Water cooled finger

Abstract: A water cooled finger for a pre-heater of a furnace top holds metal materials of a required amount in a shaft installed at the furnace top for pre-heating metal materials by introducing hot exhaust gas generated in the furnace into the shaft. The water cooled finger is formed of a pair of side faces, an upper plate and lower plate. The upper plate is fixed to an upper part of both of side face portions. The lower plate is fixed to a lower part of both of side face portions. The water cooled finger is formed to be hollow as a whole. It satisfies at least one of the conditions of (A) a thickness of the upper plate is larger than that of said lower plate, (B) the lower plate is formed with R-bending processed portions at both ends thereof, and (C) the lower plate is curved outside.

Description: The present invention relates to a water cooled finger, especially for a pre-heater of a furnace top. When metal scraps are melted, for example, in a melting furnace such as a burner furnace and an arc furnace, it is occasionally useful to previously pre-heat the metal scraps with hot exhaust gas generated in the melting furnace. For pre-heating metal scraps, various kinds of apparatuses are used. Attention has recently been paid to a pre-heating apparatus installed at the melting furnace top, which is provided with a shaft at the top of the melting furnace and holds metal scraps charged in the shaft by means of a water cooled finger so as to pre-heat them with the hot exhaust gas from the melting furnace. Conventionally, the water cooled finger of the pre-heater of the furnace top as mentioned above is generally formed as a whole to be hollow by welding steel plates (Unexamined Japanese Patent Publication (kokai) No. 8-54191, No. 8-136163 and No. 9-257377). These fingers are constructed by welding upper plates and lower plates to both side plates. These fingers are formed as a whole to be hollow structures, and the cross section is a square. Generally, the hollow part is partitioned, so that cooling water is caused to flow successively into each of the partitioned chambers. However, such a conventional finger has problems to simultaneously satisfy the requirements of providing durability against repeated dropping impact of charged metal materials and against repeated thermal stress. Since metal materials are thrown into the shaft through the upper inlet thereof, the finger holding thrown metal materials is repeatedly affected with considerable dropping impact of metal materials. Accordingly, the finger should be resistant against repeated dropping impact. On the other hand, the finger which holds thrown metal materials is heated from the outside by high temperature exhaust gas coming from the furnace and is cooled from the inside by the cooling water running in the hollow part of the finger, so that thermal stress caused by heating and cooling acts thereon. Thus, the water cooled finger should preferably at the same time have a characteristic durability against repeated thermal stress. It is the object of the present invention to overcome the drawbacks and disadvantages of the prior art. This object is solved by the water cooled finger according to independent claim 1. The scope of the invention is defined by the appended claims. The present inventors have observed that, if the water cooled finger is made of steel plates of relatively large thickness, since the lower plate of the finger exposed to high temperature exhaust gas is subject to considerable thermal stress, cracks would easily appear in the lower plate. Thermal stress is, in its nature, concentrated in welded parts between both side plates at both ends of the lower plate of the finger and the lower plates thereof, so that cracks easily occur, in particular at the welded parts. When cracks appear, the cooling water leaks, repair of the finger is frequently required, and affected portions should be exchanged in short periods of time. If, on the other hand, the water cooled finger is made of steel plates of relatively small thickness to satisfy the characteristic of durability against repeated thermal stress, since the upper plate thereof directly receiving thrown metal materials is affected with large dropping impact, the upper plate would easily be broken. Similarly in this case, repair of the finger is also frequently required, and affected portions should be exchanged in short periods of time, after all. Thus, in the conventional water cooled finger, it is not possible to simultaneously provide durability against repeated dropping impact and repeated thermal stress. In one aspect, the present invention provides a water cooled finger in a pre-heater at the furnace top capable of simultaneously providing the strength to resist repeated dropping impact of metal materials and the characteristic durability against repeated thermal stress. In a further aspect, a water cooled finger for a pre-heater of a furnace top holds metal materials of a required amount in a shaft installed at the furnace top for pre-heating metal materials by introducing exhaust gas at high temperature generated in the furnace into the shaft. The water cooled finger is formed of a pair of side faces, an upper plate and a lower plate. The upper plate is fixed to an upper part of both side face portions. The lower plate is fixed to a lower part of both side face portions. The water cooled finger is formed to be hollow as a whole; the hollow shape formed by the side faces, the upper plate and the lower plate. The water cooled finger satisfies at least one of the conditions of (A) a thickness of the upper plate is larger than that of said lower plate, (B) the lower plate is formed to be R-bending processed portions at both ends thereof, and (C) the lower plate is curved outside. The present invention provides in one aspect a water cooled finger for a pre-heater of a furnace top, for holding metal materials of a required amount in a shaft installed at the furnace top for pre-heating metal materials by introducing exhaust gas at high temperature generated in the furnace into the shaft. The water cooled finger is formed to be hollow as a whole. The present invention satisfies, in another aspect, at least one of the conditions: (A) The thickness of the upper plate of the water cooled finger is relatively large, while the thickness of the lower plate thereof is relatively small; (B) The lower plate of the water cooled finger is formed with R-bending processed portions at both ends thereof; and (C) The lower plate of the water cooled finger is curved outside. It is sufficient if only one of these conditions is fulfilled. Alternatively, it is preferable to combine the condition (A) with the condition (B) or the condition (C). The water cooled finger is preferably formed to be hollow as a whole by welding steel plates together. With respect to the entire outer configuration thereof, an upper plate and a lower plate are welded to both side plates, and are formed in an arm shape by closing the front end part and the base part with other side plates. Normally, the thus formed hollow part is partitioned. Then, cooling water is caused to flow in succession into each of the partitioned chambers. Such a water cooled finger is usually provided with a central portion of rotation at the base part, and an inlet and an outlet of the cooling water in the base part outside of the shaft. The rotating central portion is provided in the shaft wall, so that the finger is opened and closed by rotating it around the fulcrum of the rotating center. The water cooled finger receives and holds metal materials thrown into the shaft under the closing state, and pre-heats them with the high temperature exhaust gas from the furnace. The water cooled finger is preferably formed such that the upper plate thereof has a relatively large thickness, while the lower plate thereof has a relatively small thickness. A steel plate of relatively large thickness is used for forming the upper plate of the water cooled finger, and a steel plate of relatively small thickness is used for forming the lower plate of the same. The thickness of the lower plate is preferably not more than 1/2 of that of the upper plate, more preferably not more than 1/3, even more preferably not more than 1/4. For example, when the steel plate forming the upper plate is around 40 mm in thickness, a steel plate of around 6 to 9 mm thickness is preferably employed for the lower plate. The upper plate of the finger directly receives the dropping impact of metal materials thrown into the shaft. The lower plate of the finger is subject to large thermal stress generated by the heat of the high temperature exhaust gas from the furnace and the cooling due to the cooling water running in the hollow part of the finger. The considerable temperature difference between outside and inside temperature generates a large thermal stress in the lower plate. If a steel plate of larger thickness is used for the upper plate, it is given the strength to resist the repeated dropping impact. If a steel plate of smaller thickness is used for the lower plate, the thermal stress is reduced, so that it is made resistant to the repeated thermal stress. In another aspect of the invention, for simultaneously giving the water cooled finger the strength to resist the repeated dropping impact and the repeated thermal stress, R-bending processed parts may be formed at both ends of the lower plate, instead of making the thickness of the lower plate smaller than that of the upper plate, or preferably in cooperation with the latter measure. The R-worked portions are arranged preferably at both sides of the lower steel plate forming the lower plate, preferably at both sides of the steel plate of the smaller thickness so as to raise up both sides toward the side direction. Both raised parts are welded to the side steel plates forming side faces. As a result, the R-bending processed parts are formed at both ends of the lower plate. The water cooled finger is subject to thermal stress at the lower plate thereof caused by heating the outside by the high temperature exhaust gas from the furnace and by cooling the inside with cooling water. Such thermal stress is concentrated, in its nature, to both ends of the lower plate. If the steel plates forming both side faces at both ends thereof are welded to the steel plate of the lower plate, the welded parts are placed on both end parts of the lower plate. Accordingly, the thermal stress is concentrated there and may cause cracks in the welded parts. However, by forming R-bending processed parts at both ends of the lower plate, occurrences of cracks can be avoided. In a further aspect of the invention, for giving at the same time the water cooled finger the strength to resist the repeated dropping impact and the characteristic durability against repeated thermal stress, the lower plate may be curved outside, instead of making the thickness of the lower plate smaller than that of the upper surface, or preferably in cooperation therewith. Preferably, both ends of a curved steel plate of smaller thickness forming the lower plate are welded to side plates as side faces, resulting in forming an outside curve of the lower plate. The water cooled finger is subject to thermal stress at the lower plate thereof due to the heating outside by the high temperature exhaust gas from the furnace and the cooling inside by the cooling water running in the hollow part of the water cooled finger. Such thermal stress is concentrated, in its nature, to both ends of the lower plate. If the side steel plates for forming both side faces is welded to both ends of the lower steel plate for forming the lower plate, the welded parts are placed at both end parts of the lower plate. Accordingly, the thermal stress is concentrated there and causes cracks in this welded part, but by forming a lower plate which is curved outside, occurrences of cracks can be avoided. The above mentioned and other features and aspects of the present invention are illustrated by the following drawings, in which: Figure 1 is a side view of a first embodiment of a water cooled finger according to the present invention; Figure 2 is a cross sectional view seen along A-A line of Fig. 1; Figure 3 is a cross sectional view of a second embodiment of the water cooled finger according to the present invention; and Figure 4 is a cross sectional view of a third embodiment of a further water cooled finger according to the present invention. Figure 1 is a side view of a first embodiment of a water cooled finger according to the present invention. Figure 2 is a cross sectional view seen along A-A line of Fig. 1. The water cooled finger 11 is formed to be a hollow structure as a whole by welding the steel plates together. With respect to an entire outer configuration, an upper plate 23 and a lower plate 24 are welded to both side plates 21, 22 and further formed in an arm shape by closing a front end part and a base part with other side plates. The thus formed hollow part has partitioning plates 31 and 37, and cooling water is caused to successively flow into each of the partitioned chambers 41 to 48. The water cooled finger 11 is provided with a central portion 12 of rotation in the base part and with an inlet 13 and an outlet 14 of the cooling water in the base part outside of the shaft. The rotating central portion 12 is provided in a shaft wall (not shown). Accordingly, the water cooled finger is opened and closed around a fulcrum of the rotating center portion 12. The water cooled finger receives and holds metal materials thrown into a shaft (not shown) under the closing state, and pre-heats metal materials with the high temperature exhaust gas from a furnace (not shown) . The water cooled finger 11 is formed in that the upper plate 23 thereof is of relatively large thickness, while the lower surface 24 thereof is of relatively small thickness. Namely, a steel plate of relatively large thickness is used for forming the upper plate 23 of the finger 11, and a steel plate of relatively small thickness is used for forming the lower plate 24. In the first embodiment shown in Figs. 1 and 2, the thickness of the lower plate 24 is 1/3 or less than that of the upper plate 23. By using a steel plate of larger thickness as the lower plate for forming the upper plate 23, the water cooled finger is given the strength to resist the repeated dropping impact. By using a steel plate of smaller thickness for forming the lower plate 24, the thermal stress therein is reduced. Accordingly, the water cooled finger is given a characteristic durability against repeated thermal stress. Figure 3 is a cross sectional view of a second embodiment of a water cooled finger according to the present invention. The other structures not explained are the same as those of the water cooled finger shown in Figs. 1 and 2. The water cooled finger 11a is formed in that the upper plate 23a thereof is a larger thickness, while the lower plate 24a thereof is of smaller thickness. Namely, a steel plate of larger thickness is employed for forming the upper plate 23a thereof, and a steel plate of smaller thickness is employed for forming the lower plate 24a. In the second embodiment shown in Fig. 3, the thickness of the lower plate 24a is 1/4 or less than that of the upper plate 23a. The finger 11a is formed with bent portions 51, 52 having a radius R at both end parts of the lower plate 24a. The R-bent portions are arranged at both sides of the steel plate of smaller thickness forming the lower plate 24a so as to raise up both ends toward the side directions. Both raised portions are welded to the side steel plates forming side faces 21a, 22a, resulting in forming the R-bending processed portions 51, 52 at both ends of the lower plate 24a. By using the steel plate of larger thickness for the upper plate 23a, the water cooled finger is given the strength to resist the repeated dropping impact. By using the steel plate of smaller thickness for the lower plate 24a, the thermal stress is reduced, and at the same time, the R-bending processed portions 51, 52 are formed at both ends of the face 24a to be concentrated with thermal stress. Accordingly, the water cooled finger is given the characteristic durability against repeated thermal stress. Figure 4 is a cross sectional view of a third embodiment of a water cooled finger according to the present invention. The other structures not explained are the same as those of the water cooled finger shown in Figs. 1 and 2. The water cooled finger 11b is formed in that the upper plate 23b thereof is of relatively large thickness, while the lower plate 24b curved outside is of relatively small thickness. Namely, a steel plate of relatively large thickness is employed for forming the upper plate 23b thereof, while a steel plate of relatively small thickness curved outside is employed for forming a lower plate 24b. In the third embodiment shown in Fig. 4, the thickness of the steel plate forming the lower plate 24 b is 1/4 or less than that of the steel plate forming the upper plate 23a. Both end portions of the outside curved steel plate of smaller thickness forming the lower plate 24b are welded to side steel plates for forming side faces 21b, 22b, resulting in forming the outside curve of the lower plate 24b. By using the steel plate of larger thickness forming the upper plate 23b, the water cooled finger is given the strength to resist the repeated dropping impact, while by using the steel plate of smaller thickness forming the lower plate 24b, the thermal stress is reduced, and at the same time, it is dispersed, whereby the water cooled finger is given the characteristic durability against repeated thermal stress. As is apparent, the present invention as mentioned above is effective in simultaneously satisfying the strength durable against the repetition of dropping impact when receiving on the water cooled finger metal materials thrown into the shaft as well as the characteristic durability against the repetition of the thermal stress.

Claims: A water cooled finger especially for a pre-heater of a furnace top comprising: a pair of side face portions (21, 22; 21a, 22a; 21b, 22b); an upper plate portion (23; 23a; 23b) fixed to an upper part of both of said pair of side face portions (21, 22; 21a, 22a; 21b, 22b); and a lower plate portion (24; 24a; 24b) fixed to a lower part of both of said pair of side face portions (21, 22; 21a, 22a; 21b, 22b), said water cooled finger being formed to be hollow as a whole by said pair of said face portions (21, 22; 21a, 22a; 21b, 22b), said upper plate portion. (23; 23a; 23b) and said lower plate portion (24; 24a; 24b); characterised in that said water cooled finger satisfies at least one of the following conditions: (A) a thickness of said upper plate portion (23; 23a; 23b) is larger than that of said lower plate portion (24; 24a; 24b), (B) said lower plate portion (24a) is formed with R-bending processed portions (51, 52) at both ends thereof, and (C) said lower plate portion (24b) is curved outside. The water cooled finger according to claim 1, wherein said water cooled finger satisfies the conditions (A) and (B) simultaneously. The water cooled finger according to claim 1, wherein said water cooled finger satisfies the conditions (A) and (C) simultaneously. The water cooled finger according to any of claims 1 to 3, wherein (A) is satisfied and wherein the thickness of the lower plate portion (24; 24a; 24b) is not more than 1/2 of that of the upper plate portion (23; 23a; 23b). The water cooled finger according to claim 4, wherein the thickness of the lower plate portion (24; 24a; 24b) is not more than 1/3 of that of the upper plate portion (23; 23a; 23b). The water cooled finger for a pre-heater of a furnace top according to claim 5, wherein the thickness of the lower plate portion (24; 24a; 24b) is not more than 1/4 of that of the upper plate portion (23; 23a; 23b).

Inventors: MATSUO KUNIO, NOMURA TAMOTSU, NONOYAMA SEIJI, MATSUO, KUNIO, NOMURA, TAMOTSU, NONOYAMA, SEIJI
Applicants: DAIDO STEEL CO LTD, DAIDO TOKUSHUKO KABUSHIKI KAISHA
Application year: 1999
Main classification: F27D13
IPC codes: F27D13, F27D17, F27D9, C21C5