axially extending bore therethrough, an outer rim portion, and a plate portion extending between said ,SllAOB hub portion and said rim portion for joining said hub portion to said rim portion, a locus of points formed at a central portion of said plate constituting a center line which when projected to said axis of said bore forms an included angle of approximately 78 and not less than 72.

4-. A cast steel railway wheel having a hub portion having an axially extending bore therethrough, an outer rim portion, and a plate portion extending between said hub portion and said rim portion for joining said hub portion to said rim portion, a locus of points constituting a curved center line for said plate section; a line tangent to said curved center line atapproximately the center of said plate section intersecting said axis of said bore at an angle of approximately 78 and not less than 72.

References Cited by the Examiner UNITED STATES PATENTS 2,103,834 12/1937 Tyson 29527 2,768,020 10/1956 Sylvester 295--27 OTHER REFERENCES A.A.R., Manual of Standards, Section G, 1965, page G1951.

Wheels,

Claims (1)

1. IN A RAILWAY WHEEL HAVING A GEOMETRY AFFORDING A RELATIVELY HIGH RESISTANCE TO FRACTURE BY RAPID PROPAGATION OF THERMAL CRACKS, A HUB PORTION HAVING AN AXIALLY EXTENDING BORE THERETHROUGH, AN OUTER RIM PORTION, AND A PLATE PORTION EXTENDING BETWEEN SAID HUB PORTION AND SAID RIM PORTION FOR JOINING SAID HUB PORTION TO SAID RIM PORTION, SAID PLATE PORTION HAVING A CENTER LINE THROUGH THE CROSS-SECTION THEREOF WHEN PROJECTED TO SAID HUB PORTION INTERSECTING THE CENTER LINE THROUGH SAID BORE OF SAID HUB PORTION AT AN ANGLE NOT GREATER THAN ABOUT APPROXIMATELY 78* AND NOT LESS THAN 72*.

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