US1808152A

US1808152A - Continuous annealing apparatus

Info

Publication number: US1808152A
Application number: US48541A
Authority: US
Inventors: Thaddeus F Baily
Original assignee: Individual
Current assignee: Individual
Priority date: 1925-08-06
Filing date: 1925-08-06
Publication date: 1931-06-02
Anticipated expiration: 1948-06-02

Description

June 2, 1931. T. F. BAILY CONTINUOUS ANNEALING APPARATUS Filed Aug. 6, 1925 Patented June 2, 1931 UNITED STATES PATENT OFFICE THADDEUS F. BAILY, OF ALLIANCE, OHIO CONTINUOUS ANNEALING AJPIPARATUS Application filed August 6, 1925. Serial No. 48,541.

The invention relates to an apparatus for oxidized in pack annealing, in which the macontinuously annealing sheets and other terial is placed in a pile on an annealing botrolled products, wherein the material is tom, covered with a cast iron, gas tight cover passed continuously through a furnace for or box, and natural or other reducing gas heating to the desired temperature, cooling maintained within the cover or box during the 55 at a desired rate through certain critical temheating and cooling of the sheets. The obperatures and at a difierent rate through jection to this method, for deep drawing other critical temperatures, uniformly coolsheets, is that little control can be had of the ing the material throughout all surface porrate of cooling, and the edges of the sheets tions. The method of continuously annealheat faster than the centers thereof, and are 60 ing sheets and other rolled products, which liable to be overheated, roducing a coarse is described, but not claimed herein is made grain structure on the e ge portions of the the subject matter of my copending applicasheet, and also in cooling, the edges cooling tion Serial No. 130,519, filed August 20, 1926, more rapidly than the central portions of the which is a division of this application. sheets, produce a different gram structure in 65 In the production of deep drawing sheets the edges from that of the centers of the for instance, it is a common practice to take sheets. the sheets as they come from the previous Further, by this pack annealing, the length rolling, heat them above the upper critical of time required, both at the maximum temtemperature, allow them to cool in the air by perature and during the cooling, is so great 7 passing them upon a cooling table while still that a coarse grain structure is produced in at a considerable temperature, during which the sheets which adversely affects the deep period additional oxidation takes place, and drawing qualities thereof. It has been dethe edges of the sheets cool more rapidly than termined that for a steel of given analysis the center, producing different grain structhere is a certain maximum temperature tures and therefore different physical propwhich must be reached in order to produce erties between the edge portions and centers the desired grain structure, and that sufliof the sheets. cient time must be allowed, however short,

When the sheets are substantially cooled for the rearrangement of the grains to take upon the cooling table they are placed in a place. This is known to be above what is pile adjacent to the end thereof where they termed the upper critical point. still further cool on the edges more rapidly It is also known that steel in cooling northan at their centers. After the sheets are mally passes through a number of critical completely cooled they are subjected to a ranges. As steel is cooled sufliciently slow pickling operation for removing oxide and for the following grain condition to take scale produced either by previous heating or place, it. will pass from the austenite, which while the sheet was exposed to the air in a is above the upper critical point through the heated condition. martensite stage, then to'the troostite, then It will thus be seen that in the present through the sorbite, and lastly to the pearl- 0 practice little if any control can be exercised ite stage, which latter is the usual grain in the rate of cooling of the sheets from the structure found in sheets that have been box maximum temperature through the various annealed. critical ranges to the cold or normal tem- These sheets of pearlite structure have been perature, and that there is bound to be a found to be of coarse grain structure, very 4 different rate of cooling between the edges soft and ductile under preliminary strain,

and the center of the sheet, the sheet being but they rapidly lose their ductility when also left in an oxidized condition requiring strains are set up in drawing operations pickling to remove the oxidation and scale when formed into articles, or in subsequent th f o rolling or cold working.

It is well known that sheets may be de- Sheets that are kept substantially in the sorbite stage, while not so soft, nevertheless have a greater drawing or deforming range gvithout rupture, as compared with pearlite sheets.-

To obtain sheets in the sorbite, .on cooling from the austenite stage, it is necessary to have a controlled and radual rate of cooling from austenite torsor ite, and on reaching the sorbite stage the sheets should be so rapidly cooled as to prevent change of grain to pearlite. The time necessary for these changes will vary with the thickness and mass of the sheet, and if the cooling be rapid as in case of water quenching, on thin sections, sufficient time will not elapse for the grain structure to pass through the intermediate stages to sorbite. .In the case of cooling naturally in the air, as previously mentioned, in the present practice of, open annealing,

. steel will pass erhaps too slowly or too rapidly through t e intermediate stages to the sorbite, and then too slowly to atmospheric temperature, producing a coarse undesirable pearlitic grain structure.

The object of the present improvement is to provide for continuously annealing sheets or other rolled products by heating the same to the desired temperature and then controlling the rate of cooling,

determined rate through certain critical stages and then at another predetermined rate to a point below scaling temperature, the cooling being uniform throughout all surface portions of the material.

Another object of the invention is to provide' for deoxidizing the material while in the heated condition, this deoxidizing process removing any scale which the sheets may contain when they are placed in the furnace, and eliminating the necessity of pickling the sheets after they are annealed.

By my method, which may be carried out by the approved apparatus illustrated herein, the rate of cooling is controlled so as to produce, if desired, substantially a complete sorbite grain structure, or if greater softness is required, a combination of sorbite and pearlite. It will be seen that by the use of this apparatus and method any desired grain structure may be attained throughout the en- "tire area of the sheet, since provision is made for controlling the rate of cooling at any stage, and since provision is also made for cooling uniformly over all sections of the sheet, the grain structure of the entire sheet will be uniform..

It should alsobe noted, that by the deoxidizing arrangement shown, such scale as may be formed previous to the cooling stage may be deoxidized, and since provision is made for cooling below the oxidizing temperature before coming into contact with the air, the resulting product is free fromscale or oxide,

the material being cooled out of contact with the air at a preand the usual pickling operation is eliminated;

The improved apparatus, by which the method may be carried out, iS lllllStI'fltOd in the accompanying drawings, in which;

Figure 1 is a longitudinal sectional view of an electrically operated furnacev designed to carry out the improved method, and,

Fig. 2, a similar view of a gas heated furnace.

Similar numerals of reference indicate corresponding parts throughout the drawings.

The improved method of annealing'sheets and other rolled products, may be carried out in an electrically heated furnace as illustrated in Fig. 1, or in a gas heated furnace such as shown in Fi 2.

Referring first to %ig. 1, the furnace may be divided into a'series of communicating chambers, comprising the-preheating chamber 1, the heating and deoxidizin chamber 2, the initial cooling chamber 3, an the quick cooling chamber 40, arranged in alinement, in the order named, the transverse walls of the several chambers being provided with restricted openings 5, through which the material may be passed as by the rolls 6.

The heatin and deoxidizin chamber 2, may be provi ed, upon each si e of the path of the material, with electric resistors 7 for the purpose of bringing the material, mdicated generally at M, to'the maximum temperature required for the annealing.

For the purpose of deoxidizing the material to remove any scale or oxidation which may be present when the material is passed into the furnace, means are rovided for impinging a highly heated re ucing gas upon each surface of the material, this means being illustrated as comprising a series of tubular heads 8, upon each side of the path of the material, said heads being provided with nipples or jets 9, for directing a blast-of reducing gas upon all surfaces of the material.

These heads 8 are shown as connected. to pipes 10 communicating with the outlet side 11 of a blower fan 12, the gas being returned from the deoxidizing chamber to the inlet side of the fan as by a pipe 13, whereby the gas is continuously circulated through the fan and impinged upon the material, removing scale and oxidation therefrom.

It will 'be seen that this reducing gas will be quickly heated, by means of the electric resistors, to a very high temperature, although if desired,outside means may be provided for heating the gas.

A fan 14 may be provided with pipes 15 and 16 communicating with the outlet side culating a nonoxidizing gas through saidcooling chambers. -.This nonoxidizing gas is exhausted from the cooling chambers cooling chamber 4: as by the pipe 26, said gas through a pipe or conduit 17 communicating passin in the direction of the arrows, with the forward end portions of said chamthrong the chambers 4 and 3 and then hers as indicated at 18, passing the gas into the rear end portion of the preheating chamber as shown at 19. The forward end portion of the preheating chamber is connected to the inlet side of the fan 14 as by a return pipe 20. Thus a continuous circulation of nonoxidizing gas is passed through the chambers 3 and 4 for the purpose of cooling the material, and then through the preheating chamber 1 in order to preheat the material by recuperation of said gas, which is thenreturned in a closed circuit to the fan 14.

In order to very rapidly cool the material as it passes through the quick cooling chamher 4, upper and lower hollow rolls 21 are provided, the material being passed through said rolls and discharged from the furnace. These rolls are connected together in a continuous circuit and communicate with the inlet and discharge pipes 22, through which cold water, air or other cooling fluid may be passed for maintaining the surfaces of the rolls at the desired temperature, and as these surfaces of the rolls contact with the entire surface area of the material it will be seen that the material is uniformly and rapidly cooled throughout its entire surface area.

In the gas heated form of furnace, shown in Fig. 2, the preheating" and final heating of the material may be accomplished in the chambers 1 and 1 respectively while the deoxidizing alone is carried out in chamber 2 in which the deoxidizing apparatus may be substantially identical with that shown in Fig. 1; excepting only that the dpipe 11 communicating with the outlet si e of the fan 12 passes back and forth through the combustion chamber 1, as at 1 before communicating with the head 8* having the nipples 9, whereby the deoxidizing gas circulated is heated by the products of combustion in the combustion chamber.

A mufile wall 1, of carborundum or the like, separates the combustion chamber 1 from the heating chamber 1*, the products of combustion passing over the incoming material in the preheating chamber 1", and then to the stack. The initial cooling chamber 3" receives the material from the deoxidizing chamber, the rolls 6 carrying the material entirely through the furnace as above described and passing it into the quick cooling chamber 1* where it is rapidly cooled by passing between the hollow fluid cooled rolls 21*.

Cold air is continuously forced through the hollow cooling rolls 21 by means of a blower fan 23, said rolls being connected to gether in a circuit and exhausting through the pipe 24 to the gas burner 25 located in the rear end portion of the chamber 1 A nonoxidizing gas, such as natural gas, is injected into the rear end portion of the quick through the pipe 27 -to the gas burner where it is burned in combination with the heated air received from the pipe 24.

The operation of each of these forms of the furnace comprises a preheating, heating to a maximum temperature, and a deoxidizing of the material as it is passed continuouslythrough the furnace, and then an initial cooling through certain critical ranges at a controlled rate of speed, and a final cooling through other critical ranges at a diliercnt rate of speed.

In carrying out the improved method of annealing, assuming that deep drawing sheets are to be annealed, they are first heated to a point above the upper critical temperature of the particular material, and may be deoxidized while hot, the cooling being controlled at a rate which permits the grain structure of the material to pass from the austenite through the martensite and troostite stages and into the sorbite stage, when a very rapid cooling of the material from that temperature retains the fine grain sorbite condition in the finished sheet, the final cooling being preferably accomplished to a point below the scaling temperature before the material is passed out of the furnace and into contact with the atmosphere.

The different temperatures at which the different stages of the process are carried out will of course depend u on the ingredients of which the material is ormed and the particular use for which the material is intended.

Assuming that 20 gauge steel sheets, having a carbon content of .10, are desired to be annealed for deep drawing, the sheets will be first heated to substantially 1650 R, which carries them above the upper-critical temperature and produces an austenite grain structure. The sheets will then be uniformly cooled from 1650" F. to 1350 F. insubstantially 15 seconds, the grain structure passing from the austenite, through the martensite and troostite stages, and reaching the sorbite stage at about 1350 F., thecooling from 1350 F. to 350 F. being carried out very rapidly, in not over 5 seconds time, arresting the grain structure in the sorbite stage and producing a finished sheet having the maximum drawing qualities.

In some instances, as in case of cold worked strips, it may be desired to heat only to approximately the lower critical temperature, for relieving distortion of grain set up by cold rolling, after which steel is continuously cooled at a predetermined rate to below a scaling temperature.

For the purpose of deoxidizing the sheets, as they pass through the furnace, a wet carbonaceous coating, such as charcoal and water, may be applied to the surfaces of each sheet before it enters the furnace. As the sheets are brought to a red heat and then cooled below an oxidizing temperature, while I in a reducing atmosphere, all scale or oxida- -tion is removed by this process.

hollow rolls in the cooling chamber connected in series through which air for combustion in the heating chamber is heated, a ipe leadin from said rolls to the heating c amber an means for passing material through the heating chamber and between said rolls.

2. A furnace includin a combustion chamber heated with fuel, a eoxidizingchamber', means within the deoxidizing chamber for impinging heated reducing gas u on material, means for heating said deoxi 'zing gas by products of combustion in the combustion chamber, a cooling chamber, means for conveying material successively through the combustion, deoxidizin and cooling chambers, and means. for orcing reducing gas through the cooling chamber.

material in said chamber, ing chamber, and a final cooling chamber, there being transverse walls rovided with aligned restricted openings tween said chambers, rolls located in said chambers for THAD EUS, F; BAILY.

fuel fired annealing furnace including 'a combustion chamber, a preheating chamber communicating with the combustion chamber, a heating chamber communicating with the preheating chamber, a Inuflle separating the combustion chamber from the heating chamber, means for circulating the products of combustion around material in the deoxidizing chamber communicating with the heating chamber, means for impinging heated reducing gas. upon.mate rial in the deoxidizing chamber a cooling chamber communicating with the deoxidizing chamber, means for cooling the material under treatment, and means for conveying the material successively throu h the preheating, heating, deoxidizing, an cooling chambers.

4. A furnace for annealing sheets and the like including a gas tight chamber, means for impingin heated reducing gas against material in said chamber, a preliminary cooling chamber, and a final cooling chamber, there being transverse walls provided with aligned restricted openings between said chambers, rolls located in said chambers for passing successive sheets through the chambers and restricted openings, a conduit supplyin reducin gas to the final coolin chamlier, and ai i outlet conduit for leading the reducing gas from the preliminary cooling chamber, whereby the reducing gas is circulated from the final to the preliminary cooling chamber through the restricted opening in the wall between the chambers;

5. A furnace for annealing sheets and the like including a gas tight chamber, means for impinging heated reducing gas against preheating chamber, a p

a preliminary cool- I