Clamping system for coke oven heating walls
This application is a continuation of Ser. No. 655,993, filed on Sept. 28, 1984, now abandoned, which is in turn a continuation of Ser. No. 320,717, filed on Nov. 12, 1981, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to a protection system for one-layer or multi-layer brick walls, such as brick wall partitions in industrial furnaces, particularly heating walls in coke ovens or coke-oven-type industrial furnaces, which are subject both to thermal and mechanical loads and deformations. In particular, this invention relates to a clamping system for preventing such tensile and shearing stresses in the brick wall partitions of this kind, the system including clamping plates adjoining opposite faces of a brick wall partition, cross tie rods by means of which clamping forces are applied against the clamping plates by means of yoke-shaped beams and interposed springs or spacer pieces. In the following text; the terms a &#34;brick wall&#34; or a &#34;brick wall partition&#34; or a &#34;brick wall plate&#34; are interchangeable with the term &#34;a heating wall in a coke-oven-type industrial furnace&#34;. 
     In larger surfaces of brick wall partitions, the unavoidable thermal and mechanical deformations increase proportionally with the second or higher power of the height of the brick wall partition, that is in an excessive proportion to the height of the brick wall partition. As a consequence, if the clamping system designed for such increased forces is correspondingly more rigid, the changes in temperature and in operational loads result in uncontrollable regrouping or rearrangement of clamping forces, which frequently attain extreme and unacceptable values; that is, the brick wall partition is subject to excessive loads at some points, whereas at other points insufficient clamping forces are present. Due to these differences, undue stresses are generated. 
     SUMMARY OF THE INVENTION 
     It is therefore a general object of the present invention to overcome the aforementioned disadvantages. 
     More particularly, it is an object of the invention to provide a clamping system which ensures an increased operational life of the brick wall partition by preventing the formation of cracks and tears therein. 
     Another object of this invention is to facilitate the application of larger, higher and thinner brick wall partitions. 
     By increasing the effective volume of furnaces and ovens, and by improving the operational life and maintenance expenditures, a substantial improvement in economy is obtained. 
     A further object of the invention is to generate and continuously maintain a sufficient prestress in the brick wall partitions which, despite varying thermal and mechanical deformations, prevents the formation of fissures or cracks due to tensile stresses. 
     In keeping with these objects and others which will become apparent hereafter, one feature of the invention resides, in a clamping system of the above described type, in the provision of cross tie rods, upright yoke-shaped beams and intermediate resilient or spacer elements between the yoke-shaped beams and the clamping plates which fulfill at least one of the following conditions: 
     (a) Clamping forces applied approximately midway between the upper and lower edges of the face of the brick wall partition adjoining the clamping plate decrease toward respective edges over a length of about 75% of the height of the brick wall partition according to a bell-shaped or parabolic characteristic curve or according to curve meeting the equation 
     
         F=(AL.sup.2 +BL+C).sup.-1 
    
     wherein F is applied force and L is a half length of the surface portion between the edges; 
     (b) The resultants of the clamping forces in each half of the brick wall partition when viewed in longitudinal direction thereof act on midlines of two marginal areas of the brick wall partition or on intermediate planes of the outer layers of the brick wall partition these marginal areas having a width of approximately 65 mm, and the forces act at angles when considered in the longitudinal direction of the brick wall partition in the range between zero and 30°. When the forces act at a sharp angle relative to the central plane of the brick wall partition, the force vectors intersect in a line which is approximately parallel to the clamping plate; 
     (c) The effect of interfering local forces in the event of any disturbance is resiliently held within the limits of 5 to 20% of the preset clamping forces so as to maintain the desired distribution of the clamping forces over the whole clamping plate. This maintenance of the desired distribution of the clamping forces within narrow tolerances for all possible disturbances is achieved by the appropriate construction and arrangement of the cross tie rods, yoke-shaped beams, the clamping plates, and the intermediate pressing elements; 
     (d) Local roughness in excess of 2.5 mm in height is resiliently compensated by the selection of resilient or deformable materials which equalize these unevenesses of the mating surfaces resulting from manufacturing tolerances. 
     In the system of this invention, the above objects are attained by optimization of the flow of forces transmitted from the cross tie rods to the yoke-shaped beams, the intermediate resilient or spacer elements, and the clamping plates. At a lateral loading of the surfaces of the brick wall partition, the latter arches more strongly midway of its height. In order to achieve the most stabilizing effect particularly at this central region of the brick wall partition and to prevent any cracks of the brick wall partition, both in the surfaces and in its core, the largest clamping forces are applied to the center of the height of the brick wall partition, and the surfaces under attack by these forces are spaced apart laterally as far as possible to coincide with relatively narrow outer marginal zones of the end faces of the brick wall partition, whereby the resultants of the forces acting against these marginal zones are directed parallel to a center plane of the brick wall partition. 
     In order to preserve the desired pressure distribution under all kinds of interferences, the individual structural elements of the clamping system of this invention are made of materials having such an elastic quality as to compensate for the intefering influences. 
     The advantage of the springiness of the clamping system is in achieving a negligible offsetting of the force distribution on the one hand, and, particularly in brick wall partitions of larger size, in an easier and cheaper construction. 
     The desired distribution of clamping forces over the entire length of the clamping plate can be made either by the gradation of the thickness of the spacer pieces or by installing between the yoke-shaped beams and the clamping plates relaxed springy elements which are subsequently stressed by the cross tie rods or by the thermal expansion in the furnace; or, in the so-called step-in process, immediately by the springy spacer elements which are installed in a prestressed blocked condition and the support of which is adjusted in such a manner that, upon the removal of the blocking, the desired force distribution takes effect; or, in the so-called two-step method, the predetermined local clamping forces are applied accurately by means of one or more mechanical, hydraulic or pneumatic tensioning elements applying predetermined local clamping forces, and thereupon the distribution of these forces is effected by the adjustment of intermediate pressing elements such as the spacer pieces. 
     The novel features which are considered characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a cut away part of a clamping system with a single pressing element; 
     FIG. 2 is a clamping system similar to FIG. 1, but with two rows of up to nine pressing elements; 
     FIG. 3 is similar to FIG. 1 but shown with three intermediate spring elements; 
     FIG. 4 is a side view of an embodiment of the clamping system of this invention, illustrating the deformations of the yoke-shaped beam and of the clamping plate in the case of disturbances; 
     FIG. 5 is a perspective view of a system of this invention with indicated deformations of the beam and of the clamping plate; 
     FIG. 6 is a side view of the system of FIG. 5; 
     FIG. 7 shows schematically the superposition of additional deformations caused by thermal and mechanical loads, both on the yoke-shaped beams and on the clamping plates; 
     FIG. 8 is a top view, partly in section, of a brick wall plate with adjoining clamping plates for introducing the clamping forces; 
     FIGS. 9a-9i illustrate different embodiments of the yoke-shaped beams; 
     FIG. 10 is an embodiment showing in a perspective view a modified version of the yoke-shaped beam; 
     FIG. 11 illustrates in a side view of cut away portions of the system of this invention various embodiments of the pressing elements in combination with force indicators; 
     FIG. 12 illustrates in greater detail examples of intermediate spring elements; 
     FIG. 13 shows an example of the arrangement of intermediate spring elements; 
     FIG. 14 shows another example of the arrangement of intermediate spring elements for damping the effects of thermal arching of the yoke-shaped beams; 
     FIG. 15 is a variation of the arrangement of the intermediate pressing elements; 
     FIG. 16 is another modification of the arrangement of the pressing elements. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring firstly to FIGS. 1-7, there is schematically illustrated the mutual connection and interrelationship of individual elements of the clamping system of this invention. The following structural elements are used in this embodiment for clamping a heating wall or brick wall partition 9: upper cross tie rod 1, lower cross tie rod 2, upper spring 3 for the cross tie rod, lower spring 4 for the cross tie rod, an upright yoke-shaped beam (or cross tie support) 5, pressing elements 6 in the form of spacer pieces, bolts, spring pieces and the like for transmitting clamping forces; clamping plates 7 in the form of wall protecting plates, armor plates and the like; and insulating parts 8 such as sealing layers, fiberboards, and the like. Yoke-shaped 5a beam and the clamping plate 7a, before their deformation, are illustrated in FIGS. 4 by dashed lines 5a and 7a, while the deformation by interfering influences such as increasing temperature gradients or the expansion of the upper cross tie rod 1 is illustrated by full lines 5b and 7b. Cross tie rods 1 and 2 apply tensile stresses against the ends end partitions 5&#39; and 5&#34; of the yoke-shaped beam 5 through tension springs 3 and 4 and the beam 5 presses against the clamping plate 7 through the intermediate pressing elements 6. 
     As seen from FIGS. 4, 5 and 6, deformations 5b and 7b of the beams 5 and of the clamping plates 7 with respect to the initial shape 5a and 7a have the same effect as a prolongation of the cross tie rods 1 and 2 or a decrease of forces f introduced by these cross tie rods. The deformation is caused primarily by thermal effects due to the temperature gradient from the interior of the furnace, and this temperature difference varies according to operational conditions and according to ambient temperature. 
     According to this invention, the prestressing in the brick wall partitions 9 is established directly by the adjustment of the interposed pressing elements 6 installed between the clamping plates 7 and the yoke-shaped beams 5, the installation being carried out with blocked prestressing of these pressing elements and, upon installation, the prestress of these pressing elements is relieved. It is also possible to use adjustable pressing elements between the plates 7 and the beams 5 and adjust the same according to the aforementioned distribution of clamping forces. The bias or prestress acting on the end faces 9&#39; of brick wall partitions 9 is continuously maintained by the elastic quality of the cross tie rods 1, 3, 2 and 4, of yoke-shaped beams 5, of the clamping plates 7 and 8 and of the intermediate pressing pieces 6. 
     As seen from FIG. 6, the length of the tie rod 1 and thus force F of springs 3 varies proportionally to the unavoidable temperature variations caused for example by rain. 
     By selecting suitable spring constants, the load variations of conventional clamping forces can be held within the limits of 5 to 20%. The springs 3 and 4 at both ends of the yoke-shaped beams 5 can be combined in a single unilateral spring of a half spring constant when the force variations are transferred from one side to the other. 
     FIG. 7 illustrates schematically a superposition of additional thermal and mechanical deformations Δ x  caused by unavoidable deformations in temperature gradients due to introduced temperature ranges ΔT 2  and ΔT 1  and due to changes ΔS=q·F at point loads F. Factor q amounts to a maximum of 20% of the preset clamping forces. These variations of temperature take place in similar manner both in the yoke-shaped beams and in the clamping plates. The elastic qualities, particularly the angular pulses, are adjusted such that the changes in bending forces indicated by arrows are mutually neutralized at the points of attack of the forces with the allowance of a minute residual displacement, so that Δ x  thermal equals approximately Δ x  mechanical. 
     These adjusted changes of the angular impulses over the the length of the beams or height of the clamping plates should approach as closely as possible to different courses of thermal and mechanical bending lines so as to keep the resulting residual displacement as low as possible. 
     FIG. 8 illustrates schematically the layout of resultants of force vectors of the applied clamping forces when using a split clamping plate composed of parts 7a and 7b acting against contact surfaces 10 of the brick wall partition 9. The gaps between the contact surfaces are filled with pliable insulating layers 8. Forces applied in the direction of the arrows can extend either parallel to a central plane of the brick wall partition 9 α at an angle or ranging from 0° to 30°. The forces are applied into outer layers D so that the resultants of these forces act within a distance up to 65 mm from the vertical edges at both sides of the brick wall partition. 
     FIGS. 9a through 9i illustrate different configurations of yoke-like beams 5 designed for changing angular impulses of the pulsing forces. The changes are made either by varying the configuration of the beam, for example by assembling the beams of webs of various height (FIGS. 9a, 9b, 9c, 9d) or by perforating or making slots in the webs of the beams (FIGS. 9c, 9g, 9h or 9e) or by providing the webs of the beams with flanges of various strengths FIGS. 9d or 9e) or with flanges of various widths (FIGS. 9f, 9g, 9h) or by combining a plurality of beams of differen profiles (FIGS. 9c and 9i). 
     FIG. 10 shows another modification of the clamping system of this invention, in which reference numeral 21 denotes a pair of upper cross tie rods which extend immediately below the upper surface of the ceiling 25 of the furnace and are anchored in yokes 22 linked to a lateral side of the yoke-shaped beam 5. Pressing elements 23 for clamping the ceiling 25 are arranged between the yokes 22 and a separate clamping plate section 24 employed for clamping the ceiling 25, whereas another separate section of the clamping plate is used for the brick wall partition. The advantage of this type of construction of the clamping system resides particularly in the fact that a substantially amplified springy effect and energy storing capacity of the yoke-shaped beam is achieved. Moreover, a single beam is employed for the separate clamping sections both in the range of the brick wall partition and in the range of the ceiling of the furnace. 
     Different embodiments of pressing elements 6 are illustrates in FIGS. 11 and 12. The pressing elements may have the form of spaced bolts 11 interconnected by pressure springs arranged in a casing, whereby the pressure is adjusted by threaded nuts. Pressure indicators 12 are arranged between the casing and the bolt part on the clamping plate 7. In another embodiment, bellows 13 filled with pressurized gas (FIG. 11d) and provided with pressure regulator PC or connected to a position regulator (positioner) are used as the pressing elements. Pressure air consumed by the position regulator can be employed as cooling air and can be discharged at the upper part of the pressurized gas bellows so as to serve as heat-removing medium. 
     FIG. 12 illustrates an embodiment in which spring-biased pressing elements 6 are employed which are provided with means for blocking (FIG. 12b) and unblocking (FIG. 12a) the spring bias. 
     FIGS. 13-16 show schematically the arrangement of pressing elements 6 between the beam 5 and the clamping plate 7. The pressing elements in these embodiments are in the form of encased compression springs. 
     FIG. 13 illustrates a distribution of the pressing element 6 resulting in a bell-shaped characteristic curve of the applied forces, whereby the pressing springs correspond to each other and the clamping plate 7 is relatively flexible. 
     FIG. 14 illustrates a distribution of clamping forces introduced by different pressing elements 6 of which the elements at the center are softer than those at the ends of the plate 7, the latter being relatively rigid and resistant to bending. In this manner, an approximately constant load against the clamping plate 7 by regrouping of applied forces due to bending of the yoke-shaped beam 5 caused by--variations is obtained. 
     Similar effects are achievable by varying the spacing between individual spring elements 6 as shown in FIG. 15. 
     FIG. 16 illustrates an example of combined arrangements of pressing elements 6 according to FIGS. 13-15 which meets the requirement for a bell-shaped plot of the compressing forces and for mitigation of the effects of thermal arching at relatively thin clamping plates. Spring constant C m  (in kN/m) of the pressing elements are within the range of 
     
         10,000[kN]≦C.sub.m ·H·n≦110000[kN], 
    
     wherein n is the number of pressing elements and H is the height of the furnace. For example, for n=10 springs, and H=7.2 meters, the following inequality is computed: 
     
         139kN/m≦C.sub.m ≦1528kN/m 
    
     angular impulse of or divided from clamping plate is computed from the following unequality: 
     
         10.sup.-5 [m.sup.2 ]·H.sup.2 ≦n·M·I.sub.m ≦10.sup.-4 [m.sup.2 ]·H.sup.2 
    
     wherein M is the number of sections of the clamping plate pressed against the end face of a brick wall section. 
     From this unequality, the following example of average angular impulse I m  of a single piece clamping plate is computed: (for H=7 meters, n=7 pressing elements or contact points, M=1, clamping plate): 
     
         7·10.sup.-5 m.sup.4 ≦I.sub.m ≦7·10.sup.-4 m.sup.4. 
    
     The above expression, for a rectangular clamping plate of b=0.84 meters in breadth corresponds to a thickness of the plate between 0.1 and 0.215 meters. 
     The average angular impulses I m  [m 4  ] in clamping plate sections of a length H/M corresponding to a distance L&#39;=H/2M-1 from the center of respective plates to the load points at the ends, continuously or stepwise diminish approximately according to the equation I=I m  ×3×M×1/H. For example, if H=7.2 meters, M=1 plate, b=0.84 the breadth of the plate, and I m  =22×10 -5  m 4 , 
     
         ______________________________________                                    
Distance from the center                                                  
                0      1     1.2   2   (3)  (3.2)                         
(m)                                                                       
Distance from the upper                                                   
               3.6    2.6    2.4  1.6  (0.6)                              
                                            (0.4)                         
or lower load transfer                                                    
point of the plate                                                        
(meters) (m)                                                              
Local angular impulse                                                     
               330    238    220  147  (55) (37)                          
I (10.sup.-6 m.sup.4)                                                     
Thickness of an equivalent                                                
               168    150    146  128  (92) (80)                          
rectangular plate                                                         
(millimeters). (mm)                                                       
______________________________________                                    
 
    
     The values in parentheses indicate that in these ranges the deviations (marginal conditions) may be determinative for example for the manufacturability or the additional functions of the clamping system of this invention. 
     If the yoke-shaped beams or clamping plates are assembled of several parts, then according to static laws the combined angular impulse is determinative. The graduation of the angular impulses can be achieved for example by recesses or perforations in the beams or clamping plates. 
     In FIGS. 17 through 20 beams 5 are illustrated which have the form of rectangular hollow tubes provided with an inner flange 5&#39; facing the clamping plate, and an outer flange 5&#34;. Termperature at the inner flange is indicated by θ i  and at the outer flange by θ 0 . Normally, heat flow due to radiation and convection, as indicated by wavelike arrows, undergoes reflections in the interior of the beam 5. (FIG. 17a). 
     In an embodiment of this invention the outer surfaces of the inner and outer flanges are coated with a heat reflecting layer 26 and the inner surfaces of the flanges are coated with an insulating layer 27 so as to adjust the transmission of heat both by reflection and by convection (FIGS. 17b). FIG. 17c illustrates insulating layers 26&#39; provided on the outer surfaces of the flanges 5&#39; and 5&#34; to minimize the heat flow from the brick wall into the outer atmosphere. 
     FIG. 18a shows an example of the temperature compensation or neutralization by vaporizing and condensing a heat transfer medium in the interior of the beam 5. Preferably, the inner walls of the beam are also provided with a porous heat absorbing coating 27&#39;. A liquid condenses at the cooler (θ 0 ) outer flange 5&#34; and flows along the edges of the outer flange toward the hot (θ i ) inner flange. On the inner flange, the liquid vaporizes and transfers its vaporizing enthalpy by means of vapors toward the outer flange, as indicated by arrows in FIG. 18a. The return flow of the cooled down liquid is effected either by the force of gravity, or by wick-like capillary effects of the lining 27&#39; or of the outer wall surface. 
     The same functional principle is involved when using a heat pipe 29, as shown in FIG. 18b. The ends of the heat pipe are thermally connected to the opposite inner walls of the beam 5 and heat is transferred from the inner flange 5&#39; to the outer flange 5&#39;. As known, due to the high vaporizing enthalpy of heat pipes, correspondingly high density of the heat flow can be attained. 
     Another version of a temperature compensation is shown in FIG. 19 illustrating the same yoke-like beam as in FIG. 18. Vapor or steam condenses on the inner surface of the outer flange at a temperature θ 0  and the condensate is guided by a chute 30 against the hot inner flange 5&#39; where due to higher temperature θ i  is vaporized. The chute 30 in the illustrated example is constructed as a single tray of welded metal sheet. In practice, an array of superposed chutes 30 is used. The chutes either communicate with each other or are separated. 
     FIG. 20b shows a vector diagram of the distribution and values of forces F of compressing springs active under normal operational conditions between the beam and a clamping plate. 
     Due to higher temperature θ i  of the inner flange 5&#39; when no forces are applied to the beam 5 (FIG. 20a), the latter bends in the shown manner. In the same fashion bends the thinner (non-illustrated) clamping plate. By adjusting the elasticity constants of compression springs in the central region between the beam and the clamping plate to desired values, the pulling forces F u  and F i  of the upper and lower cross-tie rods are made effective and act against the thermal bending. 
     FIG. 20c depicts the beam 5 during a contingency when the temperature difference (θ i  -θ 0 ) between the inner flange and the outer flange of the beam 5 is zero. This may happen when the beams are exposed to heavy rainfalls, for example. In this case, no bending forces act on the beam and the clamping plate and, consequently, no deformation will occur. As a result, compressing forces F are subject to redistribution with respect to their normal (100%) values. In other words, when θ 0  =θ i  then the compression springs change their lengths. According to one aspect of this invention, the redistribution of the compressing forces is held within the limits of ±15% with respect to 100%, or normal operational conditions. By virtur of this measure, it is insured that clamping forces acting on the brick wall plate via the clamping plate are still sufficiently large. According to this invention, the elasticity constants of respective compression springs are adjusted such as to permit at most ±15% changes relative to their normal (100§ ) values. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in a clamping system for use in brick wall plates, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.