US1704015A - Continuous annealing and cleaning process - Google Patents

Description

March 1929' H. M. NAUGLE ET AL CONTINUOUS ANN'EALING AND CLEANING PROCESS 2 Sheets-Sheet Filed July' 1, 1925 Snow flow 17/! A aagZe and d Ybzwiseraa! 3513M CONTINUOUS ANNVEALING AND CLEANING PROCESS Filed July 1, 1925 2 Sheets-Sheet 2 gwue'ntow HM Naayle a/zd Tazwzswzd 3%LM (iv/5 Patented Mar. 5, 1929.

UNITED STATES'JJPATENT,OFFICE,

HARRY I. NAUGLE AND ARTHUR T. TOWNSEND, OF CANTON, OHIO, ASSIGNOBQ BY IESNE ASSIGNMENTS, TO THE COLUMBIA STEEL COMPANY, 01' PITTSBURGH, PENN- SILVANIA, A CORPORATION OF PENNSYLVANIA.

CONTINUOUS ANNEAIlING Application filed July 1,

The .invention relates to a continuous method for quickly annealing a strip of sheet metal, referred to in a general way in our application for method of making strip sheets, file-d August 22, 1922, Serial No. 583,612, matured in Letters Patent No. 1,536,028, issued April 28, 1925, and reissued June 14, 1927, as No. 16,652; and this application is a continuation of the common subject matter in our pending application filed November 17, 1924, Serial No. 750,271 for the same invention. v

The general object of the improvement is to anneal the metal in a-manner that will give the product the uniform ductile and other structural characteristics which are necessary for deep drawing and forming or stamping operations.

We have discovered that slow or continued heating of steel sheet metal induces a gram growth therein, and that a continued maintenance at and above scaling temperature fosters the formation of scale on the surface thereof.

The grain growth resulting from a slow or continued heating of sheet steel is increased in metal which has been critically strained as by being rolled previous to the heating and especially so in low carbon steels.

The formation of scale which is induced by a continued maintenance of the metal at and above the scaling temperature is a chemical reaction between gas in the air and the steel itself; and no doubt, like-most chemical reactions the speed at which the action takes place increases as the temperature of the steel increases, and the formation may begin actively on low carbon steel heated in the air at about 1150 F.

Furthermore the formation of scale on the surface of steel sheets ismore or less irregular, and the pickling required to remove the same must be of suflicient strength and duration to remove the heaviest deposit of scale,

' during which time the steel surface is unevenly attacked by the pickling solution, which produces an uneven surface on the steel after the scale has been removed.

A complete readjustment of the grains of the metal to relieve them of the strains pro duced by a rolling operation, and more particularly by a rapid cold rolling reduction and other reductions forming like strains, cannot be accomplished by the ordinary box vaim cnaanmo .PBCGESS.

annealin hat the longer period of time rereason t quired for properly heating the inner portions of the mass or coil, not only results in the over-annealing of the outer portion thereof, but in the production of agrain growlth' in a considerable portionof the mass or coil,-

which destroys the ductility and uniformity,

and also decreases the strength of the mate-' rial in the outer portions of the mass or coil. The present improvement is particularly concerned with the annealing of steel having a carbon content of less than 20%, for the reason that such a low carbon steel is best suited for deep drawing and forming or stamping operations; and for properl annealing the same, the metal must'be uni ormly heated to a temperature of from 1300 to 1600 F. As a rain growth,- sometimes known as Steads' rittleness, ma l a temperature less than 1300 F., i; the same is maintained long enough; one object of the present improvement is to uniformly heat the metal uickly to an annealing temperature, to maintain or continue that temperature only long enough, say about one minute, to correct the micro-structure of the steel which has been critically stressed by previous, I rolling processes while avoiding any material occur at grain growth, and then to promptly cool the 1 metal quickly and uniformly, without, how;-

ever, quenchlng the same to-harden its structure.

or other thin flat stock, by the direct action of electric resistors, while moving continuously through a heating chamber, in whichthe resistors are transverselylocated adjacent to The general object of the improveniqt may be attained by annealing a strip, a sheet,-

and parallel with the strip, by which the same may be uniformly heated and the degree of heat definitely controlled at all points in the heating furnace; and then to promptly and quickly cool the stri by moving itcontinuously through a tubu ar duct surrounded by a morving body of water or other heat absorbing liquid, by which the strip may be quickly and gradually reduced to a-non-oxidizing temperature when exposed to' the air.

A further object of the present improvement is to avoid or overcome difficulties which may accom any the continuous annealing process set ort-h in our a plication for pet ent, filed April 4, 1924, erial No. 704,157,

and the use of the continuous annealing apparatus set forth in our application for patent filed herewith, Serial No. 7 50,269; in both of which an effort is made to carry on the heating and cooling operations in the presence of a neutral or reducing gas, to the exclusion of air, for preventing or removing an oxidation or discoloration of the surface of the strip.

The very desirable and highly efiicient use of electric resistors for directly heating a strip of steel or the like for annealing the same in a chamber containing a reducing gas, requires the use of a refractory lining for the heating chamber and preferably requires the use of a liquid seal for the opening through which the strip enters the chamber. It has been found, however, that the use of a deoxidizing medium in the heating chamber has an injurious effect upon the electric resisters, and the vapors resulting from the volatilization of a liquid sealing medium has a deteriorating effect upon the refractory lin- 1n I and a particular object of the present improvement is to avoid or overcome the difficulty which may accompany the continuous annealing and cleaningv processes set forth in our application for patent filed herewith, Serial No. 7 50,270, in which a heat retaining deoxidizing duct is interposed between the heating chamber and the cooling duct for cleaning the strip from oxidation and dis-' coloration before it is cooled.

The use of such a heat retaining deoxidizing duct may sometimes maintain the metal at an annealing temperature for such an extended period, as will result in an incipient or a su stantial grain growth; and in any event the chemical reaction which results in the elimination of surface oxidation gives two products, one of which is gaseous and the other solid; and the solid product is deposited on the strip in the form of a fine dust, so that when the strip sheet is subsequently handled or' processed this dust cracks and re sults in what is known as surface breaks.

The present improvement avoids these difliculties by the use. of an unsealed heating chamber and cooling duct in which some atmospherie gas may enter and slightly oxidize or discolor the surface of the strip, but does not form a scale which cannot be removed by a continuous cleaning in a weak acid solution and by providing, in series, a cleaning tank and a washing tank immediately in rear of the cooling duct, for removing any oxidation or discoloration there may be on the strip when it leaves the cooling duct, and completely cleaning the strip with a smooth finish without leaving any deposits thereon.

By these means the detrimental effect upon the refractory lining of the heating chamber by the volatilization therein by a liquid sealing medium, and the damaging action of a reducing gas upon the electric resistors within the heating chamber, are both avoided and the cooling of the strip is effected so promptly and quickly after itis annealed that no opportunity is given for any objectionable grain growth, and the strip is subsequently subjected to the cleaning and washing operations, so that upon the completiomof the processes, the body of the strip is uniformly ductile and the surface is clean and smooth.

The improved method may be carried out by the apparatus illustrated, more or less conventionally, in the accompanying drawing forming part hereof, in which- V Figure 1 is a side elevation, partly in section of the apparatus; and

Fig. 2, a diagram showing the heat curve of the metal during the improved process.

Similar numerals refer to similar parts throughout the drawing.

The apparatus may include a coil box A, a strip leveler B, a traveling spot welder C, a solution washer D, an electric heating furnace E, a cooling duct F, a pickling tank G, a Washing tank H, conveyer rolls I, a double end shear J and a strip coiler K, all arranged in series as shown in the drawing.

The coil box A may be of any ordinary construction for holding a coil 10 of a strip 11 of steel or the like, and permitting the same to unwind for a continuous annealing; and the strip leveler B may include two sets of rolls 12 of any well known construction and operation, for flattening the sheet and removing uneven fullness or buckles which mayhavebeen caused by reducing rolls or other apparatus used in producing the strip.

The spot welder C may include a set of electrodes 13 mounted in a frame 14.- supported on a carriage 14 provided with wheels 15 riding on a track 16, together with gripping devices 14", on the front and rear sides of the frame, for clamping and holding successive strips with their ends overlapped, in position between the electrodes for a spot welding operation while the carriage is traveling forward on the track.

The solution washer D may include strip supporting rolls 17 and transverse tubes 18 suitably apertured for spraying a hot soda solution upon the strip, to remove grease and grit therefrom; and.like tubes 18 may also be provided for air drying the strip in rear of the cleaner.

The heating furnace E may include a cylindric shell 20 mounted on supports 21- lined with a thick body of heat insulating material 22, within which is provided a lining of fire brick 23 or other refractory material, forming a support for electric resistors 24 and 24' parallelly positioned above and below and forming between them a longitudinal heating chamber 25, in which are provided a series of transverse skids 26 for supporting a strip 11 as it is moved endwise through the chamber for coo 15 in a uniform manner from end to end of the furnace, and the degree and continuity of heat can be readily controlled at all points in the heatmgchamber,by referring to the series of yrometers 10 'Phe cooling duct F may be a series of end connected iron tubes 27 and 27 extending rearward from the rear end of the furnace and the sections of the same may be surrounded by tanks or troughs 28 containing water ling the conduit and the strip moving through t 0 same.

The cooling'troughs may be provided with a water inlet pipe 29, a water connecting pipe 29' and an overflow pipe 29" so as to cause 20 a continuous flow of cooling water from the forward end toward the rear end of each trough.

The cleaning tank G may include an end closed trough 30 containing a weak solution of sulphuric acid, with transverse skids 31 in its bottom for supporting the strip 11 and provided with rolls 32 in each end for guiding and holding the strip downward in the acid bath. A supporting roll 33 may be 10- 3 cated at each end of the cleaning tank for guiding the strip out of the cooling duct, into and out of the cleanin tank. 3

The washing tank. may include an end closed trough 34 containing water or other 35 washin liquid, with a guide roll 35 in each end an a supporting roll 36 at the rear end, for directing the strip through the water in the trough to wash from the same any acid or other coating which may be carried from 49 the cleaning tank.

The conveyer rolls I may include two stands of pinch rolls 38 arranged for drawin a strip through the apparatus and conveying it rearward to the double shear J and between these rolls may be provided transverse pipes 31' suitably apertured for hotair drying the strip.

The shear J is provided with a shearin die 39 on its front and rear sides, and a shearing punch 40 operating between them, for

shearing the joint of two strips in front and in rear of their overlapped ends, so as to neatly disconnect them aft-er the annealing process is completed.

The strip coilerKmay be of any well known construction for winding the annealed strip 11 into a coil 10', and it is preferably provided with an independent motor 41' for this purpose. 7

In the operation of the apparatus, a strip sheet, which has been flattened by the leveler B, joined to another strip by spot welder C,

' and acted upon by the solution washer D, is moved continuously endwise through the as heating chamber 25 and the cooling duct F wherein it is heated quickly and uniformly by the electric-resistors to an annealing temperature, which temperature of the metal is maintained and continued only for the brief period necessary for a proper annealing'of the metal, which may not exceed one minute, whereupon it is promptly cooled quickly by the heat absorbing water surroundin the tubular duct; The strip is then cleared in the cleaning tank G and the washing tank H, from any discoloration there may be on its surface. 5

In this manner a continuous quick annealin and pickling is accomplished, and the brief period during which the annealing temperature is maintamed and continued, avoids the formation of a detrimental scale and prevents the" production of an objectionable grain growthor Steads brittleness, so that the annealed strip thus produced is characterized by auniformly fine grained structure and a highly ductile quality, which adapt it for deep drawing operations.

different gauges and of more than ordinary widths can be continuously annealed without developing any objectionable grain growth. In actual practice, any given portion of a strip sheet, one-sixteenth of an inch in thickness, may be heated to a temperature of 1400 F., maintained at that temperature for about one-fourth of a minute, and then cooled to a nonoxidizing temperature, all within a period of about one and one-half minutes. This operation can be carried on continuously with respect to all portions of each stri and of successive strips which have .been oined together, without stopping the movement of the strip which is passing through the heating chamber and the cooling duct.

The total length of the heating chamber and cooling duct of the apparatus may be about one hundred twenty-six feet, and the same may be operated so that a given portion of the stripsheet will pass through the heating and coolin zone within a cycle of between three and our minutes, as diagrammatically illustrated'in Figure 2 of the drawm s. y

Ilnder these conditions, any given portion of a strip sheet one-sixteenth ofan inch in thickness, will be quickly heated by the direct action of the electric resistance, to annealing temperature, of say 1250 F., in a fraction less than one minute, and after being further heated to a maximum temperature of say 1400 F., it is promptly cooled quickly to pass below the annealing temperature of say 1250 F., during the second minute of the 'cycle; so that the heat of the strip is only maintained at an annealing temperature during a period of about one minute, thereby entirely avoiding, or reducing to a negligible minimum, the production of a grain growth in the body of the metal.

At the same time, the steel strip is quickly heated to a scaling temperature of say 1150 F, within a fraction less than one mlnute of the cycle, and after, attaining the maximum temperature, is promptly and quickly cooled to below a scaling temperature, within a fraction more than thesecond minute of the cycle; so that a given portion of the strip is only maintained at a scaling temperature during a period of little more than one min ute of the cycle, thereby avoidingthe forma tion of a detrimental scale on the surface of the metal, and permitting the discoloration. thereon to be readily removed by a weak cleaning solution, thereby producing a sheet with an even clean and clear surface.

' We claim:

1. The method of annealing a steel strip which includes heating the strip quickly to annealing temperature, promptly cooling it uickly to avoid grain growth and scale and the cleaning the strip, all during a continuous endwise movement thereof.

2. The method of annealing a steel strip which includes heating the strip quickly to annealing temperature and promptly cooling it quickly to avoid grain growth and scale in a normal atmosphere, and then cleaning the strip, all during a continuous endwise movement thereof.

3. The method of annealing a steel strip which includes heating the strip quickly to annealing temperature and promptly cooling it quickly to avoid grain growt and scale in an atmospheric gas, then cleaning the strip and subsequently washing the same, all during a continuous endwise movement of the strip.

4. The method of annealing a steel strip which includes washing the same with a cleaning solution, then heating the strip quickly to annealing temperature in an atmospheric gas,.then promptly cooling the strip quickly to avoid grain growth and scale, andthen cleaning the same, all during a continuous endwise movement of the strip.

' 5. The method of annealing a steel strip which includes washing the strip with a cleaning solution, then heating the strip quickly to annealing temperature, and. then promptly cooling the strip quickly to a nonoiridizing temperature to avoid grain growth and scale, all during a continuous endwise movement of the strip.

6. The method of annealing the body and cludes heating the strip quickly to annealing to annealing temperature, maintaining the same temperature only until the micro-structure of the metal is corrected, and then quickly cooling the strip to a non-oxidizing temperature to avoid grain growth, all during a continuous endwise movement of the strip.

9. The method of annealing a strip which includes uniformly heating the strip quickly throughout its width and thickness to annealing temperature in an atmospheric gas, maint-ainingthe same annealing temperature only until the micro-structure of the metal is corrected, then quickly cooling the strip to a non-oxidizing temperature to avoid grain growth and scale, and then cleaning the strip to clear the surface thereof, all during a continuous endwise movement of the stri 10; Apparatus for annealin steel strips, including a chamber for quickfy heatin the strip to annealing temperature, a tu ular duct surrounded by heat absorbing liquid for promptly cooling the strip ickly from annealing temperature to a-voi grain growth and scale, and a cleaning tank arranged in series for continuously annealing and cleanv ing the strip.

11. Apparatus for annealin steel strips, including a chamber for quick y heating the strip to annealing temperature, a tubular duct surrounded by. heat absorbin liquid for promptly cooling the strip quicl y from annealing temperature to avoid grain growth and scale, and a cleaning tank and a washing tank in series for continuously annealing, cleaning and washing the strip;

12. Apparatus for annealing steel stri s, including a chamber for quickly heating t e strip to annealing temperature, a tubular duct surrounded by heat absorbing liquid for quickly cooling the strip promptly from annealing temperature to avoid grain grpwth and scale, a cleaning tank, a washing tank and drying means, arranged in series for continuously annealing, cleaning, washing and drying the strip.

13. The method of annealing a steel strip which includes uniformly heating the strip quickly to annealing temperature, maintaining said temperature only until the microstructure of the metal is corrected, and then quickly cooling the strip to avoid grain growth, all during a continuous endwise movement of the strip.

14. The method of annealing sheet steel which includes uniformly heating the steel quickly to annealing temperature, maintaining said temperature only until the microstructure of the steel is corrected, and then quickly cooling the steel to avoid grain growth.

15. The method of annealing a steel strip which includes heatingthe strip quickly to annealing temperature, promptly cooling it quickly to avoid grain growth and scale, and then cleaning the strip to remove discoloration therefrom, all during a continuous endwise movement thereof.

16. The method of annealing sheet steel which includes heating the steel to annealing temperature, promptly cooling it quickly to avoid grain growth and scale, and then cleaning the steel to remove discoloration therefrom.

17. The method of annealing a steel strip which includes washing the same with a cleaning solution, then heating the strip quickly to annealing temperature in an atmospheric gas, then promptly cooling the strip quickly, and then cleaning the same, all during a continuous endwise movement of the stri 18. Tlie method of annealing a steel strip which includes uniformly heating the strip quickly by direct action of electric resistors to annealing temperature in an atmospheric gas, maintaining the same annealing temperature only until the microstructure of the metal is corrected, then quickly cooling the strip by indirect action of heat absorbing liquid, and then cleaning the strip to .clear the surface of the same, all during a continuous endwise movement of the stri In testimony that we claim the a ove, we have hereunto subscribed our names. HARRY M. NAUGLE. ARTHUR J. TOWNSEND.

Images