Girth gear for rotary kiln and method for operating a rotary kiln equipped therewith

Abstract

To provide a girth gear for a rotary kiln which causes no problems such as breakage in a fastening bolt at the joint parts of two arc-shaped members composing a girth gear.SOLUTION: There is provided a girth gear 4 with an almost toric shape composed of two arc-shaped members 10A, 10B concentrically provided at the outer circumferential part of a cylindrical body part 1 of a rotary kiln and divisible into two and having a plane-symmetric relationship with each other regarding a plane including a central axis O. Each of two parts at which the two arc-shaped members 10A, 10B are mutually joined is provided with two columnar projection parts 12 respectively projecting toward the charge end and the exhaust end of the rotary kiln, and each of them is divisible into two and is externally fitted with a shrunk ring 13. In each projection part 12 and the shrunk ring 13, a groove part G for a bevel is formed all around at an engagement part of their tip sides, and they are mutually welded in the groove part G.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a girth gear for a rotary kiln and an operating method of a rotary kiln provided with the girth gear.

Background Art

[0002] The Waelz kiln method for recovering zinc by reduction roasting from iron-based wastes containing zinc such as steel dust, electric furnace dust, zinc plating sludge, cupola dust, etc. using a rotary kiln is known. In this process, iron-based waste is charged into a rotary kiln, and iron oxides and zinc oxides contained in the iron-based waste are reduction-roasted in a reducing atmosphere at a high temperature of about 1000 to 1500 °C. The zinc vapor volatilized thereby is cooled and oxidized to produce zinc oxide in the form of fine powder. The produced fine powder of zinc oxide is discharged from the rotary kiln together with the exhaust gas, and thus can be recovered in a dust collector or the like as crude zinc oxide dust. The recovered crude zinc oxide dust is calcined in a drying and heating kiln after impurities such as halogen are removed in a wet refining process, thereby producing crude zinc oxide sinter ore as a raw material for zinc smelting.

[0003] A large-scale rotary kiln used on an industrial scale, such as the rotary kiln used in the above Waelz kiln method, has a cylindrical body portion generally having an outer diameter of about several meters and a length of about several tens of meters. Therefore, in order to stably rotate the rotary kiln supported rotatably with the central axis of the body portion slightly inclined from the horizontal direction at a rotation speed of about 0.1 to 2 rpm around the central axis, a substantially annular gear called a girth gear is provided coaxially on the outer peripheral portion of the body portion. By rotationally driving a pinion gear meshing with this girth gear with a motor, the rotary kiln can be stably rotated.

[0004] As described above, when a girth gear is installed in a large rotary kiln, its outer diameter is naturally larger than the outer diameter of the cylindrical body of the rotary kiln. Therefore, the girth gear is generally composed of two arc-shaped members that are symmetrical with respect to the plane containing its central axis. For example, Patent Document 1 discloses a two-part girth gear that is attached to the outer circumference of a rotary kiln used in cement plants, pulp mills, chemical plants, etc., via multiple leaf springs. The two arc-shaped members constituting the girth gear in Patent Document 1 each have meshing teeth cut into the outer circumference of a semi-circularly bent rectangular bar and reinforcing ribs on the inner circumference. Furthermore, connecting members made of rectangular plates are welded to both ends of the roughly arc-shaped members. These connecting members have keyways on their contact surfaces for inserting positioning keys when connecting the two arc-shaped members, and also have reamed holes for inserting fastening bolts. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 05-177454 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] By using a girth gear with a structure like that described in Patent Document 1 above, it becomes possible to accurately and efficiently position and fasten two arc-shaped members together with bolts and nuts. However, with a girth gear having a two-part structure like the one described above, intermittent forces are easily applied to the joint between the two arc-shaped members that make up the gear, and a problem has arisen where the fastening bolts at this joint have broken during long-term continuous operation of the rotary kiln.

[0007] This invention has been made in view of the problems associated with rotary kilns equipped with a two-part girth gear, and aims to provide a girth gear for a rotary kiln that is less prone to problems such as breakage of the fastening bolts at the joint of the two arc-shaped members constituting the girth gear, even when the rotary kiln equipped with a two-part girth gear is operated continuously for a long period of time. [Means for solving the problem]

[0008] To achieve the above objectives, the girth gear for a rotary kiln according to the present invention is a substantially annular girth gear composed of two arc-shaped members that are symmetrical with respect to a plane including the central axis and are provided concentrically on the outer circumference of the cylindrical body of the rotary kiln, and each of the two arc-shaped members that joins to each other is provided with two cylindrical projections that protrude toward the charging end and discharge end of the rotary kiln, respectively, and each of these two projections is divisible with respect to the plane and has a shrink-fit ring fitted to the outside, and these protrusion The shrink-fit rings are characterized in that a groove for beveling is formed around the entire circumference of the engagement portion at their tip, and that they are welded to each other in the groove. [Effects of the Invention]

[0009] According to the present invention, even when a rotary kiln is operated continuously for a long period of time, it is possible to prevent problems such as breakage in the fastening bolts at the joint portion of the two arc-shaped members constituting the girth gear installed in the rotary kiln. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic side view of a rotary kiln equipped with a girth gear according to an embodiment of the present invention. [Figure 2] This is a perspective view of a girth gear according to an embodiment of the present invention. [Figure 3] Figure 2 is a partially enlarged perspective view of the joint between the two arc-shaped members in the girth gear. [Figure 4] Figure 3 is a perspective view showing the state where the joints of the two arc-shaped members are spaced apart. [Figure 5] Figure 3 shows a vertical cross-sectional view of the cylindrical projection provided at the joint and the shrink-fit ring fitted onto the projection. [Figure 6] Figure 3 is a perspective view showing the state in which a plate-shaped member is attached to the tip surface of a cylindrical projection. [Figure 7] This is a plan view showing how the mounting bolts of the plate-shaped members in Figure 6 are fixed together with a metal rod. [Modes for carrying out the invention]

[0011] First, a specific example of a rotary kiln in which the girth gear of the embodiment of the present invention is suitably provided will be described with reference to Figure 1, using the case of producing crude zinc oxide from zinc-containing steel dust by the Wertz kiln process as an example. In the rotary kiln shown in Figure 1, two annular rails (also called tires) 2 are provided on the outer circumference of the cylindrical body 1, spaced apart from each other in the axial direction, and a roller structure (also called a receiving roller) 3 that engages with these rails supports the central axis O so as to be rotatable with the central axis O tilted slightly from the horizontal direction. On the outer circumference of this body 1, a substantially annular girth gear 4 of the embodiment of the present invention is provided concentrically with the body 1 between these two annular rails 2. A pinion gear 6, which is rotationally driven by a motor 5, meshes with this girth gear 4. With this configuration, the raw material, steel dust, which is charged together with a reducing agent such as coke from the charging port 7 located at the charging end on the left side of the paper, is churned up by the rotary kiln, which rotates in conjunction with the girth gear 4 rotated by the motor-driven pinion gear 6, and gradually moves through the rotary kiln toward the discharge end on the right side of the paper due to gravity.

[0012] In this way, as the steel dust moves through the rotary kiln, it is reductively roasted in a high-temperature reducing gas atmosphere, preferably around 1000-1500°C, more preferably around 1100-1200°C, generated by the fuel and coke of the burner 8 located at the discharge end. The zinc vapor volatilized by this reductive roasting is oxidized by oxygen in the gas phase to become finely powdered crude zinc oxide. This fine powder of crude zinc oxide is discharged along with the exhaust gas from the charging end of the rotary kiln via the duct 9 and is recovered as crude zinc oxide dust in an electrostatic precipitator or the like (not shown). On the other hand, the residue generated by the reductive roasting of the steel dust is discharged as clinker from the discharge end of the rotary kiln.

[0013] Next, the girth gear 4 of the embodiment of the present invention, which is provided on the outer circumference of the body portion 1 of the rotary kiln described above, will be described in detail. As shown in Figure 2, the girth gear 4 of the embodiment of the present invention is composed of two arc-shaped members 10A and 10B, which are symmetrical with respect to each other and can be divided into two parts with respect to the plane containing the central axis O, and which have a substantially I-shaped cross-section, and is a substantially annular gear as a whole. The size of the girth gear 4 for the rotary kiln is not limited, but for example, the outer diameter is about 4000 to 6000 mm, the difference between the outer diameter and the inner diameter is about 800 to 1600 mm, and the width is about 300 to 500 mm. The girth gear 4 is attached to the outer circumference of the body portion 1 of the rotary kiln by a plurality of leaf springs 11 provided at equal intervals in the circumferential direction, for example.

[0014] At each of the two arc-shaped members 10A and 10B described above, where they are joined to each other, there are two cylindrical projections 12, each with an outer diameter of approximately 100 mm and a height of approximately 50 mm, that project toward the charging end and discharge end of the rotary kiln, respectively. Each of these two projections 12 is composed of two semi-cylindrical bodies 12A and 12B that are symmetrical with respect to the plane containing the aforementioned central axis O. Furthermore, a shrink-fit ring 13, which is approximately the same height as the projection 12, has an outer diameter of approximately 200 mm, and its inner diameter is slightly smaller than the outer diameter of the projection 12, and is fitted onto each projection 12. As shown in Figures 3 and 4, these projections 12 and the shrink-fit ring 13 have grooves G formed around their entire circumference at the engaging ends, and they are welded together around their entire circumference in these grooves G.

[0015] In the girth gear 4 of the embodiment of the present invention, at each of the two joint locations where the two arc-shaped members 10 are joined, two semi-cylindrical bodies 12A and 12B constituting the aforementioned projections 12 are provided on a pair of opposing ribs 14A and 14B, respectively. For example, fastening bolts 16 of M10 are inserted through bolt holes 15A and 15B that extend tangentially to the girth gear 4 and are tightened with nuts 17. This prevents problems such as the shrink-fit ring 13 falling off or the fastening bolts 16 breaking as a result, even when the rotary kiln is operated continuously for a long period of time.

[0016] In other words, when two arc-shaped members 10 are joined together to assemble a roughly annular girth gear 4, the two semi-cylindrical bodies 12A and 12B overlap at their dividing surfaces to form a cylindrical projection 12. By fitting a shrink-fit ring 13 made of a metal annular member that has been expanded by heating into this projection 12, the two semi-cylindrical bodies 12A and 12B can be fixed in place so that they do not move relative to each other when the shrink-fit ring 13 cools to approximately room temperature and shrinks back to its original size. Moreover, by welding the projection 12 and the shrink-fit ring 13 to each other, even if the shrink-fit ring 13 loosens during operation and its inner diameter becomes larger than the outer diameter of the projection 12, it will not easily fall off the projection 12.

[0017] In the above welding, the cross-sectional shape of the groove portion G provided at the engaging portions on both tip ends of the protrusion 12 and the shrink fit ring 13 is not particularly limited, and general V-shaped, L-shaped, J-shaped, U-shaped, etc. can be adopted. In the case of the above L-shaped or J-shaped, beveling may be performed only on the protrusion 12 side, or beveling may be performed only on the shrink fit ring 13 side. As shown in FIG. 5, it is preferable that the depth (bevel depth) D of the groove portion G is 5 mm or more and 10 mm or less. When this depth D is less than 5 mm, the amount of welding is too small and it may be difficult to obtain sufficient joint strength. Conversely, even if this depth D exceeds 10 mm, the welding strength hardly changes, and rather, the amount of welding increases, which is uneconomical, and the time required for welding becomes long, so it is not preferable.

[0018] The girth gear 4 of the embodiment of the present invention may further have a plate-like member 20 that protrudes at least partially radially outward from the outer peripheral portion of the tip surface of each protrusion 12 and engages with the tip surface of the shrink fit ring 13 as shown in FIG. 6, coaxially attached to the protrusion 12. Thereby, as described above, even when the shrink fit ring 13 loosens and its inner diameter becomes larger than the outer diameter of the protrusion 12, and further when the strength of the welding joining the protrusion 12 and the shrink fit ring 13 decreases, it is possible to more surely prevent the shrink fit ring 13 from falling off the protrusion 12. As a result, even when the rotary kiln is continuously operated over a long period of time, it is possible to more surely prevent troubles such as the girth gear 4 being divided into two arc-shaped members 10 during operation or displacement occurring at the joint portion, and it is possible to easily find that the shrink fit ring 13 is in a loosened state before such troubles occur. And when such a problem is found, it is possible to perform a minimum repair measure such as replacing the loosened shrink fit ring 13 with a new one. Note that the plate-like member 20 may be disk-shaped or may be a regular polygonal shape such as a regular triangle, a square, or a regular hexagon.

[0019] As shown in Fig. 6, when attaching the plate-like member 20 to the protruding portion 12 by inserting the mounting bolts 21 through a plurality of through holes 20a drilled in the thickness direction of the plate-like member 20 and screwing them into the screw holes 12a provided in the protruding portion 12 in advance, it is preferable to take measures to prevent the mounting bolts 21 from rotating. As such anti-rotation measures, for example, the heads of the plurality of mounting bolts 21 and the plate-like member 20 may be fixed by welding. However, as shown in Fig. 7, it is preferable to weld the heads of the mounting bolts 21 together with an iron rod-shaped piece 22. For example, when attaching a disc-shaped plate-like member 20 with an outer diameter of 120 mm and a thickness of 12 mm to a protruding portion 12 with an outer diameter of 100 mm using three mounting bolts 21, it is preferable to weld the heads of these mounting bolts 21 together in a triangular shape with an iron rod-shaped piece 22.

[0020] As described above, the girth gear for a rotary kiln according to the embodiment of the present invention is provided with a columnar protruding portion that is bisected together with two arc-shaped members constituting the girth gear at the joint portion of the two arc-shaped members. After fitting a shrink-fit ring onto this protruding portion, the protruding portion and the shrink-fit ring are welded to each other. Therefore, even if the operation continues for a long time, it is possible to prevent the problem that the joint portion shifts and the fastening bolts are damaged.

[0021] In addition, when operating while charging a raw material containing a substance with a melting point lower than the temperature of the internal atmosphere of the rotary kiln, particularly when performing reduction roasting by the aforementioned Waelz kiln method, since a raw material containing a substance with a melting point lower than the internal atmosphere temperature of the rotary kiln is processed in the rotary kiln, deposits (also called beko) are likely to occur on the inner wall of the furnace of the rotary kiln. As a result, even when attempting to operate the rotary kiln so that it rotates at a constant rotational speed, the rotational speed may suddenly decrease or increase, and the force applied to the girth gear will vary each time.

[0022] For example, if the raw material charged into a rotary kiln operating at an internal ambient temperature of 1100-1200°C contains steel dust, the melting point of steel dust is 1000-1100°C. As a result, the raw material melts in the hottest region of the rotary kiln, and some of it adheres to the inner wall of the kiln, forming what is known as "beko." This beko grows as operation continues. Moreover, this beko does not necessarily adhere to or grow with a uniform thickness on the inner wall of the rotary kiln; its thickness varies depending on its location on the inner wall. Therefore, as mentioned above, it becomes difficult to rotate the rotary kiln at a constant rotational speed, and the force on the girth gear fluctuates as it suddenly decelerates or accelerates.

[0023] In other words, when burrs are unevenly attached to the inner wall of a rotary kiln, the girth gear may experience partially larger or smaller loads in the circumferential direction during rotation compared to normal conditions when no burrs are attached. At this time, intermittent forces are applied to the two semi-cylindrical bodies 12A and 12B that constitute the cylindrical projection 12, moving them apart from each other, or intermittent shear forces are applied to the joint surfaces of the two semi-cylindrical bodies 12A and 12B. This can cause the shrink-fit ring 13 to expand in diameter overall, or slight sliding to occur at the joint surfaces, ultimately leading to problems such as the shrink-fit ring 13 detaching from the projection 12 or the fastening bolt 15 breaking. In contrast, by using the girth gear of the embodiment of the present invention described above, it is possible to significantly reduce the occurrence of the above problems. [Explanation of Symbols]

[0024] 1. Torso 2 Circular Rails 3 Roller Structure 4 Garth Gear 5 motors 6 pinion gear 7 Charging port 8 burners 9 ducts 10A, 10B Arc-shaped members 11. Leaf spring 12 Protrusion 12A, 12B Semi-cylindrical bodies 12a Screw hole 13. Shrink-fit rings 14 Ribs 15A, 15B Bolt holes 16 fastening bolts 17 Nuts 20 Plate-shaped member 20a through hole 21 Mounting bolts 22 Rod-shaped piece G groove O center axis

Claims

1. A rotary kiln girth gear comprising two substantially annular girth gears arranged concentrically on the outer circumference of the cylindrical body of a rotary kiln, and composed of two arc-shaped members that are symmetrical with respect to a plane including the central axis, wherein each of the two arc-shaped members that joins to each other is provided with two cylindrical projections that protrude toward the loading end and discharge end of the rotary kiln, respectively, and each of these two projections is divisible with respect to the plane and fitted with a shrink-fit ring, and these projections and the shrink-fit ring have grooves formed around their entire circumference on the engaging portion at their tip and are welded to each other in the grooves.

2. The girth gear for a rotary kiln according to claim 1, characterized in that the groove portion has a depth of 5 mm or more and 10 mm or less.

3. The girth gear for a rotary kiln according to claim 1 or 2, characterized in that a disc-shaped or regular polygonal plate-shaped member is attached concentrically to the tip surface of the projection, at least partially protruding outward from the outer circumference of the tip surface and engaging with the shrink-fit ring.

4. A method for operating a rotary kiln, characterized by operating the rotary kiln equipped with the girth gear described in claim 1 while charging a raw material containing a substance with a melting point lower than the temperature of the internal atmosphere.

5. The method for operating a rotary kiln according to claim 4, characterized in that the raw material is iron-based waste containing zinc.

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