Patent Publication Number: US-6033001-A

Title: Wheel for rolling stock and manufacturing method thereof

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improvement of a wheel for rolling stock having such a form that a rim section is deflected from a boss section towards the outside of a track and relates to a manufacturing method thereof. 
     A wheel for rolling stock (hereinafter, referred to as a wheel) requires a performance against a cracking damage due to a thermal crack occurring on a tread or flange surface of the wheel, namely, requires durability against cracking damage, because of a thermal stress due to mainly brake heat under such a circumstance that the brake heat is raised in response to recent increase in high-speed travel via railroad. 
     As a conventional technique which satisfies the above requirement, there exist a method of decreasing heat sensitivity of a material or improving fracture toughness, and a method of decreasing a thermal stress generated by braking, etc. due to improvement in a form of a wheel. As a technique which belongs to the latter method, the applicant of the present invention has suggested a wheel for rolling stock in Japanese Patent Application Laid-Open No. 56-34504 (1981). 
     FIG. 1 is an explanatory drawing showing a deflection amount δ and deflection angle θ of a rim section 1 relative to a boss section 3 in a solid rolled wheel for rolling stock (hereinafter, referred to as a solid rolled wheel). In the wheel disclosed in Japanese Patent Application Laid-Open No. 56-34504 (1981), as shown in FIG. 1, an end of a curved line of the side of a fillet closer to a flange 2 of the rim section 1 of the wheel is a point A1, a position on the side opposed to the flange where a plate thickness of a wheel disk wheel disk section 4 is minimum relative to the point A1 is a point A2, and a mid-point between the points A1 and A2 is a point A3. Similarly, an end of a curved line on a side opposed to the flange of the fillet of the boss section 3 is a point B1, a position on the side closer to the flange where the plate thickness is minimum relative to the point B1 is point B2, and a mid-point between the points B1 and B2 is a point B3. Lines from the points A3 and B3, which are perpendicular to a center line O of the wheel, are represented by La and Lb respectively, and a dimension between the lines La and Lb, namely, a deflection amount of the rim section 1 is represented by δ, and an angle between a line linking the points A3 and B3 and the line La or Lb, namely, a deflection angle of the wheel disk section 4 is represented by θ. At this time, in the case where any wheel whose diameter is equivalent to the above one is used, there is a tendency that as the deflection amount δ is larger, the thermal stress which is generated in the wheel disk section 4 of the wheel is smaller. 
     Needless to say, when the deflection amount δ changes, the deflection angle θ also changes simultaneously. For this reason, the similar change is shown as to action of the thermal stress of the wheel disk section 4 with respect to the deflection angle θ. A relationship between the deflection amount δ and the maximum value of the thermal stress in the wheel disk section 4 is shown in FIG. 2. According to this result, when the deflection amount δ≧40 mm, the thermal stress generated at the time of braking can be lowered remarkably, and a wheel having excellent brake-resistance performance can be obtained. Here, since the relationship between the deflection angle θ and the maximum value of the thermal stress of the wheel disk section 4 is approximately the same as the relationship between the deflection amount δ and the maximum value of the thermal stress of the wheel disk section 4, the description thereof is omitted. 
     As mentioned above, the solid rolled wheel of conventional wheels has limitation in the manufacturing technique that the point A3 in FIG. 1 is positioned approximately in the center of an axial direction, parallel to the center line 0, of an inner diameter of the rim section 1. FIG. 3 is an explanatory drawing showing a deflection amount λ of the wheel disk section in the solid rolled wheel. As shown in FIG. 3, when a line, which is perpendicular to the center line 0 of the wheel and passes through the point A3 which is the mid-point between the points A1 and A2, is represented by La, and a mid-point in the axial direction of the inner diameter of the rim section 1 is represented by a point C, and a line, which is perpendicular to the center line 0 of the wheel and passes through the point C is represented by Lc, a distance between the lines La and Lc, namely, the deflection amount λ is approximately zero. As a result, even if the deflection amount λ is made larger in the design, the deflection amount λ according to the design cannot be obtained, and only a value of zero or close to zero is obtained in the most cases. 
     Therefore, in the case of the rolled wheel, it is necessary to satisfy the condition that the deflection amount δ≧40 mm with only by the deflection amount of the point B3 in the center of the plate thickness adjacent to the end of the curved line on the side opposed to the flange of the fillet of the boss section 3. For this reason, it is difficult to obtain the condition that the deflection amount δ≧40 mm in a wheel for locomotive, etc. having a hub cut and a larger diameter. Moreover, since the deflection amount λ is approximately zero, the maximum value of the deflection amount δ is not so larger, and thus the deflection angle θ of the wheel disk section 4 shown in FIG. 1 cannot obtain a larger value. As a result, since the occurrence of the thermal stress cannot be sufficiently suppressed, there arose a problem that the durability against a cracking damage cannot be improved more than some degree. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is invented in order to solve the above problem, and it is an object of the present invention to provide a solid rolled wheel, in which a thermal stress is lowered according to a form of the wheel, and a larger deflection amount δ is obtained by setting a deflection amount λ of a disk, which have been conventionally about 0, to not less than 5 mm, and thus an excellent durability against cracking damage is obtained. The invention also relates to a manufacturing method thereof. 
     A wheel for rolling stock of the present invention is characterized by including a boss section adapted to be fitted on a wheel set, a disk formed on a circumference of the boss section, and a rim section on an outer circumferential end of the disk, which is deflected to one side in an axial direction from the boss section wherein the disk is deflected to one side in the axial direction from the rim section so that a condition that λ≧5 mm is satisfied where λ is a deflection amount which is an axial direction distance between a center of a thickness in the axial direction of the rim section and a center of a thickness in the axial direction of an end of the disk closer to the rim section. 
     In addition, the wheel for rolling stock of the present invention is characterized in that the rim section is deflected from the boss section so that a condition that δ≧40 mm is satisfied where δ is a deflection amount which is an axial direction distance between a center of a thickness in the axial direction of an end of the disk closer to the rim section and a center of a thickness in the axial direction of an end of the disk closer to the boss section. 
     Further, the wheel for rolling stock of the present invention is characterized in that the disk is provided with a fillet at an end thereof closer to rim section, and the deflection amount λ is an axial direction distance between the center of a thickness in the axial direction of the rim section and a center of a thickness in the axial direction in the vicinity of the end of a curved line farther away from the rim section on the fillet. 
     Furthermore, the wheel for rolling stock of the present invention is characterized in that the disk is provided with a fillet at an end thereof closer to the boss section, and the deflection amount δ is an axial direction distance between a center of a thickness in the axial direction in the vicinity of the end of a curved line farther away from the rim section on the fillet closer to the rim section and a center of a thickness in the axial direction in the vicinity of the end of a curved line farther away from the boss section on the fillet closer to the boss section. 
     A method of manufacturing a wheel for rolling stock of the present invention is characterized by including the steps of: forming a boss section to be fitted on a wheel set, a disk formed on a circumference of the boss section and a rim section on an outer circumferential end of the disk by preforging; providing a fillet to an end of the disk closer to the rim section by rolling; and deforming the disk by rotational forging so that conditions that V=W, R 1  =R 3 , R 2  &gt;R 4  are satisfied. 
     Here, V is a volume of the disk from an inner circumferential surface of the rim section to the end of a curved line of the fillet after the rolling; W is a volume of the disk from the inner circumferential surface of the rim section to the end of the curved line of the fillet after the rotary forging, R 1  is a curvature of a curved line on one side in an axial direction of the fillet after the rolling, R 2  is a curvature of a curved line on the other side in the axial direction of the fillet after the rolling, R 3  is a curvature of a curved line on one side in the axial direction of the fillet after the rotary forging, and R 4  is a curvature of a curved line on the other side in the axial direction of the fillet after the rotary forging. 
     The inventors understand that when the condition that the deflection amount λ of the rim section ≧5 mm is satisfied in the state that La shown in FIG. 3 is closer to the side opposed to the flange than Lc, the condition that the deflection amount δ of the disk ≧40 mm is secured easily, and thus a wheel having an excellent durability against cracking damage can be obtained. 
     The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS 
     FIG. 1 is an explanatory drawing showing a deflection amount δ and deflection angle θ of prior art rim section in a solid rolled wheel; 
     FIG. 2 is a graph showing a relationship between the deflection amount δ and a maximum value of thermal stress of the rim section in the solid rolled wheel of FIG. 1; 
     FIG. 3 is an explanatory drawing showing a deflection amount λ of the wheel disk section in a prior art solid rolled wheel; 
     FIG. 4 is an explanatory drawing showing a prior art manufacturing method of making the solid rolled wheel; 
     FIG. 5 is an explanatory drawing showing a method of manufacturing the solid rolled wheel of the present invention; 
     FIG. 6 is an explanatory drawing showing load positions V 1 , V 2  and L 1  when a stress analyzing test is performed on the wheel of the present invention and a comparative wheel; 
     FIG. 7 is a temperature distribution chart when a thermal load is put on the newly manufactured solid rolled wheel according to an embodiment of the present invention: 
     FIG. 8 is a thermal stress distribution chart when a thermal load is put on the newly manufactured solid rolled wheel according to an embodiment of the present invention; 
     FIG. 9 is a temperature distribution chart when a thermal load is put on the solid rolled wheel in the abrasion limit state according to an embodiment of the present invention; 
     FIG. 10 is a thermal stress distribution chart when a thermal load is put on the solid rolled wheel in the abrasion limit state according to an embodiment of the present invention; 
     FIG. 11 is a temperature distribution chart when a thermal load is put on the newly manufactured solid rolled wheel according to a conventional manufacturing method; 
     FIG. 12 is a thermal stress distribution chart when a thermal load is put on the newly manufactured solid rolled wheel according to a conventional manufacturing method; 
     FIG. 13 is a temperature distribution chart when a thermal load is put on the solid rolled wheel in the abrasion limit state according to a conventional manufacturing method; 
     FIG. 14 is a thermal stress distribution chart when a thermal load is put on the solid rolled wheel in the abrasion limit state according to a conventional manufacturing method; and 
     FIG. 15 is an explanatory drawing showing positions P, Q, R and S where a maximum stress of the wheel disk section is measured in the stress analyzing test. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following details an embodiment of the present invention with reference to the drawings. 
     As is clear from FIG. 2, as a deflection amount δ of a rim section is larger, a thermal stress generated in a wheel disk section 4 of a wheel is weaker, and a condition that the deflection amount δ≧40 mm has been employed as a technique of reducing the thermal stress. In the present embodiment, besides the condition that the deflection amount δ≧40 mm, a condition that a deflection amount λ of the wheel disk section, which was nearly zero in the conventional technique, is set to not less than 5 mm. 
     The deflection amount λ is set to not less than 5 mm as mentioned above because first, the condition that the deflection amount δ≧40 mm is not easily fulfilled with the deflection amount λ of the wheel disk section being zero in a wheel for a locomotive having hub cut, etc., and even in the case of a wheel in which a value of a deflection angle θ of the wheel disk section is smaller, a form of such a wheel can be designed easily by setting the deflection amount λ to not less than 5 mm. 
     Secondly, a technique of manufacturing a wheel in which the deflection amount λ≧- 5 mm is fulfilled is established. In the method of manufacturing the conventional rolled wheel for rolling stock, as shown in FIG. 4, after a material was preforged and rolled, it was press-formed to a final target form. In the first place, in the rolling step by wheel mill, there is a limitation that the deflection amount λ of the wheel disk section 4 is nearly zero, and in the final forming step, a press is generally used. For this reason, in the conventional manufacturing method, it was actually impossible that the deflection amount λ≧5 mm. In the present invention, when the form after the rolling step is designed while setting a condition on a curvature of a fillet of the rim section 1, a technique in which it is made possible that the deflection amount λ≧_5 mm in the finally formed product is established. 
     In other words, in the steps until the rolling step by wheel mill, the wheel is designed by the manufacturing method similar to the conventional one so that the deflection amount λ of the wheel disk section 4 is zero. Then, in the final forming step, a base on the rim section 1 side is deformed by a rotary forging machine so that a solid wheel in which the deflection amount λ≧5 mm is formed. 
     At this time, the form design after rolling is important. This depends on a roll design of a mill or a preforming design. As to a volume (rim taper volume) from an end of a curved line of the fillet of the rim section 1 to the inside diameter of the rim section 1 represented by narrow-width slant lines, a volume V after rolling accords with a volume W after final forming, and a curvature R 1  of a curved line on the side closer to the flange of the fillet of the rim section 1 accords with a curvature R 3  after the final forming, and a curvature R 2  of curved line on the side opposed to the flange of the fillet of the rim section 1 is larger than a curvature R 4  after the final forming. The form of the wheel is designed as mentioned above. 
     By designing the form of the wheel after rolling as mentioned above, the deflection amount δ of the rim section 1 obtains a larger value, and the occurrence of the thermal stress can be reduced remarkably, thereby making it possible to obtain a rolling stock having excellent durability against cracking damage. 
     In order to verify the effect of the present invention, the stress analysis test was performed by the finite element method under the condition shown in Table 1 on the solid rolled wheel (the present invention) having a diameter of 1143 mm, the deflection amount δ of the rim section of 64 mm and the deflection amount λ of the wheel disk section of 12 mm (with hub cut), and on a solid rolled wheel (comparative wheel) having a diameter of 1143 mm, the deflection amount δ of the rim section of 52 mm and the deflection amount λ of the wheel disk section of 0 mm (with hub cut). The load positions V 1 , V 2  and L 1  at that time are shown in FIG. 6. 
     In the above analysis, an evaluation was made by comparing the solid rolled wheels having different forms under the same condition in the elasticity analysis as to whether or not the form setting of the wheel is satisfied under the normal use condition. The rim section having a newly manufactured form and the rim section having an abraded form were used. The results are shown in Tables 2 and 3 and FIGS. 7 through 14. 
     The maximum stress generated in the wheel disk section under each condition is shown in Table 2. This shows the evaluations of thermal expansion of the rim section generated due to a tread brake, tension and compressive stress generated in the wheel disk section by a combination of a normal force due to a rolling stock load and a lateral load at a curvilinear motion. Here, the positions P, Q, R and S of where the maximum stress is measured are shown in FIG. 15. 
     Under a condition including a thermal load where a brake head is assumed, the maximum stress of the wheel disk section obtains a large tension value, but it is found that the wheel of the present invention has the stress reducing effect of about 15% in the newly manufactured state and of about 40% in the abrasion limit state compared with the conventional wheel. Therefore, it is found that in the wheel of the present invention, the average value of a repeated stress of the wheel disk section due to the brake heat, rolling stock load, etc. is low and the safety factor for the fatigue of the wheel disk section is high. Moreover, under a condition not including the thermal load, the absolute values in both the wheels are small, and thus there arises no problem. 
     Next, a highest temperature and thermal stress generated in the rim section under the condition of only the thermal load are shown in Table 3. A cross section temperature distribution in the newly manufactured state is shown in FIG. 7 (wheel of the present invention) and FIG. 11 (conventional wheel), a cross section temperature distribution in the abrasion limit state is shown in FIG. 9 (wheel of the present invention) and FIG. 13 (conventional wheel), a thermal stress distribution in the newly manufactured state is shown in FIG. 8 (wheel of the present invention) and FIG. 12 (conventional wheel), and a thermal stress distribution in the abrasion limit state is shown in FIG. 10 (wheel of the present invention) and FIG. 14 (conventional wheel). These are evaluations of influences due to a heat of the rim section generated at the time of braking the tread. 
     The absolute value of the compressive stress generated in the rim section when the temperature rises are equivalent to each other in the wheel of the present invention and the conventional wheel in the newly manufactured state (FIG. 8 shows the wheel of the present invention, and FIG. 12 shows the conventional wheel), but in the abrasion limit state, the absolute value in the present invention is lower than that in the conventional wheel (FIG. 10 shows the present invention, and FIG. 14 shows the conventional wheel). Therefore, it is found that the durability against cracking damage of the wheel of the present invention is improved. The wheel is usually subject to a tread heat treatment in the rim section, and a residual compressive stress is loaded to the rim section. As a result, a minute crack, which is generated on the tread due to repetition of braking and is generally unavoidable, is prevented from improving. As mentioned above, by reducing the maximum stress generated in the rim section, plastic deformation of the rim section can be prevented, and the occurrence of the residual tension stress in the rim section which causes an improvement of a crack and a cracking damage can be prevented from happening. 
     As mentioned above, according to the present invention, a wheel for rolling stock having the high fatigue safety factor and excellent durability against cracking damage for the wheel disk can be obtained, and thus a moving safety can be secured in the use under a strict condition due to a congested train schedule or high speed movement of a train. 
     As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiments are therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims. 
     
                       TABLE 1                                                     
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               Wheel of the  Comparative                                  
Items          present invention                                          
                             wheel                                        
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(1) Analyzing                                                             
             Type      New φ1143 mm                                   
                                   Comparing                              
    form                           φ1143 mm                           
       Rim state                                                          
               1 Newly manufactured form                                  
               2 Abrasion limit form                                      
               (Rim thickness: 25.4 mm)                                   
               φ1041 mm  φ1041 mm                                 
(2) Load     Maximum   17 t        17 t                                   
             static load                                                  
             Normal load                                                  
                       34 t        34 t                                   
             (V)                                                          
             Lateral load                                                 
                       17 t        17 t                                   
             (L)                                                          
(3) Brak-              29.4 kw     29.4 kw                                
    ing                (20 minutes)                                       
                                   (20 minutes)                           
    condi-                                                                
    tion                                                                  
(4) Load           a.    V.sub.2                                          
    com-           b.    L.sub.1 + V.sub.1                                
    bina-          c.    Th                                               
    tion           d.    L.sub.1 + V.sub.1 + Th                           
                   e.    V.sub.2 + Th                                     
(5) Mate-          a.    Initial temperature: 24° C.               
    rial           b.    Consistency: 7.83 g/cm.sup.3                     
    chara-         c.    Specific heat: linear function:                  
    cter-                Cp = 0.434 + 0.000392T (kJ/kg · K)      
    istics         d.    Heat conductivity: linear                        
    and                  function                                         
    others               K = 0.0483 - 0.0000187T                          
                         (W/mm · K)                              
    (Boundary      e.    Heat transmissibility:                           
    condition)           constant:                                        
                         h = 2.27 × 10.sup.-5 (W/mm.sup.2           
                         · K)                                    
                   f.    Radiant heat: none                               
                   g.    Elastic modulus: 200,000 (MPa)                   
                   h.    Poisson&#39;s ratio: 0.30                            
                   i.    Thermal expansion coefficient:                   
                         linear function:                                 
                         a = 10.65 + 0.00648T (μm/mK)                  
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                                           TABLE 2                                 
__________________________________________________________________________
          Maximum stress in the plate section                             
Section                                                                   
     Rim form  V.sub.1 + L.sub.1                                          
                   V.sub.2                                                
                       Th  V.sub.2 + Th                                   
                                V.sub.1 + L.sub.1 + Th                    
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Wheel of                                                                  
     Newly                                                                
          kgf/mm.sup.2                                                    
               -17.4                                                      
                   -8.7                                                   
                       32.2                                               
                           36.3 39.7                                      
the  manufac-                                                             
          MPa  -170.3                                                     
                   -85.5                                                  
                       315.8                                              
                           355.8                                          
                                389.6                                     
present                                                                   
     tured                                                                
          Position                                                        
               P(0°)                                               
                   Q(0°)                                           
                       R(0°)                                       
                           Q(180°)                                 
                                Q(0°)                              
invention                                                                 
     Abrasion                                                             
          kgf/mm.sup.2                                                    
               -21.9                                                      
                   -23.2                                                  
                       47.8                                               
                           52.2 56.3                                      
     limit                                                                
          MPa  -214.4                                                     
                   -227.5                                                 
                       468.9                                              
                           511.6                                          
                                552.3                                     
          Position                                                        
               P(0°)                                               
                   S(0°)                                           
                       Q(0°)                                       
                           Q(90°)                                  
                                Q(0°)                              
Com- Newly                                                                
          kgf/mm.sup.2                                                    
               -13.7                                                      
                   -9.8                                                   
                       38.6                                               
                           44.1 44.7                                      
parative                                                                  
     manufac-                                                             
          MPa  -134.5                                                     
                   -96.5                                                  
                       378.5                                              
                           432.3                                          
                                438.5                                     
wheel                                                                     
     tured                                                                
          Position                                                        
               P(0°)                                               
                   Q(0°)                                           
                       Q(0°)                                       
                           Q(180°)                                 
                                Q(0°)                              
     Abrasion                                                             
          kgf/mm.sup.2                                                    
               -24.7                                                      
                   -24.0                                                  
                       81.4                                               
                           95.3 92.9                                      
     limit                                                                
          MPa  -242.7                                                     
                   -235.1                                                 
                       798.4                                              
                           934.3                                          
                                911.5                                     
          Position                                                        
               R(0°)                                               
                   S(0°)                                           
                       Q(0°)                                       
                           Q(0°)                                   
                                Q(0°)                              
__________________________________________________________________________
 
    
     
                                           TABLE 3                                 
__________________________________________________________________________
                  Maximum stress on the surface                           
                  of the rim section                                      
                           Rim surface                                    
                                  Rim surface                             
                           on the side                                    
                                  on the side                             
     Rim  Tread maximum    closer to                                      
                                  opposed to                              
Section                                                                   
     form temperature  Tread                                              
                           the flange                                     
                                  the flange                              
                                         Flange                           
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Wheel                                                                     
     Newly                                                                
          (° C.) 300                                               
                  kgf/mm.sup.2                                            
                       -21.6                                              
                           -9.7   -19.58 -12.4                            
of the                                                                    
     manufac-                                                             
          (° F.) 572                                               
                  MPa  -211.7                                             
                           -95.1  -191.0 -121.3                           
present                                                                   
     tured                                                                
          FIG. 7  FIG. 8                                                  
inven-                                                                    
     Abrasion                                                             
          (° C.) 413                                               
                  kgf/mm.sup.2                                            
                       -29.1                                              
                           -21.7  -26.7  -20.6                            
tion limit                                                                
          (° F.) 775                                               
                  MPa  -285.4                                             
                           -213.1 -262.0 202.0                            
          FIG. 9  FIG. 10                                                 
Compar-                                                                   
     Newly                                                                
          (° C.) 302                                               
                  kgf/mm.sup.2                                            
                       -21.1                                              
                           -14.1  -17.1  -14.3                            
ative                                                                     
     manufac-                                                             
          (° F.) 575                                               
                  MPa  -206.8                                             
                           -137.9 -167.5 -140.7                           
wheel                                                                     
     tured                                                                
          FIG. 11 FIG. 12                                                 
Abrasion  (° C.) 416                                               
                  kgf/mm.sup.2                                            
                       -41.0                                              
                           -44.6  -31.1  -40.0                            
limit     (° F.) 780                                               
                  MPa  -402.0                                             
                           -437.1 -305.4 -392.3                           
          FIG. 13 FIG. 14                                                 
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