US2504808A - Method of annealing - Google Patents

Description

April 18, 1950 w. H. DAILEY, JR

METHOD OF ANNEALING Filed June 2, 1945 E f m m w a maz M Patentec'l Apr. 1 8, l 95 MET QD NEAL NQ William H. Dailey, Jr.,- Library. !ia-2,; assigno-v to Caregi-Illinos Steel Corporation, acorpora Application June 2', l945, erialfNog 5975323" l Qlajmg; (CI. 1485-1716# The. present: inventionrelates: to animproved method of.. annealingwhich; while -noti -limited thereto, well isuited for annealing relativelyv widecoils of rolled. steel strip.

Itiswell known tothose skilled in the art that heretofore the annealing of coiledsteel strip hasbeen.: frequently carr-ied out by enclosing the coils within bell-like gas-tight inner coverswhose lower edges are sealed in sand or other suitable sealing material, the annealingheat having been applied externally by a bell-type radiant tube annealing-urnace. In suchconventional practice a protective deoxidizing gas is introduced into the inner covers so as to force out air and r maintain a deoxidizing atmosph ere within the inside. cover. The gas forming the-non-oxidiz-- ingatmosphere is usuallyexhausted through the sand -seal at the base of the inner cover or through suitable outlets, the' rate offiow of the deoxidizing gas being controlled by maintaining a uniform gas pressure inside the inner covers or I by-maintaining a uniform gas pressure in the non-oxidizing gas supply bymanipulation of an surfaes of the steel coils during the heating' period whichshould' be purgedirom the inner covers by the maximum rate of flow. of deoxidiz inggas duringthis heating stage of the annealing treatment, but that after the heating stage; that is to say, during the cooling period after the application of heat to the furnace has been discontinued, the purging action is no, longer; necessary and the rate of flow of the deoxidizing gas can be reduced to the minimum necessary to prevent outside air from entering the inner cover, thus effecting a great saving in deoxidizing gas Consumption.

One object of the present invention is to provide a method of involving controlling the flow of gas to the inner covers at a substantially constant rate regardless of pressure variations inside the inner covers or pressure variations of gas emanating from the inlet pipes.

Another object of the invention is to provide a method of maintaining the rat of flow oi claimsu deoxidizinggas at the maximum: necessary to obtain the desired purging action' during the heating stage and 'for: maintaining the rate of flow of deoxidizinggas during the cooling stage; atthe' 'minimum i necessary to prevent entrance of air into the inner covers.

The .invention will be more fully apparent^ fromconsideration of the following specifiea-tion; the

and the" appended accompanying-- drawings, i

Inj the I drawings:

Figura-1 is a somewhat diagrammatic-plan-viewof a novel I combination of annealing apparatus suitable for v 'carrying out thehereiir claimed? method i Figura '2 isacros-sectional i 'View 'on' -linev Referring moreparticularly to the drawings; 1 reference numerals' o and 12 represent*suitable` -framem embers; ecured to a plate !4 on which* is -mounted-- arefractorv base l6. Retained -between the members i'u and -l a body of sandy indicated;at; I 8-',- forming a'gas seal., An 'outer-`-- annealing fur-mace hood '2 0 seated at 'the ;bote tomo this sand *seal. This furnace may be of any conventionalform suchas the wel'lknown i type having; radiantheater tubes.- The refr'ac tory base- I'-6-"is'*formed-'with a plurality of raised-j platformsz-z 'each 'adapted to accommodate a stack of'coiled material suchastheoils- Cfof:

strip steeL-indicated 'in the drawings.

Each' stack of'coils'C is; adaptedto be'enclosed': by an innerbell-iike cover ziof'generally cine' cular form, closedat ,the top,;the bottom of the cover Testing; in a body of sand or other scaling;

material: such 'as indieatedatfi; the* base bein provided withsuitablecraiedportions 2 3to re tain the sand or other-,scaling mater al;

of somewhat conventional and: ,well known form. But ath ugh he peara s n l s; Chief; c m.-

po entspar sbrpadlr p ak n ar o d pr se? and' wellknown to those skilled in the art, they i &6643683 each fitting 42 and the main each branch carries a shut-otr valve 44. K

The main control valve 34 is adapted to be manually manipuated to regulate the gas flow, and' the gas passes through the flow indicator 36 which has an orifice of predetermined size and is equipped with conventional means for indicating the rate of gas flow. The orices in the fittings 42 of the branch pipes are so designed that they provide suicient pressure drop to give substantially uniform distribution of deoxidizing gas under all conditions. y

By using the apparatus and distributing system illustrated, the rate of gas flow is shown at all times by means of the rate-of-flow indicator 36, and this rate of flow can be set at the will of the operator at any desired value by manipulation of the control valve 34. It is thus apparent that-during the heating period of the annealing r treatment, a substantially constant amount of gas per unit of time can be delivered to each of the inner covers 24. By way of example, during this period when heat is being applied by the radiant heat supplied by the annealing urnace bell 29, the operator may so set the control valve 34 as to provide approximately 50 cubic feet of deoxidizing gas per hour to the interior of each inner cover 24. This amount, of course, will vary with the tonnage of steel being treated, and in this example it is assumed that approximately tons of steel strip are contained within each inner cover 24. And during the cooling period, after the outer cover has been removed and the radiant heat is no longer' being applied to the coils C, the control valve 34 will be operated so as to supply a lower rate of input of deoxidizing gas, yet this input will be maintained substantially constant so as to adequately maintain a superatmospheric pressure within the inner covers to thus exclude the entrance of air. cooling stage valve 34 may, for example, be set so as to admit approximately 20 cubic feet of nonoxidizing gas per hour, at a uniform pressure.

From the foregoing it is apparent that the layout of the deoxidizing gas distribution system is such that the branch lines 40 are equipped with orifices designed with suflicient pressure drop to provide substantially uniform distribution of deoxidizing gas under all conditions and that because of the inclusion of the flow indicator 39 and the control valve 34 the rate of gas flow is made known to the operator at all times. Such rate of flow can be set at any desired value by During this manipulation of the control valve 34. Thus it l apparent that during the heating step, when gases are evolved from oil and water accretions on the surfaces of the coil C, resulting from normal steel rolling practice, a constant maximum supply of deoxidizing gas can be supplied at a uniform pressure so as to exert a purging action.

Thereafter, during the cooling stage, upon cuttng'pfi of the heat by renroval of the outer hood zt, the supply of deoxidizing gas will be redu'c'ed to the minimum necessary to prevent outside from entering under the inner cover.

i Since gas is being constantly supplied, naniely; at a uniform high rate during the heating stage and' at a uniform low rate during the cooling stage, during both stages the excess gas escapes orfilters out through the sand seals 25 surrounding the inner covers 24. If desired, escape ports can be used. The equipment will usually :include a conventional motor-driven fan 46 for circulating the gas within each inner cover 24; i

Although an ,actual reduction to practice shows that the above described embodiment of the in-` vention is highly desirable, it is not to be construed that I am limited thereto, since various modifications may be made by those skilled in the art within the scope of the appended claim.

I claim:

In the annealing of coils of rolled steel material carrying accretions of foreign matter such as oil and Water resulting from normal steel rolling operations, the method which comprises en-.

closing the coils within a cover and heating them to a determined annealing temperature while delivering a substantially constant maximum supply of deoxidizing gas to said cover at a substantially uniform' pressure which is substantially higher than the maximum pressure under the cover so as to purge the cover of contaminating gases evolved from said accretions, then cutting oil the heat and allowing the coils to cool for a determined interval and upon cutting ofi the heat, reducing the supply of deoxidizing gas to the minimum necessary to prevent air from,

entering the cover. a

WILLIAM H. DAILEY, J R.

REFERENCES CI TED The following references are of record in the file of this 'patent:

UNITED STATES PATENTS Number Date i

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