MXPA98001884A - Method and apparatus for operating a system for galvanizing ac sheet - Google Patents

Abstract

A method and apparatus for galvanizing steel sheet in a single immersion galvanizing pan of the coreless type of electric induction ("coreless"), with greater flexibility to frequently change the composition of galvanizing alloy, and also with higher productivity and lower costs of investment and operation compared to the current practice of operating plants with two pans in continuous heating, one in operation and another in standby. The paila has associated a plurality of molds of ingots with capacity for all the contents of the paila and a pumping system to empty said paila of the galvanizable alloy and fill said ingots, also has a transport system to replace the contents of the paila with galvanized alloy ingots of a composition different from the one in operation. Part of the new galvanizing alloy can be previously melted in a furnace smaller than the stack. Preferably the battery has a heated cover while it is being emptied or filled to avoid damage to the refractory of the same.

Description

F ^ METHOD AND APPARATUS FOR OPERATING A SYSTEM FOR GALVANIZING STEEL SHEET.

BACKGROUND OF THE INVENTION Galvanizing of steel sheet is normally performed by immersing said steel sheet in a liquid metal bath, typically zinc, aluminum or mixtures of both, together with other additives, to form a thin layer of metal on the sheet. 15 Galvanizing plants normally process continuous steel sheet which is unwound at one end of the plant and cleaned, prepared and immersed in the hot liquid coating metal, cooled and rolled up at the other end of the sheet. plant. All the equipment and process are designed and operated in such a way that the surface quality of said sheet is optimum and with the aim of processing large sheet lengths without interruption. Most of the galvanizing plants, currently in operation, use two pails of the type of electric induction channel to maintain a bath of meta! hot liquid for the coating (coatings based on • zinc or aluminum), one of the pails is in operation and the other in a standby position. This type of induction pans can not be emptied and refilled very often because as a result of its design the coils of 40 induction can be damaged and lost in this operation. Consequently, they always remain filled with liquid metal, consuming electricity during 45 the waiting times at levels of the order of 8,400 kwh per day for a paila with a capacity of approximately 100 metric tons. The continuous heating of both pails can last several years. The common practice is to make several runs to produce galvanized sheet with two different HE alloys, according to the production schedule. The duration of each run for each alloy normally varies between 5 and 15 days. Some plants also have a pre-melting furnace, gas-operated type or electric induction type to melt solid zinc ingots and fill the pans in operation. Another variant of the previous art (with alternating casting by means of coreless induction furnaces) is illustrated in US Patent No. 5, 354,970 (incorporated herein by reference). The flexibility of the current galvanizing plants to carry out short runs or to change the metal coating frequently is very limited and the two-pail scheme is expensive (both because of the double capital cost and the cost of the additional heating expense ). To change the composition of the coating, the operating pan is moved to the standby position and the other pan is moved to the operating position. Another alternative is to move the sheet that is submerged in the pan in operation to a second position where it is submerged in the other pan. If three or more different coatings are desired, the The prior art practice of having a separate pail for each different coating composition is not practical and would be very expensive. The present invention overcomes the disadvantages of the prior art and uses a single immersion pan of the "coreless" type of electric induction, which is also capable of melting solid metal ingots and forming the liquid bath 40 of galvanized quickly without the need to maintain a second galvanized paila pending with the consequent costs of electrical energy and the financial cost of the second paila). If it is desired to have more than three different coating compositions, the invention provides a way to have solid ingots of each composition ready to be used, while in the Prior art practice can only contemplate two different compositions at the same time, DETAILED DESCRIPTION OF THE INVENTION.

Referring now to the figures, in figure 1, the numeral 10 designates in general form a galvanizing system typical of the prior art having two galvanizing pans, normally of the induction channel type, although there are some installations that use pans of the type of electric induction without core ("coreless"). The pan 12 is in the operating position, and the pan 14 is in the standby position. The steel sheet 16 is passed through the bath of melted coating 18 having a first composition, for coating its surface with the metallic coating. A protective channel 20 is generally provided for the treated steel sheet before it is immersed in the molten bath. When a different coating composition is desired, the pail in operation 12 moves and is replaced by the standing pail 14 having the coating the desired composition. These maneuvers require handling by means of heavy equipment 24 (paila 14 is shown suspended from a traveling crane by cable 25), which results in a loss of important production, given the weight of the pans and the molten bath). The costs of the facilities, mobile equipment, maintenance, operation, etc. They are tall. A used alternative by the prior art to prevent the movement of the pans, is to move the position of the protective channel and its associated equipment with the steel sheet 16 s fg operating position 12 to the position of the holding pail 14 (with the channel 40 indicated by dotted lines by the numeral 20 ').

The present invention offers many advantages by means of the surprising 45 simple (but so far not obvious) alternative to operate the galvanizing system as illustrated in figures 2 and 3. To change the composition of the metal coating, first empty the single galvanizing pan 50, 50 having a coating bath 52 of a first composition, by means of pumping means and ducts 54, and filling a plurality of molds 56 for storing said coating 52 for later uses. Preferably, an insulated cover 51 is provided to cover the pan 50 and avoid a thermal shock by rapid cooling which would damage the refractory that internally covers the paila while emptying. Optionally, cover 51 can be provided with heating elements 57, electric or gas burners, to maintain said pan at a predetermined temperature and to avoid the natural cooling thereof during the periods of time when the pan is empty or when it is melting ingots. As illustrated in figure 3, the coreless induction pan 50 (coreless), with Tp ability to melt solid ingots of galvanizing coatings, is is fed with ingots 58 having a second composition by means of a crane and transport system 53. The ingots 58 are melted in the only paila 50 and it is immediately put back into operation. Different galvanizing coatings can be stored as solid ingots, indicated by numerals 60 and 62, ready for quick and convenient use. This flexibility is not possible in the prior art operating practices with liquid coating baths. If desired, for a start * P 35 more efficient melting operation, a pre-melting furnace 64 can be added to the system, either heated by gas or by electricity, to melt a relatively smaller amount of a second galvanizing coating. The crane 53 of the transport system typically moves ingots of about one ton 56, 58, 60 or 62 and directly positions them in the pallet 50. If a pre-melting furnace 50 is used, smaller bars or bars are used , approximately 25 kilos and melt in the furnace and then the molten coating can be transported by means of a pump and ducts 66. 50 Although the invention has been exemplified in its application to the galvanizing of steel sheet and in the case of alternating two different compositions of ^^ galvanizing coating, the invention is easily applicable to the galvanizing of other types of metal products, and also applicable to the case in which want flexibility to switch between three or more galvanizing coatings of different composition. It should be understood, of course, that the above description is only illustrative and that numerous changes can be made to the structure of the described system and to the operating conditions. > - FIELD OF THE INVENTION The present invention relates to an improved method and apparatus for operate a galvanized steel sheet production system. More particularly, the invention relates to a method and apparatus for galvanizing steel sheet in a single dip galvanization pan of the coreless induction type ("coreless"), with high flexibility for frequent changes of galvanizing alloys, whereby the productivity of the single-blade plant and the investment costs are considerably reduced, in contrast to the current practice of operating plants with two galvanizing pans, one in operation and the other in standby. twenty OBJECTIVES OF THE INVENTION. It is therefore an object of the invention to provide a process for Galvanizing steel sheet in a system that allows changing alternately from one to the other between at least two different galvanizing coating compositions but using only one blade of the electric induction type without core ("coreless"). It is another object of the invention to provide a method of galvanizing steel sheet in a system that has lower investment and operating costs and that has high flexibility to alternate the composition of the galvanizing coatings, which can be easily extended to three or more coatings. It is another object of the invention to provide an apparatus for galvanizing steel sheet 25 in a system that has lower investment and operating costs and that has a high flexibility to switch from one to the other between two (or more) different compositions of galvanizing coatings. . Other objects of the invention will be apparent or will be pointed out below.

In accordance with the present invention, the objectives of the same T loo? providing a method of operating a system for galvanizing steel sheet having a single dip galvanization pan of the coreless electric induction type ("coreless"), where said system has a higher 40 flexibility to change the composition of the galvanizing coating without needing a second stand-up galvanizing pan; and in which said sheet 45 steel is introduced into a galvanizing coating bath with a first composition under controlled conditions to form a coating on the surface of said steel sheet and in which in order to change the composition of the metal coating, said method comprises emptying said composition. single galvanized pallet transferring said first liquid composition to ingot molds; introducing solid ingots of a second galvanizing composition and melting the ingots in said single galvanizing pan, thereby forming a molten bath with a second composition different from the composition of the first bath; and operating said system with said second molten bath until a new composition for the galvanizing coating is desired, so that the investment and operation costs are lower when compared with the costs of galvanizing systems having two galvanizing pans.

The objects of the invention are also achieved by providing an apparatus for galvanizing steel sheet which has a greater flexibility to change the * composition of the galvanizing coating without needing a second galvanized stand 20; which comprises a single immersion galvanizing pan of the type of electric induction without core ("coreless"), and where said The system comprises means for emptying said galvanizing pan by transferring a first molten galvanizing coating to ingot molds; means for introducing solid ingots of a second composition to said palette of galvanized to form a molten bath of a second galvanizing coating; whereby the apparatus of this invention is simpler and has lower investment and operating costs compared to the costs of galvanizing systems with two galvanizing pans.

BRIEF DESCRIPTION OF THE DRAWINGS. In this specification and in the accompanying drawings, they have been illustrated and described some preferred embodiments of the invention and various alternatives and modifications to them have been suggested; but it should be understood that these changes and modifications can be made within the spirit of the invention. The variants described here have been selected and included for illustration purposes so that others versed in the art can understand more The invention and the principles of the invention are easily possible and are thus able to be modified in a variety of ways, each one as best suits the * conditions of a particular use. Figure 1 shows a schematic diagram of a galvanizing system of the prior art as it is typically operated at present. Figure 2 is a schematic diagram of one of the process steps for changing the molten coating into a single dip galvanizing pan by pumping the molten coating from the pan to the molds of emptying / storage, Figure 3 is a schematic diagram of another of the process steps for changing the molten coating into a single immersion pan showing other ingots of galvanizing coatings of different compositions ready to be used, and a batch of ingots being melted in the pan. 40

Claims (7)

R E I V I N D I C A C I O N S Having sufficiently described my invention, I consider it a novelty and therefore I claim as my exclusive property, what is contained in the following clauses:

1. A method to operate a system for galvanizing steel sheet that has a single immersion galvanizing pan that incorporates an electric induction heater of the type that has no core ("coreless") and that provides * 15 an improved flexibility to change at low cost between applications of two or more different galvanizing coatings compositions without needing a second galvanizing pan to store and have available in liquid state each different composition; which comprises making successive runs of galvanized steel sheet under controlled conditions through 25 molten baths of different composition, being different successively from the composition of the immediately preceding bath; change the composition of the molten galvanized coating by emptying said single galvanizing pan > 30 transferring its content of galvanizing bath to molds of ingots; introducing solid ingots of a second galvanizing coating having a composition different from that of said first galvanizing bath; and operating said system with said second galvanizing bath until it is desired to change the bath to a new composition; so the investment and capital costs are 40 decrease when compared to the costs of systems with two galvanizing pans.

2. A method according to claim 1 further comprising melting a relatively small amount of said second galvanizing coating prior to use in a separate melting furnace and introducing said second galvanizing coating preformed to said single galvanizing pan for finish melting the ingots of said second galvanizing coating 5.

3. Apparatus for galvanizing steel sheet with improved flexibility and which is able to change frequently the composition of the galvanizing bath at low cost, between applications of two or more compositions of galvanizing coatings without needing a second galvanizing pan outside of 15 operation to keep in a liquid state and ready to use another galvanizing bath of composition different from that in operation, which comprises * a single galvanizing pan that has a heat source of the type of electric induction without core ("coreless"); a plurality of ingot molds; a liquid metal pumping system capable of emptying said bucket 25 galvanizing by transferring said galvanized melt bath of a first composition to one or more of said ingot molds; a transport system capable of selectively moving solid ingots of a different composition that were formed from a galvanizing bath previously in said galvanizing pan, and of reintroducing said ingots to said galvanizing pan to form a new molten bath of galvanizing coating in said unique paila.

4. Apparatus according to claim 3, wherein said

The transport system is capable of introducing a new source of galvanizing coating to the single galvanizing pan as a complement to an existing galvanizing bath or as a new galvanizing bath of different composition. Apparatus according to claim 3, further comprising 50 a pre-melting furnace, of a smaller size in relation to said galvanizing pan, for melting a first quantity of a galvanizing coating of different composition, and a device for introducing said amount already - * cast to a single galvanizing pan to help initiate a more efficient fusion in said pan of the remaining ingots of said galvanizing coating of different composition that have been introduced in said pan.

6. Apparatus according to claim 3, further comprising 10 a cover for covering said single galvanizing pan to avoid a thermal shock of the internal coating of refractory material of said pan while said pan is partially filled with liquid galvanizing coating, * including when said paila is empty and when the ingots are melted in it. Apparatus according to claim 6, further comprising 20 elements providing localized heat in said cover to maintain the temperature in a suitable range to avoid damage to the refractory material 25 when the pan is being emptied or filled with galvanizing coating, *