Abstract:
A furnace binding and adjustment system for maintaining a refractory furnace hearth under compression utilizes a plurality of buckstays connected at their upper and lower ends by tie members. A fluid-pressurized tensioning device, preferably a hydraulics device, is provided at the ends of at least some of the tie members to permit some relative movement between the tie member end and the buckstay to permit adjustment of compressive forces applied to the refractory hearth. The use of multiple hydraulic devices permits simultaneous activation of the tensioning devices, and also permits the hydraulic pressure in the cylinders to be accurately adjusted and monitored from a remote location.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to furnaces constructed of hearth and sidewall refractories, and more particularly relates to systems for the compressive binding of these refractories.  
         BACKGROUND OF THE INVENTION  
         [0002]    Furnaces are used extensively in the smelting and converting of ferrous and non-ferrous ores and concentrates. Furnaces of this type are generally circular or rectangular, having a bottom wall (hearth) and vertical walls comprised of refractory bricks and a roof or off gas hood. These furnaces are also characterized by a binding and support structure, the purpose of which is to maintain the refractory bricks of the hearth and walls in compression.  
           [0003]    Adequate compression of the furnace walls, and particularly the hearth, is critical to maximize furnace campaign life and to prevent costly and potentially catastrophic furnace failure. During heating of the furnace to operating temperature, the individual bricks comprising the hearth and the walls expand, resulting in outward expansion of the hearth. Conversely, cooling of the furnace results in contraction of the individual bricks and overall shrinking of the furnace. If the compressive forces on the hearth or the walls are insufficient, gaps will be formed between the bricks during cooling phases of the furnace operation. These gaps can be infiltrated with molten metal or other material, resulting in permanent growth of the furnace. Repetition of heating and cooling cycles results in further incremental expansion of the furnace (known as “ratcheting”), which usually results in a reduction of the furnace campaign life, by the potential for molten infiltration into the hearth refractory or excessive expansive forces exerted on the binding system.  
           [0004]    In rectangular furnaces, the binding system usually consists of regularly spaced vertical beams known as “buckstays”, which are held together at the top and bottom by horizontal tie members extending across the furnace, the bottom tie members passing beneath the hearth and the upper tie members passing above the furnace roof. The structure of electric furnaces is discussed in more detail in Francki et al., Design of refractories and bindings for modem high-productivity pyrometallurgical furnaces, Non-Ferrous Metallurgy, Vol. 86, No. 971, pp. 112 to 118. Frequent adjustment of the tie members, as by loosening or tightening retaining nuts at the tie member ends, is necessary to maintain relatively constant compression on the refractories during thermal cycling of the furnace. The binding systems of most large rectangular furnaces in operation today are equipped with compression spring sets sized to maintain the desired compression on the brick work, thereby permitting some expansion and contraction of the furnace while maintaining the hearth under compression.  
           [0005]    While spring sets permit some furnace movement, they do not eliminate the need for periodic adjustment of the spring loads to ensure that the forces on the tie members and the furnace hearth remain relatively constant during use of the furnace. Adjustment of the spring loads is performed with hydraulic jacking equipment, and is a difficult and unpleasant operation due the fact that the vicinity of the furnace is usually hot, dirty and ill-lit and because the adjustment screws on the spring sets usually become more difficult to turn with time. Therefore, the frequency of adjustment tends to be low and spring binding systems are often not used to their full advantage.  
           [0006]    The problems with prior art adjustment systems are exemplified by U.S. Pat. No. 3,197,385 (Wethly), issued on Jul. 27, 1965. This patent relates to the use of hydraulic jacking equipment for adjustment of tie rod tension in a coke oven battery. According to Wethly, the tension in each tie rod is adjusted by a hydraulic tensioning jack which is mounted on the ends of the rods. However, the tensioning jack must be sequentially mounted on each tension rod to adjust the tension in the rods one by one, in sequence. In the sequential adjustment system taught by Wethly, it would be difficult to control the tension in the rods with any degree of precision since adjusting the tension in one rod will have an effect on the tension in neighboring rods. Furthermore, the sequential mounting and use of a hydraulic jack in close proximity to the furnace is an unpleasant task which is likely to be performed only when absolutely necessary, and therefore the frequency of adjustment is likely to be low.  
           [0007]    Therefore, a need exists for improved furnace binding systems for both rectangular and circular furnaces. Preferably, such systems would permit the compressive forces on the refractory hearth and furnace walls to be accurately adjusted, and would permit adjustment of the compressive forces to be carried out remotely and continuously, thereby maximizing furnace life and improving safety.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention overcomes the above-described problems of the prior art by providing a furnace binding and adjustment system in which the compressive forces on the furnace hearth can be accurately controlled and monitored on a continuous basis. The system of the invention includes fluid-pressurized tensioning or compression means for maintaining compressive forces on the hearth and/or furnace walls. The compressive forces applied to the furnace by the binding system are regulated by one or more pressure regulation means adapted to simultaneously or individually adjust the fluid pressure in one or more of the tensioning or compression means, thereby overcoming the problems in the prior art.  
           [0009]    The control of the tensioning or compression means by one or more pressure regulation means is particularly well suited to remote operation, whereby a furnace operator situated in a control room can regulate the pressure in the pressure regulation means, thereby eliminating the need to carry out manual adjustments in the vicinity of the furnace. Furthermore, since the fluid pressure in the pressure regulation means and in the tensioning or compression means is proportional to the compressive forces exerted on the furnace, the binding system of the present invention permits accurate measurement and control of the compressive forces exerted on the furnace. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0011]    [0011]FIG. 1 is an end view, partly in cross-section, of an electric furnace incorporating a furnace binding and adjustment system according to a first preferred embodiment of the present invention;  
         [0012]    [0012]FIG. 2 is a side view, partly in cross-section, of the furnace shown in FIG. 1;  
         [0013]    [0013]FIG. 3 is a plan view, showing in isolation the buckstays, tie members and fluid-pressurized tensioning means in the lower portion of the furnace shown in FIG. 1;  
         [0014]    [0014]FIG. 4 is a side view showing in isolation a pair of opposed buckstays with a tie member and a fluid-pressurized tensioning means as shown in FIG. 3;  
         [0015]    [0015]FIG. 5 is a front view of the left buckstay in FIG. 4, showing the fluid-pressurized tensioning means;  
         [0016]    [0016]FIG. 6 is a front view of the right buckstay of FIG. 4, showing the retaining nut on the tie member end;  
         [0017]    [0017]FIG. 7 is an enlarged plan view showing one of the fluid-pressurized tensioning means of FIG. 3 in the lower portion of the furnace, together with its associated buckstay and tie member ends;  
         [0018]    [0018]FIG. 8 is a partial cross-section through the tensioning means of FIG. 4;  
         [0019]    [0019]FIG. 9 is a side view of a second preferred fluid-pressurized tensioning means for use in the binding and adjustment system of the invention, the tensioning means being shown with its associated buckstay and tie member end;  
         [0020]    [0020]FIG. 10 is a front view of the fluid-pressurized tensioning means of FIG. 9;  
         [0021]    [0021]FIG. 11 is a simplified, schematic plan view of a furnace binding system according to a third preferred embodiment of the present invention;  
         [0022]    [0022]FIG. 12 is a simplified, schematic side view showing one variation of the furnace binding system of FIG. 11; and  
         [0023]    [0023]FIG. 13 is a simplified, schematic side view showing a fourth preferred embodiment of the invention in which a fluid-pressurized cylinder directly applies compressive forces to a furnace. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    A first preferred furnace binding and adjustment system, adapted for maintaining compression on a refractory furnace hearth of a rectangular furnace, is now described below with reference to FIGS.  1  to  10 .  
         [0025]    [0025]FIG. 1 illustrates the basic structure of a typical rectangular electric furnace  10  to which the system of the present invention is applied. The cross-section of FIG. 1 is taken transverse to the longitudinal axis of the furnace. Furnace  10  comprises a pair of opposed sidewalls  12  and  14 , a pair of opposed end walls  16  and  18  (FIG. 2), a hearth  20 , an arched roof  22 , and a plurality of electrodes  24  spaced along the longitudinal axis of the furnace  10 .  
         [0026]    The hearth  20 , as well as the sidewalls  12 ,  14  and end walls  16 ,  18  are constructed of refractory brick in a known manner. The refractory bricks of the hearth and the side and end walls are maintained in compression by vertical metal shell plates  19  which are contained by flexible bindings comprised of regularly-spaced vertical buckstays  30  held together at the top and bottom by horizontal tie members  32 ,  33 .  
         [0027]    As best shown in FIG. 3, the buckstays  30  are arranged in regular, spaced relation around the side and end walls of the furnace  10 . Each buckstay comprises a vertical steel beam having a lower end  34  extending below the hearth  20  and the furnace bottom and an upper end  36  extending above the tops of the furnace walls  12 ,  14 ,  16 ,  18  and the furnace roof  22 .  
         [0028]    The buckstays  30  are arranged in pairs, with the buckstays of each pair being positioned on opposite sides of the furnace. In FIG. 3, the buckstays of each pair are in opposed relation to one another directly across the furnace from one another.  
         [0029]    The buckstays  30  of each pair are connected at their upper ends  36  by at least one upper tie member  32  and at their lower ends  34  by at least one lower tie member  33 . In the preferred embodiment shown in the drawings, the upper ends  36  of each pair of buckstays  30  are connected by a single upper tie member  32 , and the lower ends  34  of each pair of buckstays  30  are connected by a single lower tie member  33 . It will be appreciated that the expansive forces are greatest at the lower ends  34  of buckstays  30  due to expansion of the hearth  20 , and therefore it may be preferred to connect the lower ends  34  of each pair of buckstays  30  with two or more lower tie members  33 .  
         [0030]    As shown throughout the drawings, the upper ends  36  and lower ends  34  of buckstays  30  are apertured to permit the ends of the tie members  32 ,  33  to extend therethrough. The furnace binding and adjustment system further comprises a plurality of fluid-pressurized tensioning means  40  provided at the ends of tie members  32 ,  33 , the tensioning means  40  being adjustable so as to permit lateral expansion and contraction of the furnace  10  while applying compressive forces to the hearth, sidewall and end wall refractories through the buckstays  30 .  
         [0031]    At the lower ends of buckstays  30 , shown in FIG. 3, a tensioning means  40  is preferably provided at a first end of each lower tie member  33 .  
         [0032]    Similarly, a plurality of tensioning means  40  are provided at the ends of the upper tie members  32 . However, the tie members  32  extending across the central portions of the side walls  12 ,  14  are preferably not provided with tensioning means  40  as there is relatively little lateral expansion of the furnace  10  at these points. Since the end walls  16 ,  18  are shorter than side walls  12 ,  14 , each upper tie member  32  extending between the end walls  16 ,  18  may preferably be provided with a tensioning means at one of its ends.  
         [0033]    Several different types of tensioning means can be employed in the system of the invention, of which two types are described herein. The tensioning means  40  preferably comprises a fluid-pressurized device for applying tension to the tie members. In the first preferred embodiment illustrated in FIGS.  1  to  8 , each tensioning device includes a hydraulic cylinder  42  having a bore through which the first end of a tie member  32  or  33  extends.  
         [0034]    Specifically referring to FIG. 8, hydraulic cylinder  42  comprises a cylindrical housing  44  enclosing a piston  46 , the housing  44  having a cylindrical side wall  48 , a rear wall  50  with a central aperture  52  sized to receive the tie member  33 , and a front wall  54  having an aperture  56  sized to receive the piston  46 . The aperture  52  is surrounded by a sleeve  58  extending through the housing  44  from rear wall  50  to front wall  54 , the sleeve  58  forming a bore  60  through which the tie member  33  extends.  
         [0035]    The piston  46  has a rear portion comprising a flange  62  which forms a seal with the side wall  48  of housing  44 , thereby dividing housing  44  into a pair of chambers  64 ,  66 , which communicate with a manifold  68  (FIGS. 4 and 5) through respective hydraulic fluid lines  70  and  72 .  
         [0036]    The first end of tie member  33  is retained by a retaining nut  74  which is threaded onto the end of tie member  33  (threads omitted for clarity), the nut  74  engaging the end face  76  of piston  46 , and preferably spaced therefrom by a washer  78 .  
         [0037]    As shown in the drawings, the tie members  32 ,  33  extend through pipes  90  which are welded through the buckstays. The second end of tie member  33  passing through the buckstay  30  on the opposite side of the furnace is retained by a retaining nut  74  (FIGS. 4 and 6).  
         [0038]    As mentioned above, the fluid pressure in the tensioning means  40  is regulated by pressure regulation means, generally identified by reference numeral  67  in the drawings. In the preferred embodiment of the invention, pressure regulation means  67  are provided at each of the tensioning means  40 , thereby permitting the fluid pressure of the tensioning means  40  to be regulated simultaneously or individually. The pressure regulation means comprises manifold  68 , already mentioned above, which communicates with the two chambers  64 ,  66  of hydraulic cylinder  42  through hydraulic fluid lines  70 ,  72 . The manifold  68  controls the fluid pressure inside hydraulic cylinder  42 , and therefore controls the amount of tension in the tie members  32 ,  33 . Preferably, each pressure regulation means  67  further comprises a gas over fluid accumulator  98  (FIGS. 4 and 5) which acts to minimize changes in pressure due to changes in the forces exerted on the buckstays by the refractories.  
         [0039]    The pressure regulation means  67  further comprises a supply of fluid and pumping means for pumping the fluid to the tensioning means  40 . In the preferred embodiments of the invention, the fluid supply comprises a hydraulic fluid reservoir  97  and a pump  99  for pumping hydraulic fluid between the reservoir  97  and the manifold  68 . Reservoir  97 , pump  99  and the lines through which they are connected to the tensioning means are schematically shown in FIG. 1.  
         [0040]    The system according to the invention further comprises control means for controlling operation of the pressure regulation means. Control means are generally indicated by reference numeral  101  and schematically shown in FIG. 1 as the means by which operation of the pump  99  and the manifold  68  are controlled. As shown, control means  101  are operated from a control room  103 , schematically shown in FIG. 1, which is preferably remotely located relative to the furnace  10 .  
         [0041]    A second preferred tensioning means  100  for use in the first embodiment of the invention is illustrated in FIGS. 9 and 10, and comprises a bell crank-type hydraulic tensioning device incorporating a conventional hydraulic cylinder  102  having a piston (not shown) which reciprocates in a direction substantially perpendicular to the tie members  32 ,  33 . The cylinder  102  is mounted in a bracket  104  having a bottom plate  106  secured to an outer surface of a buckstay  30  and a pair of spaced sidewalls  108  extending from the edges of plate  106 . An aperture  110  through the top of cylinder  102  aligns with a first pair of apertures  112  in the sidewalls  108  of bracket  104  and is secured thereto by retaining pin  114 .  
         [0042]    The piston of cylinder  102  is actuated by connecting rod  116 , the distal end of which is pivotably connected to an end of a tie member  33  through a lever arm  118  having a first end  120  and a second end  122 . The first end  120  of lever arm  118  is pivotably connected to the distal end of connecting rod  116 , and the second end  122  of lever arm  118  is provided with a collar  124  through which the end of tie member  33  extends and is secured against relative movement by a retaining nut  74 . The second end  122  of lever arm  118  is pivotably connected to the side walls  108  of bracket  104  by a pin  126  extending through lever arm  118  and extending into a second pair of apertures  128  in sidewalls  108  of bracket  104 . Thus, reciprocal movement of cylinder  42  is translated to inward and outward movement of tie member  33  relative to buckstay  30 .  
         [0043]    The fluid pressure in tensioning means  40  is regulated by pressure regulation means  67  and control means  101 , as described above. Furthermore, it will be appreciated that tensioning means  100  may also include a saddle and a safety nut, similar to that described above.  
         [0044]    Further preferred aspects of the present invention are now described in connection with FIGS.  11  to  13 . FIGS.  11  to  13  are simplified drawings of some of the components of a furnace binding system. In each of these drawings, an arrangement of components is shown for applying compressive forces at one location of a furnace. However, it will be appreciated that a number of such arrangements are preferably provided to form a furnace binding system, and that the binding system is preferably controlled as described above, thereby permitting remote operation and simultaneous application of compressive forces at several points on the furnace.  
         [0045]    [0045]FIG. 11 illustrates a third preferred embodiment of a furnace binding system in which a fluid-pressurized cylinder  200 , which is similar to fluid-pressurized cylinder  42  described above, is used to apply a tensioning force to a tie member  202  extending between cylinder  200  and a retaining member  204 . Retaining nuts  206  are received on the opposite ends of tie member  202  to retain the tie member  202  relative to the cylinder  200  and retaining member  204 . The cylinder  200  is supported on a support member  208  which applies force on a furnace wall  210  in the direction of the arrows shown in FIG. 11.  
         [0046]    The arrangement of components shown in FIG. 11 is similar to that described above with reference to FIGS.  1  to  8 , except that the tie member  202  does not extend across the furnace. In one preferred embodiment, the support member  208  may comprise a buckstay and the retaining member  204  comprises a beam or other stationary member located inwardly of the furnace wall  210 , and situated either above or below the furnace wall  210 . It will be appreciated that the arrangement shown in FIG. 11 could be used to apply horizontal compressive forces to a furnace, thereby compressing the hearth as in the first preferred embodiment. The arrangement shown in FIG. 11 is applicable to furnaces of any shape, including circular and rectangular furnaces.  
         [0047]    In the arrangement shown in FIG. 11, it will be appreciated that a fluid-pressurized cylinder having a bell crank mechanism similar to that shown in FIGS. 9 and 10 could be substituted for cylinder  200 .  
         [0048]    As mentioned above, the support member  208  may comprise a buckstay similar to those shown in FIGS.  1  to  10 . However, FIG. 12 illustrates one variant of the binding system shown in FIG. 11 in which the support member  208  has a lower, pivoting end  212  pivotable about point P and an upper end  214  applying a compressive force to furnace wall  210  and hearth  216 . The cylinder  200  is located intermediate the lower and upper ends  212  and  214  and applies tension to tie member  202  extending between the cylinder  200  and a stationary retaining member  204 .  
         [0049]    It will be appreciated that the arrangement illustrated in FIG. 12 is applicable to furnaces of any shape, including circular and rectangular. Furthermore, it will be appreciated that the relative positions of the cylinder  200  and pivot point P could be varied. For example, the pivot point P could be located between the cylinder  200  and the upper end  214  of support member  208 , similar to the configuration shown in FIG. 11.  
         [0050]    Lastly, FIG. 13 illustrates a simplified arrangement in which the tie member  202  is eliminated and a fluid-pressurized cylinder  218  directly applies compressive force to the furnace sidewall  210  and hearth  216 .  
         [0051]    Although the invention has been described in connection with certain preferred embodiments, it is not intended to be limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.