MXPA00005726A - Dross collecting zinc pot - Google Patents

Abstract

A zinc-coating pot for galvanizing steel strip has two levels along its bottom surface. The first, shallower level is located under a coating roll, thereby creating an area where the molten zinc-coating metal flow rate is relatively high. Dross particles remain suspended and do not accumulate on the bottom of the zinc-coating pot in this region. A second, deeper level is located to one side of the first level. This second level creates a space wherein the molten metal flow rate is less than the terminal velocity of the dross particles. This encourages sedimentation of the dross particles in this region. It provides an accumulation area for any bottom dross to be later removed by a dross removal mechanism, such as mechanical scoops or by pumping, without interruption to the coating process.

Description

CINC COOKER SCENE COLLECTOR BACKGROUND OF THE INVENTION This invention pertains to a coating pot for coating metal strips with a metal containing zinc. More particularly, it belongs to a dies pot formed to favor the sedimentation of slag from the bottom in a recollection area of the diespot so that the bottom slag can be contained until it is removed and then removed without interfering with the process. covering. The steel is coated with zinc to protect it against corrosion.

Zinc coatings can be applied by dipping or passing the steel article to be coated through a molten metal bath containing zinc. This process is referred to as "galvanized", "hot dip galvanized" or "hot dip galvanized". The process can be operated continuously when the steel to be coated is a strip, which is typically rolled on a roll. The strip is unrolled from the roller and cleaned, annealed and / or prepared in another way before entering the molten bath. It is directed under a coating roller that is submerged in the bath. After traveling under the coating roller, the strip comes out of the bath. During the coating process, slag can form in the molten bath. One form of slag, bottom slag, is predominantly delta phase (FeZn7) of zinc-iron intermeshers. The slag particles are slightly denser than the molten zinc. As they form in the galvanized bath, they are initially small and suspended by the movement of liquid currents in the zinc bath. However, the particles typically grow by Oswald's maturation. The particles settle to the bottom of the zinc coating pot after reaching a critical size. Once a significant amount of bottom slag accumulates, the turbulence, caused for example by the steel strips that pass through the bath, can remove particles accumulated in the bottom slag and bring them into contact with the steel strip. This results in defects in the final coated strip. The resulting defective product can be disposed of or sold as a low quality product. The slag is typically removed at regular intervals from the coating pot. Generally, it is removed by spooning it from the bottom of the coating pan. In order to do this, the coating operation has to be stopped during this removal process because the slag is deposited through the entire bottom of the coating pot. This downtime is expensive and inefficient in one operation of another continuous form. It would be preferable if the slag could be removed without interrupting the coating process in a manner that would not result in surface defects in the coated metal strip. There have been many efforts to minimize the bottom scum. For example, U.S. Patent No. 220,768, issued to orewood, January 21, 1879, discloses a two-level coating tank, wherein a first part of the tank is deeper than a second part of the tank. The shallowest part of the tank has deflctors in the upper part of the tank to collect "trash" or surface slag, which is a mixture of zinc metal, zinc oxides and iron-aluminum intermetallic particles-c c. The patent does not discuss the use of a two-level tank to treat bottom slag. Unlike the present invention, the coating occurs in both the deep and the shallower sections of the tank. U.S. Patent No. 2, 159, 297, issued to Shover, July 26, 1932, describes an apparatus for coating metal. The patent describes the use of a tube attached to the bottom of the coating chamber that allows the removal of slag seated in the bottom. It does not teach the use of a two-level tank to favor the sedimentation of the slag in a specialized recovery area, far from the coating area, so that the slag does not reduce the quality of the coating. U.S. Patent No. 4,275,098, issued to Gunji et al. On June 23, 1981, discloses a method and apparatus for continuously galvanizing steel strips by hot bath. The patent discloses a two-section coating pot wherein the first section, where the metal coating occurs, has an angled bottom with an opening in a second, deeper section. The purpose of the angle coating chamber is to allow bottom slag to fall to the deeper section where it is reacted with aluminum to produce surface slag. The slag-free bottom material is recycled back to the coating section and the surface slag is removed mechanically. The patent does not disclose the use of any means to remove the slag from the bottom of the deepest chamber; rather it requires the reaction of bottom slag with aluminum to produce surface slag. The patent also teaches the use of an impeller to increase the effects of agitation and increase the reaction of bottom slag with aluminum ßl, in contrast to the present invention, which requires a collection area that minimizes agitation. In addition, the slag will not slide down the inclined portion as suggested in the Patent; it stays where it falls. This means that the slag will not accumulate in the deeper section of the patented apparatus. The slag settles where the flow regime of the molten metal is slow. The patented apparatus, favoring mixing and flow through the deeper section, will not allow the slag to be collected there. The Patent of É. U. No. 4,476,805, issued to Higuchi et al., October 16, 1984, describes an apparatus for coating only one side of a steel strip with a molten metal coating. The patent describes a two-level casting pot. The patented apparatus is a spray coater, in contrast to the dip coating method of the present invention. The patent does not discuss the benefits of a two-level casting pot.

There is no suggestion that the slag is less likely to settle at the shallow end. Nor is there any suggestion that a deeper end promotes sedimentation. In addition, the coating on the patented apparatus must be stopped to remove the collected slag. This is in contrast to the present invention where the slag can be removed from the bottom while the strip is being coated. U.S. Patent No. 5,587,017, issued to Yamanaka et al. On December 24, 1996, describes a process and apparatus for producing steel sheets coated with metal. The patent teaches the use of a shallow portion in the coating tank below the pool roll to increase sedimentation in the deeper portions of the tank created by the raised portion. The present invention provides a shallower portion under the pool ridge and in front of the pool roller. It is important to keep a shallower area in front of the pool roll to inhibit sedimentation in that area. If the slag accumulates in front of the pool roll, the coating operation must be stopped for cleaning. With the present invention, it is favored that the slag settle only in the rear, deepest portion of the pot away from the pool roll so that it can be removed without interfering with the coating operation. This structure and its related benefit is not described or suggested by the Patent. In addition, sharp edges in the patented apparatus do not suggest the angled slope of the present invention. The angled slope is easier to clean - the cleaning equipment could break the sharp edges in the patented device.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a coating pot for coating metal strip with a zinc containing metal comprising a coating portion and a collecting portion, wherein the depth of the collecting portion is greater than the depth of the portion of coating, and where the collection portion is dimensioned and placed so that: a. the collecting portion is placed on one side only of the covering portion; b. the slag accumulates in the collecting portion; c. the metal containing molten zinc circulates in the collecting portion at a speed less than the terminal velocity of the slag; and d. The slag can be removed from the collecting portion without interrupting the coating process. The present invention also provides a coating apparatus comprising a coating pan with a coating portion and a collection portion, a coating roller and a slag removal mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a lateral elevation scheme of a coating pan of the present invention. Figure 2 is a schematic of the upper part of a coating pan of the present invention. Figure 3 is a rear elevation diagram of a coating pan of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY. As shown in Figures 1-3, the coating pot 10 of the present invention has a coating portion 12 and a harvesting portion 14. The collecting portion 14 is deeper than the coating portion 12 of the pot and is positioned on one side of the coating portion. Coating pots are well known in the art. Any stla design for coating in the present invention can be used, as long as the pot engages a covering portion 12 and a picking portion 14. Typically, the coating pots comprise a metal shell 16 coated with refractory bricks 18 and high temperature mortar (not shown). Preferably, the metal shell 16 is made of structural steel. The coating pot 10 of the present invention can be made of any material that has sufficient strength to contain the molten metal and can withstand the operating temperatures of the molten bath., dS about 420 ° C to about 482 ° C. A coating roll 20, typically suspended from a frame (not shown), is immersed in the molten metal of the coating pan. The metal strip 22 to be coated enters the molten bath in the coating pan 10, is wound around the coating roller 20, and then exits the coating pan 10 to continue for further processing. There is no limit to the types of coating rollers 20s and coating processes that can be employed with the coating part 10 of the present invention. Any coating process that includes zinc in the coating melt material in the d 10 pot of the present invention can be used. The coating pan 10 of the present invention comprises a coating portion 10, which is that portion of the coating pan 10 directly below the coating roll 20. The coating portion 12 is shallower than the collector portion 14 of the pot. The shallow depth of the coating portion 12 favors the upper molten metal flowing through the coating area. This greater flow minimizes the accumulation of slag in the bottom and favors that any particles that are formed remain suspended in the bath of molten metal. Due to this circulation, the molten zinc and slag particles migrate to the collecting portion 14. The coating pot 10 further comprises a reclosing portion 14, which is cotocked to one side of the reclosing portion. The collecting portion 14 has a depth that is greater than that of the coating portion. This deeper portion creates a place where the velocity of the molten metal coating is less than the terminal velocity of the slag particles. This favors the sedimentation of the slag particles in the collection area. The deeper section of the coating pot 10 also provides an accumulation area for bottom slag that has migrated from the coating area, so that it can be removed later by the slag removal mechanism without interfering with the coating . To promote sedimentation of the slag particles in the collecting portion 14, it is necessary to avoid creating turbulence in the collecting portion 14. Therefore, the collecting portion 14 should be free of any agitators, mixers or other devices that would increase the flow rate. The slag removal mechanisms are well known and may include mechanical spoons or a pumping mechanism. Preferably, the slag removal mechanism is a slag pump 24, such as that described in U.S. Patent Application Serial No. 08 / 792,922, Method and Apparatus for Removing and Recovering Slag from the Metal Bottom Melt During Galvanizing and Galvanizing, Meneicß, filed June 19, 1996, now U.S. Patent No. 5,961, 285, and incorporated herein by reference. Generally, the depth of the coating portion 12 should be minimized and the depth of the harvest portion 14 should be maximized. The shallowness of the coating portion 12 is limited by the coating equipment, such as the coating roll 20. The coating portion 12 must be deep enough to allow complete immersion of the metal strip 22 in the molten bath. Preferably, the coating portion 12 is from about 1m to about 2.5m deep. More preferably, it is approximately 2.1 m deep. The depth of the collecting portion 14 must be sufficient to reduce the velocity of the molten metal below its terminal velocity, where the slag particles can settle out of the molten bath. It is limited by the ability to remove the scum collected in the bottom. Preferably, the harvesting portion 14 is from about 1.3 m to about 3.3 m depth. More preferably, if a slag pump 24 is used to remove the collected slag, the collection portion 14 is approximately 15.2 cm deeper than the length of the pump. More preferably, the collecting portion 14 is about 2.8 m deep. Preferably, the ratio of the depth of the harvesting portion 14 to the depth of the coating portion 12 is in the range of about 1.1 to 1.5. More preferably, it is about 1.3: 1. Because the collecting portion 14 is on one side of the coating portion, the slag can be removed without interrupting that operation. Preferably, the collection portion 14 is positioned behind the pan portion 12 of the pot. This means that the collection portion 14 is farther from the strip that comes out of the molten bath than the strip that enters the molten bath. The top 10 of the cover also comprises a transition area. The transition area is positioned between the cover portion 12 and the cover feeder collection portion 14. It can be in any form, for example, the transition area can be a 90 ° step from the shallower coating portion 12 to the deeper collection portion 14. Preferably, it is a slope 26 at an angle. More preferably, the slope is approximately 45 ° or less, measured from the horizontal. More preferably, the slope is approximately 30 °. Slag spoons can more easily clean an angled slope 26; slope 26 at an angle is less likely to be cascaded by a spoon when the slag is shoveled around than it is with sharper edges of a 90 ° scaflon.

Claims (12)

1. CLAIMS 1. A coating pot for coating metal strip with a metal containing zinc comprising a coating portion and a harvest portion, characterized in that the depth of the collection portion is greater than the depth of the coating portion, and where the collection portion is sized and positioned so that: a. the collecting portion is placed on one side only of the coating portions; b. the slag accumulates in the bottom of the collecting portion; c. the molten metal containing zinc circulates in the collecting portion at a rate less than the terminal velocity of the slag; and d. The slag can be removed from the recollection portion without interrupting the coating process.
2. 2. A coating pot according to claim 1, wherein the collecting portion is positioned behind the coating portion.
3. 3. A coating pot according to claim 1, wherein the ratio of the depth of the recollection portion to the depth of the coating portion d is approximately 1.1 to approximately 1.5.
4. 4. A coating pot according to claim 1, wherein the ratio is approximately 1.3: 1. A coating pot according to claim 1, wherein the coating portion is from about 1 m to about 2.
5. 5 m depth and the collecting portion is from about 1.3 m to about 3.3 m depth.
6. 6. A coating pot according to claim 5, wherein the coating portion is approximately 2.1 m in depth and the portion of the co-collector is approximately 2.8 m in depth.
7. 7. A coating pot according to claim 1, further comprising a transition area positioned between the covering portion d and the collecting portion, wherein the transition area is inclined.
8. 8. A coating pot according to claim 7, wherein the transition area is inclined at an angle of approximately 45 ° or less from the horizontal.
9. 9. A coating pot according to claim 8, wherein the transition area is inclined at an angle of approximately 30 °.
10. 10. A coating apparatus comprising: a coating pot comprising a coating portion and a collection portion, a coating roller suspended over said coating portion and a slag removal means, characterized in that the depth of the portion of collection is greater than the depth of the coating portion, and where the collection portion is sized and positioned so that: a. the collecting portion is positioned on one side only of the covering portions; b. the slag accumulates in the bottom of the collecting portion; c. the molten metal containing zinc circulates in the collecting portion at a speed less than the terminal velocity of the slag; and d. the slag can be removed from the reclotting portion without interrupting the coating process.
11. 11. A coating apparatus according to the claim 10, wherein said slag removal means is selected from the group consisting of a ladle or slag pump.
12. 12. A coating apparatus according to claim 11, wherein said slag removal means is a slag pump.