Patent Publication Number: US-6216362-B1

Title: Method and apparatus for control of the cooling rate of cast steel railway wheels

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to heat treatment and processing of cast steel railroad wheels. More specifically, a method and associated apparatus are disclosed for increasing or reducing the rate of heat loss from as-cast railroad wheels. 
     Historically, railroad wheels have generally been produced by forging or casting of cast iron or cast steel. The cast steel wheels are primarily produced by a bottom-pouring casting technique. However, any of the production processes require control of the cooling cycles or rates to maintain the crystalline microstructure of the cast or forged wheels. In the above-noted bottom-pouring technique, the as-cast wheels are removed from the casting mold for transfer to subsequent operations to remove the hub core, sprues and risers, for inspection and for heat treating and normalizing at various production stages. 
     Although the railroad wheels are normalized, their microstructure is influenced by the as-cast temperature and the subsequent cooling rate. This is especially influenced by mass differences from the relatively thick cross-section at the outer tread portion, through the thinner connecting web, to the most massive section of the wheel at the axle hub. The cooling rate influences the microstructure, the rate of formation of inclusions in the grain boundaries, their distribution in the microstructure, dislocation formation, dislocation movement across the grain boundaries, residual stresses and their locations, as well as other metallurgical and mechanical properties. In addition, the cooling cycle must provide the wheel at the subsequent production operation from the shake-out at the correct temperature for the next operation, which is not necessarily room temperature. 
     Production practices have required transport of railway wheels on a continuous conveyor path through an in-line kiln. In general, the structure of the kiln provided refractory lined walls and roof in an elongated chamber similar to a muffle furnace. In at least one known operation, the capacity or rate of heat transfer could be accelerated by raising the upper or roof panels to provide a greater volume of air flow past the wheels. The cooling practice did not desire or require a water or hot oil quench, and the slower cooling rate from air cooling or air quench practice to achieve the desired properties was preferred. 
     Another cooling practice utilized insulating disks poised above the axle hub to reduce the dissipation of radiant heat from the hub area of the wheel. The wheels moved in intermittent or discrete steps to perform the cooling cycle. This practice and the associated insulating disks, which are applied after the drawing furnace, are taught in U.S. Pat. No. 3,753,789 to Kucera et al. 
     No known assembly or method has provided controlled cooling of the as-cast railroad wheels with discrete or individual parametric control to provide the requisite wheel temperature for subsequent manufacturing practices. 
     SUMMARY OF THE INVENTION 
     A method and apparatus has a generally hemispherical cap for individually controlling the rate of heat transfer from an as-cast steel railroad wheel. The cap is suspended above the individual wheels to isolate the wheel to maintain its heat losses. More particularly, apparatus is connected to the insulated caps to raise or lower the cap. Increasing the height of the insulated hemispherical cap above the wheel allows more radiant energy to freely escape from the wheel, which allows the wheel to more rapidly cool.. Alternatively, maintaining the cap in proximity to the wheel maintains or retains the heat in the wheel. Control of the position of the cap close to or further from the wheel as it progresses on its path is accommodated by a controller coupled to either, or both, a motion sensor or temperature sensor to position the disks based on empirical data for a specific operation, temperature, rate of travel, wheel size or other known parameter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the several figures of the Drawing, like reference numerals identify like components, and in the drawing: 
     FIG. 1 is a schematic end view of a prior art heat-transfer kiln in a normal operating mode, showing a phantom outline of an open-roof operation; 
     FIG. 2 is a plan view of a conveyor apparatus and wheels thereon progressing through the kiln of FIG. 1; 
     FIG. 3 is an elevational side view of multiple wheels on a conveying apparatus with illustrative insulating caps and an illustrative control arrangement; 
     FIG. 4 is a schematic elevational end view of a hemispherical insulating cap over a wheel on an insulating pedestal atop a conveying apparatus; 
     FIG. 5 is a side elevational view of a wheel on a conveying apparatus with an insulating cap operable on a trolley arrangement in a cooling operation wherein the wheels are each separated by a discrete and equal distance; 
     FIG. 6 is a cross-sectional view of a typical railroad wheel; 
     FIG. 7 is an oblique side view of an exemplary railroad wheel on end; and, 
     FIG. 8 is an illustrative diagrammatic oblique view of an insulating cap. 
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     FIG. 1 illustrates an as-cast railroad wheel  10  at an elevated temperature in prior-art heat-transfer assembly or kiln  12 . Finished railroad wheels  10  in FIGS. 6 and 7 are respectively noted in cross-section and on end, as an illustration. In FIGS. 6 and 7, wheel  10  has outer diameter  40  with a shallow wall thickness  42 . Wheel  10  includes flange  44 , tread  46 , web  48 , hub  50  and axle bore  52 . 
     Kiln  12  in FIGS. 1 and 2 has first sidewall  14 , second sidewall  16  and roof  18  to enclose chamber  20 . In an alternative embodiment of kiln  12 , roof  18  may be provided with movable segments  22  and  24 , which open to increase air flow and the dissipation of radiant energy through chamber  20  and thus to increase heat transfer from wheels  10 , which segments  22  and  24  are noted in dashed outline. 
     Conveyor assembly  26  with upper surface  28  extends through chamber  20 . Wheels  10  in chamber  20  are positioned atop pedestals  30 , which are set on surface  28 . It is known in the art that surface  28  may have a plurality of discrete plates or cleats  29  shown in FIG. 2 or be a continuum, and this is not a limitation. In the as-cast state, wheels  10  may be at a temperature in excess of 2200° F. and include sprues and risers from the casting process, which sprues and risers must be removed from finished wheel  10 , as shown in FIG.  7 . Specifically, hub riser  32  is noted in FIG. 1, but it is known that there may be a plurality of sprues and risers emanating from the surface of a wheel. However, downstream processing of wheels  10  are performed at temperatures significantly below the temperature of as-cast wheel  10  when it is removed from its mold, not shown. Further, wheels  10  are allowed to cool or air quench at a controlled rate to permit the crystalline structure to form at a desired rate and to allow the grain growth to proceed in a desired manner. The resultant grain structure, as well as the related chemical, intercrystalline constituents and mechanical properties of wheel  10  are in large part a consequence of this initial controlled-cooling process. The above-noted cooling practice of kiln  12  is operable in gross and provides only nominal control of a batch, that is more than one, of wheels  10  within kiln  12 . The precise length and wheel capacity of chamber  20  may vary with the available production space, which length and heat transfer rate within chamber  20  will effect the rate of movement of conveyor  26 . 
     In FIG. 1, it can be appreciated that the broad portion of wheel  10  with web  48  across outer diameter  40  will provide a large emitting surface for emission of radiant energy. However, radiant energy is also emitted from wheel lower surface  56  toward floor  38 , as well as from tread  46  and flange  44  toward walls  14  and  16 . In elongate chamber  20 , heat is conducted from kiln  12  at kiln ends  13  and  15 , or alternatively in a kiln  12  with movable roof segments  22  and  24  heat may be dissipated through an open roof  18 . This dissipation of heat is relatively uncontrolled for each piece, wheel  10 , in the batch. It is known that delays or stoppage of conveyor  26  for any unusual length of time will result in changes in the physical and structural characteristics of wheels  10 , and may impact the downstream processing and inspection requirements of wheels  10  caught in such a delay. This negative impact is an undesirable characteristic of the kiln-style cooling practice. 
     The present invention provides apparatus for individually controlling the rate of heat transfer from wheels  10  either within a chamber  20  of a kiln-style structure or outside of such chamber  20 . The apparatus in FIG. 8 appears as a hemispherical cap  70  with outer shell  72 , inner volume  74 , lower lip  76  and outer diameter  78  at lower lip  76 . Diameter  78  is considered to be at least as large as outer diameter  40  of wheel  10 , and it is understood that diameter  40  may vary between wheel styles. In consideration of this fact, cap diameter  78  may be provided in a single diameter large enough to accommodate all wheel diameters  40  or caps  70  of varying sizes may be provided to mate with appropriately sized wheels  10 . This alternative is available to the user, but does not negate operation of the control or use of cap  70 , although it may require adjustment of the control parameters. Inner surface  73  of volume  74  may be lined with a refractory material to provide greater heat reflection, inhibit warpage of cap  70  and provide better heat-transfer control by cap  70 . Although cap  70  is illustrated as a hemisphere, it is considered that a generally symmetrical shape would be operable to provide the requisite reflective capabilities for the operating system. 
     In an exemplary structure  80  in FIG. 3, wheels  10  are noted on conveyor assembly  26 . Caps  70  are positioned over each individual wheel  10 . The caps  70  are operable to move with wheels  10  as they progress on conveyor  26  in the illustrative direction marked by arrow  84 . Various arrangements for overhead movement are available such as a monorail or the rail and wheel structure  86  in FIG.  5 . Each cap  70  is coupled to an operator  88 , which may as examples be a decade motor, stepper motor, a worm gear on a motor or other moving device, by connector  90 . Operators  88  move caps  70  closer to wheels  10  to contain or retain heat in wheels  10 , which may be viewed as a decrease in heat transfer rate. Alternatively, caps  70  may be elevated over a range of clearances, as noted by dashed outline  71  in FIG.  3 . 
     Operators  88  are coupled to controller  94  by lines  96  in FIG. 3, which is also connected to sensor  100  by line  102 , which sensor is operable to monitor the movement of conveyor line  26 , and provides a sensed signal to controller  94  of the movement of conveyor  26  and its rate of movement. Further, sensors  110  are temperature sensors providing signals over lines  112  to controller  94 . In response to these signals either individually or in concert, controller  94  is operable to compare the signals to empirical data and provide a control signal to operators  88  to raise or lower caps  70  to decrease or increase the rate of heat transfer, and a second signal may be provided to drive apparatus  114  by line  116  to control the rate of movement for conveyor  26  for similar control of the rate of heat transfer. These control signals may be correlated by controller  94  to control the rate of heat transfer for attainment of the desired wheel temperature prior to the next processing operation. In this manner, controller  94  controls the rate of heat transfer from each individual wheel  10  as it progresses along the path determined by conveyor  26 . 
     A further embodiment of the invention is shown in FIG. 4, which embodiment has pedestal  30  on conveyor  26  as a refractory mass  120  for mounting wheel  10 . In addition, refractory plates  122  and  124  are positioned on either side of mass  120  to insulate conveyor  26  and to symmetrically surround the wheel for uniform reflection of heat. 
     As noted above, rail and wheel structure  86  is available to transport caps  70 . However, in this specific structure, the cap  70  and connector  90  may be fixed in position if the wheels  10  are being transferred in repetitively discrete positions. Further, such a rail system is operable in a kiln  20  with an open roof section. 
     While this invention has been described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.