Abstract:
An extended life traveling grate side plate having a heat transfer opening formed in a front portion of the side plate. The side plates are attached to the lateral side surfaces of each chain in a traveling grate conveyor. The front portion of each side plate overlaps the back portion of the preceding side plate such that the back portion of each side plate is covered and prevented from radiating heat away from the side plate. The heat transfer opening formed in the front portion of each side plate facilitates greater heat transfer from the overlapped area of the side plate. The front portion of the side plate is generally planar and does not include any gussets, thereby eliminating the heat transfer properties of the gussets and creating a more uniform thermal expansion of the side plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority from Provisional Application Serial No. 60/191,650 filed on Mar. 23, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to traveling grates of the type used to convey material through a dryer, a furnace or a discharge zone to a rotary kiln. More particularly, the present invention relates to a side plate construction for a traveling grate that increases the life of the side plate by reducing the temperature gradients across the side plate. 
     It is conventional in the prior art to provide vertically extending side plates which travel with a traveling grate or grate conveyor to retain the material being conveyed, such as pelletized ore or the like, on the traveling grate. A plurality of such side plates are pivotally connected in overlapped relation to each other along each of the lateral sides of the conveyor. Such overlapped side plates are conventionally positioned laterally on outer ends of the respective through rods or tie rods of the grate conveyor. 
     In the construction of the prior art, the overlapped side plates of the traveling grate chain assembly experience severe cracking that requires changing side plates after 1½ to 2 years of operation. The severe cracking of the side plates is believed to be caused by several contributing factors. Severe thermal cycling from the inlet of the traveling grate to the discharge end of the grate is an obvious effect of the process that cannot be changed and will probably worsen as the capacity of the traveling grate increases. Large thermal gradients across the side plates are evident from infrared pictures, and the effect is to put a severe strain on the side plates from the differences in the thermal expansion in different areas of the side plate. Stress risers from small radii in the corners of the side plates are inherent in the casting process. Three factors that are not readily obvious but contribute to the cracking problems in conventional side plates are: the restraining effects of the existing gussets, the cooling effects of the existing gussets, and the heat concentration in the back portion of the side plate due to overlapping of the back portion by the front portion of the preceding plate. 
     Therefore, it is an object of the present invention to provide an improved side plate that promotes heat transfer away from the side plate to reduce temperature gradients across the side plate resulting in reduced thermal stress in the side plate. Further, it is an object of the present invention to provide a side plate that is devoid of any gussets, which allows the side plate a greater degree of expansion and reduces the cooling effect created by the gussets. Further, it is an object of the present invention to provide a side plate that extends the effective life of the side plate and reduces the tendency of the side plate to crack due to the temperature gradients developed over the side plate. 
     SUMMARY OF THE INVENTION 
     The present invention is a side plate for use with a traveling grate. The side plate of the present invention decreases the thermal gradients across the front portion of the side plate while allowing heat to be radiated from the overlapped, back portion of the side plate when the side plate is positioned adjacent to a leading side plate. 
     The side plate of the present invention includes a heat transfer opening formed in the front portion of the side plate. The heat transfer opening is a removed area of the front portion of the side plate and provides an opening through the front portion of the side plate. The heat transfer opening formed in the front portion of the side plate overlays the back portion of the immediately trailing side plate when the side plates are sequentially connected to the continuous length of conveyor chain. The heat transfer opening allows heat to be radiated from the overlapped area of the back portion of the side plate, such that the overlapped area of the back portion can radiate heat effectively to reduce the temperature gradient across the back portion of the side plate to reduce thermal stress in the side plate. 
     The side plate of the present invention includes a front portion that has the gussets removed such that the entire front portion is generally planar. The removal of the gussets from the front portion of the side plate eliminates the increased heat transfer that previously occurred due to the gussets extending from the front portion. Additionally, the removal of the gussets allows the entire front portion of the front plate to expand and contract at a constant rate. 
     These two advantages decrease the temperature gradients across the side plate, thereby decreasing the cracking of the side plate and extending the useful life of the side plate. 
    
    
     Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings illustrate the best mode presently contemplated of carrying out the invention. 
     In the drawings: 
     FIG. 1 is a schematic illustration of a traveling grate conveyor that is utilized to feed a stream of pellets along the length of a drying and pre-heating section of an iron-ore processing system used to condition green pellets prior to discharge into a rotary kiln for further processing; 
     FIG. 2 is an exploded view illustrating the detailed construction of the traveling grate conveyor, including the side plates of the present invention; 
     FIG. 3 is a side view of a prior art side plate; 
     FIG. 4 is a side view of the first embodiment of the side plate of the present invention; 
     FIG. 5 is a perspective view of the first embodiment of the side plate of the present invention; 
     FIG. 6 is a side view illustrating the positioning of a pair of side plates as attached to the traveling grate conveyor; 
     FIG. 7 is a side view illustrating the pivoting movement of a pair of side plates; 
     FIG. 8 is a section view taken along line  8 — 8  of FIG. 7; 
     FIG. 9 is a side view of a second embodiment of the side plate of the present invention; and 
     FIG. 10 is a side view illustrating the pivoting movement between a pair of side plates constructed in accordance with the second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIG. 1, thereshown is the pre-conditioning section  10  of an iron-ore processing system. The preconditioning section  10  receives a feed of green pellets (iron-ore) from an infeed conveyor  12 . The pellets from the infeed conveyor  12  are deposited onto a traveling grate  14  that moves the supply of pellets through the various processing zones contained within the pre-conditioning section  10 . For example, as illustrated in FIG. 1, the pellets are dried, preheated and conditioned by a flow of heated air that passes through the pellets and the traveling grate  14  prior to the pellets reaching the discharge end  15  of the preconditioning section  10 . As illustrated in FIG. 1, the traveling grate  14  is entrained between an upstream shaft  16  and a downstream, head shaft  18 . As can be understood in FIG. 1, the traveling grate  14  is a continuous member that travels around the upstream shaft  16  and the downstream, head shaft  18 . In this manner, a continuous traveling chain gate  14  can be used to transport the pellets from the infeed end to the discharge end of the pre-conditioning section  10 . 
     Referring now to FIG. 2, thereshown is a portion of the upper run of the traveling grate  14 . The traveling grate  14  includes a plurality of conveyor grates  20  that are each supported by a pipe spacer  22 . The pipe spacer  22  is coaxially mounted to a pair of tie rods  24  such that the grates  20  extend across the entire width of the traveling grate between the pair of chains  26 , as is well known in the art. 
     The width of the traveling grate is defined by a plurality of spaced chains  26  that are each comprised of a series of joined links  28 . In the embodiment of the invention illustrated, six individual chains make up the traveling grate, although only two of the chains  26  are shown in FIG.  2 . Each of the chain links  28  includes cover member  30  that protects the individual links from the heated material being transported on the conveyor grates  20 . 
     The tie rods  24  each extend through the chain links  28  and are received within a coaxial spool  32 . Mounted on the spaced spools  32  are pivotally connected side plates  34 , the details of which will be described in greater detail below. A plurality of pivotally connected side plates  34  are positioned laterally along the length of the two outermost chains to define a continuous outer edge of the grate conveyor and define a sidewall along the entire length of each outermost chain  26 . In this manner, the side plates  34  maintain a bed of pellets at a determined depth by preventing the pellets from spilling over the edges of the chains  26 . Additionally, the side plates  34  act to keep the heated air passing through the conveyor within the pre-conditioning section  10 . 
     Referring now to FIG. 3, thereshown is a prior art traveling grate side plate  36  that is positioned along the lateral side of the traveling grate to contain the particles being transferred by the traveling grate. As shown in FIG. 3, the side plate  36  includes a front portion  38  and a back portion  40  that are integrally formed as a single, monolithic member. The front portion  38  includes a series of extended gussets  42  at a thrust button hub  44 . The gussets  42  and the thrust button hub  44  extend from a planar front face surface  46  that generally defines the front portion  38 . The face surface  46  of the front portion  38  is positioned in a plane spaced forward from a flat, back face surface  48  of the back portion  40  of the side plate  36  when the side plate  36  is attached to the chain  26  of the traveling grate, as illustrated in FIG.  2 . 
     As illustrated by the phantom side plate  36   b  in FIG. 3, when a plurality of side plates  36  are connected to the links of the traveling grate, the back portion  40  of the leading side plate  36  is overlapped by the front portion of the trailing side plate  36   b.    
     As illustrated in FIG. 3, the majority of the back portion  40  is covered by the overlapping front portion of the trailing side plate  36   b,  as illustrated by the phantom lines in FIG.  3 . As shown in FIG. 3, a distorted V-shaped area  50  of the back portion  40  is not overlapped by the trailing side plate  36   b.  Since the V-shaped area  50  is exposed to open air and is not covered by any portion of the trailing side plates  36   b,  this area of the side plate  36  has the highest rate of heat transfer. Considering that the entire inside surface of the back portion  40  is directly exposed to the hot pellets contained on the traveling grate, it can be assumed that the inside surface of the back portion  40  experiences the same heat flux across the entire inside surface. Further, since the entire back portion  40  of the side plate, except for the V-shaped area  50 , is covered by the trailing plate, the overlapped area of the back portion  40  is hotter than the V-shaped area  50  because of the overlapping front portion of the trailing side plate acts as a barrier to heat transfer from the side plate. Therefore, the highest temperature occurs in the overlapped area of the back portion  40 . 
     As illustrated in FIG. 3, the gussets  42  extend from the face surface  46  and actually contribute to the amount of strain in the side plate  36  by preventing free expansion of the plate. If there were a uniform temperature across the side plate, the gussets  42  would strengthen the side plate  36 , as is their obvious intention. However, the gussets  42  are some 300°-400° cooler than the rest of the front portion  38 , since the gussets  42  act as cooling fins. Thus, the gussets  42  add to the large temperature differential between portions of the side plate, which further adds to the strain on the side plate  36 . 
     In addition to acting as cooling fins, the gussets  42  add to the stiffness of the side plate  36 . Thus, as the side plate temperature increases, the gussets  42  restrict the thermal expansion of the side plate  36 . 
     The temperature profile of the prior art side plate  36  clearly shows a high concentration of heat in the back portion  40  which is overlapped by the trailing side plate. The V-shaped area  50  of the back portion  40  that is not overlapped, but has the same heat flux applied to it, does not show the same extensive cracking as the overlapped area. The convection and radiation heat transfer that takes place in the V-shaped area  50  keeps the temperature lower than in the overlapped area, thus reducing the temperature gradients and thermal cycling that occurs in this area. 
     Referring now to FIGS. 4 and 5, thereshown is the side plate  34  constructed in accordance with the present invention. As can be seen in FIG. 5, the side plate includes a back portion  52  and a front portion  54 . The front portion  54  is defined by a generally planar front face surface  55  that is set forward from the back face surface  57  of the back portion  52  by a shoulder  56 . As was the case with the prior art side plate  36 , the side plate  34  of the present invention includes a thrust button  44  and a front pivot hole  58 . The front portion  54  further includes a rear pivot hole  60 . Both the front pivot hole and the rear pivot hole receive one of the tie rods  40  of the traveling grate  14 , as was discussed with reference to FIG.  2 . 
     Referring back to FIG. 5, the front portion  54  of the side plate  34  includes a heat transfer opening  62 . The heat transfer opening extends through the entire thickness of the side plate  34  and is dimensioned as shown in FIG.  4 . In the embodiment of the invention illustrated in FIGS. 4 and 5, the heat transfer opening  62  is a hole formed near both the top edge  64  and the leading edge  66  of the side plate  34 . 
     Referring now to FIGS. 2 and 6, thereshown are a pair of side plates  34   a  and  34   b  mounted adjacent to each other, illustrating the manner in which the side plates  34   a  and  34   b  are attached to the lateral sides of each of the chains  26 . It can be understood in FIGS. 2 and 6 that the side plates  34  are sequentially positioned along the entire length of the chain  26 , although only two of the side plates  34   a  and  34   b  are illustrated. 
     Referring now to FIG. 6, the back portion  52  of the leading side plate  34   a  is shaded to illustrate the overlapping nature of the trailing side plate  34   b  relative to the leading side plate  34   a . As can be seen in FIG. 6, the front portion  54  of the trailing side plate  34   b  overlaps the back portion  52  of the leading side plate  34   a . When the side plates  34   a  and  34   b  are positioned as shown, the heat transfer opening  62  in the trailing side plate  34   b  provides access for circulating air to the face surface  57  of the back portion  52  of the leading side plate  34   a . As can be seen in FIG. 6, the heat transfer opening  62  exposes a significant area of the overlapped back portion  52  of the leading side plate  34   a  for convection and radiation heat transfer. Thus, the heat transfer opening  62  allows the overlapped area of the back portion  52  to transfer heat away from the side plate  34   a  in approximately the same manner as the area of the back portion  52  that is not overlapped by the trailing side plate  34   b . In this manner, the thermal gradients across the back portion  52  are decreased, which in turn decreases the stresses present on the back portion  52 . 
     As can be seen in FIGS. 4 and 5, the front portion  54  of the side plate  34  of the present invention is formed without any gussets, such as those included in the prior art side plate illustrated in FIG.  3 . The removal of the gussets from the front portion  54  eliminates the cooling effect the gussets had on the front portion of the prior art side plate  36 . Additionally, the elimination of the gussets allows the front portion of the side plate to expand at a more even rate across the entire front portion  54 . As discussed previously in connection with the prior art side plate  36 , the different rates of expansion due to the gussets resulted in cracking of the front portion of the side plate. 
     Analysis done on the prior art side plate  36  illustrated in FIG. 3 illustrate a stress level on the order of 67,000 psi, which, for a thermal fatigue situation, is a high level of stress. In the embodiment of the invention illustrated in FIGS. 4 and 5, the gussets have been removed and the heat transfer opening  62  is formed in the front portion  54 . These changes to the side plate result in calculated stress levels of approximately 45,000 psi, which is a significant improvement over the prior art illustrated in FIG.  3 . 
     Referring now to FIG. 7, thereshown is the pivoting movement of the trailing side plate  34   b  relative to the leading side plate  34   a  when the conveyor chain travels around either the head shaft or the upstream shaft, as illustrated in FIG.  1 . As shown in FIG. 7, the pivoting movement of the pair of side plate  34   a  and  34   b  relative to each other exposes a larger area of the back portion  52 , which aids in further heat transfer from the side plate. 
     Referring now to FIG. 9, thereshown is a second embodiment of the side plate  34  of the present invention. As shown in FIG. 9, a gusset  68  is positioned between the front pivot hole  58  and the thrust button  44 . The gusset  68  is included on the side plate if severe chain misalignment is experienced. Chain misalignment typically results in significant loading to the thrust button  44 . Inclusion of the gusset  68  strengthens the thrust button, yet since the gusset  68  is positioned in the lower half of the side plate where the temperature gradient is not as severe, the gusset does not significantly contribute to the thermal strain applied to the side plate  34 . Typically, the most significant temperature gradient occurs in the top half of the side plate  34 . Additionally, the heat transfer opening  62  is shown in FIGS. 9 and 10 as having a larger area and a different shape than the heat transfer opening  62  shown in the first embodiment of FIGS. 4 and 5. The increased area of the heat transfer opening  62  in the second embodiment of FIGS. 9 and 10 further increases the amount of heat that can be radiated away from the back portion  52  of the side plate  34 , as illustrated in FIG.  10 . 
     Changing the physical configuration of the side plate to minimize strain due to thermal gradients across the side plate is a different approach to increasing the usable life of the one-piece side plate. Up to now, most of the effort in increasing the useful life of side plate has been in the optimization of material characteristics. Certainly, selecting the best material for the application is a major part of extending the life of side plates. However, combining optimal part configuration to reduce thermal stress with the proper material selection for the application should extend the life of the side plate. 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.