Abstract:
A railcar unit has a pair of deep sidewalls and a cradle mounted between the sidewalls for carrying coils. The sidewalls span the distance between the two railcar trucks, and act as a pair of deep beams for carrying vertical loads. The deep sidewalls are arranged to extend above and below the centre sill of the cradle and to give vertical stiffness to the car. The centre sill is a straight through sill for carrying buff and draft loads between the couplers. The cradle is made from a set of cross bearers welded to the centre sill to form a series of segmented beams, covered by plating. The cross bearers are welded to the sidewalls at lap joints. The cross bearers are all of the same design and can be made from a rolled beam. The sidewalls have their deepest section at mid-span, and are tapered to a thinner section toward the end structure of the cars. The tapering includes provision of an access way between the railcar truck wheels and the sidewall to permit brake maintenance.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to improvements in the structure railway cars for carrying metal coils, commonly referred to as coil cars.  
         BACKGROUND OF THE INVENTION  
         [0002]    Coils of steel sheet are often carried by rail cars. Coils can be mounted either longitudinally or transversely. In a longitudinal mounting, the axis of revolution of the coil is aligned to be substantially parallel with the rolling, or longitudinal, direction of the rail car. A longitudinal mounting often has the appearance of a single long trough with a number of moveable intermediate dividers. In a transverse mounting, the axis of revolution of the coil is aligned across the tracks, that is, perpendicular to the rolling direction of the rail car. Transverse mounting cars have a number of parallel bunks, rather than one long trough. A bunk is generally V-shaped, and the coil sits in the bunk with the outer circumference of the coil tangent to the V at two points such that it cannot roll. The V-shaped bunks are generally lined with wood decking to act as cushioning, thereby discouraging damage to the coils during loading or travel.  
           [0003]    In earlier times flat cars were converted to function as coil cars by adding bunks on to the flat car deck to prevent the coils from rolling off the deck during transport from the rolling mill to the customer. The basic structure of a flat car includes a main center sill that is box shaped in cross-section. The center sill of this kind of car is the main structural member of the car and runs from one end coupling of the car to the other. The center sill is the primary load path of the car both for longitudinal buff and draft loads from coupler to coupler, and for carrying the vertical load bending moment between the trucks. A wide deck is mounted above the center sill of this kind of car. Often, alternating cross-bearers and cross ties extend outwardly from the central sill. The cross bearers tend to be of deeper section and provide the majority of the support for the outboard regions of the deck.  
           [0004]    Over time, the size and weight of coils that can be carried has increased. The flat car design has evolved to have stronger and bigger main sills, sometimes reinforced by doubled sections. Further, the central sill may not necessarily be of constant section, but may have a “fish belly” profile. That is, the depth of section of the centre sill can increase toward the mid-section of the railcar to correspond to the increase in bending moment at mid-span between the rail car trucks. Further, longitudinal stringers, in the form of I-beams or wide flange beams have been located above the deck level to form the upper lip of the longitudinal bunk. In another step in the evolution of the flat car design, some or all of the flat decking can be replaced by canted decking to form the V-shaped trough. In more recent times the flat decking has been removed entirely, to leave a railcar having a dominant centre sill, a pair of elevated outboard longitudinal beams, cross-bearers cantilevered out from the centre sill like ribs; and V-shaped decking to form the trough.  
           [0005]    The present inventor has taken a different approach. Rather than having a dominant center sill, the inventor employ a pair of outboard beams of relatively deep section. The coil carrying bunk is then supported at its lateral ends to extend between the two deep side beams, A car with a pair of deep beams, well separated also has superior lateral bending resistance to a narrower car.  
           [0006]    In terms of fabrication, it is advantageous to reduce the number of different parts used in an assembly. To that end, it would be advantageous to replace the traditional arrangement of alternating cross-ties and cross-bearers with a single design of cross-bearer. When the cross-bearer is designed conceptually as a cantilevered arm or rib, it is not uncommon for the root of the arm to be of a deeper section than the tip, reflecting the relatively large moment that must be carried at the root of the arm. However, a tapered section is not as convenient as a section of constant depth. A section of constant depth can be produced by a rolling mill, and is less likely to have welding defects or irregularities than a fabricated section. By contrast, when the cross-bearer is in concept more akin to a beam supported at two ends, the use of a section of constant depth is not inappropriate.  
           [0007]    The use of a deep side beam presents the opportunity for improving the connection at the outboard tips of the cross-bearers. Formerly, the use of I-beam or wide flange beams at the upper and outer lips of the trough did not always present a convenient welding arrangement. The cross-bearer end could be trimmed to match the profile of the I-beam web, or the flange of the I-beam could be trimmed back locally to accommodate the cross-bearer tip. In either case the cross-bearer tip would butt against the I-beam section. When deep side beams are used, the beams themselves have intermediate vertical stiffeners to discourage the relatively thin webs of the beams from buckling. At the same time, the stiffeners present a flat surface, in the same plane as the plane of the web of the cross-bearer, against which a lap joint can be formed. Not only can a better joint be formed, but the fit-up process in manufacturing is, in the view of the present inventor, easier. That is, the pre-existing vertical stiffener of the beam acts as a longitudinal stop for the outboard tip of the cross-bearer, automatically locating it in the correct position.  
           [0008]    Access for brake maintenance on a car with deep side walls may be limited. To address this concern the present inventor has eased the downward profile of the side beams to permit improved access to the brakes between the trucks and the mid-span portion of the car.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides, in a first aspect, a rail car for carrying metal coils, comprising a pair of end structures each mounted on a rail car truck, a pair of side beams extending between the end structures, and a transverse cradle, for cradling metal coils, mounted between the side beams. The cradle has a longitudinally extending low central portion. The lowest point of the low central portion lies at a height that is at least as high as the lowest extremity of the side beams.  
           [0010]    In an additional feature of that aspect of the invention, the railcar has, at a transverse-section between said trucks, a second moment of area about a horizontal neutral axis, and the side beams contribute at least half of the second moment of area of the section. In another additional feature of that aspect of the invention, the side beams of the rail car contribute at least three quarters of the second moment of area of the section. In a still further additional feature of that aspect of the invention, the side beams of the railcar contribute at least 90% of the second moment of area.  
           [0011]    In still another further additional feature of that aspect of the invention, at a transverse section between the trucks, the location of the maximum longitudinal tensile stress under a gravity load is in the lowest chord of one of the side beams.  
           [0012]    In yet another additional feature of that aspect of the invention, at a transverse section between the trucks, the location of maximum longitudinal compressive stress under a gravity load is in the highest chord of one of the side beams. In still another additional feature of that aspect of the invention, the cradle has a center sill extending longitudinally along the low central portion.  
           [0013]    In still yet another additional feature of that aspect of the invention, the central sill has a top flange and a bottom flange, the rail car has, at a transverse section between the trucks, a neutral axis for bending under gravity loads, and the neutral axis lies at a height that is between the height of the top and bottom flanges.  
           [0014]    In another additional feature of that aspect of the invention, the cradle includes cross-bearers connected to the side beams. In still yet another feature of that aspect of the invention, in at least a medial portion of the rail car between the trucks, the cross bearers are of substantially uniform design. In a further feature of that aspect of the invention, at least a medial portion of the rail car between the trucks is of the type chosen from the set of rail car types consisting of rail car portions that are free of cross-ties and rail car portions in which the number of cross ties is fewer than two thirds as many as cross bearers.  
           [0015]    In still a further additional feature of that aspect of the invention, the rail car has a through centre sill of substantially constant cross-section. In still yet a further additional feature of that aspect of the invention, over at least the medial portion of the rail car, the cross-bearers are of substantially uniform design. In another further additional feature of that aspect of the invention, at least the medial portion of the rail car is of a type chosen from the set consisting of types that are free of cross-ties, and types that have less than two-thirds as many cross-ties as cross-bearers.  
           [0016]    In another aspect of the invention, there is a rail car for carrying metal coils comprising a pair of end structures each mounted on a rail car truck, a pair of side beams extending between the end structures, a transverse sling, for cradling metal coils, slung between the side beams, the rail car having a set of brakes, and at least one of the side beams having a relief permitting access to the brakes.  
           [0017]    In an additional feature of that aspect of the invention, the relief is located adjacent the truck. In another additional feature of that aspect of the invention, the one beam has a relief adjacent each of the trucks. In still another additional feature of that aspect of the invention, both the beams have reliefs adjacent the trucks. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings, which show an apparatus according to the preferred embodiment of the present invention and in which:  
         [0019]    [0019]FIG. 1 is a top view of a prior art coil car.  
         [0020]    [0020]FIG. 2 is a side view of the prior art coil car of FIG. 1.  
         [0021]    [0021]FIG. 3 a  is a cross-sectional view on section ‘ 3   a - 3   a  ’ of the prior art coil car of FIG. 1.  
         [0022]    [0022]FIG. 3 b  is the other cross-sectional view on section ‘ 3   b - 3   b  ’ of FIG. 1.  
         [0023]    [0023]FIG. 4 is a sectional view on section ‘ 4 - 4 ’ of the prior art coil car of FIG. 1.  
         [0024]    [0024]FIG. 5 a  is top view a rail car according to the present invention.  
         [0025]    [0025]FIG. 5 b  is a top view of the rail car of FIG. 5 a  with decking removed to show the skeletal structure of the rail car.  
         [0026]    [0026]FIG. 6 is a side view of half of the rail car of FIGS. 5 a  and  5   b.    
         [0027]    [0027]FIG. 7 is a cross section of the rail car of FIGS. 5 a  and  5   b  at mid span.  
         [0028]    [0028]FIG. 8 a  is a cross section of the rail car of FIG. 5 a  at the main bolster.  
         [0029]    [0029]FIG. 8 b  is a cross sectional view of the rail car of FIG. 5 b  toward the end bulkhead. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]    The description which follows, and the embodiments described therein, are provided by way of illustration of an example, or examples of particular embodiments of the principles of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention. In the description which follows, like parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features of the invention.  
         [0031]    For the purposes of better understanding the present invention, a number of s illustrations of a prior art rail car are included by way of comparison. The prior art rail car is indicated generally in FIGS. 1, 2,  3   a ,  3   b  and  4  as P 20 . It has a pair of rail car end structures P 22  and P 24 , each having a main bolster P 26 , A main center sill is indicated as P 28 . Ribs branch outwardly from main center sill P 28  and are indicated as cross-bearers P 30  and thinner cross-ties P 32 . The outer tips of cross-bearers P 30  and cross ties P 32  meet with one or other of a pair of wide flange beams P 34  and P 36 . A generally V-shaped deck P 38  runs the length of the car, spanning the pitches between cross-beams P 30  and cross-ties P 32  to terminate at end bulkheads P 40  and P 42 . Main center sill P 28  has a generally box-shaped rectangular section that has a deep central belly P 44 , shown in FIGS. 3 a  and  3   b . Main center sill P 28  has an upper flange P 46  and a thick central lower flange P 48 .  
         [0032]    In the particular embodiment illustrated the overall depth of main center sill P 28  at central belly P 44  is 28 inches. The weight of main center sill P 28  is 150 lbs per lineal foot, and its width is 22 inches over the lower flange P 48 . The thickness of bottom flange P 48  is 1 inch and the thickness or the remainder of main center sill P 28  is ⅜ inches thick. Wide flange beams P 34  and P 36  are 13.8 inches deep at 34.3 lbs. per lineal foot each. The overall weight of section is roughly 261 lbs. per lineal foot with a neutral axis in bending located 22.9 inches above top of rail, undeflected design height. The local neutral axis of main center sill P 28  is located about 23.3 inches TOR, and the local neutral axis of each of the wide flange beams is located about 56.8 inches above TOR. The second moment of area of the section shown in FIG. 3 a  is about 24,300 in 4 . Of this, 50% can be attributed to the influence of main center sill P 28 .  
         [0033]    At the mid-span line of car P 20 , it is expected conceptually that a large coil, such as an 84 inch diameter coil, will tend to place the top flange of cross bearers P 30  in tension and the lower flange in compression.  
         [0034]    In FIG. 3 a , wide flange P 36  has been trimmed locally to admit the distal tip P 50  of cross-bearer P 30 , such that the end of the tapered web P 52  and upper flange P 54  of cross-bearer P 30  abut the vertical web of wide flange beam P 36 . Cross beam P 30  and wide flange P 36  are fillet welded together in this orientation. A similar arrangement is shown in FIG. 3 b  for cross-tie P 32  and wide flange P 34 .  
         [0035]    By contrast, an example of a rail car embodying the present invention is illustrated S in FIG. 5 a . For the purposes of conceptual explanation the embodiments illustrated in FIGS. 5 a ,  5   b ,  6 ,  7 ,  8   a  and  8   b , the major structural elements are both symmetrical about the longitudinal centerline of the car (as designated by axis CL) and symmetrical about the mid-span transverse section of the car, indicated as TS. In reality a number of secondary and tertiary brake fittings, handrails, brackets, cables and other ancillary features that do not have appreciable effect on the structural performance of the car may not necessarily be symmetrical about either centerline.  
         [0036]    A rail car is indicated generally as  20 . It has a pair of end structures  22  and  24  for mounting on a pair of rail car trucks  26  and  28  respectively. A pair of left and right hand side beams  30  and  32  extend between end structures  22  and  24 , and form the main longitudinal structural elements of rail car  20  for resisting gravitational loads. A cradle  34  is hung between beams  30  and  32 . Cradle  34  resembles a trough, and is shaped to cradle steel coils, or other similar loads, between its inwardly and downwardly sloping shoulders  36 . Shoulders  36  are lined with wooden decking  37  placed to accommodate coils ranging between 30 and 84 inches in diameter. When coils are loaded in cradle  34  they are discouraged from longitudinal sliding by end bulkheads  35  and by moveable bulkheads  38  whose locating pins seat in the indexed apertures of left and right hand locating plates  39 .  
         [0037]    The structure of cradle  34  includes a center sill,  40 , cross-bearers  42  extending between center sill  40  and one or the other of side beams  30  and  32 , and deck plates  44 . Deck plates  44  include right and left hand slope plates  46 , and  48  of shoulders  36 , welded to the upper flanges of cross-bearers  42  and to the upper flange  50  of center sill  40 . Center sill  40  includes, in addition to upper flange  50 , a pair of parallel vertical webs  52  and  54  and a lower flange  56 . Center sill  40  is a through-center-sill, that is, it runs from one end of rail car  20  to the other, and is of substantially constant section throughout its length. Internal gussets  57  are welded inside center sill  40  to provide web continuity at each cross-bearer location. Center sill  40  has an overall depth of 12.719 inches. Upper flange  50  is 15 inches wide and 0.50 inches thick. Lower flange  56  is 16 inches wide and 0.50 inches thick. Vertical webs  52  and  54  are each 11.719 inches high and 0.375 inches thick. The overall weight of the section is 82.3 lbs per lineal foot, and its local moment of inertia in longitudinal bending, that is its second moment of area about its transverse neutral axis, is 664 in 4 .  
         [0038]    Since rail car  20  is symmetrical, for the purposes of the present description it will be understood that the structure of side beams  30  and  32  is identical. Each has an upper flange assembly  70 , a lower flange assembly  72 , and webbing  74 . Examining each of these in turn, upper flange assembly  70  has a top chord member in the nature of a hollow rectangular steel tube  76 , upon which pin locating plate  39  is mounted. Plate  39  has an inwardly extending perforated tongue,  80 , the perforations having a constant pitch, and being of a size and shape suitable for engagement by the locating pins of moveable bulkheads  38 . Also located intermittently along a more outboard region of plate  39  are tie-down eyes  84  for locating a cowling or cover to protect coils mounted on coil car  20  from being exposed to the rain and snow. Lower flange assembly  72  includes a main lower sill member in the nature of a hollow rectangular tube  86  to which a ¾″ thick steel lower sill reinforcement  88  has been added. Webbing  74  includes a substantially vertical steel web  90  welded at lap joints to the respective outer faces of steel tube  76  and rectangular tube  86 . Vertical braces  92  extend between tubes  76  and  86  along the inner face of web  90  at regular spacings along the length of beams  30  and  32 . A cantilevered walkway  94  is mounted on brackets  98  located on the outboard face of web  90 .  
         [0039]    Over the mid span section of car  20 , that is, the portion of car  20  at which side beams  30  and  32  have their maximum depth, the overall second moment of area of each side beam  30  or  32  is about 14,800 in 4 . The weight of each side beam section is about 100 lbs. per lineal foot. Each of side beams  30  and  32  provides just over 45% of the total second moment of area of the mid span section of car  20 .  
         [0040]    The joining of cradle  34  to each of side beams  30  or  32  is typically as shown in FIG. 7. Deck Plate,  44  has a vertical upturned lip  102  that is welded along the inwardly facing side of steel tube  76 . The web  104  of cross bearer  42  extends beyond the ends of its upper and lower flanges  106  and  108  and is cut on a mitre to yield a substantial tab  110  suitable for welding in a lap joint to the longitudinally facing side  112  of vertical brace  92 . The joint is welded at a fillet along the corner of vertical brace  92  on one face of tab  110 , and at a fillet along the distally extreme edge of tab  110  to side  112 . In this way the joint is intended to place the weldmetal predominantly in shear. Web  104  also has intermediate gussets  114  to provide reinforcement in the region of wooden decking  37 . Wooden decking  37  is provided for the known purpose of cushioning metal coils loaded in car  20 , as noted above.  
         [0041]    Considering the side view of car  20  shown in FIG. 6, moving away from the mid span centerline of car  20  on Transverse Section TS, the section of greatest depth ends at a point designates as ‘X’. Lower sill reinforcement  88  ends, and hollow rectangular tube  86  is obliquely truncated and welded to a doglegged upsweep flange  120 . Flange  120  follows the lower edge of web  90  as it narrows in a transition portion  121  from the deep, mid span portion,  122  to the narrow, or shallow, end structure portion  124 , the upward sweep of flange  120 , reaching a height sufficient to clear trucks  26  and  28 , as the case may be. The upper portion  130  of the dog leg has an exaggerated, or extended, reach to yield a relief, or accessway, indicated generally as  132  between the near wheel  134  of truck  26  or  28 , and the truncated end of lower sill tube  86 . This extended recess facilitates maintenance and repair of operating mechanisms of car  20 , such as brake linkages. It also makes for a more efficient use of material since the depth of section required at mid span is generally greater than that required near the ends of the span for a simply supported beam. This permits a saving in weight.  
         [0042]    Moving still further toward the end of car  20 , the accumulated vertical shear load in side beams  30  and  32  is carried to trucks  26  and  28  of end structures  22  and  24 , as shown in the sectional view of FIG. 8 a . Main bolster  140  has the form of a laterally extending irregular box with a pair of spaced apart, substantially parallel webs  142  and  144  of significant depth. Webs  142  and  144  extend fully between a stepped lower flange and a sloped upper flange  146  underlying deck plate  36 . Webs  142  and  144  have an extending tab  148  that reaches under and supports upper flange assembly  70 , abuts the inside face of web  90 , and also abuts the top face of upswept flange  120 .  
         [0043]    In alternative embodiments of the invention to that shown, it would be possible to design a car having a cradle with either a stepper or a shallower slope, with consequent alteration of the height of the center sill relative to the side beams. However, given the relatively higher pliability of the center sill under vertical bending loads as compared to the side beams, it is undesirable for the chord of maximum stress (and therefore strain) to be in the lower flange of the center sill. To that end, the lower flange of the center sill, that is, its lowest extremity, is no lower than the lowest extremity of the side beams. Similarly, the highest compressive stress due to vertical load will occur in the highest portions to top chord assembly  70 .  
         [0044]    S In terms of carrying compressive longitudinal loads between coupler ends, it is advantageous to retain a straight through sill. This implies a relatively high sill since standard coupler height is 33 inches above top of rail to the center of the coupler.  
         [0045]    In the embodiment illustrated, the centroid of area of car  20  is at a height just below the top of top flange  50 , within the profile of center sill  40 . As such, center sill  40  plays only a small role in resistance to vertical bending.  
         [0046]    It is possible to benefit from simplified production when all the cross bearers are of the same design, but some benefits can be obtained even when some cross ties remain, whether they are half as numerous, two thirds as numerous, one third as numerous as the cross bearers or some other fraction.  
         [0047]    A preferred embodiment has been described in detail and a number of alternatives have been considered. As changes in or additions to the above described embodiments may be made without departing from the nature, spirit or scope of the invention, the invention is not to be limited by or to those details, but only by the appended claims.