US2772084A - Heating furnace - Google Patents

Description

NOV- 27, 1956 L, 1'. PEARsALL 2,772,084

HEATING FURNACE Filed June '7, 1952 .ATToRNEY United States Patent HEATING FURNACE Luther T. Pearsall, Pittsburgh, Pa., assignor to Jones &

Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application June 7, 1952, Serial No. 292,235

4 Claims. (Cl. 263-40) This invention relates to heating furnaces for billets or similar elongated bodies and is more particularly concerned with an improved construction of such furnaces to provide more uniform heating of the charge.

Billets or like elongated metal bodies to be rolled are conventionally heated in enclosed furnaces of the type in which the fuel is burned in the same chamber with the charge. Such furnaces are commonly built of a width suicient to accommodate the longest billet to be heated. The charging door at the entry end may extend across the end of the furnace so that successive billets may be introduced broadside onto a plurality of skids or rails which extend along the furnace hearth from entry end to discharge end. Mechanical apparatus is provided to push the billets charged along the skids or rails so that when the furnace is completely charged with a layer of billets side by side the introduction of a cold billet at the entry end causes the entire charge to move along the furnace a distance equal to the width of one billet. At the same time, a heated billet is taken out at the discharge end, usually in a direction parallel to the billet axis, and introduced into the mill. It will thus be seen that conventional billet heating furnaces are relatively long and wide but need not be very high since billets are charged in a single layer. only.

lt is common practice to vsupply heat to such furnace at or 'near the discharge end so that this will be the hottest zone of the furnace. It is also common to provide a separate zone or subdivision of the furnace chamber at the discharge end, which may be provided with its own heating means, in which the billets soa or remain at rolling temperature a period of time sutiicient to equalize their temperatures from center to ends. The products of combustion both from the soaking zone and the heating zone are generally led backy over the charged billets to one or more waste gas olf-takes near thescha'rging end of the furnace. .The furnace roof is usually sloped downwardly toward the charging end Vto direct these gases down onto i the billets and so transferas much heat as possible to the billets entering the furnace. It is diihcult to bring about a uniform transfer of heat from the waste gases to the incoming billets in the region near the waste gas oi-takes as conventionally provided; consequently, the incoming billets are not heated uniformly from one end to the other.

It is an object, therefore, of my invention to provide a furnace construction which makes possible uniform heating of billets charged by controlling the flow of waste gases to the waste gas off-takes. Other objects will appear in the course of the following description of my invention.

Reference is now made to the attached drawing which illustrates an embodiment of my invention presently preferred by me.

Figure 1 is a cross section on a plane perpendicular to the axes of the billets through a billet heating furnace embodying my invention.

Figure 2 is a` cross sectional elevation through the furnace of Figure l taken on the plane II-lI.

'Ihe furnace shown is provided with a refractory hearth ICC 2 which slopes downwardly from entry end 3 to ldischarge end 4. lUpon the refractory hearth 2 are positioned skids or rails 6-6 which extend lengthwise of the furnace. The furnace at its discharge end is provided with back wall 7 in which are mounted fuel burners 9. 'I'he back wall 7 is constructed with a refractory inner lining 10. Adjacent to this back wall 7 is a roof section 12 supported by structural members 13--13 and also provided with refractory lining 15. This construction forms a soaking zone, previously mentioned, in which the billets remain at rolling temperature for a time prior to withdrawal. The roof section 12 adjoins a downwardly inclined section 17 which merges into a vertical curtain wall 18, also provided With fuel burners 19. Curtain wall 18 terminates in a more or less horizontal roof section 20 which is supported by structural members 22-22. The portion of the furnace roof nearer charging end 3 includes a downwardly inclined section 24 which merges into an upturned curtain wall 26. This curtain wall 26 forms the rear wall of a passageway 28 leading from the furnace roof, the front wall of which is the curtain wall 30 which merges into a short horizontal section 32 extending to the entry end 3. The portion of the furnace from curtain wall 18 to entry end 3 comprises the heating zone in which the charge is brought up to rolling temperature. My furnace is provided with vertical side walls 34 and 35. These may be pierced with appropriate cleanout doors 37--37 as required. Side wall 35 is also provided with a discharge door not shown near back wall 7 through which heated billets are removed in a plane perpendicular to that of Figure l.

The lower edge of curtain wall 26 together with the hearth and furnace side walls dene the minimum vertical cross section or choke 29 of the furnace chamber, which I prefer to make approximately equal to the minimum horizontal cross sectional area of passageway 28, previously mentioned.

Near its entry end my furnace is provided with a waste gas off-take chamber 39 communicating with passageway 28. This chamber may be constructed with vertical end walls 40 and 42 and an arched roof 41 which preferably merges smoothly into the upper edges of curtain walls 26 and 30, previously mentioned. A ue 43 leads olf from end wall 42 of this waste gas chamber.

Fuel burners 9 are spaced across the width of the furnace and are supplied with air through air lines 45 extending from manifold 46 which is connected with air supply line 47. Fuel burners 19 are likewise spacedacross the width of the furnace and are supplied with air through air lines 50 leading olf from manifold 51 connected to air supply line 52. Air supply lines 47 and 52 are both supplied from air line 54, which may be supported above the furnace by structural members 56 and 57. Fuel burne'rs9 vare supplied with fuel at junctions 60 by a fuel line not shown, and fuel burners 19 are supplied with fuel at junctions 61 also by a fuel line not shown. Fuel burners 9 are positioned to direct flames more or less horizontally over the work, whereas fuel burners 19 are positioned to direct flames downwardly onto the charged billets.

In operation, my furnace is charged at charging end 3 with a succession of billets positioned side by side in the manner previously described. As successive billets are charged, those within the furnace are pushed downwardly by apparatus not shown along skids or rails 6 until the entire furnace hearth is covered by a single layer of billets. Because of the furnace construction and the arrangement of the fuel burners at the discharge end, this latter end or soaking zone of the furnace is maintained at a rolling temperature, whereas the furnace temperature in successive zones back toward the charging end is successively lower. The waste gases arising from the combustion of fuel in my furnace are directed back over the charged billets toward the entry end of theV furnace. These gases, of course, tend to rise but are deflected downwardly toward the work by inclined roof portion 24. The waste gases lleave the furnace chamber through passageway 28in theY furnace. roof and rise into waste gas chamber 39 from which they escape into ue .43.

The volume of waste gas chamber 39 is .large relative to that portion of the heating furnace directly below it so that the gas pressure in chamber 39 is appreciably lower than in the furnace below and is substantially uniform throughout.V These .conditions bring about a rapid` drop in velocity of the waste gases as they enter chamber 39. Furthermore, the arched roof and smoothly contoured side walls causey no abrupt changes in the ow of gases entering this chamber andkso minimize turbulence in this ow. Because of this, these gases have no appreciable tendency to channel toward the v side Where the ue is located. The waste gases from the heating chamber of the furnace flow down over the charge at the choke 29 and upwardly into off-take chamber 39 in an evenly di'stributed layer or blanket and so transfer heat to the charge uniformly across that portion of the furnace bounded at one end by the width of passageway 28. The area of the charge to which heat is transferred from these waste gases is controlled by the width of passageway 28 relative to the furnace heating chamber as will be explained in the following paragraph and not by the relative location of the flue 43. In fact, one signicant advantage of my invention is that the flue 43 may be connected to chamber 39 at any convenient point without disturbing the waste gas distribution in the furnace itself. Thus, although I have shown ue 43 Vas entering chamber 39 through one end thereof, it may enter through the front or back side wall or the roof as is dictated by constructional requirements. y

I have shown waste gas chamber 39 as extending across less than the full width of the furnace, and passageway 28V extending the full width of chamber '39. It is not necessary that this latter condition obtain, but it simplifies construction to observe it. It is desirable that the width of the passageway 28 be less than the width of the furnace where the length of the heating zone, of the furnace is significantly greater than its width. In such a furnace the heat radiated from the side walls and the portions of the roof immediately adjacent, such as 32-32 in Figure 2, usually raises the ends of billets as they travelalong the hearth to temperatures above those of their central portions. I counteract this effect by narrowing passageway 28 somewhat, so drawing the waste gases awayfrom these hotter ends and toward the center area in order that the heat transferred from these gases to the charge by convection will tend .to equalize the temperature along the billets. The relation between the width of the passageway opening into the waste gas chamber and the width of the furnace depends on the relation between the length and width of the heating zone of the furnace. I have found that the optimum width of this passageway may be determined to a first approximation from the simple' relation W2 v X L where X is the width of the passageway, W is ythe width of the furnace, and L is the length of the heating zone of the furnace. In the furnace shown in the drawings, L from curtain wal1118 to charge end 3 is 45 feet, W is 30 feet, and X is 20 feet, which satisfies the above relation.

While I have shown and described what I consider to be a preferred embodiment of my invention, it will be understood that various modifications and rearrangements may be made therein without departing from the spirit and scope of my invention.

I claim: f

1. A heating furnace for billets or the like comprising a hearth, side walls and end walls, one end wall being provided with a charging opening, and the other end wall being provided with fuel burners positioned to direct heating flames toward the charging opening, a roof inclined downwardly toward Vthe charging opening, .an elongated ywaste gas off-take chamber extending ktransversely across the furnace above the roof thereof adjacent the charging opening, communicating with the furnace through a transversely elongated opening, said chamber having parallel end walls, an arched roof with a span materially greater than vthe width of the transversely elongated opening, and side walls converging smoothly from the base of said arched roof to the transversely elongated opening, enclosing thereby a volume materially greater than that of the portion of the furnace directly below the transversely elongated opening, and a flue communicating with the waste gas off-take chamber through a wall thereof.

2. The furnace of claim l in which the downwardly inclined roof forms a choke adjacent the charging opening and the transversely elongated opening directly adjons the choke toward the charging opening.

3. The furnace of claim 1 in which the downwardly inclined roof forms a choke adjacent the charging opening f and the transversely elongated opening directly adjoins the choke toward the charging opening and vhas a cross sectional area substantially equal to that of the choke.

4. The furnace of claim l in which the transverse dimension of theY transversely elongated opening is approximately equalto the square of the furnace Width divided by the furnace length.

Referencescifed in the me 'of this patent UNITED STATES PATENTS 65,630 Bagnall June 11, 1867 .511,800 yRice Jan. 2, 18,94 1,021,144 Gordon et al. Mar. 26, 1912 2,354,324 `Longenecker -Iuly 25, 1944 2,638,334

Jones May 12, 1953

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