US3078160A - Railroad car wheels - Google Patents

Description

NO. OF DRAG TESTS Feb. 19, 1963 R BEETLE ETAL 3,078,160

RAILROAD CAR WHEELS Filed May 7, 1959 5o-.-- ll i L 4L L O; A J .9 do l5 2 Us |.'4 L5 CARBON /o BY WEIGHT iNVENTORS ROBERT H. BEETLE BY HUGO R. LARSON AXI.

Uflitc st e This invention relates to steel railroad car wheels and more particularly tosuch Wheels which are manufactured by foundry techniques and which are characterized by an excellent resistance both to impact and to cracking produced by thermal effects caused by severe service conditions resulting from brake malfunctions.

I The railroad car wheels contemplated within the scope of this invention are produced by casting a ferrous metal alloy consisting essentially of from about 0.95 percent by weight to less than about 1.30 percent carbon, from about 0.40 percent to about 1.00 percent manganese, from about 0.15 percent to about 0.70 percent silicon, up to about 0.055'percent sulfur, up to about 0.055 percent phosphorus, and the balance substantially all iron, it being understood that other elements customarily encountered and regarded as impurities in such castings may also be present in minor and ineffective amounts. More specifically, the alloys contemplated by this invention should contain from about 0.95 percent to about 1.20 percent and preferably about 1.05 percent carbon, from about 0.55 percent to about 0.85 percent, and preferably about 0.70 percent manganese, from about 0.20 percent to about 0.50 percent, and preferably about 0.35 percent silicon, as low a sulfur and phosphorus content as is possible, and may contain up to about 0.50 percent chromium and aluminum up to about 0.15 percent, added as a deoxidizer.

According to this invention, railroad car wheels cast to substantially final form and dimension from such alloys and appropriately heat treated demonstrate an unexpectedly higher resistance to destructive thermal cracking encountered in previously known similar cast steel wheels having compositions characterized principally by a higher carbon content when subjected to severe service condi-' tions resulting from brake malfunctions or panic or emergency stops.

-It is therefore a principal object of this invention to provide a cast steel railroad car wheel which consists essentially of an alloy within the aforesaid composition ranges which is characterized by its ability to resist the formation of destructive and dangerous cracks in its tread zone when subjected to abnormally severe braking conditions encountered during emergency stops or during operation while subjected to an inadvertently constant braking elfort due to a brake malfunction known in the art as a dragging brake shoe. Other and specifically ditferent objects of this invention will become apparent from the following disclosure, of which the accompanying drawing is a part. In the drawing the FIGURE is a graphical representation of the relationship of carbon content in cast steel railroad wheels composed of the alloys of this invention and similar previously known alloys, and the ability of such wheels to resist the formation of cracks in the tread zones under controlled braking conditions.

In the manufacture of cast steel railroad car wheels, as previously understood, certain problems were encountered. Of these, it was desirable that such wheels be able to withstand as much tread wear and have as high a resistance to cracking under impact loading encountered atent time.

Patented Feb. 19, 1963 satisfactory for normal service, providing they were heattreated in a particular manner in order to completely spheroidize the metal carbides present and eliminate a carbide network.

Wheels made in this manner were found to begenerally quite satisfactory'when subjected to normal usage, however under certain conditions of severe service, otherwise satisfactory wheels were found to occasionally develop destructive and potentially dangerous cracks in the tread areas. These cracks were found to have their origin in situations where it was determined that the brakes had malfunctioned by failing to release completely, causing one or more brake shoes to continuously bear on the tread of the wheel while the railroad car was propelled and may also be caused by repeated emergency stops from high speeds. dragging brake for obvious reasons. In view of the apparent functional causes of these failures, it became apparent that the resulting cracks were engendered by the absorption of abnormally high amounts of energy in the surface of the wheel tread exposed to the brake shoes and probably were a form of thermal cracking.

In order to substantiate these conclusions a large number of actual cast steel railroad car wheels were tested under reproducible laboratory conditions which simulated very extreme braking conditions. One of the standard test procedures used consisted of mounting the wheel to be tested on a dynamometer shaft, urging a standard brake shoe against the wheel tread in a braking attitude under a load of 3000 pounds, bringing the wheel up to a rotational speed equivalent to 45 miles per hour and maintaining that speed and that braking effort thereon for 30 minutes. During this time about 49,500,000 pounds feet of energy were dissipated. Thereupon the brakes shoe was removed and the wheel air cooled at a speed equivalent to about 10 miles per hour for 15 minutes and then further cooled while still rotating at about 10 miles per hour by a water spray. The wheel was then inspected for tread cracks, the entire cycle requiring about minutes total This cycle was repeated until the wheel tread exhibited one crack one inch in length, at which time it was deemed to have failed and the test was terminated on that particular wheel. Several other similar tests were also performed, but since the results Were consistent with the results obtained from the described tests, it is not believed necessary to go into either the details of these tests or their specific results.

Prior to this invention, it was not believed that the carbon content of previously known cast steel railroad wheels could successfully be reduced below 1.30 percent carbon utilizing more or less conventional sand molding techniques and, it was further believed that the carbon content should be maintained as high as possible within the aforesaid range of 1.30 to about 1.65 percent by weight, consistent with the ability to heat treat the wheel to The former condition is usually referred to as a spheroidize the carbides to break up the carbide network. More specifically, it was believed that utilizing more or less conventional sand casting methods, that such lower carbon contents would so reduce the hardness of the Wheel that excessive wear would result, that casting defects and lack of soundness in the casting would prevent such lower carbon content wheels from being successfully cast, and that no significant difference would be achieved in other mechanical properties. We have unexpectedly found that contrary to these beliefs, cast steel railway wheels containing from about 0.95 to less than about 1.30 percent by weight carbon, from about 0.40 to about 1.00 percent manganese, from about 0.15 to about 0.70 percent silicon, up to about 0.055 percent sulfur, up to about 0.055 percent phosphorus, and which may contain minor amounts of other elements such as up to about 0.50 percent chromium and up to about 0.15 percent aluminum may be readily manufactured with no significant difficulty experienced with defects or unsoundness, that the wear rate is not distinguishably greater than the previously known higher carbon content wheels and that these wheels have an unexpectedly greater resistance to thermal cracking where exposed to the abnormally high braking efforts which tend to cause thermal cracks in the prior art wheels.

In order to more particularly point out the invention,

the following representative data is presented. As previously set forth a large number of dynamometer tests as previously described were performed on the aforesaid 1.30 to 1.65. percent carbon cast steel wheels. Similarly, a large number of such tests were similarly performed on the wheels of the present invention. Because of the time factor involved, if a given test wheel survived as many as 50 cycles of the drag test performed upon the dynamometer, as previously described, the test on that wheel was terminated. This arbitrary number of 50 cycles was selected because of the performance of the higher carbon content wheels under this test. As would be expected from a test of. this sort, a scatter band of results were observed in the results of the tests on the prior art 1.30 to 1.65 percentcarbon wheels. In addition, in order to more clearly point out rather than obscure the invention, a representative. number of wheel tests were selected for purposes of comparison and illustration. For example, a group of eight wheel tests performed on such higher carbon .content wheels containing from 1.37 to 1.38 percent carbon have been selected in order to show a representative scatter band and to compare these results with similar test results for wheels of this invention. It will be observed from the accompanying drawing that all'of the wheels according to this invention survived at least 50 cycles of the aforesaid test without failure and the tests terminated at that point as signified by the arrows.

More specifically, all the wheels so tested were cast in sand molds from alloys containing, upon subsequent analysis, the indicated carbon content as will be set forth. Further, these wheels all contained within 0.40 to 1.00 percent manganese, 0.15 to 0.70 percent silicon, not more than 0.055 percent sulfur, not more than 0.055 percent phosphorus, not more than 0.50 percent chromium and notmore than 0.15 percent aluminum. After the usual cleaning operations, including the removal of the risers and the like, the wheels were heat treated by heating to a temperature of between 1650 to 1950 F., preferably about 1800 F. for about one hour, a time sufficient to achieve a stable temperature and to dissolve the carbides. The wheels were then air cooled and reheated to a temperature between 1400 and 1600 F., preferably about 1500 F. for about. two hours, a time suflicient for stabilization and the hub portions water cooled, the rest of the wheel structures being permitted to air cool. The wheels were then finish machined and inspected to insure that there were no defects before testing.

The following tabulated data, is representative of the 4 many tests performed on such wheels and which has been plotted in the accompanying drawing.

1 Test terminated, no crack amounting to 1 in length.

From the foregoing, and from other similar tests, it has been found that wheels made according to this invention consistently resist thermal cracking, as previously set forth, for at least 50 cycles of the stated test, while the higher carbon content wheels seldom withstand as many as 20 cycles of the test. in terms of total energy absorbed during such tests, it may be stated that the railroad car wheels made according to this invention are capable of absorbing at least 2,475,000,000 pounds feet (corresponding to the energy absorbed in 50 cyclespofsaid test) whereas the prior art wheels seldom are capable of absorbing more than about 990,000,000 pounds feet (corresponding to 20 cycles). and frequently fail at a much smaller value.

From the foregoing, it will therefore be apparent that the presentinvention provides a solution to a previously unsolved problemrelating to relatively high carbon cast steel railroad car'wheelsa As indicated previously, many slight variationsfrom the specific examples given. will readily occur tothose skilled in the art and it is tobe understood that .such variations as reasonably fall within the scope of the invention are intended to be covered by tne following claims.

What we claim and desire to secure by Letters Patent.

ofthe United States is;

1. An article of manufacture comprising a-cast steel t railroad car wheel characterized by the ability to absorb at least 2,000,000,000 pounds feet of energy in the tread zone thereof without forming tread zone cracks more than one inch in length, consisting essentially of from about 0.95 to less than 1.30 percent by weight carbon,

from about 0.40 to about 1.00 percent by weight manganese, from about 0.15 to about 0.70 percent silicon, not more than 0.055 percent by weight sulfur, not more than 0.055 percent by weight phosphorus, up to about 0.50 percent by weight chromium, up to about 0.15 percent by weight aluminum and the balance substantially all iron.

2. An article of manufacture-comprising a cast steel railroad car wheel characterized by the ability to absorb at least 2,000,000,000 pounds feet of energy in the tread zone thereof without forming a single tread zone crack more than one inch in length, consisting essentially of from about 0.95 to about 1.20 percentby weight carbon,

from about 0.55 to about'0.85 percent by weight manganese, from about 0.20 to about 0.50 percent by weight silicon, less than 0.055 percent by weight sulfur, less than 0.055 percent by weight phosphorus, less than 0.50 percent by weight chromium, less than. 0.15 percent by weight aluminum, and the balance substantially all iron.

3. Anarticle of manufacture comprising a cast steel railroad car wheel characterized by the abilityto absorb at least 2,400,000,000 pounds feet of energy in treadzone thereof without forming a single thermal crack in the tread zone which is more than one inch in length, consisting essentially of about 1.05 percent by weight carbon, about 0.70 percent by weight manganese, about 0.35

5 percent by weight silicon, less than 0.055 percent by weight sulfur, less than 0.055 percent by weight phosphorus, less than about 0.50 percent by weight chronium, less than about 0.15 percent by Weight aluminum, and the balance substantially all iron.

References Cited in the file of this patent UNITED STATES PATENTS 786,248 Cowden Mar. 28, 1905 6 Brunner Sept. 13, 1938 Flinn et a1. Aug. 17, 1954 FOREIGN PATENTS Belgium Feb. 1, 1951

Claims (1)

1. AN ARTICLE OF MANUFACTURE COMPRISING A CAST STEEL RAILROAD CAR WHEEL CHARACTERIZED BY THE ABILITY TO ABSORB AT LEAST 2,000,000,000 POUNDS FEET OF ENERGY IN THE TREAD ZONE THEREOF WITHOUT FORMING TREAD ZONE CRACKS MORE THAN ONE INCH IN LENGTH, CONSISTING ESSENTIALLY OF FROM ABOUT 0.95 TO LESS THAN 1.30 PERCENT BY WEIGHT CARBON, FROM ABOUT 0.40 TO ABOUT 1.00 PERCENT BY WEIGHT MANGANESE, FROM ABOUT 0.15 TO ABOUT 0.70 PERCENT SILICON, NOT MORE THAN 0.055 PERCENT BY WEIGHT SULFUR, NOT MORE THAN AND 0.055 PERCENT BY WEIGHT PHOSPHORUS, UP TO ABOUT 0.50

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