US 3272550 A
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Description (OCR text may contain errors)
Sept. 13, 1966 w. H. PETERSON 3,272,550
WHEEL FOR RAILROAD Filed July 22, 1965 2 Sheets-Sheet l Wiiliam H. Peterson INVENTOR.
Arrorney Sept. 13, 1966 w, PETERSQN 3,272,550)
WHEEL FOR RAILROAD Filed July 22, 1965 2 Sheets-Sheet 2 5 Effect of Lower Elastic Modulus 2 in Wheel Tread Material on Load 50) Capacit as Compared to Steel E Wheel read.
Ratio of Load Wheel Can Carry to that of Steel Whee|( 20 TlTANlUM AND ITS ALLOYS |.7| L60 COPPER-BERYLLIUM "5 GRAY lRON 1.50 1.0
5 i'o 1'5 2'0 3'5 Modulus of Elasticity of Wheel Tread Material (P.S.l. XIO INVENTOR.
William H. Peterson Attorney United States Patent 3,272,550 WHEEL FOR RAILROAD William H. Peterson, Homewood, Ill., assignor to Pullman Incorporated, Chicago, Ill., a corporation of Delaware Filed July 22, 1965, Ser. No. 473,959 10 Claims. (Cl. 295-31) This invention relates to wheels for rail vehicles and, in particular, relates to an improved wheel construction which will permit an increase in the life of a rail upon which the wheel passes over.
The wheel loads for rail vehicles and, in particular, railroad cars carrying freight and the like have been increasing over the years. This increasing wheel load has been placing an ever increasing burden on the rail over which the wheel rides. With every failure of a rail in service carries with it a hazard of derailment. An average cost of a derailment is in the neighborhood of $15,000 to $20,000 per derailment, or somewhere around $5,000,- 000 per year as the cost of derailments due to broken rails on the American railroads. All sorts of remedies have been tried, including changing the cant of the rail, changing the contour of the rail head, grinding the rail, using work-hardened rail on curves, intermediate elimination of lubrication, use of alloy steels, complete heat treatment of the rail, and localized heat treatment of the rail head. The plain fact is that the shell and detail fracture from the shell of the rail are due to local loading of the steel of the rail beyond its yield point, resulting in flow of metal toward the gauge corner of the rail. If the rails are overstressed with the old loads, they are more severely stressed with the newer, heavier loads carried by the railroad cars. The size of the rail has been increased and this has been helpful, but our present rail steel is about as strong as can be obtained without heat treatment, costing approximately $65.00 per ton, when added to the cost for rail of $150.00 per ton, puts this expense out of the question economically. Also, since only about 5,000 track-miles with new railroads are being replaced with new rail each year, it would take about 50 years to get all of the main-line track relaid with heat treated rail. The same reasoning applies to any change in rail contour that might be made.
Up to the present time, 33 inch diameter wheels have been generally used on freight cars. The size of the rail has been increased, and this has been a help insofar as structural stresses are concerned. However, the critical stresses in rail today are those associated with contact pressures of the wheel on the rail. The actual contact area of the wheel on top of the rail has an ellipse on the order of A" wide and /8 long. This area must withstand the entire wheel load and its size is not affected or decreased by the size of the rail. Now, the contact surface of the rail and the wheel are subjected to high compressive stress from the wheel load which results in internal compression, tension, and shearing stresses within the rail head. This stress condition results in the development of progressive or fatigue failure. Contact pressures which result in stresses beyond the yield or fatigue strength of the rail result in excessive batter at rail ends; flow; corrugation; head checks; flaking, or shelling, and progressive fractures therefrom; head and web separations; horizontal and vertical split heads; and progressive fractures from engine burns. As a matter of fact, almost 80% of failures occurring in the past ten years rolling of controlled-cooled rail were the result of contact pressure of the Wheel on the rail. To counteract this condition, the AAR Joint Committee on Relations between track and equipment of the American Association of Railroads conducted a study and recommended covering the relationship between the wheel load and the wheel diameter and that if this relation were exceeded, then additional wheels should be used. The solution to date has been either to increase the number of wheels or to go to larger size diameter wheels when increasing the loads beyond recommended limits in order to preserve the life of the rails. At present day prices, it would cost on the order of $7.5 billion to replace all of the rail in the main line track.
It is therefore a principal object of this invention to provide a railroad wheel construction that will increase the life of the rail over which it rides, to oifer space saving advantages, and eliminate the necessity of going to either more wheels which would be costly, or increasing the diameter size of the Wheel which would also be costly and would require more space.
Another object of this invention is to provide a wheel for a railroad vehicle which would reduce the stresses near and at the surface of the rail in contact with the wheel.
A further object of this invention is to provide for a railroad vehicle wheel having a material with a lower modulus of elasticity than that of the rail in order to preserve the life of the rail, as well as the life of the wheel.
Still another object of this invention is to provide a railroad vehicle wheel having a thin layer or skin of material about its outer periphery, the skin having a modulus of elasticity lower than the modulus of elasticity of the rail material for reducing the internal and surface stresses resulting from the contact pressure between the wheel and the rail.
Another object of this invention is to provide a wheel containing an outer shell or skin or tread of hard material selected from a group consisting of titanium alloys and/ or copper beryllium alloys and/ or gray iron.
These and other objects will become apparent from reference to the following descriptions and accompanying drawings wherein:
FIG. 1 is a view in elevation of a railroad vehicle wheel;
FIG. 2 is a sectional view taken along line FIG. 1;
FIG. 3 is enlarged partial view of that shown in FIG. 2;
FIG. 4 is a plan view taken along line 4-4 of FIG. 3; and i I FIG. 5 is a graph showing the effect of a lower elastic modulus in various wheel tread materials on load capacity as compared to steel wheel tread.
With reference now to the figures, there is shown a railroad vehicle wheel 2 provided with a center of hub portion 4 and an outer or peripheral portion 6, the outer extremity which has an annular outer skin 8 engaging with the upper rail surface 10 of a rail head 12 of a rail member 14, along a distance d.
With the exception of the outer skin portion 8, the wheel 2 including its inner and outer portions is composed generally of a plain carbon steel. The chemical composition of three classes of railroad wheels expressed in percent is stated below:
Chemical composition-wheel Carbon: Percent Class A, not over 0.57 Class B 0.57-0.67 Class C 0.67-0.77
Phosphorus, not over 0.05
Sulfur, not over 0.05
Silicon, not less than 0.15
From reference to the above composition of the plain carbon steels of the wheels of Class A, B, and C, it will be seen that the manganese, phosphorus, sulfur and silicon veloped increase.
BHN values) and Rockwell C scale hardness numbers (that is, Rc values).
Hardness Minimum Hardness Maximum Hardness 255 BHN (25 RC) 321 BHN (34 RC). 277 BHN (28 Re) 341 BHN (37 Re). 321 BHN (34 Rc) 363 BHN (39 Re).
Chemical requirements-rail Nominal weight, lb. per yard Carbon, percent 0.55 to 0.68 0.64 to 0.77. Manganese, percent 0.60 to 0.90.
Phosphorus, max, percen 0.04. Silicon, percent 0.10 to 0.23.
121 and over Carbon, percent Manganese, percent Phosphorus, max., pereen Silicon, percent 0.69 to 0.82. 0.70 to 1.00.
The hardness of the steel rail must be high enough and in some instances flame hardened to provide for good wear resistance on the part of the rail as it is engaged by the wheel. Since both the rail and the wheel are of substantially the same chemical composition of a plain carbon steel, the modulus of elasticity is the same, that is -29 10 pounds per square inch (p.s.i.)
With reference now to FIG. 3 and FIG. 4 it is seen that there is a rather small area A of contact between the wheel and the rail.
This area of contact increases with the increase of the diameter of the wheel as illustrated by the following table:
Wheel diameter in inches: Area of contact surface in square inches The values given showing the relation between the wheel diameter and the areas of surface contact between the wheel and the rail are given based on a constant load on the wheel and the rail. Under a given load a particular stress is developed below the area of contact, both in the wheel and the rail. As the weight or load increases on the wheel and, therefore, on the rail, the stresses de- If these sub-surface stresses become too great, they will cause the rail to deteriorate. The rail will actually form fractures and portions of the rail will break 011?. This is called shell cracking. If shelling of the rail should occur, this will result in a derailment of the train resulting in a damage to lading and train and injury to the occupants. In order to insure against this, the various associations in the railroad industry have stated that there should be a maximum loading for a given wheel diameter as expressed by the following table:
Nominal Pounds per in. Wheel Load, Wheel Diam- Diameter Pounds eter (in.)
Due to the increase in transportation of freight weight, these limitations are placing a restriction on the growth of the carrying of cargo by the railroad system. In order to carry greater loads, larger diameter wheels must be utilized or more wheels per truck must be used to more evenly distribute the load on the rails. The wheel diarneter in most common usage is the 33 inch (33) diameter and the most commonly used truck has four wheels per truck. To go to a 38 or 40 wheel presents space problems in addition to cost problems. Similarly increasing the number of wheels per truck increases the cost of the railroad car.
The novel invention resides in the formation of a skin 8 of material about the outer periphery of the wheel 6 providing a wheel tread that will reduce the stresses in the wheel and therefore in the rail. The area A of contact stress is in the order generally or approximately of an ellipse of wide, /6" long (d) with maximum shear stresses occurring at approximately a depth of As" more or less below the surface of the wheel and the surface of the rail for steel materials varying with other materials. The contact of two solid, curved elastic bodies at a point or along a line results in an elastic and sometimes plastic deformation of the bodies in the immediate vicinity of the ellipse of contact. The contact areas become finite in extent as a result of this deformation and consist of circular, elliptical or rectangular areas. This results in surface compressive stresses and interior stresses in each contacting body in the region near the contact area. These internal or sub-surface stresses lie in shear planes below the surface and result in the shelling cracks.
It is here proposed that a tread having an elastic modulus substantially lower than that of the steel rail will reduce these contact stresses in the rail head 12 for a given wheel loading as compared to having substantially the same elastic modulus in both the wheel tread and the rail head. If the present safe contact stresses are maintained, then such a wheel could safely carry more load.
To illustrate this, consider the following formulation for contact stresses as it appears in Advanced Mechanics of Materials, by Seely and Smith, 2nd Edition, July 1962,
' J. Wiley & Sons, Inc. Publishers, Chapter 11, pp. 358-359,
as well as the prior discussion wherein the values of the maximum principal, shearing, and octahedral shearing stresses for a car wheel on a railroad track are directly proportional to the ratio b/A where b=C x PA and R =radius of rail head R =radius of car wheel P=wheel loading E =elastic modulus of rail steel=29 10 p.s.i. E =elastic modulus of wheel tread material u =Poissons ratio for rail steel, 0.29
u =Poissons ratio for wheel tread material C is a geometrical factor which is a function of the rail head radius and car wheel radius, R and R The ratio of these radii determine the shape of the ellipse of contact area which in turn, determines the value .of C Thus C is not related to the elastic properties of the materials.
In this invention it is proposed to employ a material of substantially lower elastic modulus in order to be able to carry a heavier wheel load at existing permissible contact stress levels in the rail and we are concerned with the relative increase in loading as it is related to a change in material properties. Also, because of economic and other factors, it is assumed that the track will continue to be of steel. If we let the ratio b/A represent that for existing contact stress levels in the rail and call it S, we have:
are used in wheel tread and track. Letting this factor be the constant of proportionality, C, we have:
When both wheel tread and track are steel u =u and E =E and the wheel loading, P is and P /P :1 for steel wheel on steel rail.
The ratio of wheel load with the new tread material other than steel to that for steel tread on steel wheel is:
In the case of a titanium wheel tread 11 :0433, E =15 l0 p.s.i. and
Since Poissons ratio is generally on the order of 0.3
titaninm =2.08 steel and this value is squared in the above formula its effect is small. If it is ignored, the above formula reduces to:
is insignificant. With six wheel trucks as compared to four wheel trucks, we get an increase in loading of 50% or titanium 6 wheel 1 5 4 wheel To get the same increase by using a tread material of lower elastic modulus on a four wheel truck; the required value of E can be found from the equation:
and is 10 p.s.i. Thus if a wheel tread material with this or less elastic modulus is used a four wheel truck can replace a six wheel truck insofar as rail or track contact stresses are concerned, permitting a very substantial cost and weight savings.
This invention is to provide a tread or skin for the Wheel having substantially lower modulus of elasticity 0 than that of the rail and thereby increase the contacting areas between the wheel and the rail and thereby reduce the extent of formation of internal stresses.
Examples of various metals and their alloys which produced this novel result having the proper hardness for resistance to wear equivalent to present steel wheels and also have substantially lower elastic moduli are titanium alloys, copper beryllium alloys and gray iron as shown by the following table:
Titanium and its alloys-wrought Type 6 Al-G V-2 Sn 6 A1-4 V r Composition, percent A1 6.0, V 6.0, Al 6.0, V 4.0. 4.) Sn 2.0.
Mod. of Elast. in Tension, p.s.i 1618 10 1517.5 10. Hardness (Rockwell) (335-48 030-40.
50 Type 2 Fe-Z (Jr-2 Mo 8 Mn Composition, percent Fri [2.0, Cr 2.0, Mn 8.0.
O 2.0. Mod. of Elast. in Tension, p.s.i l6l7 10 15.5-17X10i Hardness (Rockwell) 1. C32- C28-36.
Type. 13 V41 Cr-3 m Composition, percent V 13.0, Cr 11.0, A130.
Mod. of Elast. in Tension, p.s.i 14.5-16X10". Hardness (Rockwell) Copper and its alloys-wrought Type and CDA No 172 (Beryllium Copper) Nominal Composition, percent 1- Mod. of Elast. in Tension, p.s.i..
Be 1.9%), Co 0.20, Cu Bal.
B Specified minimum tensile strength, 1,000 p.s.i. (ASTM A48). b At one-fourth the tensile strength. 9 Considerably wider range obtainable by heat treatment.
The eflt'ect of lower elastic moduli in wheel tread material on increased load capacity is plotted on the graph as shown in FIG. 5.
In referring to the above tables for the titanium alloys and copper beryllium alloys and gray iron, it will be seen that the hardness of each of these materials is generally the hardness of the rail or the hardness of the carbon steel portion of the wheel, but that each have a modulus of elasticity substantially lower than the modulus of elasticity of either the central portion of the wheel or that of the rail. This area of contact between the rail and the wheel increases and therefore the damaging internal shear stresses in the rail and the wheel are substantially reduced asthe skin 8 of the type of alloy as discussed allows more flattening of the skin over the rail surface.
Summarizing, the use of the band or skin or tread of metal material of a substantially lower modulus of elasticity than rail steel about the outer periphery of the railroad vehicle wheel reduces the stresses developed in the rail where the hardness of the skin approximates the hardness of the rail, enabling the greater loads to be carried by the railroad vehicle reducing the likelihood of shell cracking of the rail. Although one embodiment of the invention has been illustrated and discussed in detail it is to be expressly understood that the invention is not from the spirit and scope of the invention as the same will now be understood by those skilled in the art.
What is claimed is:
1. A rail vehicle wheel for use on a rail, said wheel having a central portion and having an attached rail contact stress reducing tread portion having modulus of elasticity substantially lower in value than the modulus of elasticity of the rail material which is generally on the order of 29 l p.s.i., and said tread portion having a hardness substantially of at least on the Rockell C hardness scale.
2. A rail vehicle wheel for use on a rail, said wheel having a central portion and having a rail stress reducing tread portion having modulus of elasticity lower in value than the modulus of elasticity of the rail material, and having a hardness substantially of at least 10' on the Rockwell C hardness scale, and the tread being essentially of a titanium base alloy selected from the group consisting of substantially (1) 6.0% aluminum, 6.0% vanadium, 2.0% tin; (2) and 6% aluminum, 4% vanadium; (3) and 2% iron, 2% chromium, 2% molybdenum.
3. A rail vehicle wheel for use on a rail, said wheel having a central portion and having a rail stress reducing tread portion having a modulus of elasticity lower in value than the modulus of elasticity of the rail material, and having a hardness substantially of at least 10 on the Rockwell C hardness scale, and the tread of the wheel consisting essentially of a titanium alloy.
4. A rail vehicle wheel for use on a rail, said wheel having a central portion and having a rail stress reducing tread portion having modulus of elasticity lower in value than the modulus of elasticity of the rail material, and having a hardness substantially of at least 10 on the Rockwell C hardness scale, and the tread of the wheel being a copper beryllium alloy having substantially 1.90% of beryllium, 0.20% cobalt, and the balance copper.
5. The invention according to claim 1 and the tread of the wheel being substantially a cast gray iron metal.
6. The invention according to claim 1 and said stress relieving tread being selected from the group consisting of titanium alloy; copper beryllium alloys; and cast gray iron.
7. A stress reducing rail vehicle wheel comprising an outer tread of a titanium alloy having a modulus of elasticity in the range of substantially l4 10 p.s.i. to l9 10 p.s.i.
8. A rail wheel for a rail, said wheel having a central portion of one material and having a separate outer peripheral stress relieving tread for relieving contact stresses in the rail head, the tread being composed of a different material having a modulus of elasticity substantially in the range of 10x10 p.s.i. to 25 10 p.s.i., said tread having sufficient surface hardness to substantially equal the hardness of at least 10 on the Rockwell C hardness scale and having suflicient strength to Withstand the contact stresses in the rail.
9. The invention according to claim 1 and said tread portion having a hardness substantially in the range of 20 to 45 on the Rockwell C hardness scale, and said tread portion having substantially a modulus of elasticity of l5 l0 p.s.i. to 22 10 p.s.i.
10. The invention according to claim 1 and said rail vehicle wheel central periphery being steel for a steel rail and said hardness being substantially 15 or more on the Rockwell C hardness scale.
References Cited by the Examiner UNITED STATES PATENTS 1,543,971 6/1925 Abbott 29531 X 2,190,125 2/1940 Sernbdner 295-31 FOREIGN PATENTS 10,078 1896 Great Britain.
ARTHUR L. LA POINT, Primary Examiner.
C. W. HAEFELE, Assistant Examiner.