MXPA98008440A - Vertical recovered oven for an it treatment device - Google Patents

Abstract

Vertical annealing furnace for continuous bright annealing of metal strip guided through the furnace, consisting of a vertically arranged muffle having a strip inlet side and a strip outlet side, as well as heating means for externally heating the The muffle having the freedom to expand in the longitudinal direction, the muffle is arranged in such a way that the strip entry side is located on the upper side and the strip exit side is located on the lower side, the lower side of the The muffle is delimited downwards in the longitudinal direction and the muffle can extend upwards in the longitudinal direction, the vertical annealing furnace beingparticularly designed to be used in the heating section of a strip treatment device which also comprises a section of strip feeding, a cooling section located in the downward direction of the heating section and a strip removal section (

Description

VERTICAL OVEN RECOCIDED FOR A TREATMENT DEVICE Pg IPAS DESCRIPTIVE MEMORY The invention relates to a vertical annealing furnace for the continuous bright annealing of metal strips guided through the furnace »consisting of a vertically placed muffle having a side entrance strip and a side outlet strip» as well as means of heating to externally heat the muffle »the muffle having the freedom to expand in the longitudinal direction. A vertical annealing furnace of this type is known, among others »from Stahl und Eisen. Volume 93 »No 24» of November 22 »1973. pp. 1152-1157. In this case »the muffle consists of an upper flange, by means of which it is fixedly suspended in a frame. The muffle can freely expand downwards »in the longitudinal direction» with respect to the rest of the annealing furnace. This possibility of expansion of the muffle is of crucial importance in order to be able to achieve a high specific structural height (for example »20 m> of the annealing furnace.This is because» in the case of so-called bright strip annealing stainless steel, the temperature of the muffle is in the region of 1150 ° C. At such a high temperature, the expansion of the muffle in the longitudinal direction is very large.If no measures were taken to allow this expansion, this would lead to deformations in the bending of the muffle, both in the transverse direction and in the longitudinal direction of the muffle The strip to be heated passes through the muffle from the lower part to the upper one, the point where the strip reaches its highest temperature In the muffle it is therefore located in the upper part of the muffle In order to guide the strip through the muffle and be able to hold the strip at a specific tension »a specific tension of strip is exerted on the strip »this tension is transmitted to the strip by means of cylinders. In the downstream direction of the muffle, a cooling section is located which, due to the high final temperature that the strip has reached at the end of the muffle, must be placed directly after the outlet side of the muffle strip. As a result, the chiller section is located entirely or almost directly above the muffle arranged vertically. A vertical annealing furnace of the same type is also known from JP-A-2 282 687 and JP-A-4 225 780. These furnaces are further provided with counterweight mechanisms that give a compression load acting on the lower part of the furnace. the muffle. Thus, the downward approach caused by the weight of the muffle and the thermal expansion of the muffle are reduced. A disadvantage of these known vertical annealing furnaces is that the structural height is limited.

There are two reasons for this limitation of structural height. First »the full weight of the muffle is suspended from the upper flange» which means that the maximum permissible tension for the material of the muffle in the region of the upper flange is decisive for the maximum allowable weight of the muffle suspended from it . It can be noted at this point that »in those known annealing furnaces where the strip runs through the muffle from the bottom to the top, the muffle is exposed in its upper section at high temperatures» because that is where the strip to be heated has to reach its final temperature. This high temperature in the upper section of the muffle reduces the maximum allowable stress stress. In order, however, to achieve structural heights from 22 to 24 °, the wall thickness of the muffle should be increased progressively towards the top, so as not to exceed the tensile stress that is permissible for the material of the muffle. Secondly, the hottest point of the strip is also located on the upper side of the muffle. This most critical point of the strip is as a result subjected to relatively heavy loads due to the inherent weight of the strip located below it and due to the strip tension exerted on the strip. This also entails limitations for the maximum height at which a vertical annealing furnace of this type can be constructed. This is because if the oven is too tall, the strip will deform at its weakest point, ie on the upper side of the muffle The ovens as described in JP-A-2 282 687 and JP-A-4 225 780 have the greatest disadvantage that the mechanisms of counterweight counterbalance the expansion of the muffle. All this places limitations on increasing the production capacity, because the construction of a higher annealing muffle furnace is limited in technical terms. The object of the present invention is to provide a vertical annealing furnace in which a much higher structural height and / or production capacity can be achieved. This object is achieved according to the invention by a vertical annealing furnace for the continuous bright recoating of metal strip guided through the furnace consisting of a vertically arranged muffle having a strip inlet side and an outlet side of strip, as well as heating means to externally heat the muffle. the muffle has the freedom to expand in the longitudinal direction »in which the muffle is positioned in such a way that the entrance side of the strip is located on the upper side and the exit side of the strip is located on the lower side, the lower side of the muffle is fixedly supported in such a way that it is delimited downwards in the longitudinal direction and an expansion section is provided on the upper side of the muffle to withstand the thermal expansion in the longitudinal direction of mainly the muffle, The upper part of the muffle is connected to vertical support means for exerting a support force directed upwards on the muffle. In a vertical annealing furnace of this type, the strip is passed through the muffle from the top to the bottom. As a result »the hottest point of the strip is located at the bottom of the muffle» so this most critical point on the strip is subject to minimum load from its own weight. As a result, it is advantageously possible to build a higher vertical annealing furnace »as a result of which a higher production capacity can be achieved. Yes. in this structural form, the known fixed suspension of the muffle from its upper side must still be chosen "ie" with the possibility of expanding downwards "would appear the need to provide a section of expansion very sealed to the gas and resistant to high temperature between the outlet side of the muffle strip and the cooling section located below the last one or otherwise possibly allow the entire chiller section to move together with the muffle. In terms of construction, it is scarcely possible to carry out any of the two solutions, and even if it were possible, this would be extremely expensive. According to the invention, the muffle can be expanded upwards in the longitudinal direction. This is advantageous, because the chiller section can then be placed directly below the muffle without having to provide particular measures to withstand the expansion of the muffle in this transition region which is critical for the annealing process. The necessary expansion section can now advantageously be arranged on the upper side of the muffle, in the relatively cold section. The upper side of the muffle is connected to support means for exerting a support force directed upwards on the muffle. As a result »it is advantageously possible to relieve the pressure to a considerable degree on the most critical point of the muffle» let's say the part in the region of the outlet side of the strip, where the highest temperatures are required, and even advantageously to keep it virtually free of pressures. It is noted that US-A-2 594 876 discloses an apparatus for carburizing steel strips, consisting of a muffle furnace arranged vertically. The muffle furnace has one strip inlet side at the top and one strip outlet side at the bottom, so that the steel strip to be treated runs in a continuous process through the muffle in a downward direction. Heating means are provided to externally heat the muffle. In any way »US-A-2 594 876 does not show or mention measures for the problems of weight and expansion of the muffle. Instead »the muffle is reinforced and supported by steel structural members and supported by them on the floor. This is because the maximum possible structural height and operating temperature for this known type of muffle furnace are very limited, thus making it impossible to further increase the production capacity and to perform heating treatments at higher temperatures. The most preferred embodiments of the invention are specified in claims 2 to 10. The invention will be explained in more detail with reference to the accompanying drawings, wherein: Figure 1 is a diagrarographic illustration of a strip treatment device having a vertical annealing furnace according to the invention; Figure 2 is a sectional view of a preferred embodiment of part of the strip treatment device of Figure i; and Figure 3 shows, very schematically, an embodiment of the support means of the muffle with counterweights. In the embodiment shown in figure 1 of a strip treatment device having a vertical annealing furnace, it is possible to distinguish substantially four sections, namely a section 1 of the mention of strips, a heating section 2 »a chilling section 3 and a strip removal section 4. In the strip feeding section »the metal strip 10» in particular stainless steel strip »is fed in» onto said strip, if desired, a number of operations can be performed additionally, tap as »for example» welding or degreasing. The strip 10 is then stopped inside the heating section 2 »where the strip is annealed, preferably free of oxidation, in a vertical annealing furnace. Otherwise, "the oxidation of the strip during the annealing treatment could cause discoloration and a loss of quality" and can be avoided by annealing the strip in a chamber filled with protective gas. The heating section 2 »consists» in a known manner »of a so-called vertical muffle furnace. This muffle furnace is provided with a long cylindrical muffle 16, which is enclosed by a packing 17, in which the heating means are arranged to externally heat the muffle 16. In turn »the muffle 16 heats the strip 10 which is fed through it. This indirect heating of strip 10 is characteristic of a muffle furnace. Advantageously »at least the muffle 16 is filled with protective gas. After the strip 10 has been annealed in the muffle, it must be cooled very quickly to a predetermined low temperature. This takes place in the chiller section 3. Finally »the strip 10 passes inside the section of strip removal 4 where it can» for example »be post-treated, inspected and rolled up. According to the invention, the muffle furnace is positioned in such a way that the strip 10 to be annealed is introduced on the upper side of the muffle 16 and is discharged on the underside of the muffle 16. As a result, the The hottest, and therefore most critical, point of the strip is located at the bottom of the muffle 16. This has the major advantage that the hottest point of the strip 10 is subject to relatively little load of its own weight, as a result of which its inherent strength at this most critical point of the strip 10 will be exceeded less quickly. As a result, the muffle furnace can be of a higher design and the pitch proportion of the strip can be increased, as a result of which it is possible to achieve higher production. Because the muffle reaches very high temperatures, it will expand considerably in the longitudinal direction. This expansion is supported on the upper side of the muffle by flexible means 18 which are suitable for this purpose. In the embodiment shown in Fig. 2 of the muffle furnace, the muffle 20 is suspended movably within a package 21. such that the expansion can take place upwards. For this purpose, the muffle 20 is connected at the top to a flexible structure 23 of bellows. Advantageously »the bellows structure 23 is produced from a joint of expansion fabrics, which in particular consist, for example, of gas-impermeable Teflon-coated fabrics. This bellows structure 23 is so flexible that it can be compressed without great forces when the muffle 20 is expanded upwards. As stated, the annealing preferably takes place in a protective gas which, for example, consists mainly of hydrogen. The use of this protective gas must, for reasons of cost, be kept as low as possible. Even more. It is extremely dangerous if large amounts of protective gas could escape suddenly. For this purpose, the bellows structure 23. which is inherently impervious to gas, is incorporated, as an extra protection, into a steel case 24 enclosing a liquid seal.

Advantageously, the muffle 20 is connected in the upper part to supporting means 25 which exert a supporting force F directed upwards on the muffle 20. As a result, the muffle 20 can be balanced in such a way that the lower side of the muffle 20 which is connected in a manner against leakage of gas to the chiller section located under it, can be supported in a more or less "floating" manner. The supporting force F directed upwards can, for example, be exerted by means of counterweights which are connected to the upper side of the muffle 20. The load of the muffle 20 can be influenced by making the said counterweights more l geros or more heavy. The advantage of counterweights is that they are capable of operating virtually without failure and maintenance. In another embodiment, the muffle 20 is suspended in the upper part in a frame that is displaceable in the vertical direction. By then connecting the muffle 20 in the lower part to a censor 30. the downward force exerted by the muffle 20 can be measured. In particular, the control means may be provided to adjust the support force F exerted by the support means 25 as a function of a p-value measured by the sensor 30. If. For example, p passes beyond a specific minimum or maximum value. The frame can be moved in the vertical direction until it returns to within the established limits. In the counterweights mode, consideration can also be given to adjusting the counterweights (making them lighter or heavier) as a function of p, which can be carried out either manually or automatically. An optimum load condition for the muffle 20 can thus be maintained using either the vertically adjustable frame and using the counter weights. A mixed form of support means is also easily possible. Consideration can be given to a stationary load using counterweights on which an adjustable load is superimposed. By virtue of the expansion section in the upper part of the muffle and the adjustable support, balanced from the upper side of the muffle, it is possible to keep the lower part of the muffle virtually pressure free. For this purpose, the support means compensates for the weight of the muffle and any other load on the muffle (for example, friction forces that occur as a result of the expansion). Advantageously »the measuring means are located in the lower part of the muffle, where the most critical section of the muffle is also located. Due to the very low and rapidly measurable load of the lower part of the muffle, if necessary it is still possible to allow a higher temperature in that region than in the previous techniques. This can also result in an even greater increase in production capacity. Figure 3 shows a modality of the support means in the form of counterweights. For this purpose, a flange 51 is welded to the upper section of the muffle 50. The flange 51 is connected to counterweights 55 via cables 53 and pulleys 54. The counterweights 55 thus exert an upwardly directed force on the muffle 50. If the muffle 50 is expanded upwards, the counterweights 55 can be moved downwards in their respective guides 56. At the same time, a section of bellows 58 which is incorporated in a water seal will be compressed. The gasket 60, the pulleys 54 and the upper side of the bellows section 58 are fixedly connected to a frame 65 which is resting on the ground. Due to the fact that the strip 22 passes through the muffle 20 from the upper part to the lower one, and therefore only has to reach its highest temperature in the lower part of the muffle, it is possible to advantageously select the temperatures a that the heating means heat the muffle 20 so that the upper part of the muffle is lower than that for the lower part of the muffle 20. This is because the upper part of the muffle 20 must support virtually all the inherent weight of the muffle 20. Selecting the temperature to be lower in that region, the muffle 20 can support a greater inherent weight in its upper part, as a result of which it is possible to redesign the muffle furnace to be larger and thus increase the production capacity considerably. The thickness of the walls of the muffle 20 will normally increase towards the top. By reducing the temperature in the upper part of the muffle 20, the thickness of the walls of the upper part does not have to be increased, or has to be increased to the lowest possible degree, and can nevertheless support a higher inherent weight. It is possible to preheat strip 22. in order to save energy and / or achieve a greater increase in production. The residual heat of the muffle furnace, for example, can be used for this purpose. For this purpose, in Figure 2 a preheating section 35 is provided in the raising part of the strip 22. An upper chamber 37 with two upper cylinders for guiding the strip 22 is placed between the preheater section 35 and the structure of bellows 23. In order to be able to repair »maintain or replace the muffle 20» it is important that it be possible to remove it from the gasket 21 quickly and easily. For this purpose »the package 21 is provided with a removable cover plate either on the top or on the side. Due to the fact that the chiller section 36 is located according to the invention on the lateral bottom side of the muffle 20, it can advantageously remain in place. In the prior art. in which the chiller section is located on the upper side of the muffle »the chiller section must first be dismantled before the muffle can be removed up out of the package. The muffle 20 in the vertical annealing furnace described in Figure 2 can be replaced as follows. By placing the upper chamber 37 with the two upper cylinders on a movable frame, it can be moved laterally. The bellows structure 23, together with the steel case 24, can then be lifted with the aid of fastening means, in such a way that the upper cover of the gasket 21 is released. The cover is removed and the muffle 20 can be removed from the package 21 also with the aid of fastening means. The connection, and therefore the supply, of protective (expensive) gas with a high hydrogen content is quickly limited to the current annealing process, ie to the chamber inside the muffle and the cooling section. In order to reduce protective gas losses and to improve the process conditions, special seals are provided in the region of the side entrance of the muffle strip and on the lateral side of the chiller outlet. In the part that rises from the heating section, if desired, a non-expensive protective gas with low hydrogen content can then be provided. This protective gas consists substantially. for example »of nitrogen, and serves to wash off any contaminant that enters along with the strip. Due to the considerably increased production capacity and the associated increasing speeds of the strips, it is of great importance "for the purpose of obtaining a good product" that the adherent layer of air is removed from the surface of the strip before the strip is heated. In the muffle furnace proposed here »a large prewash time is now advantageously available. This achieves a distribution of protective gas types that are supplied to several points on the heating section. According to the invention, a vertical annealing furnace is thus obtained in which a high production rate can be achieved with low costs due to the fact that the muffle furnace can be made larger than in the prior art. Furthermore, a very advantageous structure is provided to compensate upwardly the expansion of the muffle in the longitudinal direction.

Claims (1)

NOVELTY OF THE INVENTION REiviNP,? CAq? PES

1-- Vertical annealing furnace for continuous bright annealing of metal strips guided through the furnace, consisting of a vertically placed muffle having a side entrance strip and a side strip outlet, as well as heating means for heating externally the muffle, the muffle has the freedom to expand in the longitudinal direction »in which the muffle (20) is arranged in such a way that the strip inlet side is located on the upper side and the strip outlet side is located on the underside »the underside of the muffle is fixedly supported in such a way that it is delimited downwards in the longitudinal direction and an expansion section is provided on the upper side of the muffle to withstand thermal expansion in the longitudinal direction of mainly the muffle »the upper part of the muffle (20) is connected to movable vertical support means (25) to exert a direct support force a upwards (F) on the muffle (20). 2. Vertical annealing furnace according to claim 1 »further characterized in that the support force (F) exerted by the support means (25) is adjustable. 3. Vertical annealing furnace according to claim 1 or 2 »further characterized in that the supporting force (F) substantially compensates the weight of the muffle (20). 4. Vertical annealing furnace according to one of claims 1 to 3, further characterized in that the support means consist of counterweights (55). 5. Vertical annealing furnace according to one of claims 1 to 4, further characterized in that the support means (25) consist of a vertically movable frame in which the muffle (20) is suspended. 6.- Vertical annealing furnace in accordance with one of the lare referenced 1 to 5 »further characterized in that the lower side of the muffle (20) is connected to a sensor (30) to measure the downward force exerted by the muffle (twenty). 7. Vertical annealing furnace according to claim 6 »further characterized in that the control means are provided to adjust the support force (F) exerted by the support means (25) as a function of the measured value (p) by the censor (30). 8.- Vertical annealing furnace according to one of the preceding recitations »further characterized in that the muffle (20) is connected, on the strip inlet side, to a bellows structure (23) in order to form a flexible connection to media located in the downward direction thereof. 9.- Vertical annealing furnace according to one of the preceding claims, further characterized in that the heating means are designed to allow the temperature of the muffle (20) during the operation to be lower on the inlet side of the strip than in the the exit side of the strip. 10. A strip treatment device consisting of a strip feeding section (1) »a heating section (2) having a vertical annealing furnace according to one of claims 1 to 9» a section of cooling (3) located in the downward direction thereof and a strip removal section (4).