US2141192A - Apparatus for annealing - Google Patents

Description

Dec. 27, 1938. w. N. MccUTcHEoN 2,141,192

APPARATUS FORI ANNEALING Filed Jan. 2, 1937 2 Sheets-Sheet 1 INVENTOR mf/7mm ATTORNEY;

Dec. 27, 1938. w. N. MccuTcHEoN APPARATUS FOR ANNEALING 2 Sheets-Sheet 2 Filed Jan. 2, 1937 RX www;

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Patentedv Dec. 27, 1938 UNITED STATES PATENT OFFICE v 2,141,192 V APPARATUS FR EALNG William N. McCutclieon, ThornburgyPa.

Application January 2, 1937, Serial No, 118,738

l 3 i Claims.

This invention relates to the art of annealing and/or heat treating metals, and more specifically to a method of box annealing ferrous metal sheets, plates and coils, and to apparatus to ef- 5 fectuate such method. i

Heretofore, it has been the practice in box annealing to stack a plurality of sheets, plates or coils on a suitable base, lower a cover over the entire charge of metal, secure thesame to the base and then place thebox with the metal disposed therein in a suitable heating furnace. The furnace was fired by the introduction of a combustible mixture into thefurnace chamber, the

- flame produced thereby being directed upon the annealing boX. Unless the furnace. was heated at a relatively slow rate, it was found that certain` zones in the charge of metal would reach the desired temperature sooner than other portions of the metal and in some instances such zones in the charge of metal would become overheated or burned. For example, in firing the furnace, the

greatest intensity of heat would be concentrated or localized within the upper regions of the furnace chamber. The material disposed in such regions would be subjected to this intense heat, resulting in such material becoming overheated or attaining the required temperature for annealing befo e those portions of the charge of metal disposed djacent the bottom of theannealing box. As a. result, it wasv found that it was impossible under such practices to obtain a product which had been uniformly heat treated through out the extent of the charge. Also it was diilicult to obtain a product which was uniform in grain structure and possessed uniform physical properties. It was found that a single sheet of metal would possess highly variable characteristics throughout its extent, which metal would not only react differently but would give totally different results throughout the extent of a sheet of such metal when subjected to fabrication. The cost of box annealing was, therefore, excessive not only from the standpoint of furnace operation but also from the standpoint of scrap loss. Those portions of the charge of metal which had become overheated or burned because of excessive heating, on had been underheated, had either to be scrapped or be subjected to a subsequent heat treatment. y

It has been recognized that to obtain a box annealed product having uniform characteristics, the product must be uniformly heated and that the failure to obtain suchv product was due to an uneven heating of the charge of metal dispose within the annealing box.

(ci. 26e- 51 Variousmethods of ring furnaces have been proposed in an effort to obtain uniform heating of the products. Efforts have been made to obtain uniform heating of the metal by maintaining a uniform temperature within the furnace chamber. `But a uniform furnace temperature does not produce a uniform product because the rate at which a unit of metal absorbs heat is in direct ratio to the amount of surface area of such volume exposed to the heat. For example, in a charge of metal, a unit volume of the metal at one of thecorners of the charge absorbs heat three times as rapidly as an equal volume on the side mid-way between the ends and the top and v bottom of the charge. If therefore,-the two volumes are subjected to the same temperature, the. one at the corner of the charge having the greater exposed area will reach the desired temperature sooner than the volume having the lesser exposed area. Even if the volume first reaching the desired temperature is held at that temperature while the remainder of the metal is being heated to the desired point, a uniform heat treatment cannot result because the length of time during which the metal is held at the desired temperature is a factor in producing the grain structure in the metal by the heat treatment. 4

By the present invention, I have provided a method of box annealing which produces a product which does not possess any of the undesirable characteristics which have characterized products produced by prior methods of box annealing. The resultant product under this present invention is fully annealed, has substantially uniform grain structure throughout the charge of metal, has substantially uniform physical properties and gives uniform results when subjected to fabrication., The time during which the charge of metal is in the furnace, subjected to treatment, is greatly reduced andthe cost of annealing is thereby less for a specified volume of metal. A further reduction in cost is alsorealized through the avoidance of re-annealing arid scrapping the portions of a heatjwhich, heretofore, had become overheated or' had been held at annealing temperatu're for too great a length of time.

' of metal will be subjected to this temperature for an appreciably greater length of time than any other portion. Also by the present invention,

the heating and'cooling cycles of the metal may be so controlled that during these cycles all portions of the charge are subjected to the same heat treatment.

I have found that to obtain a uniform heat treatment of a charge of metal, heat must be introduced unevenly into the charge. In heat treating metal, it is desirable to maintain the input of heat at a rate equal to the maximum rate at which heat can be efliciently absorbed by the entire volume of the charge of metal. The maximum rate of absorption cannot be increased. I have discovered that a uniform heating of the entire charge in the minimum time may be obtained -by maintaining the heat input into those volumes of the charge of metal having the least amount of exposed area at the maximum rate of absorption for the material, and the heat input in` those portions having a greater exposed area at a rate proportionately lower.

In carrying out my invention, I have found that a uniform heating of a charge of metal may be obtained by directingall of the heat at the charge from the sides and none from the top and ends, and, because of the volume of the base on which the charge is stacked, directing the maximum amount of heat to the lower regions of the charge and somewhat less, progressively, to the regions above. f

The invention also includes new and improved apparatus for practicing the foregoing method. The apparatus comprises an annealing furnace having heating means so disposed along the side walls of the furnace as to radiate heat directly to the desired portions of the charge of metal positioned within the furnace chamber. The heating means can be so controlled and operated that varying amounts of heat can be radiated to the charge of metal. The furnace may be so constructed that portions of the charge of metal disposed within the furnace chamber and having the lowest rate of heat absorption is subjected to radiated heat whereas the rate of heating of other portions of the charge is limited by the influence of the furnace walls adjacent such portions.

rlfhe foregoing and other advantages of the invention and the invention itselfwill become more apparent from the following detailed description thereof taken in conjunction with the accompanying drawings wherein similar reference characters denote correspon-ding parts wherein:

Figure l is a transverse sectional elevation of an annealing furnace embodying the present invention,

Figure 2 is a horizontal sectional View taken on the line 2-2.of Figure l,

Figure 3 is a transverse sectional view of another form of furnace for practicing the present invention, and

Figure 4 is a horizontal sectional View taken on the line v(1I- il of Figure 3.

With reference to the accompanying drawings and particularly Figures 1 and 2, there is illustrated one embodiment ofan apparatus for carrying out my invention,v comprising an annealing furnace of the box annealing type, designated in itsentirety by the numeral IQ and including a bottom II preferably made of a heat insulating refractory. `The furnace bottom 5I is provided with parallely rails I2. upon which an annealing box ismoved into and out of the heating chambei'` o f the furnace II). The annealing box includes an insulating refractory base It upon which the metal I5 is stacked,` and a cover IB and Vfurnace chamber. rtop .portion thereof are in effect blankete-d or shielded from direct radiated heat through` the.

which is adapted to be lowered over the metal I5 and sealed within groove I1 of the base I4, in any suitable manner as by means of sand. Suitable skids I8 are provided along the bottom of the base I4 to engage the rails I2 on the bottom of the furnace I0.

The furnace I0 comprises end walls I9 and 20, side wallsA 2I and 22, and an arched roof 23, preferably disposed within a frame work 24 consisting of vertical buckstays 25 and horizontal cross members 26. The roof 23 is suspended from the cross members 26 by 'means of hangers 21. The end walls I9 and 20, and the roof 23 may be constructed of a heat absorbing refractory, whereas, the side walls 2I and 22 are made of a heat insulating refractory. The advantages and purpose of the use of these particular types of refractories for different portions of the furnace will become more apparent as the description of this invention progresses. The end wall I9 is provided with a doorway 28 through which the annealing box is moved into the furnace which is sealed by a door 28a.

The opposed side walls 2| and 22 of the furnace are provided with elongated openings 29 extending therethrough which openings are spaced from the ends and top of the side walls and are so positioned with respect to the charge of metal disposed in the furnace chamber as to be adjacent that portion of the charge which has the least amount of exposed surface area per unit volume of metal. These openings 29 connect with ring chambers 30 defined by offsets or bays formed along the side walls 2l and 22, coextensive with the openings. A radiant panel 32 having its peripheral edges extending into the side walls separates the furnace chamber from the firing chamber. As illustrated in the drawings, the plane of the radiant panel 32 is spaced outwardlv from the inner surface of the side walls. but if desired the radiating surface of this panel may be coincident with the inner surface of the side walls. Each firing chamber 30 is provided at its opposed ends with firing ports 33 through which extend suitable nozzles for introducing combustible mixtures into the firing chamber. 'Ihe products of combustion are conveyed from the firing chamber through a plurality of fiues 34 extending through the bottom of the ring chamber 30. Each of the fiues 34 is provided with a slide valve 34a for controlling the amount of gases conveyed from the chamber 30 through any particular flue 3 4. These flues connect with a longitudinally extending duct 35 which leads to a stack (not shown).

By controlling the length of the flame projected into the firing chamber through the'ring ports 33 an'd the effective area of iiues 34, the amount of heat radiated from any particular area ofthe panel 32 to the charge of metal I5 Vmay be regulated.- Since it is desirable to have absorbing refractory, are not effective in im.

parting any heat to the charge through radiation, but rather tend to absorb heat from the heated gas which circulates-in that portion of the The ends of the charge and construction of the furnace adjacent such portions and the arrangement ofthe radiant panels which direct substantially all of the radiated heat against those portions of the stack having the -is preferably so operated that during the cooling cycle all portions of the charge cool at substantially equal rates. At the conclusion of the heating cycle, the operation of the furnace may be reversed and cool air introduced into the firing chambers 30, which cool air will be effective in causing a more rapid cooling of those portions of the charge which are slowest to cool, such portions being the ones which have the minimum amount of exposed area per unit volume of metal. The refractory of the furnace adjacent the ends and top of the charge, being of a heat absorbing character, gives off heat during the cooling cycle and prevents too rapid a cooling of the ends and the top of the charge.

It willbe seen, therefore, that in the operation of a furnace as illustrated hereinabove, it is possible during the heating cycle to so flre the furnace that all portions of the charge will reach the desired annealing temperature at or about the same time, and that during the cooling cycle all portions of the charge are uniformly cooled.l

Firing the furnace as above described results in the product having substantially uniform characteristics such as grain structure and physical properties throughout all portions of the charge of metal.

With reference to Figures 3 and 4, there is illustrated a bell type annealing furnace em- The' metal 39 bodying the present invention. to be heat treated is stacked on a plurality of skids 40 which rest upon the furnace base 4I. A cover 42 is lowered over the charge of metal and the edges thereof inserted within the groove 43 which may be filled with sand to eilect a seal. The furnace 44 is adapted to be lowered over the charge of metal and sealed to the base 4| as at 45.

'I'he bell type furnace 44 comprises end walls 46 and 41, side walls 48 and 49 and a roof 50 suitably constructed within a frame work 5l..

In this construction, the end walls 46 and 41 and the roof 5|) may be constructed of' a heat absorbing refractory whereas the side walls 45 and 49 may be constructed of a heat insulating refractory in a manner similar to that disclosed in Figures 1 and 2. The side walls 48 and 49 are provided with a plurality of spaced recesses in which are disposed rectangular metallic firing chambers 52. These firing chambersare of relatively small .depth as compared with their width and are disposed adjacent those portions of the charge of metal which have the least amount oi' exposed'area per unit volume of metal. The outer surface of the ring 'chambers constitute rectangularradiant panels which are coincident with the plane of the side walls. Each of the ring chambers 52 are red by projecting a combustible mixture into the bottom of the chambers from pipes 53 which are connected to a suitable supply line 54. A suitable valve 55 in each of the pipes 53 controls the amount of combustible mixtures introduced into each firing chamber 52. The products of combustion are conveyed from the firing chamber 52 through the exhaust ues 56 extending through the side walls of the furnace chamber.

Each of the ring chambers 52 is separately red and the amount of combustible mixtures introduced into these firing chambers is so controlled that the amount of heat radiated from the radiating panels 52 may be correspondingly controlled. In other words, the firing chambers adjacent those portions of the charge to which the greatest amount of heat is to be directed may be'fired at the maximum rate and other chambers may be fired at a rate in accordance with the amount of heat it is desired to radiate from the respective panels to the particular portion of the charge of metal opposite each radiating surface.` The operation of this type of furnace may be carried on in a manner similar` to that followed in the furnace disclosed in Figures 1 and 2 so that a substantially uniform heating and cooling cycle may be maintained throughout the charge of metal.

Having thus described myinvention, what I desire to obtain by Letters Patent is dened in what is claimed.

I claim 1. A muflie type furnace, for heating stacked sheet metal, having vertical end and side walls and a roof defining a heating chamber, the side walls having recesses opening into the heating chamber along the lower middle portion of said walls, said recesses stopping short of the ends and tops of the side walls, heat radiating means closing the heating chamber side of said recesses, and means for conducting heat to said radiating means.

2. A muiiie type furnace, for heating stacked sheet metal, having vertical end and side walls Yand a roof defining a heating chamber, the side walls having recesses opening into the heating chamber along the lower middle portion of said walls, said recesses stopping short of the ends and tops of the side walls, heat radiating means closing the heating chamber side of said re` cesses, said radiating means comprising rectangular tubes carrying heated gases.

3. A munie type furnace, for heating stacked sheet metal, having vertical end and side walls and a roof defining a heating chamber, the side walls having recesses opening into the heating chamber along the lower middle portion of said walls, said recesses stopping short of the ends and tops of the side walls, heat radiating panels closing the heating chamber side of' said recesses, and means for conducting heat to said radiating means.

WILLIAM N. MCCUTCHEON.

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