[0001] The present subject matter relates to furnaces constructed of hearth and sidewall refractories, and more particularly relates to systems for the compressive binding of these refractories.

BACKGROUND

[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, or in the worst case, catastrophic failure of the refractory with a resulting run out of the furnace contents. 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. Additionally, in the case of rectangular furnaces, it is beneficial to maintain the verticality (plumbness) of the buckstays during operation to ensure that the binding load is delivered to the appropriate locations along the furnace wall. A buckstay that is out-of-plumb can redistribute the binding load along the length of the buckstay and has the potential to unload the furnace hearth which could lead to a run out.

SUMMARY

[0008] The following summary is intended to introduce the reader to the more detailed description that follows and not to define or limit the claimed subject matter.

[0009] In accordance with the present subject matter, an auto-adjusting device is provided for a binding system of a metallurgical furnace. The auto-adjusting device comprises a gauge or sensor that constantly or intermittently measures one of either the furnace binding forces or the pressure of an associated hydraulic system. A load adjustment mechanism responsive to a measurement by the gauge or sensor that exceeds a predetermined amount either above or below the desired load, then automatically adjusts the load of the binding system.

[0010] In some embodiments, the auto-adjusting device includes a gear train. In other embodiments, the device includes two hydraulic cylinders installed in series. Yet other embodiments include a worm drive and motor. Such embodiments can be used with or without springs to reduce the frequency of the required adjustments.

[0011] In addition to maintaining the binding loads within a preset limit, a sensor can be utilized to measure the total movement of each buckstay at the top and bottom. The auto-adjusting device is able to maintain the plumbness of the buckstays ensuring the appropriate load is applied along the length of the buckstay.

[0012] The present subject matter overcomes the 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 present subject matter avoids continuous reliance on an applied hydraulic load. As a result, a leak of the hydraulic system does not result in a loss of the load on the binding system. Moreover, avoiding reliance on a hydraulic system that remains static under a high load for a long period helps to avoid having seals become set.

[0013] The present subject matter can automate the binding adjustment procedure for all forms of furnace bindings; primary and secondary hearth bindings, horizontal wall bindings, vertical wall hold down binding, and circular shell bindings. Specifically, the apparatus is intended to apply the specified design binding loads to the furnace refractory through all phases of the furnace operation without requiring regular manual adjustment.

[0014] The proposed apparatus can be applied to new smelting furnaces being built or retrofitted to improve existing smelting furnaces. The proposed apparatus can be applied to furnaces with a large number of binding load points or furnaces with as little as one binding system.

BRIEF DESCRIPTION OF DRAWINGS

[0015] The subject matter will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0016] 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 subject matter;

[0017] Fig. 2 is a side view, partly in cross-section, of the furnace shown in Fig. 1 ;

[0018] 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 ;

[0019] Fig. 4 is an isometric cut away view of an auto-adjusting device for a binding system of a metallurgical furnace according to a first embodiment;

[0020] Fig. 5 is an isometric view showing the exterior of the device;

[0021] Fig. 6 is an isometric view of the load cells shown on the unsprung end of the tie rod portion of the same device; [0022] Fig. 7 is an isometric view of an auto-adjusting device for a binding system of a metallurgical furnace according to a second embodiment;

[0023] Fig. 8 is a cross sectional view of a portion of the same device.

[0024] Fig. 9 is a cross sectional view of an auto-adjusting device for a binding system of a metallurgical furnace according to a third embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Figures 1 to 3 illustrate the basic structure of a typical rectangular electric furnace 10 to which the auto-adjustment binding system of the present subject matter 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. In some cases, a tensioning means may be provided on both sides.

[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] The fluid pressure in the tensioning means 40 is regulated by pressure regulating means, generally identified by reference numeral 99 in the drawings. In the preferred embodiment of the invention, pressure regulation means 99 are provided for each of the tensioning means 40 and the motors 7, thereby permitting the fluid pressure of both the tensioning means 40 and the motor 7 to be regulated simultaneously or individually. The tensioning means 40 and motor 7 are powered by a hydraulic power unit (HPU) 97. Both the pressure regulation 99 and the HPU 97 may be located remotely relative to the furnace 10. [0034] The system further comprises a means for controlling the operation of the adjustment system. Control means 101 are schematically shown in Fig. 1 as the means by which the HPU 97 and pressure regulation 99 are controlled. As shown, control means 101 are operated from a control room 103, schematically shown in Fig. 1 , which may be remotely located relative to the furnace 10.

[0035] The system further comprises optional displacement sensors 122 located at the top and bottom of each buckstay. The sensors measure the buckstay movement relative to its starting position and fed back to a control room 103, schematically shown in Fig. 1 , which may be remotely located relative to the furnace 10. Data interpretation is fed back through the control means 101 to operate the tensioning means 40 when it is determined that the buckstay plumbness is outside of allowable limits.

[0036] Turning to Figures 4 to 6, one embodiment of an auto tensioning device is shown. It can be described as having vertical components including a hydraulic motor and a gear train in which the last gear is made of a gear and a nut joined together, and horizontal components including a hub and a hydraulic cylinder in series. A load cell or cells 21 are used to determine the load within the system. The system can be connected directly to a tie rod, or use a set of springs to assist with regulating the load and to decrease the frequency of the adjustments. The basic principle of operation is the load cell measures the furnace binding forces and determines when the load varies by more than the predefined limit from the set point indicating that the system requires adjustment. When it has been determined that the binding load requires adjustment, the hydraulic cylinder is engaged and set to exceed the load being applied in order to off-load the gear nut. The hydraulic motor is then engaged to set the gear nut back with a preset number of revolutions. The hydraulic cylinder sets the binding load to the design load. The hydraulic motor is engaged to set the gear nut back into contact with the bearing plate. The hydraulic cylinder is unloaded and the load cell or cells check to ensure the proper load is being applied to the system.

[0037] In locations requiring small loads a variation of the above can be utilized which does not include the hydraulic cylinder. Instead the hydraulic motor is designed as a power screw and is able to turn the gear nut while the nut is still under load. [0038] A load cell or cells are installed within the system to give feedback of binding load and adjustment will take place once the load deviates from the predefined upper or lower limit. One possible configuration is shown in Fig. 6 where the load cells are placed on the unsprung end of the tie rod 33. If the load cell malfunctions or is not calibrated properly the hydraulic jack can be utilized to determine the load within the system.

[0039] If it is determined that the system load is outside of the predefined limits, the cylinder 1 will be activated to unload the gear nut 3. A hub 2 transmits the force from the hydraulic cylinder 1 to the binding plate 11 while allowing the gear nut 3 to rotate. Once the gear nut 3 is unloaded the motor 7 will be engaged in order to rotate the pinion 5 which is mounted directly on the shaft of the motor 7. The purpose of the pinion 5 is to transmit the rotational power of the motor 7 to the gear nut 3. Due to space requirements, in some instances an idle gear 4 will be installed between the pinion 5 and the gear nut 3. Its purpose is only to transmit the motion between the two. A gear set cover 6 protects the gear train against dirt and dust and also provides a reaction force acting opposite the rotational force of the motor 7. The motor 7 is engaged such that the gear nut 3 will be rotated away from the binding plate 1 allowing room for the cylinder to adjust the binding load. The load in the hydraulic cylinder 1 will be set to match the design force thereby restoring the proper load to the system. At this point the motor 7 rotates the gear nut 3 back until it makes contact with the binding plate 1 1. After the gear nut 3 stops rotating, the remaining pressure is released from the hydraulic circuit and the system comes to rest. The frequency of these actions will depend on the furnace operation and the frequency of adjustment can be reduced by installing compressions springs 9 within the system.

[0040] The hydraulic cylinder 1 is installed close to its fully extended position during the initial installation. Over time this extension will compensate for the expansion of the furnace 10. As the furnace grows the cylinder 1 will get shorter. It is worth noting that the estimated expansion of the furnace should correspond to the length of the stroke of the hydraulic cylinder 1 to prevent having to reset the hydraulic system prior to the furnace end of life.

[0041] The gear nut 3 serves a dual purpose; during normal operation the gear nut 3 transfers the binding load between the tie rod 33 and the binding plate 1 1. During the self- adjusting period the gear nut 3 is disengaged and the gear is used to move the gear nut 3 back and forth in order to keep the load on the tie rod 33 constant.

[0042] A hydraulic cylinder saddle 8 can be utilized to support the weight of the cylinder 1 while the cylinder 1 is unloaded.

[0043] An alternative arrangement of a similar embodiment utilizes a sprocket and chain in place of the gear train to transfer the motor rotation to the nut.

[0044] For rectangular furnaces, in addition to maintaining the proper design loads the verticality, or plumbness, of the buckstays will be monitored to ensure that the buckstays remain plumb within a certain predefined distance. If the buckstays exceed the allowable out-of-plumbness the hydraulic motors and jacks will be utilized as described above to re-plumb the buckstays.

[0045] This method eliminates the need for a manual check and adjustment of the binding loads.

[0046] Turning to Figures 7 and 8, a second embodiment of an auto-tensioning device is shown. It can be described as made of two hollow jacks in series coupled with accumulators and an associated gas (nitrogen, air, or other) supply system. Based on the pressure applied by the furnace on the jacks a PLC controls the pressure on the accumulator increasing or decreasing it based on the design load.

[0047] The basic principle of operation is the two hydraulic cylinders 21 are installed in series close to their fully extended position. Over time this extension will compensate for the expansion of the furnace 10. As the furnace 10 grows, the cylinder will get shorter. The back-to-back cylinders 21 provide two important functions: 1) allowing the cylinders to cycle through their stroke while maintaining a constant load on the furnace and 2) redundancy, in the event that one hydraulic cylinder fails, the second will maintain the design load. The hydraulic cylinders 21 apply the design load to the furnace through a tie rod 32 or 33. A pressure gauge measures the pressure within the accumulator 29 and determines if the pressure varies from the design pressure by more than the predefined limit which would indicate that the system requires adjustment. The accumulator 29 acts as a spring, as the furnace expands and contracts, the gas within the accumulator is compressed and expands. A valve adds additional gas to the system through the gas supply line 25 to increase the load and a relief valve releases gas to decrease the load within the system. A non-flammable hydraulic fluid is supplied to the hydraulic cylinders 21 through the hydraulic supply line attached to the accumulator 29. Rubber bellows 26 are positioned at either end of the hydraulic cylinder to seal and protect the internal components from heat and dust contamination. An isolation nut 23 is included and serves two purposes: 1) it can be tightened thereby removing load from the hydraulic system while maintaining load on the buckstay allowing the system to be serviced or replaced with the load removed; or 2) it acts as a mechanical failsafe in the event that there is a failure of the hydraulic system. A standoff 28 offsets the hydraulic binding system away from the furnace to allow space for the isolation nut 23.

[0048] The gas pressure within each accumulator 29 is monitored through pressure gauges and the data fed back to the PLC which equates the pressure to an applied load. The load will be monitored to determine if it deviates from the prescribed load range. The hydraulic system has three modes of adjustment; decreasing binding load, increasing binding load, and cycling the jacks to ensure all seals are properly lubricated and to prevent seizure. The three modes of adjustment are described below.

Decreasing Binding Load

[0049] As the furnace expands the binding forces increase as the non-flammable hydraulic fluid is pushed out of the hydraulic cylinders into the accumulator 29 thus increasing the gas pressure within the accumulator 29.

[0050] The gas pressure within the accumulator 29 is allowed to increase up to a set maximum pressure. As the pressure increases within the accumulator 29 it acts as a spring buffering the load applied to the furnace.

[0051] If the maximum pressure is reached some gas is released from the system through a relief valve thereby decreasing the pressure within the accumulator 29 and in turn decreasing the binding load back to the design load. Increasing Binding Loads

[0052] As the furnace contracts the binding load decrease as the non-flammable hydraulic fluid is pushed into the hydraulic cylinders from the accumulator thus decreasing the gas pressure within the accumulator.

[0053] The gas pressure within the accumulator is allowed to decrease down to a set minimum pressure. As the pressure is decreases within the accumulator it is acting as a spring maintaining load onto the furnace.

[0054] If the minimum pressure is reached some gas is inserted into the system from the gas supply line through a valve thereby increasing the pressure within the accumulator and in turn increasing the binding load back to the design load.

Cylinder Cycling

[0055] Periodically the cylinders are cycled in order to ensure the seals are properly lubricated and the cylinders do not seize. The binding load is to be maintained within the defined load range throughout the cycling operation.

[0056] One of the two accumulators decreases the pressure by releasing gas through the relief valve. Gas is added to the second accumulator to accommodate the decreased pressure from the first. This method, while decreasing the stroke of one cylinder, increases the stroke of the second cylinder to match through a series of small steps to ensure proper binding loads are maintained throughout the process.

[0057] Once one cylinder has reached its maximum stroke, and the other its minimum stroke the process reverses until the two cylinders reach the opposite range of their stroke.

[0058] The two cylinders then return to their starting position such that the two cylinders each have the same stroke.

[0059] The third embodiment of an auto-adjusting device is shown in Figure 9. It can be likened to a screw jack powered by a hydraulic or electric motor.

[0060] The basic principle of operation is the binding load on each tie rod will be monitored through load cells 121 and the data fed back to the PCP. The load is monitored to determine if it deviates from the prescribed load range. When the binding load is determined to be outside of the prescribed range, the motor 7 turns the worm 1 13 which in turn rotates the worm gear 112. The binding load can be increased or decreased dependent upon the direction of rotation of the motor 7. A load bearing 11 1 is included to take both the vertical and horizontal loads. A housing 1 14 and a housing cap 1 10 protect the worm drive and associated hardware from dirt and dust. A spring 9 can be utilized to reduce the frequency of adjustment.

[0061] The worm drive can be custom designed or utilize an existing screw jack design depending on the load and space requirements.

[0062] For rectangular furnaces, in addition to maintaining the proper design loads, the verticality, or plumbness, of the buckstays will be monitored to ensure that the buckstays remain plumb within a certain predefined distance. If the buckstays exceed the allowable out-of-plumbness, the hydraulic motors and jacks will be utilized as described above will be utilized to re-plumb the buckstays.

[0063] The present subject matter can thus automate the binding adjustment procedure for all forms of furnace bindings; primary and secondary hearth bindings, horizontal wall bindings, vertical wall hold down binding, and circular shell bindings. Specifically, the apparatus is intended to apply the specified design binding loads to the furnace refractory through all phases of the furnace operation without requiring regular manual adjustment. The hydraulic systems can be used with or without binding springs.

[0064] The proposed apparatus can be applied to new smelting furnaces being built or retrofitted to improve existing smelting furnaces. The proposed apparatus can be applied to furnaces with a large number of binding load points or furnaces with as little as one binding system.