DE1233692B - Process for the continuous heat treatment and subsequent hot-dip galvanizing of strip material - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

C23c

GERMAN

PATENT OFFICE

EDITORIAL

Int. σ .:

German KL;

Number. 1233692

File: K 31714 VI b / 4 «b Date: April 17, 1957 Release day: February 2, 1%?

CMc invention relates to a method for continuous heat treatment and subsequent hot-dip galvanizing of strip material made of ferrous metal, e.g. B. steel band or wire

It is known. Strip material for hot-dip galvanizing continuously, initially by two lying one behind the other in the direction of movement of the belt To lead blribiider and to it between the two pictures by electrical resistance heating Heat, the first lead bath for preheating, the second lead bath for cooling the additional Electrically heated metal strip is used to the temperature of the zinc bath, which is then passed through by the metal strip. Here it is necessary to use the lead baths as power supply, the BarKlraatcrial in the area its * largest Heating between the swimming pools by using tube filled with neutral or reducing gas direct to it against air contact and oxidation protect, and, moreover, low-voltage electricity must be available to prevent local burns. tings of the metal strip tlurcb arcing to avoid standing between the surfaces of the unier stream BlcibSdcr and the MctaHband.

It is also known to use steel belt before heating and galvanizing by an alkali bath and, if given, also by a subsequent acid bath to clean it from adhering wax and to achieve a better hold of the zinc coating. Kc heating of the steel belt takes place after cleaning in an annealing furnace, behind which the highly heated metal strip has a long cooling zone must run through a pipe filled with nitrogen, in which it is cooled to the temperature of the galvanizing bath.

The invention is directed to the preparation of the tape material! ouch! to simplify galvanizing and cleaning and heating as well the subsequent cooling to the temperature of the zinc bath in one operation and one container To be carried out in such a way that the strip material is not exposed to any air circulation during cleaning and heating and requires neither an electrical resistance device nor an annealing furnace The simplified treatment is achieved by the fact that the tape material for jamming and cleaning at the same time by a molten metal bath of sodium, potassium, lithium or a mixture of these metals and 2A) Cooling down to zinc-plated metal is carried out in the reverse direction through the alkali metal bath. In the process of galvanizing, go ahead

Process for continuous Wirrnebehwdeln and subsequent Hot-dip galvanizing of strip material

Register

John D. Keller, Pittsburgh, Pa. (V. St. A.)

Represent

Dipl.-Ing. G. Wcinbauscn, patent attorney, Munich 22, Wtdenmaveratr. 45 Named as inventor: John D. Keller, Pittsburgh, Pa. (V.St.A.)

Heat treatment in a molten bath made of alkali metal at different temperatures

»« Metal, the cleaning of the strip material is so intensive that in most cases a flux is used to apply the Zinc coating is dispensable In a preferred embodiment of the method according to

It is the invention of the strip material before galvanizing in a protective gas atmosphere additionally by a Roller straightening machine or a KaltnachwalzweTk, because this treatment of the heated and cleaned tape malcrial a compensation of the Gcfugcs

3 »causes, which results in an increased material strength.

When you leave the alkali metal bath that will Tape material has been largely freed from the adhering alkali metal, but it has become solid Adhesion of the zinc coating proved to be advantageous,

$ 5 when it has cooled to the decomposition temperature Tape material still a thin film of alkali metal bcb & lt and with this film-like coating in since $ anchoring bath is conducted. The method according to the invention is according to '

«O related to those in the drawing illustrated treatment devices described in more detail, namely shows

F i g. 1 shows a vertical longitudinal section through a casting and galvanizing plant according to the invention, F i g. 2 m schentatecber representation just part of the Plant with one between the alkali metal bath and roller straightener arranged in the galvanizing bath and Fig. 3 and 4 modified designs as the same

S »chen part de" Investment, which is verseben in Fig. 3 with RkhtroUen, In Figure 4 with CMEM skin pass or Kaltoachwalzwcrk.

mmm

F i g. 1 shows an annealing chamber 1 which contains a bath 2 of molten alkali metal, such as sodium, potassium, lithium or mixtures of these metals. In front of this chamber, the strip material 3 to be annealed, driven by rollers 4 and 5, runs in the direction of the arrow to an inlet opening of the annealing chamber, which is sealed with sealing rollers 7 resting against the strip material. B. is introduced through an inlet pipe la above the level of the molten liquid in order to maintain a neutral atmosphere in the container. The band material 3 is guided through the molten metal with the aid of drums 8, 9 and 10 and through a drum 11 in such a way that the band moving forward and the band moving backward 3 are kept at a small distance from each other and the bands are guided through openings 12 between the partition walls 13.

The partition walls 13 are preferably, without absolutely necessary, provided to the longitudinal migration of the molten liquid caused by the viscous behavior as a result of the movement of the band is due to the melt liquid, and further to reduce the heat conduction in in a horizontal direction from one part of the bathroom to the other. The zones between the Partition walls can be considered as zones of different temperatures 14, 15, 16, 17 and 18, which are heated or cooled with the help of tubes 19, 20 and 21, in which electrical heating elements or a gas flame is provided for heating or in which cool gas is provided for cooling is blown in. Since the separated zone 14 is closest to the entry side of the strip to be glowed is located, it can be either with a heating medium of low temperature or a cooling medium are supplied, which is fed through lines 19 arranged in it, depending on it for adjustment of the emerging strip to the desired temperature is required. Since the tape is to moving the hot end of the annealing chamber, zone 17 can be heated to a much higher temperature, while zone 18 has the final annealing temperature, so that strip 3 progressively moves out of a zone low temperature moves to zone 18 with the highest temperature in which it is annealed, whereupon it is followed by zones with gradually decreasing temperature in the sealed chamber 1 is returned.

After exiting the bath 2 of molten alkali metal, the band passes between wipers 22 and two sealing rollers 23 through and into a chamber generally designated 24, through which it is conveyed by means of drums 25, 26 and 27 to a channel 28 leading to the galvanizing tank 29 leads.

The rollers 25 and 26 act as pinch or drive rollers, which serve to pull the tape through the To pull the annealing chamber while the pinch rollers 4 and 5 pull the tape to the inlet of the annealing chamber. The rollers 25 and 26 can either via a slip clutch from the same motor or from a different power source than the rollers 4 and 5 are driven to compensate for the To create thermal expansion of the tape as it passes through the sodium bath, or preferably it can the rotational movement of the rollers 25 and 26 can be controlled so that a constant tension is maintained in the band emerging from the annealing chamber, which is achieved by using a the usual voltage regulating devices can happen, which, since they are known per se, not here are described in more detail.

In the chamber 24 there is a protective gas atmosphere consisting of an inert or reducing atmosphere Gas that is introduced through an inlet line 26 "

to conducts, for which is made up of the molten metal belt moving to the galvanizing tank, so that the chemically pure surface of the belt, the generated by the action of the sodium bath, is maintained until the tape is in the zinc bath enters the container 29. The walls of the chamber 24 and channel 28 are preferably insulated and can with heating means either inside the chamber or outside it, but between the chamber wall and the insulation must be provided,

ao to prevent the temperature of the strip between its exit from the annealing chamber and its entry into the galvanizing bath drops significantly. In the embodiment shown, the Heating means shown as electrical band heating elements 24 a.

The end 28 a of the channel 28, which leads to a galvanizing bath tank 29 leads, is suitably made of a material that is resistant to attack by molten zinc, and preferably immersed in a zinc bath 29 a to a depth which is sufficient for a liquid seal Form against the escape of gas, however, can optionally directly above the level of the molten zinc ends up without being immersed in the same.

The arrangement of the annealing chamber containing the molten sodium is not limited to, for example The horizontal type shown in Fig. 1 is limited, but can also be vertical or inclined be.

Since it is sometimes desirable to have an atmosphere in the chamber 24 which consists of a weakly reducing gas that contains about 10% hydrogen or even a hydrochloric acid vapor Containing gas mixture and there in those cases in which on the top the zinc bath at the point where the tape enters this, a flux is used, it can be done that hydrochloric acid escapes and enters the channel 28, and furthermore these gases do not enter the sodium containing chamber 2 α are allowed to enter because of their violent reaction with sodium, the inflow of inert gas through the inlet 7 a into the chamber 2 a through a pressure-sensitive regulator Usually controlled in such a way that the gas pressure above the sealing rollers 23 is always slightly is lower than the gas pressure below these rollers, which prevents gas backflow which could otherwise enter by leaking past the sealing rollers 23.

The strip 3 is guided through the galvanizing bath in the container 29 by means of drums 30 and 31 and then passed out of the bath through a drum 32, from which it is fed to a reel or is directed to another treatment device. The galvanizing tank is with suitable insulating walls 33 and burners 34 are provided in the usual manner and do not form part of the invention. Upper

half of the container, a vent 35 is arranged for discharging the vapors.

For those belt qualities in which a greater hardness and rigidity is desired than can be achieved without consolidation, means for consolidating the material or tape can be provided be e.g. B. the roller straightener shown in Fig. 2, in which the rollers 36, between through which the tape is passed, bend the tape successively in opposite directions. This roll straightening machine is then arranged in the chamber 24 between the annealing chamber and the galvanizing chamber, as in FIG. 3, where instead of Roller straightening machines clamping roller pairs 25, 26 or 38, 39 can be provided, of which the the latter pair driven at a slightly higher speed than the pinch rollers 26, 27 is to cause an elongation of the tape by tension with a few percent of its length. Such a consolidation device is also arranged in the protective atmosphere of the chamber 24.

If an even stronger consolidation is desired, the strip can be on its way to the galvanizing bath from the chamber 24 through the rolls 40 of a cold re-rolling mill of conventional design, as in FIG F i g. 4 shown. The rolls of the cold re-rolling mill are insulated within a gas-tight Housing 41 arranged, wherein preferably heating elements 42 are provided to the housing and to keep the rollers located therein at a temperature which is sufficiently high to to prevent the belt from cooling down. In the mentioned housing and in the channels can either a non-oxidizing atmosphere, such as nitrogen, or a weakly reducing atmosphere Atmosphere. When the tape is in the manner described in a protective gas atmosphere solidifying after annealing rather than after the strip has been galvanized, there is less danger for the formation of cracks in the zinc coating. However, if the solidification is not higher than can be achieved without cracking the zinc after the coating has been applied it may be more practical to carry out the cold re-rolling after galvanizing.

In the operation of the apparatus described above, that is usually prior to galvanizing Immersion in acid and the need to set the tape to 95 ° C or below after annealing to cool off. Furthermore, through the use of the simple and compactly built Container for the molten metal bath made of sodium, potassium, lithium or a mixture of these Metals the large, expensive furnaces that require flammable protective gas atmospheres and currently used, replaced.

Because of the extremely high thermal conductivity of the molten metal bath of sodium or the like, only a short conveying distance is required for the belt through the bath and at the same time the heating of the belt to the annealing temperature and its subsequent cooling to about 425 ° C is made possible. If z. B. in the arrangement according to F i g. 1, the molten metal is held in the zone 14 to 425 ⁰ C, the strip enters the annealer through a series of temperature zones in a high or Glühtemperaturzone 18 a in which the temperature of the molten bath can 730 ⁰ C or higher.

When the strip from zone 14 reaches the high-temperature zone 18 at a temperature of about 425 ° C., it moves in close proximity to the returning strip emerging from the high-temperature chambers 17 and 18, and because of the high thermal conductivity of the sodium, it quickly removes heat from the annealed Tape, which travels to the coolest zone 14 and from this into the neutral chamber 24, where it has a temperature of about 425 to 480 ⁰ C, which is approximately the same temperature as that of the molten zinc bath in which it enters. During this conveying movement from the annealing chamber to the galvanizing chamber, the belt is protected against oxidation, so that it retains its chemically pure surface that it obtained from its contact with the molten sodium annealing bath, the fat, carbon impurities, the iron oxide surface film that is always on the Surface of the supplied tape is present, even if it is very thin and practically invisible, or completely removes other foreign objects. The metallic steel surface that is actually exposed in this way will immediately alloy with the zinc when the strip enters the galvanizing bath, so that no flux is required for galvanizing.

Furthermore, it is not necessary that the mopping pads 22 and the sealing rollers 23, which are so formed can be that they exert a wiping or squeezing effect on the surface of the belt, and form a seal for the protective gas atmosphere in the chamber, every trace Remove the sodium from the tape before it enters the zinc bath, as the sodium in the during the temperature reached during the annealing process wets the steel surface, which is advantageous in that it the subsequent formation of the zinc coating is supported as if a weak film of sodium or other metals of the type mentioned remained on the strip as it entered the zinc bath is, the wetted area supports the initial alloy or bond of the zinc with the steel. Because only a very thin layer of zinc-iron alloy is required to bond the zinc to the steel, a small percentage of aluminum can be present in the zinc bath, as is known from continuous hot-dip galvanizing can be used to prevent the alloy layer from growing.

Since the two strands of the tape, of which one is heated and the other is cooled, move in opposite directions approximately parallel to one another and preferably closely adjacent to one another, because of the extremely high thermal conductivity of sodium, that part of the heat which is required is the To increase the temperature of the strip from 425 ° C to the annealing temperature, which is usually between 565 and 730 ⁰ C, recovered so that the annealing device only needs to be supplied with that heat that is necessary to raise the temperature of the strip from room temperature to about 425 ° C, which corresponds to a very considerable saving in fuel or electrical energy. Furthermore, because of the much smaller size of the sodium annealing device and because of the much lower average internal temperature, the heat losses through the walls of the annealing device are reduced to a small

newly reduced fraction of the losses incurred in the extremely large gas-filled continuously operating annealing devices of the type previously used occur.

Patent claims:

1. Process for the continuous heat treatment and subsequent hot-dip galvanizing of Strip material made of ferrous metal, in which the strip material to achieve the desired heat treatment temperature is first carried out by successive zones of increasing temperature Molten metal bath out, then in a protective gas atmosphere to galvanizing temperature is cooled and finally passed through the galvanizing bath, characterized in that the strip material for heat treatment and simultaneous cleaning by a molten metal bath of sodium, potassium, lithium ao or from a mixture of these metals and for

Cooling to galvanizing temperature is carried out in the opposite direction through the alkali metal bath.

2. The method according to claim 1, characterized in that the strip material before Galvanizing in a protective gas atmosphere is also carried out through a roller leveler or a cold re-rolling mill.

3. The method according to claim 1 or 2, characterized in that the strip material according to Passing through the alkali metal bath adhering alkali metal down to the remainder of a thin one film-like coating of alkali metal is stripped off.

Considered publications: German Patent No. 702,976; U.S. Patent No. 2,592,282; "Chemisches Zentralblatt", 1944/1, p. 1323; Paper on a paper by H. Simon in »Chem. Age ", 48,481.

1 sheet of drawings

709 507/337 1.67 Q Bundesdruckerei Berlin

Claims (3)

newly reduced fraction of the losses that occur in the extraordinarily large gas-filled, continuously operating annealing devices of the type previously used. Patent claims: 1. Process for the continuous heat treatment and subsequent hot-dip galvanizing of Strip material made of ferrous metal, in which the strip material to achieve the desired heat treatment temperature is first carried out by successive zones of increasing temperature Molten metal bath out, then in a protective gas atmosphere to galvanizing temperature is cooled and finally passed through the galvanizing bath, characterized in that the strip material for heat treatment and simultaneous cleaning by a molten metal bath of sodium, potassium, lithium ao or from a mixture of these metals and for Cooling to galvanizing temperature is carried out in the opposite direction through the alkali metal bath. 2. The method according to claim 1, characterized in that the strip material before Galvanizing in a protective gas atmosphere is also carried out through a roller leveler or a cold re-rolling mill. 3. The method according to claim 1 or 2, characterized in that the strip material according to Passing through the alkali metal bath adhering alkali metal down to the remainder of a thin one film-like coating of alkali metal is stripped off. Considered publications: German Patent No. 702,976; U.S. Patent No. 2,592,282; "Chemisches Zentralblatt", 1944/1, p. 1323; Paper on a paper by H. Simon in »Chem. Age ", 48,481. 1 sheet of drawings 709 507/337 1.67 Q Bundesdruckerei Berlin