US2794630A - Apparatus for heat treating strip material - Google Patents

Description

- June 4, 1957 c. A. TURNER, JR

APPARATUS PoR HEAT TREATING STRIP MATERIAL Filed Dec. 12. 1951 w INVENToR. CHARLES A. TURNER JR. BY/Z o FIG.

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ATTORNEY.

United tates Fatent 2,7 94,630 Y APPARATUS FR HEAT TREATING STRIP MATERIAL Charles A. Turner, I'r., Philadelphia, Pa., assigner to Selas Corporation of America, Philadelphia, Pa., a corporation of Pennsylvania Application December 12, 1951, Serial No. 261,311 3 Ciainis. (Cl. 26d-S) The present invention relates to the continuous heat treatment of strip or strand material, and more particularly to the treatment of strip metal to place an oxide coating of a predetermined color or thickness on the surface thereof.

ln continuous annealing Vor normalizing of strip metal as presently practiced, the aim and result is to produce bright strip which, when exposed to air immediately following the cooling under a protective atmosphere Will not oxidize on its surface. Subsequently, if the strip is to be coated, it is subjected to `a light pickle to remove any traces of grease or stain that might interfere with the coating process.

it has been found, however, that a very light, thin oxide film on the strip at the pickling stage would have merit in acting as the means for providing a light surface layer of reduced iron. Such a surface will provide the optimum condition for producing a tightly adherent tin-plate or galvanizing coating, for example. In such a case, the oxide film should be of a uniform color or thickness ranging from light straw to blue in appearance'. Care must be exercised, however, to avoid thicker oxide films since they may have a damaging effect on the polished roll surfaces used in temper rolling which follows annealing and precedes coating. An added advantage of a tightly `adherent oxide film is that it prevents atmospheric rusting or oxidation during the interval between annealing and coating, which in some cases, may be several days. y

lt is an object of the invention to provide a method and apparatus for placing an oxide film of controlled thickness upon the surface of a metal strip or strand.

It is a further object of the invention to provide a method and apparatus for placing an oxide film of controlled thickness upon the surface of a continuously moving metal strip. Such method and apparatus is preferably used in combination with a continuous strip annealing or normalizing apparatus.

In carrying out the invention, strip is heated and cooled in a conventional strip annealing or normalizing apparatus that is designed to produce a bright strip. The strip is removed from said apparatus at a temperature' at which it will oxidize in air, and is kept in an oxidizing atmosphere for the time required for the strip to obtain an oxide lm of the desired thickness. Thereafter, the strip is quenched to a temperature below that at which it will oxidize inthe air. The color or thickness of oxide coating obtained will vary with the time the strip is exposed to said atmosphere. This time may be varied either by moving the strip varying distances at a given speed before it is quenched, or by moving it a given distance at varying speeds before quenching.

In the description, the material being treated is referred to as a strip. It should be understood, however, that the material can be in strand or other form adapted for continuous treatment. YWhile the apparatus is particularly designed for the treatment of tin-plate stock such as cold rolled, low carbon strip, it will be understood that it may be used with any material for which the treatment is beneficial or desired.

The various features of novelty whichcharacterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specicobjects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

' Figure l is a diagrammatic view, partly in section, of the apparatus for carrying out the invention, and

Figure 2 is a view in section showing a modified form of the invention.

Referring to Figure l, the strip S is brought in from the left of the drawing from some suitable source of supply and is passed over a guide roller 1. From here, it moves vertically downward through a furnace 2 having in it a furnace chamber 3. This furnace serves to heat the strip to an annealing or normalizing temperature in the range of 1200 F. to l700 F. From the furnace, the strip passes through a suitable seal 4 and into a cooling chamber 5 that is normally filled with a protective atmosphere which will insure that the surface of the strip is bright when it leaves the chamber. The cooling chamber is provided with'a series of guide rollers 6 over which the strip travels in a series of loops while it is being cooled from the temperature to which it was heated in the furnace to a temperature below which the desired metallurgical changes have occurred, but above a temperature at which it will oxidize in the atmosphere. Preferably, however, the temperature will be in the range of from 450 F. Yto 900 F. It is noted that partitions 7 may be placed in the cooling chamber between each of the convolutions ofthe strip in order that the cooling thereof may be controlled more closely than would otherwise be the case.

The strip leaves the cooling chamber through a Vsuitable roll seal 8, that serves to prevent the entrance of air to the cooling chamber, and passes around a pair of guide rollers 9 and 10 that are located in a quench tank 11. Upon leavingV the quench tank, the strip goes over a guide roller12 and through pinch rollers 13. These rollers serve to move the strip through the heating and cooling chambers as Well as through the quench tank. They are driven by a motor 14 whose speed may be controlled with a conventional controller 15. The cooling tank is provided with a partition 16 which serves to divide it into an entrance portion that is supplied with a quench fluid, such as water, through a pipe 17 at a rate that .is controlled by a valve 13 in the pipe. The quench uid ows from the tank through an outlet 19 having a swivel joint 20 therein, and an adjustable pipe 21 into a drain 22. The angle of the pipe 21 may be adjusted, thereby adjusting the level of the Yliquid in the quench tank. To this end, pipe 21 is provided with a yoke 23 that has pivoted to it a threaded shaft 24. This shaft passes through a frame 26 and receives thereon a hand Vwheel 25. The angle of the pipe 21 can be adjusted, thereby varying the level of the-liquid in the tank, by the rotation of hand Wheel 25.

In the operation of this system, strip is fed into the heating chamber continuously and `at ya speed that is regulated by the adjustment of motor 14. This speed is such that in conjunction with the tiring of the furnace, fthe temperature of the strip is raised to l200 F. to 1700 F. during its passage 'through the furnace chamber 3 depending upon whether it is being annealed or normalized. Upon leaving the furnace, the strip passes through the seal 4 :and into the cooling chamber 5. A

. is coiled to be stored until use.

protective atmosphere is maintained in this chamber so that the strip will be kept bright while it is cooling. In other words, the heating 'and cooling chambers actually heat treat the stripiand deliver a bright strip through the roll seal 8 into Ythe air.

After the strip has been heated, `it-must be cooled at a controlled rate until its temperature has been reduced Vto a point where the desired metallurgical characteristics are obtained. This usually occurs by the time the strip has reached 900 F. Any cooling beyond a small amount below this poinlt is ordinarily -undesirable because of the expense and the mechanical diiculties that yare-encountered. In order to carry out the present invention, however, it is only necessary that the strip be above a temperature at which itwill readily oxidize lin air. This is about 450 F. Therefore, thecooling effect of the cooling chamber is adjusted by conventional means so that the strip is discharged into the air at any temperature ine-the range Vof 450 F. to 900 F., bult preferably between 750 F. and 800 F. At this temperature, the amount of oxidation will depend upon the time of exposure. Therefore, at a given speed of the strip, a predetermined color or thickness of oxide coating will be placed -upon its surface, depending upon .fthe 'length Vof time required for the strip to move from the roll seal 8 into the quench liquid in tank 11. By varying the llevel of the liquid in the tank, the distance that the strip travels and |the time that the strip is exposed to the air Vwill be varied, and therefore, the color of the oxide lm placed on `the strip will be varied.

It has been found in a number of cases, particularly where the strip is later to be used for tin-plating or galvanizing, that it fis advantageous to have a thin oxide lm on the surface of the strip. When the strip is subjected to a pickle prior to the coating, reduction of the oxide lm by the pickle bath will leave a microscopioally thin layer ofV sponge yiron on the surface to which the coating seems lto adhere more tightly than if the` layer were nolt there. The thickness of the layer of spo-nge iron can be varied by the thickness of the oxide coating placed on the strip surface. Generally this will be from light straw to blue. Such a coating vcan be placed on the surface of the strip in a few seconds, so that the distance the strip `travels in rthe, air after it leaves the cooling chamber and before entering the quench tank can be relatively short.

Alternately, the level of the liquid in thequench tank can be maintained constant,l and thefthickness of the coa-'ting on the strip can be varied by varying the speed thereof. In either case, the result is the same. VThe thickness of the oxide hlm placed on the surface of the strip is strictly a function of time |and temperature. If the strip is at a given temperature, the yoxide iilm wiil be placed on its surface in a given time. The annealing apparatus is so adjusted that the exit temperature of the strip can be predetermined. Therefore, the thickness of the oxide hlm Vis varied .by either changing thespeed of the strip orby vaiying the level of the quench'liquid since both of these determine the time that the strip is traveling inthe air. Y

The temperature of the quench Huid, ordinarily water, can be maintained at any desired value just so that the strip, when it leaves the quench tank, is below a temperature at which it will oxidize in the air. Normally, it is desirable to keep the temperature of the water at approximately l80 F. When this `is Vthecase, .the strip can be dried in the air due to evaporation of the water from it with a minimum of trouble. Whenthe liquid Yis cooler, say at room temperature, provisions must be made for blowing hot air over therstrip in order to dryrit'before it The temperature of the quench water can be controlled by varying the volume of water that passes -through the quench tank. The arrangement of the'tank is such that water is'introduced into -a compartment which is Vseparated from Vthe main This insures that the level of the water `can be main-L; tained accurately. The arrangement is also such that the v heated water is removed from a point adjacent to the 5 entrance of the hot strip. This makes it easier to keep f: the temperature of thel water at the desired value than would be the case if the water was withdrawn from the f tank at some point remote from that at which the strip entered.

At times, it may be diicult to obtain an even oxide coating on both sides of the strip due to various plant conditions. if there is a draft blowing in one direction, for example, the strip may be oxidized more on one side than on the other side. For this reason, it may be desirable to protect the strip between the roll seal 3 and the quench liquid. lf such a construction is necessary, there can be provided a shield 27, as indicated in Figure 2. This shield will extend from the rolls downwardly to a point beyond the lowest level that the water inV the 'quench Atank will reach. The supply of oxygen in the -shield will soon be exhausted unless a continuous supply thereof is provided. To this end, an inlet pipe 23 extends into each side ofthe shield through which air or oxygen :enriched air maybe introduced. The inner end of each pipe terminates in a discharge outlet 29 which outlets i are so arranged that the air blown through them will .-impingeagainst the side walls of the shield and be diffused evenly through the area thereof. In view of the fact that the strip isheated, it will raise the temperature of the quench liquid above the boiling point so that the shield eventually will become filled with steam unless provision is made to remove it. For this reason, there .is provided an outlet'l through which the steam can be removed from the shield. This outlet will have to be above thelevel of the quench water at its highest point. If desired, the outlet could be arranged to move upwardly and downwardly with the level of the quench liquid so that it is just above the liquid level. ln this manner, steam can be Vwithdrawn from. the shield `at the point where it is formed.

As was mentioned above, the atmosphere `in the cooling chamber 5 is a protective atmosphere that will deliver a bright strip through the roll seal. If air, or oxygen enriched air is introduced at a high pressureV into the sleeve 27, there will be a tendency for this air to flow upwardly through the roll seal ,S into the cooling chamber. Such a procedure is undesirable, since the effect of ythe protective atmosphere in the cooling chamber would be ruined. VTherefore it is necessary by the use ofany conventional pressure control apparatus toV maintain in the sleeve 27 a pressure which is slightly lower than the `pressure which is maintained in the cooling chamber 5. in practice, air or other oxidizing gas is continuously introduced through inlets 28 and exhausted along with the steam through outlets 31. TheV slight circulation of air in the` sleeve 27 insures that there will be at all times an oxidizing atmosphere which is suliicient to place an oxide coating on the surface of the strip.

Whether the strip is open to the air as shown in Figure l, vor is in a protective sleeve as is shown in Figure 2, theresult and operation of the system is the same. In eachcase, the hot strip is moved through an oxidizing atmosphere for a time suiiicient for an oxide coating of desired color to be placed on its surface. Whether or notthe shield is used will depend mainly upon the conditions in a particular plant.

From the above description, it will be seen that I have provided a method and apparatus for placing Yan oxide hlm of predetermined thickness upon the surface of a stripV of material. The process and apparatus are particularly adapted for use in connection with the annealing of cold rolled, low carbon steel of the type that is generally used for tin-plate. It will be apparent, however, that Lthe apparatus can be used in connection with any material upon which it is desired to place an oxide iilml It is also useful in connection With strands or wires as well as with strip material.

While in accordance with the provisions of the statutes, l have illustrated and described the best form of ernbodiment of my invention now known to me it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention, as set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. Apparatus for heat treating a metal strip comprising in combination means to deliver bright strip metal at a temperature in the range of 450 F., to 900 F., an open quench tank located directly in line with the delivery end of said means, guide rollers to guide the strip through said quench tank, means to direct an oxidizing atmosphere against the strip as it moves between said means to deliver and through said quench tank, means to move the strip from said means to deliver and through said quench tank at a constant speed, means to vary the level of a quenching uid in said quench tank to thereby vary the time required for the strip to travel through said oxidizing atmosphere from `said means to deliver until it is immersed in the quenching fluid said means to direct including a duct through which the strip travels between said means to deliver and said quench tank, and means to introduce an atmosphere having an oxidizing eiect into said duct.

2. Apparatus for placing an oxide coating on the surface of a strip of metal comprising in combination mechanism to bright anneal continuously a strip of metal and having a delivery opening through which said strip is discharged in a downward direction into the air, said mechanism having means to deliver strip therefrom at a temperature above which it will oxidize in air, quench means located immediately below the delivery opening of said mechanism, the strip traveling through air between the delivery opening and said quench means, drive means to move said strip at a constant speed, and means to vary the height of said quench means relative to said delivery opening to thereby vary the time said strip is exposed to the air.

3. Apparatus for heat treating a metal strip comprising in combination mechanism to heat and cool a strip, said mechanism including means to discharge said strip at a temperature above which it will oxidize in air, a

quench tank, guide means to guide said strip directly from said discharge means to and through said tank, means to move said strip through said mechanism and said tank, adjustable means to maintain various predetermined levels of a quenching uid in said tank, a shield surrounding said strip and extending from said discharge means to a point below any level of the quenching fluid in said tank, and means to supply an atmosphere having an oxidizing effect on said strip into said shield.

References Cited in the le of this patent UNITED STATES PATENTS 627,022 Theobald June 13, 1899 854,810 Daniels May 28, 1907 1,362,213 Andrews Dec. 14, 1920 1,704,015 Naugle et al. Mar. 5, 1929 2,110,893 Sendzimir Mar. 15, 1938 2,137,817 Tueri Nov. 28, 1938 2,283,109 Von Ende May 12, 1942 2,340,461 Gage et al. Feb. 1, 1944 2,418,087 Nachtman Mar. 25, 1947 2,420,377 Jones May 13, 1947 2,546,538 Erhardt, Ir. Mar. 27, 1951 2.594.876 Cope Apr. 29, 1952

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