Patent Application
20050263048
The present invention relates to furnaces constructed of hearth and wall refractories, and more particularly relates to systems for the compressive binding of furnace wall refractories.
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), vertical walls comprised of refractory bricks and a roof or off-gas hood. Furnaces of this type 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.
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 the cooling phase 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 material infiltrating into the hearth refractory or excessive expansive forces exerted on the binding system.
Furnace binding systems are known for applying horizontally directed compressive forces on the walls and hearth of a furnace in order to control outward expansion of the furnace. Such binding systems are discussed in detail in the applicant's co-pending U.S. patent application Ser. No. 10/269,392, filed on Oct. 11, 2002.
The inventors have found that infiltration of materials into the joints between refractory bricks in a furnace wall can result in vertical expansion or “ratcheting” in the wall, which is also detrimental to furnace campaign life. At present, there are no furnace binding systems known to the inventors which are able to effectively control vertical expansion of the furnace walls.
The present invention overcomes the above-described problems of the prior art by providing a binding system for controlling vertical expansion of a furnace wall. The binding system according to the invention comprises a compressive member which engages a laterally extending surface in an upper portion of the furnace wall. The compressive member applies downwardly directed compressive force on the wall to prevent infiltration of molten metal or other material into the gaps between the bricks making up the wall. The system also comprises a support member which is located close to the furnace for supporting the compressive member.
In one aspect, the present invention provides a vertical furnace binding system for controlling vertical expansion of a vertically-extending wall of a furnace. The furnace wall has a laterally extending surface in an upper portion thereof and is constructed of refractory bricks arranged in stacked relation to one another. The binding system comprises: (a) a compressive member engaging the laterally extending surface so as to apply a downwardly directed compressive force on the wall, the force being applied through the laterally extending surface; and (b) a support member proximate the furnace to which the compressive member is connected. The force applied by the compressive member is sufficient to control vertical expansion of the wall and substantially prevent vertical expansion of the wall due to infiltration of material into joints between the refractory bricks during operation of the furnace.
The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
The binding systems described herein may be applied to rectangular or circular furnaces. Unless otherwise indicated, the terms “wall” and “furnace wall” as used herein include side walls and end walls of a rectangular furnace and the cylindrical sidewall of a circular furnace. Where the furnace is rectangular, it will be appreciated that a binding system is preferably provided for each side and end wall.
The term “laterally extending surface” as used herein is intended to include any portion of a furnace wall through which a downwardly directed compressive force can be transmitted to the refractory bricks making up the wall. The laterally extending surface may be horizontal as shown in
The binding system 10 is comprised of at least one compressive member 26. Each compressive member 26 engages the laterally extending surface 16 (the upper surface of flange 20) so as to apply a downwardly directed compressive force (parallel to arrow F in
The binding system 10 also comprises at least one support member 28 located proximate the furnace, preferably adjacent to the wall 12, with each compressive member 26 being connected to a support member 28. In the first preferred binding system 10, each of the support members 28 comprises a vertically extending beam, for example a buckstay, and each of the compressive members 26 along wall 12 is connected to a single support member 28 by a support bracket 30. In the preferred embodiment shown in the drawings, the support member 28 comprises a buckstay which is in the form of an I-beam and comprises a pair of flanges 32, 34 and a connecting web portion 36. The support bracket 30 is attached to the flange 32 facing the furnace wall 12 and comprises a pair of arms 38, 40 which support the compressive member 28.
As shown in
The compression assembly 46 comprises a threaded compression assembly shaft 48, the lower end of which extends into the housing 44 and engages the top of the spring 42, and a compression nut 50 threaded onto the shaft 48. The compressive force applied to the wall 12 by spring 42 can be adjusted by turning the compression nut 50 with a wrench (not shown), thereby moving the shaft 48 upwardly to decrease the compression of spring 42 or downwardly to increase the compression of spring 42. Alternatively, adjustment of the compression assembly 46 may involve application of a hydraulic device (not shown) to the compression assembly shaft 48, adjustment of the spring pressure using the hydraulic device, and then re-tightening of the compression nut 50.
The compressive force applied to the wall 12 by the compressive members 26 is sufficient to substantially prevent vertical expansion of the wall 12 caused by infiltration of material into joints between the refractory bricks during operation of the furnace.
It will be appreciated that there are two causes of vertical expansion of furnace walls. The first is vertical expansion which occurs during heating of the furnace to its operating temperature. This type of vertical expansion is caused by expansion of the individual refractory bricks as they are heated, and is reversible since the bricks will contract to their original dimensions when the furnace is cooled. The second type of vertical expansion is that referred to above, which is caused by infiltration of molten metal into the joints between the refractory bricks. This type of vertical expansion, also known as “ratcheting”, is not reversible. The binding system according to the invention prevents the second type of vertical expansion caused by infiltration of material into the joints between refractory bricks, and does not substantially prevent vertical expansion caused by expansion of the bricks. Thus, when it is stated herein that the inventive binding systems prevent vertical expansion of furnace walls, this is intended to mean that the binding systems substantially prevent irreversible vertical expansion due to ratcheting.
It may be preferred to provide a pair of compressive members 26 at each of the support members 28, although the provision of only one compressive member at some or all of the support members 28 may be sufficient. When the compressive members 26 are paired, each member 26 of a pair is preferably arranged on either side of the support member 28.
As in the first preferred embodiment, the binding system 60 comprises a compressive member 74 and a support member which, in this preferred embodiment, comprises the buckstay 64. The binding system 60 differs from that of the first preferred embodiment in that the compressive member 74 comprises a separate force-generating member 76 which generates the compressive force, and a force-applying member 78 through which the vertical compressive force is applied to a laterally extending surface 80 of the wall 62.
As in the first preferred embodiment, the force generating member 76 of compressive member 74 comprises a coil spring 82 having a vertically aligned axis A. However, in this preferred embodiment, the spring 82 is mounted on a support bracket 84 extending from the rear flange 68 of buckstay 64 so that the axis A of spring 82 extends along the rear flange 68 of the buckstay 64, rather than through the furnace wall 62. The coil spring 82 is compressed between an upper spring mount 86 and a lower spring mount 88 which is supported on the upper face of bracket 84. A spring rod 90 extends vertically through the spring 82, the spring mounts 86 and 88, and through the support bracket 84. The upper end of spring rod 90 is threaded and protrudes through the upper spring mount 86. A compression nut 92 is threaded onto the upper end of rod 90 and engages the upper spring mount 86. The compression of spring 82 is adjusted as described above in relation to the first preferred embodiment, for example by turning the nut 92 with a wrench or by use of a hydraulic device. It will be appreciated that the spring 82, when compressed, exerts an upwardly directed force on the upper spring mount 86 and the compression nut 92 on its upper surface, thereby biasing the spring rod 90 upwardly.
As shown in
In the second preferred embodiment, the furnace wall 62 is comprised of refractory brick 104 with a metal structural shell 106. As shown in
It will be appreciated that arrangements other than that shown in
Secured to the outer face of the ring beam 136 at regularly spaced intervals are a plurality of support brackets 146, only one of which is shown in
As will be appreciated from
Although the invention has been described in connection with certain preferred embodiments, it is not limited thereto. Rather, the invention is intended to include all embodiments which may fall within the scope of the following claims.
